{"gene":"SH2D1A","run_date":"2026-06-10T07:46:31","timeline":{"discoveries":[{"year":1999,"finding":"Crystal structures of SAP/SH2D1A reveal that its single SH2 domain binds both phosphorylated and non-phosphorylated SLAM peptides by engaging residues N-terminal to the tyrosine (in addition to C-terminal residues), defining a phosphotyrosine-independent, extended 'three-pronged' binding mode distinct from canonical SH2 domains. The consensus binding motif was identified as TIpYXX(V/I). XLP patient mutations that disrupt these extended interactions abolish SAP function.","method":"X-ray crystallography, phosphopeptide library screen, XLP mutation analysis","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structures with functional validation by peptide library screen and disease-mutation analysis, replicated by NMR studies in same year","pmids":["10549287"],"is_preprint":false},{"year":1999,"finding":"NMR studies of 15N/13C-labeled SAP complexed with SLAM peptides confirm that the SAP SH2 domain binds phosphorylated and non-phosphorylated SLAM peptides with comparable affinity (Kd ~150 nM pTyr, ~330 nM Tyr), recognizing both N-terminal and C-terminal sequences relative to the tyrosine residue ('three-pronged' mechanism).","method":"NMR spectroscopy, peptide binding affinity measurements","journal":"Current biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — NMR structural analysis with quantitative binding data, orthogonal to crystallography study","pmids":["10607564"],"is_preprint":false},{"year":2002,"finding":"NMR structure of SAP/SH2D1A complexed with two distinct peptides confirms the 'three-pronged' binding mechanism; the SAP SH2 domain contains a consensus binding motif T/S-x-x-x-x-V/I lacking Tyr or pTyr, and disease-causing SAP mutants show binding defects that explain their pathogenicity. Hydrogen exchange studies reveal considerable flexibility in the SH2 domain.","method":"NMR spectroscopy, synthetic peptide screening, hydrogen exchange","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1 / Strong — NMR structures of two independent complexes with functional validation of disease mutants","pmids":["11823424"],"is_preprint":false},{"year":2001,"finding":"SAP/SH2D1A regulates the association of CD150 (SLAM) with either SHIP or SHP-2: in SH2D1A-expressing B cells CD150 coprecipitates with SH2D1A and SHIP, whereas in SH2D1A-negative cells CD150 associates only with SHP-2. GST-fusion pulldowns show that phosphorylated Y281 and Y327 in the CD150 cytoplasmic tail are essential for SHP-2 and SHIP binding, and SH2D1A facilitates SHIP recruitment to CD150, acting as a switch between these two phosphatases.","method":"Co-immunoprecipitation, GST-fusion pulldown with tyrosine mutants","journal":"Journal of immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal co-IP and mutagenesis in a single lab with two orthogonal methods","pmids":["11313386"],"is_preprint":false},{"year":2001,"finding":"NTB-A, a novel SLAM-family glycoprotein on NK/T/B cells, undergoes tyrosine phosphorylation and associates with SAP/SH2D1A as well as SHP phosphatases. In XLP NK cells lacking SH2D1A, NTB-A mediates inhibitory rather than activating signals, contributing to the inability to kill EBV-infected B cells. Masking both NTB-A and 2B4 simultaneously maximally restores cytotoxicity in XLP-NK cells.","method":"Co-immunoprecipitation, mAb masking experiments, cytotoxicity assays with XLP patient NK cells","journal":"The Journal of experimental medicine","confidence":"High","confidence_rationale":"Tier 2 / Strong — co-IP plus functional NK cytotoxicity rescue experiments with patient cells, multiple orthogonal methods","pmids":["11489943"],"is_preprint":false},{"year":2002,"finding":"SAP functions dually in SLAM signaling: (1) it competitively inhibits SHP-2 and SHIP binding to SLAM family receptors, and (2) it acts as an adaptor recruiting FynT kinase to SLAM via a direct interaction between the SAP SH2 domain surface and the FynT SH3 domain. FynT is required for SLAM tyrosine phosphorylation, which is dramatically enhanced by SAP. Disease-causing SAP mutants show reduced affinity for both FynT and SLAM.","method":"In vitro and in vivo binding assays, peptide array, cell transfection, co-immunoprecipitation, mutagenesis","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — multiple orthogonal methods (peptide arrays, in vitro binding, cellular co-IP, mutagenesis), dual functional mechanism established","pmids":["12458214"],"is_preprint":false},{"year":2001,"finding":"Analysis of 10 XLP missense mutations in SH2D1A reveals two mechanistic classes: (i) mutations causing markedly decreased protein half-life (Y7C, S28R, Q99P, P101L, V102G, X129R), and (ii) mutations causing structural changes that differentially affect binding to SLAM, 2B4, CD84, and CD229. Mutation T68I disrupts the hydrophobic cleft interaction with Val+3 of the binding motif, C42W disrupts the phosphotyrosine-binding pocket, and T53I specifically impairs non-phosphotyrosine interactions while preserving phosphorylated CD150 binding.","method":"In vitro binding assays, protein half-life measurement, site-directed mutagenesis, co-immunoprecipitation","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — systematic mutagenesis of 10 disease-causing mutations with multiple functional readouts in a single rigorous study","pmids":["11477068"],"is_preprint":false},{"year":2001,"finding":"SAP-deficient mice (Sh2d1a−/−) display normal lymphocyte development but, upon infection with LCMV or Toxoplasma gondii, show increased T cell activation, elevated IFN-γ production, reduced Ig-secreting cells, and decreased IL-4. Anti-CD3-stimulated splenocytes from uninfected SAP− mice produce increased IFN-γ and decreased IL-4 (Th1 skewing), with decreased serum IgE in vivo, indicating SAP controls cytokine balance downstream of T cell activation.","method":"Targeted gene knockout mouse model, cytokine measurement, infection challenge","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean KO mouse with defined cellular phenotype, multiple infection models","pmids":["11404475"],"is_preprint":false},{"year":2005,"finding":"SAP encoded by SH2D1A is essential for NKT cell development: Sh2d1a−/− mice completely lack NKT cells in thymus and periphery. The defect is hematopoietic cell-autonomous and can be rescued by reconstituting SAP expression in Sh2d1a−/− bone marrow. Seventeen XLP patients with germline SH2D1A mutations also lacked NKT cells, and female XLP carriers show completely skewed X-chromosome inactivation in NKT cells but not T or B cells.","method":"Knockout mouse phenotyping, bone marrow reconstitution, alpha-galactosylceramide stimulation, X-chromosome inactivation analysis in human carriers","journal":"Nature medicine","confidence":"High","confidence_rationale":"Tier 2 / Strong — KO mouse plus bone marrow rescue plus human patient validation, replicated mechanistic finding across species","pmids":["15711562"],"is_preprint":false},{"year":2004,"finding":"SH2D1A is required for T-dependent humoral immune responses and germinal center formation. SH2D1A−/− mice are protected from experimental lupus (hypergammaglobulinemia, autoantibodies, renal disease) specifically because of defective germinal center formation and impaired T-dependent antigen-specific IgG responses, while T-independent responses remain normal.","method":"KO mouse model, immunization, germinal center analysis, autoimmune disease model (lupus), EAE model","journal":"The Journal of experimental medicine","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean KO with multiple defined phenotypic readouts and epistasis using T-independent vs T-dependent antigen responses","pmids":["15263031"],"is_preprint":false},{"year":2005,"finding":"SH2D1A is required in both T cells and B cells for productive humoral immune responses. Adoptive cotransfer experiments show that SH2D1A−/− B cells are intrinsically defective in contributing to antigen-specific IgG production even when paired with wild-type CD4+ T cells, indicating a B cell-autonomous signaling role for SH2D1A. Germinal centers are absent in SH2D1A−/− mice after primary immunization.","method":"Adoptive cotransfer into irradiated or Rag2−/− hosts, immunization, germinal center analysis","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Strong — adoptive transfer epistasis experiment isolating B-cell-intrinsic defect, multiple recipient models","pmids":["15774582"],"is_preprint":false},{"year":2002,"finding":"SAP association with 2B4 (CD244) in NK cells requires PI3K activity: ligation of 2B4 leads to 2B4 phosphorylation, SAP recruitment, and association of PI3K p85 subunit. Pharmacological inhibition of PI3K (wortmannin or LY294002) prevents SAP recruitment to 2B4 without disrupting PI3K-p85 association with 2B4, and abolishes NK cytotoxicity in normal but not XLP NK cells.","method":"Co-immunoprecipitation, pharmacological inhibition, NK cytotoxicity assay with patient cells","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — co-IP plus functional cytotoxicity assay, single lab, two methods","pmids":["11815622"],"is_preprint":false},{"year":2004,"finding":"SH2D1A regulates CD150-mediated Akt signaling in B cells: using DT40 sublines deficient in specific signaling molecules, CD150-mediated Akt phosphorylation requires Syk and SH2D1A, is negatively regulated by Lyn and Btk, and is SHIP-independent. CD150-mediated ERK pathway activation requires SHIP but not SH2D1A.","method":"DT40 gene-deficient B cell sublines, CD150 ligation, Akt and ERK phosphorylation assays","journal":"Blood","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic epistasis in defined DT40 knockout sublines, single lab","pmids":["15315965"],"is_preprint":false},{"year":2000,"finding":"SH2D1A associates with Dok1 (p62dok) via its SH2 domain in a manner dependent on phosphorylation of Dok1 Y449 (in the sequence ALYSQVQK). An XLP-associated SH2 domain mutant fails to associate with Dok1. Overexpression of SH2D1A activates NF-κB in 293T cells via a pathway dependent on IκB kinase β but independent of the wild-type SH2 domain.","method":"Co-immunoprecipitation, site-directed mutagenesis, NF-κB reporter assay, dominant-negative kinase","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — co-IP plus phospho-mutant plus reporter assay, single lab","pmids":["10852966"],"is_preprint":false},{"year":2008,"finding":"SAP interacts with SH3 domains of Fyn and NCK1 via a surface on the SAP SH2 domain distinct from the phosphotyrosine-binding surface. NMR shows NCK1 and Fyn SH3 domains engage the same SAP residues with comparable affinities. SAP knockdown reduces NCK1 tyrosine phosphorylation and phosphorylation of downstream TCR signaling proteins LAT and SLP-76. SAP regulates T cell proliferation through ERK/MAP kinase.","method":"NMR analysis of SAP–SH3 interactions, siRNA knockdown, phosphorylation assays, T cell proliferation assay","journal":"Cellular signalling","confidence":"Medium","confidence_rationale":"Tier 1–2 / Moderate — NMR structural data plus cellular knockdown with defined downstream readouts, single lab","pmids":["18951976"],"is_preprint":false},{"year":2006,"finding":"SAP-deficient T cells exhibit impaired TCR restimulation-induced cell death (RICD) due to diminished TCR-induced inhibition of diacylglycerol kinase α (DGKα), leading to increased diacylglycerol metabolism and decreased Ras and PKCθ signaling. Pharmacological inhibition of DGKα in SAP-deficient T cells restores diacylglycerol signaling at the immune synapse and rescues RICD via induction of pro-apoptotic proteins NUR77 and NOR1. DGKα inhibition prevents excessive CD8+ T cell expansion and IFN-γ production in SAP-deficient mice after LCMV infection.","method":"SAP-KO mouse LCMV infection model, RICD assay, diacylglycerol signaling measurements, pharmacological DGKα inhibition, NUR77/NOR1 induction","journal":"Science translational medicine","confidence":"High","confidence_rationale":"Tier 2 / Strong — KO mouse model plus primary patient T cells plus pharmacological rescue, multiple orthogonal methods defining signaling pathway","pmids":["26764158"],"is_preprint":false},{"year":2011,"finding":"SAP expression in CD8+ T cells is specifically required for their response to antigen presented by B cells but not other antigen-presenting cells. In female XLP carriers with mixed SAP+/SAP− cells, EBV-specific memory CD8+ T cells are exclusively SAP+, while CMV- and influenza-specific cells distribute equally. Blocking SLAM receptors NTB-A and 2B4 overcomes the inability of SAP− CD8+ T cells to respond to B cell antigen presentation; ectopic NTB-A expression on fibroblasts inhibits SAP− CD8+ T cell cytotoxicity, demonstrating that SLAM receptors acquire inhibitory function in the absence of SAP.","method":"Analysis of female XLP carrier cells (natural mixed chimerism), antigen-specific T cell response assays, receptor blocking antibodies, ectopic NTB-A expression on fibroblasts","journal":"PLoS biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — unique human natural experiment (carrier cells as mixed chimera) plus mechanistic rescue/inhibition experiments","pmids":["22069374"],"is_preprint":false},{"year":2004,"finding":"SH2D1A gene expression is controlled by a combination of transcriptional and post-transcriptional mechanisms: a 22–33 bp basal promoter element containing an Ets consensus site is required for transcription, with Ets-1 and Ets-2 binding confirmed by gel mobility supershift and dominant-negative overexpression. SH2D1A mRNA decays rapidly in T cells, and its 3' UTR has RNA-destabilizing activity dependent on a balance between AUF1 and HuR binding.","method":"Reporter assays, gel mobility shift/supershift assays, dominant-negative Ets overexpression, RNA decay assays, RNA-gel mobility shift","journal":"European journal of immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reporter assays plus protein binding assays plus mRNA stability analysis, single lab, multiple methods","pmids":["15459902"],"is_preprint":false},{"year":2006,"finding":"SAP deficiency causes profound germinal center defects and hypogammaglobulinemia during chronic LCMV infection in mice. Depletion of SAP-deficient CD8+ T cells blocks the immunopathology and clinical illness, providing the first direct demonstration that SAP-deficient CD8+ T cells are the primary cause of immunopathology in an XLP model.","method":"SAP-KO mouse chronic LCMV infection, CD8+ T cell depletion, germinal center analysis, viral load measurement","journal":"Blood","confidence":"High","confidence_rationale":"Tier 2 / Strong — KO mouse plus CD8 depletion epistasis, multiple immunological readouts","pmids":["16788096"],"is_preprint":false},{"year":2003,"finding":"Differential DNA methylation of CpG-rich regions in the 5' region and exon 1 of SH2D1A correlates with cell lineage-specific transcription: T and NK cells (which express SH2D1A) show hypomethylation, while B cells and granulocytes (which do not express it) show hypermethylation.","method":"Bisulfite sequencing, methylation-sensitive restriction enzyme digestion","journal":"Immunogenetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — two orthogonal methylation methods correlating epigenetic state with expression, single lab","pmids":["12709835"],"is_preprint":false},{"year":2006,"finding":"Four XLP missense mutations (Y54C, I84T, F87S) and a frameshift insertion (fs82→X103) each dramatically reduce SAP protein half-life. The I84T mutation does not prevent SAP binding to SLAM, CD84, or 2B4 but reduces downstream SLAM signaling, demonstrating that impaired signal transduction can be mechanistically separable from impaired receptor binding.","method":"Protein half-life measurement, co-immunoprecipitation binding assays, downstream signaling assays in primary lymphocytes and transfected cell lines","journal":"International immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — systematic analysis in patient cells and transfectants, single lab, multiple methods","pmids":["16720617"],"is_preprint":false},{"year":2005,"finding":"A new XLP disease-causing SAP missense mutation (p.G16D) results in a protein with normal half-life but defective binding to SLAM and 2B4 ligands, as demonstrated by expressing the mutant cDNA in COS cells and testing binding to physiological ligands.","method":"Site-directed mutagenesis, COS cell expression, co-immunoprecipitation binding assay","journal":"Human mutation","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — mutagenesis plus functional binding assay, single lab","pmids":["15841490"],"is_preprint":false},{"year":2013,"finding":"A new murine SAP isoform (SAP-2) arising from a cryptic exon contains 18 additional amino acids inserted into the phosphotyrosine-binding structural region of the SH2 domain. Functional analysis in vitro shows SAP-2 is non-functional due to decreased protein stability, suggesting cells could modulate SAP-mediated activity by regulating isoform ratios.","method":"RT-PCR isoform identification, protein stability assay, in vitro functional analysis","journal":"Science China. Life sciences","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, partial mechanistic follow-up with limited functional assays","pmids":["24369347"],"is_preprint":false},{"year":2019,"finding":"A novel SH2D1A variant (c.49G>A, p.E17K) results in a SAP protein with normal expression levels but >95% reduction in binding to phosphorylated CD244 (2B4), demonstrating that loss of receptor binding, rather than protein instability, can be the sole mechanistic defect in some XLP mutations.","method":"Flow cytometry (SAP protein expression), biochemical binding assay to phosphorylated CD244","journal":"Pediatric blood & cancer","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — quantitative binding assay plus protein expression, single lab, two orthogonal methods","pmids":["31994322"],"is_preprint":false}],"current_model":"SH2D1A encodes SAP, a single SH2 domain adaptor protein expressed in T cells and NK cells that binds SLAM-family receptors (SLAM/CD150, 2B4/CD244, NTB-A, CD84, Ly9/CD229) via a unique 'three-pronged' phosphotyrosine-independent mechanism recognizing the TxYxx(V/I) motif; SAP functions dually as a competitive inhibitor of SHP-2/SHIP recruitment to these receptors and as an adaptor recruiting FynT kinase (via SH3 domain interaction) to promote receptor phosphorylation and downstream signaling, while in its absence SLAM-family receptors default to inhibitory signaling; SAP is required for NKT cell development, germinal center formation and T-dependent humoral immunity, and restrains CD8+ T cell-mediated immunopathology by promoting RICD through DGKα inhibition and diacylglycerol/Ras/PKCθ signaling at the immune synapse."},"narrative":{"mechanistic_narrative":"SH2D1A encodes SAP, a single-SH2-domain adaptor that transduces signaling from SLAM-family receptors and is the gene mutated in X-linked lymphoproliferative disease (XLP), where missense mutations disrupt either protein stability or receptor binding [PMID:10549287, PMID:11477068, PMID:16720617]. Structurally, the SAP SH2 domain recognizes its targets through an unusual phosphotyrosine-independent 'three-pronged' mode, engaging both N-terminal and C-terminal residues flanking the tyrosine and binding phosphorylated and non-phosphorylated SLAM peptides with comparable affinity around a T/S-x-x-x-x-V/I consensus motif [PMID:10549287, PMID:10607564, PMID:11823424]. SAP acts dually at SLAM-family receptors (SLAM/CD150, 2B4/CD244, NTB-A, CD84, CD229): it competitively displaces the inhibitory phosphatases SHP-2 and SHIP from the receptor cytoplasmic tail, and it uses a second surface on its SH2 domain to recruit the FynT kinase SH3 domain, driving receptor tyrosine phosphorylation and activating signaling [PMID:11313386, PMID:11489943, PMID:12458214, PMID:18951976]. In the absence of SAP, these receptors default to inhibitory output, explaining the failure of XLP NK and CD8+ T cells to kill EBV-infected B cells and to respond to B-cell antigen presentation [PMID:11489943, PMID:22069374]. Through SLAM signaling SAP is required for NKT cell development, T-dependent humoral immunity and germinal center formation, with both a T-cell and a B-cell-intrinsic requirement [PMID:15711562, PMID:15263031, PMID:15774582], and it controls cytokine balance and restrains CD8+ T-cell-driven immunopathology, in part by promoting restimulation-induced cell death (RICD) via inhibition of diacylglycerol kinase α and consequent diacylglycerol/Ras/PKCθ signaling at the immune synapse [PMID:11404475, PMID:26764158, PMID:16788096]. SH2D1A expression is restricted to T and NK cells by lineage-specific promoter CpG demethylation, Ets-dependent transcription, and 3'UTR-mediated mRNA destabilization [PMID:15459902, PMID:12709835].","teleology":[{"year":1999,"claim":"Structural studies answered how a single SH2 domain recognizes SLAM despite weak dependence on tyrosine phosphorylation, defining the unique 'three-pronged' binding mode that distinguishes SAP from canonical SH2 adaptors.","evidence":"X-ray crystallography and NMR of SAP–SLAM peptide complexes with phosphopeptide library screening and XLP mutation analysis","pmids":["10549287","10607564"],"confidence":"High","gaps":["Did not establish the in vivo signaling consequence of phosphotyrosine-independent binding","Receptor partners beyond SLAM not structurally tested at this stage"]},{"year":2002,"claim":"A second NMR study generalized the three-pronged mechanism across distinct peptides and tied disease-causing mutants to specific binding defects, consolidating the structural basis for XLP pathogenicity.","evidence":"NMR of two SAP–peptide complexes, synthetic peptide screening, hydrogen exchange","pmids":["11823424"],"confidence":"High","gaps":["SH2 domain flexibility not linked to a functional regulatory mechanism"]},{"year":2001,"claim":"Co-IP and mutagenesis on CD150 showed SAP acts as a switch between phosphatase partners, redirecting the receptor from SHP-2 to SHIP and thereby altering signaling output.","evidence":"Reciprocal co-immunoprecipitation and GST-fusion pulldown with tyrosine mutants in B cells","pmids":["11313386"],"confidence":"Medium","gaps":["Single-lab data","Functional consequence of the SHIP/SHP-2 switch on cell behavior not directly measured here"]},{"year":2001,"claim":"Identification of NTB-A as a SAP-associated SLAM-family receptor demonstrated that loss of SAP converts an activating receptor to an inhibitory one, explaining the NK cytotoxicity defect against EBV-infected targets in XLP.","evidence":"Co-IP, mAb masking and cytotoxicity assays with XLP patient NK cells","pmids":["11489943"],"confidence":"High","gaps":["Mechanism by which SAP loss flips receptor polarity not molecularly defined here"]},{"year":2002,"claim":"The dual-function model was established: SAP both blocks inhibitory phosphatases and actively recruits FynT to drive SLAM phosphorylation, unifying its competitive and adaptor roles.","evidence":"Peptide arrays, in vitro and cellular binding assays, co-IP and mutagenesis","pmids":["12458214"],"confidence":"High","gaps":["Relative contribution of phosphatase exclusion vs FynT recruitment in vivo not quantified"]},{"year":2002,"claim":"SAP recruitment to 2B4 was shown to require PI3K activity, adding an upstream regulatory input to SAP-dependent NK signaling.","evidence":"Co-IP, pharmacological PI3K inhibition, NK cytotoxicity with patient cells","pmids":["11815622"],"confidence":"Medium","gaps":["Single-lab finding","Molecular link between PI3K product and SAP recruitment unresolved"]},{"year":2001,"claim":"Systematic analysis of XLP mutations resolved two mechanistic classes—destabilizing versus binding-disrupting—providing a genotype-to-mechanism framework for the disease.","evidence":"Site-directed mutagenesis, protein half-life measurement, co-IP across SLAM/2B4/CD84/CD229","pmids":["11477068"],"confidence":"High","gaps":["Did not connect each class to distinct clinical phenotypes"]},{"year":2001,"claim":"The first SAP knockout mouse showed normal lymphocyte development but dysregulated cytokine output (Th1 skewing, reduced IL-4/IgE) after infection, placing SAP downstream of T-cell activation in immune regulation.","evidence":"Sh2d1a-/- mice with LCMV/Toxoplasma challenge and cytokine measurement","pmids":["11404475"],"confidence":"High","gaps":["Receptor-level mechanism linking SAP to cytokine balance not defined in this model"]},{"year":2004,"claim":"SAP was shown to be required for germinal center formation and T-dependent IgG responses, mechanistically explaining the humoral immunodeficiency of XLP and protection from a lupus model.","evidence":"KO mouse immunization, germinal center analysis, lupus/EAE models with T-independent controls","pmids":["15263031"],"confidence":"High","gaps":["Did not assign the defect to a specific cell lineage"]},{"year":2005,"claim":"Adoptive cotransfer revealed a B-cell-intrinsic requirement for SAP in humoral responses, refining the view that SAP acts only in T cells.","evidence":"Cotransfer of SH2D1A-/- B cells with WT T cells into irradiated/Rag2-/- hosts","pmids":["15774582"],"confidence":"High","gaps":["The B-cell SLAM-receptor circuit responsible was not molecularly identified"]},{"year":2005,"claim":"SAP was established as essential and cell-autonomous for NKT cell development, confirmed by bone marrow rescue in mice and skewed X-inactivation in human carriers.","evidence":"KO phenotyping, BM reconstitution, α-GalCer stimulation, X-inactivation analysis in XLP carriers","pmids":["15711562"],"confidence":"High","gaps":["Developmental signaling step at which SAP acts in NKT lineage not pinpointed"]},{"year":2004,"claim":"Genetic epistasis in DT40 sublines separated SAP-dependent CD150-Akt signaling (Syk-dependent, SHIP-independent) from SAP-independent ERK signaling, mapping branch points downstream of the receptor.","evidence":"CD150 ligation in gene-deficient DT40 B-cell sublines with Akt/ERK phospho-readouts","pmids":["15315965"],"confidence":"Medium","gaps":["Single-lab chicken cell system","Relevance to primary human B cells not confirmed"]},{"year":2000,"claim":"Early co-IP work proposed SAP partners beyond SLAM (Dok1) and an NF-κB activation activity, expanding candidate downstream pathways.","evidence":"Co-IP with phospho-Dok1, mutagenesis, NF-κB reporter with dominant-negative IKKβ","pmids":["10852966"],"confidence":"Medium","gaps":["Single-lab data not integrated with the dominant SLAM-receptor model","NF-κB activity was SH2-domain-independent and physiological relevance unclear"]},{"year":2003,"claim":"Lineage-restricted expression of SH2D1A was tied to differential CpG methylation, providing an epigenetic basis for its T/NK-cell-specific function.","evidence":"Bisulfite sequencing and methylation-sensitive digestion across expressing vs non-expressing lineages","pmids":["12709835"],"confidence":"Medium","gaps":["Causality of methylation vs transcription not established by perturbation"]},{"year":2004,"claim":"SH2D1A expression was shown to be jointly controlled by Ets-dependent transcription and AUF1/HuR-balanced mRNA stability, defining its regulatory logic.","evidence":"Reporter assays, gel supershift, dominant-negative Ets, RNA decay and RNA-gel shift assays","pmids":["15459902"],"confidence":"Medium","gaps":["Single-lab data","Signals tuning AUF1/HuR balance in activated T cells unknown"]},{"year":2006,"claim":"CD8+ T-cell depletion in chronic LCMV infection demonstrated that SAP-deficient CD8+ T cells are the direct cause of XLP-like immunopathology, linking SAP loss to disease mechanism in vivo.","evidence":"SAP-KO chronic LCMV infection with CD8 depletion, germinal center and viral load readouts","pmids":["16788096"],"confidence":"High","gaps":["Did not yet define the cell-intrinsic signaling lesion driving pathogenic CD8 expansion"]},{"year":2006,"claim":"The RICD pathway was defined: SAP normally inhibits DGKα to sustain diacylglycerol/Ras/PKCθ signaling and NUR77/NOR1-driven apoptosis, and DGKα inhibition rescues RICD and curbs CD8 immunopathology, providing a mechanistic and therapeutic axis.","evidence":"SAP-KO LCMV model and patient T cells, RICD and DAG signaling assays, pharmacological DGKα inhibition","pmids":["26764158"],"confidence":"High","gaps":["Molecular link from SAP to DGKα inhibition not fully resolved","Translation to human therapy not established"]},{"year":2008,"claim":"SAP was shown to engage NCK1 as well as Fyn SH3 domains through the same SH2 surface and to support LAT/SLP-76 phosphorylation, broadening the kinase/adaptor network it nucleates at the TCR.","evidence":"NMR of SAP–SH3 interactions, siRNA knockdown, phospho-assays, T-cell proliferation","pmids":["18951976"],"confidence":"Medium","gaps":["Single-lab data","Relative in vivo importance of NCK1 vs Fyn recruitment unclear"]},{"year":2011,"claim":"Human carrier mixed-chimerism experiments demonstrated SAP is specifically required for CD8+ T-cell responses to B-cell antigen presentation, and that NTB-A/2B4 acquire inhibitory function without SAP, explaining the selective EBV vulnerability of XLP.","evidence":"Female XLP carrier mixed cells, antigen-specific response assays, receptor blocking and ectopic NTB-A expression","pmids":["22069374"],"confidence":"High","gaps":["Why B-cell APCs specifically depend on SAP signaling not fully resolved"]},{"year":2019,"claim":"Continued XLP mutation analysis (e.g. E17K, G16D) reinforced that selective loss of receptor binding with preserved protein stability is sufficient to cause disease, separating binding from stability defects.","evidence":"Mutant expression with quantitative binding assays to phosphorylated CD244 and SLAM/2B4","pmids":["31994322","15841490","16720617"],"confidence":"Medium","gaps":["Genotype-phenotype severity correlations not established","In vivo signaling consequences of partial binding loss untested"]},{"year":null,"claim":"How SAP biochemically inhibits DGKα and how SLAM-family receptors are reprogrammed from activating to inhibitory output in SAP's absence remain mechanistically unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No defined molecular intermediary between SAP and DGKα","Structural basis of inhibitory phosphatase default not determined","Isoform-based regulation (SAP-2) lacks functional in vivo evidence"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[3,5,14]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[3,5]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[5,16]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[5]}],"pathway":[{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[4,7,8,9,16]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[3,5,12,15]},{"term_id":"R-HSA-5357801","term_label":"Programmed Cell Death","supporting_discovery_ids":[15]}],"complexes":[],"partners":["SLAMF1","CD244","SLAMF6","FYN","NCK1","PTPN11","INPP5D","DOK1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"O60880","full_name":"SH2 domain-containing protein 1A","aliases":["Duncan disease SH2-protein","Signaling lymphocytic activation molecule-associated protein","SLAM-associated protein","T-cell signal transduction molecule SAP"],"length_aa":128,"mass_kda":14.2,"function":"Cytoplasmic adapter regulating receptors of the signaling lymphocytic activation molecule (SLAM) family such as SLAMF1, CD244, LY9, CD84, SLAMF6 and SLAMF7. In SLAM signaling seems to cooperate with SH2D1B/EAT-2. Initially it has been proposed that association with SLAMF1 prevents SLAMF1 binding to inhibitory effectors including INPP5D/SHIP1 and PTPN11/SHP-2 (PubMed:11806999). However, by simultaneous interactions, recruits FYN which subsequently phosphorylates and activates SLAMF1 (PubMed:12458214). Positively regulates CD244/2B4- and CD84-mediated natural killer (NK) cell functions. Can also promote CD48-, SLAMF6 -, LY9-, and SLAMF7-mediated NK cell activation. In the context of NK cell-mediated cytotoxicity enhances conjugate formation with target cells (By similarity). May also regulate the activity of the neurotrophin receptors NTRK1, NTRK2 and NTRK3","subcellular_location":"Cytoplasm","url":"https://www.uniprot.org/uniprotkb/O60880/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/SH2D1A","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/SH2D1A","total_profiled":1310},"omim":[{"mim_id":"615122","title":"LYMPHOPROLIFERATIVE SYNDROME 2; LPFS2","url":"https://www.omim.org/entry/615122"},{"mim_id":"606784","title":"GLYCOGEN SYNTHASE KINASE 3-ALPHA; GSK3A","url":"https://www.omim.org/entry/606784"},{"mim_id":"606446","title":"SLAM FAMILY, MEMBER 6; SLAMF6","url":"https://www.omim.org/entry/606446"},{"mim_id":"605554","title":"CD244 ANTIGEN; CD244","url":"https://www.omim.org/entry/605554"},{"mim_id":"605004","title":"GLYCOGEN SYNTHASE KINASE 3-BETA; GSK3B","url":"https://www.omim.org/entry/605004"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Cytosol","reliability":"Approved"}],"tissue_specificity":"Tissue enriched","tissue_distribution":"Detected in some","driving_tissues":[{"tissue":"lymphoid tissue","ntpm":200.5}],"url":"https://www.proteinatlas.org/search/SH2D1A"},"hgnc":{"alias_symbol":["XLP","MTCP1","DSHP","XLPD","EBVS","SAP"],"prev_symbol":["IMD5","LYP"]},"alphafold":{"accession":"O60880","domains":[{"cath_id":"3.30.505.10","chopping":"6-100","consensus_level":"high","plddt":92.1523,"start":6,"end":100}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/O60880","model_url":"https://alphafold.ebi.ac.uk/files/AF-O60880-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-O60880-F1-predicted_aligned_error_v6.png","plddt_mean":83.69},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=SH2D1A","jax_strain_url":"https://www.jax.org/strain/search?query=SH2D1A"},"sequence":{"accession":"O60880","fasta_url":"https://rest.uniprot.org/uniprotkb/O60880.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/O60880/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/O60880"}},"corpus_meta":[{"pmid":"15711562","id":"PMC_15711562","title":"Regulation 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methylation pattern of the X-linked lymphoproliferative (XLP) disease gene SH2D1A correlates with the cell lineage-specific transcription.","date":"2003","source":"Immunogenetics","url":"https://pubmed.ncbi.nlm.nih.gov/12709835","citation_count":8,"is_preprint":false},{"pmid":"21996454","id":"PMC_21996454","title":"CD4+ T Lymphocytes with follicular helper phenotype (T(FH)) in patients with SH2D1A deficiency (XLP).","date":"2011","source":"Clinical immunology (Orlando, Fla.)","url":"https://pubmed.ncbi.nlm.nih.gov/21996454","citation_count":8,"is_preprint":false},{"pmid":"25982576","id":"PMC_25982576","title":"Study of SH2D1A gene mutation in paediatric patients with B-cell lymphoma.","date":"2015","source":"Allergologia et immunopathologia","url":"https://pubmed.ncbi.nlm.nih.gov/25982576","citation_count":6,"is_preprint":false},{"pmid":"28267077","id":"PMC_28267077","title":"Novel Mutations in SH2D1A Gene in X-linked Lymphoproliferative Syndrome, Diagnosed After B-Cell Non-Hodgkin Lymphoma.","date":"2017","source":"Journal of pediatric hematology/oncology","url":"https://pubmed.ncbi.nlm.nih.gov/28267077","citation_count":6,"is_preprint":false},{"pmid":"31994322","id":"PMC_31994322","title":"Diagnostic challenges for a novel SH2D1A mutation associated with X-linked lymphoproliferative disease.","date":"2020","source":"Pediatric blood & cancer","url":"https://pubmed.ncbi.nlm.nih.gov/31994322","citation_count":6,"is_preprint":false},{"pmid":"24723092","id":"PMC_24723092","title":"The value of DNA storage and pedigree analysis in rare diseases: a 17-year-old boy with X-linked lymphoproliferative disease (XLP) caused by a de novo SH2D1A mutation.","date":"2014","source":"European journal of pediatrics","url":"https://pubmed.ncbi.nlm.nih.gov/24723092","citation_count":6,"is_preprint":false},{"pmid":"17302894","id":"PMC_17302894","title":"Factors involved in the generation of memory CD8+ T cells in patients with X-linked lymphoproliferative disease (XLP).","date":"2007","source":"Clinical and experimental immunology","url":"https://pubmed.ncbi.nlm.nih.gov/17302894","citation_count":6,"is_preprint":false},{"pmid":"8256804","id":"PMC_8256804","title":"Evaluation of families wherein a single male manifests a phenotype of X-linked lymphoproliferative disease (XLP).","date":"1993","source":"American journal of medical genetics","url":"https://pubmed.ncbi.nlm.nih.gov/8256804","citation_count":6,"is_preprint":false},{"pmid":"22425739","id":"PMC_22425739","title":"The -346T polymorphism of the SH2D1A gene is a risk factor for development of autoimmunity/lymphoproliferation in males with defective Fas function.","date":"2012","source":"Human immunology","url":"https://pubmed.ncbi.nlm.nih.gov/22425739","citation_count":5,"is_preprint":false},{"pmid":"25572984","id":"PMC_25572984","title":"Maternal onset de novo SH2D1A mutation and lymphocytic choriomeningitis virus infection in a patient with X‑linked lymphoproliferative disease type 1: a case report.","date":"2015","source":"Molecular medicine reports","url":"https://pubmed.ncbi.nlm.nih.gov/25572984","citation_count":5,"is_preprint":false},{"pmid":"3030340","id":"PMC_3030340","title":"Epstein-Barr virus (EBV) and X-linked lymphoproliferative syndrome (XLP).","date":"1986","source":"AIDS research","url":"https://pubmed.ncbi.nlm.nih.gov/3030340","citation_count":5,"is_preprint":false},{"pmid":"21541208","id":"PMC_21541208","title":"X-Linked Lymphoproliferative Syndrome and Common Variable Immunodeficiency May Not Be Differentiated by SH2D1A and XIAP/BIRC4 Genes Sequence Analysis.","date":"2011","source":"Case reports in medicine","url":"https://pubmed.ncbi.nlm.nih.gov/21541208","citation_count":5,"is_preprint":false},{"pmid":"28231257","id":"PMC_28231257","title":"Targeted sequencing identifies a novel SH2D1A pathogenic variant in a Chinese family: Carrier screening and prenatal genetic testing.","date":"2017","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/28231257","citation_count":5,"is_preprint":false},{"pmid":"23143765","id":"PMC_23143765","title":"Fatal EBV infection and variable clinical manifestations in an XLP-1 pedigree - rapid diagnosis of primary immunodeficiencies may save lives.","date":"2012","source":"Klinische Padiatrie","url":"https://pubmed.ncbi.nlm.nih.gov/23143765","citation_count":5,"is_preprint":false},{"pmid":"30138256","id":"PMC_30138256","title":"Fatal Central Nervous System Lymphocytic Vasculitis after Treatment for Burkitt Lymphoma in a Patient with a SH2D1A Mutation.","date":"2019","source":"The Pediatric infectious disease journal","url":"https://pubmed.ncbi.nlm.nih.gov/30138256","citation_count":5,"is_preprint":false},{"pmid":"23280491","id":"PMC_23280491","title":"Intronic SH2D1A mutation with impaired SAP expression and agammaglobulinemia.","date":"2012","source":"Clinical immunology (Orlando, Fla.)","url":"https://pubmed.ncbi.nlm.nih.gov/23280491","citation_count":4,"is_preprint":false},{"pmid":"36254040","id":"PMC_36254040","title":"Potential pathogenic mechanism of type 1 X-linked lymphoproliferative syndrome caused by a mutation of SH2D1A gene in an infant: A case report.","date":"2022","source":"Medicine","url":"https://pubmed.ncbi.nlm.nih.gov/36254040","citation_count":4,"is_preprint":false},{"pmid":"35092357","id":"PMC_35092357","title":"Exon skipping caused by a complex structural variation in SH2D1A resulted in X-linked lymphoproliferative syndrome type 1.","date":"2022","source":"Molecular genetics & genomic medicine","url":"https://pubmed.ncbi.nlm.nih.gov/35092357","citation_count":4,"is_preprint":false},{"pmid":"19576857","id":"PMC_19576857","title":"Increased lymphocyte viability after non-stimulated peripheral blood mononuclear cell (PBMC) culture in patients with X-linked lymphoproliferative disease (XLP).","date":"2009","source":"Clinical immunology (Orlando, Fla.)","url":"https://pubmed.ncbi.nlm.nih.gov/19576857","citation_count":4,"is_preprint":false},{"pmid":"29649976","id":"PMC_29649976","title":"Identification of a novel nonsense mutation in SH2D1A in a patient with X-linked lymphoproliferative syndrome type 1: a case report.","date":"2018","source":"BMC medical genetics","url":"https://pubmed.ncbi.nlm.nih.gov/29649976","citation_count":4,"is_preprint":false},{"pmid":"28196537","id":"PMC_28196537","title":"Characterization of a novel disease-causing mutation in exon 1 of SH2D1A gene through amplicon sequencing: a case report on HLH.","date":"2017","source":"BMC medical genetics","url":"https://pubmed.ncbi.nlm.nih.gov/28196537","citation_count":4,"is_preprint":false},{"pmid":"34987501","id":"PMC_34987501","title":"Case Report: Meningoencephalitis With Thrombotic Occlusive Vasculopathy in a Young EBV-Naïve Boy Is Associated With a Novel SH2D1A Mutation.","date":"2021","source":"Frontiers in immunology","url":"https://pubmed.ncbi.nlm.nih.gov/34987501","citation_count":4,"is_preprint":false},{"pmid":"24369347","id":"PMC_24369347","title":"Identification of a new isoform of the murine Sh2d1a gene and its functional implications.","date":"2013","source":"Science China. 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The consensus binding motif was identified as TIpYXX(V/I). XLP patient mutations that disrupt these extended interactions abolish SAP function.\",\n      \"method\": \"X-ray crystallography, phosphopeptide library screen, XLP mutation analysis\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structures with functional validation by peptide library screen and disease-mutation analysis, replicated by NMR studies in same year\",\n      \"pmids\": [\"10549287\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"NMR studies of 15N/13C-labeled SAP complexed with SLAM peptides confirm that the SAP SH2 domain binds phosphorylated and non-phosphorylated SLAM peptides with comparable affinity (Kd ~150 nM pTyr, ~330 nM Tyr), recognizing both N-terminal and C-terminal sequences relative to the tyrosine residue ('three-pronged' mechanism).\",\n      \"method\": \"NMR spectroscopy, peptide binding affinity measurements\",\n      \"journal\": \"Current biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — NMR structural analysis with quantitative binding data, orthogonal to crystallography study\",\n      \"pmids\": [\"10607564\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"NMR structure of SAP/SH2D1A complexed with two distinct peptides confirms the 'three-pronged' binding mechanism; the SAP SH2 domain contains a consensus binding motif T/S-x-x-x-x-V/I lacking Tyr or pTyr, and disease-causing SAP mutants show binding defects that explain their pathogenicity. Hydrogen exchange studies reveal considerable flexibility in the SH2 domain.\",\n      \"method\": \"NMR spectroscopy, synthetic peptide screening, hydrogen exchange\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — NMR structures of two independent complexes with functional validation of disease mutants\",\n      \"pmids\": [\"11823424\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"SAP/SH2D1A regulates the association of CD150 (SLAM) with either SHIP or SHP-2: in SH2D1A-expressing B cells CD150 coprecipitates with SH2D1A and SHIP, whereas in SH2D1A-negative cells CD150 associates only with SHP-2. GST-fusion pulldowns show that phosphorylated Y281 and Y327 in the CD150 cytoplasmic tail are essential for SHP-2 and SHIP binding, and SH2D1A facilitates SHIP recruitment to CD150, acting as a switch between these two phosphatases.\",\n      \"method\": \"Co-immunoprecipitation, GST-fusion pulldown with tyrosine mutants\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal co-IP and mutagenesis in a single lab with two orthogonal methods\",\n      \"pmids\": [\"11313386\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"NTB-A, a novel SLAM-family glycoprotein on NK/T/B cells, undergoes tyrosine phosphorylation and associates with SAP/SH2D1A as well as SHP phosphatases. In XLP NK cells lacking SH2D1A, NTB-A mediates inhibitory rather than activating signals, contributing to the inability to kill EBV-infected B cells. Masking both NTB-A and 2B4 simultaneously maximally restores cytotoxicity in XLP-NK cells.\",\n      \"method\": \"Co-immunoprecipitation, mAb masking experiments, cytotoxicity assays with XLP patient NK cells\",\n      \"journal\": \"The Journal of experimental medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — co-IP plus functional NK cytotoxicity rescue experiments with patient cells, multiple orthogonal methods\",\n      \"pmids\": [\"11489943\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"SAP functions dually in SLAM signaling: (1) it competitively inhibits SHP-2 and SHIP binding to SLAM family receptors, and (2) it acts as an adaptor recruiting FynT kinase to SLAM via a direct interaction between the SAP SH2 domain surface and the FynT SH3 domain. FynT is required for SLAM tyrosine phosphorylation, which is dramatically enhanced by SAP. Disease-causing SAP mutants show reduced affinity for both FynT and SLAM.\",\n      \"method\": \"In vitro and in vivo binding assays, peptide array, cell transfection, co-immunoprecipitation, mutagenesis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — multiple orthogonal methods (peptide arrays, in vitro binding, cellular co-IP, mutagenesis), dual functional mechanism established\",\n      \"pmids\": [\"12458214\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Analysis of 10 XLP missense mutations in SH2D1A reveals two mechanistic classes: (i) mutations causing markedly decreased protein half-life (Y7C, S28R, Q99P, P101L, V102G, X129R), and (ii) mutations causing structural changes that differentially affect binding to SLAM, 2B4, CD84, and CD229. Mutation T68I disrupts the hydrophobic cleft interaction with Val+3 of the binding motif, C42W disrupts the phosphotyrosine-binding pocket, and T53I specifically impairs non-phosphotyrosine interactions while preserving phosphorylated CD150 binding.\",\n      \"method\": \"In vitro binding assays, protein half-life measurement, site-directed mutagenesis, co-immunoprecipitation\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — systematic mutagenesis of 10 disease-causing mutations with multiple functional readouts in a single rigorous study\",\n      \"pmids\": [\"11477068\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"SAP-deficient mice (Sh2d1a−/−) display normal lymphocyte development but, upon infection with LCMV or Toxoplasma gondii, show increased T cell activation, elevated IFN-γ production, reduced Ig-secreting cells, and decreased IL-4. Anti-CD3-stimulated splenocytes from uninfected SAP− mice produce increased IFN-γ and decreased IL-4 (Th1 skewing), with decreased serum IgE in vivo, indicating SAP controls cytokine balance downstream of T cell activation.\",\n      \"method\": \"Targeted gene knockout mouse model, cytokine measurement, infection challenge\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean KO mouse with defined cellular phenotype, multiple infection models\",\n      \"pmids\": [\"11404475\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"SAP encoded by SH2D1A is essential for NKT cell development: Sh2d1a−/− mice completely lack NKT cells in thymus and periphery. The defect is hematopoietic cell-autonomous and can be rescued by reconstituting SAP expression in Sh2d1a−/− bone marrow. Seventeen XLP patients with germline SH2D1A mutations also lacked NKT cells, and female XLP carriers show completely skewed X-chromosome inactivation in NKT cells but not T or B cells.\",\n      \"method\": \"Knockout mouse phenotyping, bone marrow reconstitution, alpha-galactosylceramide stimulation, X-chromosome inactivation analysis in human carriers\",\n      \"journal\": \"Nature medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — KO mouse plus bone marrow rescue plus human patient validation, replicated mechanistic finding across species\",\n      \"pmids\": [\"15711562\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"SH2D1A is required for T-dependent humoral immune responses and germinal center formation. SH2D1A−/− mice are protected from experimental lupus (hypergammaglobulinemia, autoantibodies, renal disease) specifically because of defective germinal center formation and impaired T-dependent antigen-specific IgG responses, while T-independent responses remain normal.\",\n      \"method\": \"KO mouse model, immunization, germinal center analysis, autoimmune disease model (lupus), EAE model\",\n      \"journal\": \"The Journal of experimental medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean KO with multiple defined phenotypic readouts and epistasis using T-independent vs T-dependent antigen responses\",\n      \"pmids\": [\"15263031\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"SH2D1A is required in both T cells and B cells for productive humoral immune responses. Adoptive cotransfer experiments show that SH2D1A−/− B cells are intrinsically defective in contributing to antigen-specific IgG production even when paired with wild-type CD4+ T cells, indicating a B cell-autonomous signaling role for SH2D1A. Germinal centers are absent in SH2D1A−/− mice after primary immunization.\",\n      \"method\": \"Adoptive cotransfer into irradiated or Rag2−/− hosts, immunization, germinal center analysis\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — adoptive transfer epistasis experiment isolating B-cell-intrinsic defect, multiple recipient models\",\n      \"pmids\": [\"15774582\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"SAP association with 2B4 (CD244) in NK cells requires PI3K activity: ligation of 2B4 leads to 2B4 phosphorylation, SAP recruitment, and association of PI3K p85 subunit. Pharmacological inhibition of PI3K (wortmannin or LY294002) prevents SAP recruitment to 2B4 without disrupting PI3K-p85 association with 2B4, and abolishes NK cytotoxicity in normal but not XLP NK cells.\",\n      \"method\": \"Co-immunoprecipitation, pharmacological inhibition, NK cytotoxicity assay with patient cells\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — co-IP plus functional cytotoxicity assay, single lab, two methods\",\n      \"pmids\": [\"11815622\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"SH2D1A regulates CD150-mediated Akt signaling in B cells: using DT40 sublines deficient in specific signaling molecules, CD150-mediated Akt phosphorylation requires Syk and SH2D1A, is negatively regulated by Lyn and Btk, and is SHIP-independent. CD150-mediated ERK pathway activation requires SHIP but not SH2D1A.\",\n      \"method\": \"DT40 gene-deficient B cell sublines, CD150 ligation, Akt and ERK phosphorylation assays\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic epistasis in defined DT40 knockout sublines, single lab\",\n      \"pmids\": [\"15315965\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"SH2D1A associates with Dok1 (p62dok) via its SH2 domain in a manner dependent on phosphorylation of Dok1 Y449 (in the sequence ALYSQVQK). An XLP-associated SH2 domain mutant fails to associate with Dok1. Overexpression of SH2D1A activates NF-κB in 293T cells via a pathway dependent on IκB kinase β but independent of the wild-type SH2 domain.\",\n      \"method\": \"Co-immunoprecipitation, site-directed mutagenesis, NF-κB reporter assay, dominant-negative kinase\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — co-IP plus phospho-mutant plus reporter assay, single lab\",\n      \"pmids\": [\"10852966\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"SAP interacts with SH3 domains of Fyn and NCK1 via a surface on the SAP SH2 domain distinct from the phosphotyrosine-binding surface. NMR shows NCK1 and Fyn SH3 domains engage the same SAP residues with comparable affinities. SAP knockdown reduces NCK1 tyrosine phosphorylation and phosphorylation of downstream TCR signaling proteins LAT and SLP-76. SAP regulates T cell proliferation through ERK/MAP kinase.\",\n      \"method\": \"NMR analysis of SAP–SH3 interactions, siRNA knockdown, phosphorylation assays, T cell proliferation assay\",\n      \"journal\": \"Cellular signalling\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — NMR structural data plus cellular knockdown with defined downstream readouts, single lab\",\n      \"pmids\": [\"18951976\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"SAP-deficient T cells exhibit impaired TCR restimulation-induced cell death (RICD) due to diminished TCR-induced inhibition of diacylglycerol kinase α (DGKα), leading to increased diacylglycerol metabolism and decreased Ras and PKCθ signaling. Pharmacological inhibition of DGKα in SAP-deficient T cells restores diacylglycerol signaling at the immune synapse and rescues RICD via induction of pro-apoptotic proteins NUR77 and NOR1. DGKα inhibition prevents excessive CD8+ T cell expansion and IFN-γ production in SAP-deficient mice after LCMV infection.\",\n      \"method\": \"SAP-KO mouse LCMV infection model, RICD assay, diacylglycerol signaling measurements, pharmacological DGKα inhibition, NUR77/NOR1 induction\",\n      \"journal\": \"Science translational medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — KO mouse model plus primary patient T cells plus pharmacological rescue, multiple orthogonal methods defining signaling pathway\",\n      \"pmids\": [\"26764158\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"SAP expression in CD8+ T cells is specifically required for their response to antigen presented by B cells but not other antigen-presenting cells. In female XLP carriers with mixed SAP+/SAP− cells, EBV-specific memory CD8+ T cells are exclusively SAP+, while CMV- and influenza-specific cells distribute equally. Blocking SLAM receptors NTB-A and 2B4 overcomes the inability of SAP− CD8+ T cells to respond to B cell antigen presentation; ectopic NTB-A expression on fibroblasts inhibits SAP− CD8+ T cell cytotoxicity, demonstrating that SLAM receptors acquire inhibitory function in the absence of SAP.\",\n      \"method\": \"Analysis of female XLP carrier cells (natural mixed chimerism), antigen-specific T cell response assays, receptor blocking antibodies, ectopic NTB-A expression on fibroblasts\",\n      \"journal\": \"PLoS biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — unique human natural experiment (carrier cells as mixed chimera) plus mechanistic rescue/inhibition experiments\",\n      \"pmids\": [\"22069374\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"SH2D1A gene expression is controlled by a combination of transcriptional and post-transcriptional mechanisms: a 22–33 bp basal promoter element containing an Ets consensus site is required for transcription, with Ets-1 and Ets-2 binding confirmed by gel mobility supershift and dominant-negative overexpression. SH2D1A mRNA decays rapidly in T cells, and its 3' UTR has RNA-destabilizing activity dependent on a balance between AUF1 and HuR binding.\",\n      \"method\": \"Reporter assays, gel mobility shift/supershift assays, dominant-negative Ets overexpression, RNA decay assays, RNA-gel mobility shift\",\n      \"journal\": \"European journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reporter assays plus protein binding assays plus mRNA stability analysis, single lab, multiple methods\",\n      \"pmids\": [\"15459902\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"SAP deficiency causes profound germinal center defects and hypogammaglobulinemia during chronic LCMV infection in mice. Depletion of SAP-deficient CD8+ T cells blocks the immunopathology and clinical illness, providing the first direct demonstration that SAP-deficient CD8+ T cells are the primary cause of immunopathology in an XLP model.\",\n      \"method\": \"SAP-KO mouse chronic LCMV infection, CD8+ T cell depletion, germinal center analysis, viral load measurement\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — KO mouse plus CD8 depletion epistasis, multiple immunological readouts\",\n      \"pmids\": [\"16788096\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Differential DNA methylation of CpG-rich regions in the 5' region and exon 1 of SH2D1A correlates with cell lineage-specific transcription: T and NK cells (which express SH2D1A) show hypomethylation, while B cells and granulocytes (which do not express it) show hypermethylation.\",\n      \"method\": \"Bisulfite sequencing, methylation-sensitive restriction enzyme digestion\",\n      \"journal\": \"Immunogenetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — two orthogonal methylation methods correlating epigenetic state with expression, single lab\",\n      \"pmids\": [\"12709835\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Four XLP missense mutations (Y54C, I84T, F87S) and a frameshift insertion (fs82→X103) each dramatically reduce SAP protein half-life. The I84T mutation does not prevent SAP binding to SLAM, CD84, or 2B4 but reduces downstream SLAM signaling, demonstrating that impaired signal transduction can be mechanistically separable from impaired receptor binding.\",\n      \"method\": \"Protein half-life measurement, co-immunoprecipitation binding assays, downstream signaling assays in primary lymphocytes and transfected cell lines\",\n      \"journal\": \"International immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — systematic analysis in patient cells and transfectants, single lab, multiple methods\",\n      \"pmids\": [\"16720617\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"A new XLP disease-causing SAP missense mutation (p.G16D) results in a protein with normal half-life but defective binding to SLAM and 2B4 ligands, as demonstrated by expressing the mutant cDNA in COS cells and testing binding to physiological ligands.\",\n      \"method\": \"Site-directed mutagenesis, COS cell expression, co-immunoprecipitation binding assay\",\n      \"journal\": \"Human mutation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — mutagenesis plus functional binding assay, single lab\",\n      \"pmids\": [\"15841490\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"A new murine SAP isoform (SAP-2) arising from a cryptic exon contains 18 additional amino acids inserted into the phosphotyrosine-binding structural region of the SH2 domain. Functional analysis in vitro shows SAP-2 is non-functional due to decreased protein stability, suggesting cells could modulate SAP-mediated activity by regulating isoform ratios.\",\n      \"method\": \"RT-PCR isoform identification, protein stability assay, in vitro functional analysis\",\n      \"journal\": \"Science China. Life sciences\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, partial mechanistic follow-up with limited functional assays\",\n      \"pmids\": [\"24369347\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"A novel SH2D1A variant (c.49G>A, p.E17K) results in a SAP protein with normal expression levels but >95% reduction in binding to phosphorylated CD244 (2B4), demonstrating that loss of receptor binding, rather than protein instability, can be the sole mechanistic defect in some XLP mutations.\",\n      \"method\": \"Flow cytometry (SAP protein expression), biochemical binding assay to phosphorylated CD244\",\n      \"journal\": \"Pediatric blood & cancer\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — quantitative binding assay plus protein expression, single lab, two orthogonal methods\",\n      \"pmids\": [\"31994322\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"SH2D1A encodes SAP, a single SH2 domain adaptor protein expressed in T cells and NK cells that binds SLAM-family receptors (SLAM/CD150, 2B4/CD244, NTB-A, CD84, Ly9/CD229) via a unique 'three-pronged' phosphotyrosine-independent mechanism recognizing the TxYxx(V/I) motif; SAP functions dually as a competitive inhibitor of SHP-2/SHIP recruitment to these receptors and as an adaptor recruiting FynT kinase (via SH3 domain interaction) to promote receptor phosphorylation and downstream signaling, while in its absence SLAM-family receptors default to inhibitory signaling; SAP is required for NKT cell development, germinal center formation and T-dependent humoral immunity, and restrains CD8+ T cell-mediated immunopathology by promoting RICD through DGKα inhibition and diacylglycerol/Ras/PKCθ signaling at the immune synapse.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"SH2D1A encodes SAP, a single-SH2-domain adaptor that transduces signaling from SLAM-family receptors and is the gene mutated in X-linked lymphoproliferative disease (XLP), where missense mutations disrupt either protein stability or receptor binding [#0, #6, #20]. Structurally, the SAP SH2 domain recognizes its targets through an unusual phosphotyrosine-independent 'three-pronged' mode, engaging both N-terminal and C-terminal residues flanking the tyrosine and binding phosphorylated and non-phosphorylated SLAM peptides with comparable affinity around a T/S-x-x-x-x-V/I consensus motif [#0, #1, #2]. SAP acts dually at SLAM-family receptors (SLAM/CD150, 2B4/CD244, NTB-A, CD84, CD229): it competitively displaces the inhibitory phosphatases SHP-2 and SHIP from the receptor cytoplasmic tail, and it uses a second surface on its SH2 domain to recruit the FynT kinase SH3 domain, driving receptor tyrosine phosphorylation and activating signaling [#3, #4, #5, #14]. In the absence of SAP, these receptors default to inhibitory output, explaining the failure of XLP NK and CD8+ T cells to kill EBV-infected B cells and to respond to B-cell antigen presentation [#4, #16]. Through SLAM signaling SAP is required for NKT cell development, T-dependent humoral immunity and germinal center formation, with both a T-cell and a B-cell-intrinsic requirement [#8, #9, #10], and it controls cytokine balance and restrains CD8+ T-cell-driven immunopathology, in part by promoting restimulation-induced cell death (RICD) via inhibition of diacylglycerol kinase \\u03b1 and consequent diacylglycerol/Ras/PKC\\u03b8 signaling at the immune synapse [#7, #15, #18]. SH2D1A expression is restricted to T and NK cells by lineage-specific promoter CpG demethylation, Ets-dependent transcription, and 3'UTR-mediated mRNA destabilization [#17, #19].\",\n  \"teleology\": [\n    {\n      \"year\": 1999,\n      \"claim\": \"Structural studies answered how a single SH2 domain recognizes SLAM despite weak dependence on tyrosine phosphorylation, defining the unique 'three-pronged' binding mode that distinguishes SAP from canonical SH2 adaptors.\",\n      \"evidence\": \"X-ray crystallography and NMR of SAP\\u2013SLAM peptide complexes with phosphopeptide library screening and XLP mutation analysis\",\n      \"pmids\": [\"10549287\", \"10607564\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not establish the in vivo signaling consequence of phosphotyrosine-independent binding\", \"Receptor partners beyond SLAM not structurally tested at this stage\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"A second NMR study generalized the three-pronged mechanism across distinct peptides and tied disease-causing mutants to specific binding defects, consolidating the structural basis for XLP pathogenicity.\",\n      \"evidence\": \"NMR of two SAP\\u2013peptide complexes, synthetic peptide screening, hydrogen exchange\",\n      \"pmids\": [\"11823424\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"SH2 domain flexibility not linked to a functional regulatory mechanism\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Co-IP and mutagenesis on CD150 showed SAP acts as a switch between phosphatase partners, redirecting the receptor from SHP-2 to SHIP and thereby altering signaling output.\",\n      \"evidence\": \"Reciprocal co-immunoprecipitation and GST-fusion pulldown with tyrosine mutants in B cells\",\n      \"pmids\": [\"11313386\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab data\", \"Functional consequence of the SHIP/SHP-2 switch on cell behavior not directly measured here\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Identification of NTB-A as a SAP-associated SLAM-family receptor demonstrated that loss of SAP converts an activating receptor to an inhibitory one, explaining the NK cytotoxicity defect against EBV-infected targets in XLP.\",\n      \"evidence\": \"Co-IP, mAb masking and cytotoxicity assays with XLP patient NK cells\",\n      \"pmids\": [\"11489943\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism by which SAP loss flips receptor polarity not molecularly defined here\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"The dual-function model was established: SAP both blocks inhibitory phosphatases and actively recruits FynT to drive SLAM phosphorylation, unifying its competitive and adaptor roles.\",\n      \"evidence\": \"Peptide arrays, in vitro and cellular binding assays, co-IP and mutagenesis\",\n      \"pmids\": [\"12458214\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relative contribution of phosphatase exclusion vs FynT recruitment in vivo not quantified\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"SAP recruitment to 2B4 was shown to require PI3K activity, adding an upstream regulatory input to SAP-dependent NK signaling.\",\n      \"evidence\": \"Co-IP, pharmacological PI3K inhibition, NK cytotoxicity with patient cells\",\n      \"pmids\": [\"11815622\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab finding\", \"Molecular link between PI3K product and SAP recruitment unresolved\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Systematic analysis of XLP mutations resolved two mechanistic classes\\u2014destabilizing versus binding-disrupting\\u2014providing a genotype-to-mechanism framework for the disease.\",\n      \"evidence\": \"Site-directed mutagenesis, protein half-life measurement, co-IP across SLAM/2B4/CD84/CD229\",\n      \"pmids\": [\"11477068\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not connect each class to distinct clinical phenotypes\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"The first SAP knockout mouse showed normal lymphocyte development but dysregulated cytokine output (Th1 skewing, reduced IL-4/IgE) after infection, placing SAP downstream of T-cell activation in immune regulation.\",\n      \"evidence\": \"Sh2d1a-/- mice with LCMV/Toxoplasma challenge and cytokine measurement\",\n      \"pmids\": [\"11404475\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Receptor-level mechanism linking SAP to cytokine balance not defined in this model\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"SAP was shown to be required for germinal center formation and T-dependent IgG responses, mechanistically explaining the humoral immunodeficiency of XLP and protection from a lupus model.\",\n      \"evidence\": \"KO mouse immunization, germinal center analysis, lupus/EAE models with T-independent controls\",\n      \"pmids\": [\"15263031\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not assign the defect to a specific cell lineage\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Adoptive cotransfer revealed a B-cell-intrinsic requirement for SAP in humoral responses, refining the view that SAP acts only in T cells.\",\n      \"evidence\": \"Cotransfer of SH2D1A-/- B cells with WT T cells into irradiated/Rag2-/- hosts\",\n      \"pmids\": [\"15774582\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"The B-cell SLAM-receptor circuit responsible was not molecularly identified\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"SAP was established as essential and cell-autonomous for NKT cell development, confirmed by bone marrow rescue in mice and skewed X-inactivation in human carriers.\",\n      \"evidence\": \"KO phenotyping, BM reconstitution, \\u03b1-GalCer stimulation, X-inactivation analysis in XLP carriers\",\n      \"pmids\": [\"15711562\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Developmental signaling step at which SAP acts in NKT lineage not pinpointed\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Genetic epistasis in DT40 sublines separated SAP-dependent CD150-Akt signaling (Syk-dependent, SHIP-independent) from SAP-independent ERK signaling, mapping branch points downstream of the receptor.\",\n      \"evidence\": \"CD150 ligation in gene-deficient DT40 B-cell sublines with Akt/ERK phospho-readouts\",\n      \"pmids\": [\"15315965\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab chicken cell system\", \"Relevance to primary human B cells not confirmed\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Early co-IP work proposed SAP partners beyond SLAM (Dok1) and an NF-\\u03baB activation activity, expanding candidate downstream pathways.\",\n      \"evidence\": \"Co-IP with phospho-Dok1, mutagenesis, NF-\\u03baB reporter with dominant-negative IKK\\u03b2\",\n      \"pmids\": [\"10852966\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab data not integrated with the dominant SLAM-receptor model\", \"NF-\\u03baB activity was SH2-domain-independent and physiological relevance unclear\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Lineage-restricted expression of SH2D1A was tied to differential CpG methylation, providing an epigenetic basis for its T/NK-cell-specific function.\",\n      \"evidence\": \"Bisulfite sequencing and methylation-sensitive digestion across expressing vs non-expressing lineages\",\n      \"pmids\": [\"12709835\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Causality of methylation vs transcription not established by perturbation\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"SH2D1A expression was shown to be jointly controlled by Ets-dependent transcription and AUF1/HuR-balanced mRNA stability, defining its regulatory logic.\",\n      \"evidence\": \"Reporter assays, gel supershift, dominant-negative Ets, RNA decay and RNA-gel shift assays\",\n      \"pmids\": [\"15459902\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab data\", \"Signals tuning AUF1/HuR balance in activated T cells unknown\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"CD8+ T-cell depletion in chronic LCMV infection demonstrated that SAP-deficient CD8+ T cells are the direct cause of XLP-like immunopathology, linking SAP loss to disease mechanism in vivo.\",\n      \"evidence\": \"SAP-KO chronic LCMV infection with CD8 depletion, germinal center and viral load readouts\",\n      \"pmids\": [\"16788096\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not yet define the cell-intrinsic signaling lesion driving pathogenic CD8 expansion\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"The RICD pathway was defined: SAP normally inhibits DGK\\u03b1 to sustain diacylglycerol/Ras/PKC\\u03b8 signaling and NUR77/NOR1-driven apoptosis, and DGK\\u03b1 inhibition rescues RICD and curbs CD8 immunopathology, providing a mechanistic and therapeutic axis.\",\n      \"evidence\": \"SAP-KO LCMV model and patient T cells, RICD and DAG signaling assays, pharmacological DGK\\u03b1 inhibition\",\n      \"pmids\": [\"26764158\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular link from SAP to DGK\\u03b1 inhibition not fully resolved\", \"Translation to human therapy not established\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"SAP was shown to engage NCK1 as well as Fyn SH3 domains through the same SH2 surface and to support LAT/SLP-76 phosphorylation, broadening the kinase/adaptor network it nucleates at the TCR.\",\n      \"evidence\": \"NMR of SAP\\u2013SH3 interactions, siRNA knockdown, phospho-assays, T-cell proliferation\",\n      \"pmids\": [\"18951976\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab data\", \"Relative in vivo importance of NCK1 vs Fyn recruitment unclear\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Human carrier mixed-chimerism experiments demonstrated SAP is specifically required for CD8+ T-cell responses to B-cell antigen presentation, and that NTB-A/2B4 acquire inhibitory function without SAP, explaining the selective EBV vulnerability of XLP.\",\n      \"evidence\": \"Female XLP carrier mixed cells, antigen-specific response assays, receptor blocking and ectopic NTB-A expression\",\n      \"pmids\": [\"22069374\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Why B-cell APCs specifically depend on SAP signaling not fully resolved\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Continued XLP mutation analysis (e.g. E17K, G16D) reinforced that selective loss of receptor binding with preserved protein stability is sufficient to cause disease, separating binding from stability defects.\",\n      \"evidence\": \"Mutant expression with quantitative binding assays to phosphorylated CD244 and SLAM/2B4\",\n      \"pmids\": [\"31994322\", \"15841490\", \"16720617\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Genotype-phenotype severity correlations not established\", \"In vivo signaling consequences of partial binding loss untested\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How SAP biochemically inhibits DGK\\u03b1 and how SLAM-family receptors are reprogrammed from activating to inhibitory output in SAP's absence remain mechanistically unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No defined molecular intermediary between SAP and DGK\\u03b1\", \"Structural basis of inhibitory phosphatase default not determined\", \"Isoform-based regulation (SAP-2) lacks functional in vivo evidence\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [3, 5, 14]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [3, 5]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [5, 16]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [5]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [4, 7, 8, 9, 16]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [3, 5, 12, 15]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [15]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"SLAMF1\", \"CD244\", \"SLAMF6\", \"FYN\", \"NCK1\", \"PTPN11\", \"INPP5D\", \"DOK1\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}