{"gene":"LY9","run_date":"2026-06-10T02:59:50","timeline":{"discoveries":[{"year":2001,"finding":"LY9 (Ly-9) recruits the SAP/SH2D1A protein via specific tyrosine residues in its cytoplasmic tail; this interaction is most efficient when those tyrosines are phosphorylated. Interactions were demonstrated by yeast two-hybrid, COS cell transfections, and in lymphoid cells.","method":"Yeast two-hybrid, COS cell transfection, lymphoid cell biochemical assays","journal":"Blood","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal yeast two-hybrid and cell-based co-transfection, replicated in endogenous lymphoid cells, multiple orthogonal methods in one study","pmids":["11389028"],"is_preprint":false},{"year":2004,"finding":"SAP is required for phosphorylation of Ly9 in thymocytes and peripheral T cells. SAP directly binds FynT (via both SH3 and kinase domains) and Lck (via kinase domain only), and addition of SAP to autoinhibited FynT causes a large increase in FynT catalytic activity in vitro. The SAP mutant R78E, which cannot bind the FynT SH3 domain, neither increases FynT activity nor functions as an adaptor in T cells, demonstrating SAP bridges Ly9 with Src-family kinases.","method":"In vitro protein interaction (yeast two-hybrid, pull-down), in vitro kinase activity assay, T-cell transfection with SAP mutants, primary thymocyte/T-cell phosphorylation analysis","journal":"International immunology","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — in vitro kinase reconstitution plus yeast two-hybrid plus primary cell mutagenesis, single lab but multiple orthogonal methods","pmids":["15096483"],"is_preprint":false},{"year":2005,"finding":"CD229 (LY9) binds homophilically through its N-terminal Ig-domain. A soluble CD229-Ig fusion protein bound CD229-transfected cells but not cells expressing other CD150 family receptors. Charged residues E27, E29 (B-C loop) and R89 (F-G loop) of the N-terminal domain are required for homophilic adhesion; mutation R44A enhanced the interaction. Confocal microscopy showed CD229 relocalizes to the T–B cell contact area during antigen-dependent immunological synapse formation.","method":"Soluble Ig-fusion protein binding assay, domain deletion and point mutagenesis, confocal microscopy of immune synapse","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — reconstitution with soluble fusion protein, confirmed by mutagenesis of specific residues, direct imaging of synapse localization; multiple orthogonal methods","pmids":["15905546"],"is_preprint":false},{"year":2005,"finding":"CD229 interacts with Grb2 in a phosphorylation-dependent manner; the SH2 domain of Grb2 binds tyrosine Y606 of CD229. This interaction is distinct from the SAP-binding motif. CD229 co-precipitates with Grb2 in T lymphocytes after pervanadate treatment and after CD229 or TCR ligation. The Grb2-binding site is required for CD229 internalization; a dominant-negative Grb2 (SH2-domain only) impairs CD229 endocytosis. CD229 ligation partially inhibits ERK phosphorylation and TCR-driven NFAT signaling.","method":"Co-immunoprecipitation, phospho-tyrosine mapping, dominant-negative transfection, NFAT-luciferase reporter assay, endocytosis assay","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 2 / Moderate — reciprocal Co-IP in endogenous T cells, site-specific mutagenesis, dominant-negative functional assay, multiple orthogonal readouts","pmids":["15879090"],"is_preprint":false},{"year":2003,"finding":"CD229 cell-surface expression is regulated by its interaction with the µ2 chain of the clathrin-associated AP-2 adaptor complex via the Y470EKL motif in its cytoplasmic tail. This motif is required for CD229 internalization but not for SAP recruitment. TCR and BCR signaling increase the rate of CD229 endocytosis; cross-linking with intact (but not F(ab')2) antibodies inhibits internalization on B cells, implicating Fcγ receptors.","method":"Co-immunoprecipitation of AP-2 complex, site-directed mutagenesis of Y470, internalization assay, T- and B-cell receptor co-ligation experiments","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Moderate — Co-IP with endogenous AP-2 complex, specific residue mutagenesis, functional internalization assay, multiple cell-type validations","pmids":["12621057"],"is_preprint":false},{"year":2006,"finding":"Ly9-deficient mice exhibit reduced IL-4 production (Th2 defect) and poor T-cell proliferation with little IL-2 after suboptimal anti-CD3 stimulation in vitro, distinct from SLAM-/- and SAP-/- phenotypes. Ly9-/- macrophages show no cytokine or bacterial killing defects. Ly9-/- mice foster normal NKT cell development and appropriate lymphocytic choriomeningitis virus responses, unlike SAP-/- mice.","method":"Ly9 knockout mouse generation, in vitro T-cell stimulation assays, cytokine measurement (IL-4, IL-2), comparison with SLAM-/- and SAP-/- mice","journal":"Journal of immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — clean KO with defined cellular phenotype, compared against multiple control strains, single lab","pmids":["16365421"],"is_preprint":false},{"year":2007,"finding":"Ligation of mouse CD229 with a specific monoclonal antibody inhibited expression of activation markers CD69 and CD25 on T lymphocytes in response to anti-CD3 stimulation in vitro, with concomitant reduction in cytokine production, demonstrating CD229 functions as an inhibitory co-receptor on T cells.","method":"In vitro T-cell stimulation with anti-CD229 mAb, flow cytometric measurement of CD69/CD25 and cytokine production","journal":"Tissue antigens","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — clean mAb-based functional assay with defined readouts, single lab, single method","pmids":["17919264"],"is_preprint":false},{"year":2011,"finding":"SLAMF3 (CD229) co-engagement with CD3 under Th17-polarizing conditions increases IL-17 production in CD4+ T cells, and this effect requires the adaptor molecule SAP. Both naïve and memory CD4+ T cells produce more IL-17 in response to SLAMF3/SLAMF6 co-stimulation than to CD28 co-stimulation.","method":"In vitro T-cell stimulation with anti-SLAMF3/SLAMF6 antibodies, cytokine (IL-17) measurement, SAP-dependent signaling analysis","journal":"Journal of immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional co-stimulation assay with SAP requirement established, two cell types tested, single lab","pmids":["22184727"],"is_preprint":false},{"year":2012,"finding":"CD3/TCR co-stimulation through SLAMF3 (and SLAMF6) recruits the transcription factor RORγt to the IL17A promoter in human T lymphocytes, cooperating with the canonical CD28/NFAT1 pathway to drive IL-17A expression. The dominance of the SLAMF3/SLAMF6 pathway in IL-17A induction is attributed to increased nuclear abundance and promoter recruitment of RORγt.","method":"Chromatin immunoprecipitation (ChIP) of NFAT1 and RORγt at IL17A promoter, nuclear fractionation, T-cell co-stimulation assay","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ChIP demonstrating promoter recruitment, multiple transcription factors analyzed, single lab","pmids":["22989874"],"is_preprint":false},{"year":2012,"finding":"Ly9 (CD229) acts as a negative regulator of thymic innate memory-like CD8+ T cell development and invariant NKT cell numbers. Ly9-deficient thymi show expanded innate CD8+ SP cells and increased iNKT cells; gene expression profiling revealed upregulation of IL-4 and PLZF. Double-deficient Ly9-/-IL4ra-/- mice lacked the expanded innate CD8+ subset, placing IL-4 signaling downstream of Ly9. Anti-Ly9 mAb in wild-type mice inhibited IL-4 levels induced by α-galactosylceramide.","method":"Ly9 KO mouse analysis, gene expression profiling, Ly9-/-IL4ra-/- double-KO epistasis, mCMV infection model, in vivo anti-Ly9 mAb treatment","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic epistasis (double-KO), gene expression profiling, in vivo mAb validation, multiple orthogonal approaches","pmids":["23225888"],"is_preprint":false},{"year":2013,"finding":"Ly9-deficient mice spontaneously develop anti-nuclear, anti-dsDNA, and anti-nucleosome autoantibodies on both B6.129 and BALB/c.129 backgrounds, with expansion of T follicular helper and germinal center B cells in aged mice. In vitro experiments showed Ly9 acts as an inhibitory receptor suppressing IFN-γ production by CD4+ T cells.","method":"Ly9 KO mouse phenotyping (ANA, anti-dsDNA ELISA), flow cytometry of Tfh and GC B cells, in vitro CD4+ T-cell cytokine assay","journal":"Frontiers in immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — KO with autoimmune phenotype plus in vitro inhibitory function, two genetic backgrounds, single lab","pmids":["23914190"],"is_preprint":false},{"year":2013,"finding":"SLAMF3 expression in hepatocytes inhibits HCC cell proliferation and migration, promotes apoptosis, and suppresses xenograft progression. SLAMF3 restoration decreases phosphorylation of MAPK ERK1/2, JNK, and mTOR in HCC cell lines.","method":"siRNA knockdown/overexpression in HCC cell lines, proliferation/apoptosis/migration assays, nude mouse xenograft, Western blot of ERK/JNK/mTOR phosphorylation","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — KD/OE with multiple functional readouts and in vivo validation, single lab","pmids":["24376606"],"is_preprint":false},{"year":2014,"finding":"SLAMF3 (CD229) interacts with HCV envelope protein E2 via its first N-terminal extracellular domain, and this interaction facilitates HCV entry into hepatocytes. siRNA knockdown and blocking antibodies against SLAMF3 decrease hepatocyte susceptibility to HCV infection, while overexpression increases susceptibility. Recombinant E2 binds SLAMF3 and anti-SLAMF3 antibodies inhibit this interaction.","method":"siRNA knockdown, SLAMF3 overexpression, blocking antibody, domain peptide competition, recombinant E2 binding assay, HCV infectivity assay","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple functional approaches (KD, OE, blocking Ab, domain mapping, direct protein binding), single lab","pmids":["24927415"],"is_preprint":false},{"year":2015,"finding":"In Ly9-deficient mice, splenic transitional 1, marginal zone, and B1a B cells are expanded; bone marrow B cell development is unaltered. Ly9-/- mice show elevated IgG3 natural antibodies and increased T-independent type II antibody responses. Anti-Ly9 mAb administered to wild-type mice selectively eliminates MZ B cells, reduces B1 and T1 B cells, downregulates the CD19/CD21/CD81 complex, and impairs B cell survival and activation in an Fc-independent manner.","method":"Ly9 KO mouse phenotyping, flow cytometry, in vivo mAb treatment, TNP-Ficoll immunization, serum Ab measurement","journal":"Journal of immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — KO phenotype confirmed by in vivo mAb targeting, multiple B cell subsets characterized, single lab","pmids":["26667173"],"is_preprint":false},{"year":2015,"finding":"The SLE-associated Met602 variant of CD229 (rs509749) has approximately two-fold higher affinity for SAP compared with the Val602 variant. Val602 CD229 is more highly expressed on the T-cell surface than Met602 CD229. Cells expressing Val602 show diminished activation (CD69 upregulation) compared with Met602 cells.","method":"Surface plasmon resonance/binding affinity assay, T-cell line expression analysis, CD69 activation assay","journal":"Immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct binding affinity measurement plus functional T-cell assay, single lab, two orthogonal methods","pmids":["26221972"],"is_preprint":false},{"year":2016,"finding":"SLAMF3 ligation on CD4+ T cells promotes sensitivity to IL-2 by upregulating CD25 via a Smad3-dependent mechanism, enhancing the IL-2/IL-2R/STAT5 signaling pathway and cell proliferation. SLAMF3 costimulation also promotes Treg differentiation from naïve CD4+ T cells.","method":"In vitro T-cell stimulation, CD25 surface measurement, Smad3 inhibition, STAT5 phosphorylation assay, Treg differentiation assay","journal":"Proceedings of the National Academy of Sciences","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple signaling pathway readouts and Smad3-dependence established, single lab","pmids":["27482100"],"is_preprint":false},{"year":2016,"finding":"SLAMF3 overexpression in HCC cells retains the Retinoblastoma (RB) factor in its hypophosphorylated (active) form, leading to inactivation of E2F transcription factor and repression of PLK1 expression and activation, thereby inhibiting mitosis and proliferation. An inverse correlation between SLAMF3 and PLK1 expression was observed in HCC patient samples.","method":"Western blot of RB phosphorylation, E2F activity assay, PLK1 expression analysis, SLAMF3 overexpression in HCC cells, patient sample correlation","journal":"Oncotarget","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — mechanistic pathway dissection with multiple molecular readouts and patient validation, single lab","pmids":["26799423"],"is_preprint":false},{"year":2016,"finding":"SLAMF3 overexpression in HCC cells specifically reduces MRP-1 (multidrug resistance protein 1) expression and its function as a drug efflux transporter, without affecting ABCG2 or MDR expression. This correlates inversely with MRP-1 expression in HCC patient samples, and sensitizes cells to anti-cancer drugs.","method":"Western blot, flow cytometry of MRP-1 expression/function, drug sensitivity assay in SLAMF3-overexpressing HCC cells, patient sample IHC correlation","journal":"Oncotarget","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — gain-of-function with specific molecular target identified (MRP-1), multiple assays, patient correlation, single lab","pmids":["27081035"],"is_preprint":false},{"year":2017,"finding":"Ly9 (SLAMF3) negatively regulates iNKT cell lineage differentiation. Ly9-deficient BALB/c mice show expanded thymic NKT2 cells with near-absent NKT1 cells. Anti-Ly9 agonistic mAb in wild-type mice impairs IL-4 and IFN-γ production and reduces splenic iNKT cells, with significant decrease in NKT2 proportion.","method":"Ly9 KO mouse analysis on BALB/c and C57BL/6 backgrounds, flow cytometry of iNKT subsets, in vivo anti-Ly9 agonistic mAb treatment, cytokine measurement","journal":"European journal of immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — KO on two genetic backgrounds plus in vivo mAb confirmation, single lab","pmids":["28980301"],"is_preprint":false},{"year":2019,"finding":"Palmitic acid induces SLAMF3 upregulation on human T cells through the STAT5-PI3K/Akt signaling pathway. Inhibition of PI3K/Akt or its upstream mediator STAT5 prevents palmitic acid-induced SLAMF3 upregulation, establishing this pathway as a regulatory mechanism of SLAMF3 expression.","method":"Palmitic acid treatment of T cells and Jurkat cells, RNA sequencing, PI3K/Akt and STAT5 inhibitor studies, flow cytometry of SLAMF3 expression","journal":"Cell death & disease","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — RNA-seq plus pharmacological inhibition of two pathway components, single lab","pmids":["31332162"],"is_preprint":false},{"year":2020,"finding":"SLAMF3 in multiple myeloma cells interacts directly with adaptor proteins SHP2 and GRB2 (which also interact with each other), activating the MAPK/ERK signaling pathway to promote myeloma proliferation and drug resistance. SLAMF3 knockdown/knockout or cytoplasmic domain truncation decreases phosphorylated ERK and suppresses proliferation. Self-ligand (homophilic CD229–CD229) interaction between MM cells mediates this activation.","method":"Co-immunoprecipitation of SHP2 and GRB2 with SLAMF3, SLAMF3 KD/KO, cytoplasmic domain truncation mutant, Western blot of pERK, SHP2 inhibitor treatment, xenograft model","journal":"Molecular cancer research","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP identifying two adaptor partners, KD/KO, domain truncation, pharmacological inhibition, and in vivo validation","pmids":["31974290"],"is_preprint":false},{"year":2022,"finding":"SLAMF3 and SLAMF4 function as 'don't eat me' receptors on macrophages, inhibiting macrophage phagocytosis of hematopoietic cells through SH2-domain-containing phosphatases (SHP-1/2). These receptors inhibit 'eat me' signals including LRP1-mediated mTOR and Syk activation. SFR deficiency triggers macrophage phagocytosis of hematopoietic cells and combined deletion of SFRs and CD47 causes hematopoietic cytopenia.","method":"SFR-deficient mouse models, phagocytosis assays, LRP1/mTOR/Syk signaling analysis, combined SFR/CD47 deletion, hematopoietic graft rejection model","journal":"Science immunology","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple genetic KO models, defined signaling mechanism (SHP-1/2, LRP1/mTOR/Syk), epistasis with CD47, in vivo hematopoietic phenotype","pmids":["35061505"],"is_preprint":false},{"year":2022,"finding":"CD229 promotes MM cell proliferation via the RAS/ERK signaling pathway. Co-immunoprecipitation coupled with mass spectrometry identified RASAL3 as a downstream interacting protein of CD229. Intercellular tyrosine phosphorylation mediates self-activation of CD229 which activates RAS/ERK signaling through RASAL3.","method":"Co-immunoprecipitation coupled with mass spectrometry, RASAL3 interaction validation, immunofluorescence co-culture assay, RAS/ERK pathway analysis, xenograft mouse model","journal":"Aging","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP/MS for partner identification with follow-up functional validation, in vivo xenograft, single lab","pmids":["36445333"],"is_preprint":false},{"year":2022,"finding":"Loss of SLAMF3 expression corresponds to sorafenib-resistant phenotypes in HCC cells undergoing epithelial-to-mesenchymal transition (EMT). Overexpression of SLAMF3 in resistant cells reverses EMT, decreases metastatic potential, and inhibits mTOR/ERK1/2 signaling, restoring sorafenib sensitivity.","method":"Sorafenib-resistant cell line generation, flow cytometry and Western blot of SLAMF3 and EMT markers, SLAMF3 overexpression, mTOR/ERK1/2 pathway analysis, migration assay","journal":"Cancers","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — mechanistic pathway (mTOR/ERK) with EMT linkage, gain-of-function rescue, single lab","pmids":["35205659"],"is_preprint":false},{"year":2023,"finding":"SLAMF3 co-stimulation promotes CD4+ T cell differentiation toward Th17 cells and IL-17A secretion via enrichment of RORγt and activation of the JAK1/STAT3 pathway. The drug iguratimod reverses SLAMF3-induced Th17 differentiation by inhibiting pJAK1 and pSTAT3.","method":"Anti-CD3/SLAMF3 T-cell stimulation, Th17 differentiation assay, RNA sequencing, Western blot of RORγt/pJAK1/pSTAT3, JAK1 inhibitor (iguratimod) treatment","journal":"International immunopharmacology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — transcriptomic plus protein-level pathway validation with pharmacological rescue, single lab","pmids":["38061117"],"is_preprint":false},{"year":2025,"finding":"Autosomal recessive LY9 deficiency in humans causes selective impairment of IFN-γ production by TH1* (CCR4-CCR6+CXCR3+T-bet+RORγT+) CD4+ memory T cells, underlying susceptibility to Mycobacterium tuberculosis. Mechanistically, LY9 polarizes naïve CD4+ T cells toward memory TH1* cells by inducing T-bet via SAP and RORγT without SAP. LY9 costimulation enhances TCR-driven IFN-γ production of memory TH1* cells in a T cell-intrinsic manner via NFAT1 and RORγT.","method":"Human AR LY9-deficient patient T-cell functional assays, T-bet/SAP/RORγT pathway analysis, in vitro TH1* polarization, NFAT1 and RORγT requirement established, TCR co-stimulation assays","journal":"Science immunology","confidence":"High","confidence_rationale":"Tier 2 / Strong — human loss-of-function genetics combined with mechanistic dissection of SAP-dependent/independent signaling, multiple transcription factor requirements, T cell-intrinsic validation","pmids":["40446017"],"is_preprint":false},{"year":2008,"finding":"A non-synonymous SNP rs509749 in exon 8 of LY9 (encoding Val/Met at position 602 in the cytoplasmic domain within the SAP/SH2D1a consensus binding site) is associated with SLE susceptibility and skews T-cell populations in Canadian SLE family members carrying the risk allele, increasing CD8+ memory T cells while decreasing CD4+ naïve and activated T cells.","method":"Family-based association study, T-cell phenotyping by flow cytometry in SLE families stratified by rs509749 genotype","journal":"Genes and immunity","confidence":"Low","confidence_rationale":"Tier 3 / Weak — genetic association with T-cell phenotype correlation, no direct molecular mechanism established in this paper","pmids":["18216865"],"is_preprint":false}],"current_model":"LY9 (CD229/SLAMF3) is a homophilic cell-surface receptor of the SLAM family that, upon tyrosine phosphorylation of its cytoplasmic tail, recruits SAP/SH2D1A (which bridges LY9 to FynT kinase and activates it), Grb2 (via Y606, controlling receptor endocytosis and attenuating TCR/ERK signaling), and the AP-2/clathrin endocytic machinery (via Y470EKL); it co-stimulates CD4+ T cells to produce IL-17 via a SAP–RORγt–JAK1/STAT3 axis, polarizes naïve CD4+ T cells to IFN-γ-producing TH1* effectors via SAP-dependent T-bet and SAP-independent RORγT induction, negatively regulates innate-like lymphocyte development (thymic innate CD8+ T cells, iNKT, marginal-zone and B1 B cells) through IL-4-dependent and IL-4-independent mechanisms, and on macrophages acts as a 'don't eat me' checkpoint through SHP-1/2-mediated inhibition of LRP1/mTOR/Syk pro-phagocytic signals, while in myeloma cells its homophilic self-ligation drives RAS/ERK/MAPK proliferative signaling via SHP2–GRB2–RASAL3 complexes."},"narrative":{"mechanistic_narrative":"LY9 (CD229/SLAMF3) is a homophilic cell-surface receptor of the SLAM family that uses tyrosine phosphorylation of its cytoplasmic tail to assemble distinct signaling complexes and tune both adaptive and innate immune cell behavior [PMID:11389028, PMID:15905546, PMID:15879090]. Its N-terminal Ig domain mediates homophilic self-adhesion through defined charged residues (E27, E29, R89) and drives receptor relocalization to the T–B immunological synapse [PMID:15905546]. The phosphorylated tail recruits the adaptor SAP/SH2D1A, which in turn binds and activates FynT to couple LY9 to Src-family kinase signaling [PMID:11389028, PMID:15096483]; a separate phosphotyrosine (Y606) engages Grb2 to drive receptor endocytosis and to attenuate TCR-driven ERK and NFAT signaling [PMID:15879090], while a Y470EKL motif binds the AP-2/clathrin adaptor to control internalization independently of SAP recruitment [PMID:12621057]. As a T-cell costimulator, LY9 ligation promotes CD4+ T-cell IL-17 production through SAP-dependent recruitment of RORγt to the IL17A promoter and JAK1/STAT3 activation [PMID:22184727, PMID:22989874, PMID:38061117], enhances IL-2 sensitivity and Treg differentiation via a Smad3/STAT5 axis [PMID:27482100], and polarizes naive CD4+ T cells toward IFN-γ-producing TH1* memory cells by inducing T-bet via SAP and RORγT independently of SAP, with TCR-driven IFN-γ requiring NFAT1 and RORγT [PMID:40446017]. Loss-of-function studies establish LY9 as a negative regulator of innate-like lymphocyte development, restraining thymic innate CD8+ T cells, iNKT cells, and marginal-zone/B1 B cells through IL-4-dependent and IL-4-independent mechanisms, with its deficiency leading to autoantibody production [PMID:23225888, PMID:23914190, PMID:26667173, PMID:28980301]. On macrophages LY9 functions as a 'don't eat me' checkpoint, inhibiting phagocytosis of hematopoietic cells via SHP-1/2-mediated suppression of LRP1/mTOR/Syk pro-phagocytic signals [PMID:35061505], and in multiple myeloma its homophilic self-ligation drives RAS/ERK proliferative signaling through SHP2–GRB2 and RASAL3 complexes [PMID:31974290, PMID:36445333]. Autosomal recessive LY9 deficiency in humans selectively impairs IFN-γ production by TH1* CD4+ memory T cells, underlying susceptibility to Mycobacterium tuberculosis [PMID:40446017].","teleology":[{"year":2001,"claim":"Established the proximal signaling logic of LY9 by showing its cytoplasmic tail recruits the adaptor SAP in a tyrosine-phosphorylation-dependent manner, defining LY9 as a SLAM-family receptor coupled to SAP-based signaling.","evidence":"Yeast two-hybrid, COS cell co-transfection, and lymphoid cell biochemistry","pmids":["11389028"],"confidence":"High","gaps":["Did not identify the kinase phosphorylating LY9","Downstream effectors of recruited SAP not yet defined"]},{"year":2003,"claim":"Resolved how LY9 surface levels are controlled by mapping a Y470EKL motif that binds the AP-2/clathrin adaptor to drive internalization separately from SAP recruitment, linking receptor signaling to receptor trafficking.","evidence":"Co-IP of AP-2, Y470 mutagenesis, and internalization assays with TCR/BCR co-ligation","pmids":["12621057"],"confidence":"High","gaps":["Functional consequence of endocytosis for signaling outcome not established","Did not connect trafficking to a specific T-cell response"]},{"year":2004,"claim":"Defined the mechanism by which SAP transduces LY9 signals, showing SAP bridges the receptor to FynT (via SH3 and kinase domains) and directly increases FynT catalytic activity, with the R78E mutant abolishing both bridging and kinase activation.","evidence":"In vitro kinase reconstitution, yeast two-hybrid/pull-down, and SAP mutant transfection in primary T cells","pmids":["15096483"],"confidence":"High","gaps":["Substrates of FynT downstream of LY9 not mapped","Relative contribution of Lck versus FynT not resolved"]},{"year":2005,"claim":"Demonstrated that LY9 is a homophilic ligand acting through its N-terminal Ig domain and that it relocalizes to the immunological synapse, establishing the structural basis for self-recognition between apposing cells.","evidence":"Soluble CD229-Ig binding, B-C/F-G loop point mutagenesis (E27, E29, R89), and confocal synapse imaging","pmids":["15905546"],"confidence":"High","gaps":["Affinity of the homophilic interaction not quantified","How homophilic engagement triggers tail phosphorylation not shown"]},{"year":2005,"claim":"Identified a second, SAP-independent signaling branch in which phospho-Y606 recruits Grb2 to drive LY9 endocytosis and to attenuate TCR-driven ERK and NFAT signaling, revealing LY9 as a negative modulator of T-cell activation.","evidence":"Reciprocal Co-IP, phosphotyrosine mapping, dominant-negative Grb2, NFAT-luciferase and endocytosis assays","pmids":["15879090"],"confidence":"High","gaps":["Mechanistic link between Grb2 binding and ERK attenuation not fully traced","Interplay between Grb2 and AP-2 trafficking pathways unresolved"]},{"year":2006,"claim":"Genetic dissection in Ly9-knockout mice revealed a non-redundant role distinct from SLAM and SAP, with defective IL-4/Th2 responses and impaired T-cell proliferation but normal NKT development and viral responses.","evidence":"Ly9 KO mouse with in vitro T-cell stimulation and cytokine measurement, compared to SLAM-/- and SAP-/-","pmids":["16365421"],"confidence":"Medium","gaps":["Molecular basis of the IL-4 defect not defined","Single lab, phenotype not yet mechanistically connected to signaling complexes"]},{"year":2007,"claim":"Antibody ligation of CD229 was shown to suppress activation markers and cytokine output, providing functional evidence that LY9 acts as an inhibitory co-receptor on T cells.","evidence":"In vitro anti-CD229 mAb stimulation with flow cytometric CD69/CD25 and cytokine readouts","pmids":["17919264"],"confidence":"Medium","gaps":["Single method, single lab","Inhibitory mechanism at the signaling level not dissected"]},{"year":2012,"claim":"Mouse genetics established LY9 as a negative regulator of innate-like lymphocyte development, with IL-4 signaling placed downstream by epistasis, reframing LY9 as a brake on thymic innate CD8+ T cell and iNKT expansion.","evidence":"Ly9 KO analysis, gene expression profiling, Ly9-/-IL4ra-/- double-KO epistasis, and in vivo anti-Ly9 mAb","pmids":["23225888"],"confidence":"High","gaps":["The receptor-proximal signal restraining innate lineages not specified","IL-4-independent component not molecularly defined"]},{"year":2011,"claim":"Functional costimulation studies showed LY9 co-engagement with CD3 drives IL-17 production in CD4+ T cells in a SAP-dependent manner, connecting LY9 to Th17 effector programs.","evidence":"In vitro anti-SLAMF3/SLAMF6 co-stimulation with IL-17 measurement and SAP-dependence","pmids":["22184727"],"confidence":"Medium","gaps":["Transcriptional mechanism not yet identified at this stage","Naive versus memory contributions only partially separated"]},{"year":2012,"claim":"Defined the transcriptional output of LY9 Th17 costimulation by showing recruitment of RORγt to the IL17A promoter cooperating with the CD28/NFAT1 pathway, attributing dominance to increased nuclear RORγt.","evidence":"ChIP of NFAT1 and RORγt at IL17A promoter, nuclear fractionation, and T-cell costimulation","pmids":["22989874"],"confidence":"Medium","gaps":["Upstream signal driving RORγt nuclear accumulation not mapped","Single lab"]},{"year":2013,"claim":"Extended the inhibitory-receptor model to autoimmunity by showing Ly9 deficiency yields spontaneous anti-nuclear autoantibodies and Tfh/GC expansion, with LY9 suppressing CD4+ IFN-γ production.","evidence":"Ly9 KO phenotyping (ANA, anti-dsDNA), Tfh/GC flow cytometry on two backgrounds, in vitro cytokine assay","pmids":["23914190"],"confidence":"Medium","gaps":["Causal link between IFN-γ suppression and autoantibody formation not established","Cell-intrinsic versus extrinsic effects not separated"]},{"year":2015,"claim":"B-cell-focused genetics revealed LY9 restrains marginal-zone, B1a, and transitional B cell compartments and natural antibody output, with in vivo mAb targeting selectively depleting these subsets Fc-independently.","evidence":"Ly9 KO phenotyping, in vivo anti-Ly9 mAb, TNP-Ficoll immunization, serum antibody measurement","pmids":["26667173"],"confidence":"Medium","gaps":["Signaling pathway controlling B-cell subset homeostasis not defined","CD19/CD21/CD81 downregulation mechanism unknown"]},{"year":2015,"claim":"Linked an SLE-associated coding variant to receptor function by showing the Met602 allele binds SAP with ~2-fold higher affinity than Val602, while Val602 shows higher surface expression and diminished activation, providing a molecular handle on disease association.","evidence":"Binding affinity measurement and T-cell line expression/CD69 activation assays","pmids":["26221972"],"confidence":"Medium","gaps":["In vivo consequence of altered SAP affinity not demonstrated","Single lab, single cell system"]},{"year":2016,"claim":"Established additional positive-costimulatory branches in which LY9 promotes IL-2 sensitivity and Treg differentiation via a Smad3-dependent CD25/STAT5 mechanism, broadening its role beyond inhibition.","evidence":"In vitro T-cell stimulation, Smad3 inhibition, STAT5 phosphorylation, and Treg differentiation assays","pmids":["27482100"],"confidence":"Medium","gaps":["How a single receptor produces both inhibitory and costimulatory outcomes not reconciled","Smad3 activation mechanism downstream of LY9 unclear"]},{"year":2013,"claim":"Opened a tumor-suppressor role for LY9 in hepatocellular carcinoma, showing SLAMF3 restoration inhibits proliferation/migration and reduces ERK/JNK/mTOR phosphorylation.","evidence":"siRNA KD/OE in HCC lines, proliferation/apoptosis/migration assays, xenograft, and pathway Western blots","pmids":["24376606"],"confidence":"Medium","gaps":["Receptor-proximal mechanism in hepatocytes not defined","Why LY9 is tumor-suppressive in HCC but proliferative in myeloma unexplained"]},{"year":2016,"claim":"Detailed the antiproliferative HCC mechanism by linking SLAMF3 to RB hypophosphorylation, E2F inactivation, and PLK1 repression, with patient-sample correlation supporting the axis.","evidence":"RB phosphorylation/E2F/PLK1 analysis with SLAMF3 overexpression and patient correlation","pmids":["26799423"],"confidence":"Medium","gaps":["Connection between surface receptor and RB/E2F not mechanistically bridged","Single lab"]},{"year":2016,"claim":"Identified a chemosensitization function in which SLAMF3 specifically lowers MRP-1 drug-efflux transporter expression, inversely correlated in patient samples.","evidence":"MRP-1 expression/function and drug sensitivity assays in SLAMF3-overexpressing HCC cells with IHC correlation","pmids":["27081035"],"confidence":"Medium","gaps":["Mechanism linking SLAMF3 to MRP-1 regulation unknown","Specificity over other transporters not mechanistically explained"]},{"year":2014,"claim":"Revealed a pathogen-exploited function by showing SLAMF3's first extracellular domain binds HCV envelope E2 to facilitate hepatocyte entry.","evidence":"siRNA KD, OE, blocking antibody, domain peptide competition, recombinant E2 binding, and HCV infectivity assays","pmids":["24927415"],"confidence":"Medium","gaps":["Whether LY9 is an obligate entry factor or accessory not resolved","Structural basis of the E2 interaction not determined"]},{"year":2017,"claim":"Refined the innate-lymphocyte role by showing LY9 negatively regulates iNKT lineage choice, restraining NKT2 expansion and enabling NKT1 development.","evidence":"Ly9 KO on two backgrounds, iNKT subset flow cytometry, and in vivo agonistic anti-Ly9 mAb with cytokine readouts","pmids":["28980301"],"confidence":"Medium","gaps":["Signal controlling NKT1/NKT2 balance not molecularly defined","Cell-intrinsic versus thymic-niche effects not separated"]},{"year":2019,"claim":"Identified a regulatory input controlling LY9 expression, showing palmitic acid induces SLAMF3 upregulation through STAT5-PI3K/Akt signaling on T cells.","evidence":"Palmitic acid treatment, RNA-seq, and PI3K/Akt and STAT5 inhibitor studies","pmids":["31332162"],"confidence":"Medium","gaps":["Functional consequence of metabolite-driven upregulation for immunity not tested","Direct transcriptional control of LY9 not mapped"]},{"year":2020,"claim":"Established the oncogenic signaling mechanism in multiple myeloma, showing SLAMF3 homophilic self-ligation recruits SHP2 and GRB2 to activate MAPK/ERK and drive proliferation and drug resistance.","evidence":"Reciprocal Co-IP of SHP2/GRB2, KD/KO, cytoplasmic truncation, pERK Western, SHP2 inhibitor, and xenograft","pmids":["31974290"],"confidence":"High","gaps":["How identical homophilic ligation produces opposite outcomes in T cells versus myeloma not resolved","Order of SHP2/GRB2 assembly on the tail not defined"]},{"year":2022,"claim":"Expanded the myeloma RAS/ERK mechanism by identifying RASAL3 as a CD229 interactor through which intercellular tyrosine phosphorylation self-activates the receptor.","evidence":"Co-IP/mass spectrometry, RASAL3 validation, co-culture immunofluorescence, RAS/ERK analysis, and xenograft","pmids":["36445333"],"confidence":"Medium","gaps":["Direct biochemical role of RASAL3 in ERK activation not fully resolved","Single lab"]},{"year":2022,"claim":"Defined LY9 as a macrophage 'don't eat me' checkpoint, inhibiting phagocytosis of hematopoietic cells via SHP-1/2-mediated suppression of LRP1/mTOR/Syk, with epistasis to CD47.","evidence":"SFR-deficient mouse models, phagocytosis assays, LRP1/mTOR/Syk signaling analysis, and combined SFR/CD47 deletion","pmids":["35061505"],"confidence":"High","gaps":["Individual contribution of LY9 versus SLAMF4 to the macrophage checkpoint not isolated","Ligand triggering the inhibitory signal on macrophages not defined"]},{"year":2022,"claim":"Connected LY9 loss to therapy resistance in HCC, showing SLAMF3 reverses EMT and restores sorafenib sensitivity through mTOR/ERK1/2 inhibition.","evidence":"Sorafenib-resistant lines, SLAMF3 overexpression rescue, EMT marker and mTOR/ERK analysis, migration assay","pmids":["35205659"],"confidence":"Medium","gaps":["Receptor-proximal events upstream of mTOR/ERK in hepatocytes still unknown","Single lab"]},{"year":2025,"claim":"Human loss-of-function genetics established LY9 as essential for IFN-γ production by TH1* CD4+ memory T cells and anti-mycobacterial immunity, integrating SAP-dependent T-bet induction and SAP-independent RORγT/NFAT1 signaling into a coherent costimulatory mechanism.","evidence":"Human AR LY9-deficient patient T-cell assays, T-bet/SAP/RORγT pathway dissection, TH1* polarization, and NFAT1/RORγT requirement","pmids":["40446017"],"confidence":"High","gaps":["Full reconciliation of inhibitory mouse phenotypes with costimulatory human role not complete","Why TH1* memory cells are selectively dependent on LY9 not fully explained"]},{"year":null,"claim":"It remains unresolved how a single homophilic receptor produces opposite outcomes across contexts — inhibitory on T cells and macrophages, tumor-suppressive in HCC, yet proliferative in myeloma — i.e. what dictates assembly of SAP/FynT versus Grb2 versus SHP1/2/SHP2-GRB2-RASAL3 complexes on the same cytoplasmic tail.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No unifying structural model of context-dependent adaptor selection","Stoichiometry and competition among SAP, Grb2, AP-2, and SHP1/2 on the tail not defined","Determinants of cell-type-specific output unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0098631","term_label":"cell adhesion mediator activity","supporting_discovery_ids":[2]},{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[0,3,6,25]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[3,21]},{"term_id":"GO:0001618","term_label":"virus receptor activity","supporting_discovery_ids":[12]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[2,3,4]}],"pathway":[{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[7,21,25]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[3,20,25]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[9,13,18]}],"complexes":[],"partners":["SH2D1A","FYN","GRB2","SHP2","RASAL3","AP-2","LY9"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q9HBG7","full_name":"T-lymphocyte surface antigen Ly-9","aliases":["Cell surface molecule Ly-9","Lymphocyte antigen 9","SLAM family member 3","SLAMF3","Signaling lymphocytic activation molecule 3"],"length_aa":655,"mass_kda":72.1,"function":"Self-ligand receptor of the signaling lymphocytic activation molecule (SLAM) family. SLAM receptors triggered by homo- or heterotypic cell-cell interactions are modulating the activation and differentiation of a wide variety of immune cells and thus are involved in the regulation and interconnection of both innate and adaptive immune response. Activities are controlled by presence or absence of small cytoplasmic adapter proteins, SH2D1A/SAP and/or SH2D1B/EAT-2. May participate in adhesion reactions between T lymphocytes and accessory cells by homophilic interaction. Promotes T-cell differentiation into a helper T-cell Th17 phenotype leading to increased IL-17 secretion; the costimulatory activity requires SH2D1A (PubMed:22184727). Promotes recruitment of RORC to the IL-17 promoter (PubMed:22989874). May be involved in the maintenance of peripheral cell tolerance by serving as a negative regulator of the immune response. May disable autoantibody responses and inhibit IFN-gamma secretion by CD4(+) T-cells. May negatively regulate the size of thymic innate CD8(+) T-cells and the development of invariant natural killer T (iNKT) cells (By similarity)","subcellular_location":"Membrane; Cell membrane","url":"https://www.uniprot.org/uniprotkb/Q9HBG7/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/LY9","classification":"Not Classified","n_dependent_lines":8,"n_total_lines":1208,"dependency_fraction":0.006622516556291391},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/LY9","total_profiled":1310},"omim":[{"mim_id":"606625","title":"SLAM FAMILY, MEMBER 7; SLAMF7","url":"https://www.omim.org/entry/606625"},{"mim_id":"605554","title":"CD244 ANTIGEN; CD244","url":"https://www.omim.org/entry/605554"},{"mim_id":"604513","title":"CD84 ANTIGEN; CD84","url":"https://www.omim.org/entry/604513"},{"mim_id":"600684","title":"T-LYMPHOCYTE SURFACE ANTIGEN LY-9; LY9","url":"https://www.omim.org/entry/600684"},{"mim_id":"300490","title":"SH2 DOMAIN PROTEIN 1A; SH2D1A","url":"https://www.omim.org/entry/300490"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Plasma membrane","reliability":"Approved"},{"location":"Centriolar satellite","reliability":"Additional"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"bone marrow","ntpm":10.9},{"tissue":"intestine","ntpm":11.2},{"tissue":"lymphoid tissue","ntpm":29.2}],"url":"https://www.proteinatlas.org/search/LY9"},"hgnc":{"alias_symbol":["CD229","mLY9","SLAMF3","hly9"],"prev_symbol":[]},"alphafold":{"accession":"Q9HBG7","domains":[{"cath_id":"2.60.40.10","chopping":"54-152","consensus_level":"high","plddt":91.4712,"start":54,"end":152},{"cath_id":"2.60.40.10","chopping":"159-242","consensus_level":"high","plddt":84.9507,"start":159,"end":242},{"cath_id":"2.60.40.10","chopping":"256-295_309-358","consensus_level":"high","plddt":84.2168,"start":256,"end":358},{"cath_id":"2.60.40,2.60.40","chopping":"365-441","consensus_level":"high","plddt":83.1245,"start":365,"end":441}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9HBG7","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9HBG7-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9HBG7-F1-predicted_aligned_error_v6.png","plddt_mean":66.06},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=LY9","jax_strain_url":"https://www.jax.org/strain/search?query=LY9"},"sequence":{"accession":"Q9HBG7","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9HBG7.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9HBG7/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9HBG7"}},"corpus_meta":[{"pmid":"11389028","id":"PMC_11389028","title":"Cell 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Interactions were demonstrated by yeast two-hybrid, COS cell transfections, and in lymphoid cells.\",\n      \"method\": \"Yeast two-hybrid, COS cell transfection, lymphoid cell biochemical assays\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal yeast two-hybrid and cell-based co-transfection, replicated in endogenous lymphoid cells, multiple orthogonal methods in one study\",\n      \"pmids\": [\"11389028\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"SAP is required for phosphorylation of Ly9 in thymocytes and peripheral T cells. SAP directly binds FynT (via both SH3 and kinase domains) and Lck (via kinase domain only), and addition of SAP to autoinhibited FynT causes a large increase in FynT catalytic activity in vitro. The SAP mutant R78E, which cannot bind the FynT SH3 domain, neither increases FynT activity nor functions as an adaptor in T cells, demonstrating SAP bridges Ly9 with Src-family kinases.\",\n      \"method\": \"In vitro protein interaction (yeast two-hybrid, pull-down), in vitro kinase activity assay, T-cell transfection with SAP mutants, primary thymocyte/T-cell phosphorylation analysis\",\n      \"journal\": \"International immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — in vitro kinase reconstitution plus yeast two-hybrid plus primary cell mutagenesis, single lab but multiple orthogonal methods\",\n      \"pmids\": [\"15096483\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"CD229 (LY9) binds homophilically through its N-terminal Ig-domain. A soluble CD229-Ig fusion protein bound CD229-transfected cells but not cells expressing other CD150 family receptors. Charged residues E27, E29 (B-C loop) and R89 (F-G loop) of the N-terminal domain are required for homophilic adhesion; mutation R44A enhanced the interaction. Confocal microscopy showed CD229 relocalizes to the T–B cell contact area during antigen-dependent immunological synapse formation.\",\n      \"method\": \"Soluble Ig-fusion protein binding assay, domain deletion and point mutagenesis, confocal microscopy of immune synapse\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — reconstitution with soluble fusion protein, confirmed by mutagenesis of specific residues, direct imaging of synapse localization; multiple orthogonal methods\",\n      \"pmids\": [\"15905546\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"CD229 interacts with Grb2 in a phosphorylation-dependent manner; the SH2 domain of Grb2 binds tyrosine Y606 of CD229. This interaction is distinct from the SAP-binding motif. CD229 co-precipitates with Grb2 in T lymphocytes after pervanadate treatment and after CD229 or TCR ligation. The Grb2-binding site is required for CD229 internalization; a dominant-negative Grb2 (SH2-domain only) impairs CD229 endocytosis. CD229 ligation partially inhibits ERK phosphorylation and TCR-driven NFAT signaling.\",\n      \"method\": \"Co-immunoprecipitation, phospho-tyrosine mapping, dominant-negative transfection, NFAT-luciferase reporter assay, endocytosis assay\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal Co-IP in endogenous T cells, site-specific mutagenesis, dominant-negative functional assay, multiple orthogonal readouts\",\n      \"pmids\": [\"15879090\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"CD229 cell-surface expression is regulated by its interaction with the µ2 chain of the clathrin-associated AP-2 adaptor complex via the Y470EKL motif in its cytoplasmic tail. This motif is required for CD229 internalization but not for SAP recruitment. TCR and BCR signaling increase the rate of CD229 endocytosis; cross-linking with intact (but not F(ab')2) antibodies inhibits internalization on B cells, implicating Fcγ receptors.\",\n      \"method\": \"Co-immunoprecipitation of AP-2 complex, site-directed mutagenesis of Y470, internalization assay, T- and B-cell receptor co-ligation experiments\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP with endogenous AP-2 complex, specific residue mutagenesis, functional internalization assay, multiple cell-type validations\",\n      \"pmids\": [\"12621057\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Ly9-deficient mice exhibit reduced IL-4 production (Th2 defect) and poor T-cell proliferation with little IL-2 after suboptimal anti-CD3 stimulation in vitro, distinct from SLAM-/- and SAP-/- phenotypes. Ly9-/- macrophages show no cytokine or bacterial killing defects. Ly9-/- mice foster normal NKT cell development and appropriate lymphocytic choriomeningitis virus responses, unlike SAP-/- mice.\",\n      \"method\": \"Ly9 knockout mouse generation, in vitro T-cell stimulation assays, cytokine measurement (IL-4, IL-2), comparison with SLAM-/- and SAP-/- mice\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean KO with defined cellular phenotype, compared against multiple control strains, single lab\",\n      \"pmids\": [\"16365421\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Ligation of mouse CD229 with a specific monoclonal antibody inhibited expression of activation markers CD69 and CD25 on T lymphocytes in response to anti-CD3 stimulation in vitro, with concomitant reduction in cytokine production, demonstrating CD229 functions as an inhibitory co-receptor on T cells.\",\n      \"method\": \"In vitro T-cell stimulation with anti-CD229 mAb, flow cytometric measurement of CD69/CD25 and cytokine production\",\n      \"journal\": \"Tissue antigens\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — clean mAb-based functional assay with defined readouts, single lab, single method\",\n      \"pmids\": [\"17919264\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"SLAMF3 (CD229) co-engagement with CD3 under Th17-polarizing conditions increases IL-17 production in CD4+ T cells, and this effect requires the adaptor molecule SAP. Both naïve and memory CD4+ T cells produce more IL-17 in response to SLAMF3/SLAMF6 co-stimulation than to CD28 co-stimulation.\",\n      \"method\": \"In vitro T-cell stimulation with anti-SLAMF3/SLAMF6 antibodies, cytokine (IL-17) measurement, SAP-dependent signaling analysis\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional co-stimulation assay with SAP requirement established, two cell types tested, single lab\",\n      \"pmids\": [\"22184727\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"CD3/TCR co-stimulation through SLAMF3 (and SLAMF6) recruits the transcription factor RORγt to the IL17A promoter in human T lymphocytes, cooperating with the canonical CD28/NFAT1 pathway to drive IL-17A expression. The dominance of the SLAMF3/SLAMF6 pathway in IL-17A induction is attributed to increased nuclear abundance and promoter recruitment of RORγt.\",\n      \"method\": \"Chromatin immunoprecipitation (ChIP) of NFAT1 and RORγt at IL17A promoter, nuclear fractionation, T-cell co-stimulation assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ChIP demonstrating promoter recruitment, multiple transcription factors analyzed, single lab\",\n      \"pmids\": [\"22989874\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Ly9 (CD229) acts as a negative regulator of thymic innate memory-like CD8+ T cell development and invariant NKT cell numbers. Ly9-deficient thymi show expanded innate CD8+ SP cells and increased iNKT cells; gene expression profiling revealed upregulation of IL-4 and PLZF. Double-deficient Ly9-/-IL4ra-/- mice lacked the expanded innate CD8+ subset, placing IL-4 signaling downstream of Ly9. Anti-Ly9 mAb in wild-type mice inhibited IL-4 levels induced by α-galactosylceramide.\",\n      \"method\": \"Ly9 KO mouse analysis, gene expression profiling, Ly9-/-IL4ra-/- double-KO epistasis, mCMV infection model, in vivo anti-Ly9 mAb treatment\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic epistasis (double-KO), gene expression profiling, in vivo mAb validation, multiple orthogonal approaches\",\n      \"pmids\": [\"23225888\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Ly9-deficient mice spontaneously develop anti-nuclear, anti-dsDNA, and anti-nucleosome autoantibodies on both B6.129 and BALB/c.129 backgrounds, with expansion of T follicular helper and germinal center B cells in aged mice. In vitro experiments showed Ly9 acts as an inhibitory receptor suppressing IFN-γ production by CD4+ T cells.\",\n      \"method\": \"Ly9 KO mouse phenotyping (ANA, anti-dsDNA ELISA), flow cytometry of Tfh and GC B cells, in vitro CD4+ T-cell cytokine assay\",\n      \"journal\": \"Frontiers in immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — KO with autoimmune phenotype plus in vitro inhibitory function, two genetic backgrounds, single lab\",\n      \"pmids\": [\"23914190\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"SLAMF3 expression in hepatocytes inhibits HCC cell proliferation and migration, promotes apoptosis, and suppresses xenograft progression. SLAMF3 restoration decreases phosphorylation of MAPK ERK1/2, JNK, and mTOR in HCC cell lines.\",\n      \"method\": \"siRNA knockdown/overexpression in HCC cell lines, proliferation/apoptosis/migration assays, nude mouse xenograft, Western blot of ERK/JNK/mTOR phosphorylation\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — KD/OE with multiple functional readouts and in vivo validation, single lab\",\n      \"pmids\": [\"24376606\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"SLAMF3 (CD229) interacts with HCV envelope protein E2 via its first N-terminal extracellular domain, and this interaction facilitates HCV entry into hepatocytes. siRNA knockdown and blocking antibodies against SLAMF3 decrease hepatocyte susceptibility to HCV infection, while overexpression increases susceptibility. Recombinant E2 binds SLAMF3 and anti-SLAMF3 antibodies inhibit this interaction.\",\n      \"method\": \"siRNA knockdown, SLAMF3 overexpression, blocking antibody, domain peptide competition, recombinant E2 binding assay, HCV infectivity assay\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple functional approaches (KD, OE, blocking Ab, domain mapping, direct protein binding), single lab\",\n      \"pmids\": [\"24927415\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"In Ly9-deficient mice, splenic transitional 1, marginal zone, and B1a B cells are expanded; bone marrow B cell development is unaltered. Ly9-/- mice show elevated IgG3 natural antibodies and increased T-independent type II antibody responses. Anti-Ly9 mAb administered to wild-type mice selectively eliminates MZ B cells, reduces B1 and T1 B cells, downregulates the CD19/CD21/CD81 complex, and impairs B cell survival and activation in an Fc-independent manner.\",\n      \"method\": \"Ly9 KO mouse phenotyping, flow cytometry, in vivo mAb treatment, TNP-Ficoll immunization, serum Ab measurement\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — KO phenotype confirmed by in vivo mAb targeting, multiple B cell subsets characterized, single lab\",\n      \"pmids\": [\"26667173\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"The SLE-associated Met602 variant of CD229 (rs509749) has approximately two-fold higher affinity for SAP compared with the Val602 variant. Val602 CD229 is more highly expressed on the T-cell surface than Met602 CD229. Cells expressing Val602 show diminished activation (CD69 upregulation) compared with Met602 cells.\",\n      \"method\": \"Surface plasmon resonance/binding affinity assay, T-cell line expression analysis, CD69 activation assay\",\n      \"journal\": \"Immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct binding affinity measurement plus functional T-cell assay, single lab, two orthogonal methods\",\n      \"pmids\": [\"26221972\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"SLAMF3 ligation on CD4+ T cells promotes sensitivity to IL-2 by upregulating CD25 via a Smad3-dependent mechanism, enhancing the IL-2/IL-2R/STAT5 signaling pathway and cell proliferation. SLAMF3 costimulation also promotes Treg differentiation from naïve CD4+ T cells.\",\n      \"method\": \"In vitro T-cell stimulation, CD25 surface measurement, Smad3 inhibition, STAT5 phosphorylation assay, Treg differentiation assay\",\n      \"journal\": \"Proceedings of the National Academy of Sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple signaling pathway readouts and Smad3-dependence established, single lab\",\n      \"pmids\": [\"27482100\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"SLAMF3 overexpression in HCC cells retains the Retinoblastoma (RB) factor in its hypophosphorylated (active) form, leading to inactivation of E2F transcription factor and repression of PLK1 expression and activation, thereby inhibiting mitosis and proliferation. An inverse correlation between SLAMF3 and PLK1 expression was observed in HCC patient samples.\",\n      \"method\": \"Western blot of RB phosphorylation, E2F activity assay, PLK1 expression analysis, SLAMF3 overexpression in HCC cells, patient sample correlation\",\n      \"journal\": \"Oncotarget\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — mechanistic pathway dissection with multiple molecular readouts and patient validation, single lab\",\n      \"pmids\": [\"26799423\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"SLAMF3 overexpression in HCC cells specifically reduces MRP-1 (multidrug resistance protein 1) expression and its function as a drug efflux transporter, without affecting ABCG2 or MDR expression. This correlates inversely with MRP-1 expression in HCC patient samples, and sensitizes cells to anti-cancer drugs.\",\n      \"method\": \"Western blot, flow cytometry of MRP-1 expression/function, drug sensitivity assay in SLAMF3-overexpressing HCC cells, patient sample IHC correlation\",\n      \"journal\": \"Oncotarget\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — gain-of-function with specific molecular target identified (MRP-1), multiple assays, patient correlation, single lab\",\n      \"pmids\": [\"27081035\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Ly9 (SLAMF3) negatively regulates iNKT cell lineage differentiation. Ly9-deficient BALB/c mice show expanded thymic NKT2 cells with near-absent NKT1 cells. Anti-Ly9 agonistic mAb in wild-type mice impairs IL-4 and IFN-γ production and reduces splenic iNKT cells, with significant decrease in NKT2 proportion.\",\n      \"method\": \"Ly9 KO mouse analysis on BALB/c and C57BL/6 backgrounds, flow cytometry of iNKT subsets, in vivo anti-Ly9 agonistic mAb treatment, cytokine measurement\",\n      \"journal\": \"European journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — KO on two genetic backgrounds plus in vivo mAb confirmation, single lab\",\n      \"pmids\": [\"28980301\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Palmitic acid induces SLAMF3 upregulation on human T cells through the STAT5-PI3K/Akt signaling pathway. Inhibition of PI3K/Akt or its upstream mediator STAT5 prevents palmitic acid-induced SLAMF3 upregulation, establishing this pathway as a regulatory mechanism of SLAMF3 expression.\",\n      \"method\": \"Palmitic acid treatment of T cells and Jurkat cells, RNA sequencing, PI3K/Akt and STAT5 inhibitor studies, flow cytometry of SLAMF3 expression\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — RNA-seq plus pharmacological inhibition of two pathway components, single lab\",\n      \"pmids\": [\"31332162\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"SLAMF3 in multiple myeloma cells interacts directly with adaptor proteins SHP2 and GRB2 (which also interact with each other), activating the MAPK/ERK signaling pathway to promote myeloma proliferation and drug resistance. SLAMF3 knockdown/knockout or cytoplasmic domain truncation decreases phosphorylated ERK and suppresses proliferation. Self-ligand (homophilic CD229–CD229) interaction between MM cells mediates this activation.\",\n      \"method\": \"Co-immunoprecipitation of SHP2 and GRB2 with SLAMF3, SLAMF3 KD/KO, cytoplasmic domain truncation mutant, Western blot of pERK, SHP2 inhibitor treatment, xenograft model\",\n      \"journal\": \"Molecular cancer research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP identifying two adaptor partners, KD/KO, domain truncation, pharmacological inhibition, and in vivo validation\",\n      \"pmids\": [\"31974290\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"SLAMF3 and SLAMF4 function as 'don't eat me' receptors on macrophages, inhibiting macrophage phagocytosis of hematopoietic cells through SH2-domain-containing phosphatases (SHP-1/2). These receptors inhibit 'eat me' signals including LRP1-mediated mTOR and Syk activation. SFR deficiency triggers macrophage phagocytosis of hematopoietic cells and combined deletion of SFRs and CD47 causes hematopoietic cytopenia.\",\n      \"method\": \"SFR-deficient mouse models, phagocytosis assays, LRP1/mTOR/Syk signaling analysis, combined SFR/CD47 deletion, hematopoietic graft rejection model\",\n      \"journal\": \"Science immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple genetic KO models, defined signaling mechanism (SHP-1/2, LRP1/mTOR/Syk), epistasis with CD47, in vivo hematopoietic phenotype\",\n      \"pmids\": [\"35061505\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"CD229 promotes MM cell proliferation via the RAS/ERK signaling pathway. Co-immunoprecipitation coupled with mass spectrometry identified RASAL3 as a downstream interacting protein of CD229. Intercellular tyrosine phosphorylation mediates self-activation of CD229 which activates RAS/ERK signaling through RASAL3.\",\n      \"method\": \"Co-immunoprecipitation coupled with mass spectrometry, RASAL3 interaction validation, immunofluorescence co-culture assay, RAS/ERK pathway analysis, xenograft mouse model\",\n      \"journal\": \"Aging\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP/MS for partner identification with follow-up functional validation, in vivo xenograft, single lab\",\n      \"pmids\": [\"36445333\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Loss of SLAMF3 expression corresponds to sorafenib-resistant phenotypes in HCC cells undergoing epithelial-to-mesenchymal transition (EMT). Overexpression of SLAMF3 in resistant cells reverses EMT, decreases metastatic potential, and inhibits mTOR/ERK1/2 signaling, restoring sorafenib sensitivity.\",\n      \"method\": \"Sorafenib-resistant cell line generation, flow cytometry and Western blot of SLAMF3 and EMT markers, SLAMF3 overexpression, mTOR/ERK1/2 pathway analysis, migration assay\",\n      \"journal\": \"Cancers\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — mechanistic pathway (mTOR/ERK) with EMT linkage, gain-of-function rescue, single lab\",\n      \"pmids\": [\"35205659\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"SLAMF3 co-stimulation promotes CD4+ T cell differentiation toward Th17 cells and IL-17A secretion via enrichment of RORγt and activation of the JAK1/STAT3 pathway. The drug iguratimod reverses SLAMF3-induced Th17 differentiation by inhibiting pJAK1 and pSTAT3.\",\n      \"method\": \"Anti-CD3/SLAMF3 T-cell stimulation, Th17 differentiation assay, RNA sequencing, Western blot of RORγt/pJAK1/pSTAT3, JAK1 inhibitor (iguratimod) treatment\",\n      \"journal\": \"International immunopharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — transcriptomic plus protein-level pathway validation with pharmacological rescue, single lab\",\n      \"pmids\": [\"38061117\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Autosomal recessive LY9 deficiency in humans causes selective impairment of IFN-γ production by TH1* (CCR4-CCR6+CXCR3+T-bet+RORγT+) CD4+ memory T cells, underlying susceptibility to Mycobacterium tuberculosis. Mechanistically, LY9 polarizes naïve CD4+ T cells toward memory TH1* cells by inducing T-bet via SAP and RORγT without SAP. LY9 costimulation enhances TCR-driven IFN-γ production of memory TH1* cells in a T cell-intrinsic manner via NFAT1 and RORγT.\",\n      \"method\": \"Human AR LY9-deficient patient T-cell functional assays, T-bet/SAP/RORγT pathway analysis, in vitro TH1* polarization, NFAT1 and RORγT requirement established, TCR co-stimulation assays\",\n      \"journal\": \"Science immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — human loss-of-function genetics combined with mechanistic dissection of SAP-dependent/independent signaling, multiple transcription factor requirements, T cell-intrinsic validation\",\n      \"pmids\": [\"40446017\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"A non-synonymous SNP rs509749 in exon 8 of LY9 (encoding Val/Met at position 602 in the cytoplasmic domain within the SAP/SH2D1a consensus binding site) is associated with SLE susceptibility and skews T-cell populations in Canadian SLE family members carrying the risk allele, increasing CD8+ memory T cells while decreasing CD4+ naïve and activated T cells.\",\n      \"method\": \"Family-based association study, T-cell phenotyping by flow cytometry in SLE families stratified by rs509749 genotype\",\n      \"journal\": \"Genes and immunity\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — genetic association with T-cell phenotype correlation, no direct molecular mechanism established in this paper\",\n      \"pmids\": [\"18216865\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"LY9 (CD229/SLAMF3) is a homophilic cell-surface receptor of the SLAM family that, upon tyrosine phosphorylation of its cytoplasmic tail, recruits SAP/SH2D1A (which bridges LY9 to FynT kinase and activates it), Grb2 (via Y606, controlling receptor endocytosis and attenuating TCR/ERK signaling), and the AP-2/clathrin endocytic machinery (via Y470EKL); it co-stimulates CD4+ T cells to produce IL-17 via a SAP–RORγt–JAK1/STAT3 axis, polarizes naïve CD4+ T cells to IFN-γ-producing TH1* effectors via SAP-dependent T-bet and SAP-independent RORγT induction, negatively regulates innate-like lymphocyte development (thymic innate CD8+ T cells, iNKT, marginal-zone and B1 B cells) through IL-4-dependent and IL-4-independent mechanisms, and on macrophages acts as a 'don't eat me' checkpoint through SHP-1/2-mediated inhibition of LRP1/mTOR/Syk pro-phagocytic signals, while in myeloma cells its homophilic self-ligation drives RAS/ERK/MAPK proliferative signaling via SHP2–GRB2–RASAL3 complexes.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"LY9 (CD229/SLAMF3) is a homophilic cell-surface receptor of the SLAM family that uses tyrosine phosphorylation of its cytoplasmic tail to assemble distinct signaling complexes and tune both adaptive and innate immune cell behavior [#0, #2, #3]. Its N-terminal Ig domain mediates homophilic self-adhesion through defined charged residues (E27, E29, R89) and drives receptor relocalization to the T\\u2013B immunological synapse [#2]. The phosphorylated tail recruits the adaptor SAP/SH2D1A, which in turn binds and activates FynT to couple LY9 to Src-family kinase signaling [#0, #1]; a separate phosphotyrosine (Y606) engages Grb2 to drive receptor endocytosis and to attenuate TCR-driven ERK and NFAT signaling [#3], while a Y470EKL motif binds the AP-2/clathrin adaptor to control internalization independently of SAP recruitment [#4]. As a T-cell costimulator, LY9 ligation promotes CD4+ T-cell IL-17 production through SAP-dependent recruitment of ROR\\u03b3t to the IL17A promoter and JAK1/STAT3 activation [#7, #8, #24], enhances IL-2 sensitivity and Treg differentiation via a Smad3/STAT5 axis [#15], and polarizes naive CD4+ T cells toward IFN-\\u03b3-producing TH1* memory cells by inducing T-bet via SAP and ROR\\u03b3T independently of SAP, with TCR-driven IFN-\\u03b3 requiring NFAT1 and ROR\\u03b3T [#25]. Loss-of-function studies establish LY9 as a negative regulator of innate-like lymphocyte development, restraining thymic innate CD8+ T cells, iNKT cells, and marginal-zone/B1 B cells through IL-4-dependent and IL-4-independent mechanisms, with its deficiency leading to autoantibody production [#9, #10, #13, #18]. On macrophages LY9 functions as a 'don't eat me' checkpoint, inhibiting phagocytosis of hematopoietic cells via SHP-1/2-mediated suppression of LRP1/mTOR/Syk pro-phagocytic signals [#21], and in multiple myeloma its homophilic self-ligation drives RAS/ERK proliferative signaling through SHP2\\u2013GRB2 and RASAL3 complexes [#20, #22]. Autosomal recessive LY9 deficiency in humans selectively impairs IFN-\\u03b3 production by TH1* CD4+ memory T cells, underlying susceptibility to Mycobacterium tuberculosis [#25].\",\n  \"teleology\": [\n    {\n      \"year\": 2001,\n      \"claim\": \"Established the proximal signaling logic of LY9 by showing its cytoplasmic tail recruits the adaptor SAP in a tyrosine-phosphorylation-dependent manner, defining LY9 as a SLAM-family receptor coupled to SAP-based signaling.\",\n      \"evidence\": \"Yeast two-hybrid, COS cell co-transfection, and lymphoid cell biochemistry\",\n      \"pmids\": [\"11389028\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not identify the kinase phosphorylating LY9\", \"Downstream effectors of recruited SAP not yet defined\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Resolved how LY9 surface levels are controlled by mapping a Y470EKL motif that binds the AP-2/clathrin adaptor to drive internalization separately from SAP recruitment, linking receptor signaling to receptor trafficking.\",\n      \"evidence\": \"Co-IP of AP-2, Y470 mutagenesis, and internalization assays with TCR/BCR co-ligation\",\n      \"pmids\": [\"12621057\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional consequence of endocytosis for signaling outcome not established\", \"Did not connect trafficking to a specific T-cell response\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Defined the mechanism by which SAP transduces LY9 signals, showing SAP bridges the receptor to FynT (via SH3 and kinase domains) and directly increases FynT catalytic activity, with the R78E mutant abolishing both bridging and kinase activation.\",\n      \"evidence\": \"In vitro kinase reconstitution, yeast two-hybrid/pull-down, and SAP mutant transfection in primary T cells\",\n      \"pmids\": [\"15096483\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Substrates of FynT downstream of LY9 not mapped\", \"Relative contribution of Lck versus FynT not resolved\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Demonstrated that LY9 is a homophilic ligand acting through its N-terminal Ig domain and that it relocalizes to the immunological synapse, establishing the structural basis for self-recognition between apposing cells.\",\n      \"evidence\": \"Soluble CD229-Ig binding, B-C/F-G loop point mutagenesis (E27, E29, R89), and confocal synapse imaging\",\n      \"pmids\": [\"15905546\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Affinity of the homophilic interaction not quantified\", \"How homophilic engagement triggers tail phosphorylation not shown\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Identified a second, SAP-independent signaling branch in which phospho-Y606 recruits Grb2 to drive LY9 endocytosis and to attenuate TCR-driven ERK and NFAT signaling, revealing LY9 as a negative modulator of T-cell activation.\",\n      \"evidence\": \"Reciprocal Co-IP, phosphotyrosine mapping, dominant-negative Grb2, NFAT-luciferase and endocytosis assays\",\n      \"pmids\": [\"15879090\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanistic link between Grb2 binding and ERK attenuation not fully traced\", \"Interplay between Grb2 and AP-2 trafficking pathways unresolved\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Genetic dissection in Ly9-knockout mice revealed a non-redundant role distinct from SLAM and SAP, with defective IL-4/Th2 responses and impaired T-cell proliferation but normal NKT development and viral responses.\",\n      \"evidence\": \"Ly9 KO mouse with in vitro T-cell stimulation and cytokine measurement, compared to SLAM-/- and SAP-/-\",\n      \"pmids\": [\"16365421\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular basis of the IL-4 defect not defined\", \"Single lab, phenotype not yet mechanistically connected to signaling complexes\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Antibody ligation of CD229 was shown to suppress activation markers and cytokine output, providing functional evidence that LY9 acts as an inhibitory co-receptor on T cells.\",\n      \"evidence\": \"In vitro anti-CD229 mAb stimulation with flow cytometric CD69/CD25 and cytokine readouts\",\n      \"pmids\": [\"17919264\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single method, single lab\", \"Inhibitory mechanism at the signaling level not dissected\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Mouse genetics established LY9 as a negative regulator of innate-like lymphocyte development, with IL-4 signaling placed downstream by epistasis, reframing LY9 as a brake on thymic innate CD8+ T cell and iNKT expansion.\",\n      \"evidence\": \"Ly9 KO analysis, gene expression profiling, Ly9-/-IL4ra-/- double-KO epistasis, and in vivo anti-Ly9 mAb\",\n      \"pmids\": [\"23225888\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"The receptor-proximal signal restraining innate lineages not specified\", \"IL-4-independent component not molecularly defined\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Functional costimulation studies showed LY9 co-engagement with CD3 drives IL-17 production in CD4+ T cells in a SAP-dependent manner, connecting LY9 to Th17 effector programs.\",\n      \"evidence\": \"In vitro anti-SLAMF3/SLAMF6 co-stimulation with IL-17 measurement and SAP-dependence\",\n      \"pmids\": [\"22184727\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Transcriptional mechanism not yet identified at this stage\", \"Naive versus memory contributions only partially separated\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Defined the transcriptional output of LY9 Th17 costimulation by showing recruitment of ROR\\u03b3t to the IL17A promoter cooperating with the CD28/NFAT1 pathway, attributing dominance to increased nuclear ROR\\u03b3t.\",\n      \"evidence\": \"ChIP of NFAT1 and ROR\\u03b3t at IL17A promoter, nuclear fractionation, and T-cell costimulation\",\n      \"pmids\": [\"22989874\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Upstream signal driving ROR\\u03b3t nuclear accumulation not mapped\", \"Single lab\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Extended the inhibitory-receptor model to autoimmunity by showing Ly9 deficiency yields spontaneous anti-nuclear autoantibodies and Tfh/GC expansion, with LY9 suppressing CD4+ IFN-\\u03b3 production.\",\n      \"evidence\": \"Ly9 KO phenotyping (ANA, anti-dsDNA), Tfh/GC flow cytometry on two backgrounds, in vitro cytokine assay\",\n      \"pmids\": [\"23914190\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Causal link between IFN-\\u03b3 suppression and autoantibody formation not established\", \"Cell-intrinsic versus extrinsic effects not separated\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"B-cell-focused genetics revealed LY9 restrains marginal-zone, B1a, and transitional B cell compartments and natural antibody output, with in vivo mAb targeting selectively depleting these subsets Fc-independently.\",\n      \"evidence\": \"Ly9 KO phenotyping, in vivo anti-Ly9 mAb, TNP-Ficoll immunization, serum antibody measurement\",\n      \"pmids\": [\"26667173\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Signaling pathway controlling B-cell subset homeostasis not defined\", \"CD19/CD21/CD81 downregulation mechanism unknown\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Linked an SLE-associated coding variant to receptor function by showing the Met602 allele binds SAP with ~2-fold higher affinity than Val602, while Val602 shows higher surface expression and diminished activation, providing a molecular handle on disease association.\",\n      \"evidence\": \"Binding affinity measurement and T-cell line expression/CD69 activation assays\",\n      \"pmids\": [\"26221972\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"In vivo consequence of altered SAP affinity not demonstrated\", \"Single lab, single cell system\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Established additional positive-costimulatory branches in which LY9 promotes IL-2 sensitivity and Treg differentiation via a Smad3-dependent CD25/STAT5 mechanism, broadening its role beyond inhibition.\",\n      \"evidence\": \"In vitro T-cell stimulation, Smad3 inhibition, STAT5 phosphorylation, and Treg differentiation assays\",\n      \"pmids\": [\"27482100\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"How a single receptor produces both inhibitory and costimulatory outcomes not reconciled\", \"Smad3 activation mechanism downstream of LY9 unclear\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Opened a tumor-suppressor role for LY9 in hepatocellular carcinoma, showing SLAMF3 restoration inhibits proliferation/migration and reduces ERK/JNK/mTOR phosphorylation.\",\n      \"evidence\": \"siRNA KD/OE in HCC lines, proliferation/apoptosis/migration assays, xenograft, and pathway Western blots\",\n      \"pmids\": [\"24376606\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Receptor-proximal mechanism in hepatocytes not defined\", \"Why LY9 is tumor-suppressive in HCC but proliferative in myeloma unexplained\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Detailed the antiproliferative HCC mechanism by linking SLAMF3 to RB hypophosphorylation, E2F inactivation, and PLK1 repression, with patient-sample correlation supporting the axis.\",\n      \"evidence\": \"RB phosphorylation/E2F/PLK1 analysis with SLAMF3 overexpression and patient correlation\",\n      \"pmids\": [\"26799423\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Connection between surface receptor and RB/E2F not mechanistically bridged\", \"Single lab\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Identified a chemosensitization function in which SLAMF3 specifically lowers MRP-1 drug-efflux transporter expression, inversely correlated in patient samples.\",\n      \"evidence\": \"MRP-1 expression/function and drug sensitivity assays in SLAMF3-overexpressing HCC cells with IHC correlation\",\n      \"pmids\": [\"27081035\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism linking SLAMF3 to MRP-1 regulation unknown\", \"Specificity over other transporters not mechanistically explained\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Revealed a pathogen-exploited function by showing SLAMF3's first extracellular domain binds HCV envelope E2 to facilitate hepatocyte entry.\",\n      \"evidence\": \"siRNA KD, OE, blocking antibody, domain peptide competition, recombinant E2 binding, and HCV infectivity assays\",\n      \"pmids\": [\"24927415\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether LY9 is an obligate entry factor or accessory not resolved\", \"Structural basis of the E2 interaction not determined\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Refined the innate-lymphocyte role by showing LY9 negatively regulates iNKT lineage choice, restraining NKT2 expansion and enabling NKT1 development.\",\n      \"evidence\": \"Ly9 KO on two backgrounds, iNKT subset flow cytometry, and in vivo agonistic anti-Ly9 mAb with cytokine readouts\",\n      \"pmids\": [\"28980301\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Signal controlling NKT1/NKT2 balance not molecularly defined\", \"Cell-intrinsic versus thymic-niche effects not separated\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Identified a regulatory input controlling LY9 expression, showing palmitic acid induces SLAMF3 upregulation through STAT5-PI3K/Akt signaling on T cells.\",\n      \"evidence\": \"Palmitic acid treatment, RNA-seq, and PI3K/Akt and STAT5 inhibitor studies\",\n      \"pmids\": [\"31332162\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional consequence of metabolite-driven upregulation for immunity not tested\", \"Direct transcriptional control of LY9 not mapped\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Established the oncogenic signaling mechanism in multiple myeloma, showing SLAMF3 homophilic self-ligation recruits SHP2 and GRB2 to activate MAPK/ERK and drive proliferation and drug resistance.\",\n      \"evidence\": \"Reciprocal Co-IP of SHP2/GRB2, KD/KO, cytoplasmic truncation, pERK Western, SHP2 inhibitor, and xenograft\",\n      \"pmids\": [\"31974290\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How identical homophilic ligation produces opposite outcomes in T cells versus myeloma not resolved\", \"Order of SHP2/GRB2 assembly on the tail not defined\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Expanded the myeloma RAS/ERK mechanism by identifying RASAL3 as a CD229 interactor through which intercellular tyrosine phosphorylation self-activates the receptor.\",\n      \"evidence\": \"Co-IP/mass spectrometry, RASAL3 validation, co-culture immunofluorescence, RAS/ERK analysis, and xenograft\",\n      \"pmids\": [\"36445333\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct biochemical role of RASAL3 in ERK activation not fully resolved\", \"Single lab\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Defined LY9 as a macrophage 'don't eat me' checkpoint, inhibiting phagocytosis of hematopoietic cells via SHP-1/2-mediated suppression of LRP1/mTOR/Syk, with epistasis to CD47.\",\n      \"evidence\": \"SFR-deficient mouse models, phagocytosis assays, LRP1/mTOR/Syk signaling analysis, and combined SFR/CD47 deletion\",\n      \"pmids\": [\"35061505\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Individual contribution of LY9 versus SLAMF4 to the macrophage checkpoint not isolated\", \"Ligand triggering the inhibitory signal on macrophages not defined\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Connected LY9 loss to therapy resistance in HCC, showing SLAMF3 reverses EMT and restores sorafenib sensitivity through mTOR/ERK1/2 inhibition.\",\n      \"evidence\": \"Sorafenib-resistant lines, SLAMF3 overexpression rescue, EMT marker and mTOR/ERK analysis, migration assay\",\n      \"pmids\": [\"35205659\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Receptor-proximal events upstream of mTOR/ERK in hepatocytes still unknown\", \"Single lab\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Human loss-of-function genetics established LY9 as essential for IFN-\\u03b3 production by TH1* CD4+ memory T cells and anti-mycobacterial immunity, integrating SAP-dependent T-bet induction and SAP-independent ROR\\u03b3T/NFAT1 signaling into a coherent costimulatory mechanism.\",\n      \"evidence\": \"Human AR LY9-deficient patient T-cell assays, T-bet/SAP/ROR\\u03b3T pathway dissection, TH1* polarization, and NFAT1/ROR\\u03b3T requirement\",\n      \"pmids\": [\"40446017\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full reconciliation of inhibitory mouse phenotypes with costimulatory human role not complete\", \"Why TH1* memory cells are selectively dependent on LY9 not fully explained\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"It remains unresolved how a single homophilic receptor produces opposite outcomes across contexts \\u2014 inhibitory on T cells and macrophages, tumor-suppressive in HCC, yet proliferative in myeloma \\u2014 i.e. what dictates assembly of SAP/FynT versus Grb2 versus SHP1/2/SHP2-GRB2-RASAL3 complexes on the same cytoplasmic tail.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unifying structural model of context-dependent adaptor selection\", \"Stoichiometry and competition among SAP, Grb2, AP-2, and SHP1/2 on the tail not defined\", \"Determinants of cell-type-specific output unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0098631\", \"supporting_discovery_ids\": [2]},\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [0, 3, 6, 25]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [3, 21]},\n      {\"term_id\": \"GO:0001618\", \"supporting_discovery_ids\": [12]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [2, 3, 4]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [7, 21, 25]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [3, 20, 25]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [9, 13, 18]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"SH2D1A\", \"FYN\", \"GRB2\", \"SHP2\", \"RASAL3\", \"AP-2\", \"LY9\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":7,"faith_pct":100.0}}