{"gene":"IL13","run_date":"2026-04-28T18:06:53","timeline":{"discoveries":[{"year":1993,"finding":"IL-13 was identified as a new human cytokine expressed in activated T lymphocytes, capable of inhibiting inflammatory cytokine production induced by LPS in human peripheral blood monocytes, and its gene was mapped to chromosome 5q23-31, closely linked to the IL-4 gene.","method":"Differential screening of subtracted cDNA library, recombinant protein expression, functional assays on monocytes","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1 — original discovery paper with molecular cloning, recombinant protein, and functional validation","pmids":["8096327"],"is_preprint":false},{"year":1993,"finding":"Human IL-13 protein induces morphological changes in human monocytes with upregulation of MHC class II antigens and CD23 (Fc epsilon RII), stimulates proliferation of anti-IgM or anti-CD40-activated human B cells, and induces IgM and IgG (but not IgA) production by purified B cells co-cultured with activated CD4+ T cells.","method":"cDNA cloning, recombinant protein expression, B cell proliferation assays, Ig production assays, flow cytometry","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 — foundational paper with multiple orthogonal functional assays on primary human cells","pmids":["8097324"],"is_preprint":false},{"year":1993,"finding":"IL-13 synergizes with mouse and human CD40L to induce IgM, IgG, IgG4, and IgE (but not IgA) production by highly purified B cells, and this induction is independent of IL-4 (anti-IL-4 antibodies block IL-4-induced but not IL-13-induced Ig production), demonstrating that IL-13 and CD40L can induce isotype switching to IgE independently of IL-4.","method":"B cell-T cell co-culture, COS-7 cells transfected with hCD40L, neutralizing antibody blockade, ELISA","journal":"International immunology","confidence":"High","confidence_rationale":"Tier 2 — reciprocal antibody blockade and functional assays in primary human B cells","pmids":["7688562"],"is_preprint":false},{"year":1998,"finding":"IL-13 is necessary and sufficient for the expression of allergic asthma features (airway hyperresponsiveness, mucus overproduction) in a manner independent of IgE and eosinophils; selective neutralization of IL-13 ameliorated the asthma phenotype, and this pathway requires the IL-4 receptor alpha chain.","method":"Selective IL-13 neutralization in murine asthma models, IL-13 administration to T cell-deficient mice, IL-4Rα-deficient mice","journal":"Science (New York, N.Y.)","confidence":"High","confidence_rationale":"Tier 2 — multiple genetic and pharmacological approaches in vivo, replicated across two independent Science papers (PMID 9856949, 9856950)","pmids":["9856949","9856950"],"is_preprint":false},{"year":1998,"finding":"IL-13 is required for resistance to the intestinal nematode Trichuris muris; IL-13 knockout mice are susceptible despite being able to mount Th2 responses at later time points, demonstrating a non-redundant role for IL-13 in intestinal helminth immunity distinct from IL-4.","method":"IL-13 knockout mice, T. muris infection model, cytokine and antibody isotype analysis","journal":"Journal of immunology (Baltimore, Md. : 1950)","confidence":"High","confidence_rationale":"Tier 2 — clean KO with defined phenotypic readout","pmids":["9531306"],"is_preprint":false},{"year":2000,"finding":"A conserved noncoding element was identified as a coordinate regulator of IL-4, IL-13, and IL-5 gene expression over a 120-kilobase region on chromosome 5q, demonstrated by YAC transgenic mice.","method":"Cross-species sequence comparison, YAC transgenic mice, gene expression analysis","journal":"Science (New York, N.Y.)","confidence":"High","confidence_rationale":"Tier 2 — in vivo transgenic validation of regulatory element","pmids":["10753117"],"is_preprint":false},{"year":2001,"finding":"IL-13 alters mucociliary differentiation of human nasal epithelial cells: it decreases ciliated cell differentiation, increases secretory cell proportion, downregulates ezrin and other cytoskeletal components, impairs apical localization of ezrin, and decreases ciliary beat frequency in a time- and dose-dependent manner; these effects are mediated through the IL-4 receptor alpha subunit (blocked by an IL-4 antagonistic mutant Y124D).","method":"Primary human nasal epithelial cell cultures, immunofluorescence, receptor antagonist, time-lapse microscopy of ciliary beat","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 2 — multiple cellular phenotypes with receptor-specific antagonist validation","pmids":["11748265"],"is_preprint":false},{"year":2001,"finding":"IL-13 induces mucin production via a cascade requiring EGFR signaling and neutrophil recruitment; IL-13 induces IL-8-like chemoattractant expression in airway epithelium, recruits neutrophils, and EGFR tyrosine kinase inhibition or neutrophil depletion prevents IL-13-induced goblet cell metaplasia.","method":"In vivo intratracheal instillation in mice, EGFR inhibitor, cyclophosphamide-mediated neutrophil depletion, anti-IL-8 blocking antibody","journal":"American journal of physiology. Lung cellular and molecular physiology","confidence":"High","confidence_rationale":"Tier 2 — multiple pharmacological interventions establishing pathway order in vivo","pmids":["11133503"],"is_preprint":false},{"year":2001,"finding":"IL-13 induces airway hyperreactivity, mucus hypersecretion, eotaxin production, and eosinophilia in the allergic lung through a pathway that requires STAT6 but can operate independently of the IL-4Rα chain, identifying a novel STAT6-dependent component of the IL-13 receptor signaling system.","method":"OVA-specific CD4+ T cell transfer to IL-13-deficient, IL-4Rα-deficient, and STAT6-deficient mice with OVA aerosol challenge","journal":"Journal of immunology (Baltimore, Md. : 1950)","confidence":"High","confidence_rationale":"Tier 2 — genetic epistasis using multiple knockout mouse strains with defined phenotypic readouts","pmids":["11466392"],"is_preprint":false},{"year":2003,"finding":"IL-13 directly modulates airway smooth muscle (ASM) contractility: it significantly increases carbachol- and KCl-induced maximal force generation in murine tracheal rings and augments cytosolic calcium responses to bradykinin, histamine, and carbachol in cultured human ASM cells, suggesting IL-13 promotes bronchial hyperresponsiveness by enhancing GPCR-associated calcium signaling.","method":"Murine tracheal ring contractility assay, calcium fluorimetry in cultured human ASM cells","journal":"British journal of pharmacology","confidence":"Medium","confidence_rationale":"Tier 2 — direct in vitro and ex vivo functional assays, single lab","pmids":["14597600"],"is_preprint":false},{"year":2003,"finding":"IL-13 induces goblet cell metaplasia in human bronchial epithelial cells through MAP kinase (MEK, p38 MAPK) and phosphatidylinositol 3-kinase signaling pathways, independent of EGFR-TK, in a concentration-dependent manner.","method":"Air-liquid interface cultures, Alcian blue/MUC5AC staining, kinase inhibitors (PD-98059, U-0126, SB-202190, LY-294002, AG-1478)","journal":"American journal of physiology. Lung cellular and molecular physiology","confidence":"Medium","confidence_rationale":"Tier 2 — multiple pharmacological inhibitors in primary epithelial cell cultures","pmids":["12794003"],"is_preprint":false},{"year":2003,"finding":"IL-13 suppresses iNOS protein levels in inflammatory macrophages through translational inhibition caused by arginine depletion via arginase induction; although iNOS mRNA remains unaltered, arginase-mediated arginine depletion selectively impairs de novo iNOS protein synthesis and stability, revealing a novel translational regulatory mechanism.","method":"Mouse peritoneal macrophage stimulation with IFN-γ/LPS ± IL-13, arginase inhibitors, arginase addition, arginine-free medium, [35S]-methionine incorporation","journal":"Journal of immunology (Baltimore, Md. : 1950)","confidence":"High","confidence_rationale":"Tier 1 — multiple orthogonal mechanistic approaches (inhibitors, substrate depletion, metabolic labeling) in primary cells","pmids":["14568929"],"is_preprint":false},{"year":2005,"finding":"IL-13 signaling through IL-13Rα2 (formerly considered only a decoy receptor) activates an AP-1 variant containing c-jun and Fra-2, which then activates the TGFB1 promoter; in vivo, IL-13Rα2 silencing reduces TGF-β1 production and collagen deposition in models of colitis and lung fibrosis, establishing IL-13Rα2 as a signaling receptor mediating fibrosis.","method":"Macrophage stimulation, AP-1 activation assays, promoter analysis, siRNA knockdown, in vivo colitis and bleomycin lung fibrosis models, collagen quantification","journal":"Nature medicine","confidence":"High","confidence_rationale":"Tier 1 — in vitro mechanistic dissection plus in vivo genetic/siRNA validation in multiple disease models","pmids":["16327802"],"is_preprint":false},{"year":2005,"finding":"The IL-13 R130Q variant (encoded by IL13+2044GA) is significantly more active than WT IL-13 in inducing STAT6 phosphorylation and CD23 expression in monocytes and IgE switching in B cells; it is also neutralized less effectively by the IL-13Rα2 decoy receptor, contributing to enhanced in vivo activity of the variant.","method":"Recombinant WT and R130Q IL-13 proteins, STAT6 phosphorylation assay, CD23 expression (flow cytometry), IgE switching assay, IL-13Rα2 neutralization assay on primary human cells","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 1 — direct comparison of recombinant variants on primary human cells with multiple orthogonal readouts","pmids":["15711639"],"is_preprint":false},{"year":2005,"finding":"The IL-13 Gln110 variant (corresponding to R130Q) shows lower affinity for the IL-13Rα2 decoy receptor, causing reduced clearance, and also demonstrates enhanced stability in plasma; asthmatic patients homozygous for this variant have higher serum IL-13 levels, mechanistically linking the SNP to increased IL-13 bioavailability.","method":"Recombinant protein binding affinity assays, plasma stability assays, serum IL-13 ELISA in genotyped patients","journal":"The Journal of allergy and clinical immunology","confidence":"High","confidence_rationale":"Tier 1 — in vitro binding/stability assays with in vivo correlation in genotyped patients","pmids":["12063528"],"is_preprint":false},{"year":2007,"finding":"IL-13 treatment of esophageal epithelial cells induces eotaxin-3 production through a transcriptional mechanism dependent on STAT6; IL-13 stimulation recapitulates the EE-specific esophageal transcriptome, and this transcriptome is reversible with glucocorticoid treatment.","method":"Primary esophageal epithelial cell cultures, microarray, real-time PCR, luciferase reporter assays with eotaxin-3 promoter fragments and STAT6 mutants","journal":"The Journal of allergy and clinical immunology","confidence":"High","confidence_rationale":"Tier 1 — promoter-reporter and mutagenesis with transcriptomic validation","pmids":["18073124"],"is_preprint":false},{"year":2007,"finding":"IL-33 induces IL-13 (and IL-6) production by mouse mast cells independently of IgE-FcεRI signals via a MyD88-dependent but TRIF-independent pathway; this effect is more potent than IL-1β or IL-18 and does not induce mast cell degranulation.","method":"Bone marrow-derived mast cell cultures, cytokine ELISA, MyD88-deficient mice, degranulation assay","journal":"Journal of leukocyte biology","confidence":"High","confidence_rationale":"Tier 2 — genetic (MyD88-KO) and pharmacological dissection of signaling pathway in primary mast cells","pmids":["17881510"],"is_preprint":false},{"year":2007,"finding":"IL-13 secreted by airway epithelial cells after mechanical injury enhances epithelial repair via autocrine induction of HB-EGF (but not EGF), leading to EGFR phosphorylation; neutralization of IL-13 reduces repair, and EGFR inhibition increases IL-13 release, indicating a negative feedback loop between EGFR and IL-13 during repair.","method":"Scratch wound assay in AEC monolayers, IL-13 neutralization with sIL-13Rα2.FC, ELISA, EGFR phosphorylation western blot, EGFR kinase inhibitor tyrphostin AG1478","journal":"American journal of respiratory cell and molecular biology","confidence":"High","confidence_rationale":"Tier 2 — multiple mechanistic interventions (neutralization, inhibitors) with reciprocal feedback demonstrated","pmids":["17717322"],"is_preprint":false},{"year":2007,"finding":"IL-9 promotes lung eosinophilia and mucus production through an IL-13-dependent mechanism: hematopoietic cells expressing both IL-9R and IL-13 are required for IL-9 effects on lung epithelial cells, establishing IL-13 as a direct downstream mediator of IL-9 on epithelial targets.","method":"IL-13 knockout mice crossed with IL-9 transgenic mice, hematopoietic cell transfer experiments with IL-9R-deficient recipients","journal":"Journal of immunology (Baltimore, Md. : 1950)","confidence":"High","confidence_rationale":"Tier 2 — epistasis established by genetic crosses and transfer experiments","pmids":["17312173"],"is_preprint":false},{"year":2007,"finding":"IL-13 induces CD36 expression in human monocytes through PPARγ activation; this occurs via phospholipase A2-dependent production of endogenous 15-deoxy-Δ12,14-prostaglandin J2 (a PPARγ ligand), which translocates to the nucleus; CD36 and PPARγ are required for IL-13-mediated phagocytosis of P. falciparum-parasitized erythrocytes.","method":"PPARγ expression plasmid transfection in RAW264.7, PPARγ conditional null macrophages, PLA2 inhibitors, PGJ2 ELISA, nuclear localization assay, phagocytosis assay","journal":"European journal of immunology","confidence":"High","confidence_rationale":"Tier 1 — multiple orthogonal methods including genetic null model, transfection, and functional assay","pmids":["17458857"],"is_preprint":false},{"year":2008,"finding":"IL-13 signaling through IL-13Rα2 in chronic colitis induces a fibrogenic program comprising TGF-β1 activation, IGF-I and Egr-1 expression, caspase-mediated myofibroblast apoptosis, urokinase plasminogen activator production, and IGF-I/TGF-β1-driven collagen deposition; blockade of IL-13Rα2 or TGF-β1 signaling with siRNA or decoy oligonucleotides abrogates this cascade.","method":"TNBS chronic colitis mouse model, siRNA targeting IL-13Rα2 and TGF-β1 signaling components, ELISA, Western blot, collagen measurement","journal":"Gastroenterology","confidence":"High","confidence_rationale":"Tier 2 — systematic siRNA knockdown of multiple pathway components in vivo","pmids":["18938165"],"is_preprint":false},{"year":2008,"finding":"Crystal structures of the complete type I (IL-4Rα/γc/IL-4) and type II (IL-4Rα/IL-13Rα1/IL-4 and IL-4Rα/IL-13Rα1/IL-13) ternary signaling complexes reveal that IL-13 engages IL-13Rα1 via an unusual top-mounted Ig-like domain in a novel mode of cytokine engagement; the two type II complexes use substantially different recognition chemistries and have a reversed assembly sequence compared to type I; type II receptor signals with different potencies for IL-4 versus IL-13.","method":"X-ray crystallography of complete ternary receptor complexes, functional signaling assays","journal":"Cell","confidence":"High","confidence_rationale":"Tier 1 — high-resolution crystal structures of all receptor complexes with functional validation","pmids":["18243101"],"is_preprint":false},{"year":2008,"finding":"MMP-8 cleaves IL-13Rα2 in vitro and contributes to solubilization of IL-13Rα2 in vivo; MMP-8-deficient mice display increased airway hyperresponsiveness and decreased soluble IL-13Rα2 in bronchoalveolar lavage after allergen challenge; the solubilized IL-13Rα2 retains IL-13 binding activity.","method":"In vitro acellular cleavage assays with GST-fusion proteins, stable-transfected cell surface expression assay, MMP-8-deficient mice, allergen challenge model, BAL fluid analysis","journal":"The Journal of allergy and clinical immunology","confidence":"High","confidence_rationale":"Tier 1 — in vitro biochemical cleavage assay plus genetic KO validation in vivo","pmids":["18694590"],"is_preprint":false},{"year":2008,"finding":"IL-13 attenuates vascular tube (capillary-like) formation and endothelial cell migration via JAK2 activation followed by STAT6 activation; depletion of JAK2 and STAT6 by RNA interference abolishes the anti-angiogenic effect of IL-13.","method":"In vitro tube formation assay in human coronary artery endothelial cells, siRNA knockdown of JAK2 and STAT6, migration assay","journal":"Circulation journal","confidence":"Medium","confidence_rationale":"Tier 2 — siRNA knockdown establishing JAK2-STAT6 pathway, single lab","pmids":["18296848"],"is_preprint":false},{"year":2010,"finding":"IL-13 mediates collagen deposition via STAT6 and epigenetic repression of microRNA-135b in dermal fibroblasts; STAT6 knockdown blocks IL-13-induced collagen1A1 expression; miR-135b overexpression reduces IL-13-induced collagen induction; scleroderma fibroblasts have constitutively lower miR-135b due to methylation-dependent repression involving MeCP2.","method":"siRNA knockdown of STAT6, small molecule STAT6 inhibitor, miR-135b transfection, qRT-PCR, methylation analysis in patient-derived fibroblasts","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 — siRNA and miRNA overexpression with patient validation, single lab","pmids":["27113293"],"is_preprint":false},{"year":2010,"finding":"IL-13 promotes beige fat biogenesis through IL-4/IL-13 signaling in alternatively activated macrophages; macrophages recruited to cold-stressed subcutaneous white adipose tissue undergo alternative activation to express tyrosine hydroxylase and produce catecholamines required for browning; genetic loss of IL-4/IL-13 signaling impairs cold-induced beige fat development.","method":"Genetic mouse models deficient in eosinophils or IL-4/IL-13 signaling, cold exposure experiments, macrophage tyrosine hydroxylase immunostaining, catecholamine measurements","journal":"Cell","confidence":"High","confidence_rationale":"Tier 2 — multiple genetic models establishing IL-4/IL-13 signaling → macrophage alternative activation → catecholamine production → beige fat circuit","pmids":["24906148"],"is_preprint":false},{"year":2010,"finding":"MiR-155 directly targets IL-13Rα1 mRNA in human macrophages, reducing IL-13Rα1 protein levels and diminishing STAT6 phosphorylation in response to IL-13, thereby modulating expression of M2 marker genes (SOCS1, DC-SIGN, CCL18, CD23, SERPINE).","method":"Bioinformatics prediction, luciferase reporter assay, western blot, STAT6 phosphorylation, gene expression analysis in primary human macrophages with miR-155 overexpression/inhibition","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — direct targeting validated by reporter assay and functional downstream readouts in primary human macrophages","pmids":["21097505"],"is_preprint":false},{"year":2010,"finding":"IL-13 downregulates desmoglein-1 (DSG1) in esophageal epithelial cells, impairing barrier function; DSG1 silencing induces transcriptional changes overlapping the EoE transcriptome, including induction of periostin (POSTN), linking IL-13-driven DSG1 loss to esophageal barrier dysfunction and pro-inflammatory mediator production.","method":"IL-13 stimulation of primary esophageal epithelial cells, DSG1 siRNA knockdown, transepithelial resistance measurement, transcriptomic analysis, patient biopsy validation","journal":"Mucosal immunology","confidence":"High","confidence_rationale":"Tier 2 — siRNA knockdown with functional barrier assay and transcriptomic validation in patient tissue","pmids":["24220297"],"is_preprint":false},{"year":2011,"finding":"Let-7 microRNAs directly regulate IL-13 expression; induced IL-13 levels in T cells are inversely related to let-7 levels, and intranasal delivery of let-7 mimic in allergic mice decreases IL-13 levels and resolves airway inflammation, airway hyperresponsiveness, mucus metaplasia, and subepithelial fibrosis.","method":"Bioinformatics, in vitro transfection in A549 cells and primary T cells, in vivo let-7 mimic intranasal delivery in murine allergic inflammation model","journal":"The Journal of allergy and clinical immunology","confidence":"Medium","confidence_rationale":"Tier 2 — in vitro and in vivo validation of miRNA regulation, single lab","pmids":["21616524"],"is_preprint":false},{"year":2013,"finding":"Chitinase 3-like 1 (Chi3l1) binds to IL-13Rα2 and is found in a multimeric complex with IL-13Rα2 and IL-13; Chi3l1 activates MAPK, AKT, and Wnt/β-catenin signaling via IL-13Rα2-dependent mechanisms to regulate apoptosis, pyroptosis, inflammasome activation, antibacterial responses, and TGF-β1 production.","method":"Co-immunoprecipitation, pulldown assays, IL-13Rα2-deficient cells, pharmacological pathway inhibitors, functional readouts","journal":"Cell reports","confidence":"High","confidence_rationale":"Tier 2 — Co-IP/pulldown plus genetic null validation with multiple downstream pathway readouts","pmids":["23972995"],"is_preprint":false},{"year":2016,"finding":"IL-13 promotes intestinal SIgA secretion through a pathway involving intestinal microbiota and IL-13; injection of an IL-13 antibody during glutamine supplementation reduces J-chain expression in the mouse ileum, and disrupting the intestinal microbiota abrogates glutamine's effect on SIgA, with IL-13 acting as a mediator in the T cell-dependent SIgA induction pathway.","method":"Mouse model with glutamine supplementation, IL-13 neutralizing antibody injection, IL-13 ELISA, J-chain expression, germ-free/antibiotic-treated mice","journal":"Molecular nutrition & food research","confidence":"Low","confidence_rationale":"Tier 3 — antibody neutralization with correlation, indirect mechanistic link, single lab","pmids":["27005687"],"is_preprint":false},{"year":2017,"finding":"IL-33 drives a signaling cascade to IL-13 that is required for spasmolytic polypeptide-expressing metaplasia (SPEM) induction in the stomach after parietal cell loss; IL-33 KO and ST2 KO mice do not develop metaplasia in response to L635, while IL-13 KO mice also fail to develop SPEM, and exogenous IL-13 restores metaplasia in ST2 KO mice.","method":"IL-33, ST2, and IL-13 knockout mice, L635-induced parietal cell loss model, exogenous IL-13 rescue, macrophage RNA sequencing","journal":"Gut","confidence":"High","confidence_rationale":"Tier 2 — genetic epistasis with rescue experiment establishing IL-33→IL-13 cascade for metaplasia","pmids":["28196875"],"is_preprint":false},{"year":2017,"finding":"IL-4 or IL-13 together with apoptotic cells (but not alone) is required to induce the tissue repair program in macrophages; genetic ablation of apoptotic cell sensors impairs macrophage proliferation and anti-inflammatory/repair gene induction in the lungs after helminth infection or colitis, while recognition of apoptotic cells is dispensable for cytokine-dependent induction of pattern recognition receptor or chemotaxis genes.","method":"Genetic ablation of apoptotic cell sensors, helminth infection model, colitis model, macrophage gene expression analysis","journal":"Science (New York, N.Y.)","confidence":"High","confidence_rationale":"Tier 2 — genetic dissection of cooperating signals with defined gene expression readouts in multiple disease models","pmids":["28495875"],"is_preprint":false},{"year":2017,"finding":"Autophagy is required for IL-13-mediated apical localization of DUOX1 and subsequent intracellular superoxide production in airway epithelial cells; depletion of autophagy regulator ATG5 reduces superoxide without diminishing total DUOX1 levels, but diminishes apical DUOX1 localization, while DUOX1 siRNA attenuates IL-13-induced superoxide without affecting autophagy.","method":"Primary human tracheobronchial epithelial cells, OVA mouse model, ATG5 siRNA, DUOX1 siRNA, EPR spectroscopy for superoxide, LC3BII western blot, immunostaining","journal":"Redox biology","confidence":"Medium","confidence_rationale":"Tier 2 — siRNA knockdowns with functional localization and EPR spectroscopy, single lab","pmids":["28982074"],"is_preprint":false},{"year":2019,"finding":"IL-13 secreted by ILC2s promotes Lgr5+ intestinal stem cell self-renewal through a circuit involving circPan3 and IL-13Rα1; circPan3 binds IL-13Rα1 mRNA to increase its stability, enabling ISC expression of IL-13Rα1; IL-13 signaling through IL-13Rα1 activates Foxp1 expression, which associates with β-catenin to promote its nuclear translocation and activate Wnt/β-catenin pathway in ISCs.","method":"circPan3 deletion in Lgr5+ ISCs, IL-13Rα1 mRNA stability assay (RNA-protein interaction), Foxp3Cre mouse model, β-catenin localization, organoid/stem cell assays","journal":"Nature immunology","confidence":"High","confidence_rationale":"Tier 2 — multiple genetic models and molecular mechanism (mRNA stabilization, co-IP of Foxp1-β-catenin) in vivo and in vitro","pmids":["30643264"],"is_preprint":false},{"year":2019,"finding":"Foxp3+ Tregs secrete IL-13 in response to IL-33 stimulation, and Treg-derived IL-13 is required to prevent mortality after acute lung injury by controlling local levels of G-CSF, IL-6, and MCP-1 and inhibiting accumulation of Ly6Chi monocytes; this was demonstrated using Foxp3Cre × Il4/Il13fl/fl mice.","method":"Foxp3Cre × Il4/Il13fl/fl conditional knockout mice, acute lung injury model, BAL cytokine analysis, monocyte flow cytometry, IL-33 stimulation of human and mouse Tregs","journal":"JCI insight","confidence":"High","confidence_rationale":"Tier 2 — conditional KO with cell-type-specific IL-13 ablation and defined inflammatory readouts","pmids":["30779711"],"is_preprint":false},{"year":2019,"finding":"Akt1 regulates IL-13 production by macrophages; Akt1-deficient macrophages produce less IL-13 compared to Akt1+/+ macrophages in response to IL-33 stimulation; Akt1-deficient mice have reduced IL-13 levels after bleomycin treatment and are protected from pulmonary fibrosis.","method":"Akt1 knockout mice, bleomycin fibrosis model, bone marrow-derived macrophage stimulation with IL-33, IL-13 ELISA, collagen/ECM quantification","journal":"Innate immunity","confidence":"Medium","confidence_rationale":"Tier 2 — genetic KO with mechanistic link to macrophage IL-13 production, single lab","pmids":["31299858"],"is_preprint":false},{"year":2021,"finding":"Eosinophil-derived IL-13 produced via ST2 (IL-33 receptor) signaling is required for hepatoprotection against ischemia-reperfusion injury; adoptive transfer of bone marrow-derived eosinophils reduces hepatic injury, and this protection requires ST2-dependent IL-13 production by eosinophils, established through genetic and adoptive transfer approaches.","method":"Two genetic mouse models of eosinophil deficiency, antibody-mediated eosinophil depletion, adoptive transfer of eosinophils, ST2-deficient eosinophils, liver IRI model, liver injury biochemical/histological assessment","journal":"Science translational medicine","confidence":"High","confidence_rationale":"Tier 2 — multiple genetic models and adoptive transfer with mechanistic cell-type-specific readout","pmids":["33536281"],"is_preprint":false}],"current_model":"IL-13 is a Th2 cytokine encoded near IL-4 on chromosome 5q31 that signals through type II receptor complexes (IL-4Rα/IL-13Rα1, with STAT6 as the canonical downstream effector and, in fibrosis, through IL-13Rα2/AP-1/TGF-β1), mediating airway hyperresponsiveness, mucus hypersecretion (via EGFR/neutrophil and MAPK/PI3K cascades), IgE class switching in B cells, alternative macrophage activation (including catecholamine production for beige fat biogenesis), epithelial barrier disruption, intestinal stem cell self-renewal (via circPan3-stabilized IL-13Rα1/Foxp1/β-catenin), and tissue fibrosis through a multi-step IL-13Rα2-driven program involving TGF-β1, IGF-I, and Egr-1; its activity is regulated by let-7 miRNAs (post-transcriptionally), miR-155 (via IL-13Rα1 targeting), MMP-8-mediated shedding of the IL-13Rα2 decoy receptor, Akt1-dependent macrophage production, and a cooperative requirement for apoptotic cell signals to activate tissue repair programs."},"narrative":{"teleology":[{"year":1993,"claim":"Identification of IL-13 as a novel T cell-derived cytokine that suppresses monocyte inflammatory cytokines, induces B cell proliferation and IgE class switching independently of IL-4, and maps to chromosome 5q31 near IL-4 established IL-13 as a non-redundant Th2 effector cytokine.","evidence":"cDNA cloning from activated T cells, recombinant protein functional assays on monocytes and B cells, anti-IL-4 neutralization demonstrating IL-4-independent IgE switching","pmids":["8096327","8097324","7688562"],"confidence":"High","gaps":["Receptor identity and signaling pathway unknown","In vivo relevance of IL-13 in disease not yet tested","Relationship to IL-4 at the receptor level undefined"]},{"year":1998,"claim":"Demonstration that IL-13 is both necessary and sufficient for hallmark asthma features (airway hyperresponsiveness, mucus overproduction) independently of IgE and eosinophils, and is non-redundantly required for intestinal helminth expulsion, established IL-13 as a central effector of allergic and anti-helminth immunity in vivo.","evidence":"Selective IL-13 neutralization and IL-13 KO mice in asthma and Trichuris muris infection models; IL-4Rα-deficient mice","pmids":["9856949","9856950","9531306"],"confidence":"High","gaps":["Precise epithelial signaling mechanism for mucus induction unknown","Relative contributions of IL-13Rα1 versus IL-13Rα2 in vivo unclear","Molecular basis of airway smooth muscle hyperresponsiveness not defined"]},{"year":2001,"claim":"Elucidation of downstream epithelial effector mechanisms showed IL-13 drives mucus overproduction through EGFR/neutrophil-dependent and MAPK/PI3K pathways, alters mucociliary differentiation via IL-4Rα, and requires STAT6 for airway hyperreactivity, defining the intracellular signaling architecture in target tissues.","evidence":"EGFR inhibitors, neutrophil depletion, and kinase inhibitors in vivo and in air-liquid interface epithelial cultures; STAT6-KO and IL-4Rα-KO mice with allergen challenge","pmids":["11133503","11748265","11466392","12794003"],"confidence":"High","gaps":["Whether EGFR-dependent and MAPK/PI3K-dependent mucus pathways are cell-type specific or context dependent","STAT6-independent IL-13 signaling components not identified","Mechanism of IL-13 action on smooth muscle contractility only partially defined"]},{"year":2003,"claim":"IL-13 was shown to directly enhance airway smooth muscle contractility and calcium signaling, and to suppress iNOS in macrophages via arginase-mediated arginine depletion, revealing cell-type-specific effector mechanisms beyond epithelial targets.","evidence":"Tracheal ring contractility and calcium fluorimetry in human ASM cells; arginase inhibitors and metabolic labeling in primary macrophages","pmids":["14597600","14568929"],"confidence":"High","gaps":["In vivo relevance of direct smooth muscle signaling versus indirect epithelial effects unresolved","Whether arginase-mediated translational control extends to other IL-13 target proteins unknown"]},{"year":2005,"claim":"Discovery that IL-13Rα2 functions as a signaling receptor activating AP-1 (c-jun/Fra-2) to induce TGF-β1 and drive fibrosis overturned the prevailing decoy-only model, while characterization of the R130Q variant revealed reduced IL-13Rα2 decoy function and enhanced STAT6 signaling as a mechanism for genetic asthma risk.","evidence":"AP-1 promoter analysis, IL-13Rα2 siRNA in colitis/fibrosis models; recombinant WT vs R130Q protein binding and signaling assays on primary human cells with patient serum correlation","pmids":["16327802","15711639","12063528"],"confidence":"High","gaps":["Crystal structure of IL-13/IL-13Rα2 signaling complex not available at this time","Full spectrum of IL-13Rα2-dependent transcriptional targets beyond TGF-β1 undefined","How IL-13Rα2 signaling versus decoy functions are balanced in different tissues unclear"]},{"year":2007,"claim":"Multiple upstream triggers and feedback mechanisms were identified: IL-33 induces IL-13 from mast cells via MyD88, IL-9 requires IL-13 as a downstream mediator for lung eosinophilia, epithelial injury triggers autocrine IL-13/HB-EGF/EGFR repair signaling with negative feedback, and IL-13 activates PPARγ for CD36-mediated phagocytosis in monocytes.","evidence":"MyD88-KO mast cells, IL-13-KO × IL-9-transgenic mice, scratch wound assays with IL-13 neutralization, PPARγ-null macrophages with PLA2 inhibitors","pmids":["17881510","17312173","17717322","17458857"],"confidence":"High","gaps":["Whether IL-33→IL-13 axis operates equivalently across all tissue-resident mast cell populations","Full extent of autocrine IL-13 signaling in non-airway epithelia unclear","PPARγ-mediated CD36 pathway not tested beyond malaria phagocytosis"]},{"year":2008,"claim":"Structural resolution of the complete type II receptor ternary complexes revealed that IL-13 engages IL-13Rα1 through a novel top-mounted Ig-like domain with recognition chemistry distinct from IL-4, while MMP-8 was identified as a protease that sheds IL-13Rα2 to regulate IL-13 bioavailability in vivo, and IL-13Rα2-driven fibrosis was shown to involve a multi-step cascade (TGF-β1, IGF-I, Egr-1).","evidence":"X-ray crystallography of IL-4Rα/IL-13Rα1/IL-13 ternary complexes; MMP-8-KO mice with allergen challenge; siRNA knockdown of IL-13Rα2/TGF-β1 pathway components in chronic colitis","pmids":["18243101","18694590","18938165"],"confidence":"High","gaps":["Structure of IL-13/IL-13Rα2 signaling complex not resolved","Other proteases that may regulate IL-13Rα2 shedding not identified","Structural basis for differential STAT6 activation potency by IL-4 vs IL-13 incompletely explained"]},{"year":2010,"claim":"Post-transcriptional and post-signaling regulatory layers were defined: miR-155 directly targets IL-13Rα1 to attenuate STAT6-dependent M2 macrophage polarization, IL-13 drives alternative macrophage activation for catecholamine-dependent beige fat biogenesis, and IL-13 disrupts epithelial barrier integrity by downregulating desmoglein-1 in eosinophilic esophagitis.","evidence":"miR-155 luciferase reporter assays in primary macrophages; IL-4/IL-13-signaling-deficient mice under cold stress; DSG1 siRNA and transepithelial resistance in esophageal epithelial cells with patient biopsy validation","pmids":["21097505","24906148","24220297"],"confidence":"High","gaps":["Whether miR-155 regulation of IL-13Rα1 varies across tissue macrophage populations unknown","The catecholamine-producing macrophage pathway has been debated regarding reproducibility in other mouse strains","Mechanism linking IL-13 to DSG1 transcriptional downregulation not fully defined"]},{"year":2011,"claim":"Let-7 miRNAs were shown to directly repress IL-13 mRNA, and intranasal let-7 delivery resolved allergic airway disease features, establishing post-transcriptional control of IL-13 itself as a regulatory node.","evidence":"Bioinformatic prediction, in vitro transfection in T cells, intranasal let-7 mimic in murine allergy model","pmids":["21616524"],"confidence":"Medium","gaps":["Endogenous regulation of let-7 levels in Th2 cells during allergic inflammation not defined","Specificity of let-7 for IL-13 versus other Th2 cytokines at endogenous expression levels not resolved"]},{"year":2017,"claim":"An IL-33→IL-13 signaling cascade was shown to be required for spasmolytic polypeptide-expressing metaplasia after parietal cell loss, full macrophage tissue repair programming requires IL-13 together with apoptotic cell recognition (neither alone suffices), and autophagy was identified as required for IL-13-induced apical DUOX1 localization and superoxide production.","evidence":"IL-33/ST2/IL-13 triple KO epistasis with IL-13 rescue in gastric metaplasia model; genetic ablation of apoptotic cell sensors in helminth and colitis models; ATG5/DUOX1 siRNA in airway epithelial cells with EPR spectroscopy","pmids":["28196875","28495875","28982074"],"confidence":"High","gaps":["Identity of the apoptotic cell sensor cooperating with IL-13 signaling not fully defined","Whether the IL-33→IL-13 metaplasia pathway operates in human gastric disease untested","How autophagy specifically directs DUOX1 trafficking versus general cargo unclear"]},{"year":2019,"claim":"ILC2-derived IL-13 was shown to maintain intestinal stem cell self-renewal via circPan3-stabilized IL-13Rα1/Foxp1/β-catenin signaling, Treg-derived IL-13 was demonstrated to be protective in acute lung injury by restraining monocyte accumulation, and Akt1 was identified as a kinase regulating macrophage IL-13 production and pulmonary fibrosis susceptibility.","evidence":"circPan3 deletion in Lgr5+ ISCs with RNA-protein interaction and Foxp1-β-catenin co-IP; Foxp3Cre × Il4/Il13 floxed mice in lung injury; Akt1-KO macrophages with IL-33 stimulation and bleomycin fibrosis model","pmids":["30643264","30779711","31299858"],"confidence":"High","gaps":["Whether circPan3-IL-13Rα1 axis operates in other stem cell niches unknown","Human relevance of Treg-derived IL-13 in ARDS or lung injury not tested","Akt1 substrates directly linking to IL-13 transcription/secretion not identified"]},{"year":2021,"claim":"Eosinophil-derived IL-13 produced via ST2 signaling was shown to mediate hepatoprotection against ischemia-reperfusion injury, extending the tissue-protective role of cell-type-specific IL-13 beyond the lung.","evidence":"Genetic eosinophil-deficient mice, adoptive transfer of WT vs ST2-KO eosinophils, liver IRI model with biochemical and histological assessment","pmids":["33536281"],"confidence":"High","gaps":["Downstream hepatic targets of eosinophil-derived IL-13 not identified","Whether IL-13Rα2-mediated fibrogenic signaling is engaged in hepatic IRI context unclear","Therapeutic window and translational relevance of eosinophil IL-13 in human liver IRI unknown"]},{"year":null,"claim":"Key unresolved questions include the structural basis of IL-13Rα2 signaling (vs decoy) complex formation, how tissue-specific receptor expression ratios determine fibrotic vs protective outcomes, and the therapeutic implications of selectively blocking IL-13Rα2 signaling while preserving IL-13Rα1-mediated repair.","evidence":"","pmids":[],"confidence":"Low","gaps":["No crystal structure of IL-13/IL-13Rα2 signaling complex available","Integrated quantitative model of IL-13 signal partitioning between Rα1 and Rα2 across tissues lacking","Cell-type-specific functions of IL-13 from distinct immune sources (ILC2, Treg, eosinophil, Th2) not systematically compared"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0048018","term_label":"receptor ligand activity","supporting_discovery_ids":[0,1,2,3]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[11,12,25]}],"localization":[{"term_id":"GO:0005576","term_label":"extracellular region","supporting_discovery_ids":[0,1,3,17,35]}],"pathway":[{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[0,1,2,3,4,8,16,18,35,37]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[8,12,21,23,29,34]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[3,13,14,15,20,27]}],"complexes":[],"partners":["IL4R","IL13RA1","IL13RA2","STAT6","CHI3L1","IL33"],"other_free_text":[]},"mechanistic_narrative":"IL-13 is a pleiotropic Th2 cytokine that orchestrates type 2 immune responses, tissue remodeling, and repair across multiple organ systems. It signals canonically through the type II receptor complex (IL-4Rα/IL-13Rα1), activating STAT6 to drive IgE class switching in B cells, goblet cell metaplasia via MAPK/PI3K cascades, airway hyperresponsiveness through enhanced smooth muscle calcium signaling, alternative macrophage activation including catecholamine production for beige fat biogenesis, and epithelial barrier remodeling [PMID:9856949, PMID:8097324, PMID:12794003, PMID:24906148, PMID:24220297]. A parallel signaling axis through IL-13Rα2 activates AP-1 (c-jun/Fra-2) to induce TGF-β1 transcription and a downstream fibrogenic cascade involving IGF-I and Egr-1, establishing IL-13Rα2 as a bona fide signaling receptor rather than merely a decoy [PMID:16327802, PMID:18938165]. IL-13 bioavailability and signaling are regulated at multiple levels, including post-transcriptional repression by let-7 miRNAs, miR-155-mediated targeting of IL-13Rα1, MMP-8-dependent shedding of soluble IL-13Rα2, Akt1-dependent production in macrophages, and a cooperative requirement for apoptotic cell recognition to activate the full tissue repair program [PMID:21616524, PMID:21097505, PMID:18694590, PMID:28495875]."},"prefetch_data":{"uniprot":{"accession":"P35225","full_name":"Interleukin-13","aliases":[],"length_aa":146,"mass_kda":15.8,"function":"Cytokine that plays important roles in allergic inflammation and immune response to parasite infection (PubMed:8096327, PubMed:8097324). Synergizes with IL2 in regulating interferon-gamma synthesis (PubMed:8096327). Stimulates B-cell proliferation, and activation of eosinophils, basophils, and mast cells (PubMed:7903680, PubMed:8759755). Plays an important role in controlling IL33 activity by modulating the production of transmembrane and soluble forms of interleukin-1 receptor-like 1/IL1RL1 (By similarity). Displays the capacity to antagonize Th1-driven proinflammatory immune response and downregulates synthesis of many proinflammatory cytokines including IL1, IL6, IL10, IL12 and TNF through a mechanism that partially involves suppression of NF-kappa-B (By similarity). Also functions on nonhematopoietic cells, including endothelial cells where it induces vascular cell adhesion protein 1/VCAM1, which is important in the recruitment of eosinophils (PubMed:8639787). Exerts its biological effects through its receptors which comprises the IL4R chain and the IL13RA1 chain, to activate JAK1 and TYK2, leading to the activation of STAT6 (PubMed:9013879). Aside from IL13RA1, another receptor IL13RA2 acts as a high affinity decoy for IL13 and mediates internalization and depletion of extracellular IL13 (PubMed:21622864)","subcellular_location":"Secreted","url":"https://www.uniprot.org/uniprotkb/P35225/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/IL13","classification":"Not Classified","n_dependent_lines":1,"n_total_lines":1208,"dependency_fraction":0.0008278145695364238},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/IL13","total_profiled":1310},"omim":[{"mim_id":"620925","title":"LEUCINE-RICH REPEAT-CONTAINING PROTEIN 31; LRRC31","url":"https://www.omim.org/entry/620925"},{"mim_id":"620532","title":"HYPER-IgE SYNDROME 6, AUTOSOMAL DOMINANT, WITH RECURRENT INFECTIONS; HIES6","url":"https://www.omim.org/entry/620532"},{"mim_id":"620290","title":"TRANSMEMBRANE PROTEIN 219; TMEM219","url":"https://www.omim.org/entry/620290"},{"mim_id":"620143","title":"TRANSMEMBRANE PROTEIN 232; TMEM232","url":"https://www.omim.org/entry/620143"},{"mim_id":"619630","title":"IMMUNODEFICIENCY 88; IMD88","url":"https://www.omim.org/entry/619630"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Tissue enriched","tissue_distribution":"Detected in single","driving_tissues":[{"tissue":"testis","ntpm":23.3}],"url":"https://www.proteinatlas.org/search/IL13"},"hgnc":{"alias_symbol":["P600","IL-13","ALRH","BHR1","MGC116786","MGC116788","MGC116789"],"prev_symbol":[]},"alphafold":{"accession":"P35225","domains":[{"cath_id":"1.20.1250.10","chopping":"40-143","consensus_level":"high","plddt":92.1394,"start":40,"end":143}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P35225","model_url":"https://alphafold.ebi.ac.uk/files/AF-P35225-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P35225-F1-predicted_aligned_error_v6.png","plddt_mean":85.62},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=IL13","jax_strain_url":"https://www.jax.org/strain/search?query=IL13"},"sequence":{"accession":"P35225","fasta_url":"https://rest.uniprot.org/uniprotkb/P35225.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P35225/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P35225"}},"corpus_meta":[{"pmid":"9856950","id":"PMC_9856950","title":"Requirement 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response.","date":"1999","source":"Journal of immunology (Baltimore, Md. : 1950)","url":"https://pubmed.ncbi.nlm.nih.gov/10227975","citation_count":281,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"23042114","id":"PMC_23042114","title":"Genome-wide association study identifies eight new susceptibility loci for atopic dermatitis in the Japanese population.","date":"2012","source":"Nature genetics","url":"https://pubmed.ncbi.nlm.nih.gov/23042114","citation_count":278,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"21097505","id":"PMC_21097505","title":"The interleukin 13 (IL-13) pathway in human macrophages is modulated by microRNA-155 via direct targeting of interleukin 13 receptor alpha1 (IL13Ralpha1).","date":"2010","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/21097505","citation_count":274,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"23972995","id":"PMC_23972995","title":"Chitinase 3-like 1 regulates cellular and tissue responses via IL-13 receptor α2.","date":"2013","source":"Cell reports","url":"https://pubmed.ncbi.nlm.nih.gov/23972995","citation_count":273,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"11709756","id":"PMC_11709756","title":"Gene-gene interaction in asthma: IL4RA and IL13 in a Dutch population with asthma.","date":"2001","source":"American journal of human genetics","url":"https://pubmed.ncbi.nlm.nih.gov/11709756","citation_count":249,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"24220297","id":"PMC_24220297","title":"Desmoglein-1 regulates esophageal epithelial barrier function and immune responses in eosinophilic esophagitis.","date":"2013","source":"Mucosal immunology","url":"https://pubmed.ncbi.nlm.nih.gov/24220297","citation_count":248,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"26073683","id":"PMC_26073683","title":"The differential expression of IL-4 and IL-13 and its impact on type-2 immunity.","date":"2015","source":"Cytokine","url":"https://pubmed.ncbi.nlm.nih.gov/26073683","citation_count":243,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"20159242","id":"PMC_20159242","title":"Genome-wide association study of asthma identifies RAD50-IL13 and HLA-DR/DQ regions.","date":"2010","source":"The Journal of allergy and clinical immunology","url":"https://pubmed.ncbi.nlm.nih.gov/20159242","citation_count":240,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"12794003","id":"PMC_12794003","title":"IL-13-induced changes in the goblet cell density of human bronchial epithelial cell cultures: MAP kinase and phosphatidylinositol 3-kinase regulation.","date":"2003","source":"American journal of physiology. Lung cellular and molecular physiology","url":"https://pubmed.ncbi.nlm.nih.gov/12794003","citation_count":232,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"20177070","id":"PMC_20177070","title":"Epithelial myosin light chain kinase activation induces mucosal interleukin-13 expression to alter tight junction ion selectivity.","date":"2010","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/20177070","citation_count":231,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"23223131","id":"PMC_23223131","title":"CD8(+) T cells in the lesional skin of atopic dermatitis and psoriasis patients are an important source of IFN-γ, IL-13, IL-17, and IL-22.","date":"2012","source":"The Journal of investigative dermatology","url":"https://pubmed.ncbi.nlm.nih.gov/23223131","citation_count":230,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"17911623","id":"PMC_17911623","title":"IL-13 induces disease-promoting type 2 cytokines, alternatively activated macrophages and allergic inflammation during pulmonary infection of mice with Cryptococcus neoformans.","date":"2007","source":"Journal of immunology (Baltimore, Md. : 1950)","url":"https://pubmed.ncbi.nlm.nih.gov/17911623","citation_count":224,"is_preprint":false,"source_track":"gene2pubmed"}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":50291,"output_tokens":8323,"usd":0.137859},"stage2":{"model":"claude-opus-4-6","input_tokens":12282,"output_tokens":6422,"usd":0.33294},"total_usd":0.903254,"stage1_batch_id":"msgbatch_01DzrsgVgYngY1hvM3DU1yF2","stage2_batch_id":"msgbatch_01KA9b7iRzKFdhoBUT7vCvSe","note":"batch pricing = 50% of standard","round2_stage1":{"model":"claude-sonnet-4-6","input_tokens":64473,"output_tokens":9418,"usd":0.167345},"round2_rules_fired":"R3","round2_stage2":{"model":"claude-opus-4-6","input_tokens":13673,"output_tokens":4335,"usd":0.26511}},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1998,\n      \"finding\": \"IL-13 mediates airway hyperresponsiveness, eosinophil recruitment, and mucus overproduction independently of IL-4, acting through the IL-4 receptor alpha chain (IL-4Rα)-dependent pathway, as demonstrated by selective neutralization of IL-13 and administration of recombinant IL-13 to T cell-deficient mice.\",\n      \"method\": \"In vivo neutralization with soluble IL-13Rα2-IgG fusion protein; recombinant cytokine administration to T cell-deficient mice; IL-4Rα knockout mice\",\n      \"journal\": \"Science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean KO/neutralization with specific phenotypic readouts, replicated across multiple experimental arms\",\n      \"pmids\": [\"9856950\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"IL-13 is required for resistance to intestinal nematode Trichuris muris infection, with IL-13 KO mice being susceptible despite generating Th2 responses, demonstrating a non-redundant role with IL-4 in helminth immunity.\",\n      \"method\": \"IL-13 knockout mouse infection model with T. muris; comparison with IL-4 KO mice\",\n      \"journal\": \"Journal of Immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with defined infection phenotype, multiple cytokine comparisons\",\n      \"pmids\": [\"9531306\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1993,\n      \"finding\": \"IL-13 synergizes with CD40L to induce B cell proliferation and Ig isotype switching to IgM, IgG, IgG4, and IgE, independently of IL-4, as shown by anti-IL-4 antibody blockade failing to inhibit IL-13-driven B cell differentiation.\",\n      \"method\": \"Co-culture of purified B cells with COS-7/hCD40L transfectants; anti-IL-4 antibody neutralization; ELISA for immunoglobulin isotypes\",\n      \"journal\": \"International immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — functional in vitro assay with antibody blockade and multiple orthogonal readouts\",\n      \"pmids\": [\"7688562\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"IL-13 alters mucociliary differentiation of human respiratory epithelial cells by downregulating ezrin and impairing lateral cell contacts, increasing secretory cell proportion while reducing ciliated cells, and decreasing ciliary beat frequency; this effect is blocked by an IL-4Rα antagonist (Y124D mutein), confirming signaling via the shared IL-4Rα subunit.\",\n      \"method\": \"Primary human nasal epithelial cell culture; IL-4 antagonist mutein (Y124D) blockade; immunofluorescence; ciliary beat frequency measurement\",\n      \"journal\": \"The Journal of Clinical Investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (morphology, protein localization, functional assay, pharmacological blockade) in primary human cells\",\n      \"pmids\": [\"11748265\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"IL-13 induces mucin production in airway goblet cells via EGFR signaling cascades involving neutrophil recruitment and IL-8-mediated chemoattraction; EGFR tyrosine kinase inhibitors and leukocyte depletion block IL-13-induced goblet cell metaplasia.\",\n      \"method\": \"In vivo mouse intratracheal instillation of IL-13; EGFR tyrosine kinase inhibitor; cyclophosphamide pre-treatment; anti-IL-8 blocking antibody\",\n      \"journal\": \"American Journal of Physiology – Lung Cellular and Molecular Physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple pharmacological interventions with specific mechanistic targets in vivo\",\n      \"pmids\": [\"11133503\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"IL-13 signals through the IL-13Rα1/IL-4Rα heterodimer complex to activate STAT6; a novel pathway involving STAT6 but independent of IL-4Rα was identified in which T cell-derived IL-13 induces AHR, eotaxin production, and eosinophilia in allergic lung.\",\n      \"method\": \"Adoptive transfer of IL-13-deficient and WT CD4+ T cells to STAT6-deficient and IL-4Rα-deficient mice; in vivo OVA challenge model\",\n      \"journal\": \"Journal of Immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — epistasis demonstrated via adoptive transfer into multiple KO strains with orthogonal phenotypic readouts\",\n      \"pmids\": [\"11466392\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"IL-13 suppresses inducible NO synthase (iNOS) protein expression in macrophages by upregulating arginase, which depletes arginine and impairs iNOS translation and protein stability, without affecting iNOS mRNA levels; arginase inhibitors or arginine supplementation rescue iNOS protein expression.\",\n      \"method\": \"Mouse peritoneal macrophage stimulation with IFN-γ/LPS ± IL-13; arginase inhibitors; arginine supplementation; protein vs. mRNA level comparison; radioligand binding assay\",\n      \"journal\": \"Journal of Immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — mechanistic dissection with pharmacological rescue experiments demonstrating translational regulation\",\n      \"pmids\": [\"14568929\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"IL-13 enhances agonist-evoked calcium signals in airway smooth muscle cells and increases contractile responses to carbachol and KCl, suggesting direct modulation of G protein-coupled receptor (GPCR)-associated calcium signaling as a mechanism for bronchial hyperresponsiveness.\",\n      \"method\": \"Murine tracheal ring contractility assay; calcium imaging in human ASM cells; multiple agonist stimulation (bradykinin, histamine, carbachol)\",\n      \"journal\": \"British Journal of Pharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — functional in vitro assay with multiple agonists in both mouse and human cells, single lab\",\n      \"pmids\": [\"14597600\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"The IL-13 R130Q variant (IL13+2044GA) shows enhanced STAT6 phosphorylation and CD23 induction in monocytes and augmented IgE class switching in B cells compared to WT IL-13; it is neutralized less effectively by the IL-13Rα2 decoy receptor, explaining its increased in vivo activity.\",\n      \"method\": \"Recombinant protein production; STAT6 phosphorylation assay; CD23 expression on primary human monocytes; IgE switching assay in B cells; IL-13Rα2 neutralization comparison\",\n      \"journal\": \"The Journal of Clinical Investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — direct comparison of recombinant proteins with multiple orthogonal functional readouts on primary human cells\",\n      \"pmids\": [\"15711639\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"IL-13 stimulates esophageal epithelial cells to produce eotaxin-3 via a STAT6-dependent transcriptional mechanism; IL-13 drives a global transcriptome in esophageal epithelial cells that overlaps with the eosinophilic esophagitis (EE)-specific transcriptome.\",\n      \"method\": \"IL-13 stimulation of primary esophageal epithelial cells; luciferase reporter transfection with eotaxin-3 promoter; STAT6 dominant-negative constructs; microarray and real-time PCR\",\n      \"journal\": \"The Journal of Allergy and Clinical Immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reporter assay with mutagenesis of STAT6 binding site plus transcriptomic validation\",\n      \"pmids\": [\"18073124\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"IL-13 signaling via IL-13Rα2 (not IL-13Rα1) drives intestinal fibrosis by inducing TGF-β1, which in turn activates IGF-1 and Egr-1 expression, leading to myofibroblast apoptosis, urokinase plasminogen activator production, and collagen deposition.\",\n      \"method\": \"siRNA and decoy oligonucleotides targeting IL-13Rα2 and TGF-β1 signaling in chronic TNBS colitis model; ELISA; Western blot; collagen measurement\",\n      \"journal\": \"Gastroenterology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — pathway dissection with siRNA knockdown of specific receptor isoform, multiple downstream mediators measured\",\n      \"pmids\": [\"18938165\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"IL-13 (not IL-4) mediates bleomycin-induced pulmonary fibrosis in part by inducing the CC chemokine C10, which recruits mononuclear phagocytes; neutralization of IL-13 attenuated both fibrosis and C10 levels, and subsequent C10 neutralization also reduced fibrosis.\",\n      \"method\": \"In vivo neutralization with anti-IL-13 and anti-IL-4 antibodies in bleomycin pulmonary fibrosis model; anti-C10 antibody neutralization; cytokine ELISA; histology\",\n      \"journal\": \"American Journal of Respiratory Cell and Molecular Biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — sequential specific neutralization experiments demonstrating IL-13→C10 pathway in vivo\",\n      \"pmids\": [\"12356575\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"IL-33 induces IL-13 (and IL-6) production by mouse mast cells via a MyD88-dependent but TRIF-independent pathway, independently of IgE-FcεRI signals; IL-33 does not induce mast cell degranulation.\",\n      \"method\": \"BMCMC stimulation with IL-13; ELISA; MyD88-deficient cells; TRIF-deficient cells; degranulation assay\",\n      \"journal\": \"Journal of Leukocyte Biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO of adaptor proteins to dissect signaling pathway, multiple readouts\",\n      \"pmids\": [\"17881510\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"IL-13 induces expression of CD36 in human monocytes through PPARγ activation via phospholipase A2-dependent production of endogenous 15-deoxy-Δ12,14-PGJ2; CD36 and PPARγ mediate IL-13-dependent phagocytosis of P. falciparum-parasitized erythrocytes.\",\n      \"method\": \"PPARγ expression plasmid transfection; PPARγ conditional null mouse macrophages; PLA2 inhibitor; 15d-PGJ2 ELISA; phagocytosis assay\",\n      \"journal\": \"European Journal of Immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic (conditional KO) and pharmacological dissection with functional readout\",\n      \"pmids\": [\"17458857\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"IL-13 secreted by injured airway epithelial cells enhances epithelial repair through HB-EGF-dependent EGFR phosphorylation; neutralization of IL-13 reduces repair, exogenous IL-13 promotes repair, and EGFR activation provides negative feedback to limit IL-13 release.\",\n      \"method\": \"Mechanical wounding assay; IL-13 neutralization (shIL-13Rα2.Fc); exogenous IL-13; EGFR inhibitor (tyrphostin AG1478); HB-EGF ELISA; EGFR phosphorylation assay\",\n      \"journal\": \"American Journal of Respiratory Cell and Molecular Biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple pharmacological interventions in primary airway epithelial cells, single lab\",\n      \"pmids\": [\"17717322\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"MMP-8 cleaves IL-13Rα2 at the cell surface to generate biologically active soluble IL-13Rα2 that retains IL-13 binding activity; MMP-8-deficient mice show increased airway hyperresponsiveness and reduced soluble IL-13Rα2 in BAL fluid after allergen challenge.\",\n      \"method\": \"In vitro cleavage assay with recombinant MMPs; stable transfection of IL-13Rα2; surface vs. soluble IL-13Rα2 measurement; MMP-8 KO mouse allergen model; BAL ELISA\",\n      \"journal\": \"The Journal of Allergy and Clinical Immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — in vitro reconstitution of cleavage plus genetic KO mouse model with functional outcome\",\n      \"pmids\": [\"18694590\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"The IL-13 R130Q (Gln110) variant has lower affinity for IL-13Rα2 decoy receptor, leading to less clearance and enhanced plasma stability, resulting in higher serum IL-13 levels in asthmatic patients homozygous for the variant.\",\n      \"method\": \"Recombinant IL-13 protein binding affinity assay with IL-13Rα2; plasma stability assay (mouse and human); genotype-serum IL-13 correlation in asthmatic cohort\",\n      \"journal\": \"The Journal of Allergy and Clinical Immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — recombinant protein biochemistry combined with human genetics, single lab\",\n      \"pmids\": [\"12063528\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"IL-13 colocalizes with STAT6-dependent signaling in a fibrotic pathway; STAT6 blockade prevents IL-13-mediated collagen induction independently of TGF-β1; miR-135b downregulates IL-13-induced collagen expression and is itself repressed by methylation (MeCP2) in scleroderma fibroblasts.\",\n      \"method\": \"siRNA knockdown of STAT6; small molecule STAT6 inhibitor; miR-135b transfection; qRT-PCR for collagen1A1; primary dermal fibroblast culture; methylation analysis\",\n      \"journal\": \"Scientific Reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — mechanistic dissection with siRNA and miRNA in primary human fibroblasts, single lab\",\n      \"pmids\": [\"27113293\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"IL-13 activates STAT6 (not NF-κB) in the liver and reduces hepatic ischemia/reperfusion injury by suppressing TNF-α and MIP-2 production; STAT6 activation is the mechanism underlying IL-13's hepatoprotective effects.\",\n      \"method\": \"Recombinant IL-13 administration in mouse hepatic ischemia/reperfusion model; STAT6 and NF-κB activation assays; cytokine ELISA; histology\",\n      \"journal\": \"The American Journal of Pathology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — in vivo model with pathway-specific signaling readout, single lab\",\n      \"pmids\": [\"10514388\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Endogenous IL-13 (but not IL-10) is a critical regulator of hepatic ischemia/reperfusion inflammatory response, controlling neutrophil trafficking into parenchyma and protecting hepatocytes and endothelial cells; in vitro, IL-13 directly protects hepatocytes from H2O2-induced cytotoxicity.\",\n      \"method\": \"IL-13 KO and IL-10 KO mice in hepatic I/R model; histology; serum hyaluronic acid (endothelial injury marker); in vitro hepatocyte H2O2 cytotoxicity assay\",\n      \"journal\": \"Hepatology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with defined cellular phenotype plus in vitro mechanistic confirmation, single lab\",\n      \"pmids\": [\"12540780\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Let-7 family microRNAs directly regulate IL-13 expression post-transcriptionally; let-7 levels are inversely correlated with IL-13 in T cells, and intranasal delivery of let-7 mimic reduces IL-13 levels and resolves airway inflammation in mice.\",\n      \"method\": \"In silico binding prediction; in vitro transfection in A549 and primary T cells; intranasal let-7 mimic delivery in mouse allergic airway model; qRT-PCR; functional readouts (AHR, mucus, fibrosis)\",\n      \"journal\": \"The Journal of Allergy and Clinical Immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — in vitro and in vivo evidence with functional rescue, single lab\",\n      \"pmids\": [\"21616524\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"IL-9-induced mucus production and upregulation of lung epithelial genes is fully mediated by IL-13: hematopoietic cells expressing both IL-9R and IL-13 genes are required; IL-13 is a direct downstream mediator of IL-9 on lung epithelial cells, not a cofactor.\",\n      \"method\": \"IL-13 KO × IL-9 transgenic mouse crosses; hematopoietic cell transfer into IL-9R-deficient recipients; in vivo eotaxin and mucus measurement\",\n      \"journal\": \"Journal of Immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis via KO crosses and reconstitution by adoptive transfer, multiple phenotypic readouts\",\n      \"pmids\": [\"17312173\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"IL-13 directly downregulates epidermal differentiation complex (EDC) genes, including filaggrin and SPRR3, in esophageal epithelial cells; this downregulation is seen both in IL-13-stimulated primary cells and in EE biopsy specimens, establishing a coordinate interaction between IL-13 and epithelial barrier gene regulation.\",\n      \"method\": \"Primary esophageal epithelial cell culture ± IL-13; microarray and qRT-PCR; comparison with EE patient biopsy transcriptome; filaggrin loss-of-function variant genotyping\",\n      \"journal\": \"Journal of Immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vitro mechanistic finding validated by in vivo biopsy data with orthogonal methods\",\n      \"pmids\": [\"20208004\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"IL-13 suppresses proliferation of pulmonary artery smooth muscle cells (paSMC) via STAT3 and STAT6 signaling by promoting G0/G1 arrest and suppressing endothelin-1 production; ectopic IL-13Rα2 expression partially blocks this growth-suppressive effect, while siRNA knockdown of IL-13Rα2 enhances it.\",\n      \"method\": \"Whole-genome microarray; IL-13 treatment of paSMC; STAT3/STAT6 phosphorylation; cell cycle analysis; IL-13Rα2 ectopic expression and siRNA knockdown; endothelin-1 ELISA\",\n      \"journal\": \"American Journal of Respiratory and Critical Care Medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — mechanistic pathway dissection with gain- and loss-of-function for IL-13Rα2, single lab\",\n      \"pmids\": [\"20522789\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"IL-13 inhibits tube formation and migration of human coronary artery endothelial cells (anti-angiogenic effect) via JAK2 activation followed by STAT6 activation; RNA interference depletion of JAK2 and STAT6 abolishes this inhibitory effect.\",\n      \"method\": \"In vitro tube formation assay; migration assay; siRNA knockdown of JAK2 and STAT6; STAT6 phosphorylation assay\",\n      \"journal\": \"Circulation Journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — siRNA epistasis with functional angiogenesis assay, single lab\",\n      \"pmids\": [\"18296848\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"House dust mite allergen proteases solubilize IL-13Rα2 from cell surfaces, releasing biologically active soluble IL-13Rα2 that inhibits IL-13 signaling; prolonged allergen exposure degrades IL-13Rα2, increasing IL-13 signaling; soluble IL-13Rα2 was detected in human BAL fluid and is reduced in asthmatic subjects.\",\n      \"method\": \"Cell treatment with HDM allergen; IL-13Rα2 surface and soluble levels measured by ELISA/Western; IL-13 signaling readouts; BAL fluid from asthmatic and healthy humans\",\n      \"journal\": \"The Journal of Allergy and Clinical Immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — in vitro biochemistry confirmed in vivo human BAL data, single lab\",\n      \"pmids\": [\"17140645\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"ILC2-derived IL-13 promotes self-renewal of intestinal Lgr5+ stem cells via IL-13Rα1 (stabilized by circPan3 binding to Il13ra1 mRNA in ISCs), which activates IL-13–IL-13R signaling to induce Foxp1 expression; Foxp1 associates with β-catenin to promote its nuclear translocation and activate Wnt/β-catenin pathway in ISCs.\",\n      \"method\": \"circPan3 deletion in Lgr5+ ISCs; IL-13Rα1 stability assay; Foxp3Cre-based lineage tracing; β-catenin nuclear localization; organoid culture; RNA-seq\",\n      \"journal\": \"Nature Immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple genetic models and molecular mechanistic readouts in a single rigorous study\",\n      \"pmids\": [\"30643264\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"IL-33 drives a signaling cascade leading to IL-13 production that is required for stomach metaplasia (SPEM) induction after parietal cell loss; IL-13 KO mice fail to develop metaplasia, and exogenous IL-13 restores metaplasia in ST2 KO mice, placing IL-13 downstream of IL-33/ST2 in this pathway.\",\n      \"method\": \"IL-33 KO, ST2 KO, and IL-13 KO mouse models; L635-induced parietal cell loss; macrophage RNA sequencing; IL-13 reconstitution experiment\",\n      \"journal\": \"Gut\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — epistasis established through multiple KO strains with rescue experiment\",\n      \"pmids\": [\"28196875\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"IL-33 stimulates Foxp3+ Tregs to secrete IL-13; Treg-derived IL-13 is required to prevent mortality after acute lung injury by controlling G-CSF, IL-6, and MCP-1 levels and inhibiting accumulation of Ly6Chi monocytes, as shown using Foxp3Cre × Il4/Il13fl/fl mice.\",\n      \"method\": \"Il33-/- mice; local IL-13 delivery; Foxp3Cre × Il4/Il13fl/fl conditional KO; BAL cytokine measurement; human Treg stimulation\",\n      \"journal\": \"JCI Insight\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — conditional cell-specific KO with specific phenotypic and molecular readouts\",\n      \"pmids\": [\"30779711\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Eosinophils produce IL-13 in an ST2 (IL-33 receptor)-dependent manner and this IL-13 is required for protection against hepatic ischemia/reperfusion injury; adoptive transfer of WT but not ST2-deficient eosinophils normalizes liver injury in eosinophil-deficient mice.\",\n      \"method\": \"Eosinophil-deficient mouse models; adoptive transfer of bone marrow-derived eosinophils; ST2-deficient eosinophil transfer; liver injury histology and biochemistry\",\n      \"journal\": \"Science Translational Medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic and adoptive transfer approaches orthogonally identifying ST2-dependent IL-13 as mechanistic mediator\",\n      \"pmids\": [\"33536281\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"IL-13 signaling via IL-13Rα2 induces TGF-β1 and causes allograft fibrosis; siRNA blockade of IL-13Rα2 prevents collagen deposition and reduces immune infiltration in a murine cardiac allograft model.\",\n      \"method\": \"Heterotopic cardiac transplant model; IL-13Rα2 siRNA; ELISA for IL-13 and TGF-β1; Sircol collagen assay; flow cytometry; fibrosis PCR array\",\n      \"journal\": \"Transplantation Research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — siRNA-mediated knockdown with multiple downstream fibrosis readouts, single lab\",\n      \"pmids\": [\"24143891\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"IL-13 alone is insufficient but IL-13 together with apoptotic cell signals induces the tissue repair program in macrophages; genetic ablation of apoptotic cell sensors impairs macrophage proliferation and tissue repair gene induction after helminth infection, demonstrating that apoptotic cell recognition spatially compartmentalizes IL-13/IL-4 activity.\",\n      \"method\": \"Genetic ablation of apoptotic cell sensors; lung helminth infection and gut colitis models; macrophage proliferation and gene expression readouts\",\n      \"journal\": \"Science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean genetic KO with defined cellular and molecular phenotypes, published in high-impact journal\",\n      \"pmids\": [\"28495875\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Autophagy (via ATG5) is required for DUOX1 localization to the apical membrane in airway epithelial cells during chronic IL-13 stimulation, and this localization is necessary for IL-13-mediated intracellular superoxide production; DUOX1 siRNA reduces IL-13-mediated superoxide without affecting autophagy.\",\n      \"method\": \"Primary human airway epithelial cells; siRNA knockdown of DUOX1 and ATG5; EPR spectroscopy for superoxide; immunostaining for DUOX1 localization; OVA mouse model\",\n      \"journal\": \"Redox Biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — siRNA epistasis with subcellular localization and functional readout, single lab\",\n      \"pmids\": [\"28982074\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"IL-13 induces diminished glucocorticoid receptor (GCR) binding affinity specifically in monocytes (not T cells), functionally impairing hydrocortisone suppression of LPS-induced IL-6 production; no additive effect with IL-2 or IL-4 was observed.\",\n      \"method\": \"[3H]dexamethasone radioligand binding assay; Scatchard analysis; LPS-stimulated monocyte IL-6 production assay; cell fractionation\",\n      \"journal\": \"Journal of Immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — quantitative receptor binding assay with functional consequence, single lab\",\n      \"pmids\": [\"8805670\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"IL-13 acts on macrophages to block completion of HIV-1 reverse transcription (inhibiting gag DNA formation while allowing LTR DNA), decrease virus production, and reduce progeny virion infectivity in a manner redundant with IL-4.\",\n      \"method\": \"HIV-1 infection of monocyte-derived macrophages; IL-13 treatment at various time points; viral DNA PCR for LTR and gag species; infectivity assay\",\n      \"journal\": \"Journal of Leukocyte Biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct in vitro mechanistic dissection with viral DNA intermediate analysis, single lab\",\n      \"pmids\": [\"9226003\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"IL-13 is a pleiotropic Th2 cytokine that signals primarily through the IL-13Rα1/IL-4Rα heterodimeric receptor complex via JAK/STAT6 (and in some contexts STAT3) pathways, with IL-13Rα2 acting as a regulatory decoy receptor that is shed by MMP-8 to generate soluble inhibitory forms; downstream, IL-13 drives goblet cell metaplasia, airway smooth muscle hyperreactivity, IgE class switching in B cells, alternative macrophage activation (including arginase-mediated suppression of iNOS via arginine depletion), tissue fibrosis via the IL-13Rα2/TGF-β1/IGF-1/Egr-1 axis, intestinal stem cell self-renewal via IL-13R/Foxp1/β-catenin, epithelial repair through HB-EGF/EGFR, and DUOX1-dependent ROS production via autophagy-mediated apical localization.\"\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\n```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1993,\n      \"finding\": \"IL-13 was identified as a new human cytokine expressed in activated T lymphocytes, capable of inhibiting inflammatory cytokine production induced by LPS in human peripheral blood monocytes, and its gene was mapped to chromosome 5q23-31, closely linked to the IL-4 gene.\",\n      \"method\": \"Differential screening of subtracted cDNA library, recombinant protein expression, functional assays on monocytes\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — original discovery paper with molecular cloning, recombinant protein, and functional validation\",\n      \"pmids\": [\"8096327\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1993,\n      \"finding\": \"Human IL-13 protein induces morphological changes in human monocytes with upregulation of MHC class II antigens and CD23 (Fc epsilon RII), stimulates proliferation of anti-IgM or anti-CD40-activated human B cells, and induces IgM and IgG (but not IgA) production by purified B cells co-cultured with activated CD4+ T cells.\",\n      \"method\": \"cDNA cloning, recombinant protein expression, B cell proliferation assays, Ig production assays, flow cytometry\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — foundational paper with multiple orthogonal functional assays on primary human cells\",\n      \"pmids\": [\"8097324\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1993,\n      \"finding\": \"IL-13 synergizes with mouse and human CD40L to induce IgM, IgG, IgG4, and IgE (but not IgA) production by highly purified B cells, and this induction is independent of IL-4 (anti-IL-4 antibodies block IL-4-induced but not IL-13-induced Ig production), demonstrating that IL-13 and CD40L can induce isotype switching to IgE independently of IL-4.\",\n      \"method\": \"B cell-T cell co-culture, COS-7 cells transfected with hCD40L, neutralizing antibody blockade, ELISA\",\n      \"journal\": \"International immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal antibody blockade and functional assays in primary human B cells\",\n      \"pmids\": [\"7688562\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"IL-13 is necessary and sufficient for the expression of allergic asthma features (airway hyperresponsiveness, mucus overproduction) in a manner independent of IgE and eosinophils; selective neutralization of IL-13 ameliorated the asthma phenotype, and this pathway requires the IL-4 receptor alpha chain.\",\n      \"method\": \"Selective IL-13 neutralization in murine asthma models, IL-13 administration to T cell-deficient mice, IL-4Rα-deficient mice\",\n      \"journal\": \"Science (New York, N.Y.)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple genetic and pharmacological approaches in vivo, replicated across two independent Science papers (PMID 9856949, 9856950)\",\n      \"pmids\": [\"9856949\", \"9856950\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"IL-13 is required for resistance to the intestinal nematode Trichuris muris; IL-13 knockout mice are susceptible despite being able to mount Th2 responses at later time points, demonstrating a non-redundant role for IL-13 in intestinal helminth immunity distinct from IL-4.\",\n      \"method\": \"IL-13 knockout mice, T. muris infection model, cytokine and antibody isotype analysis\",\n      \"journal\": \"Journal of immunology (Baltimore, Md. : 1950)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with defined phenotypic readout\",\n      \"pmids\": [\"9531306\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"A conserved noncoding element was identified as a coordinate regulator of IL-4, IL-13, and IL-5 gene expression over a 120-kilobase region on chromosome 5q, demonstrated by YAC transgenic mice.\",\n      \"method\": \"Cross-species sequence comparison, YAC transgenic mice, gene expression analysis\",\n      \"journal\": \"Science (New York, N.Y.)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vivo transgenic validation of regulatory element\",\n      \"pmids\": [\"10753117\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"IL-13 alters mucociliary differentiation of human nasal epithelial cells: it decreases ciliated cell differentiation, increases secretory cell proportion, downregulates ezrin and other cytoskeletal components, impairs apical localization of ezrin, and decreases ciliary beat frequency in a time- and dose-dependent manner; these effects are mediated through the IL-4 receptor alpha subunit (blocked by an IL-4 antagonistic mutant Y124D).\",\n      \"method\": \"Primary human nasal epithelial cell cultures, immunofluorescence, receptor antagonist, time-lapse microscopy of ciliary beat\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple cellular phenotypes with receptor-specific antagonist validation\",\n      \"pmids\": [\"11748265\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"IL-13 induces mucin production via a cascade requiring EGFR signaling and neutrophil recruitment; IL-13 induces IL-8-like chemoattractant expression in airway epithelium, recruits neutrophils, and EGFR tyrosine kinase inhibition or neutrophil depletion prevents IL-13-induced goblet cell metaplasia.\",\n      \"method\": \"In vivo intratracheal instillation in mice, EGFR inhibitor, cyclophosphamide-mediated neutrophil depletion, anti-IL-8 blocking antibody\",\n      \"journal\": \"American journal of physiology. Lung cellular and molecular physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple pharmacological interventions establishing pathway order in vivo\",\n      \"pmids\": [\"11133503\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"IL-13 induces airway hyperreactivity, mucus hypersecretion, eotaxin production, and eosinophilia in the allergic lung through a pathway that requires STAT6 but can operate independently of the IL-4Rα chain, identifying a novel STAT6-dependent component of the IL-13 receptor signaling system.\",\n      \"method\": \"OVA-specific CD4+ T cell transfer to IL-13-deficient, IL-4Rα-deficient, and STAT6-deficient mice with OVA aerosol challenge\",\n      \"journal\": \"Journal of immunology (Baltimore, Md. : 1950)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis using multiple knockout mouse strains with defined phenotypic readouts\",\n      \"pmids\": [\"11466392\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"IL-13 directly modulates airway smooth muscle (ASM) contractility: it significantly increases carbachol- and KCl-induced maximal force generation in murine tracheal rings and augments cytosolic calcium responses to bradykinin, histamine, and carbachol in cultured human ASM cells, suggesting IL-13 promotes bronchial hyperresponsiveness by enhancing GPCR-associated calcium signaling.\",\n      \"method\": \"Murine tracheal ring contractility assay, calcium fluorimetry in cultured human ASM cells\",\n      \"journal\": \"British journal of pharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct in vitro and ex vivo functional assays, single lab\",\n      \"pmids\": [\"14597600\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"IL-13 induces goblet cell metaplasia in human bronchial epithelial cells through MAP kinase (MEK, p38 MAPK) and phosphatidylinositol 3-kinase signaling pathways, independent of EGFR-TK, in a concentration-dependent manner.\",\n      \"method\": \"Air-liquid interface cultures, Alcian blue/MUC5AC staining, kinase inhibitors (PD-98059, U-0126, SB-202190, LY-294002, AG-1478)\",\n      \"journal\": \"American journal of physiology. Lung cellular and molecular physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple pharmacological inhibitors in primary epithelial cell cultures\",\n      \"pmids\": [\"12794003\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"IL-13 suppresses iNOS protein levels in inflammatory macrophages through translational inhibition caused by arginine depletion via arginase induction; although iNOS mRNA remains unaltered, arginase-mediated arginine depletion selectively impairs de novo iNOS protein synthesis and stability, revealing a novel translational regulatory mechanism.\",\n      \"method\": \"Mouse peritoneal macrophage stimulation with IFN-γ/LPS ± IL-13, arginase inhibitors, arginase addition, arginine-free medium, [35S]-methionine incorporation\",\n      \"journal\": \"Journal of immunology (Baltimore, Md. : 1950)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — multiple orthogonal mechanistic approaches (inhibitors, substrate depletion, metabolic labeling) in primary cells\",\n      \"pmids\": [\"14568929\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"IL-13 signaling through IL-13Rα2 (formerly considered only a decoy receptor) activates an AP-1 variant containing c-jun and Fra-2, which then activates the TGFB1 promoter; in vivo, IL-13Rα2 silencing reduces TGF-β1 production and collagen deposition in models of colitis and lung fibrosis, establishing IL-13Rα2 as a signaling receptor mediating fibrosis.\",\n      \"method\": \"Macrophage stimulation, AP-1 activation assays, promoter analysis, siRNA knockdown, in vivo colitis and bleomycin lung fibrosis models, collagen quantification\",\n      \"journal\": \"Nature medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro mechanistic dissection plus in vivo genetic/siRNA validation in multiple disease models\",\n      \"pmids\": [\"16327802\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"The IL-13 R130Q variant (encoded by IL13+2044GA) is significantly more active than WT IL-13 in inducing STAT6 phosphorylation and CD23 expression in monocytes and IgE switching in B cells; it is also neutralized less effectively by the IL-13Rα2 decoy receptor, contributing to enhanced in vivo activity of the variant.\",\n      \"method\": \"Recombinant WT and R130Q IL-13 proteins, STAT6 phosphorylation assay, CD23 expression (flow cytometry), IgE switching assay, IL-13Rα2 neutralization assay on primary human cells\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct comparison of recombinant variants on primary human cells with multiple orthogonal readouts\",\n      \"pmids\": [\"15711639\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"The IL-13 Gln110 variant (corresponding to R130Q) shows lower affinity for the IL-13Rα2 decoy receptor, causing reduced clearance, and also demonstrates enhanced stability in plasma; asthmatic patients homozygous for this variant have higher serum IL-13 levels, mechanistically linking the SNP to increased IL-13 bioavailability.\",\n      \"method\": \"Recombinant protein binding affinity assays, plasma stability assays, serum IL-13 ELISA in genotyped patients\",\n      \"journal\": \"The Journal of allergy and clinical immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro binding/stability assays with in vivo correlation in genotyped patients\",\n      \"pmids\": [\"12063528\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"IL-13 treatment of esophageal epithelial cells induces eotaxin-3 production through a transcriptional mechanism dependent on STAT6; IL-13 stimulation recapitulates the EE-specific esophageal transcriptome, and this transcriptome is reversible with glucocorticoid treatment.\",\n      \"method\": \"Primary esophageal epithelial cell cultures, microarray, real-time PCR, luciferase reporter assays with eotaxin-3 promoter fragments and STAT6 mutants\",\n      \"journal\": \"The Journal of allergy and clinical immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — promoter-reporter and mutagenesis with transcriptomic validation\",\n      \"pmids\": [\"18073124\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"IL-33 induces IL-13 (and IL-6) production by mouse mast cells independently of IgE-FcεRI signals via a MyD88-dependent but TRIF-independent pathway; this effect is more potent than IL-1β or IL-18 and does not induce mast cell degranulation.\",\n      \"method\": \"Bone marrow-derived mast cell cultures, cytokine ELISA, MyD88-deficient mice, degranulation assay\",\n      \"journal\": \"Journal of leukocyte biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic (MyD88-KO) and pharmacological dissection of signaling pathway in primary mast cells\",\n      \"pmids\": [\"17881510\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"IL-13 secreted by airway epithelial cells after mechanical injury enhances epithelial repair via autocrine induction of HB-EGF (but not EGF), leading to EGFR phosphorylation; neutralization of IL-13 reduces repair, and EGFR inhibition increases IL-13 release, indicating a negative feedback loop between EGFR and IL-13 during repair.\",\n      \"method\": \"Scratch wound assay in AEC monolayers, IL-13 neutralization with sIL-13Rα2.FC, ELISA, EGFR phosphorylation western blot, EGFR kinase inhibitor tyrphostin AG1478\",\n      \"journal\": \"American journal of respiratory cell and molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple mechanistic interventions (neutralization, inhibitors) with reciprocal feedback demonstrated\",\n      \"pmids\": [\"17717322\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"IL-9 promotes lung eosinophilia and mucus production through an IL-13-dependent mechanism: hematopoietic cells expressing both IL-9R and IL-13 are required for IL-9 effects on lung epithelial cells, establishing IL-13 as a direct downstream mediator of IL-9 on epithelial targets.\",\n      \"method\": \"IL-13 knockout mice crossed with IL-9 transgenic mice, hematopoietic cell transfer experiments with IL-9R-deficient recipients\",\n      \"journal\": \"Journal of immunology (Baltimore, Md. : 1950)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — epistasis established by genetic crosses and transfer experiments\",\n      \"pmids\": [\"17312173\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"IL-13 induces CD36 expression in human monocytes through PPARγ activation; this occurs via phospholipase A2-dependent production of endogenous 15-deoxy-Δ12,14-prostaglandin J2 (a PPARγ ligand), which translocates to the nucleus; CD36 and PPARγ are required for IL-13-mediated phagocytosis of P. falciparum-parasitized erythrocytes.\",\n      \"method\": \"PPARγ expression plasmid transfection in RAW264.7, PPARγ conditional null macrophages, PLA2 inhibitors, PGJ2 ELISA, nuclear localization assay, phagocytosis assay\",\n      \"journal\": \"European journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — multiple orthogonal methods including genetic null model, transfection, and functional assay\",\n      \"pmids\": [\"17458857\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"IL-13 signaling through IL-13Rα2 in chronic colitis induces a fibrogenic program comprising TGF-β1 activation, IGF-I and Egr-1 expression, caspase-mediated myofibroblast apoptosis, urokinase plasminogen activator production, and IGF-I/TGF-β1-driven collagen deposition; blockade of IL-13Rα2 or TGF-β1 signaling with siRNA or decoy oligonucleotides abrogates this cascade.\",\n      \"method\": \"TNBS chronic colitis mouse model, siRNA targeting IL-13Rα2 and TGF-β1 signaling components, ELISA, Western blot, collagen measurement\",\n      \"journal\": \"Gastroenterology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — systematic siRNA knockdown of multiple pathway components in vivo\",\n      \"pmids\": [\"18938165\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Crystal structures of the complete type I (IL-4Rα/γc/IL-4) and type II (IL-4Rα/IL-13Rα1/IL-4 and IL-4Rα/IL-13Rα1/IL-13) ternary signaling complexes reveal that IL-13 engages IL-13Rα1 via an unusual top-mounted Ig-like domain in a novel mode of cytokine engagement; the two type II complexes use substantially different recognition chemistries and have a reversed assembly sequence compared to type I; type II receptor signals with different potencies for IL-4 versus IL-13.\",\n      \"method\": \"X-ray crystallography of complete ternary receptor complexes, functional signaling assays\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — high-resolution crystal structures of all receptor complexes with functional validation\",\n      \"pmids\": [\"18243101\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"MMP-8 cleaves IL-13Rα2 in vitro and contributes to solubilization of IL-13Rα2 in vivo; MMP-8-deficient mice display increased airway hyperresponsiveness and decreased soluble IL-13Rα2 in bronchoalveolar lavage after allergen challenge; the solubilized IL-13Rα2 retains IL-13 binding activity.\",\n      \"method\": \"In vitro acellular cleavage assays with GST-fusion proteins, stable-transfected cell surface expression assay, MMP-8-deficient mice, allergen challenge model, BAL fluid analysis\",\n      \"journal\": \"The Journal of allergy and clinical immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro biochemical cleavage assay plus genetic KO validation in vivo\",\n      \"pmids\": [\"18694590\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"IL-13 attenuates vascular tube (capillary-like) formation and endothelial cell migration via JAK2 activation followed by STAT6 activation; depletion of JAK2 and STAT6 by RNA interference abolishes the anti-angiogenic effect of IL-13.\",\n      \"method\": \"In vitro tube formation assay in human coronary artery endothelial cells, siRNA knockdown of JAK2 and STAT6, migration assay\",\n      \"journal\": \"Circulation journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — siRNA knockdown establishing JAK2-STAT6 pathway, single lab\",\n      \"pmids\": [\"18296848\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"IL-13 mediates collagen deposition via STAT6 and epigenetic repression of microRNA-135b in dermal fibroblasts; STAT6 knockdown blocks IL-13-induced collagen1A1 expression; miR-135b overexpression reduces IL-13-induced collagen induction; scleroderma fibroblasts have constitutively lower miR-135b due to methylation-dependent repression involving MeCP2.\",\n      \"method\": \"siRNA knockdown of STAT6, small molecule STAT6 inhibitor, miR-135b transfection, qRT-PCR, methylation analysis in patient-derived fibroblasts\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — siRNA and miRNA overexpression with patient validation, single lab\",\n      \"pmids\": [\"27113293\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"IL-13 promotes beige fat biogenesis through IL-4/IL-13 signaling in alternatively activated macrophages; macrophages recruited to cold-stressed subcutaneous white adipose tissue undergo alternative activation to express tyrosine hydroxylase and produce catecholamines required for browning; genetic loss of IL-4/IL-13 signaling impairs cold-induced beige fat development.\",\n      \"method\": \"Genetic mouse models deficient in eosinophils or IL-4/IL-13 signaling, cold exposure experiments, macrophage tyrosine hydroxylase immunostaining, catecholamine measurements\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple genetic models establishing IL-4/IL-13 signaling → macrophage alternative activation → catecholamine production → beige fat circuit\",\n      \"pmids\": [\"24906148\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"MiR-155 directly targets IL-13Rα1 mRNA in human macrophages, reducing IL-13Rα1 protein levels and diminishing STAT6 phosphorylation in response to IL-13, thereby modulating expression of M2 marker genes (SOCS1, DC-SIGN, CCL18, CD23, SERPINE).\",\n      \"method\": \"Bioinformatics prediction, luciferase reporter assay, western blot, STAT6 phosphorylation, gene expression analysis in primary human macrophages with miR-155 overexpression/inhibition\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct targeting validated by reporter assay and functional downstream readouts in primary human macrophages\",\n      \"pmids\": [\"21097505\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"IL-13 downregulates desmoglein-1 (DSG1) in esophageal epithelial cells, impairing barrier function; DSG1 silencing induces transcriptional changes overlapping the EoE transcriptome, including induction of periostin (POSTN), linking IL-13-driven DSG1 loss to esophageal barrier dysfunction and pro-inflammatory mediator production.\",\n      \"method\": \"IL-13 stimulation of primary esophageal epithelial cells, DSG1 siRNA knockdown, transepithelial resistance measurement, transcriptomic analysis, patient biopsy validation\",\n      \"journal\": \"Mucosal immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — siRNA knockdown with functional barrier assay and transcriptomic validation in patient tissue\",\n      \"pmids\": [\"24220297\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Let-7 microRNAs directly regulate IL-13 expression; induced IL-13 levels in T cells are inversely related to let-7 levels, and intranasal delivery of let-7 mimic in allergic mice decreases IL-13 levels and resolves airway inflammation, airway hyperresponsiveness, mucus metaplasia, and subepithelial fibrosis.\",\n      \"method\": \"Bioinformatics, in vitro transfection in A549 cells and primary T cells, in vivo let-7 mimic intranasal delivery in murine allergic inflammation model\",\n      \"journal\": \"The Journal of allergy and clinical immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — in vitro and in vivo validation of miRNA regulation, single lab\",\n      \"pmids\": [\"21616524\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Chitinase 3-like 1 (Chi3l1) binds to IL-13Rα2 and is found in a multimeric complex with IL-13Rα2 and IL-13; Chi3l1 activates MAPK, AKT, and Wnt/β-catenin signaling via IL-13Rα2-dependent mechanisms to regulate apoptosis, pyroptosis, inflammasome activation, antibacterial responses, and TGF-β1 production.\",\n      \"method\": \"Co-immunoprecipitation, pulldown assays, IL-13Rα2-deficient cells, pharmacological pathway inhibitors, functional readouts\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — Co-IP/pulldown plus genetic null validation with multiple downstream pathway readouts\",\n      \"pmids\": [\"23972995\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"IL-13 promotes intestinal SIgA secretion through a pathway involving intestinal microbiota and IL-13; injection of an IL-13 antibody during glutamine supplementation reduces J-chain expression in the mouse ileum, and disrupting the intestinal microbiota abrogates glutamine's effect on SIgA, with IL-13 acting as a mediator in the T cell-dependent SIgA induction pathway.\",\n      \"method\": \"Mouse model with glutamine supplementation, IL-13 neutralizing antibody injection, IL-13 ELISA, J-chain expression, germ-free/antibiotic-treated mice\",\n      \"journal\": \"Molecular nutrition & food research\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — antibody neutralization with correlation, indirect mechanistic link, single lab\",\n      \"pmids\": [\"27005687\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"IL-33 drives a signaling cascade to IL-13 that is required for spasmolytic polypeptide-expressing metaplasia (SPEM) induction in the stomach after parietal cell loss; IL-33 KO and ST2 KO mice do not develop metaplasia in response to L635, while IL-13 KO mice also fail to develop SPEM, and exogenous IL-13 restores metaplasia in ST2 KO mice.\",\n      \"method\": \"IL-33, ST2, and IL-13 knockout mice, L635-induced parietal cell loss model, exogenous IL-13 rescue, macrophage RNA sequencing\",\n      \"journal\": \"Gut\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis with rescue experiment establishing IL-33→IL-13 cascade for metaplasia\",\n      \"pmids\": [\"28196875\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"IL-4 or IL-13 together with apoptotic cells (but not alone) is required to induce the tissue repair program in macrophages; genetic ablation of apoptotic cell sensors impairs macrophage proliferation and anti-inflammatory/repair gene induction in the lungs after helminth infection or colitis, while recognition of apoptotic cells is dispensable for cytokine-dependent induction of pattern recognition receptor or chemotaxis genes.\",\n      \"method\": \"Genetic ablation of apoptotic cell sensors, helminth infection model, colitis model, macrophage gene expression analysis\",\n      \"journal\": \"Science (New York, N.Y.)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic dissection of cooperating signals with defined gene expression readouts in multiple disease models\",\n      \"pmids\": [\"28495875\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Autophagy is required for IL-13-mediated apical localization of DUOX1 and subsequent intracellular superoxide production in airway epithelial cells; depletion of autophagy regulator ATG5 reduces superoxide without diminishing total DUOX1 levels, but diminishes apical DUOX1 localization, while DUOX1 siRNA attenuates IL-13-induced superoxide without affecting autophagy.\",\n      \"method\": \"Primary human tracheobronchial epithelial cells, OVA mouse model, ATG5 siRNA, DUOX1 siRNA, EPR spectroscopy for superoxide, LC3BII western blot, immunostaining\",\n      \"journal\": \"Redox biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — siRNA knockdowns with functional localization and EPR spectroscopy, single lab\",\n      \"pmids\": [\"28982074\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"IL-13 secreted by ILC2s promotes Lgr5+ intestinal stem cell self-renewal through a circuit involving circPan3 and IL-13Rα1; circPan3 binds IL-13Rα1 mRNA to increase its stability, enabling ISC expression of IL-13Rα1; IL-13 signaling through IL-13Rα1 activates Foxp1 expression, which associates with β-catenin to promote its nuclear translocation and activate Wnt/β-catenin pathway in ISCs.\",\n      \"method\": \"circPan3 deletion in Lgr5+ ISCs, IL-13Rα1 mRNA stability assay (RNA-protein interaction), Foxp3Cre mouse model, β-catenin localization, organoid/stem cell assays\",\n      \"journal\": \"Nature immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple genetic models and molecular mechanism (mRNA stabilization, co-IP of Foxp1-β-catenin) in vivo and in vitro\",\n      \"pmids\": [\"30643264\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Foxp3+ Tregs secrete IL-13 in response to IL-33 stimulation, and Treg-derived IL-13 is required to prevent mortality after acute lung injury by controlling local levels of G-CSF, IL-6, and MCP-1 and inhibiting accumulation of Ly6Chi monocytes; this was demonstrated using Foxp3Cre × Il4/Il13fl/fl mice.\",\n      \"method\": \"Foxp3Cre × Il4/Il13fl/fl conditional knockout mice, acute lung injury model, BAL cytokine analysis, monocyte flow cytometry, IL-33 stimulation of human and mouse Tregs\",\n      \"journal\": \"JCI insight\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — conditional KO with cell-type-specific IL-13 ablation and defined inflammatory readouts\",\n      \"pmids\": [\"30779711\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Akt1 regulates IL-13 production by macrophages; Akt1-deficient macrophages produce less IL-13 compared to Akt1+/+ macrophages in response to IL-33 stimulation; Akt1-deficient mice have reduced IL-13 levels after bleomycin treatment and are protected from pulmonary fibrosis.\",\n      \"method\": \"Akt1 knockout mice, bleomycin fibrosis model, bone marrow-derived macrophage stimulation with IL-33, IL-13 ELISA, collagen/ECM quantification\",\n      \"journal\": \"Innate immunity\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO with mechanistic link to macrophage IL-13 production, single lab\",\n      \"pmids\": [\"31299858\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Eosinophil-derived IL-13 produced via ST2 (IL-33 receptor) signaling is required for hepatoprotection against ischemia-reperfusion injury; adoptive transfer of bone marrow-derived eosinophils reduces hepatic injury, and this protection requires ST2-dependent IL-13 production by eosinophils, established through genetic and adoptive transfer approaches.\",\n      \"method\": \"Two genetic mouse models of eosinophil deficiency, antibody-mediated eosinophil depletion, adoptive transfer of eosinophils, ST2-deficient eosinophils, liver IRI model, liver injury biochemical/histological assessment\",\n      \"journal\": \"Science translational medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple genetic models and adoptive transfer with mechanistic cell-type-specific readout\",\n      \"pmids\": [\"33536281\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"IL-13 is a Th2 cytokine encoded near IL-4 on chromosome 5q31 that signals through type II receptor complexes (IL-4Rα/IL-13Rα1, with STAT6 as the canonical downstream effector and, in fibrosis, through IL-13Rα2/AP-1/TGF-β1), mediating airway hyperresponsiveness, mucus hypersecretion (via EGFR/neutrophil and MAPK/PI3K cascades), IgE class switching in B cells, alternative macrophage activation (including catecholamine production for beige fat biogenesis), epithelial barrier disruption, intestinal stem cell self-renewal (via circPan3-stabilized IL-13Rα1/Foxp1/β-catenin), and tissue fibrosis through a multi-step IL-13Rα2-driven program involving TGF-β1, IGF-I, and Egr-1; its activity is regulated by let-7 miRNAs (post-transcriptionally), miR-155 (via IL-13Rα1 targeting), MMP-8-mediated shedding of the IL-13Rα2 decoy receptor, Akt1-dependent macrophage production, and a cooperative requirement for apoptotic cell signals to activate tissue repair programs.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"IL-13 is a pleiotropic type 2 cytokine that orchestrates allergic inflammation, tissue remodeling, and mucosal immunity by signaling through the IL-13Rα1/IL-4Rα heterodimer to activate JAK2/STAT6, with IL-13Rα2 serving as a decoy receptor whose soluble form is generated by MMP-8 cleavage and whose loss amplifies IL-13 bioactivity [PMID:9856950, PMID:18694590, PMID:18296848]. In the airways, IL-13 drives goblet cell metaplasia, mucus hypersecretion, and bronchial hyperresponsiveness through EGFR-dependent and calcium-signaling pathways, while in macrophages it induces arginase to deplete arginine and suppress iNOS at the translational level, and activates PPARγ-dependent CD36 expression for phagocytic clearance [PMID:11133503, PMID:14568929, PMID:17458857]. IL-13 promotes tissue fibrosis via an IL-13Rα2/TGF-β1/IGF-1/Egr-1 axis in intestine and lung, independently drives IgE class switching in B cells synergistically with CD40L, and supports intestinal stem cell self-renewal through IL-13R/Foxp1/β-catenin signaling [PMID:18938165, PMID:7688562, PMID:30643264]. IL-13 is produced by Th2 cells, ILC2s, mast cells, eosinophils, and Tregs, often downstream of IL-33/ST2 signaling, and plays non-redundant roles in helminth expulsion, hepatoprotection from ischemia-reperfusion injury, and epithelial barrier regulation including filaggrin downregulation in eosinophilic esophagitis [PMID:9531306, PMID:33536281, PMID:20208004].\",\n  \"teleology\": [\n    {\n      \"year\": 1993,\n      \"claim\": \"Establishing that IL-13 is a B cell differentiation factor capable of driving IgE class switching independently of IL-4 defined it as a functionally distinct Th2 cytokine rather than a simple IL-4 redundancy.\",\n      \"evidence\": \"Co-culture of purified B cells with CD40L-expressing cells plus anti-IL-4 blocking antibody; ELISA for immunoglobulin isotypes\",\n      \"pmids\": [\"7688562\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Transcription factor requirements for IL-13-driven IgE switching not defined\", \"Whether IL-13 acts on the same or different B cell subsets as IL-4 not resolved\"]\n    },\n    {\n      \"year\": 1996,\n      \"claim\": \"Demonstrating that IL-13 reduces glucocorticoid receptor binding affinity in monocytes provided a mechanistic basis for cytokine-mediated steroid resistance in inflammatory disease.\",\n      \"evidence\": \"Radioligand binding with Scatchard analysis on monocytes; functional readout via LPS-induced IL-6 suppression\",\n      \"pmids\": [\"8805670\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular mechanism of GCR affinity reduction not identified\", \"In vivo relevance to steroid-resistant asthma not tested\"]\n    },\n    {\n      \"year\": 1997,\n      \"claim\": \"Showing that IL-13 blocks HIV-1 reverse transcription at the gag DNA stage in macrophages identified a specific viral replication step targeted by type 2 cytokines.\",\n      \"evidence\": \"HIV-1 infection of monocyte-derived macrophages with PCR for specific viral DNA intermediates\",\n      \"pmids\": [\"9226003\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Host factor mediating the reverse transcription block not identified\", \"In vivo relevance during HIV infection unknown\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"Demonstrating that IL-13 is both necessary and sufficient for airway hyperresponsiveness, eosinophilia, and mucus overproduction — independently of IL-4 but dependent on IL-4Rα — established IL-13 as the central effector cytokine in allergic airway disease and defined its receptor usage.\",\n      \"evidence\": \"In vivo neutralization with sIL-13Rα2-Fc; recombinant IL-13 in T cell-deficient and IL-4Rα KO mice\",\n      \"pmids\": [\"9856950\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Downstream signaling from IL-4Rα in structural cells not dissected\", \"Cell types producing IL-13 in vivo not identified at this stage\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"IL-13 knockout mice succumbing to intestinal nematode infection despite intact Th2 polarization established a non-redundant role for IL-13 in helminth expulsion distinct from IL-4.\",\n      \"evidence\": \"IL-13 KO mouse T. muris infection model compared with IL-4 KO\",\n      \"pmids\": [\"9531306\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Effector mechanism of IL-13 in worm expulsion (goblet cell vs. smooth muscle) not resolved\", \"Whether IL-13 acts on epithelial or immune cells for expulsion not determined\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Identifying STAT6 (not NF-κB) activation as the mechanism of IL-13-mediated hepatoprotection during ischemia-reperfusion established that IL-13's anti-inflammatory action operates through a distinct signaling branch.\",\n      \"evidence\": \"Recombinant IL-13 in mouse hepatic I/R model; STAT6 and NF-κB activation assays\",\n      \"pmids\": [\"10514388\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Hepatocyte vs. Kupffer cell contribution not resolved\", \"Direct STAT6 target genes mediating protection not identified\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Showing that IL-13 remodels airway epithelial differentiation — shifting mucociliary balance toward secretory cells, downregulating ezrin, and reducing ciliary beat frequency via IL-4Rα — moved understanding beyond immune cell effects to direct epithelial reprogramming.\",\n      \"evidence\": \"Primary human nasal epithelial cells; IL-4Rα antagonist mutein blockade; immunofluorescence; ciliary beat measurement\",\n      \"pmids\": [\"11748265\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Transcriptional program downstream of IL-4Rα in epithelial cells not fully mapped\", \"Whether ezrin loss is cause or consequence of lateral contact disruption unclear\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Linking IL-13-induced goblet cell metaplasia to EGFR signaling and neutrophil recruitment identified a cross-talk pathway between type 2 cytokines and innate immune/growth factor cascades in mucus production.\",\n      \"evidence\": \"Mouse intratracheal IL-13 with EGFR kinase inhibitor, leukocyte depletion, and anti-IL-8 blockade\",\n      \"pmids\": [\"11133503\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct vs. indirect action of IL-13 on goblet cells not fully resolved\", \"Identity of EGFR ligand released by neutrophils not determined\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Demonstrating that the R130Q (Gln110) coding variant reduces IL-13Rα2 decoy receptor affinity and increases plasma stability of IL-13 provided a biochemical explanation for genetic association with asthma severity.\",\n      \"evidence\": \"Recombinant protein binding assays; plasma stability; genotype-serum IL-13 correlation in asthmatic cohort\",\n      \"pmids\": [\"12063528\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether enhanced STAT6 activation by R130Q occurs in vivo not shown at this point\", \"Population-level effect size on disease risk not firmly established\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Identifying IL-13 (not IL-4) as the driver of bleomycin-induced pulmonary fibrosis through CC chemokine C10-mediated macrophage recruitment separated IL-13's fibrotic role from its shared immune functions with IL-4.\",\n      \"evidence\": \"Sequential in vivo neutralization of IL-13 and C10 in bleomycin model; cytokine and histology readouts\",\n      \"pmids\": [\"12356575\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether IL-13 directly induces collagen or acts solely through macrophage recruitment not resolved\", \"Receptor isoform mediating fibrosis not yet identified\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Dissecting how IL-13 suppresses macrophage iNOS via arginase-mediated arginine depletion — affecting translation and protein stability rather than mRNA — revealed a metabolic mechanism of alternative macrophage activation.\",\n      \"evidence\": \"Mouse peritoneal macrophage stimulation; arginase inhibitors and arginine supplementation rescuing iNOS protein; mRNA vs. protein comparison\",\n      \"pmids\": [\"14568929\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether this mechanism applies to human macrophages not tested\", \"Impact on pathogen killing in vivo not established\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Adoptive transfer experiments showing that T cell-derived IL-13 requires STAT6 but can partly bypass IL-4Rα for airway effects refined the receptor signaling model and suggested additional receptor complexes.\",\n      \"evidence\": \"CD4+ T cell transfer into STAT6-KO and IL-4Rα-KO mice with OVA challenge\",\n      \"pmids\": [\"11466392\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of the IL-4Rα-independent receptor complex not determined\", \"Whether this pathway operates in human airways unknown\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Biochemical characterization of the R130Q variant showing enhanced STAT6 activation and reduced IL-13Rα2 neutralization in primary human cells provided the functional link between genotype and augmented IL-13 signaling.\",\n      \"evidence\": \"Recombinant WT vs. R130Q IL-13 on primary monocytes and B cells; STAT6 phosphorylation; CD23; IgE switching\",\n      \"pmids\": [\"15711639\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Crystal structure of R130Q–receptor interaction not available\", \"Whether therapeutic anti-IL-13 antibodies differentially neutralize R130Q not tested\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Discovering that house dust mite proteases solubilize IL-13Rα2 from cell surfaces, and that this soluble decoy is reduced in asthmatics, provided a mechanism by which environmental allergens amplify IL-13 signaling.\",\n      \"evidence\": \"HDM allergen treatment of cells; surface vs. soluble IL-13Rα2 measurement; human BAL fluid comparison\",\n      \"pmids\": [\"17140645\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Specific protease within HDM extract responsible not identified\", \"Whether IL-13Rα2 shedding precedes or follows sensitization not resolved\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Defining IL-13's role in eotaxin-3 induction via STAT6-dependent transcription in esophageal epithelium, with transcriptomic overlap with eosinophilic esophagitis, established IL-13 as a central mediator of this disease's molecular signature.\",\n      \"evidence\": \"Eotaxin-3 promoter reporter with STAT6 site mutation; primary esophageal cell microarray; comparison with EE biopsy transcriptome\",\n      \"pmids\": [\"18073124\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether IL-13 blockade reverses established EE not tested\", \"Source of IL-13 in the esophageal microenvironment not identified\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Showing that IL-13 upregulates CD36 in monocytes through a PLA2/15d-PGJ2/PPARγ axis, enabling phagocytosis of parasitized erythrocytes, linked type 2 immunity to lipid signaling and innate clearance of malaria.\",\n      \"evidence\": \"PPARγ conditional KO macrophages; PLA2 inhibitor; phagocytosis assay for P. falciparum-infected erythrocytes\",\n      \"pmids\": [\"17458857\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo relevance during malaria infection not established\", \"Whether IL-4 engages the same PPARγ pathway not resolved\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Genetic epistasis placing IL-13 downstream of IL-9 and IL-33 clarified the cytokine hierarchy: IL-33 activates mast cells and other cells to produce IL-13 via MyD88, and IL-9's mucus-inducing effects operate entirely through IL-13.\",\n      \"evidence\": \"IL-13 KO × IL-9 transgenic crosses; IL-33 stimulation of BMMCs from MyD88-KO and TRIF-KO mice\",\n      \"pmids\": [\"17312173\", \"17881510\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether IL-33-induced IL-13 from ILC2s vs. mast cells is functionally equivalent not resolved\", \"Quantitative contribution of each upstream inducer in vivo unknown\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Demonstrating that IL-13 promotes epithelial repair via autocrine HB-EGF/EGFR signaling, with EGFR providing negative feedback on IL-13 release, identified a wound repair circuit distinct from IL-13's inflammatory roles.\",\n      \"evidence\": \"Mechanical wounding of primary airway epithelial cells; IL-13 neutralization; EGFR inhibitor; HB-EGF measurement\",\n      \"pmids\": [\"17717322\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"In vivo relevance of autocrine IL-13 wound repair not demonstrated\", \"Whether this loop operates in non-airway epithelia unknown\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Identifying IL-13Rα2 (not IL-13Rα1) as the signaling receptor for IL-13-driven fibrosis through a TGF-β1/IGF-1/Egr-1 cascade overturned the simple 'decoy receptor' model of IL-13Rα2 and established it as an active pro-fibrotic signal transducer.\",\n      \"evidence\": \"siRNA targeting IL-13Rα2 and TGF-β1 in chronic TNBS colitis model; downstream mediator measurement\",\n      \"pmids\": [\"18938165\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Signaling mechanism downstream of IL-13Rα2 cytoplasmic domain not fully characterized\", \"Whether IL-13Rα2 fibrotic signaling operates in all tissues not established\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"MMP-8 was identified as the protease that cleaves membrane IL-13Rα2 to generate soluble decoy receptor; MMP-8 KO mice showed exaggerated airway hyperresponsiveness, establishing enzymatic regulation of IL-13 bioavailability.\",\n      \"evidence\": \"In vitro cleavage assay with recombinant MMPs; MMP-8 KO allergen challenge model; BAL sIL-13Rα2 measurement\",\n      \"pmids\": [\"18694590\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether other MMPs contribute in vivo not excluded\", \"Regulation of MMP-8 expression in the context of allergic inflammation not explored\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Demonstrating coordinate downregulation of epidermal differentiation complex genes including filaggrin by IL-13 in esophageal epithelium connected type 2 inflammation to epithelial barrier dysfunction in eosinophilic esophagitis.\",\n      \"evidence\": \"IL-13 stimulation of primary esophageal cells; microarray validation against EE biopsy transcriptome\",\n      \"pmids\": [\"20208004\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether filaggrin loss is functionally sufficient for disease phenotype not tested\", \"Mechanism of transcriptional repression not defined\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Identifying let-7 miRNAs as direct post-transcriptional repressors of IL-13, with therapeutic let-7 delivery resolving airway inflammation in mice, introduced RNA-based regulation of IL-13 expression.\",\n      \"evidence\": \"let-7 mimic transfection in vitro; intranasal delivery in OVA mouse model; AHR, mucus, and fibrosis readouts\",\n      \"pmids\": [\"21616524\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct binding site validation by luciferase reporter not shown in this study\", \"Endogenous regulation of let-7 levels during allergic inflammation not defined\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Establishing that STAT6 mediates IL-13-induced collagen expression independently of TGF-β1, and that miR-135b acts as a negative regulator repressed by methylation in scleroderma, added epigenetic regulation to the fibrosis pathway.\",\n      \"evidence\": \"STAT6 siRNA and inhibitor; miR-135b transfection; methylation analysis in primary scleroderma fibroblasts\",\n      \"pmids\": [\"27113293\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"In vivo relevance of miR-135b in fibrosis models not demonstrated\", \"Whether MeCP2-mediated repression is specific to scleroderma fibroblasts unknown\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Placing IL-13 downstream of IL-33/ST2 as required for gastric spasmolytic polypeptide-expressing metaplasia (SPEM) after parietal cell loss revealed IL-13 as the effector cytokine in stomach pre-neoplastic remodeling.\",\n      \"evidence\": \"IL-33 KO, ST2 KO, and IL-13 KO mice with L635 parietal cell ablation; IL-13 reconstitution rescuing metaplasia in ST2 KO\",\n      \"pmids\": [\"28196875\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Cell source of IL-13 in gastric tissue not definitively identified\", \"Whether IL-13 blockade could prevent cancer progression from SPEM not tested\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Showing that IL-13 alone is insufficient for tissue repair macrophage programming — requiring concurrent apoptotic cell recognition signals — added a spatial gating mechanism to type 2 immune activation.\",\n      \"evidence\": \"Genetic ablation of apoptotic cell sensors; helminth and colitis models; macrophage proliferation and repair gene readouts\",\n      \"pmids\": [\"28495875\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of the apoptotic cell sensor(s) that synergize with IL-13 signaling not fully defined\", \"Whether this principle applies to fibrosis-promoting macrophage programs unknown\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Demonstrating that chronic IL-13 stimulation requires autophagy (ATG5) for apical DUOX1 localization and superoxide production in airway epithelium connected IL-13 to ROS-mediated innate defense via membrane trafficking.\",\n      \"evidence\": \"ATG5 and DUOX1 siRNA in primary human airway epithelial cells; EPR spectroscopy; DUOX1 immunostaining; OVA mouse model\",\n      \"pmids\": [\"28982074\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether autophagy-dependent DUOX1 localization contributes to airway remodeling or defense in vivo not resolved\", \"Mechanism by which autophagy delivers DUOX1 to apical membrane not characterized\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"ILC2-derived IL-13 was found to promote intestinal stem cell self-renewal via IL-13Rα1/Foxp1/β-catenin, with circPan3 stabilizing IL-13Rα1 mRNA in stem cells, revealing a regenerative circuit connecting innate immunity to Wnt signaling.\",\n      \"evidence\": \"circPan3 deletion; IL-13Rα1 mRNA stability assays; Foxp1 induction; β-catenin nuclear localization; organoid culture\",\n      \"pmids\": [\"30643264\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether this circuit operates during helminth-induced intestinal remodeling not tested\", \"Generalizability to other stem cell niches unknown\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Conditional deletion of IL-4/IL-13 in Foxp3+ Tregs revealed that Treg-derived IL-13 prevents mortality after acute lung injury by controlling inflammatory monocyte accumulation, establishing a tissue-protective role for Treg-produced IL-13.\",\n      \"evidence\": \"Foxp3Cre × Il4/Il13fl/fl conditional KO; acute lung injury model; BAL cytokine and cell analysis\",\n      \"pmids\": [\"30779711\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relative contribution of IL-13 vs. IL-4 from Tregs not separated due to double-floxed design\", \"Whether Treg IL-13 acts on macrophages or epithelial cells not determined\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Eosinophil-derived, ST2-dependent IL-13 was identified as the mediator of eosinophil-conferred hepatoprotection during ischemia-reperfusion, closing the loop on IL-33→eosinophil→IL-13→liver protection.\",\n      \"evidence\": \"Adoptive transfer of WT vs. ST2-KO eosinophils into eosinophil-deficient mice; liver histology and biochemistry\",\n      \"pmids\": [\"33536281\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Downstream hepatocyte signaling pathway activated by eosinophil-derived IL-13 not characterized\", \"Whether this mechanism is relevant to human liver transplantation not established\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key open questions include: how IL-13Rα2 transduces pro-fibrotic signals at the structural level, whether IL-13's stem cell renewal function extends beyond intestinal crypts, the therapeutic window for IL-13 blockade in fibrotic vs. regenerative contexts, and the in vivo hierarchy among multiple IL-13-producing cell types (Th2, ILC2, mast cells, eosinophils, Tregs) in different tissue niches.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"IL-13Rα2 signaling domain structure and adaptor usage unresolved\", \"Relative in vivo contribution of different IL-13-producing cell types in specific disease contexts unknown\", \"Whether IL-13's regenerative and fibrotic functions can be therapeutically separated remains undefined\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0048018\", \"supporting_discovery_ids\": [0, 2, 5, 8, 26]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [6, 33]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [0, 8, 16, 15]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [0, 1, 2, 5, 8, 9, 12, 21, 27, 28, 29]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [5, 8, 9, 18, 24, 26]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [26]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [9, 10, 11, 22, 30]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"IL4R\",\n      \"IL13RA1\",\n      \"IL13RA2\",\n      \"STAT6\",\n      \"EGFR\",\n      \"TGFB1\",\n      \"FOXP1\",\n      \"CTNNB1\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\n```json\n{\n  \"mechanistic_narrative\": \"IL-13 is a pleiotropic Th2 cytokine that orchestrates type 2 immune responses, tissue remodeling, and repair across multiple organ systems. It signals canonically through the type II receptor complex (IL-4Rα/IL-13Rα1), activating STAT6 to drive IgE class switching in B cells, goblet cell metaplasia via MAPK/PI3K cascades, airway hyperresponsiveness through enhanced smooth muscle calcium signaling, alternative macrophage activation including catecholamine production for beige fat biogenesis, and epithelial barrier remodeling [PMID:9856949, PMID:8097324, PMID:12794003, PMID:24906148, PMID:24220297]. A parallel signaling axis through IL-13Rα2 activates AP-1 (c-jun/Fra-2) to induce TGF-β1 transcription and a downstream fibrogenic cascade involving IGF-I and Egr-1, establishing IL-13Rα2 as a bona fide signaling receptor rather than merely a decoy [PMID:16327802, PMID:18938165]. IL-13 bioavailability and signaling are regulated at multiple levels, including post-transcriptional repression by let-7 miRNAs, miR-155-mediated targeting of IL-13Rα1, MMP-8-dependent shedding of soluble IL-13Rα2, Akt1-dependent production in macrophages, and a cooperative requirement for apoptotic cell recognition to activate the full tissue repair program [PMID:21616524, PMID:21097505, PMID:18694590, PMID:28495875].\",\n  \"teleology\": [\n    {\n      \"year\": 1993,\n      \"claim\": \"Identification of IL-13 as a novel T cell-derived cytokine that suppresses monocyte inflammatory cytokines, induces B cell proliferation and IgE class switching independently of IL-4, and maps to chromosome 5q31 near IL-4 established IL-13 as a non-redundant Th2 effector cytokine.\",\n      \"evidence\": \"cDNA cloning from activated T cells, recombinant protein functional assays on monocytes and B cells, anti-IL-4 neutralization demonstrating IL-4-independent IgE switching\",\n      \"pmids\": [\"8096327\", \"8097324\", \"7688562\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Receptor identity and signaling pathway unknown\",\n        \"In vivo relevance of IL-13 in disease not yet tested\",\n        \"Relationship to IL-4 at the receptor level undefined\"\n      ]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"Demonstration that IL-13 is both necessary and sufficient for hallmark asthma features (airway hyperresponsiveness, mucus overproduction) independently of IgE and eosinophils, and is non-redundantly required for intestinal helminth expulsion, established IL-13 as a central effector of allergic and anti-helminth immunity in vivo.\",\n      \"evidence\": \"Selective IL-13 neutralization and IL-13 KO mice in asthma and Trichuris muris infection models; IL-4Rα-deficient mice\",\n      \"pmids\": [\"9856949\", \"9856950\", \"9531306\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Precise epithelial signaling mechanism for mucus induction unknown\",\n        \"Relative contributions of IL-13Rα1 versus IL-13Rα2 in vivo unclear\",\n        \"Molecular basis of airway smooth muscle hyperresponsiveness not defined\"\n      ]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Elucidation of downstream epithelial effector mechanisms showed IL-13 drives mucus overproduction through EGFR/neutrophil-dependent and MAPK/PI3K pathways, alters mucociliary differentiation via IL-4Rα, and requires STAT6 for airway hyperreactivity, defining the intracellular signaling architecture in target tissues.\",\n      \"evidence\": \"EGFR inhibitors, neutrophil depletion, and kinase inhibitors in vivo and in air-liquid interface epithelial cultures; STAT6-KO and IL-4Rα-KO mice with allergen challenge\",\n      \"pmids\": [\"11133503\", \"11748265\", \"11466392\", \"12794003\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Whether EGFR-dependent and MAPK/PI3K-dependent mucus pathways are cell-type specific or context dependent\",\n        \"STAT6-independent IL-13 signaling components not identified\",\n        \"Mechanism of IL-13 action on smooth muscle contractility only partially defined\"\n      ]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"IL-13 was shown to directly enhance airway smooth muscle contractility and calcium signaling, and to suppress iNOS in macrophages via arginase-mediated arginine depletion, revealing cell-type-specific effector mechanisms beyond epithelial targets.\",\n      \"evidence\": \"Tracheal ring contractility and calcium fluorimetry in human ASM cells; arginase inhibitors and metabolic labeling in primary macrophages\",\n      \"pmids\": [\"14597600\", \"14568929\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"In vivo relevance of direct smooth muscle signaling versus indirect epithelial effects unresolved\",\n        \"Whether arginase-mediated translational control extends to other IL-13 target proteins unknown\"\n      ]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Discovery that IL-13Rα2 functions as a signaling receptor activating AP-1 (c-jun/Fra-2) to induce TGF-β1 and drive fibrosis overturned the prevailing decoy-only model, while characterization of the R130Q variant revealed reduced IL-13Rα2 decoy function and enhanced STAT6 signaling as a mechanism for genetic asthma risk.\",\n      \"evidence\": \"AP-1 promoter analysis, IL-13Rα2 siRNA in colitis/fibrosis models; recombinant WT vs R130Q protein binding and signaling assays on primary human cells with patient serum correlation\",\n      \"pmids\": [\"16327802\", \"15711639\", \"12063528\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Crystal structure of IL-13/IL-13Rα2 signaling complex not available at this time\",\n        \"Full spectrum of IL-13Rα2-dependent transcriptional targets beyond TGF-β1 undefined\",\n        \"How IL-13Rα2 signaling versus decoy functions are balanced in different tissues unclear\"\n      ]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Multiple upstream triggers and feedback mechanisms were identified: IL-33 induces IL-13 from mast cells via MyD88, IL-9 requires IL-13 as a downstream mediator for lung eosinophilia, epithelial injury triggers autocrine IL-13/HB-EGF/EGFR repair signaling with negative feedback, and IL-13 activates PPARγ for CD36-mediated phagocytosis in monocytes.\",\n      \"evidence\": \"MyD88-KO mast cells, IL-13-KO × IL-9-transgenic mice, scratch wound assays with IL-13 neutralization, PPARγ-null macrophages with PLA2 inhibitors\",\n      \"pmids\": [\"17881510\", \"17312173\", \"17717322\", \"17458857\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Whether IL-33→IL-13 axis operates equivalently across all tissue-resident mast cell populations\",\n        \"Full extent of autocrine IL-13 signaling in non-airway epithelia unclear\",\n        \"PPARγ-mediated CD36 pathway not tested beyond malaria phagocytosis\"\n      ]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Structural resolution of the complete type II receptor ternary complexes revealed that IL-13 engages IL-13Rα1 through a novel top-mounted Ig-like domain with recognition chemistry distinct from IL-4, while MMP-8 was identified as a protease that sheds IL-13Rα2 to regulate IL-13 bioavailability in vivo, and IL-13Rα2-driven fibrosis was shown to involve a multi-step cascade (TGF-β1, IGF-I, Egr-1).\",\n      \"evidence\": \"X-ray crystallography of IL-4Rα/IL-13Rα1/IL-13 ternary complexes; MMP-8-KO mice with allergen challenge; siRNA knockdown of IL-13Rα2/TGF-β1 pathway components in chronic colitis\",\n      \"pmids\": [\"18243101\", \"18694590\", \"18938165\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Structure of IL-13/IL-13Rα2 signaling complex not resolved\",\n        \"Other proteases that may regulate IL-13Rα2 shedding not identified\",\n        \"Structural basis for differential STAT6 activation potency by IL-4 vs IL-13 incompletely explained\"\n      ]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Post-transcriptional and post-signaling regulatory layers were defined: miR-155 directly targets IL-13Rα1 to attenuate STAT6-dependent M2 macrophage polarization, IL-13 drives alternative macrophage activation for catecholamine-dependent beige fat biogenesis, and IL-13 disrupts epithelial barrier integrity by downregulating desmoglein-1 in eosinophilic esophagitis.\",\n      \"evidence\": \"miR-155 luciferase reporter assays in primary macrophages; IL-4/IL-13-signaling-deficient mice under cold stress; DSG1 siRNA and transepithelial resistance in esophageal epithelial cells with patient biopsy validation\",\n      \"pmids\": [\"21097505\", \"24906148\", \"24220297\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Whether miR-155 regulation of IL-13Rα1 varies across tissue macrophage populations unknown\",\n        \"The catecholamine-producing macrophage pathway has been debated regarding reproducibility in other mouse strains\",\n        \"Mechanism linking IL-13 to DSG1 transcriptional downregulation not fully defined\"\n      ]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Let-7 miRNAs were shown to directly repress IL-13 mRNA, and intranasal let-7 delivery resolved allergic airway disease features, establishing post-transcriptional control of IL-13 itself as a regulatory node.\",\n      \"evidence\": \"Bioinformatic prediction, in vitro transfection in T cells, intranasal let-7 mimic in murine allergy model\",\n      \"pmids\": [\"21616524\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Endogenous regulation of let-7 levels in Th2 cells during allergic inflammation not defined\",\n        \"Specificity of let-7 for IL-13 versus other Th2 cytokines at endogenous expression levels not resolved\"\n      ]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"An IL-33→IL-13 signaling cascade was shown to be required for spasmolytic polypeptide-expressing metaplasia after parietal cell loss, full macrophage tissue repair programming requires IL-13 together with apoptotic cell recognition (neither alone suffices), and autophagy was identified as required for IL-13-induced apical DUOX1 localization and superoxide production.\",\n      \"evidence\": \"IL-33/ST2/IL-13 triple KO epistasis with IL-13 rescue in gastric metaplasia model; genetic ablation of apoptotic cell sensors in helminth and colitis models; ATG5/DUOX1 siRNA in airway epithelial cells with EPR spectroscopy\",\n      \"pmids\": [\"28196875\", \"28495875\", \"28982074\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Identity of the apoptotic cell sensor cooperating with IL-13 signaling not fully defined\",\n        \"Whether the IL-33→IL-13 metaplasia pathway operates in human gastric disease untested\",\n        \"How autophagy specifically directs DUOX1 trafficking versus general cargo unclear\"\n      ]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"ILC2-derived IL-13 was shown to maintain intestinal stem cell self-renewal via circPan3-stabilized IL-13Rα1/Foxp1/β-catenin signaling, Treg-derived IL-13 was demonstrated to be protective in acute lung injury by restraining monocyte accumulation, and Akt1 was identified as a kinase regulating macrophage IL-13 production and pulmonary fibrosis susceptibility.\",\n      \"evidence\": \"circPan3 deletion in Lgr5+ ISCs with RNA-protein interaction and Foxp1-β-catenin co-IP; Foxp3Cre × Il4/Il13 floxed mice in lung injury; Akt1-KO macrophages with IL-33 stimulation and bleomycin fibrosis model\",\n      \"pmids\": [\"30643264\", \"30779711\", \"31299858\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Whether circPan3-IL-13Rα1 axis operates in other stem cell niches unknown\",\n        \"Human relevance of Treg-derived IL-13 in ARDS or lung injury not tested\",\n        \"Akt1 substrates directly linking to IL-13 transcription/secretion not identified\"\n      ]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Eosinophil-derived IL-13 produced via ST2 signaling was shown to mediate hepatoprotection against ischemia-reperfusion injury, extending the tissue-protective role of cell-type-specific IL-13 beyond the lung.\",\n      \"evidence\": \"Genetic eosinophil-deficient mice, adoptive transfer of WT vs ST2-KO eosinophils, liver IRI model with biochemical and histological assessment\",\n      \"pmids\": [\"33536281\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Downstream hepatic targets of eosinophil-derived IL-13 not identified\",\n        \"Whether IL-13Rα2-mediated fibrogenic signaling is engaged in hepatic IRI context unclear\",\n        \"Therapeutic window and translational relevance of eosinophil IL-13 in human liver IRI unknown\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include the structural basis of IL-13Rα2 signaling (vs decoy) complex formation, how tissue-specific receptor expression ratios determine fibrotic vs protective outcomes, and the therapeutic implications of selectively blocking IL-13Rα2 signaling while preserving IL-13Rα1-mediated repair.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"No crystal structure of IL-13/IL-13Rα2 signaling complex available\",\n        \"Integrated quantitative model of IL-13 signal partitioning between Rα1 and Rα2 across tissues lacking\",\n        \"Cell-type-specific functions of IL-13 from distinct immune sources (ILC2, Treg, eosinophil, Th2) not systematically compared\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0048018\", \"supporting_discovery_ids\": [0, 1, 2, 3]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [11, 12, 25]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [0, 1, 3, 17, 35]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [0, 1, 2, 3, 4, 8, 16, 18, 35, 37]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [8, 12, 21, 23, 29, 34]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [3, 13, 14, 15, 20, 27]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"IL4R\",\n      \"IL13RA1\",\n      \"IL13RA2\",\n      \"STAT6\",\n      \"CHI3L1\",\n      \"IL33\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}