{"gene":"IL21R","run_date":"2026-06-10T01:55:22","timeline":{"discoveries":[{"year":2012,"finding":"Crystal structure of IL-21 bound to IL-21R revealed that the WSXWS motif of IL-21R is C-mannosylated at the first tryptophan, and a sugar chain bridges the two fibronectin type III domains of IL-21R, anchoring at the WSXWS motif through an extensive hydrogen bonding network including mannosylation, transforming the V-shaped receptor into an A-frame structure.","method":"X-ray crystallography of IL-21:IL-21R complex with structural validation","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structure with atomic-level detail of glycosylation and domain architecture; single rigorous structural study with multiple orthogonal validations","pmids":["22235133"],"is_preprint":false},{"year":2015,"finding":"The sugar bridge connecting the two fibronectin type III domains of IL-21R forms independently of IL-21 binding, and mutations within the WSXWS motif impair export of IL-21R and γc to the plasma membrane, providing a molecular explanation for how WSXWS mutations cause primary immunodeficiency.","method":"Crystal structure of unbound IL-21R; mutagenesis and cell-surface expression assays","journal":"Genes and immunity","confidence":"High","confidence_rationale":"Tier 1 / Moderate — crystal structure combined with functional mutagenesis and trafficking assays in a single study","pmids":["26043171"],"is_preprint":false},{"year":2006,"finding":"IL-21R expression on CLL B cells is up-regulated by CD40 triggering; IL-21 signaling through IL-21R induces JAK1, JAK3 autophosphorylation and STAT1, STAT3, STAT5 tyrosine phosphorylation, and promotes apoptosis via caspase-8, caspase-3 activation, Bid cleavage to t-Bid, and PARP and p27Kip-1 cleavage rather than proliferation in CLL B cells.","method":"Western blot phosphorylation assays, caspase activity assays, flow cytometry, CD40 stimulation of primary CLL B cells","journal":"Blood","confidence":"High","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal biochemical assays (JAK/STAT phosphorylation, caspase cleavage, Bid processing) in primary patient cells with functional readouts","pmids":["16391014"],"is_preprint":false},{"year":2009,"finding":"Cell-autonomous IL-21R signaling in CD8+ T cells is required for sustained proliferation and cytokine production during chronic LCMV infection in mice; IL-21R is dispensable for CD8+ T cell expansion, effector function, memory homeostasis, and recall responses during acute/resolved infections.","method":"Il21r-/- mouse model, adoptive transfer experiments, flow cytometry for T cell phenotype and function","journal":"Science (New York, N.Y.)","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic KO with cell-autonomous epistasis demonstrated by adoptive transfer; replicated across multiple viral infection models","pmids":["19478140"],"is_preprint":false},{"year":2007,"finding":"IL-21R-mediated signaling is required for IL-21-dependent isotype switching and differentiation of B cells into antibody-secreting cells; blockade with IL-21R.Fc fusion protein in lupus-prone mice reduced autoantibody production, total IgG, and splenic B lymphocyte function.","method":"IL-21R.Fc fusion protein blockade in MRL-Fas(lpr) mice; measurement of autoantibodies, IgG levels, and splenic B cell function ex vivo","journal":"Journal of immunology (Baltimore, Md. : 1950)","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo pharmacological blockade with multiple immunological readouts, single lab","pmids":["17339481"],"is_preprint":false},{"year":2008,"finding":"IL-21R signaling is required for CCR7 upregulation on skin dendritic cells and their migration toward CCR7 ligands; IL-21 treatment of epidermal and dermal cells activates MMP2, which is implicated in skin DC trafficking to draining lymph nodes and subsequent allergic skin inflammation.","method":"Il21r-/- mice, Il21r-/- bone marrow reconstitution, adoptive transfer of OVA-specific CD4+ T cells, CCR7 expression by flow cytometry, MMP2 activation assay","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple genetic approaches (KO, BM reconstitution, adoptive transfer) with defined mechanistic readouts (CCR7 upregulation, MMP2 activation) establishing DC trafficking pathway","pmids":["19075398"],"is_preprint":false},{"year":2004,"finding":"IFN-α/β down-regulates IL-21R mRNA expression in NK and T cells, resulting in reduced STAT3 phosphorylation and DNA binding after IL-21 stimulation; the IL-21 gene promoter contains a putative IFN-gamma activation site (GAS) element that binds STAT1, STAT2, STAT3, and STAT4 in IFN-α/β-stimulated cells.","method":"RT-PCR for IL-21R mRNA, Western blot/EMSA for STAT phosphorylation and DNA binding, promoter analysis with gel-shift assays","journal":"Journal of leukocyte biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (mRNA, STAT phosphorylation, EMSA), single lab","pmids":["15178704"],"is_preprint":false},{"year":2006,"finding":"IL-21 inhibits IL-4-induced IgE production in PBMC/splenocyte cultures through an IFN-γ-dependent mechanism mediated via IL-21R; a polymorphism (T-83C) in the IL-21R gene is associated with lower IL-21-induced IFN-γ production and reduced sensitivity to IL-21-mediated inhibition of IgE.","method":"Ex vivo cytokine production assays, gene reporter assay for Cε promoter, germline Cε mRNA measurements, polymorphism genotyping with functional correlation","journal":"Journal of immunology (Baltimore, Md. : 1950)","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple functional assays (IgE, IFN-γ production, Cε reporter, germline mRNA) with genotype-function correlation, single lab","pmids":["17015683"],"is_preprint":false},{"year":2023,"finding":"IL-21R plus CD40 signals synergize to induce c-MYC and phospho-S6 in germinal center B cells, engage unique molecular mechanisms distinct from BCR+CD40 signaling, and specifically drive IRF4hi/CD138+ plasma cell differentiation and CCR6+/CD38+ memory B cell precursor formation, revealing a second positive selection pathway in GC B cells.","method":"Bulk RNA-seq, single-cell RNA-seq, flow cytometry of GC B cells in vitro and in vivo; signal combination experiments with genetic and pharmacological perturbations","journal":"Science immunology","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (bulk RNA-seq, scRNA-seq, flow cytometry) in both in vitro and in vivo systems; distinct mechanistic pathway placement","pmids":["36800413"],"is_preprint":false},{"year":2015,"finding":"IL-21R signaling supports generation and stabilization of pathogenic Th17 cells by maintaining IL-23R expression on Th17 cells and expression of key molecules for pathogenic Th17 generation; IL-21R deficiency in 2D2xTH transgenic mice reduced Th17 differentiation and spontaneous EAE incidence and severity.","method":"Il21r genetic deletion in 2D2xTH transgenic EAE mice; flow cytometry for Th17 cells and IL-23R expression; disease scoring","journal":"The Journal of clinical investigation","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic epistasis in transgenic model with defined molecular readouts (IL-23R expression, Th17 frequency), single lab","pmids":["26413871"],"is_preprint":false},{"year":2012,"finding":"IL-21R signaling directly in CD8+ T cells promotes their activation (IFN-γ production) and is required for CVB3-induced myocarditis; this was demonstrated as cell-autonomous by adoptive transfer of IL-21RKO vs. WT CD8+ T cells into CD8KO recipients.","method":"IL-21RKO mice, adoptive transfer of purified CD8+ T cells into CD8KO recipients, flow cytometry for CD8+IFN-γ+ cells, myocarditis scoring","journal":"Experimental and molecular pathology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — cell-autonomous epistasis established by adoptive transfer with defined functional readout (IFNγ production, disease severity), single lab","pmids":["22465422"],"is_preprint":false},{"year":2010,"finding":"IL-21R signaling in donor CD4+ T cells promotes effector T cell differentiation and is required for full GVHD pathology; recipients of IL-21R-deficient CD4+ T cells had reduced inflammatory cell infiltration in liver and intestine, impaired MLR, and reduced cytokine production, with the effect attributable to impaired effector T cell differentiation rather than changes in regulatory T cells.","method":"Allogeneic BMT with Il21r-/- splenocytes, CD25 depletion experiments, MLR, cytokine production assays, histopathology","journal":"Journal of immunology (Baltimore, Md. : 1950)","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic KO with multiple functional readouts and CD25 depletion control to distinguish effector from regulatory T cell mechanisms, single lab","pmids":["20574002"],"is_preprint":false},{"year":2015,"finding":"IL-21R signaling intrinsically suppresses the accumulation of IL-17-producing γδ T cells in the respiratory tract both at steady state and after influenza A virus infection, without affecting adaptive T cell responses or virus clearance.","method":"IL-21R KO mice, influenza A virus infection model, flow cytometry for γδ T cells and Th17 cells, BAL cytokine measurements","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic KO with intrinsic suppression established, multiple cell-type readouts, single lab","pmids":["25849970"],"is_preprint":false},{"year":2010,"finding":"Defective JAK3 expression in follicular lymphoma cell line DOHH2 results in resistance to IL-21-mediated apoptosis despite high IL-21R surface expression, demonstrating that functional JAK/STAT signaling downstream of IL-21R is required for IL-21-induced apoptosis; IL-21 upregulates SOCS3 in responsive but not refractory cells.","method":"Western blot for JAK/STAT phosphorylation, RT-PCR for JAK3 and SOCS3, Annexin-V apoptosis assay, immunofluorescence","journal":"Experimental hematology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — mechanistic dissection linking JAK3 absence to signaling failure downstream of IL-21R, multiple orthogonal methods, single lab","pmids":["20193734"],"is_preprint":false},{"year":2017,"finding":"IL-21R overexpression in CD14+CD16+ bone marrow monocytes from multiple myeloma patients increases osteoclast formation; inhibition of IL-21R signaling with JAK inhibitor Janex-1 suppressed osteoclast differentiation from these monocytes.","method":"Flow cytometry and transcriptional profiling of sorted BM CD14+ monocytes; ex vivo osteoclastogenesis cultures; Janex-1 pharmacological inhibition","journal":"Haematologica","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — transcriptional and functional assays with pharmacological inhibition establishing IL-21R role in osteoclast differentiation, single lab","pmids":["28057743"],"is_preprint":false},{"year":2018,"finding":"Increased binding of transcription factor SP1 to the IL21R promoter in RA B cells drives enhanced IL-21R expression, increased pSTAT3 signaling, greater plasmablast differentiation, and elevated IL-6 production in response to IL-21 stimulation.","method":"ChIP-qPCR for SP1 binding to IL21R promoter, flow cytometry for IL-21R and pSTAT3, cytokine ELISA, plasmablast differentiation assay","journal":"Frontiers in immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ChIP-qPCR establishes direct SP1 binding to IL21R promoter with correlated functional outcomes; multiple orthogonal assays, single lab","pmids":["30233580"],"is_preprint":false},{"year":2021,"finding":"Targeting Cbx3/HP1γ in CD8+ T cells increases transcriptional activity at the Il21r locus, upregulating IL-21R expression; both LEF-1 and IL-21R are necessary for Cbx3/HP1γ-deficient CD8+ T cells to persist and control tumor growth in vivo.","method":"Cbx3/HP1γ KO CD8+ T cells, chromatin remodeling/ChIP-seq analysis, in vivo tumor models (ovarian cancer, melanoma, neuroblastoma), flow cytometry","journal":"Frontiers in immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — chromatin remodeling linked to IL-21R upregulation with genetic epistasis in multiple tumor models, single lab","pmids":["34721405"],"is_preprint":false},{"year":2016,"finding":"miR-30a directly targets the IL-21R 3'UTR (validated by dual luciferase reporter assay), downregulating IL-21R expression to inhibit Th17 differentiation; overexpression of IL-21R reversed the inhibitory effects of miR-30a on Th17 differentiation.","method":"Dual luciferase reporter assay, miR-30a overexpression in naïve T cells, IL-21R overexpression rescue experiments, in vivo EAE model","journal":"Brain, behavior, and immunity","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct target validation by luciferase assay with rescue experiment establishing IL-21R as functional mediator; multiple in vitro and in vivo methods, single lab","pmids":["27006279"],"is_preprint":false},{"year":2025,"finding":"IL-21R signals through the IL-21R-STAT3/JAK-STAT3 pathway; a chimeric receptor TRII/21R (extracellular TGF-βRII fused to transmembrane and intracellular IL-21R domains) converts TGF-β immunosuppressive signals into NK cell activation signals via the IL-21R-STAT3 pathway, enhancing CAR-NK cell cytotoxicity, proliferation, and survival.","method":"Chimeric receptor construct design and expression, in vitro cytotoxicity assays, xenograft mouse tumor models, JAK-STAT3 pathway readouts","journal":"Pharmacological research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — domain-swap chimeric receptor experiment mechanistically assigns intracellular IL-21R domain to STAT3 activation and NK cell functional outcomes; single lab","pmids":["39884449"],"is_preprint":false},{"year":2025,"finding":"PTEN negatively regulates IL-21R signaling strength in germinal center B cells; PTEN deletion in established GC B cells results in more sustained IL-21R signaling and enhanced CD40 signaling, selectively promoting plasma cell differentiation without affecting class switching or memory precursor differentiation.","method":"Tamoxifen-inducible Cre PTEN deletion in B cells after GC establishment; GC B cell transfer system with WT and PTEN-deficient cells in same recipients; flow cytometry for plasma cell and memory B cell markers","journal":"Journal of immunology (Baltimore, Md. : 1950)","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic deletion in established GC with competitive transfer system establishing PTEN as negative regulator of IL-21R signaling amplitude; multiple experimental systems, single lab","pmids":["40795247"],"is_preprint":false},{"year":2024,"finding":"B cell-intrinsic IL-21R signaling promotes proliferation of pre-activated/class-switched IgG1+ B cells but induces Bim-dependent apoptosis in naïve B cells; B cell-specific Il21r deletion causes severe defects in IgG1 antibody responses and impairs the transition of B cells from a pre-GC to GC state in vivo.","method":"Conditional Il21r KO mouse model, ex vivo B cell culture systems, in vivo immunization, flow cytometry for GC/plasmablast markers, apoptosis assays","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — conditional KO with context-dependent phenotypic dissection using ex vivo and in vivo systems; preprint, not yet peer-reviewed","pmids":["bio_10.1101_2024.07.13.600808"],"is_preprint":true},{"year":2023,"finding":"ChIP-seq analysis identified IL21R as a target gene of GTF2I in CD19+ B cells, with GTF2I binding peaks detected in the upstream region and 5'UTR of the IL21R locus, suggesting GTF2I regulates IL-21R expression at the transcriptional level.","method":"ChIP-seq in CD19+ B cells, motif analysis by MEME-ChIP, comparison with ENCODE GTF2I ChIP-seq datasets","journal":"Hepatology international","confidence":"Low","confidence_rationale":"Tier 3 / Weak — ChIP-seq identifies binding without direct functional validation of transcriptional regulation; single lab","pmids":["37713154"],"is_preprint":false}],"current_model":"IL-21R is a class I cytokine receptor that forms a heterodimeric complex with the common γ-chain; its extracellular domain is C-mannosylated at the WSXWS motif, forming a sugar bridge that stabilizes an A-frame domain architecture essential for plasma membrane trafficking. Upon IL-21 binding, IL-21R signals through JAK1/JAK3-mediated phosphorylation of STAT1, STAT3, and STAT5, with the strength of this signal negatively regulated by PTEN in germinal center B cells. In a context-dependent manner, IL-21R drives apoptosis in naïve B cells (Bim-dependent) but promotes proliferation and plasma cell differentiation in pre-activated/GC B cells, particularly when combined with CD40 signaling that synergistically induces c-MYC and p-S6. In T cells, IL-21R signaling cell-autonomously sustains CD8+ T cell proliferation and cytokine production during chronic infection, supports pathogenic Th17 cell generation via IL-23R maintenance, and suppresses IL-17-producing γδ T cells. IL-21R expression is transcriptionally regulated by SP1 binding to its promoter (enhanced in rheumatoid arthritis B cells), post-transcriptionally suppressed by miR-30a targeting its 3'UTR, and at the mRNA level is down-regulated by IFN-α/β signaling."},"narrative":{"mechanistic_narrative":"IL-21R is a class I cytokine receptor that couples IL-21 binding to JAK/STAT signaling to control B-cell and T-cell fate decisions across humoral immunity, anti-viral responses, and autoimmunity [PMID:16391014, PMID:19478140, PMID:36800413]. Its extracellular domain carries a C-mannose modification at the first tryptophan of the WSXWS motif, where a sugar chain bridges the two fibronectin type III domains to convert the receptor from a V-shaped to an A-frame architecture; this bridge forms independently of ligand and is required for export of IL-21R and the common γ-chain to the plasma membrane, explaining why WSXWS mutations cause primary immunodeficiency [PMID:22235133, PMID:26043171]. Ligand engagement triggers JAK1/JAK3 autophosphorylation and tyrosine phosphorylation of STAT1, STAT3, and STAT5, and intact downstream JAK/STAT signaling—not mere surface expression—is required for IL-21 responses, as JAK3-deficient cells remain refractory despite abundant receptor [PMID:16391014, PMID:20193734, PMID:39884449]. The cellular outcome of signaling is strictly context-dependent: in naïve B cells and CLL/follicular lymphoma cells IL-21R drives caspase-dependent, Bim-mediated apoptosis, whereas in pre-activated, class-switched, and germinal-center B cells it promotes proliferation, isotype switching, and antibody-secreting-cell formation, with signal amplitude tuned by PTEN [PMID:16391014, PMID:20193734, PMID:40795247, PMID:bio_10.1101_2024.07.13.600808]. In germinal centers, combined IL-21R and CD40 signaling synergistically induces c-MYC and phospho-S6 to drive plasma-cell and memory-precursor differentiation as a distinct positive-selection pathway [PMID:36800413]. In T cells, cell-autonomous IL-21R signaling sustains CD8+ T-cell proliferation and IFN-γ production during chronic infection and tissue inflammation, supports pathogenic Th17 generation by maintaining IL-23R, drives effector CD4+ differentiation in GVHD, and intrinsically restrains IL-17-producing γδ T cells [PMID:19478140, PMID:26413871, PMID:22465422, PMID:20574002, PMID:25849970]. IL-21R abundance is set transcriptionally by SP1 binding to its promoter, post-transcriptionally by miR-30a targeting its 3'UTR, and at the mRNA level by IFN-α/β-mediated down-regulation [PMID:30233580, PMID:27006279, PMID:15178704].","teleology":[{"year":2004,"claim":"Established that IL-21R responsiveness is dynamically controlled by type I interferon, linking innate cytokine context to the strength of IL-21/STAT3 signaling in NK and T cells.","evidence":"RT-PCR, Western blot, and EMSA of STAT phosphorylation and DNA binding after IFN-α/β treatment","pmids":["15178704"],"confidence":"Medium","gaps":["Mechanism of IFN-α/β-driven IL-21R mRNA down-regulation not defined","No in vivo confirmation of the regulatory axis"]},{"year":2006,"claim":"Showed that IL-21R engages canonical JAK1/JAK3-STAT1/3/5 signaling yet drives apoptosis rather than proliferation in malignant B cells, revealing the context-dependence of receptor output.","evidence":"Phosphorylation and caspase-cleavage Western blots and flow cytometry in CD40-stimulated primary CLL B cells","pmids":["16391014"],"confidence":"High","gaps":["Does not explain what cellular context switches output from apoptosis to proliferation","Pro-apoptotic vs pro-survival determinants downstream of STATs unresolved"]},{"year":2006,"claim":"Identified an IL-21R polymorphism (T-83C) altering IL-21-induced IFN-γ output and IgE suppression, providing the first genotype-function link for receptor variation.","evidence":"Ex vivo cytokine assays, Cε promoter reporter, germline mRNA measurement, and genotype correlation","pmids":["17015683"],"confidence":"Medium","gaps":["Molecular mechanism by which the polymorphism alters signaling unknown","Single-cohort genotype correlation"]},{"year":2007,"claim":"Demonstrated in vivo that IL-21R is required for IL-21-dependent isotype switching and antibody-secreting-cell differentiation, and that its blockade dampens autoantibody-driven disease.","evidence":"IL-21R.Fc fusion blockade in lupus-prone MRL-Fas(lpr) mice with autoantibody and B-cell function readouts","pmids":["17339481"],"confidence":"Medium","gaps":["Pharmacological blockade does not isolate B-cell-intrinsic from extrinsic effects","Downstream transcriptional program not defined"]},{"year":2008,"claim":"Extended IL-21R function beyond lymphocytes by showing it controls dendritic-cell CCR7 upregulation and MMP2-dependent migration to lymph nodes during skin inflammation.","evidence":"Il21r-/- mice, bone-marrow reconstitution, adoptive transfer, CCR7 flow cytometry, and MMP2 activation assay","pmids":["19075398"],"confidence":"High","gaps":["Direct signaling link between IL-21R and CCR7/MMP2 induction not mapped","Whether DC effect is fully cell-intrinsic not resolved"]},{"year":2009,"claim":"Defined a cell-autonomous, context-restricted T-cell role: IL-21R sustains CD8+ T-cell proliferation and cytokine production specifically during chronic, but not acute, viral infection.","evidence":"Il21r-/- mice and adoptive transfer during LCMV infection with T-cell phenotype/function readouts","pmids":["19478140"],"confidence":"High","gaps":["Molecular basis for chronic-specific dependence unknown","Transcriptional targets sustaining CD8+ persistence not identified"]},{"year":2010,"claim":"Established that functional JAK/STAT signaling downstream of IL-21R, not surface expression, determines responsiveness, by showing JAK3-deficient lymphoma cells resist IL-21 apoptosis.","evidence":"JAK/STAT and SOCS3 analysis and apoptosis assays in JAK3-defective vs responsive lymphoma lines","pmids":["20193734"],"confidence":"Medium","gaps":["Single cell-line comparison","SOCS3 role in setting response threshold not functionally tested"]},{"year":2010,"claim":"Showed donor T-cell-intrinsic IL-21R signaling drives effector CD4+ differentiation and GVHD pathology independently of regulatory T cells.","evidence":"Allogeneic BMT with Il21r-/- splenocytes, CD25-depletion controls, MLR, cytokine and histopathology readouts","pmids":["20574002"],"confidence":"Medium","gaps":["Transcriptional effector program downstream of IL-21R not defined","Single-model GVHD setting"]},{"year":2012,"claim":"Solved the IL-21:IL-21R structure, revealing C-mannosylation at the WSXWS motif and a sugar bridge that converts the receptor into an A-frame architecture.","evidence":"X-ray crystallography of the IL-21:IL-21R complex with structural validation","pmids":["22235133"],"confidence":"High","gaps":["Did not test functional requirement of the sugar bridge","Glycosylation enzymology in cells not addressed"]},{"year":2012,"claim":"Confirmed cell-autonomous IL-21R signaling in CD8+ T cells drives IFN-γ production required for CVB3 myocarditis, generalizing the chronic-inflammation CD8+ dependence.","evidence":"Adoptive transfer of IL-21RKO vs WT CD8+ T cells into CD8KO recipients with disease scoring","pmids":["22465422"],"confidence":"Medium","gaps":["Single disease model","Signaling intermediates linking IL-21R to IFN-γ not mapped"]},{"year":2015,"claim":"Connected the structural sugar bridge to function and disease by showing it forms ligand-independently and that WSXWS mutations block IL-21R/γc plasma-membrane export, explaining immunodeficiency.","evidence":"Crystal structure of unbound IL-21R plus mutagenesis and cell-surface trafficking assays","pmids":["26043171"],"confidence":"High","gaps":["Cellular C-mannosyltransferase machinery not identified","Quantitative impact on signaling output not measured"]},{"year":2015,"claim":"Identified IL-21R as a driver of pathogenic Th17 cells by maintaining IL-23R expression, linking it to autoimmune neuroinflammation.","evidence":"Il21r deletion in 2D2xTH transgenic EAE mice with Th17 and IL-23R flow cytometry and disease scoring","pmids":["26413871"],"confidence":"Medium","gaps":["Direct mechanism maintaining IL-23R unknown","Single transgenic model"]},{"year":2015,"claim":"Revealed an opposing T-cell role: intrinsic IL-21R signaling suppresses IL-17-producing γδ T cells in the respiratory tract, highlighting cell-type-specific outcomes.","evidence":"IL-21R KO mice in influenza A infection with γδ/Th17 flow cytometry and BAL cytokines","pmids":["25849970"],"confidence":"Medium","gaps":["Mechanism of γδ T-cell suppression unknown","Whether suppression is direct on γδ cells not fully resolved"]},{"year":2016,"claim":"Established post-transcriptional control of IL-21R by miR-30a targeting its 3'UTR, with receptor overexpression rescuing Th17 differentiation.","evidence":"Dual luciferase 3'UTR reporter, miR-30a overexpression, IL-21R rescue, and EAE model","pmids":["27006279"],"confidence":"Medium","gaps":["Physiological signals controlling miR-30a not defined","In vivo contribution of this axis to receptor levels not quantified"]},{"year":2017,"claim":"Extended IL-21R signaling to the myeloid compartment, showing overexpression on myeloma-associated monocytes promotes JAK-dependent osteoclast differentiation.","evidence":"Profiling of sorted BM CD14+ monocytes, ex vivo osteoclastogenesis, and Janex-1 JAK inhibition","pmids":["28057743"],"confidence":"Medium","gaps":["STAT effectors in osteoclast program not defined","Single patient-derived system"]},{"year":2018,"claim":"Identified SP1 as a direct transcriptional activator of IL21R whose increased promoter binding amplifies pSTAT3 signaling and plasmablast differentiation in rheumatoid arthritis B cells.","evidence":"ChIP-qPCR for SP1 at the IL21R promoter with pSTAT3, plasmablast, and IL-6 readouts","pmids":["30233580"],"confidence":"Medium","gaps":["Upstream signals driving SP1 recruitment unknown","Correlative link between SP1 binding and disease activity"]},{"year":2021,"claim":"Linked chromatin regulation to IL-21R expression, showing Cbx3/HP1γ loss opens the Il21r locus and that IL-21R is required for enhanced anti-tumor CD8+ T-cell persistence.","evidence":"Cbx3/HP1γ KO CD8+ T cells, chromatin/ChIP-seq, and multiple in vivo tumor models","pmids":["34721405"],"confidence":"Medium","gaps":["Direct epigenetic mechanism at the locus not fully resolved","Relative contribution of IL-21R vs LEF-1 not separated"]},{"year":2023,"claim":"Defined IL-21R + CD40 as a distinct germinal-center positive-selection pathway that synergistically induces c-MYC and phospho-S6 to drive plasma-cell and memory-precursor differentiation.","evidence":"Bulk and single-cell RNA-seq with flow cytometry of GC B cells in vitro and in vivo and signal-combination perturbations","pmids":["36800413"],"confidence":"High","gaps":["Molecular integration of IL-21R and CD40 signals not fully mapped","How this pathway interfaces with BCR-based selection unresolved"]},{"year":2023,"claim":"Nominated GTF2I as an additional transcriptional regulator of IL21R based on binding at the upstream/5'UTR region in B cells.","evidence":"ChIP-seq in CD19+ B cells with motif analysis and ENCODE comparison","pmids":["37713154"],"confidence":"Low","gaps":["Binding identified without functional validation of transcriptional regulation","No perturbation of GTF2I to confirm effect on IL-21R levels","Single dataset"]},{"year":2024,"claim":"Dissected the apoptosis-versus-proliferation switch genetically, showing B-cell-intrinsic IL-21R drives Bim-dependent apoptosis in naïve B cells but proliferation in class-switched B cells and is required for the pre-GC-to-GC transition.","evidence":"Conditional Il21r KO mice with ex vivo culture, immunization, and apoptosis assays (preprint)","pmids":["bio_10.1101_2024.07.13.600808"],"confidence":"Medium","gaps":["Preprint, not yet peer-reviewed","Molecular determinant gating apoptosis vs proliferation not identified"]},{"year":2025,"claim":"Established PTEN as a negative regulator of IL-21R signaling amplitude in germinal-center B cells, selectively biasing toward plasma-cell differentiation when relieved.","evidence":"Inducible PTEN deletion in established GC B cells with competitive transfer and flow cytometry","pmids":["40795247"],"confidence":"Medium","gaps":["Biochemical node where PTEN restrains IL-21R signaling not pinpointed","Single-lab GC system"]},{"year":2025,"claim":"Functionally assigned the intracellular IL-21R domain to STAT3-mediated activation by using a TGF-βRII/IL-21R chimera to convert suppressive signals into NK-cell activation.","evidence":"Domain-swap chimeric receptor with cytotoxicity assays, xenograft models, and JAK-STAT3 readouts","pmids":["39884449"],"confidence":"Medium","gaps":["Engineered receptor context may not reflect native signaling","STAT3-specific vs broader STAT contributions not separated"]},{"year":null,"claim":"How a single IL-21R/JAK-STAT signal is mechanistically converted into opposing apoptotic versus proliferative outcomes across cell states remains the central unresolved question.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No defined molecular switch linking signal amplitude/context to fate decision","Differential STAT target gene programs across cell types not catalogued","Quantitative role of negative regulators (PTEN, SOCS3, miRNA) in setting thresholds not integrated"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[2,13,18]},{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[2]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[0,1,2]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[2,13,18]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[3,8,9]},{"term_id":"R-HSA-5357801","term_label":"Programmed Cell Death","supporting_discovery_ids":[2,20]}],"complexes":[],"partners":["IL21","JAK1","JAK3","STAT3","STAT1","STAT5"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q9HBE5","full_name":"Interleukin-21 receptor","aliases":["Novel interleukin receptor"],"length_aa":538,"mass_kda":59.1,"function":"This is a receptor for interleukin-21","subcellular_location":"Membrane","url":"https://www.uniprot.org/uniprotkb/Q9HBE5/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/IL21R","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/IL21R","total_profiled":1310},"omim":[{"mim_id":"621524","title":"WD REPEAT- AND SOCS BOX-CONTAINING PROTEIN 2; WSB2","url":"https://www.omim.org/entry/621524"},{"mim_id":"615207","title":"IMMUNODEFICIENCY 56; IMD56","url":"https://www.omim.org/entry/615207"},{"mim_id":"607531","title":"KLF TRANSCRIPTION FACTOR 12; KLF12","url":"https://www.omim.org/entry/607531"},{"mim_id":"605384","title":"INTERLEUKIN 21; IL21","url":"https://www.omim.org/entry/605384"},{"mim_id":"605383","title":"INTERLEUKIN 21 RECEPTOR; IL21R","url":"https://www.omim.org/entry/605383"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Plasma membrane","reliability":"Approved"},{"location":"Cytosol","reliability":"Approved"}],"tissue_specificity":"Group enriched","tissue_distribution":"Detected in some","driving_tissues":[{"tissue":"bone marrow","ntpm":7.1},{"tissue":"lymphoid 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tryptophan, and a sugar chain bridges the two fibronectin type III domains of IL-21R, anchoring at the WSXWS motif through an extensive hydrogen bonding network including mannosylation, transforming the V-shaped receptor into an A-frame structure.\",\n      \"method\": \"X-ray crystallography of IL-21:IL-21R complex with structural validation\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structure with atomic-level detail of glycosylation and domain architecture; single rigorous structural study with multiple orthogonal validations\",\n      \"pmids\": [\"22235133\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"The sugar bridge connecting the two fibronectin type III domains of IL-21R forms independently of IL-21 binding, and mutations within the WSXWS motif impair export of IL-21R and γc to the plasma membrane, providing a molecular explanation for how WSXWS mutations cause primary immunodeficiency.\",\n      \"method\": \"Crystal structure of unbound IL-21R; mutagenesis and cell-surface expression assays\",\n      \"journal\": \"Genes and immunity\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — crystal structure combined with functional mutagenesis and trafficking assays in a single study\",\n      \"pmids\": [\"26043171\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"IL-21R expression on CLL B cells is up-regulated by CD40 triggering; IL-21 signaling through IL-21R induces JAK1, JAK3 autophosphorylation and STAT1, STAT3, STAT5 tyrosine phosphorylation, and promotes apoptosis via caspase-8, caspase-3 activation, Bid cleavage to t-Bid, and PARP and p27Kip-1 cleavage rather than proliferation in CLL B cells.\",\n      \"method\": \"Western blot phosphorylation assays, caspase activity assays, flow cytometry, CD40 stimulation of primary CLL B cells\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal biochemical assays (JAK/STAT phosphorylation, caspase cleavage, Bid processing) in primary patient cells with functional readouts\",\n      \"pmids\": [\"16391014\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Cell-autonomous IL-21R signaling in CD8+ T cells is required for sustained proliferation and cytokine production during chronic LCMV infection in mice; IL-21R is dispensable for CD8+ T cell expansion, effector function, memory homeostasis, and recall responses during acute/resolved infections.\",\n      \"method\": \"Il21r-/- mouse model, adoptive transfer experiments, flow cytometry for T cell phenotype and function\",\n      \"journal\": \"Science (New York, N.Y.)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic KO with cell-autonomous epistasis demonstrated by adoptive transfer; replicated across multiple viral infection models\",\n      \"pmids\": [\"19478140\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"IL-21R-mediated signaling is required for IL-21-dependent isotype switching and differentiation of B cells into antibody-secreting cells; blockade with IL-21R.Fc fusion protein in lupus-prone mice reduced autoantibody production, total IgG, and splenic B lymphocyte function.\",\n      \"method\": \"IL-21R.Fc fusion protein blockade in MRL-Fas(lpr) mice; measurement of autoantibodies, IgG levels, and splenic B cell function ex vivo\",\n      \"journal\": \"Journal of immunology (Baltimore, Md. : 1950)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo pharmacological blockade with multiple immunological readouts, single lab\",\n      \"pmids\": [\"17339481\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"IL-21R signaling is required for CCR7 upregulation on skin dendritic cells and their migration toward CCR7 ligands; IL-21 treatment of epidermal and dermal cells activates MMP2, which is implicated in skin DC trafficking to draining lymph nodes and subsequent allergic skin inflammation.\",\n      \"method\": \"Il21r-/- mice, Il21r-/- bone marrow reconstitution, adoptive transfer of OVA-specific CD4+ T cells, CCR7 expression by flow cytometry, MMP2 activation assay\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple genetic approaches (KO, BM reconstitution, adoptive transfer) with defined mechanistic readouts (CCR7 upregulation, MMP2 activation) establishing DC trafficking pathway\",\n      \"pmids\": [\"19075398\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"IFN-α/β down-regulates IL-21R mRNA expression in NK and T cells, resulting in reduced STAT3 phosphorylation and DNA binding after IL-21 stimulation; the IL-21 gene promoter contains a putative IFN-gamma activation site (GAS) element that binds STAT1, STAT2, STAT3, and STAT4 in IFN-α/β-stimulated cells.\",\n      \"method\": \"RT-PCR for IL-21R mRNA, Western blot/EMSA for STAT phosphorylation and DNA binding, promoter analysis with gel-shift assays\",\n      \"journal\": \"Journal of leukocyte biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (mRNA, STAT phosphorylation, EMSA), single lab\",\n      \"pmids\": [\"15178704\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"IL-21 inhibits IL-4-induced IgE production in PBMC/splenocyte cultures through an IFN-γ-dependent mechanism mediated via IL-21R; a polymorphism (T-83C) in the IL-21R gene is associated with lower IL-21-induced IFN-γ production and reduced sensitivity to IL-21-mediated inhibition of IgE.\",\n      \"method\": \"Ex vivo cytokine production assays, gene reporter assay for Cε promoter, germline Cε mRNA measurements, polymorphism genotyping with functional correlation\",\n      \"journal\": \"Journal of immunology (Baltimore, Md. : 1950)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple functional assays (IgE, IFN-γ production, Cε reporter, germline mRNA) with genotype-function correlation, single lab\",\n      \"pmids\": [\"17015683\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"IL-21R plus CD40 signals synergize to induce c-MYC and phospho-S6 in germinal center B cells, engage unique molecular mechanisms distinct from BCR+CD40 signaling, and specifically drive IRF4hi/CD138+ plasma cell differentiation and CCR6+/CD38+ memory B cell precursor formation, revealing a second positive selection pathway in GC B cells.\",\n      \"method\": \"Bulk RNA-seq, single-cell RNA-seq, flow cytometry of GC B cells in vitro and in vivo; signal combination experiments with genetic and pharmacological perturbations\",\n      \"journal\": \"Science immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (bulk RNA-seq, scRNA-seq, flow cytometry) in both in vitro and in vivo systems; distinct mechanistic pathway placement\",\n      \"pmids\": [\"36800413\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"IL-21R signaling supports generation and stabilization of pathogenic Th17 cells by maintaining IL-23R expression on Th17 cells and expression of key molecules for pathogenic Th17 generation; IL-21R deficiency in 2D2xTH transgenic mice reduced Th17 differentiation and spontaneous EAE incidence and severity.\",\n      \"method\": \"Il21r genetic deletion in 2D2xTH transgenic EAE mice; flow cytometry for Th17 cells and IL-23R expression; disease scoring\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic epistasis in transgenic model with defined molecular readouts (IL-23R expression, Th17 frequency), single lab\",\n      \"pmids\": [\"26413871\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"IL-21R signaling directly in CD8+ T cells promotes their activation (IFN-γ production) and is required for CVB3-induced myocarditis; this was demonstrated as cell-autonomous by adoptive transfer of IL-21RKO vs. WT CD8+ T cells into CD8KO recipients.\",\n      \"method\": \"IL-21RKO mice, adoptive transfer of purified CD8+ T cells into CD8KO recipients, flow cytometry for CD8+IFN-γ+ cells, myocarditis scoring\",\n      \"journal\": \"Experimental and molecular pathology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — cell-autonomous epistasis established by adoptive transfer with defined functional readout (IFNγ production, disease severity), single lab\",\n      \"pmids\": [\"22465422\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"IL-21R signaling in donor CD4+ T cells promotes effector T cell differentiation and is required for full GVHD pathology; recipients of IL-21R-deficient CD4+ T cells had reduced inflammatory cell infiltration in liver and intestine, impaired MLR, and reduced cytokine production, with the effect attributable to impaired effector T cell differentiation rather than changes in regulatory T cells.\",\n      \"method\": \"Allogeneic BMT with Il21r-/- splenocytes, CD25 depletion experiments, MLR, cytokine production assays, histopathology\",\n      \"journal\": \"Journal of immunology (Baltimore, Md. : 1950)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic KO with multiple functional readouts and CD25 depletion control to distinguish effector from regulatory T cell mechanisms, single lab\",\n      \"pmids\": [\"20574002\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"IL-21R signaling intrinsically suppresses the accumulation of IL-17-producing γδ T cells in the respiratory tract both at steady state and after influenza A virus infection, without affecting adaptive T cell responses or virus clearance.\",\n      \"method\": \"IL-21R KO mice, influenza A virus infection model, flow cytometry for γδ T cells and Th17 cells, BAL cytokine measurements\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic KO with intrinsic suppression established, multiple cell-type readouts, single lab\",\n      \"pmids\": [\"25849970\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Defective JAK3 expression in follicular lymphoma cell line DOHH2 results in resistance to IL-21-mediated apoptosis despite high IL-21R surface expression, demonstrating that functional JAK/STAT signaling downstream of IL-21R is required for IL-21-induced apoptosis; IL-21 upregulates SOCS3 in responsive but not refractory cells.\",\n      \"method\": \"Western blot for JAK/STAT phosphorylation, RT-PCR for JAK3 and SOCS3, Annexin-V apoptosis assay, immunofluorescence\",\n      \"journal\": \"Experimental hematology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — mechanistic dissection linking JAK3 absence to signaling failure downstream of IL-21R, multiple orthogonal methods, single lab\",\n      \"pmids\": [\"20193734\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"IL-21R overexpression in CD14+CD16+ bone marrow monocytes from multiple myeloma patients increases osteoclast formation; inhibition of IL-21R signaling with JAK inhibitor Janex-1 suppressed osteoclast differentiation from these monocytes.\",\n      \"method\": \"Flow cytometry and transcriptional profiling of sorted BM CD14+ monocytes; ex vivo osteoclastogenesis cultures; Janex-1 pharmacological inhibition\",\n      \"journal\": \"Haematologica\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — transcriptional and functional assays with pharmacological inhibition establishing IL-21R role in osteoclast differentiation, single lab\",\n      \"pmids\": [\"28057743\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Increased binding of transcription factor SP1 to the IL21R promoter in RA B cells drives enhanced IL-21R expression, increased pSTAT3 signaling, greater plasmablast differentiation, and elevated IL-6 production in response to IL-21 stimulation.\",\n      \"method\": \"ChIP-qPCR for SP1 binding to IL21R promoter, flow cytometry for IL-21R and pSTAT3, cytokine ELISA, plasmablast differentiation assay\",\n      \"journal\": \"Frontiers in immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ChIP-qPCR establishes direct SP1 binding to IL21R promoter with correlated functional outcomes; multiple orthogonal assays, single lab\",\n      \"pmids\": [\"30233580\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Targeting Cbx3/HP1γ in CD8+ T cells increases transcriptional activity at the Il21r locus, upregulating IL-21R expression; both LEF-1 and IL-21R are necessary for Cbx3/HP1γ-deficient CD8+ T cells to persist and control tumor growth in vivo.\",\n      \"method\": \"Cbx3/HP1γ KO CD8+ T cells, chromatin remodeling/ChIP-seq analysis, in vivo tumor models (ovarian cancer, melanoma, neuroblastoma), flow cytometry\",\n      \"journal\": \"Frontiers in immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — chromatin remodeling linked to IL-21R upregulation with genetic epistasis in multiple tumor models, single lab\",\n      \"pmids\": [\"34721405\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"miR-30a directly targets the IL-21R 3'UTR (validated by dual luciferase reporter assay), downregulating IL-21R expression to inhibit Th17 differentiation; overexpression of IL-21R reversed the inhibitory effects of miR-30a on Th17 differentiation.\",\n      \"method\": \"Dual luciferase reporter assay, miR-30a overexpression in naïve T cells, IL-21R overexpression rescue experiments, in vivo EAE model\",\n      \"journal\": \"Brain, behavior, and immunity\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct target validation by luciferase assay with rescue experiment establishing IL-21R as functional mediator; multiple in vitro and in vivo methods, single lab\",\n      \"pmids\": [\"27006279\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"IL-21R signals through the IL-21R-STAT3/JAK-STAT3 pathway; a chimeric receptor TRII/21R (extracellular TGF-βRII fused to transmembrane and intracellular IL-21R domains) converts TGF-β immunosuppressive signals into NK cell activation signals via the IL-21R-STAT3 pathway, enhancing CAR-NK cell cytotoxicity, proliferation, and survival.\",\n      \"method\": \"Chimeric receptor construct design and expression, in vitro cytotoxicity assays, xenograft mouse tumor models, JAK-STAT3 pathway readouts\",\n      \"journal\": \"Pharmacological research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — domain-swap chimeric receptor experiment mechanistically assigns intracellular IL-21R domain to STAT3 activation and NK cell functional outcomes; single lab\",\n      \"pmids\": [\"39884449\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"PTEN negatively regulates IL-21R signaling strength in germinal center B cells; PTEN deletion in established GC B cells results in more sustained IL-21R signaling and enhanced CD40 signaling, selectively promoting plasma cell differentiation without affecting class switching or memory precursor differentiation.\",\n      \"method\": \"Tamoxifen-inducible Cre PTEN deletion in B cells after GC establishment; GC B cell transfer system with WT and PTEN-deficient cells in same recipients; flow cytometry for plasma cell and memory B cell markers\",\n      \"journal\": \"Journal of immunology (Baltimore, Md. : 1950)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic deletion in established GC with competitive transfer system establishing PTEN as negative regulator of IL-21R signaling amplitude; multiple experimental systems, single lab\",\n      \"pmids\": [\"40795247\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"B cell-intrinsic IL-21R signaling promotes proliferation of pre-activated/class-switched IgG1+ B cells but induces Bim-dependent apoptosis in naïve B cells; B cell-specific Il21r deletion causes severe defects in IgG1 antibody responses and impairs the transition of B cells from a pre-GC to GC state in vivo.\",\n      \"method\": \"Conditional Il21r KO mouse model, ex vivo B cell culture systems, in vivo immunization, flow cytometry for GC/plasmablast markers, apoptosis assays\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — conditional KO with context-dependent phenotypic dissection using ex vivo and in vivo systems; preprint, not yet peer-reviewed\",\n      \"pmids\": [\"bio_10.1101_2024.07.13.600808\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"ChIP-seq analysis identified IL21R as a target gene of GTF2I in CD19+ B cells, with GTF2I binding peaks detected in the upstream region and 5'UTR of the IL21R locus, suggesting GTF2I regulates IL-21R expression at the transcriptional level.\",\n      \"method\": \"ChIP-seq in CD19+ B cells, motif analysis by MEME-ChIP, comparison with ENCODE GTF2I ChIP-seq datasets\",\n      \"journal\": \"Hepatology international\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — ChIP-seq identifies binding without direct functional validation of transcriptional regulation; single lab\",\n      \"pmids\": [\"37713154\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"IL-21R is a class I cytokine receptor that forms a heterodimeric complex with the common γ-chain; its extracellular domain is C-mannosylated at the WSXWS motif, forming a sugar bridge that stabilizes an A-frame domain architecture essential for plasma membrane trafficking. Upon IL-21 binding, IL-21R signals through JAK1/JAK3-mediated phosphorylation of STAT1, STAT3, and STAT5, with the strength of this signal negatively regulated by PTEN in germinal center B cells. In a context-dependent manner, IL-21R drives apoptosis in naïve B cells (Bim-dependent) but promotes proliferation and plasma cell differentiation in pre-activated/GC B cells, particularly when combined with CD40 signaling that synergistically induces c-MYC and p-S6. In T cells, IL-21R signaling cell-autonomously sustains CD8+ T cell proliferation and cytokine production during chronic infection, supports pathogenic Th17 cell generation via IL-23R maintenance, and suppresses IL-17-producing γδ T cells. IL-21R expression is transcriptionally regulated by SP1 binding to its promoter (enhanced in rheumatoid arthritis B cells), post-transcriptionally suppressed by miR-30a targeting its 3'UTR, and at the mRNA level is down-regulated by IFN-α/β signaling.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"IL-21R is a class I cytokine receptor that couples IL-21 binding to JAK/STAT signaling to control B-cell and T-cell fate decisions across humoral immunity, anti-viral responses, and autoimmunity [#2, #3, #8]. Its extracellular domain carries a C-mannose modification at the first tryptophan of the WSXWS motif, where a sugar chain bridges the two fibronectin type III domains to convert the receptor from a V-shaped to an A-frame architecture; this bridge forms independently of ligand and is required for export of IL-21R and the common γ-chain to the plasma membrane, explaining why WSXWS mutations cause primary immunodeficiency [#0, #1]. Ligand engagement triggers JAK1/JAK3 autophosphorylation and tyrosine phosphorylation of STAT1, STAT3, and STAT5, and intact downstream JAK/STAT signaling—not mere surface expression—is required for IL-21 responses, as JAK3-deficient cells remain refractory despite abundant receptor [#2, #13, #18]. The cellular outcome of signaling is strictly context-dependent: in naïve B cells and CLL/follicular lymphoma cells IL-21R drives caspase-dependent, Bim-mediated apoptosis, whereas in pre-activated, class-switched, and germinal-center B cells it promotes proliferation, isotype switching, and antibody-secreting-cell formation, with signal amplitude tuned by PTEN [#2, #13, #19, #20]. In germinal centers, combined IL-21R and CD40 signaling synergistically induces c-MYC and phospho-S6 to drive plasma-cell and memory-precursor differentiation as a distinct positive-selection pathway [#8]. In T cells, cell-autonomous IL-21R signaling sustains CD8+ T-cell proliferation and IFN-γ production during chronic infection and tissue inflammation, supports pathogenic Th17 generation by maintaining IL-23R, drives effector CD4+ differentiation in GVHD, and intrinsically restrains IL-17-producing γδ T cells [#3, #9, #10, #11, #12]. IL-21R abundance is set transcriptionally by SP1 binding to its promoter, post-transcriptionally by miR-30a targeting its 3'UTR, and at the mRNA level by IFN-α/β-mediated down-regulation [#15, #17, #6].\",\n  \"teleology\": [\n    {\n      \"year\": 2004,\n      \"claim\": \"Established that IL-21R responsiveness is dynamically controlled by type I interferon, linking innate cytokine context to the strength of IL-21/STAT3 signaling in NK and T cells.\",\n      \"evidence\": \"RT-PCR, Western blot, and EMSA of STAT phosphorylation and DNA binding after IFN-α/β treatment\",\n      \"pmids\": [\"15178704\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism of IFN-α/β-driven IL-21R mRNA down-regulation not defined\", \"No in vivo confirmation of the regulatory axis\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Showed that IL-21R engages canonical JAK1/JAK3-STAT1/3/5 signaling yet drives apoptosis rather than proliferation in malignant B cells, revealing the context-dependence of receptor output.\",\n      \"evidence\": \"Phosphorylation and caspase-cleavage Western blots and flow cytometry in CD40-stimulated primary CLL B cells\",\n      \"pmids\": [\"16391014\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Does not explain what cellular context switches output from apoptosis to proliferation\", \"Pro-apoptotic vs pro-survival determinants downstream of STATs unresolved\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Identified an IL-21R polymorphism (T-83C) altering IL-21-induced IFN-γ output and IgE suppression, providing the first genotype-function link for receptor variation.\",\n      \"evidence\": \"Ex vivo cytokine assays, Cε promoter reporter, germline mRNA measurement, and genotype correlation\",\n      \"pmids\": [\"17015683\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular mechanism by which the polymorphism alters signaling unknown\", \"Single-cohort genotype correlation\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Demonstrated in vivo that IL-21R is required for IL-21-dependent isotype switching and antibody-secreting-cell differentiation, and that its blockade dampens autoantibody-driven disease.\",\n      \"evidence\": \"IL-21R.Fc fusion blockade in lupus-prone MRL-Fas(lpr) mice with autoantibody and B-cell function readouts\",\n      \"pmids\": [\"17339481\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Pharmacological blockade does not isolate B-cell-intrinsic from extrinsic effects\", \"Downstream transcriptional program not defined\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Extended IL-21R function beyond lymphocytes by showing it controls dendritic-cell CCR7 upregulation and MMP2-dependent migration to lymph nodes during skin inflammation.\",\n      \"evidence\": \"Il21r-/- mice, bone-marrow reconstitution, adoptive transfer, CCR7 flow cytometry, and MMP2 activation assay\",\n      \"pmids\": [\"19075398\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct signaling link between IL-21R and CCR7/MMP2 induction not mapped\", \"Whether DC effect is fully cell-intrinsic not resolved\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Defined a cell-autonomous, context-restricted T-cell role: IL-21R sustains CD8+ T-cell proliferation and cytokine production specifically during chronic, but not acute, viral infection.\",\n      \"evidence\": \"Il21r-/- mice and adoptive transfer during LCMV infection with T-cell phenotype/function readouts\",\n      \"pmids\": [\"19478140\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular basis for chronic-specific dependence unknown\", \"Transcriptional targets sustaining CD8+ persistence not identified\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Established that functional JAK/STAT signaling downstream of IL-21R, not surface expression, determines responsiveness, by showing JAK3-deficient lymphoma cells resist IL-21 apoptosis.\",\n      \"evidence\": \"JAK/STAT and SOCS3 analysis and apoptosis assays in JAK3-defective vs responsive lymphoma lines\",\n      \"pmids\": [\"20193734\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single cell-line comparison\", \"SOCS3 role in setting response threshold not functionally tested\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Showed donor T-cell-intrinsic IL-21R signaling drives effector CD4+ differentiation and GVHD pathology independently of regulatory T cells.\",\n      \"evidence\": \"Allogeneic BMT with Il21r-/- splenocytes, CD25-depletion controls, MLR, cytokine and histopathology readouts\",\n      \"pmids\": [\"20574002\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Transcriptional effector program downstream of IL-21R not defined\", \"Single-model GVHD setting\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Solved the IL-21:IL-21R structure, revealing C-mannosylation at the WSXWS motif and a sugar bridge that converts the receptor into an A-frame architecture.\",\n      \"evidence\": \"X-ray crystallography of the IL-21:IL-21R complex with structural validation\",\n      \"pmids\": [\"22235133\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not test functional requirement of the sugar bridge\", \"Glycosylation enzymology in cells not addressed\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Confirmed cell-autonomous IL-21R signaling in CD8+ T cells drives IFN-γ production required for CVB3 myocarditis, generalizing the chronic-inflammation CD8+ dependence.\",\n      \"evidence\": \"Adoptive transfer of IL-21RKO vs WT CD8+ T cells into CD8KO recipients with disease scoring\",\n      \"pmids\": [\"22465422\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single disease model\", \"Signaling intermediates linking IL-21R to IFN-γ not mapped\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Connected the structural sugar bridge to function and disease by showing it forms ligand-independently and that WSXWS mutations block IL-21R/γc plasma-membrane export, explaining immunodeficiency.\",\n      \"evidence\": \"Crystal structure of unbound IL-21R plus mutagenesis and cell-surface trafficking assays\",\n      \"pmids\": [\"26043171\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Cellular C-mannosyltransferase machinery not identified\", \"Quantitative impact on signaling output not measured\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Identified IL-21R as a driver of pathogenic Th17 cells by maintaining IL-23R expression, linking it to autoimmune neuroinflammation.\",\n      \"evidence\": \"Il21r deletion in 2D2xTH transgenic EAE mice with Th17 and IL-23R flow cytometry and disease scoring\",\n      \"pmids\": [\"26413871\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct mechanism maintaining IL-23R unknown\", \"Single transgenic model\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Revealed an opposing T-cell role: intrinsic IL-21R signaling suppresses IL-17-producing γδ T cells in the respiratory tract, highlighting cell-type-specific outcomes.\",\n      \"evidence\": \"IL-21R KO mice in influenza A infection with γδ/Th17 flow cytometry and BAL cytokines\",\n      \"pmids\": [\"25849970\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism of γδ T-cell suppression unknown\", \"Whether suppression is direct on γδ cells not fully resolved\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Established post-transcriptional control of IL-21R by miR-30a targeting its 3'UTR, with receptor overexpression rescuing Th17 differentiation.\",\n      \"evidence\": \"Dual luciferase 3'UTR reporter, miR-30a overexpression, IL-21R rescue, and EAE model\",\n      \"pmids\": [\"27006279\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Physiological signals controlling miR-30a not defined\", \"In vivo contribution of this axis to receptor levels not quantified\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Extended IL-21R signaling to the myeloid compartment, showing overexpression on myeloma-associated monocytes promotes JAK-dependent osteoclast differentiation.\",\n      \"evidence\": \"Profiling of sorted BM CD14+ monocytes, ex vivo osteoclastogenesis, and Janex-1 JAK inhibition\",\n      \"pmids\": [\"28057743\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"STAT effectors in osteoclast program not defined\", \"Single patient-derived system\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Identified SP1 as a direct transcriptional activator of IL21R whose increased promoter binding amplifies pSTAT3 signaling and plasmablast differentiation in rheumatoid arthritis B cells.\",\n      \"evidence\": \"ChIP-qPCR for SP1 at the IL21R promoter with pSTAT3, plasmablast, and IL-6 readouts\",\n      \"pmids\": [\"30233580\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Upstream signals driving SP1 recruitment unknown\", \"Correlative link between SP1 binding and disease activity\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Linked chromatin regulation to IL-21R expression, showing Cbx3/HP1γ loss opens the Il21r locus and that IL-21R is required for enhanced anti-tumor CD8+ T-cell persistence.\",\n      \"evidence\": \"Cbx3/HP1γ KO CD8+ T cells, chromatin/ChIP-seq, and multiple in vivo tumor models\",\n      \"pmids\": [\"34721405\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct epigenetic mechanism at the locus not fully resolved\", \"Relative contribution of IL-21R vs LEF-1 not separated\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Defined IL-21R + CD40 as a distinct germinal-center positive-selection pathway that synergistically induces c-MYC and phospho-S6 to drive plasma-cell and memory-precursor differentiation.\",\n      \"evidence\": \"Bulk and single-cell RNA-seq with flow cytometry of GC B cells in vitro and in vivo and signal-combination perturbations\",\n      \"pmids\": [\"36800413\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular integration of IL-21R and CD40 signals not fully mapped\", \"How this pathway interfaces with BCR-based selection unresolved\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Nominated GTF2I as an additional transcriptional regulator of IL21R based on binding at the upstream/5'UTR region in B cells.\",\n      \"evidence\": \"ChIP-seq in CD19+ B cells with motif analysis and ENCODE comparison\",\n      \"pmids\": [\"37713154\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Binding identified without functional validation of transcriptional regulation\", \"No perturbation of GTF2I to confirm effect on IL-21R levels\", \"Single dataset\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Dissected the apoptosis-versus-proliferation switch genetically, showing B-cell-intrinsic IL-21R drives Bim-dependent apoptosis in naïve B cells but proliferation in class-switched B cells and is required for the pre-GC-to-GC transition.\",\n      \"evidence\": \"Conditional Il21r KO mice with ex vivo culture, immunization, and apoptosis assays (preprint)\",\n      \"pmids\": [\"bio_10.1101_2024.07.13.600808\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Preprint, not yet peer-reviewed\", \"Molecular determinant gating apoptosis vs proliferation not identified\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Established PTEN as a negative regulator of IL-21R signaling amplitude in germinal-center B cells, selectively biasing toward plasma-cell differentiation when relieved.\",\n      \"evidence\": \"Inducible PTEN deletion in established GC B cells with competitive transfer and flow cytometry\",\n      \"pmids\": [\"40795247\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Biochemical node where PTEN restrains IL-21R signaling not pinpointed\", \"Single-lab GC system\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Functionally assigned the intracellular IL-21R domain to STAT3-mediated activation by using a TGF-βRII/IL-21R chimera to convert suppressive signals into NK-cell activation.\",\n      \"evidence\": \"Domain-swap chimeric receptor with cytotoxicity assays, xenograft models, and JAK-STAT3 readouts\",\n      \"pmids\": [\"39884449\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Engineered receptor context may not reflect native signaling\", \"STAT3-specific vs broader STAT contributions not separated\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How a single IL-21R/JAK-STAT signal is mechanistically converted into opposing apoptotic versus proliferative outcomes across cell states remains the central unresolved question.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No defined molecular switch linking signal amplitude/context to fate decision\", \"Differential STAT target gene programs across cell types not catalogued\", \"Quantitative role of negative regulators (PTEN, SOCS3, miRNA) in setting thresholds not integrated\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [2, 13, 18]},\n      {\"term_id\": \"GO:0004896\", \"supporting_discovery_ids\": [2]},\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [2]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 1, 2]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [2, 13, 18]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [3, 8, 9]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [2, 20]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"IL21\", \"JAK1\", \"JAK3\", \"STAT3\", \"STAT1\", \"STAT5\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"faith_supported":7,"faith_total":7,"faith_pct":100.0}}