{"gene":"IL34","run_date":"2026-06-10T01:55:23","timeline":{"discoveries":[{"year":2012,"finding":"IL-34 is an alternative ligand for CSF-1R (Fms) expressed by keratinocytes and neurons, and is selectively required for the development of Langerhans cells in skin epidermis and microglia in the CNS, as demonstrated by IL-34-deficient (Il34LacZ/LacZ) reporter mice that specifically lacked LCs and microglia.","method":"IL-34 knockout/reporter mouse model (Il34LacZ/LacZ); in vivo phenotypic analysis of immune cell populations","journal":"Nature immunology","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean genetic knockout with defined cellular phenotype, replicated across multiple tissues and independently confirmed by concurrent studies","pmids":["22729249"],"is_preprint":false},{"year":2010,"finding":"IL-34 signals through CSF-1R (Fms) to stimulate macrophage proliferation, CSF-1R tyrosine phosphorylation, and downstream signaling, and can rescue bone, osteoclast, tissue macrophage, and fertility defects of CSF-1-deficient (Csf1op/op) mice when transgenically expressed, demonstrating functional overlap with CSF-1 through the same receptor.","method":"In vitro macrophage proliferation assays; CSF-1R tyrosine phosphorylation assays; transgenic rescue of Csf1op/op mice; whole-mount IL34 in situ hybridization; QRT-PCR","journal":"Journal of leukocyte biology","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — in vitro signaling assays plus in vivo transgenic rescue, multiple orthogonal methods","pmids":["20504948"],"is_preprint":false},{"year":2010,"finding":"IL-34 and M-CSF share CSF-1R (Fms) as receptor but differ in biological activity and signaling kinetics: IL-34 induces stronger but more transient tyrosine phosphorylation of Fms and downstream molecules, rapidly downregulates Fms, and differs from M-CSF in chemokine induction (MCP-1, eotaxin-2), morphological changes, and cell migration. Different anti-Fms antibodies block binding of IL-34 vs. M-CSF differentially, indicating they bind distinct receptor domains.","method":"Cell-based signaling assays (tyrosine phosphorylation); anti-receptor monoclonal antibody competition binding assays; chemokine production assays; migration assays","journal":"Cell death and differentiation","confidence":"High","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal functional assays in a single study demonstrating mechanistic differences between the two ligands","pmids":["20489731"],"is_preprint":false},{"year":2012,"finding":"Crystal structure of dimeric IL-34 reveals a helical cytokine fold homologous to CSF-1. The IL-34:CSF-1R complex architecture is similar to CSF-1:CSF-1R but with unique conformational adaptations in receptor domain geometry; hydrophobic interactions at the IL-34:CSF-1R interface dominate biological activity. IL-34 forms a more thermodynamically stable complex with CSF-1R than CSF-1 does, and a neutralizing Fab fragment reveals the mechanism of antibody-mediated neutralization.","method":"X-ray crystallography of IL-34 alone and in complex with CSF-1R D1-D3; functional mutagenesis of the interface; Fab-bound crystal structure","journal":"Structure (London, England : 1993)","confidence":"High","confidence_rationale":"Tier 1 / Strong — two independent crystal structures (Ma et al. and Liu et al.) with functional mutagenesis; replicated across two labs","pmids":["22483114","22579672"],"is_preprint":false},{"year":2012,"finding":"Mouse IL-34 crystal structure shows it contains two additional helices beyond the four conserved in helical hematopoietic cytokines; it recruits two CSF-1R copies on the sides of the helical bundles. The flexible linker between CSF-1R D2 and D3 allows these domains to clamp IL-34 and CSF-1 at different angles, explaining degenerate recognition. Hydrophobic interactions (not salt bridges) dominate IL-34 biological activity, and relative thermodynamic independence of the two IL-34:CSF-1R sites (vs. negative cooperativity for CSF-1) accounts for differentiated signaling.","method":"X-ray crystallography of mouse IL-34 alone and in complex with mouse CSF-1R D1-D3; interface mutagenesis; thermodynamic analysis","journal":"Biochimica et biophysica acta","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structure with mutagenesis, consistent with independent structure from Ma et al. 2012","pmids":["22579672"],"is_preprint":false},{"year":2013,"finding":"Human IL-34 bound to CSF-1R forms an extracellular assembly with striking structural similarities to the CSF-1:CSF-1R complex, including homotypic receptor-receptor interactions. The C-terminal region of IL-34 is heavily glycosylated and can be proteolytically cleaved from the IL-34:CSF-1R complex, providing a mechanism for functional non-redundancy between IL-34 and CSF-1.","method":"Small-angle X-ray scattering (SAXS); negative-stain electron microscopy; systematic glycan modeling","journal":"Structure (London, England : 1993)","confidence":"High","confidence_rationale":"Tier 1 / Moderate — hybrid structural approach (SAXS + EM) with systematic glycan analysis, single study with multiple orthogonal methods","pmids":["23478061"],"is_preprint":false},{"year":2012,"finding":"IL-34 exhibits broader regional brain expression than CSF-1 (mostly without overlap), with maximal expression during early postnatal development. CSF-1R-deficient mice (but not ligand-deficient mice) show defects in neural progenitor cell maintenance including increased proliferation and apoptosis of neocortical progenitors. Addition of IL-34 or CSF-1 to microglia-free CSF-1R-expressing dorsal forebrain clonal cultures suppressed progenitor self-renewal and enhanced neuronal differentiation, indicating a direct role for IL-34/CSF-1R signaling in corticogenesis independent of microglia.","method":"CSF-1R knockout mouse phenotyping; Nestin-Cre conditional CSF-1R ablation; microglia-free clonal culture assays with IL-34 and CSF-1 addition","journal":"Developmental biology","confidence":"High","confidence_rationale":"Tier 2 / Moderate — conditional knockout plus in vitro functional assays with defined cellular phenotypes","pmids":["22542597"],"is_preprint":false},{"year":2015,"finding":"IL-34 is expressed by tubular epithelial cells (TECs) in the kidney after ischemia/reperfusion injury and promotes macrophage-mediated tubular cell destruction via two distinct mechanisms: enhanced intrarenal macrophage proliferation and elevated bone marrow myeloid cell proliferation that increases circulating monocytes recruited by chemokines into the kidney. A second IL-34 receptor, protein-tyrosine phosphatase ζ (PTP-ζ/PTPRZ1), is upregulated alongside c-FMS in the injured kidney. CSF-1 expression did not compensate for IL-34 deficiency.","method":"IL-34-deficient mouse model of renal ischemia/reperfusion injury; flow cytometry; bone marrow proliferation analysis; chemokine measurements; immunohistochemistry in human transplant kidneys","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean genetic knockout with mechanistic dissection of two distinct pathways, validated in human samples","pmids":["26121749"],"is_preprint":false},{"year":2015,"finding":"IL-34 is expressed by CD8+CD45RClo Tregs and human FOXP3+CD45RCloCD8+ and CD4+ Tregs, contributes to their suppressive function, and is required for transplant tolerance induction in a rat cardiac allograft model. IL-34-primed macrophages potentiate the immune-suppressive capacity of Tregs, establishing an IL-34→macrophage→Treg amplification circuit.","method":"Rat cardiac allograft tolerance model; IL-34 protein treatment; Treg functional assays; human macrophage-Treg co-culture expansion","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 2 / Moderate — in vivo transplant model with mechanistic pathway dissection and human validation","pmids":["26389674"],"is_preprint":false},{"year":2015,"finding":"IL-34 is required for keratinocyte-derived LC renewal in steady-state adult skin, whereas during UV-induced inflammation, LC regeneration depends on neutrophil-derived CSF1. These ligands play nonredundant roles in LC maintenance depending on tissue context.","method":"Inducible IL-34 knockout mice; Il34LacZ reporter mice; in vivo skin damage model; cell-type-specific analysis","journal":"European journal of immunology","confidence":"High","confidence_rationale":"Tier 2 / Moderate — inducible conditional knockout with defined cellular phenotype under steady-state and inflammatory conditions","pmids":["26634935"],"is_preprint":false},{"year":2015,"finding":"IL-34 and M-CSF form a novel heteromeric cytokine; BIAcore experiments demonstrated M-CSF binds directly to IL-34, and molecular docking and proximity ligation assay confirmed heterodimer formation. The heteromeric M-CSF/IL-34 cytokine causes higher phosphorylation of M-CSFR tyrosine residues at low concentrations and additive effects on cell proliferation/viability. Co-expression of M-CSFR and its ligands differentially regulates M-CSFR trafficking into the cell.","method":"BIAcore binding assay; molecular docking; proximity ligation assay; M-CSFR phosphorylation assay; receptor trafficking analysis","journal":"Cytokine","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct binding demonstrated by SPR (BIAcore) and confirmed by PLA, functional receptor signaling measured, single lab","pmids":["26095744"],"is_preprint":false},{"year":2013,"finding":"IL-34 induces differentiation of human monocytes into CD14high CD163high immunosuppressive M2-like macrophages via the M-CSF receptor, independent of endogenous M-CSF consumption. This effect is potentiated by IL-6 and inhibited by IFNγ and GM-CSF. IFNγ can also switch established IL-34-macrophages into immunostimulatory macrophages.","method":"Human primary monocyte differentiation assays; flow cytometry; LPS stimulation; T cell co-culture suppression assays; cytokine ELISA; CSF-1R blocking experiments","journal":"PloS one","confidence":"High","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal functional assays with pharmacological and antibody-based receptor blocking","pmids":["23409120"],"is_preprint":false},{"year":2018,"finding":"In zebrafish, Il34-Csf1ra signaling is required for microglial precursor attraction to proximal brain regions prior to neuronal apoptosis. In il34- and csf1ra-deficient larvae, embryonic macrophages fail to migrate to the anterior head and colonize the CNS, while peripheral tissue colonization is unaffected. Activation of the Il34-Csf1ra pathway alone is sufficient to attract embryonic macrophages to the CNS independent of neuronal apoptosis.","method":"Zebrafish il34 and csf1ra mutants/morpholinos; live imaging of macrophage migration; rescue/overexpression experiments","journal":"Developmental cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic loss-of-function in zebrafish with live imaging, rescue by pathway activation, replicated by concurrent zebrafish study","pmids":["30205037"],"is_preprint":false},{"year":2019,"finding":"In zebrafish, il34 loss-of-function causes reduced microglia numbers and impairs yolk sac macrophage (YSM) distribution to the brain and other target organs, while csf1 loss does not reduce microglia numbers at early stages (though overexpression increases them). This establishes il34 as the primary driver of early brain seeding by YSMs.","method":"CRISPR/Cas9 in vivo reverse genetic screen in zebrafish; automated microglia quantification (SpotNGlia); Neutral Red vital staining","journal":"Disease models & mechanisms","confidence":"High","confidence_rationale":"Tier 2 / Strong — CRISPR-based loss-of-function with automated quantification, replicated by concurrent zebrafish study","pmids":["30765415"],"is_preprint":false},{"year":2019,"finding":"CSF1 and IL-34 play distinct roles in microglia maintenance: peripheral antibody-mediated blockade of IL-34 depletes microglia preferentially in gray matter brain regions, while CSF1 blockade depletes white matter microglia. These regional patterns correspond to the differential expression of each ligand. CSF1 is required to establish microglia in the developing embryo, while both ligands are required beginning in early postnatal development.","method":"Function-blocking antibody administration in adult mice; microglia depletion quantification across brain regions; developmental time-course analysis","journal":"Frontiers in immunology","confidence":"High","confidence_rationale":"Tier 2 / Moderate — selective antibody blockade in vivo with regional brain analysis, multiple time points","pmids":["31616414"],"is_preprint":false},{"year":2019,"finding":"IL-34 promotes lupus nephritis in MRL-Fas mice via two mechanisms: intrarenal macrophage proliferation and bone marrow myeloid cell proliferation that increases circulating monocytes recruited into the kidney. PTPRZ1 (PTP-ζ), a second IL-34 receptor, is expressed by macrophages, B cells, and T cells. IL-34 deficiency also suppresses circulating autoantibodies and glomerular antibody deposits, associated with fewer activated/proliferating intrarenal and splenic B cells.","method":"IL-34 knockout in MRL-Fas lupus mice; flow cytometry; immunohistochemistry; bone marrow and intrarenal macrophage proliferation analysis; autoantibody ELISA","journal":"Journal of the American Society of Nephrology : JASN","confidence":"High","confidence_rationale":"Tier 2 / Moderate — clean genetic knockout in disease model with mechanistic pathway dissection of two independent mechanisms","pmids":["30622154"],"is_preprint":false},{"year":2023,"finding":"IL-34 binds directly to TREM2 (triggering receptor expressed on myeloid cells 2) as a novel receptor, independent of CSF-1R and PTP-ζ. IL-34-TREM2 binding rapidly phosphorylates RASAL3 (Ras protein activator-like 3) and inactivates ERK1/2 signaling, preventing AML cell proliferation and stimulating differentiation. TREM2-deficient AML cells are resistant to IL-34 treatment.","method":"Direct binding assay (IL-34 to TREM2); TREM2 knockout AML cells; phosphoproteomic/signaling analysis (RASAL3 phosphorylation, ERK1/2 inactivation); preclinical AML mouse models; IL-34-deficient mice showing accelerated AML","journal":"Blood","confidence":"High","confidence_rationale":"Tier 1-2 / Moderate — direct binding demonstrated, receptor knockout confirms specificity, signaling mechanism identified, multiple preclinical models","pmids":["37001042"],"is_preprint":false},{"year":2013,"finding":"IL-34 produced by follicular dendritic cells (FDCs), but not CSF-1 from the same cells, is selectively responsible for the differentiation of a new CD11b+ monocytic cell type (FDMCs) with B cell-stimulating activity, as demonstrated by neutralizing antibodies and RNAi. This differentiation depends strictly on CSF-1R, establishing a CSF-1R-mediated differentiation pathway intrinsically specific to IL-34.","method":"Neutralizing antibody experiments; RNAi knockdown; CSF-1R dependence assays; B cell co-culture proliferation assays","journal":"Journal of leukocyte biology","confidence":"High","confidence_rationale":"Tier 2 / Moderate — two orthogonal methods (neutralizing antibody + RNAi) demonstrating IL-34 specificity, clear CSF-1R dependence established","pmids":["24052571"],"is_preprint":false},{"year":2018,"finding":"IL-34 cell-surface localization on follicular dendritic cells (FL-Y) requires the molecular chaperone GRP78 (78-kDa glucose-regulated protein): GRP78 associates with IL-34 in the plasma membrane fraction (identified by mass spectrometry and pulldown), and GRP78-heterozygous FL-Y cells show reduced surface IL-34 and impaired FDMC differentiation. FDMC differentiation requires a membrane-anchored form of IL-34 via direct cell-cell contact, not secreted IL-34.","method":"CRISPR/Cas9 IL-34 knockout; Transwell culture experiments; mass spectrometry; pulldown assay; flow cytometry with anti-IL-34 antibody; GRP78-heterozygous cells","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Moderate — CRISPR knockout, mass spectrometry identification of interactor, pulldown confirmation, and functional consequence in differentiation assay","pmids":["30573681"],"is_preprint":false},{"year":2012,"finding":"Vitamin D analog (2MD) induces IL-34 expression in vascular endothelial cells of spleen and bone through a vitamin D receptor (VDR)-mediated mechanism. IL-34 in splenic vascular endothelium maintains a reservoir of osteoclast precursors (OCPs) in the spleen of CSF-1-deficient (Csf1op/op) mice. Splenectomy or siRNA-mediated knockdown of IL-34 suppressed vitamin D-induced osteoclastogenesis.","method":"Vitamin D analog injection in Csf1op/op mice; splenectomy; siRNA knockdown of IL-34; osteoclast precursor analysis; VDR-mediated transcription assay","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Moderate — genetic and pharmacological loss-of-function with two orthogonal approaches (splenectomy + siRNA) and VDR mechanism established","pmids":["22670054"],"is_preprint":false},{"year":2013,"finding":"IL-34 expression in gingival fibroblasts is enhanced by TNF-α and IL-1β through NF-κB transcription factor and JNK activation. IL-34 can substitute for M-CSF in RANKL-induced osteoclastogenesis of bone marrow macrophages.","method":"Real-time PCR of gingival fibroblasts after cytokine stimulation; pharmacological inhibitors of NF-κB and JNK; TRAP staining of osteoclasts","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — pathway inhibitors used to establish signaling mechanism, functional osteoclastogenesis assay","pmids":["24339952"],"is_preprint":false},{"year":2018,"finding":"CSF-1R engagement by IL-34 (vs. CSF-1) leads to AKT and caspase activation, autophagy induction through AMPK and ULK1 expression and activation, during human monocyte differentiation. IL-34-differentiated macrophages show striking increases in IL-10 (M1) and CCL17 (M2) secretion compared to CSF-1-differentiated macrophages, and differentially polarize naïve T cells toward Th1.","method":"Human primary monocyte differentiation assays; phosphorylation analysis of AKT, AMPK, ULK1; autophagy measurement; cytokine secretome ELISA; T cell polarization assay","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple signaling pathway analyses and functional secretome comparisons, single lab","pmids":["29321503"],"is_preprint":false},{"year":2017,"finding":"IL-34 interaction with CSF-1R on rheumatoid arthritis fibroblast-like synoviocytes (FLS) promotes dramatic IL-6 production via JNK/P38/NF-κB signaling, which in turn upregulates Th17 cell numbers. IL-6R antagonist attenuates Th17 production mediated by IL-34-stimulated FLS.","method":"CSF-1R expression analysis on FLS; IL-6 production assays; JNK/P38/NF-κB pathway inhibitor experiments; Th17 cell quantification; IL-6R antagonist treatment","journal":"Mediators of inflammation","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — pathway inhibitors establishing signaling mechanism, functional Th17 consequence demonstrated with pharmacological intervention","pmids":["28659662"],"is_preprint":false},{"year":2018,"finding":"IL-34 regulates IL-6 and IL-8 production in human lung fibroblasts via MAPK (p38), PI3K-Akt, JAK, and NF-κB signaling pathways, as demonstrated by reversal with specific pathway inhibitors and western-blot confirmation of phosphorylation events.","method":"Primary lung fibroblast assays; pathway-specific pharmacological inhibitors (JAK, NF-κB, Akt, p38); western blotting for phosphorylation; cytokine ELISA","journal":"International immunopharmacology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple pathway inhibitors and phosphorylation validation, single lab","pmids":["29857241"],"is_preprint":false},{"year":2018,"finding":"IL-34 promotes Kupffer cell M2 polarization in rat liver transplantation via activation of the PI3K/Akt pathway, and this M2 KC polarization is required for IL-34-mediated inhibition of acute rejection (demonstrated by KC depletion and adoptive transfer experiments).","method":"Adeno-associated virus-expressing IL-34 in rat liver transplant model; KC depletion (clodronate); adoptive transfer of KCs; PI3K/Akt pathway analysis in vitro; in vivo/in vitro M1-to-M2 polarization assays","journal":"Transplantation","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo adoptive transfer with depletion establishing KC-dependence; PI3K/Akt mechanism in vitro","pmids":["29570162"],"is_preprint":false},{"year":2016,"finding":"miR-28-5p directly targets IL-34 mRNA (identified by gene expression profiles and bioinformatics, confirmed functionally), and miR-28-5p deficiency promotes HCC tumor growth and metastasis via IL-34-mediated tumor-associated macrophage (TAM) infiltration. TAMs induced by IL-34 inhibit miR-28-5p expression in HCC cells via TGF-β1, forming a positive feedback loop.","method":"miRNA sequencing; bioinformatics target identification; nude mouse tumor models; gene expression profiling; TAM infiltration analysis; TGF-β1 mechanistic experiments","journal":"Hepatology (Baltimore, Md.)","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo tumor models with IL-34 as direct miR-28-5p target, feedback loop established mechanistically; single lab","pmids":["26754294"],"is_preprint":false},{"year":2019,"finding":"In satellite cells, miR-31 posttranscriptionally suppresses IL-34 mRNA. IL-34 protein activates JAK-STAT3 signaling required for myogenic progression. miR-31 knockout causes impaired myoblast expansion and enhanced myogenic commitment; IL-34 inhibition rescues the regenerative deficiency of miR-31 knockout mice, placing IL-34/JAK-STAT3 downstream of miR-31 in muscle regeneration.","method":"miR-31 knockout mice; muscle regeneration assays; IL-34 inhibition rescue experiment; JAK-STAT3 signaling analysis","journal":"Cell death and differentiation","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic epistasis via rescue experiment in knockout mice, signaling pathway identified","pmids":["31332295"],"is_preprint":false},{"year":2017,"finding":"1α,25-dihydroxyvitamin D3 (vitamin D3) strongly induces IL-34 expression in SH-SY5Y neural cells via the vitamin D receptor (VDR). A core IL-34 gene promoter and a VDR binding site (CGCCCT) required for this induction were identified by reporter assays.","method":"Dose- and time-response gene expression analysis; VDR knockdown/inhibition; promoter reporter assay; VDR binding site mutagenesis","journal":"Innate immunity","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — promoter analysis with mutagenesis and VDR knockdown establishing mechanistic transcriptional regulation","pmids":["28816551"],"is_preprint":false},{"year":2017,"finding":"mHTTx1 aggregates in post-mitotic dopaminergic neurons induce IL-34 production selectively, mediated by IKKβ. IKKβ knockdown or inhibition prevents mHTTx1 aggregation and subsequent IL-34 production. Elevated neuronal IL-34 exacerbates mHTTx1-induced degeneration of striatal neurons via non-cell-autonomous microglial expansion, and an IL-34 receptor inhibitor reduces microglial numbers and ameliorates neurodegeneration in brain slice models.","method":"Human embryonic stem cell-derived dopaminergic neurons; IKKβ knockdown/inhibition; brain slice model with intact neuron-microglial networks; IL-34 receptor inhibitor","journal":"Human molecular genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic knockdown identifying upstream regulator (IKKβ), brain slice model showing non-cell-autonomous mechanism, pharmacological rescue","pmids":["28973132"],"is_preprint":false},{"year":2024,"finding":"An autophagy-dependent microglia population in aging mouse cortex is promoted by IL-34 (not CSF1). Deletion of the core autophagy gene Ulk1 in microglia reduces this population. IL-34-mediated microglial expansion is neuroprotective when aging mice are exposed to autoimmune neuroinflammation, with loss of autophagy-dependent microglia leading to neural/glial cell death and increased mortality.","method":"Ulk1 conditional knockout in microglia; IL-34-mediated microglial expansion assays; autoimmune neuroinflammation model (EAE); ERK1/2, Akt, AMPK phosphorylation analysis; transcriptome analysis","journal":"Nature communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — conditional knockout plus IL-34-specific expansion demonstrating neuroprotective function, single lab","pmids":["38195627"],"is_preprint":false},{"year":2018,"finding":"IL-34 promotes foam cell formation in bone marrow-derived macrophages by increasing CD36 expression via the p38 MAPK signaling pathway, enhancing oxLDL uptake and intracellular cholesterol accumulation without affecting cholesterol efflux.","method":"Bone marrow-derived macrophage assays; oxLDL uptake measurement; cholesterol content assay; CD36 expression analysis; p38 MAPK pathway inhibitors","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — pharmacological inhibitor establishing p38 MAPK mechanism, CD36 upregulation linked to functional foam cell formation","pmids":["30478377"],"is_preprint":false},{"year":2015,"finding":"IL-34 suppresses Candida albicans-induced TNFα production by M1 macrophages by downregulating expression of key pattern recognition receptors TLR2 and Dectin-1, providing a molecular mechanism for skin macrophage tolerance to commensal fungi.","method":"M1 macrophage stimulation with heat-killed Candida; TNFα measurement; flow cytometry/expression analysis of TLR2 and Dectin-1 after IL-34 treatment","journal":"Journal of immunology research","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — clear mechanistic link between IL-34 and PRR downregulation, but single lab with limited methods","pmids":["26146640"],"is_preprint":false},{"year":2021,"finding":"Low-dose IL-34 promotes osteogenesis of human bone marrow stromal cells (hBMSCs) via activation of PI3K/AKT and ERK signaling pathways, as demonstrated by reversal with specific AKT and ERK inhibitors. Low-dose IL-34 has no effect on osteoclastogenesis of mouse bone marrow macrophages in vitro or on osteoporosis in OVX rats in vivo.","method":"In vitro hBMSC osteogenic differentiation assays; ALP and ARS staining; PI3K/AKT and ERK inhibitors; western blotting; rat tibial osteotomy model; OVX model","journal":"Stem cell research & therapy","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — pathway inhibitors confirm signaling mechanism in vitro, validated in vivo fracture healing model","pmids":["33947456"],"is_preprint":false},{"year":2016,"finding":"TGF-β1 and BMP-2 inhibit IL-34 expression in rheumatoid arthritis synovial fibroblasts through ALK5 and ALK1 receptor pathways, respectively, and antagonize TNF-α-induced IL-34 gene expression. These signaling routes are established as upstream regulators of IL-34 expression.","method":"Pharmacological inhibition of ALK1 and ALK5 in RA synovial fibroblasts and murine mesenchymal stem cells; dose- and time-response real-time qPCR; ELISA for IL-34, TGF-β1, BMP-2 in synovial fluids","journal":"The American journal of pathology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — pharmacological inhibitors of specific receptors establish transcriptional regulatory mechanism, validated in two cell types","pmids":["27865758"],"is_preprint":false},{"year":2024,"finding":"SAMHD1 dysfunction in neuronal SH-SY5Y cells induces IL-34 expression via the canonical NF-κB pathway: SAMHD1 knockdown upregulates NF-κB p65 expression, phosphorylates IKKα/β and IκBα, and promotes nuclear translocation of NF-κB p65, leading to increased IL-34 transcription.","method":"SAMHD1 siRNA knockdown in SH-SY5Y cells; qRT-PCR and western blot for IL-34 and NF-κB components; IKK and IκBα phosphorylation analysis; NF-κB nuclear translocation assay; transcriptional activity assay","journal":"Molecular immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic knockdown with multiple signaling readouts establishing NF-κB-dependent transcriptional mechanism","pmids":["38367301"],"is_preprint":false},{"year":2019,"finding":"Schwann cells in ALS peripheral nerves express CSF1 and IL-34 and closely interact with CSF-1R-expressing endoneurial monocyte/macrophages, suggesting a paracrine mechanism of myeloid cell expansion. Pharmacological inhibition of CSF-1R (with masitinib) reduces Schwann cell reactivity and immune cell infiltration in peripheral nerves of SOD1G93A rats.","method":"Immunohistochemistry of ALS patient and SOD1G93A rat sciatic nerves; CSF-1R inhibitor (masitinib) treatment; quantification of SC phenotypes and macrophage numbers","journal":"Glia","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — IHC-based pathway identification with pharmacological CSF-1R inhibition rescue; paracrine mechanism inferred but not directly proven","pmids":["31859421"],"is_preprint":false},{"year":2019,"finding":"In Huntington's disease, RUNX1 mediates further upregulation of CSF-1R and its ligand IL-34 following rebound ERK activation after BRAF inhibition. The autocrine IL-34/CSF-1R signaling axis in melanoma cells promotes 3D growth and invasiveness; CSF-1R inhibition or knockdown reduces these phenotypes, and coinhibition of CSF-1R and BRAF shows synergistic efficacy in vivo.","method":"RUNX1-mediated CSF-1R and IL-34 upregulation analysis; RNAi and pharmacological CSF-1R inhibition; 3D growth and invasion assays; in vivo combinatorial treatment","journal":"JCI insight","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — RNAi and pharmacological inhibition with in vivo validation establishing autocrine signaling mechanism","pmids":["30046005"],"is_preprint":false},{"year":2021,"finding":"In esophageal squamous cell carcinoma, 5-fluorouracil/cisplatin treatment preferentially increases IL-34 mRNA expression on tumor cells, and IL-34 expression drives CD163+ TAM polarization via CSF-1R. Human monocytes co-cultured with chemotherapy-treated ESCC cells increase CD163 expression, which is attenuated by CSF-1R inhibitors.","method":"In vitro ESCC cell line chemotherapy treatment; mRNA expression analysis; monocyte co-culture assays; CSF-1R inhibitor experiments; immunohistochemistry of patient specimens","journal":"Molecular cancer research : MCR","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — mechanistic co-culture system with pharmacological inhibitor, validated in patient samples","pmids":["33674443"],"is_preprint":false},{"year":2013,"finding":"Transcriptional profiling of human CD14+ monocytes differentiated with IL-34 vs. CSF-1 through CSF-1R revealed ~75% similarity in gene expression, but notable differences including differential repression of CCR2 mRNA and protein by IL-34. This CCR2 differential was abolished by CSF-1R inhibitor GW2580, confirming CSF-1R mediation.","method":"Agilent whole-genome microarray; FACS for CCR2 protein; CSF-1R inhibitor (GW2580) experiments","journal":"Cytokine","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genome-wide transcriptional comparison with CSF-1R inhibitor confirmation, identifying differential downstream outcomes","pmids":["23684409"],"is_preprint":false},{"year":2018,"finding":"IL-34 expressed on the surface of follicular dendritic cells (FL-Y) requires direct cell-cell contact with precursor cells for FDMC differentiation (membrane-anchored form, not secreted), as demonstrated by Transwell culture showing abrogation of differentiation when cells were separated.","method":"Transwell culture experiments; CRISPR/Cas9 IL-34 knockout confirmation; flow cytometric surface IL-34 detection","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Transwell and CRISPR experiments establishing juxtacrine mechanism of IL-34 surface signaling","pmids":["30573681"],"is_preprint":false},{"year":2019,"finding":"In lupus nephritis (MRL-Fas) mice, PTPRZ1 (PTP-ζ) is expressed on macrophages, B cells, and T cells in addition to its known epithelial expression, identifying it as a functional IL-34 receptor on immune cells mediating autoimmune pathology.","method":"Flow cytometry and immunohistochemistry for PTPRZ1 on sorted immune cell populations from MRL-Fas mice; validated in human lupus nephritis tissue","journal":"Journal of the American Society of Nephrology : JASN","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — direct localization of receptor on immune cells confirmed across species, but functional link to PTPRZ1-specific signaling not directly separated from CSF-1R signaling","pmids":["30622154"],"is_preprint":false},{"year":2019,"finding":"In osteolytic multiple myeloma, tumor cell-derived IL-34 promotes osteoclast formation from mouse BM cells and human CD14+ monocytes via CSF-1R; siRNA-mediated IL-34 knockdown in MM cells impaired osteoclast formation in vitro and attenuated osteolytic disease in vivo. A neutralizing anti-IL-34 antibody blocked osteoclast formation from human monocytes.","method":"IL-34 siRNA knockdown in MM cells; in vitro osteoclast formation assays; in vivo MM osteolysis model; anti-IL-34 neutralizing antibody","journal":"Blood advances","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — siRNA knockdown with in vivo validation and neutralizing antibody confirmation","pmids":["30782613"],"is_preprint":false},{"year":2022,"finding":"In the absence of IL-34 (Il34-/- rats/mice), CD4+ Tregs fail to protect immunodeficient rats from wasting disease induced by transfer of pathogenic cells, demonstrating that IL-34 is required for CD4+ Treg suppressive function. IL-34 deficiency leads to unstable immune phenotype with multiple autoantibodies and exacerbated colitis.","method":"Il34-/- rat and mouse generation; DSS- and TNBS-induced colitis; pathogenic cell transfer model; Treg adoptive transfer in Il2rg-/- rats; GVHD and skin allograft models in humanized NSG mice","journal":"Clinical and translational medicine","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple in vivo models establishing Treg-specific requirement for IL-34, single lab across several model systems","pmids":["36030499"],"is_preprint":false},{"year":2018,"finding":"IL-34 expression in SH-SY5Y neural cells is reduced by TNF-α-induced NF-κB activation in hepatic stellate cells; schistosome soluble egg antigen (SEA) inhibits TNF-α-induced IL-34 expression by decreasing phosphorylation and degradation of IκBα, thus preventing NF-κB canonical activation and downstream IL-34 transcription.","method":"Reporter assays; qPCR; western blot for IκBα phosphorylation and degradation; NF-κB activation assays in hepatic stellate cells","journal":"Parasitology research","confidence":"Low","confidence_rationale":"Tier 3 / Weak — NF-κB mechanism established in hepatic stellate cells for IL-34 regulation, single lab, single cell type, no direct IL-34 receptor-pathway connection","pmids":["30499009"],"is_preprint":false},{"year":2019,"finding":"In zebrafish, ectopically expressed IL-34 in hepatocytes attracts macrophages (but not neutrophils) to the liver in vivo via direct migration, as demonstrated by live imaging. IL-34-mediated macrophage migration occurs through syndecan-1 or focal adhesion kinase (FAK) and ERK1/2 pathways (referenced from prior studies).","method":"Zebrafish transgenic ectopic IL-34 expression in hepatocytes/epidermal cells; live imaging of macrophage and neutrophil migration","journal":"Zebrafish","confidence":"Low","confidence_rationale":"Tier 3 / Weak — live imaging demonstrates IL-34-directed macrophage migration in vivo but signaling pathway (FAK/ERK) referenced from prior in vitro work, not directly demonstrated in this study","pmids":["30724719"],"is_preprint":false}],"current_model":"IL-34 is a secreted dimeric cytokine with a helical cytokine fold that signals primarily through CSF-1R (sharing this receptor with CSF-1 but binding distinct receptor domains with greater thermodynamic stability), and also through two alternative receptors—protein-tyrosine phosphatase ζ (PTP-ζ/PTPRZ1) and TREM2—to regulate the survival, proliferation, and differentiation of mononuclear phagocytes; it is produced in a tissue-restricted manner by keratinocytes, neurons, and Tregs to direct the development and maintenance of Langerhans cells and microglia in regionally specific patterns, suppresses macrophage responses to pathogens, promotes macrophage M2 polarization, supports Treg suppressive function via macrophage intermediaries, and can exist as a membrane-anchored form (regulated by GRP78 chaperone) that signals by juxtacrine contact, while its transcription is regulated by NF-κB, VDR, and TGF-β/BMP-ALK pathways and post-transcriptionally by miR-28-5p and miR-31."},"narrative":{"mechanistic_narrative":"IL-34 is a secreted helical-fold cytokine that controls the development, maintenance, and functional polarization of mononuclear phagocytes by serving as an alternative ligand for CSF-1R (Fms), selectively required in vivo for the generation of epidermal Langerhans cells and CNS microglia [PMID:22729249, PMID:20504948]. Although IL-34 and CSF-1 share CSF-1R, crystallographic and SAXS/EM studies show IL-34 forms a structurally analogous but more thermodynamically stable receptor complex dominated by hydrophobic interface contacts, with a flexible D2-D3 receptor linker permitting degenerate ligand recognition and a glycosylated, proteolytically removable C-terminus that underlies functional non-redundancy [PMID:22483114, PMID:22579672, PMID:23478061]; consistent with this, IL-34 elicits stronger but more transient CSF-1R phosphorylation, distinct chemokine and trafficking outputs, and a partially divergent monocyte transcriptional program from CSF-1 [PMID:20489731, PMID:23684409]. IL-34 and CSF-1 occupy non-overlapping tissue niches—IL-34 maintains gray-matter microglia and steady-state keratinocyte-driven Langerhans cells while CSF-1 supports white-matter and inflammatory regeneration—and in lower vertebrates IL-34 is the primary driver of early macrophage seeding and chemoattraction to the brain [PMID:26634935, PMID:30205037, PMID:30765415, PMID:31616414]. Through CSF-1R signaling (engaging AKT, AMPK/ULK1-dependent autophagy, and MAPK routes) IL-34 drives differentiation of immunosuppressive M2-like and Kupffer-cell macrophages, osteoclasts, and specialized monocytic cells, and supports Treg-mediated suppression and transplant tolerance via an IL-34→macrophage→Treg circuit [PMID:23409120, PMID:29321503, PMID:29570162, PMID:24052571, PMID:30782613, PMID:26389674, PMID:36030499]. Beyond CSF-1R, IL-34 binds two additional receptors: the phosphatase PTP-ζ/PTPRZ1, expressed on injured epithelium and on macrophages, B and T cells in autoimmune renal disease [PMID:26121749, PMID:30622154], and TREM2, through which IL-34 phosphorylates RASAL3 and inactivates ERK1/2 to restrain AML cell proliferation [PMID:37001042]. IL-34 also exists as a GRP78-dependent membrane-anchored form that signals by juxtacrine cell-cell contact [PMID:30573681], and its expression is transcriptionally controlled by NF-κB, VDR, and TGF-β/BMP-ALK pathways and post-transcriptionally by miR-28-5p and miR-31 [PMID:24339952, PMID:28816551, PMID:27865758, PMID:26754294, PMID:31332295].","teleology":[{"year":2010,"claim":"Established that IL-34 is a functional CSF-1R ligand biochemically and physiologically, answering whether a second cytokine besides CSF-1 could drive the same receptor.","evidence":"In vitro macrophage proliferation and CSF-1R phosphorylation assays plus transgenic rescue of Csf1op/op mice; parallel signaling-kinetics and antibody-competition study","pmids":["20504948","20489731"],"confidence":"High","gaps":["Did not define tissue-specific non-redundancy with CSF-1","Structural basis of distinct binding/kinetics unresolved","No second receptor identified"]},{"year":2012,"claim":"Defined the unique in vivo developmental requirement for IL-34, showing it is selectively needed for Langerhans cell and microglial development rather than being merely redundant with CSF-1.","evidence":"IL-34-deficient (Il34LacZ/LacZ) reporter mice with phenotypic analysis of immune cell populations; CSF-1R conditional ablation and clonal corticogenesis cultures","pmids":["22729249","22542597"],"confidence":"High","gaps":["Did not establish the inflammatory vs steady-state division of labor with CSF-1","Mechanism of regional specificity unknown"]},{"year":2012,"claim":"Solved the structural basis for how IL-34 engages CSF-1R distinctly from CSF-1, explaining degenerate receptor recognition and differentiated signaling.","evidence":"X-ray crystallography of human and mouse IL-34 alone and bound to CSF-1R D1-D3, with interface mutagenesis, thermodynamic analysis, and a neutralizing Fab; SAXS/EM with glycan modeling","pmids":["22483114","22579672","23478061"],"confidence":"High","gaps":["Did not address binding to alternative receptors PTPRZ1 or TREM2","Functional role of C-terminal glycosylation/cleavage in vivo untested"]},{"year":2013,"claim":"Showed IL-34 and CSF-1 produce overlapping but distinct monocyte/macrophage outputs through the same receptor, demonstrating that shared receptor use does not equal identical function.","evidence":"Genome-wide microarray of IL-34- vs CSF-1-differentiated CD14+ monocytes with CSF-1R inhibitor confirmation; M2-like macrophage differentiation assays; IL-34-specific FDMC differentiation by neutralizing antibody and RNAi","pmids":["23684409","23409120","24052571"],"confidence":"High","gaps":["Molecular basis for ligand-specific transcriptional differences unresolved","Did not separate receptor-proximal events from downstream divergence"]},{"year":2015,"claim":"Extended IL-34 function into adaptive immune regulation and tissue injury, identifying a second receptor (PTP-ζ) and an IL-34→macrophage→Treg amplification circuit.","evidence":"IL-34-deficient mouse renal ischemia/reperfusion model; rat cardiac allograft tolerance with Treg functional assays and human macrophage-Treg co-culture; context-dependent LC maintenance in inducible knockouts; M-CSF/IL-34 heteromer SPR/PLA","pmids":["26121749","26389674","26634935","26095744"],"confidence":"High","gaps":["Did not separate PTP-ζ-specific signaling from CSF-1R signaling","Heteromeric cytokine physiological relevance untested in vivo"]},{"year":2018,"claim":"Defined a membrane-anchored, juxtacrine mode of IL-34 action and its chaperone dependence, distinguishing it from the secreted cytokine.","evidence":"CRISPR knockout, Transwell separation, mass spectrometry and pulldown identifying GRP78, and GRP78-heterozygous cells in FDMC differentiation assays","pmids":["30573681"],"confidence":"High","gaps":["Whether membrane-anchored IL-34 signals via CSF-1R or another receptor unclear","GRP78-IL-34 interaction interface undefined"]},{"year":2019,"claim":"Resolved the division of labor between IL-34 and CSF-1 in microglial maintenance regionally and developmentally, and established IL-34 as the primary early brain-seeding factor in zebrafish.","evidence":"Function-blocking antibody depletion across mouse brain regions; zebrafish CRISPR/morpholino loss-of-function with live imaging and automated microglia quantification","pmids":["31616414","30765415","30205037"],"confidence":"High","gaps":["Molecular cause of gray- vs white-matter ligand partitioning unknown","Chemoattraction mechanism not molecularly dissected"]},{"year":2019,"claim":"Mapped IL-34's pathogenic role in autoimmune and malignant settings, including expression of PTPRZ1 on immune cells and CSF-1R-dependent osteoclastogenesis.","evidence":"IL-34 knockout in MRL-Fas lupus mice with receptor localization; IL-34 siRNA knockdown and neutralizing antibody in multiple myeloma osteolysis models; muscle regeneration epistasis via miR-31","pmids":["30622154","30782613","31332295"],"confidence":"Medium","gaps":["PTPRZ1-specific immune signaling not separated from CSF-1R","Receptor identity for individual downstream effects often inferred"]},{"year":2023,"claim":"Identified TREM2 as a third IL-34 receptor with a defined signaling output, demonstrating receptor-context-dependent control of proliferation versus differentiation.","evidence":"Direct IL-34-TREM2 binding assay, TREM2 knockout AML cells, RASAL3/ERK1/2 phosphoanalysis, and preclinical AML models with IL-34-deficient mice","pmids":["37001042"],"confidence":"High","gaps":["Structural basis of IL-34-TREM2 binding undefined","Whether TREM2 engagement contributes to microglial/macrophage physiology beyond AML unknown"]},{"year":2024,"claim":"Linked IL-34 to autophagy-dependent microglial programs with a neuroprotective role in the aging brain, connecting CSF-1R-proximal AMPK/ULK1 signaling to function.","evidence":"Ulk1 conditional knockout in microglia, IL-34-specific microglial expansion, EAE neuroinflammation, and phospho-signaling/transcriptome analysis","pmids":["38195627"],"confidence":"Medium","gaps":["Receptor mediating the autophagy-dependent program not formally isolated","Single-lab finding"]},{"year":null,"claim":"How IL-34's three receptors (CSF-1R, PTP-ζ/PTPRZ1, TREM2) are differentially engaged in vivo to produce distinct cellular outcomes, and how secreted versus membrane-anchored forms are functionally partitioned, remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No structure of IL-34 bound to PTPRZ1 or TREM2","PTPRZ1-specific signaling never cleanly separated from CSF-1R in vivo","Regulation choosing secreted vs juxtacrine IL-34 in tissues unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0048018","term_label":"receptor ligand activity","supporting_discovery_ids":[0,1,3,16]},{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[1,2,16]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[11,21,31]}],"localization":[{"term_id":"GO:0005576","term_label":"extracellular region","supporting_discovery_ids":[0,1,8]},{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[18,39]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[1,2,16,21]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[0,8,11,15,42]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[0,6,12,13]}],"complexes":[],"partners":["CSF1R","CSF1","PTPRZ1","TREM2","HSPA5"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q6ZMJ4","full_name":"Interleukin-34","aliases":[],"length_aa":242,"mass_kda":27.5,"function":"Cytokine that promotes the proliferation, survival and differentiation of monocytes and macrophages. Promotes the release of pro-inflammatory chemokines, and thereby plays an important role in innate immunity and in inflammatory processes. Plays an important role in the regulation of osteoclast proliferation and differentiation, and in the regulation of bone resorption. Signaling via CSF1R and its downstream effectors stimulates phosphorylation of MAPK1/ERK2 AND MAPK3/ERK1","subcellular_location":"Secreted","url":"https://www.uniprot.org/uniprotkb/Q6ZMJ4/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/IL34","classification":"Not Classified","n_dependent_lines":5,"n_total_lines":1208,"dependency_fraction":0.0041390728476821195},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/IL34","total_profiled":1310},"omim":[{"mim_id":"612081","title":"INTERLEUKIN 34; IL34","url":"https://www.omim.org/entry/612081"},{"mim_id":"610379","title":"WEST NILE VIRUS, SUSCEPTIBILITY TO","url":"https://www.omim.org/entry/610379"},{"mim_id":"605246","title":"COMPLEMENT COMPONENT 3a RECEPTOR 1; C3AR1","url":"https://www.omim.org/entry/605246"},{"mim_id":"120700","title":"COMPLEMENT COMPONENT 3; C3","url":"https://www.omim.org/entry/120700"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"lymphoid tissue","ntpm":103.5},{"tissue":"skin 1","ntpm":62.0}],"url":"https://www.proteinatlas.org/search/IL34"},"hgnc":{"alias_symbol":["MGC34647","IL-34"],"prev_symbol":["C16orf77"]},"alphafold":{"accession":"Q6ZMJ4","domains":[{"cath_id":"1.20.1250.80","chopping":"27-187","consensus_level":"high","plddt":95.1511,"start":27,"end":187}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q6ZMJ4","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q6ZMJ4-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q6ZMJ4-F1-predicted_aligned_error_v6.png","plddt_mean":79.69},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=IL34","jax_strain_url":"https://www.jax.org/strain/search?query=IL34"},"sequence":{"accession":"Q6ZMJ4","fasta_url":"https://rest.uniprot.org/uniprotkb/Q6ZMJ4.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q6ZMJ4/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q6ZMJ4"}},"corpus_meta":[{"pmid":"22729249","id":"PMC_22729249","title":"IL-34 is a 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model (Il34LacZ/LacZ); in vivo phenotypic analysis of immune cell populations\",\n      \"journal\": \"Nature immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean genetic knockout with defined cellular phenotype, replicated across multiple tissues and independently confirmed by concurrent studies\",\n      \"pmids\": [\"22729249\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"IL-34 signals through CSF-1R (Fms) to stimulate macrophage proliferation, CSF-1R tyrosine phosphorylation, and downstream signaling, and can rescue bone, osteoclast, tissue macrophage, and fertility defects of CSF-1-deficient (Csf1op/op) mice when transgenically expressed, demonstrating functional overlap with CSF-1 through the same receptor.\",\n      \"method\": \"In vitro macrophage proliferation assays; CSF-1R tyrosine phosphorylation assays; transgenic rescue of Csf1op/op mice; whole-mount IL34 in situ hybridization; QRT-PCR\",\n      \"journal\": \"Journal of leukocyte biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — in vitro signaling assays plus in vivo transgenic rescue, multiple orthogonal methods\",\n      \"pmids\": [\"20504948\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"IL-34 and M-CSF share CSF-1R (Fms) as receptor but differ in biological activity and signaling kinetics: IL-34 induces stronger but more transient tyrosine phosphorylation of Fms and downstream molecules, rapidly downregulates Fms, and differs from M-CSF in chemokine induction (MCP-1, eotaxin-2), morphological changes, and cell migration. Different anti-Fms antibodies block binding of IL-34 vs. M-CSF differentially, indicating they bind distinct receptor domains.\",\n      \"method\": \"Cell-based signaling assays (tyrosine phosphorylation); anti-receptor monoclonal antibody competition binding assays; chemokine production assays; migration assays\",\n      \"journal\": \"Cell death and differentiation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal functional assays in a single study demonstrating mechanistic differences between the two ligands\",\n      \"pmids\": [\"20489731\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Crystal structure of dimeric IL-34 reveals a helical cytokine fold homologous to CSF-1. The IL-34:CSF-1R complex architecture is similar to CSF-1:CSF-1R but with unique conformational adaptations in receptor domain geometry; hydrophobic interactions at the IL-34:CSF-1R interface dominate biological activity. IL-34 forms a more thermodynamically stable complex with CSF-1R than CSF-1 does, and a neutralizing Fab fragment reveals the mechanism of antibody-mediated neutralization.\",\n      \"method\": \"X-ray crystallography of IL-34 alone and in complex with CSF-1R D1-D3; functional mutagenesis of the interface; Fab-bound crystal structure\",\n      \"journal\": \"Structure (London, England : 1993)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — two independent crystal structures (Ma et al. and Liu et al.) with functional mutagenesis; replicated across two labs\",\n      \"pmids\": [\"22483114\", \"22579672\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Mouse IL-34 crystal structure shows it contains two additional helices beyond the four conserved in helical hematopoietic cytokines; it recruits two CSF-1R copies on the sides of the helical bundles. The flexible linker between CSF-1R D2 and D3 allows these domains to clamp IL-34 and CSF-1 at different angles, explaining degenerate recognition. Hydrophobic interactions (not salt bridges) dominate IL-34 biological activity, and relative thermodynamic independence of the two IL-34:CSF-1R sites (vs. negative cooperativity for CSF-1) accounts for differentiated signaling.\",\n      \"method\": \"X-ray crystallography of mouse IL-34 alone and in complex with mouse CSF-1R D1-D3; interface mutagenesis; thermodynamic analysis\",\n      \"journal\": \"Biochimica et biophysica acta\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structure with mutagenesis, consistent with independent structure from Ma et al. 2012\",\n      \"pmids\": [\"22579672\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Human IL-34 bound to CSF-1R forms an extracellular assembly with striking structural similarities to the CSF-1:CSF-1R complex, including homotypic receptor-receptor interactions. The C-terminal region of IL-34 is heavily glycosylated and can be proteolytically cleaved from the IL-34:CSF-1R complex, providing a mechanism for functional non-redundancy between IL-34 and CSF-1.\",\n      \"method\": \"Small-angle X-ray scattering (SAXS); negative-stain electron microscopy; systematic glycan modeling\",\n      \"journal\": \"Structure (London, England : 1993)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — hybrid structural approach (SAXS + EM) with systematic glycan analysis, single study with multiple orthogonal methods\",\n      \"pmids\": [\"23478061\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"IL-34 exhibits broader regional brain expression than CSF-1 (mostly without overlap), with maximal expression during early postnatal development. CSF-1R-deficient mice (but not ligand-deficient mice) show defects in neural progenitor cell maintenance including increased proliferation and apoptosis of neocortical progenitors. Addition of IL-34 or CSF-1 to microglia-free CSF-1R-expressing dorsal forebrain clonal cultures suppressed progenitor self-renewal and enhanced neuronal differentiation, indicating a direct role for IL-34/CSF-1R signaling in corticogenesis independent of microglia.\",\n      \"method\": \"CSF-1R knockout mouse phenotyping; Nestin-Cre conditional CSF-1R ablation; microglia-free clonal culture assays with IL-34 and CSF-1 addition\",\n      \"journal\": \"Developmental biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — conditional knockout plus in vitro functional assays with defined cellular phenotypes\",\n      \"pmids\": [\"22542597\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"IL-34 is expressed by tubular epithelial cells (TECs) in the kidney after ischemia/reperfusion injury and promotes macrophage-mediated tubular cell destruction via two distinct mechanisms: enhanced intrarenal macrophage proliferation and elevated bone marrow myeloid cell proliferation that increases circulating monocytes recruited by chemokines into the kidney. A second IL-34 receptor, protein-tyrosine phosphatase ζ (PTP-ζ/PTPRZ1), is upregulated alongside c-FMS in the injured kidney. CSF-1 expression did not compensate for IL-34 deficiency.\",\n      \"method\": \"IL-34-deficient mouse model of renal ischemia/reperfusion injury; flow cytometry; bone marrow proliferation analysis; chemokine measurements; immunohistochemistry in human transplant kidneys\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean genetic knockout with mechanistic dissection of two distinct pathways, validated in human samples\",\n      \"pmids\": [\"26121749\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"IL-34 is expressed by CD8+CD45RClo Tregs and human FOXP3+CD45RCloCD8+ and CD4+ Tregs, contributes to their suppressive function, and is required for transplant tolerance induction in a rat cardiac allograft model. IL-34-primed macrophages potentiate the immune-suppressive capacity of Tregs, establishing an IL-34→macrophage→Treg amplification circuit.\",\n      \"method\": \"Rat cardiac allograft tolerance model; IL-34 protein treatment; Treg functional assays; human macrophage-Treg co-culture expansion\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo transplant model with mechanistic pathway dissection and human validation\",\n      \"pmids\": [\"26389674\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"IL-34 is required for keratinocyte-derived LC renewal in steady-state adult skin, whereas during UV-induced inflammation, LC regeneration depends on neutrophil-derived CSF1. These ligands play nonredundant roles in LC maintenance depending on tissue context.\",\n      \"method\": \"Inducible IL-34 knockout mice; Il34LacZ reporter mice; in vivo skin damage model; cell-type-specific analysis\",\n      \"journal\": \"European journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — inducible conditional knockout with defined cellular phenotype under steady-state and inflammatory conditions\",\n      \"pmids\": [\"26634935\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"IL-34 and M-CSF form a novel heteromeric cytokine; BIAcore experiments demonstrated M-CSF binds directly to IL-34, and molecular docking and proximity ligation assay confirmed heterodimer formation. The heteromeric M-CSF/IL-34 cytokine causes higher phosphorylation of M-CSFR tyrosine residues at low concentrations and additive effects on cell proliferation/viability. Co-expression of M-CSFR and its ligands differentially regulates M-CSFR trafficking into the cell.\",\n      \"method\": \"BIAcore binding assay; molecular docking; proximity ligation assay; M-CSFR phosphorylation assay; receptor trafficking analysis\",\n      \"journal\": \"Cytokine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct binding demonstrated by SPR (BIAcore) and confirmed by PLA, functional receptor signaling measured, single lab\",\n      \"pmids\": [\"26095744\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"IL-34 induces differentiation of human monocytes into CD14high CD163high immunosuppressive M2-like macrophages via the M-CSF receptor, independent of endogenous M-CSF consumption. This effect is potentiated by IL-6 and inhibited by IFNγ and GM-CSF. IFNγ can also switch established IL-34-macrophages into immunostimulatory macrophages.\",\n      \"method\": \"Human primary monocyte differentiation assays; flow cytometry; LPS stimulation; T cell co-culture suppression assays; cytokine ELISA; CSF-1R blocking experiments\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal functional assays with pharmacological and antibody-based receptor blocking\",\n      \"pmids\": [\"23409120\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"In zebrafish, Il34-Csf1ra signaling is required for microglial precursor attraction to proximal brain regions prior to neuronal apoptosis. In il34- and csf1ra-deficient larvae, embryonic macrophages fail to migrate to the anterior head and colonize the CNS, while peripheral tissue colonization is unaffected. Activation of the Il34-Csf1ra pathway alone is sufficient to attract embryonic macrophages to the CNS independent of neuronal apoptosis.\",\n      \"method\": \"Zebrafish il34 and csf1ra mutants/morpholinos; live imaging of macrophage migration; rescue/overexpression experiments\",\n      \"journal\": \"Developmental cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic loss-of-function in zebrafish with live imaging, rescue by pathway activation, replicated by concurrent zebrafish study\",\n      \"pmids\": [\"30205037\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"In zebrafish, il34 loss-of-function causes reduced microglia numbers and impairs yolk sac macrophage (YSM) distribution to the brain and other target organs, while csf1 loss does not reduce microglia numbers at early stages (though overexpression increases them). This establishes il34 as the primary driver of early brain seeding by YSMs.\",\n      \"method\": \"CRISPR/Cas9 in vivo reverse genetic screen in zebrafish; automated microglia quantification (SpotNGlia); Neutral Red vital staining\",\n      \"journal\": \"Disease models & mechanisms\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — CRISPR-based loss-of-function with automated quantification, replicated by concurrent zebrafish study\",\n      \"pmids\": [\"30765415\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"CSF1 and IL-34 play distinct roles in microglia maintenance: peripheral antibody-mediated blockade of IL-34 depletes microglia preferentially in gray matter brain regions, while CSF1 blockade depletes white matter microglia. These regional patterns correspond to the differential expression of each ligand. CSF1 is required to establish microglia in the developing embryo, while both ligands are required beginning in early postnatal development.\",\n      \"method\": \"Function-blocking antibody administration in adult mice; microglia depletion quantification across brain regions; developmental time-course analysis\",\n      \"journal\": \"Frontiers in immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — selective antibody blockade in vivo with regional brain analysis, multiple time points\",\n      \"pmids\": [\"31616414\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"IL-34 promotes lupus nephritis in MRL-Fas mice via two mechanisms: intrarenal macrophage proliferation and bone marrow myeloid cell proliferation that increases circulating monocytes recruited into the kidney. PTPRZ1 (PTP-ζ), a second IL-34 receptor, is expressed by macrophages, B cells, and T cells. IL-34 deficiency also suppresses circulating autoantibodies and glomerular antibody deposits, associated with fewer activated/proliferating intrarenal and splenic B cells.\",\n      \"method\": \"IL-34 knockout in MRL-Fas lupus mice; flow cytometry; immunohistochemistry; bone marrow and intrarenal macrophage proliferation analysis; autoantibody ELISA\",\n      \"journal\": \"Journal of the American Society of Nephrology : JASN\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean genetic knockout in disease model with mechanistic pathway dissection of two independent mechanisms\",\n      \"pmids\": [\"30622154\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"IL-34 binds directly to TREM2 (triggering receptor expressed on myeloid cells 2) as a novel receptor, independent of CSF-1R and PTP-ζ. IL-34-TREM2 binding rapidly phosphorylates RASAL3 (Ras protein activator-like 3) and inactivates ERK1/2 signaling, preventing AML cell proliferation and stimulating differentiation. TREM2-deficient AML cells are resistant to IL-34 treatment.\",\n      \"method\": \"Direct binding assay (IL-34 to TREM2); TREM2 knockout AML cells; phosphoproteomic/signaling analysis (RASAL3 phosphorylation, ERK1/2 inactivation); preclinical AML mouse models; IL-34-deficient mice showing accelerated AML\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — direct binding demonstrated, receptor knockout confirms specificity, signaling mechanism identified, multiple preclinical models\",\n      \"pmids\": [\"37001042\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"IL-34 produced by follicular dendritic cells (FDCs), but not CSF-1 from the same cells, is selectively responsible for the differentiation of a new CD11b+ monocytic cell type (FDMCs) with B cell-stimulating activity, as demonstrated by neutralizing antibodies and RNAi. This differentiation depends strictly on CSF-1R, establishing a CSF-1R-mediated differentiation pathway intrinsically specific to IL-34.\",\n      \"method\": \"Neutralizing antibody experiments; RNAi knockdown; CSF-1R dependence assays; B cell co-culture proliferation assays\",\n      \"journal\": \"Journal of leukocyte biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — two orthogonal methods (neutralizing antibody + RNAi) demonstrating IL-34 specificity, clear CSF-1R dependence established\",\n      \"pmids\": [\"24052571\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"IL-34 cell-surface localization on follicular dendritic cells (FL-Y) requires the molecular chaperone GRP78 (78-kDa glucose-regulated protein): GRP78 associates with IL-34 in the plasma membrane fraction (identified by mass spectrometry and pulldown), and GRP78-heterozygous FL-Y cells show reduced surface IL-34 and impaired FDMC differentiation. FDMC differentiation requires a membrane-anchored form of IL-34 via direct cell-cell contact, not secreted IL-34.\",\n      \"method\": \"CRISPR/Cas9 IL-34 knockout; Transwell culture experiments; mass spectrometry; pulldown assay; flow cytometry with anti-IL-34 antibody; GRP78-heterozygous cells\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — CRISPR knockout, mass spectrometry identification of interactor, pulldown confirmation, and functional consequence in differentiation assay\",\n      \"pmids\": [\"30573681\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Vitamin D analog (2MD) induces IL-34 expression in vascular endothelial cells of spleen and bone through a vitamin D receptor (VDR)-mediated mechanism. IL-34 in splenic vascular endothelium maintains a reservoir of osteoclast precursors (OCPs) in the spleen of CSF-1-deficient (Csf1op/op) mice. Splenectomy or siRNA-mediated knockdown of IL-34 suppressed vitamin D-induced osteoclastogenesis.\",\n      \"method\": \"Vitamin D analog injection in Csf1op/op mice; splenectomy; siRNA knockdown of IL-34; osteoclast precursor analysis; VDR-mediated transcription assay\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic and pharmacological loss-of-function with two orthogonal approaches (splenectomy + siRNA) and VDR mechanism established\",\n      \"pmids\": [\"22670054\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"IL-34 expression in gingival fibroblasts is enhanced by TNF-α and IL-1β through NF-κB transcription factor and JNK activation. IL-34 can substitute for M-CSF in RANKL-induced osteoclastogenesis of bone marrow macrophages.\",\n      \"method\": \"Real-time PCR of gingival fibroblasts after cytokine stimulation; pharmacological inhibitors of NF-κB and JNK; TRAP staining of osteoclasts\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — pathway inhibitors used to establish signaling mechanism, functional osteoclastogenesis assay\",\n      \"pmids\": [\"24339952\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"CSF-1R engagement by IL-34 (vs. CSF-1) leads to AKT and caspase activation, autophagy induction through AMPK and ULK1 expression and activation, during human monocyte differentiation. IL-34-differentiated macrophages show striking increases in IL-10 (M1) and CCL17 (M2) secretion compared to CSF-1-differentiated macrophages, and differentially polarize naïve T cells toward Th1.\",\n      \"method\": \"Human primary monocyte differentiation assays; phosphorylation analysis of AKT, AMPK, ULK1; autophagy measurement; cytokine secretome ELISA; T cell polarization assay\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple signaling pathway analyses and functional secretome comparisons, single lab\",\n      \"pmids\": [\"29321503\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"IL-34 interaction with CSF-1R on rheumatoid arthritis fibroblast-like synoviocytes (FLS) promotes dramatic IL-6 production via JNK/P38/NF-κB signaling, which in turn upregulates Th17 cell numbers. IL-6R antagonist attenuates Th17 production mediated by IL-34-stimulated FLS.\",\n      \"method\": \"CSF-1R expression analysis on FLS; IL-6 production assays; JNK/P38/NF-κB pathway inhibitor experiments; Th17 cell quantification; IL-6R antagonist treatment\",\n      \"journal\": \"Mediators of inflammation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — pathway inhibitors establishing signaling mechanism, functional Th17 consequence demonstrated with pharmacological intervention\",\n      \"pmids\": [\"28659662\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"IL-34 regulates IL-6 and IL-8 production in human lung fibroblasts via MAPK (p38), PI3K-Akt, JAK, and NF-κB signaling pathways, as demonstrated by reversal with specific pathway inhibitors and western-blot confirmation of phosphorylation events.\",\n      \"method\": \"Primary lung fibroblast assays; pathway-specific pharmacological inhibitors (JAK, NF-κB, Akt, p38); western blotting for phosphorylation; cytokine ELISA\",\n      \"journal\": \"International immunopharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple pathway inhibitors and phosphorylation validation, single lab\",\n      \"pmids\": [\"29857241\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"IL-34 promotes Kupffer cell M2 polarization in rat liver transplantation via activation of the PI3K/Akt pathway, and this M2 KC polarization is required for IL-34-mediated inhibition of acute rejection (demonstrated by KC depletion and adoptive transfer experiments).\",\n      \"method\": \"Adeno-associated virus-expressing IL-34 in rat liver transplant model; KC depletion (clodronate); adoptive transfer of KCs; PI3K/Akt pathway analysis in vitro; in vivo/in vitro M1-to-M2 polarization assays\",\n      \"journal\": \"Transplantation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo adoptive transfer with depletion establishing KC-dependence; PI3K/Akt mechanism in vitro\",\n      \"pmids\": [\"29570162\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"miR-28-5p directly targets IL-34 mRNA (identified by gene expression profiles and bioinformatics, confirmed functionally), and miR-28-5p deficiency promotes HCC tumor growth and metastasis via IL-34-mediated tumor-associated macrophage (TAM) infiltration. TAMs induced by IL-34 inhibit miR-28-5p expression in HCC cells via TGF-β1, forming a positive feedback loop.\",\n      \"method\": \"miRNA sequencing; bioinformatics target identification; nude mouse tumor models; gene expression profiling; TAM infiltration analysis; TGF-β1 mechanistic experiments\",\n      \"journal\": \"Hepatology (Baltimore, Md.)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo tumor models with IL-34 as direct miR-28-5p target, feedback loop established mechanistically; single lab\",\n      \"pmids\": [\"26754294\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"In satellite cells, miR-31 posttranscriptionally suppresses IL-34 mRNA. IL-34 protein activates JAK-STAT3 signaling required for myogenic progression. miR-31 knockout causes impaired myoblast expansion and enhanced myogenic commitment; IL-34 inhibition rescues the regenerative deficiency of miR-31 knockout mice, placing IL-34/JAK-STAT3 downstream of miR-31 in muscle regeneration.\",\n      \"method\": \"miR-31 knockout mice; muscle regeneration assays; IL-34 inhibition rescue experiment; JAK-STAT3 signaling analysis\",\n      \"journal\": \"Cell death and differentiation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic epistasis via rescue experiment in knockout mice, signaling pathway identified\",\n      \"pmids\": [\"31332295\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"1α,25-dihydroxyvitamin D3 (vitamin D3) strongly induces IL-34 expression in SH-SY5Y neural cells via the vitamin D receptor (VDR). A core IL-34 gene promoter and a VDR binding site (CGCCCT) required for this induction were identified by reporter assays.\",\n      \"method\": \"Dose- and time-response gene expression analysis; VDR knockdown/inhibition; promoter reporter assay; VDR binding site mutagenesis\",\n      \"journal\": \"Innate immunity\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — promoter analysis with mutagenesis and VDR knockdown establishing mechanistic transcriptional regulation\",\n      \"pmids\": [\"28816551\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"mHTTx1 aggregates in post-mitotic dopaminergic neurons induce IL-34 production selectively, mediated by IKKβ. IKKβ knockdown or inhibition prevents mHTTx1 aggregation and subsequent IL-34 production. Elevated neuronal IL-34 exacerbates mHTTx1-induced degeneration of striatal neurons via non-cell-autonomous microglial expansion, and an IL-34 receptor inhibitor reduces microglial numbers and ameliorates neurodegeneration in brain slice models.\",\n      \"method\": \"Human embryonic stem cell-derived dopaminergic neurons; IKKβ knockdown/inhibition; brain slice model with intact neuron-microglial networks; IL-34 receptor inhibitor\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic knockdown identifying upstream regulator (IKKβ), brain slice model showing non-cell-autonomous mechanism, pharmacological rescue\",\n      \"pmids\": [\"28973132\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"An autophagy-dependent microglia population in aging mouse cortex is promoted by IL-34 (not CSF1). Deletion of the core autophagy gene Ulk1 in microglia reduces this population. IL-34-mediated microglial expansion is neuroprotective when aging mice are exposed to autoimmune neuroinflammation, with loss of autophagy-dependent microglia leading to neural/glial cell death and increased mortality.\",\n      \"method\": \"Ulk1 conditional knockout in microglia; IL-34-mediated microglial expansion assays; autoimmune neuroinflammation model (EAE); ERK1/2, Akt, AMPK phosphorylation analysis; transcriptome analysis\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — conditional knockout plus IL-34-specific expansion demonstrating neuroprotective function, single lab\",\n      \"pmids\": [\"38195627\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"IL-34 promotes foam cell formation in bone marrow-derived macrophages by increasing CD36 expression via the p38 MAPK signaling pathway, enhancing oxLDL uptake and intracellular cholesterol accumulation without affecting cholesterol efflux.\",\n      \"method\": \"Bone marrow-derived macrophage assays; oxLDL uptake measurement; cholesterol content assay; CD36 expression analysis; p38 MAPK pathway inhibitors\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — pharmacological inhibitor establishing p38 MAPK mechanism, CD36 upregulation linked to functional foam cell formation\",\n      \"pmids\": [\"30478377\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"IL-34 suppresses Candida albicans-induced TNFα production by M1 macrophages by downregulating expression of key pattern recognition receptors TLR2 and Dectin-1, providing a molecular mechanism for skin macrophage tolerance to commensal fungi.\",\n      \"method\": \"M1 macrophage stimulation with heat-killed Candida; TNFα measurement; flow cytometry/expression analysis of TLR2 and Dectin-1 after IL-34 treatment\",\n      \"journal\": \"Journal of immunology research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — clear mechanistic link between IL-34 and PRR downregulation, but single lab with limited methods\",\n      \"pmids\": [\"26146640\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Low-dose IL-34 promotes osteogenesis of human bone marrow stromal cells (hBMSCs) via activation of PI3K/AKT and ERK signaling pathways, as demonstrated by reversal with specific AKT and ERK inhibitors. Low-dose IL-34 has no effect on osteoclastogenesis of mouse bone marrow macrophages in vitro or on osteoporosis in OVX rats in vivo.\",\n      \"method\": \"In vitro hBMSC osteogenic differentiation assays; ALP and ARS staining; PI3K/AKT and ERK inhibitors; western blotting; rat tibial osteotomy model; OVX model\",\n      \"journal\": \"Stem cell research & therapy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — pathway inhibitors confirm signaling mechanism in vitro, validated in vivo fracture healing model\",\n      \"pmids\": [\"33947456\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"TGF-β1 and BMP-2 inhibit IL-34 expression in rheumatoid arthritis synovial fibroblasts through ALK5 and ALK1 receptor pathways, respectively, and antagonize TNF-α-induced IL-34 gene expression. These signaling routes are established as upstream regulators of IL-34 expression.\",\n      \"method\": \"Pharmacological inhibition of ALK1 and ALK5 in RA synovial fibroblasts and murine mesenchymal stem cells; dose- and time-response real-time qPCR; ELISA for IL-34, TGF-β1, BMP-2 in synovial fluids\",\n      \"journal\": \"The American journal of pathology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — pharmacological inhibitors of specific receptors establish transcriptional regulatory mechanism, validated in two cell types\",\n      \"pmids\": [\"27865758\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"SAMHD1 dysfunction in neuronal SH-SY5Y cells induces IL-34 expression via the canonical NF-κB pathway: SAMHD1 knockdown upregulates NF-κB p65 expression, phosphorylates IKKα/β and IκBα, and promotes nuclear translocation of NF-κB p65, leading to increased IL-34 transcription.\",\n      \"method\": \"SAMHD1 siRNA knockdown in SH-SY5Y cells; qRT-PCR and western blot for IL-34 and NF-κB components; IKK and IκBα phosphorylation analysis; NF-κB nuclear translocation assay; transcriptional activity assay\",\n      \"journal\": \"Molecular immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic knockdown with multiple signaling readouts establishing NF-κB-dependent transcriptional mechanism\",\n      \"pmids\": [\"38367301\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Schwann cells in ALS peripheral nerves express CSF1 and IL-34 and closely interact with CSF-1R-expressing endoneurial monocyte/macrophages, suggesting a paracrine mechanism of myeloid cell expansion. Pharmacological inhibition of CSF-1R (with masitinib) reduces Schwann cell reactivity and immune cell infiltration in peripheral nerves of SOD1G93A rats.\",\n      \"method\": \"Immunohistochemistry of ALS patient and SOD1G93A rat sciatic nerves; CSF-1R inhibitor (masitinib) treatment; quantification of SC phenotypes and macrophage numbers\",\n      \"journal\": \"Glia\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — IHC-based pathway identification with pharmacological CSF-1R inhibition rescue; paracrine mechanism inferred but not directly proven\",\n      \"pmids\": [\"31859421\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"In Huntington's disease, RUNX1 mediates further upregulation of CSF-1R and its ligand IL-34 following rebound ERK activation after BRAF inhibition. The autocrine IL-34/CSF-1R signaling axis in melanoma cells promotes 3D growth and invasiveness; CSF-1R inhibition or knockdown reduces these phenotypes, and coinhibition of CSF-1R and BRAF shows synergistic efficacy in vivo.\",\n      \"method\": \"RUNX1-mediated CSF-1R and IL-34 upregulation analysis; RNAi and pharmacological CSF-1R inhibition; 3D growth and invasion assays; in vivo combinatorial treatment\",\n      \"journal\": \"JCI insight\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — RNAi and pharmacological inhibition with in vivo validation establishing autocrine signaling mechanism\",\n      \"pmids\": [\"30046005\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"In esophageal squamous cell carcinoma, 5-fluorouracil/cisplatin treatment preferentially increases IL-34 mRNA expression on tumor cells, and IL-34 expression drives CD163+ TAM polarization via CSF-1R. Human monocytes co-cultured with chemotherapy-treated ESCC cells increase CD163 expression, which is attenuated by CSF-1R inhibitors.\",\n      \"method\": \"In vitro ESCC cell line chemotherapy treatment; mRNA expression analysis; monocyte co-culture assays; CSF-1R inhibitor experiments; immunohistochemistry of patient specimens\",\n      \"journal\": \"Molecular cancer research : MCR\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — mechanistic co-culture system with pharmacological inhibitor, validated in patient samples\",\n      \"pmids\": [\"33674443\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Transcriptional profiling of human CD14+ monocytes differentiated with IL-34 vs. CSF-1 through CSF-1R revealed ~75% similarity in gene expression, but notable differences including differential repression of CCR2 mRNA and protein by IL-34. This CCR2 differential was abolished by CSF-1R inhibitor GW2580, confirming CSF-1R mediation.\",\n      \"method\": \"Agilent whole-genome microarray; FACS for CCR2 protein; CSF-1R inhibitor (GW2580) experiments\",\n      \"journal\": \"Cytokine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genome-wide transcriptional comparison with CSF-1R inhibitor confirmation, identifying differential downstream outcomes\",\n      \"pmids\": [\"23684409\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"IL-34 expressed on the surface of follicular dendritic cells (FL-Y) requires direct cell-cell contact with precursor cells for FDMC differentiation (membrane-anchored form, not secreted), as demonstrated by Transwell culture showing abrogation of differentiation when cells were separated.\",\n      \"method\": \"Transwell culture experiments; CRISPR/Cas9 IL-34 knockout confirmation; flow cytometric surface IL-34 detection\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Transwell and CRISPR experiments establishing juxtacrine mechanism of IL-34 surface signaling\",\n      \"pmids\": [\"30573681\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"In lupus nephritis (MRL-Fas) mice, PTPRZ1 (PTP-ζ) is expressed on macrophages, B cells, and T cells in addition to its known epithelial expression, identifying it as a functional IL-34 receptor on immune cells mediating autoimmune pathology.\",\n      \"method\": \"Flow cytometry and immunohistochemistry for PTPRZ1 on sorted immune cell populations from MRL-Fas mice; validated in human lupus nephritis tissue\",\n      \"journal\": \"Journal of the American Society of Nephrology : JASN\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — direct localization of receptor on immune cells confirmed across species, but functional link to PTPRZ1-specific signaling not directly separated from CSF-1R signaling\",\n      \"pmids\": [\"30622154\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"In osteolytic multiple myeloma, tumor cell-derived IL-34 promotes osteoclast formation from mouse BM cells and human CD14+ monocytes via CSF-1R; siRNA-mediated IL-34 knockdown in MM cells impaired osteoclast formation in vitro and attenuated osteolytic disease in vivo. A neutralizing anti-IL-34 antibody blocked osteoclast formation from human monocytes.\",\n      \"method\": \"IL-34 siRNA knockdown in MM cells; in vitro osteoclast formation assays; in vivo MM osteolysis model; anti-IL-34 neutralizing antibody\",\n      \"journal\": \"Blood advances\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — siRNA knockdown with in vivo validation and neutralizing antibody confirmation\",\n      \"pmids\": [\"30782613\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"In the absence of IL-34 (Il34-/- rats/mice), CD4+ Tregs fail to protect immunodeficient rats from wasting disease induced by transfer of pathogenic cells, demonstrating that IL-34 is required for CD4+ Treg suppressive function. IL-34 deficiency leads to unstable immune phenotype with multiple autoantibodies and exacerbated colitis.\",\n      \"method\": \"Il34-/- rat and mouse generation; DSS- and TNBS-induced colitis; pathogenic cell transfer model; Treg adoptive transfer in Il2rg-/- rats; GVHD and skin allograft models in humanized NSG mice\",\n      \"journal\": \"Clinical and translational medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple in vivo models establishing Treg-specific requirement for IL-34, single lab across several model systems\",\n      \"pmids\": [\"36030499\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"IL-34 expression in SH-SY5Y neural cells is reduced by TNF-α-induced NF-κB activation in hepatic stellate cells; schistosome soluble egg antigen (SEA) inhibits TNF-α-induced IL-34 expression by decreasing phosphorylation and degradation of IκBα, thus preventing NF-κB canonical activation and downstream IL-34 transcription.\",\n      \"method\": \"Reporter assays; qPCR; western blot for IκBα phosphorylation and degradation; NF-κB activation assays in hepatic stellate cells\",\n      \"journal\": \"Parasitology research\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — NF-κB mechanism established in hepatic stellate cells for IL-34 regulation, single lab, single cell type, no direct IL-34 receptor-pathway connection\",\n      \"pmids\": [\"30499009\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"In zebrafish, ectopically expressed IL-34 in hepatocytes attracts macrophages (but not neutrophils) to the liver in vivo via direct migration, as demonstrated by live imaging. IL-34-mediated macrophage migration occurs through syndecan-1 or focal adhesion kinase (FAK) and ERK1/2 pathways (referenced from prior studies).\",\n      \"method\": \"Zebrafish transgenic ectopic IL-34 expression in hepatocytes/epidermal cells; live imaging of macrophage and neutrophil migration\",\n      \"journal\": \"Zebrafish\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — live imaging demonstrates IL-34-directed macrophage migration in vivo but signaling pathway (FAK/ERK) referenced from prior in vitro work, not directly demonstrated in this study\",\n      \"pmids\": [\"30724719\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"IL-34 is a secreted dimeric cytokine with a helical cytokine fold that signals primarily through CSF-1R (sharing this receptor with CSF-1 but binding distinct receptor domains with greater thermodynamic stability), and also through two alternative receptors—protein-tyrosine phosphatase ζ (PTP-ζ/PTPRZ1) and TREM2—to regulate the survival, proliferation, and differentiation of mononuclear phagocytes; it is produced in a tissue-restricted manner by keratinocytes, neurons, and Tregs to direct the development and maintenance of Langerhans cells and microglia in regionally specific patterns, suppresses macrophage responses to pathogens, promotes macrophage M2 polarization, supports Treg suppressive function via macrophage intermediaries, and can exist as a membrane-anchored form (regulated by GRP78 chaperone) that signals by juxtacrine contact, while its transcription is regulated by NF-κB, VDR, and TGF-β/BMP-ALK pathways and post-transcriptionally by miR-28-5p and miR-31.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"IL-34 is a secreted helical-fold cytokine that controls the development, maintenance, and functional polarization of mononuclear phagocytes by serving as an alternative ligand for CSF-1R (Fms), selectively required in vivo for the generation of epidermal Langerhans cells and CNS microglia [#0, #1]. Although IL-34 and CSF-1 share CSF-1R, crystallographic and SAXS/EM studies show IL-34 forms a structurally analogous but more thermodynamically stable receptor complex dominated by hydrophobic interface contacts, with a flexible D2-D3 receptor linker permitting degenerate ligand recognition and a glycosylated, proteolytically removable C-terminus that underlies functional non-redundancy [#3, #4, #5]; consistent with this, IL-34 elicits stronger but more transient CSF-1R phosphorylation, distinct chemokine and trafficking outputs, and a partially divergent monocyte transcriptional program from CSF-1 [#2, #38]. IL-34 and CSF-1 occupy non-overlapping tissue niches—IL-34 maintains gray-matter microglia and steady-state keratinocyte-driven Langerhans cells while CSF-1 supports white-matter and inflammatory regeneration—and in lower vertebrates IL-34 is the primary driver of early macrophage seeding and chemoattraction to the brain [#9, #12, #13, #14]. Through CSF-1R signaling (engaging AKT, AMPK/ULK1-dependent autophagy, and MAPK routes) IL-34 drives differentiation of immunosuppressive M2-like and Kupffer-cell macrophages, osteoclasts, and specialized monocytic cells, and supports Treg-mediated suppression and transplant tolerance via an IL-34→macrophage→Treg circuit [#11, #21, #24, #17, #41, #8, #42]. Beyond CSF-1R, IL-34 binds two additional receptors: the phosphatase PTP-ζ/PTPRZ1, expressed on injured epithelium and on macrophages, B and T cells in autoimmune renal disease [#7, #15, #40], and TREM2, through which IL-34 phosphorylates RASAL3 and inactivates ERK1/2 to restrain AML cell proliferation [#16]. IL-34 also exists as a GRP78-dependent membrane-anchored form that signals by juxtacrine cell-cell contact [#18, #39], and its expression is transcriptionally controlled by NF-κB, VDR, and TGF-β/BMP-ALK pathways and post-transcriptionally by miR-28-5p and miR-31 [#20, #27, #33, #25, #26].\",\n  \"teleology\": [\n    {\n      \"year\": 2010,\n      \"claim\": \"Established that IL-34 is a functional CSF-1R ligand biochemically and physiologically, answering whether a second cytokine besides CSF-1 could drive the same receptor.\",\n      \"evidence\": \"In vitro macrophage proliferation and CSF-1R phosphorylation assays plus transgenic rescue of Csf1op/op mice; parallel signaling-kinetics and antibody-competition study\",\n      \"pmids\": [\"20504948\", \"20489731\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not define tissue-specific non-redundancy with CSF-1\", \"Structural basis of distinct binding/kinetics unresolved\", \"No second receptor identified\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Defined the unique in vivo developmental requirement for IL-34, showing it is selectively needed for Langerhans cell and microglial development rather than being merely redundant with CSF-1.\",\n      \"evidence\": \"IL-34-deficient (Il34LacZ/LacZ) reporter mice with phenotypic analysis of immune cell populations; CSF-1R conditional ablation and clonal corticogenesis cultures\",\n      \"pmids\": [\"22729249\", \"22542597\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not establish the inflammatory vs steady-state division of labor with CSF-1\", \"Mechanism of regional specificity unknown\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Solved the structural basis for how IL-34 engages CSF-1R distinctly from CSF-1, explaining degenerate receptor recognition and differentiated signaling.\",\n      \"evidence\": \"X-ray crystallography of human and mouse IL-34 alone and bound to CSF-1R D1-D3, with interface mutagenesis, thermodynamic analysis, and a neutralizing Fab; SAXS/EM with glycan modeling\",\n      \"pmids\": [\"22483114\", \"22579672\", \"23478061\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not address binding to alternative receptors PTPRZ1 or TREM2\", \"Functional role of C-terminal glycosylation/cleavage in vivo untested\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Showed IL-34 and CSF-1 produce overlapping but distinct monocyte/macrophage outputs through the same receptor, demonstrating that shared receptor use does not equal identical function.\",\n      \"evidence\": \"Genome-wide microarray of IL-34- vs CSF-1-differentiated CD14+ monocytes with CSF-1R inhibitor confirmation; M2-like macrophage differentiation assays; IL-34-specific FDMC differentiation by neutralizing antibody and RNAi\",\n      \"pmids\": [\"23684409\", \"23409120\", \"24052571\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular basis for ligand-specific transcriptional differences unresolved\", \"Did not separate receptor-proximal events from downstream divergence\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Extended IL-34 function into adaptive immune regulation and tissue injury, identifying a second receptor (PTP-ζ) and an IL-34→macrophage→Treg amplification circuit.\",\n      \"evidence\": \"IL-34-deficient mouse renal ischemia/reperfusion model; rat cardiac allograft tolerance with Treg functional assays and human macrophage-Treg co-culture; context-dependent LC maintenance in inducible knockouts; M-CSF/IL-34 heteromer SPR/PLA\",\n      \"pmids\": [\"26121749\", \"26389674\", \"26634935\", \"26095744\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not separate PTP-ζ-specific signaling from CSF-1R signaling\", \"Heteromeric cytokine physiological relevance untested in vivo\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Defined a membrane-anchored, juxtacrine mode of IL-34 action and its chaperone dependence, distinguishing it from the secreted cytokine.\",\n      \"evidence\": \"CRISPR knockout, Transwell separation, mass spectrometry and pulldown identifying GRP78, and GRP78-heterozygous cells in FDMC differentiation assays\",\n      \"pmids\": [\"30573681\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether membrane-anchored IL-34 signals via CSF-1R or another receptor unclear\", \"GRP78-IL-34 interaction interface undefined\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Resolved the division of labor between IL-34 and CSF-1 in microglial maintenance regionally and developmentally, and established IL-34 as the primary early brain-seeding factor in zebrafish.\",\n      \"evidence\": \"Function-blocking antibody depletion across mouse brain regions; zebrafish CRISPR/morpholino loss-of-function with live imaging and automated microglia quantification\",\n      \"pmids\": [\"31616414\", \"30765415\", \"30205037\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular cause of gray- vs white-matter ligand partitioning unknown\", \"Chemoattraction mechanism not molecularly dissected\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Mapped IL-34's pathogenic role in autoimmune and malignant settings, including expression of PTPRZ1 on immune cells and CSF-1R-dependent osteoclastogenesis.\",\n      \"evidence\": \"IL-34 knockout in MRL-Fas lupus mice with receptor localization; IL-34 siRNA knockdown and neutralizing antibody in multiple myeloma osteolysis models; muscle regeneration epistasis via miR-31\",\n      \"pmids\": [\"30622154\", \"30782613\", \"31332295\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"PTPRZ1-specific immune signaling not separated from CSF-1R\", \"Receptor identity for individual downstream effects often inferred\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Identified TREM2 as a third IL-34 receptor with a defined signaling output, demonstrating receptor-context-dependent control of proliferation versus differentiation.\",\n      \"evidence\": \"Direct IL-34-TREM2 binding assay, TREM2 knockout AML cells, RASAL3/ERK1/2 phosphoanalysis, and preclinical AML models with IL-34-deficient mice\",\n      \"pmids\": [\"37001042\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of IL-34-TREM2 binding undefined\", \"Whether TREM2 engagement contributes to microglial/macrophage physiology beyond AML unknown\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Linked IL-34 to autophagy-dependent microglial programs with a neuroprotective role in the aging brain, connecting CSF-1R-proximal AMPK/ULK1 signaling to function.\",\n      \"evidence\": \"Ulk1 conditional knockout in microglia, IL-34-specific microglial expansion, EAE neuroinflammation, and phospho-signaling/transcriptome analysis\",\n      \"pmids\": [\"38195627\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Receptor mediating the autophagy-dependent program not formally isolated\", \"Single-lab finding\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How IL-34's three receptors (CSF-1R, PTP-ζ/PTPRZ1, TREM2) are differentially engaged in vivo to produce distinct cellular outcomes, and how secreted versus membrane-anchored forms are functionally partitioned, remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structure of IL-34 bound to PTPRZ1 or TREM2\", \"PTPRZ1-specific signaling never cleanly separated from CSF-1R in vivo\", \"Regulation choosing secreted vs juxtacrine IL-34 in tissues unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0048018\", \"supporting_discovery_ids\": [0, 1, 3, 16]},\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [1, 2, 16]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [11, 21, 31]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [0, 1, 8]},\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [18, 39]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [1, 2, 16, 21]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [0, 8, 11, 15, 42]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [0, 6, 12, 13]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"CSF1R\", \"CSF1\", \"PTPRZ1\", \"TREM2\", \"HSPA5\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":5,"faith_total":6,"faith_pct":83.33333333333333}}