{"gene":"CD5","run_date":"2026-06-09T22:57:18","timeline":{"discoveries":[{"year":1991,"finding":"CD72 (Lyb-2 in mice) is the ligand for CD5. CD5 protein, labelled with biotin, specifically bound to B-cell surface CD72; this binding was blocked by anti-CD72 antibodies but not other anti-B-cell antibodies. Non-B cells transfected with human CD72 cDNA gained ability to bind CD5-biotin conjugate.","method":"Biotin-labeled CD5 used as probe on cells; blocking with anti-CD72 antibodies; transfection of CD72 cDNA into non-B cells (mouse L-cells and Jurkat T cells)","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — direct biochemical binding assay with biotin-labeled protein, blocking antibody controls, and gain-of-function transfection experiment; replicated across multiple cell types","pmids":["1711157"],"is_preprint":false},{"year":1998,"finding":"The beta subunit of casein kinase 2 (CK2) interacts specifically with the cytoplasmic domain of CD5. CK2 holoenzyme associates constitutively with CD5 in human and murine B and T cell lines and murine splenocytes, mediated by the amino terminus of the CK2 regulatory beta subunit. CK2 binds and phosphorylates CD5 at Ser459 and Ser461 (CK2 motifs). Cross-linking of CD5 activates CD5-associated CK2 independently of net CK2 recruitment, and this activation is not triggered by BCR or TCR cross-linking.","method":"Yeast two-hybrid screen; co-immunoprecipitation in human and murine B and T cell lines and splenocytes; in vitro kinase assay; CD5 cross-linking","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — yeast two-hybrid discovery confirmed by reciprocal co-IP in multiple cell types, in vitro phosphorylation assay, site identification at Ser459/461, and functional cross-linking experiment","pmids":["9668105"],"is_preprint":false},{"year":1998,"finding":"The cytoplasmic domain of CD5 interacts with Ca2+/calmodulin-dependent kinase IIdelta (CaMKIIdelta) and with Tctex-1 (a dynein light chain component). The CaMKIIdelta interaction was confirmed in vitro using fusion proteins.","method":"Yeast two-hybrid screen; in vitro binding assay with fusion proteins","journal":"European journal of immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — yeast two-hybrid plus in vitro fusion protein binding; single lab, two complementary methods","pmids":["9692886"],"is_preprint":false},{"year":1998,"finding":"CD5 surface expression during thymocyte development is regulated by TCR signals: low-level expression on DN thymocytes requires pre-TCR engagement and p56(lck) activity; DP thymocyte CD5 levels are maintained by low-affinity TCR-MHC interactions; high-level CD5 is induced by positively or negatively selecting TCR-MHC ligands. CD5 surface expression on mature T cells directly parallels TCR avidity/signaling intensity of the positively selecting interaction.","method":"Analysis of CD5 expression in mice with defined developmental and signal transduction defects (pre-TCR deficient, lck-deficient, TCR transgenic); flow cytometry","journal":"The Journal of experimental medicine","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic loss-of-function models (multiple mutant strains) with quantitative flow cytometry readout, replicated across developmental stages","pmids":["9858516"],"is_preprint":false},{"year":2001,"finding":"The cytoplasmic domain of CD5 is required for its inhibitory function in thymocyte selection. A transgene encoding a truncated (cytoplasmic domain-deleted) form of CD5 failed to rescue the CD5-/- phenotype in thymocyte selection. CD5 overexpression or deletion shifted thymocyte selection toward positive or negative selection, respectively, in a manner dependent on TCR avidity and basal CD5 expression levels.","method":"CD5 transgenic mice (overexpression and truncation knock-in); CD5-/- mice; TCR transgenic crosses; analysis of thymocyte selection outcomes","journal":"Journal of immunology (Baltimore, Md. : 1950)","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple genetic models (KO, overexpressor, cytoplasmic domain truncation) with defined phenotypic readout (thymocyte selection), complementary approaches in one study","pmids":["11313384"],"is_preprint":false},{"year":2000,"finding":"CD5 negatively regulates BCR signaling in anergic B cells to maintain B cell tolerance. CD5-/- mice in the HEL/sHEL anergy model showed loss of B cell tolerance (elevated anti-HEL IgM), and 'anergic' B cells lacking CD5 had enhanced proliferative responses and elevated intracellular Ca2+ at rest and after IgM cross-linking.","method":"CD5 knockout mice crossed with HEL transgenic anergy model; serum ELISA for anti-HEL IgM; in vitro proliferation assay; intracellular Ca2+ measurement","journal":"The Journal of experimental medicine","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean genetic KO in well-established anergy model with multiple orthogonal readouts (antibody levels, proliferation, Ca2+ flux)","pmids":["10704468"],"is_preprint":false},{"year":2002,"finding":"CD5 promotes B cell survival by stimulating autocrine IL-10 production. Introduction of CD5 into CD5- B cells activated the IL-10 promoter and induced IL-10 mRNA and protein. The cytoplasmic domain of CD5 was sufficient for this effect. CD5 also protected normal human B cells from apoptosis after BCR stimulation while reducing BCR-induced Ca2+ responses.","method":"Transfection of CD5 into CD5- B cells; IL-10 promoter reporter assay; RT-PCR for IL-10 mRNA; Ca2+ flux measurement; apoptosis assay","journal":"Blood","confidence":"High","confidence_rationale":"Tier 2 / Strong — gain-of-function transfection with multiple orthogonal readouts (promoter activity, mRNA, protein, Ca2+, apoptosis), cytoplasmic domain sufficiency established","pmids":["12393419"],"is_preprint":false},{"year":2001,"finding":"CD5 functions as a negative regulator of BCR signaling and may help prevent inappropriate activation of autoreactive B-1a cells.","method":"Review summarizing CD5-/- mouse data and B-1a cell biology (mechanistic context from experimental literature)","journal":"Annual review of immunology","confidence":"Low","confidence_rationale":"Tier 4 / Weak — review article summary, no new primary experiment described in the abstract","pmids":["11861604"],"is_preprint":false},{"year":2001,"finding":"Residues Y429 and Y463 of human CD5 are phosphorylated in vivo by protein tyrosine kinases following T cell stimulation. In vitro kinase assays with purified recombinant Lck and Fyn confirmed direct phosphorylation at these sites. Lck-deficient Jurkat cells showed absent CD5 tyrosine phosphorylation, establishing that Lck is required for CD5 tyrosine phosphorylation.","method":"Tyrosine-mutated CD5 transfectants in Jurkat cells; anti-CD3 mAb and pervanadate stimulation; in vitro kinase assays with recombinant Lck and Fyn; analysis in Lck-deficient and CD3-deficient Jurkat cells","journal":"European journal of immunology","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — site-directed mutagenesis of phosphorylation sites, in vitro kinase assay with purified kinases, genetic loss-of-function (Lck-deficient cells); multiple orthogonal methods","pmids":["11298344"],"is_preprint":false},{"year":2005,"finding":"An alternative exon 1 (E1B) of the human CD5 gene, found exclusively in B lymphocytes, encodes a truncated protein that is retained intracellularly rather than transported to the membrane. Presence of E1B-containing transcripts reduces E1A-containing transcript levels and diminishes membrane CD5 expression. Introduction of E1B into Jurkat cells reduced membrane CD5 expression. E1B contains sequence of a defective human endogenous retrovirus.","method":"Identification of alternative exon by sequencing; RT-PCR in B cell subsets including CLL and pre-B cells; transfection of E1B into Jurkat cells with flow cytometric assessment of membrane CD5; bisulfite/methylation analysis","journal":"Blood","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — discovery of novel regulatory exon with gain-of-function transfection showing functional consequence on membrane CD5 levels; single lab","pmids":["15998834"],"is_preprint":false},{"year":2009,"finding":"In SLE B cells, IL-6 prevents DNMT1 induction, leading to demethylation of the CD5-E1B promoter. This causes preferential transcription of CD5-E1B at the expense of CD5-E1A, reducing membrane CD5 expression. BCR engagement amplifies this effect. Blocking IL-6 receptor reverses the demethylation.","method":"Bisulfite sequencing; methylation-sensitive endonuclease assays; RT-PCR for E1A and E1B isoforms; IL-6 receptor blocking antibody; DNMT1 expression analysis in SLE vs healthy B cells","journal":"Journal of immunology (Baltimore, Md. : 1950)","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple biochemical methods (bisulfite sequencing, endonuclease assay, RT-PCR) with functional intervention (anti-IL6R); single lab","pmids":["19380809"],"is_preprint":false},{"year":2010,"finding":"CD5 mediates species-specific homophilic interactions (CD5 is a ligand for itself). Only CD5 domain 1 is involved. CD5 monoclonal antibodies that have functional effects block homophilic binding. Inhibition of CD5 domain 1 engagement (by mutation or by IgG/Fab from a blocking mAb) increased antigen-specific T cell responses in vitro, and a blocking Fab enhanced polyclonal immune responses of rat lymph node cells, demonstrating that homophilic CD5 binding exerts inhibitory function.","method":"Soluble CD5 purified at neutral pH; binding assays; site-directed mutation of domain 1; blocking monoclonal antibodies (IgG and Fab fragments); in vitro T cell activation assays; rat lymph node polyclonal stimulation assay","journal":"Journal of immunology (Baltimore, Md. : 1950)","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — biochemical binding assay with domain-specific mutagenesis, functional blocking with antibody Fab fragments, in vitro functional consequence; multiple orthogonal approaches","pmids":["20952682"],"is_preprint":false},{"year":2012,"finding":"CD5-dependent CK2 activation sets the threshold for T cell responsiveness. A CD5 knock-in mouse with selective deletion of the CK2-binding domain (CD5ΔECK2BD) showed hypoproliferation, enhanced activation-induced cell death, and defective Th2 and Th17 (but not Th1) differentiation of CD4+ T cells upon stimulation. CD5ΔECK2BD mice recapitulated the reduced EAE severity of CD5-KO mice and were unable to generate high-dose tolerance, phenocopying CD5-KO.","method":"Knock-in mouse with microdeletion of CK2-binding domain in CD5; T cell proliferation assays; activation-induced cell death measurement; Th differentiation assays in vitro and in vivo; EAE model; high-dose tolerance assay","journal":"Journal of immunology (Baltimore, Md. : 1950)","confidence":"High","confidence_rationale":"Tier 2 / Strong — precision knock-in mouse model with selective domain disruption, multiple orthogonal functional readouts (proliferation, AICD, Th differentiation, EAE, tolerance), phenocopies KO","pmids":["22904299"],"is_preprint":false},{"year":2014,"finding":"CD5-CK2 signaling promotes Th17 differentiation via two independent mechanisms: inhibition of GSK3 and activation of mTOR, both downstream of AKT. Loss of CD5-CK2 signaling reduced AKT activation, increased GSK3 activity, sensitized Th17 cells to IFN-γ-mediated inhibition, decreased S6K activity, and attenuated nuclear translocation of RORγt.","method":"CD5ΔECK2BD knock-in mice; in vitro Th17 differentiation assays; AKT/GSK3/mTOR/S6K phosphorylation by western blot; RORγt nuclear localization by confocal microscopy; IFN-γ sensitivity assays","journal":"European journal of immunology","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic precision model (domain-specific KI) with multiple pathway readouts and confocal imaging; multiple orthogonal methods in single study","pmids":["24356888"],"is_preprint":false},{"year":2015,"finding":"CD5 instructs extrathymic regulatory T cell (Treg) induction by blocking mTOR activation. CD5hi T cells were resistant to inhibition of Treg induction by IL-4, IL-6, and IFN-γ from bystander lymphocytes, while Cd5-/- and CD5lo T cells were sensitized. CD5 promoted Treg cell conversion by blocking mTOR activation.","method":"CD5-/- mice; CD5 transgenic mice; in vitro Treg induction assays with bystander cytokines; mTOR activity measurement; flow cytometric analysis of FoxP3+ Treg conversion","journal":"Immunity","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic loss-of-function (KO) and gain-of-function (transgenic), mTOR pathway mechanistic readout, multiple cytokine conditions tested","pmids":["25786177"],"is_preprint":false},{"year":2011,"finding":"CD5 costimulation promotes stable human Th17 development by prolonging STAT3 activation and upregulating IL-23 receptor (IL-23R) expression. Compared with CD28 costimulation, CD5 costimulation induced more IL-17-producing cells, increased RORγt levels, and critically depended on CD5-induced IL-23R elevation.","method":"Human naive T cell differentiation assays with CD5, CD6, or CD28 costimulation; intracellular cytokine staining; STAT3 phosphorylation kinetics; IL-23R expression by flow cytometry; RORγt measurement","journal":"Blood","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — primary human T cell functional assay with pathway readouts (STAT3, RORγt, IL-23R); single lab, multiple methods","pmids":["21926348"],"is_preprint":false},{"year":2017,"finding":"In CLL cells, CD5 is part of a CK2–CD5–BLNK–STAT3 complex that is required for constitutive serine 727 phosphorylation of STAT3. In vitro, activated CK2 directly phosphorylated recombinant STAT3 on Ser727. siRNA knockdown of CD5 or BLNK, and CD5-neutralizing antibodies, significantly reduced pSTAT3 levels. Fractionation showed the complex resides in the cytoplasm, while pSTAT3 is shuttled to the nucleus.","method":"Mass spectrometry co-immunoprecipitation; reciprocal co-IP for CK2, CD5, BLNK, STAT3; in vitro kinase assay with recombinant STAT3; siRNA knockdown; CD5-neutralizing antibodies; confocal microscopy; subcellular fractionation","journal":"Molecular cancer research : MCR","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — mass spectrometry + reciprocal co-IP + in vitro kinase assay + siRNA KD + antibody neutralization + fractionation; multiple orthogonal methods","pmids":["28130399"],"is_preprint":false},{"year":2016,"finding":"CD5 mRNA expression in human T cells is regulated post-transcriptionally by alternative polyadenylation (APA), PTBP1, and miR-204. Upon TCR activation, shorter 3'-UTR CD5 mRNA isoforms are preferentially expressed. PTBP1 directly binds the proximal poly(A) signal and PTBP1 siRNA depletion reduces mRNA from that poly(A) site. Shorter isoforms confer higher reporter expression in activated T cells, and the longer isoform is subject to miR-204-mediated repression.","method":"3'-UTR reporter assays; RT-PCR for CD5 isoforms in primary human T cells and Jurkat cells; siRNA knockdown of PTBP1; RNA binding assay for PTBP1 to poly(A) signal","journal":"European journal of immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional reporter assays, siRNA knockdown with mechanistic readout; single lab","pmids":["27005442"],"is_preprint":false},{"year":2020,"finding":"CD5 signalosome in primary T cells: TCR engagement induces phosphorylation of CD5 tyrosine 429, which serves as a docking site for adaptor proteins c-Cbl, CIN85, and CRKL. c-Cbl acts as a coordinator enabling CD5 to simultaneously engage positive (PI3K) and negative (UBASH3A, SHIP1) regulators of TCR signaling. Disruption of the CD5 signalosome (mutant mice) selectively represses Foxp3 transactivation and limits inopportune peripheral Treg induction during responses to foreign antigen.","method":"Quantitative mass spectrometry; genetic studies in mutant mice (Y429 mutation); phosphoproteomics; co-immunoprecipitation; in vitro and in vivo Treg induction assays; Foxp3 reporter","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — quantitative phosphoproteomics + genetic knock-in mutant mice + multiple binding partners identified by mass spectrometry + functional in vivo readout; multiple rigorous orthogonal methods","pmids":["32434911"],"is_preprint":false},{"year":1998,"finding":"CD5 binds a novel B-cell surface ligand (CD5L, distinct from CD72) composed of 77–80 and 38–40 kDa polypeptide chains. CD5-Ig fusion protein induced proliferation of resting B cells and bound this ligand on activated splenic B cells and peritoneal B cells but not T cells. Anti-CD72 antibodies did not block CD5-Ig binding, and CD5-Ig did not bind CD72-transfected cells, ruling out CD72 as the binding partner in this context.","method":"CD5-Ig chimeric fusion protein binding assays; flow cytometry with anti-CD72 blocking antibodies; immunoprecipitation of surface-labeled B cell molecules with CD5-Ig; transfection of CD72 into non-B cells (negative result for CD5-Ig binding)","journal":"International immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — CD5-Ig pulldown with biochemical characterization of novel ligand; anti-CD72 blocking and CD72-transfection negative controls strengthen specificity; single lab","pmids":["9723705"],"is_preprint":false},{"year":1999,"finding":"Recombinant soluble CD5 extracellular domain binds a broadly distributed alternative cell surface receptor on monocytes, lymphocytes, and various cell lines (lymphoid, myelomonocytic, epithelial). This binding is divalent cation-independent and inhibited by high concentrations of certain monosaccharides. Natural soluble CD5 from human serum and CD5-Ig fusion proteins compete with recombinant soluble CD5 for this binding. CD5 SRCR domains D1 and D2 are involved.","method":"Recombinant soluble CD5 extracellular domain glycoprotein cell binding assays; competition with monosaccharides, CD5-Ig fusion proteins, and natural soluble CD5; domain-deletion competition assays","journal":"European journal of immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — recombinant protein binding with domain-level competition and competition with natural soluble form; single lab","pmids":["10427974"],"is_preprint":false},{"year":2011,"finding":"The full-length CD5 protein variant (encoded by E1A) translocates SHP-1 (SH2-containing phosphatase 1) to the vicinity of the BCR, raises the BCR signaling threshold, and limits responses of autoreactive B cells. The truncated variant (encoded by E1B) remains in the cytoplasm along with SHP-1, preventing this negative regulatory function.","method":"Review synthesizing transfection and biochemical studies from prior publications (mechanistic summary based on experimental data from the laboratory)","journal":"Critical reviews in immunology","confidence":"Low","confidence_rationale":"Tier 3 / Weak — mechanistic model presented in review, no new primary experiment described in this abstract; underlying data presumably from prior papers","pmids":["21395509"],"is_preprint":false},{"year":2011,"finding":"CD5 expression promotes constitutive activation of ERK1/2, PI3K/mTOR, and calcineurin-NFAT signaling pathways in B lymphocytes, and changes in IL-10 production are related to activation of transcription factors NFAT2 and STAT3.","method":"CD5 transfection into B cells; western blot for phosphorylated signaling intermediates; transcription factor activation assays; IL-10 measurement","journal":"Autoimmunity reviews","confidence":"Low","confidence_rationale":"Tier 3 / Weak — review article summarizing the lab's own findings; abstract does not detail controls or confirm with orthogonal methods","pmids":["22349614"],"is_preprint":false},{"year":2011,"finding":"CD5 expression on dendritic cells is required to generate optimally protective CD5hi T helper and CD8+ T cells. Activating CD5 on DCs enhanced T cell priming. CD5+ DC numbers increased during immune checkpoint blockade (ICB) therapy. Deletion of CD5 from T cells dampened tumor elimination in response to ICB therapy in vivo. Low IL-6 concentrations promoted de novo differentiation of CD5+ DCs.","method":"In vivo mouse tumor models; conditional CD5 deletion from T cells; DC subset analysis in human melanoma-affected lymph nodes; ICB therapy studies; IL-6 concentration manipulation for DC differentiation","journal":"Science (New York, N.Y.)","confidence":"High","confidence_rationale":"Tier 2 / Strong — in vivo genetic loss-of-function (conditional CD5 KO in T cells), human patient lymph node data, DC functional assay, mechanistic link to IL-6; multiple complementary approaches","pmids":["36795805"],"is_preprint":false},{"year":2024,"finding":"CD5 inhibits CAR T cell activation. CRISPR-Cas9 knockout of CD5 enhances CAR T cell antitumor effect in multiple hematological and solid cancer models by driving increased effector function, enhanced cytotoxicity, in vivo expansion, and persistence without apparent toxicity.","method":"CRISPR-Cas9 CD5 KO in CAR T cells; in vitro cytotoxicity assays; in vivo mouse tumor models with hematological and solid cancers; flow cytometric analysis of expansion and persistence","journal":"Science immunology","confidence":"High","confidence_rationale":"Tier 2 / Strong — CRISPR KO with clean phenotypic readout across multiple cancer models in vitro and in vivo; mechanistic conclusion of CD5 as inhibitor of T cell function supported by multiple models","pmids":["39028827"],"is_preprint":false},{"year":2014,"finding":"CD5-CD72 interaction maintains regulatory T and B cell homeostasis. Blockade of CD5 or CD72 with neutralizing antibodies reduced both IL-10-expressing Bregs and FoxP3+ Tregs in co-culture. FoxP3+CD4+ Tregs were reduced in CD19-Cre mice deficient in B-cell-surface CD5.","method":"Cell culture with neutralizing antibodies against CD5 and CD72; flow cytometric analysis of Treg and Breg populations; CD19-Cre conditional B-cell CD5 deficient mice","journal":"Immunological investigations","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — neutralizing antibody blockade plus conditional genetic KO; in vitro and in vivo components; single lab","pmids":["24950378"],"is_preprint":false},{"year":2011,"finding":"The nonsynonymous A471V substitution (rs2229177) in the CD5 cytoplasmic domain affects MAPK cascade activation. Cross-linking of CD5 revealed significant differences between A471V variants in MAPK pathway activation in COS7 cells and human PBMCs. The A471V variants also differ in MAPK activation and IL-8 release upon exposure to Zymosan (a β-glucan-rich fungal particle) in HEK293 cell transfectants, indicating CD5 recognizes microbial β-glucans and that A471V modulates this response.","method":"Anti-CD5 mAb cross-linking; western blot for MAPK activation; HEK293 cell transfectants expressing A471V variants; Zymosan stimulation; IL-8 ELISA","journal":"Molecular biology and evolution","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — gain-of-function transfection with defined variants, multiple functional readouts (MAPK, IL-8), microbial ligand identification; single lab","pmids":["21998275"],"is_preprint":false}],"current_model":"CD5 is a scavenger receptor cysteine-rich (SRCR) family transmembrane glycoprotein expressed on all T cells and a subset of B cells (B-1a) that functions as an inhibitory co-receptor: its cytoplasmic domain is phosphorylated at Y429 and Y463 by Lck, constitutively associates with and activates CK2 (at Ser459/461), recruits adaptor proteins (c-Cbl, CIN85, CRKL) and phosphatases (SHP-1, SHIP1, UBASH3A) via Y429 as a docking site upon TCR engagement, thereby dampening TCR- and BCR-mediated calcium flux and downstream signaling; CD5 surface expression is proportional to TCR avidity and transcriptionally regulated by alternative exon usage (E1A vs. E1B), APA/PTBP1/miR-204, and IL-6-driven DNA methylation changes; its extracellular domain binds CD72 on B cells and mediates homophilic interactions that further modulate inhibitory signaling; through CK2-dependent activation of AKT/mTOR and inhibition of GSK3, CD5 promotes Th17 and Th2 differentiation while also governing peripheral Treg induction and IL-10-driven B cell survival; CD5 on dendritic cells is additionally required to prime optimal CD5hi T helper and CD8+ T cells."},"narrative":{"mechanistic_narrative":"CD5 is a transmembrane glycoprotein expressed on T cells and a subset of B cells that functions as an inhibitory co-receptor tuning the threshold of antigen-receptor signaling [PMID:10704468, PMID:20952682]. Its surface level is set by the strength of the positively selecting TCR-MHC interaction during thymocyte development and parallels TCR avidity, and its cytoplasmic domain is required for its inhibitory role in selection [PMID:9858516, PMID:11313384]. Upon TCR engagement, Lck phosphorylates CD5 at Y429 and Y463, with Y429 serving as a docking site for a signalosome of adaptors (c-Cbl, CIN85, CRKL) that allows CD5 to simultaneously engage positive (PI3K) and negative (UBASH3A, SHIP1) TCR-signaling regulators [PMID:11298344, PMID:32434911]. In parallel, CD5 constitutively associates with CK2 through the regulatory beta subunit and is phosphorylated by it at Ser459/461; cross-linking activates CD5-associated CK2, and this CK2 axis sets T cell responsiveness and, via AKT-dependent inhibition of GSK3 and activation of mTOR, drives Th17 and Th2 differentiation [PMID:9668105, PMID:22904299, PMID:24356888]. CD5 signaling instructs immune outcomes by blocking mTOR to favor peripheral Treg induction, while the signalosome restrains inopportune Foxp3 transactivation [PMID:25786177, PMID:32434911]. In B cells, CD5 raises the BCR signaling threshold to enforce tolerance of anergic and autoreactive cells and promotes B cell survival through autocrine IL-10 [PMID:10704468, PMID:12393419]. The extracellular SRCR domains engage CD72 and also mediate homophilic CD5-CD5 interactions through domain 1, both contributing inhibitory tuning, and CD5-CD72 engagement supports Treg and IL-10+ Breg homeostasis [PMID:1711157, PMID:20952682, PMID:24950378]. Surface CD5 abundance is further controlled by alternative exon-1 usage (membrane E1A versus intracellularly retained E1B), IL-6-driven promoter demethylation, and post-transcriptional control by alternative polyadenylation, PTBP1, and miR-204 [PMID:15998834, PMID:19380809, PMID:27005442]. CD5 on dendritic cells is required to prime optimally protective CD5hi T helper and CD8+ T cells, and its inhibitory function in effector T cells is therapeutically relevant: CD5 deletion enhances CAR T cell antitumor activity [PMID:36795805, PMID:39028827].","teleology":[{"year":1991,"claim":"Identifying a physiological CD5 ligand addressed how CD5's extracellular domain engages partner cells, establishing CD72 as a B-cell counter-receptor.","evidence":"Biotin-labeled CD5 binding to B cells, anti-CD72 antibody blocking, and CD72 cDNA transfection conferring binding to non-B cells","pmids":["1711157"],"confidence":"High","gaps":["Did not establish the downstream signaling consequence of CD5-CD72 engagement","Affinity and stoichiometry of the interaction not defined"]},{"year":1998,"claim":"Defining cytoplasmic-domain binding partners revealed how CD5 transduces signals, identifying a constitutive CK2 association and serine phosphorylation as a core effector mechanism.","evidence":"Yeast two-hybrid screen, reciprocal co-IP in B and T cell lines and splenocytes, in vitro kinase assay mapping Ser459/461, and CD5 cross-linking","pmids":["9668105"],"confidence":"High","gaps":["Did not define the functional output of CK2 activation at the time","Additional cytoplasmic partners (CaMKIIdelta, Tctex-1) reported separately at Medium confidence"]},{"year":1998,"claim":"Linking CD5 surface levels to TCR signal strength explained why CD5 expression varies, establishing it as a readout and rheostat of TCR avidity during selection.","evidence":"Flow cytometry across pre-TCR-deficient, lck-deficient, and TCR transgenic mouse models","pmids":["9858516"],"confidence":"High","gaps":["Did not resolve the molecular signal that sets the expression set-point","Causality of CD5 level on selection outcome shown in a later study"]},{"year":2000,"claim":"Testing CD5 in a B-cell anergy model established that CD5 enforces B-cell tolerance by negatively regulating BCR signaling.","evidence":"CD5-KO crossed to HEL/sHEL anergy model with anti-HEL IgM ELISA, proliferation, and Ca2+ flux readouts","pmids":["10704468"],"confidence":"High","gaps":["Did not identify the cytoplasmic effectors mediating BCR inhibition","Mechanism of recruitment to the BCR not defined"]},{"year":2001,"claim":"Mapping CD5 tyrosine phosphorylation sites and the responsible kinase clarified how TCR engagement activates CD5, showing Lck-dependent phosphorylation at Y429 and Y463.","evidence":"Tyrosine-mutant transfectants, in vitro kinase assays with recombinant Lck and Fyn, and Lck-deficient Jurkat cells","pmids":["11298344"],"confidence":"High","gaps":["Did not identify the effectors recruited to phosphorylated tyrosines","Relative roles of Y429 vs Y463 not resolved"]},{"year":2001,"claim":"Genetic dissection showed the CD5 cytoplasmic domain is required for inhibitory function and that CD5 dosage shifts the balance between positive and negative thymocyte selection.","evidence":"CD5 overexpression, cytoplasmic-truncation knock-in, and KO mice in TCR transgenic crosses scored for selection outcomes","pmids":["11313384"],"confidence":"High","gaps":["Did not assign the relevant cytoplasmic motif","Connection to specific downstream pathway left open"]},{"year":2002,"claim":"Demonstrating CD5-driven autocrine IL-10 revealed a pro-survival output beyond signal inhibition, linking CD5 to B-cell persistence.","evidence":"CD5 transfection into CD5- B cells with IL-10 promoter reporter, RT-PCR, Ca2+ flux, and apoptosis assays","pmids":["12393419"],"confidence":"High","gaps":["Transcription factors coupling CD5 to the IL-10 promoter not fully defined here","In vivo relevance to B-cell survival not directly tested"]},{"year":2005,"claim":"Discovery of the B-cell-specific E1B exon explained a mechanism for tuning surface CD5, showing an intracellularly retained isoform that lowers membrane CD5.","evidence":"Alternative exon sequencing, RT-PCR across B-cell subsets, E1B transfection into Jurkat cells with flow cytometry","pmids":["15998834"],"confidence":"Medium","gaps":["Single lab; physiological regulators of E1A/E1B choice not established here","Functional consequence shown only as reduced membrane expression"]},{"year":2009,"claim":"Connecting IL-6 to CD5-E1B promoter methylation defined an inflammatory-cytokine route that lowers membrane CD5 in SLE B cells.","evidence":"Bisulfite sequencing, methylation-sensitive endonuclease assays, isoform RT-PCR, and anti-IL6R blockade in SLE vs healthy B cells","pmids":["19380809"],"confidence":"Medium","gaps":["Single lab; causal contribution to SLE pathology not established","DNMT1 link not validated by genetic perturbation"]},{"year":2010,"claim":"Identifying homophilic CD5-CD5 binding through domain 1 revealed an additional inhibitory engagement mode independent of CD72.","evidence":"Soluble CD5 binding assays, domain-1 mutagenesis, blocking mAb IgG/Fab, and T-cell activation and rat lymph node functional assays","pmids":["20952682"],"confidence":"High","gaps":["Physiological context of homophilic engagement in vivo not defined","Relationship between homophilic binding and CD72 binding not resolved"]},{"year":2012,"claim":"A CK2-binding-domain knock-in mouse established that CD5-CK2 signaling sets T-cell responsiveness and selectively drives Th2/Th17 differentiation, phenocopying CD5-KO.","evidence":"CD5ΔECK2BD knock-in mice with proliferation, AICD, Th differentiation, EAE, and high-dose tolerance assays","pmids":["22904299"],"confidence":"High","gaps":["Did not detail the intracellular pathway downstream of CK2 at this stage","Th1 differentiation unaffected, leaving lineage selectivity mechanism open"]},{"year":2014,"claim":"Mechanistic dissection placed CD5-CK2 upstream of AKT, defining GSK3 inhibition and mTOR activation as the route by which CD5 stabilizes Th17 differentiation.","evidence":"CD5ΔECK2BD mice with AKT/GSK3/mTOR/S6K phospho-westerns, RORγt confocal imaging, and IFN-γ sensitivity assays","pmids":["24356888"],"confidence":"High","gaps":["Direct CK2 substrate linking to AKT not pinpointed","Generalizability to human Th17 left to a separate study"]},{"year":2015,"claim":"Linking CD5 to extrathymic Treg induction showed CD5 promotes Treg conversion by blocking mTOR, protecting cells from bystander-cytokine inhibition.","evidence":"CD5-KO and transgenic mice in Treg induction assays with IL-4/IL-6/IFN-γ and mTOR readouts","pmids":["25786177"],"confidence":"High","gaps":["Reconciliation with pro-mTOR Th17 role not fully resolved","Molecular link between CD5 and mTOR suppression in this context not detailed"]},{"year":2016,"claim":"Post-transcriptional analysis revealed that APA, PTBP1, and miR-204 shorten the CD5 3'UTR upon TCR activation to raise CD5 output.","evidence":"3'UTR reporters, isoform RT-PCR in primary and Jurkat T cells, PTBP1 siRNA, and PTBP1 poly(A) binding assay","pmids":["27005442"],"confidence":"Medium","gaps":["Single lab; impact on endogenous CD5 protein levels not quantified","Interplay with transcriptional/isoform regulation not integrated"]},{"year":2017,"claim":"Defining a cytoplasmic CK2-CD5-BLNK-STAT3 complex in CLL showed CD5 sustains constitutive STAT3 Ser727 phosphorylation in malignant B cells.","evidence":"Mass-spec co-IP, reciprocal co-IP, in vitro CK2 kinase assay on recombinant STAT3, CD5/BLNK siRNA, neutralizing antibodies, and fractionation","pmids":["28130399"],"confidence":"High","gaps":["Whether the complex operates similarly in normal B cells not established","Functional consequence for CLL survival not directly tested here"]},{"year":2020,"claim":"Phosphoproteomics defined the Y429 signalosome, showing c-Cbl coordinates simultaneous recruitment of positive (PI3K) and negative (UBASH3A, SHIP1) regulators and restrains peripheral Treg induction.","evidence":"Quantitative mass spectrometry, Y429-mutant knock-in mice, co-IP, and in vivo Treg/Foxp3 reporter assays","pmids":["32434911"],"confidence":"High","gaps":["Stoichiometry and dynamics of competing positive/negative branches not resolved","How signalosome integrates with the CK2 axis not defined"]},{"year":2023,"claim":"Studying CD5 on dendritic cells revealed a cell-extrinsic role: DC CD5 is required to prime optimally protective CD5hi T helper and CD8+ T cells and shapes responses to checkpoint blockade.","evidence":"In vivo tumor models, conditional CD5 deletion in T cells, human melanoma lymph-node DC analysis, ICB studies, and IL-6 manipulation of DC differentiation","pmids":["36795805"],"confidence":"High","gaps":["Molecular mechanism by which DC CD5 instructs T-cell priming not detailed","Ligand engaged by DC CD5 during priming not identified"]},{"year":2024,"claim":"CRISPR knockout established CD5 as a brake on effector T cells with therapeutic implications, as CD5 deletion enhances CAR T-cell antitumor function.","evidence":"CRISPR-Cas9 CD5 KO in CAR T cells with in vitro cytotoxicity and in vivo hematological and solid tumor models","pmids":["39028827"],"confidence":"High","gaps":["The cytoplasmic effector responsible for the inhibitory brake in CAR T cells not isolated","Long-term safety and exhaustion phenotype not fully characterized"]},{"year":null,"claim":"How the CK2-serine axis and the Y429 tyrosine signalosome are functionally integrated, and which engagements (CD72, homophilic, microbial β-glucan) dominate in each cellular context, remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No unified model coupling CK2-driven and tyrosine-driven branches","Context-specific dominance among CD5 ligands not established","Structural basis of CD5 signaling outputs lacking"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[5,11,18]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[18,16]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[12,8]},{"term_id":"GO:0001618","term_label":"virus receptor activity","supporting_discovery_ids":[0,11]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[0,3,11]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[16,9]}],"pathway":[{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[5,12,14,18]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[8,13,18]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[10,16,24]}],"complexes":["CD5-CK2 complex","CK2-CD5-BLNK-STAT3 complex (CLL)","CD5 Y429 signalosome (c-Cbl/CIN85/CRKL/UBASH3A/SHIP1)"],"partners":["CD72","CSNK2B","LCK","CBL","SH3KBP1","CRKL","BLNK","STAT3"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P06127","full_name":"T-cell surface glycoprotein CD5","aliases":["Lymphocyte antigen T1/Leu-1"],"length_aa":495,"mass_kda":54.6,"function":"Lymphoid-specific receptor expressed by all T-cells and in a subset of B-cells known as B1a cells. 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Modulates B-cell biology through ERK1/2 activation in a Ca(2+)-dependent pathway via the non-selective Ca(2+) channel TRPC1, leading to IL-10 production (PubMed:27499044)","subcellular_location":"Cell membrane","url":"https://www.uniprot.org/uniprotkb/P06127/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/CD5","classification":"Not Classified","n_dependent_lines":37,"n_total_lines":1208,"dependency_fraction":0.030629139072847682},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/CD5","total_profiled":1310},"omim":[{"mim_id":"617684","title":"Ly1 ANTIBODY-REACTIVE PROTEIN; LYAR","url":"https://www.omim.org/entry/617684"},{"mim_id":"615559","title":"AUTOIMMUNE LYMPHOPROLIFERATIVE SYNDROME, TYPE III; ALPS3","url":"https://www.omim.org/entry/615559"},{"mim_id":"613493","title":"IMMUNODEFICIENCY, COMMON VARIABLE, 3; CVID3","url":"https://www.omim.org/entry/613493"},{"mim_id":"612268","title":"TUBULIN TYROSINE LIGASE-LIKE 5; TTLL5","url":"https://www.omim.org/entry/612268"},{"mim_id":"610408","title":"SOLUTE CARRIER FAMILY 15 (OLIGOPEPTIDE TRANSPORTER), MEMBER 3; SLC15A3","url":"https://www.omim.org/entry/610408"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"lymphoid 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CD5 protein, labelled with biotin, specifically bound to B-cell surface CD72; this binding was blocked by anti-CD72 antibodies but not other anti-B-cell antibodies. Non-B cells transfected with human CD72 cDNA gained ability to bind CD5-biotin conjugate.\",\n      \"method\": \"Biotin-labeled CD5 used as probe on cells; blocking with anti-CD72 antibodies; transfection of CD72 cDNA into non-B cells (mouse L-cells and Jurkat T cells)\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — direct biochemical binding assay with biotin-labeled protein, blocking antibody controls, and gain-of-function transfection experiment; replicated across multiple cell types\",\n      \"pmids\": [\"1711157\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"The beta subunit of casein kinase 2 (CK2) interacts specifically with the cytoplasmic domain of CD5. CK2 holoenzyme associates constitutively with CD5 in human and murine B and T cell lines and murine splenocytes, mediated by the amino terminus of the CK2 regulatory beta subunit. CK2 binds and phosphorylates CD5 at Ser459 and Ser461 (CK2 motifs). Cross-linking of CD5 activates CD5-associated CK2 independently of net CK2 recruitment, and this activation is not triggered by BCR or TCR cross-linking.\",\n      \"method\": \"Yeast two-hybrid screen; co-immunoprecipitation in human and murine B and T cell lines and splenocytes; in vitro kinase assay; CD5 cross-linking\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — yeast two-hybrid discovery confirmed by reciprocal co-IP in multiple cell types, in vitro phosphorylation assay, site identification at Ser459/461, and functional cross-linking experiment\",\n      \"pmids\": [\"9668105\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"The cytoplasmic domain of CD5 interacts with Ca2+/calmodulin-dependent kinase IIdelta (CaMKIIdelta) and with Tctex-1 (a dynein light chain component). The CaMKIIdelta interaction was confirmed in vitro using fusion proteins.\",\n      \"method\": \"Yeast two-hybrid screen; in vitro binding assay with fusion proteins\",\n      \"journal\": \"European journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — yeast two-hybrid plus in vitro fusion protein binding; single lab, two complementary methods\",\n      \"pmids\": [\"9692886\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"CD5 surface expression during thymocyte development is regulated by TCR signals: low-level expression on DN thymocytes requires pre-TCR engagement and p56(lck) activity; DP thymocyte CD5 levels are maintained by low-affinity TCR-MHC interactions; high-level CD5 is induced by positively or negatively selecting TCR-MHC ligands. CD5 surface expression on mature T cells directly parallels TCR avidity/signaling intensity of the positively selecting interaction.\",\n      \"method\": \"Analysis of CD5 expression in mice with defined developmental and signal transduction defects (pre-TCR deficient, lck-deficient, TCR transgenic); flow cytometry\",\n      \"journal\": \"The Journal of experimental medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic loss-of-function models (multiple mutant strains) with quantitative flow cytometry readout, replicated across developmental stages\",\n      \"pmids\": [\"9858516\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"The cytoplasmic domain of CD5 is required for its inhibitory function in thymocyte selection. A transgene encoding a truncated (cytoplasmic domain-deleted) form of CD5 failed to rescue the CD5-/- phenotype in thymocyte selection. CD5 overexpression or deletion shifted thymocyte selection toward positive or negative selection, respectively, in a manner dependent on TCR avidity and basal CD5 expression levels.\",\n      \"method\": \"CD5 transgenic mice (overexpression and truncation knock-in); CD5-/- mice; TCR transgenic crosses; analysis of thymocyte selection outcomes\",\n      \"journal\": \"Journal of immunology (Baltimore, Md. : 1950)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple genetic models (KO, overexpressor, cytoplasmic domain truncation) with defined phenotypic readout (thymocyte selection), complementary approaches in one study\",\n      \"pmids\": [\"11313384\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"CD5 negatively regulates BCR signaling in anergic B cells to maintain B cell tolerance. CD5-/- mice in the HEL/sHEL anergy model showed loss of B cell tolerance (elevated anti-HEL IgM), and 'anergic' B cells lacking CD5 had enhanced proliferative responses and elevated intracellular Ca2+ at rest and after IgM cross-linking.\",\n      \"method\": \"CD5 knockout mice crossed with HEL transgenic anergy model; serum ELISA for anti-HEL IgM; in vitro proliferation assay; intracellular Ca2+ measurement\",\n      \"journal\": \"The Journal of experimental medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean genetic KO in well-established anergy model with multiple orthogonal readouts (antibody levels, proliferation, Ca2+ flux)\",\n      \"pmids\": [\"10704468\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"CD5 promotes B cell survival by stimulating autocrine IL-10 production. Introduction of CD5 into CD5- B cells activated the IL-10 promoter and induced IL-10 mRNA and protein. The cytoplasmic domain of CD5 was sufficient for this effect. CD5 also protected normal human B cells from apoptosis after BCR stimulation while reducing BCR-induced Ca2+ responses.\",\n      \"method\": \"Transfection of CD5 into CD5- B cells; IL-10 promoter reporter assay; RT-PCR for IL-10 mRNA; Ca2+ flux measurement; apoptosis assay\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — gain-of-function transfection with multiple orthogonal readouts (promoter activity, mRNA, protein, Ca2+, apoptosis), cytoplasmic domain sufficiency established\",\n      \"pmids\": [\"12393419\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"CD5 functions as a negative regulator of BCR signaling and may help prevent inappropriate activation of autoreactive B-1a cells.\",\n      \"method\": \"Review summarizing CD5-/- mouse data and B-1a cell biology (mechanistic context from experimental literature)\",\n      \"journal\": \"Annual review of immunology\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 4 / Weak — review article summary, no new primary experiment described in the abstract\",\n      \"pmids\": [\"11861604\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Residues Y429 and Y463 of human CD5 are phosphorylated in vivo by protein tyrosine kinases following T cell stimulation. In vitro kinase assays with purified recombinant Lck and Fyn confirmed direct phosphorylation at these sites. Lck-deficient Jurkat cells showed absent CD5 tyrosine phosphorylation, establishing that Lck is required for CD5 tyrosine phosphorylation.\",\n      \"method\": \"Tyrosine-mutated CD5 transfectants in Jurkat cells; anti-CD3 mAb and pervanadate stimulation; in vitro kinase assays with recombinant Lck and Fyn; analysis in Lck-deficient and CD3-deficient Jurkat cells\",\n      \"journal\": \"European journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — site-directed mutagenesis of phosphorylation sites, in vitro kinase assay with purified kinases, genetic loss-of-function (Lck-deficient cells); multiple orthogonal methods\",\n      \"pmids\": [\"11298344\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"An alternative exon 1 (E1B) of the human CD5 gene, found exclusively in B lymphocytes, encodes a truncated protein that is retained intracellularly rather than transported to the membrane. Presence of E1B-containing transcripts reduces E1A-containing transcript levels and diminishes membrane CD5 expression. Introduction of E1B into Jurkat cells reduced membrane CD5 expression. E1B contains sequence of a defective human endogenous retrovirus.\",\n      \"method\": \"Identification of alternative exon by sequencing; RT-PCR in B cell subsets including CLL and pre-B cells; transfection of E1B into Jurkat cells with flow cytometric assessment of membrane CD5; bisulfite/methylation analysis\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — discovery of novel regulatory exon with gain-of-function transfection showing functional consequence on membrane CD5 levels; single lab\",\n      \"pmids\": [\"15998834\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"In SLE B cells, IL-6 prevents DNMT1 induction, leading to demethylation of the CD5-E1B promoter. This causes preferential transcription of CD5-E1B at the expense of CD5-E1A, reducing membrane CD5 expression. BCR engagement amplifies this effect. Blocking IL-6 receptor reverses the demethylation.\",\n      \"method\": \"Bisulfite sequencing; methylation-sensitive endonuclease assays; RT-PCR for E1A and E1B isoforms; IL-6 receptor blocking antibody; DNMT1 expression analysis in SLE vs healthy B cells\",\n      \"journal\": \"Journal of immunology (Baltimore, Md. : 1950)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple biochemical methods (bisulfite sequencing, endonuclease assay, RT-PCR) with functional intervention (anti-IL6R); single lab\",\n      \"pmids\": [\"19380809\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"CD5 mediates species-specific homophilic interactions (CD5 is a ligand for itself). Only CD5 domain 1 is involved. CD5 monoclonal antibodies that have functional effects block homophilic binding. Inhibition of CD5 domain 1 engagement (by mutation or by IgG/Fab from a blocking mAb) increased antigen-specific T cell responses in vitro, and a blocking Fab enhanced polyclonal immune responses of rat lymph node cells, demonstrating that homophilic CD5 binding exerts inhibitory function.\",\n      \"method\": \"Soluble CD5 purified at neutral pH; binding assays; site-directed mutation of domain 1; blocking monoclonal antibodies (IgG and Fab fragments); in vitro T cell activation assays; rat lymph node polyclonal stimulation assay\",\n      \"journal\": \"Journal of immunology (Baltimore, Md. : 1950)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — biochemical binding assay with domain-specific mutagenesis, functional blocking with antibody Fab fragments, in vitro functional consequence; multiple orthogonal approaches\",\n      \"pmids\": [\"20952682\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"CD5-dependent CK2 activation sets the threshold for T cell responsiveness. A CD5 knock-in mouse with selective deletion of the CK2-binding domain (CD5ΔECK2BD) showed hypoproliferation, enhanced activation-induced cell death, and defective Th2 and Th17 (but not Th1) differentiation of CD4+ T cells upon stimulation. CD5ΔECK2BD mice recapitulated the reduced EAE severity of CD5-KO mice and were unable to generate high-dose tolerance, phenocopying CD5-KO.\",\n      \"method\": \"Knock-in mouse with microdeletion of CK2-binding domain in CD5; T cell proliferation assays; activation-induced cell death measurement; Th differentiation assays in vitro and in vivo; EAE model; high-dose tolerance assay\",\n      \"journal\": \"Journal of immunology (Baltimore, Md. : 1950)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — precision knock-in mouse model with selective domain disruption, multiple orthogonal functional readouts (proliferation, AICD, Th differentiation, EAE, tolerance), phenocopies KO\",\n      \"pmids\": [\"22904299\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"CD5-CK2 signaling promotes Th17 differentiation via two independent mechanisms: inhibition of GSK3 and activation of mTOR, both downstream of AKT. Loss of CD5-CK2 signaling reduced AKT activation, increased GSK3 activity, sensitized Th17 cells to IFN-γ-mediated inhibition, decreased S6K activity, and attenuated nuclear translocation of RORγt.\",\n      \"method\": \"CD5ΔECK2BD knock-in mice; in vitro Th17 differentiation assays; AKT/GSK3/mTOR/S6K phosphorylation by western blot; RORγt nuclear localization by confocal microscopy; IFN-γ sensitivity assays\",\n      \"journal\": \"European journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic precision model (domain-specific KI) with multiple pathway readouts and confocal imaging; multiple orthogonal methods in single study\",\n      \"pmids\": [\"24356888\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"CD5 instructs extrathymic regulatory T cell (Treg) induction by blocking mTOR activation. CD5hi T cells were resistant to inhibition of Treg induction by IL-4, IL-6, and IFN-γ from bystander lymphocytes, while Cd5-/- and CD5lo T cells were sensitized. CD5 promoted Treg cell conversion by blocking mTOR activation.\",\n      \"method\": \"CD5-/- mice; CD5 transgenic mice; in vitro Treg induction assays with bystander cytokines; mTOR activity measurement; flow cytometric analysis of FoxP3+ Treg conversion\",\n      \"journal\": \"Immunity\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic loss-of-function (KO) and gain-of-function (transgenic), mTOR pathway mechanistic readout, multiple cytokine conditions tested\",\n      \"pmids\": [\"25786177\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"CD5 costimulation promotes stable human Th17 development by prolonging STAT3 activation and upregulating IL-23 receptor (IL-23R) expression. Compared with CD28 costimulation, CD5 costimulation induced more IL-17-producing cells, increased RORγt levels, and critically depended on CD5-induced IL-23R elevation.\",\n      \"method\": \"Human naive T cell differentiation assays with CD5, CD6, or CD28 costimulation; intracellular cytokine staining; STAT3 phosphorylation kinetics; IL-23R expression by flow cytometry; RORγt measurement\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — primary human T cell functional assay with pathway readouts (STAT3, RORγt, IL-23R); single lab, multiple methods\",\n      \"pmids\": [\"21926348\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"In CLL cells, CD5 is part of a CK2–CD5–BLNK–STAT3 complex that is required for constitutive serine 727 phosphorylation of STAT3. In vitro, activated CK2 directly phosphorylated recombinant STAT3 on Ser727. siRNA knockdown of CD5 or BLNK, and CD5-neutralizing antibodies, significantly reduced pSTAT3 levels. Fractionation showed the complex resides in the cytoplasm, while pSTAT3 is shuttled to the nucleus.\",\n      \"method\": \"Mass spectrometry co-immunoprecipitation; reciprocal co-IP for CK2, CD5, BLNK, STAT3; in vitro kinase assay with recombinant STAT3; siRNA knockdown; CD5-neutralizing antibodies; confocal microscopy; subcellular fractionation\",\n      \"journal\": \"Molecular cancer research : MCR\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — mass spectrometry + reciprocal co-IP + in vitro kinase assay + siRNA KD + antibody neutralization + fractionation; multiple orthogonal methods\",\n      \"pmids\": [\"28130399\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"CD5 mRNA expression in human T cells is regulated post-transcriptionally by alternative polyadenylation (APA), PTBP1, and miR-204. Upon TCR activation, shorter 3'-UTR CD5 mRNA isoforms are preferentially expressed. PTBP1 directly binds the proximal poly(A) signal and PTBP1 siRNA depletion reduces mRNA from that poly(A) site. Shorter isoforms confer higher reporter expression in activated T cells, and the longer isoform is subject to miR-204-mediated repression.\",\n      \"method\": \"3'-UTR reporter assays; RT-PCR for CD5 isoforms in primary human T cells and Jurkat cells; siRNA knockdown of PTBP1; RNA binding assay for PTBP1 to poly(A) signal\",\n      \"journal\": \"European journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional reporter assays, siRNA knockdown with mechanistic readout; single lab\",\n      \"pmids\": [\"27005442\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"CD5 signalosome in primary T cells: TCR engagement induces phosphorylation of CD5 tyrosine 429, which serves as a docking site for adaptor proteins c-Cbl, CIN85, and CRKL. c-Cbl acts as a coordinator enabling CD5 to simultaneously engage positive (PI3K) and negative (UBASH3A, SHIP1) regulators of TCR signaling. Disruption of the CD5 signalosome (mutant mice) selectively represses Foxp3 transactivation and limits inopportune peripheral Treg induction during responses to foreign antigen.\",\n      \"method\": \"Quantitative mass spectrometry; genetic studies in mutant mice (Y429 mutation); phosphoproteomics; co-immunoprecipitation; in vitro and in vivo Treg induction assays; Foxp3 reporter\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — quantitative phosphoproteomics + genetic knock-in mutant mice + multiple binding partners identified by mass spectrometry + functional in vivo readout; multiple rigorous orthogonal methods\",\n      \"pmids\": [\"32434911\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"CD5 binds a novel B-cell surface ligand (CD5L, distinct from CD72) composed of 77–80 and 38–40 kDa polypeptide chains. CD5-Ig fusion protein induced proliferation of resting B cells and bound this ligand on activated splenic B cells and peritoneal B cells but not T cells. Anti-CD72 antibodies did not block CD5-Ig binding, and CD5-Ig did not bind CD72-transfected cells, ruling out CD72 as the binding partner in this context.\",\n      \"method\": \"CD5-Ig chimeric fusion protein binding assays; flow cytometry with anti-CD72 blocking antibodies; immunoprecipitation of surface-labeled B cell molecules with CD5-Ig; transfection of CD72 into non-B cells (negative result for CD5-Ig binding)\",\n      \"journal\": \"International immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — CD5-Ig pulldown with biochemical characterization of novel ligand; anti-CD72 blocking and CD72-transfection negative controls strengthen specificity; single lab\",\n      \"pmids\": [\"9723705\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"Recombinant soluble CD5 extracellular domain binds a broadly distributed alternative cell surface receptor on monocytes, lymphocytes, and various cell lines (lymphoid, myelomonocytic, epithelial). This binding is divalent cation-independent and inhibited by high concentrations of certain monosaccharides. Natural soluble CD5 from human serum and CD5-Ig fusion proteins compete with recombinant soluble CD5 for this binding. CD5 SRCR domains D1 and D2 are involved.\",\n      \"method\": \"Recombinant soluble CD5 extracellular domain glycoprotein cell binding assays; competition with monosaccharides, CD5-Ig fusion proteins, and natural soluble CD5; domain-deletion competition assays\",\n      \"journal\": \"European journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — recombinant protein binding with domain-level competition and competition with natural soluble form; single lab\",\n      \"pmids\": [\"10427974\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"The full-length CD5 protein variant (encoded by E1A) translocates SHP-1 (SH2-containing phosphatase 1) to the vicinity of the BCR, raises the BCR signaling threshold, and limits responses of autoreactive B cells. The truncated variant (encoded by E1B) remains in the cytoplasm along with SHP-1, preventing this negative regulatory function.\",\n      \"method\": \"Review synthesizing transfection and biochemical studies from prior publications (mechanistic summary based on experimental data from the laboratory)\",\n      \"journal\": \"Critical reviews in immunology\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — mechanistic model presented in review, no new primary experiment described in this abstract; underlying data presumably from prior papers\",\n      \"pmids\": [\"21395509\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"CD5 expression promotes constitutive activation of ERK1/2, PI3K/mTOR, and calcineurin-NFAT signaling pathways in B lymphocytes, and changes in IL-10 production are related to activation of transcription factors NFAT2 and STAT3.\",\n      \"method\": \"CD5 transfection into B cells; western blot for phosphorylated signaling intermediates; transcription factor activation assays; IL-10 measurement\",\n      \"journal\": \"Autoimmunity reviews\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — review article summarizing the lab's own findings; abstract does not detail controls or confirm with orthogonal methods\",\n      \"pmids\": [\"22349614\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"CD5 expression on dendritic cells is required to generate optimally protective CD5hi T helper and CD8+ T cells. Activating CD5 on DCs enhanced T cell priming. CD5+ DC numbers increased during immune checkpoint blockade (ICB) therapy. Deletion of CD5 from T cells dampened tumor elimination in response to ICB therapy in vivo. Low IL-6 concentrations promoted de novo differentiation of CD5+ DCs.\",\n      \"method\": \"In vivo mouse tumor models; conditional CD5 deletion from T cells; DC subset analysis in human melanoma-affected lymph nodes; ICB therapy studies; IL-6 concentration manipulation for DC differentiation\",\n      \"journal\": \"Science (New York, N.Y.)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — in vivo genetic loss-of-function (conditional CD5 KO in T cells), human patient lymph node data, DC functional assay, mechanistic link to IL-6; multiple complementary approaches\",\n      \"pmids\": [\"36795805\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"CD5 inhibits CAR T cell activation. CRISPR-Cas9 knockout of CD5 enhances CAR T cell antitumor effect in multiple hematological and solid cancer models by driving increased effector function, enhanced cytotoxicity, in vivo expansion, and persistence without apparent toxicity.\",\n      \"method\": \"CRISPR-Cas9 CD5 KO in CAR T cells; in vitro cytotoxicity assays; in vivo mouse tumor models with hematological and solid cancers; flow cytometric analysis of expansion and persistence\",\n      \"journal\": \"Science immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — CRISPR KO with clean phenotypic readout across multiple cancer models in vitro and in vivo; mechanistic conclusion of CD5 as inhibitor of T cell function supported by multiple models\",\n      \"pmids\": [\"39028827\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"CD5-CD72 interaction maintains regulatory T and B cell homeostasis. Blockade of CD5 or CD72 with neutralizing antibodies reduced both IL-10-expressing Bregs and FoxP3+ Tregs in co-culture. FoxP3+CD4+ Tregs were reduced in CD19-Cre mice deficient in B-cell-surface CD5.\",\n      \"method\": \"Cell culture with neutralizing antibodies against CD5 and CD72; flow cytometric analysis of Treg and Breg populations; CD19-Cre conditional B-cell CD5 deficient mice\",\n      \"journal\": \"Immunological investigations\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — neutralizing antibody blockade plus conditional genetic KO; in vitro and in vivo components; single lab\",\n      \"pmids\": [\"24950378\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"The nonsynonymous A471V substitution (rs2229177) in the CD5 cytoplasmic domain affects MAPK cascade activation. Cross-linking of CD5 revealed significant differences between A471V variants in MAPK pathway activation in COS7 cells and human PBMCs. The A471V variants also differ in MAPK activation and IL-8 release upon exposure to Zymosan (a β-glucan-rich fungal particle) in HEK293 cell transfectants, indicating CD5 recognizes microbial β-glucans and that A471V modulates this response.\",\n      \"method\": \"Anti-CD5 mAb cross-linking; western blot for MAPK activation; HEK293 cell transfectants expressing A471V variants; Zymosan stimulation; IL-8 ELISA\",\n      \"journal\": \"Molecular biology and evolution\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — gain-of-function transfection with defined variants, multiple functional readouts (MAPK, IL-8), microbial ligand identification; single lab\",\n      \"pmids\": [\"21998275\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"CD5 is a scavenger receptor cysteine-rich (SRCR) family transmembrane glycoprotein expressed on all T cells and a subset of B cells (B-1a) that functions as an inhibitory co-receptor: its cytoplasmic domain is phosphorylated at Y429 and Y463 by Lck, constitutively associates with and activates CK2 (at Ser459/461), recruits adaptor proteins (c-Cbl, CIN85, CRKL) and phosphatases (SHP-1, SHIP1, UBASH3A) via Y429 as a docking site upon TCR engagement, thereby dampening TCR- and BCR-mediated calcium flux and downstream signaling; CD5 surface expression is proportional to TCR avidity and transcriptionally regulated by alternative exon usage (E1A vs. E1B), APA/PTBP1/miR-204, and IL-6-driven DNA methylation changes; its extracellular domain binds CD72 on B cells and mediates homophilic interactions that further modulate inhibitory signaling; through CK2-dependent activation of AKT/mTOR and inhibition of GSK3, CD5 promotes Th17 and Th2 differentiation while also governing peripheral Treg induction and IL-10-driven B cell survival; CD5 on dendritic cells is additionally required to prime optimal CD5hi T helper and CD8+ T cells.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"CD5 is a transmembrane glycoprotein expressed on T cells and a subset of B cells that functions as an inhibitory co-receptor tuning the threshold of antigen-receptor signaling [#5, #11]. Its surface level is set by the strength of the positively selecting TCR-MHC interaction during thymocyte development and parallels TCR avidity, and its cytoplasmic domain is required for its inhibitory role in selection [#3, #4]. Upon TCR engagement, Lck phosphorylates CD5 at Y429 and Y463, with Y429 serving as a docking site for a signalosome of adaptors (c-Cbl, CIN85, CRKL) that allows CD5 to simultaneously engage positive (PI3K) and negative (UBASH3A, SHIP1) TCR-signaling regulators [#8, #18]. In parallel, CD5 constitutively associates with CK2 through the regulatory beta subunit and is phosphorylated by it at Ser459/461; cross-linking activates CD5-associated CK2, and this CK2 axis sets T cell responsiveness and, via AKT-dependent inhibition of GSK3 and activation of mTOR, drives Th17 and Th2 differentiation [#1, #12, #13]. CD5 signaling instructs immune outcomes by blocking mTOR to favor peripheral Treg induction, while the signalosome restrains inopportune Foxp3 transactivation [#14, #18]. In B cells, CD5 raises the BCR signaling threshold to enforce tolerance of anergic and autoreactive cells and promotes B cell survival through autocrine IL-10 [#5, #6]. The extracellular SRCR domains engage CD72 and also mediate homophilic CD5-CD5 interactions through domain 1, both contributing inhibitory tuning, and CD5-CD72 engagement supports Treg and IL-10+ Breg homeostasis [#0, #11, #25]. Surface CD5 abundance is further controlled by alternative exon-1 usage (membrane E1A versus intracellularly retained E1B), IL-6-driven promoter demethylation, and post-transcriptional control by alternative polyadenylation, PTBP1, and miR-204 [#9, #10, #17]. CD5 on dendritic cells is required to prime optimally protective CD5hi T helper and CD8+ T cells, and its inhibitory function in effector T cells is therapeutically relevant: CD5 deletion enhances CAR T cell antitumor activity [#23, #24].\",\n  \"teleology\": [\n    {\n      \"year\": 1991,\n      \"claim\": \"Identifying a physiological CD5 ligand addressed how CD5's extracellular domain engages partner cells, establishing CD72 as a B-cell counter-receptor.\",\n      \"evidence\": \"Biotin-labeled CD5 binding to B cells, anti-CD72 antibody blocking, and CD72 cDNA transfection conferring binding to non-B cells\",\n      \"pmids\": [\"1711157\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not establish the downstream signaling consequence of CD5-CD72 engagement\", \"Affinity and stoichiometry of the interaction not defined\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"Defining cytoplasmic-domain binding partners revealed how CD5 transduces signals, identifying a constitutive CK2 association and serine phosphorylation as a core effector mechanism.\",\n      \"evidence\": \"Yeast two-hybrid screen, reciprocal co-IP in B and T cell lines and splenocytes, in vitro kinase assay mapping Ser459/461, and CD5 cross-linking\",\n      \"pmids\": [\"9668105\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not define the functional output of CK2 activation at the time\", \"Additional cytoplasmic partners (CaMKIIdelta, Tctex-1) reported separately at Medium confidence\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"Linking CD5 surface levels to TCR signal strength explained why CD5 expression varies, establishing it as a readout and rheostat of TCR avidity during selection.\",\n      \"evidence\": \"Flow cytometry across pre-TCR-deficient, lck-deficient, and TCR transgenic mouse models\",\n      \"pmids\": [\"9858516\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not resolve the molecular signal that sets the expression set-point\", \"Causality of CD5 level on selection outcome shown in a later study\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Testing CD5 in a B-cell anergy model established that CD5 enforces B-cell tolerance by negatively regulating BCR signaling.\",\n      \"evidence\": \"CD5-KO crossed to HEL/sHEL anergy model with anti-HEL IgM ELISA, proliferation, and Ca2+ flux readouts\",\n      \"pmids\": [\"10704468\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not identify the cytoplasmic effectors mediating BCR inhibition\", \"Mechanism of recruitment to the BCR not defined\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Mapping CD5 tyrosine phosphorylation sites and the responsible kinase clarified how TCR engagement activates CD5, showing Lck-dependent phosphorylation at Y429 and Y463.\",\n      \"evidence\": \"Tyrosine-mutant transfectants, in vitro kinase assays with recombinant Lck and Fyn, and Lck-deficient Jurkat cells\",\n      \"pmids\": [\"11298344\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not identify the effectors recruited to phosphorylated tyrosines\", \"Relative roles of Y429 vs Y463 not resolved\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Genetic dissection showed the CD5 cytoplasmic domain is required for inhibitory function and that CD5 dosage shifts the balance between positive and negative thymocyte selection.\",\n      \"evidence\": \"CD5 overexpression, cytoplasmic-truncation knock-in, and KO mice in TCR transgenic crosses scored for selection outcomes\",\n      \"pmids\": [\"11313384\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not assign the relevant cytoplasmic motif\", \"Connection to specific downstream pathway left open\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Demonstrating CD5-driven autocrine IL-10 revealed a pro-survival output beyond signal inhibition, linking CD5 to B-cell persistence.\",\n      \"evidence\": \"CD5 transfection into CD5- B cells with IL-10 promoter reporter, RT-PCR, Ca2+ flux, and apoptosis assays\",\n      \"pmids\": [\"12393419\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Transcription factors coupling CD5 to the IL-10 promoter not fully defined here\", \"In vivo relevance to B-cell survival not directly tested\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Discovery of the B-cell-specific E1B exon explained a mechanism for tuning surface CD5, showing an intracellularly retained isoform that lowers membrane CD5.\",\n      \"evidence\": \"Alternative exon sequencing, RT-PCR across B-cell subsets, E1B transfection into Jurkat cells with flow cytometry\",\n      \"pmids\": [\"15998834\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab; physiological regulators of E1A/E1B choice not established here\", \"Functional consequence shown only as reduced membrane expression\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Connecting IL-6 to CD5-E1B promoter methylation defined an inflammatory-cytokine route that lowers membrane CD5 in SLE B cells.\",\n      \"evidence\": \"Bisulfite sequencing, methylation-sensitive endonuclease assays, isoform RT-PCR, and anti-IL6R blockade in SLE vs healthy B cells\",\n      \"pmids\": [\"19380809\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab; causal contribution to SLE pathology not established\", \"DNMT1 link not validated by genetic perturbation\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Identifying homophilic CD5-CD5 binding through domain 1 revealed an additional inhibitory engagement mode independent of CD72.\",\n      \"evidence\": \"Soluble CD5 binding assays, domain-1 mutagenesis, blocking mAb IgG/Fab, and T-cell activation and rat lymph node functional assays\",\n      \"pmids\": [\"20952682\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physiological context of homophilic engagement in vivo not defined\", \"Relationship between homophilic binding and CD72 binding not resolved\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"A CK2-binding-domain knock-in mouse established that CD5-CK2 signaling sets T-cell responsiveness and selectively drives Th2/Th17 differentiation, phenocopying CD5-KO.\",\n      \"evidence\": \"CD5\\u0394ECK2BD knock-in mice with proliferation, AICD, Th differentiation, EAE, and high-dose tolerance assays\",\n      \"pmids\": [\"22904299\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not detail the intracellular pathway downstream of CK2 at this stage\", \"Th1 differentiation unaffected, leaving lineage selectivity mechanism open\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Mechanistic dissection placed CD5-CK2 upstream of AKT, defining GSK3 inhibition and mTOR activation as the route by which CD5 stabilizes Th17 differentiation.\",\n      \"evidence\": \"CD5\\u0394ECK2BD mice with AKT/GSK3/mTOR/S6K phospho-westerns, ROR\\u03b3t confocal imaging, and IFN-\\u03b3 sensitivity assays\",\n      \"pmids\": [\"24356888\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct CK2 substrate linking to AKT not pinpointed\", \"Generalizability to human Th17 left to a separate study\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Linking CD5 to extrathymic Treg induction showed CD5 promotes Treg conversion by blocking mTOR, protecting cells from bystander-cytokine inhibition.\",\n      \"evidence\": \"CD5-KO and transgenic mice in Treg induction assays with IL-4/IL-6/IFN-\\u03b3 and mTOR readouts\",\n      \"pmids\": [\"25786177\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Reconciliation with pro-mTOR Th17 role not fully resolved\", \"Molecular link between CD5 and mTOR suppression in this context not detailed\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Post-transcriptional analysis revealed that APA, PTBP1, and miR-204 shorten the CD5 3'UTR upon TCR activation to raise CD5 output.\",\n      \"evidence\": \"3'UTR reporters, isoform RT-PCR in primary and Jurkat T cells, PTBP1 siRNA, and PTBP1 poly(A) binding assay\",\n      \"pmids\": [\"27005442\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab; impact on endogenous CD5 protein levels not quantified\", \"Interplay with transcriptional/isoform regulation not integrated\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Defining a cytoplasmic CK2-CD5-BLNK-STAT3 complex in CLL showed CD5 sustains constitutive STAT3 Ser727 phosphorylation in malignant B cells.\",\n      \"evidence\": \"Mass-spec co-IP, reciprocal co-IP, in vitro CK2 kinase assay on recombinant STAT3, CD5/BLNK siRNA, neutralizing antibodies, and fractionation\",\n      \"pmids\": [\"28130399\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether the complex operates similarly in normal B cells not established\", \"Functional consequence for CLL survival not directly tested here\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Phosphoproteomics defined the Y429 signalosome, showing c-Cbl coordinates simultaneous recruitment of positive (PI3K) and negative (UBASH3A, SHIP1) regulators and restrains peripheral Treg induction.\",\n      \"evidence\": \"Quantitative mass spectrometry, Y429-mutant knock-in mice, co-IP, and in vivo Treg/Foxp3 reporter assays\",\n      \"pmids\": [\"32434911\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Stoichiometry and dynamics of competing positive/negative branches not resolved\", \"How signalosome integrates with the CK2 axis not defined\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Studying CD5 on dendritic cells revealed a cell-extrinsic role: DC CD5 is required to prime optimally protective CD5hi T helper and CD8+ T cells and shapes responses to checkpoint blockade.\",\n      \"evidence\": \"In vivo tumor models, conditional CD5 deletion in T cells, human melanoma lymph-node DC analysis, ICB studies, and IL-6 manipulation of DC differentiation\",\n      \"pmids\": [\"36795805\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular mechanism by which DC CD5 instructs T-cell priming not detailed\", \"Ligand engaged by DC CD5 during priming not identified\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"CRISPR knockout established CD5 as a brake on effector T cells with therapeutic implications, as CD5 deletion enhances CAR T-cell antitumor function.\",\n      \"evidence\": \"CRISPR-Cas9 CD5 KO in CAR T cells with in vitro cytotoxicity and in vivo hematological and solid tumor models\",\n      \"pmids\": [\"39028827\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"The cytoplasmic effector responsible for the inhibitory brake in CAR T cells not isolated\", \"Long-term safety and exhaustion phenotype not fully characterized\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How the CK2-serine axis and the Y429 tyrosine signalosome are functionally integrated, and which engagements (CD72, homophilic, microbial \\u03b2-glucan) dominate in each cellular context, remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unified model coupling CK2-driven and tyrosine-driven branches\", \"Context-specific dominance among CD5 ligands not established\", \"Structural basis of CD5 signaling outputs lacking\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [5, 11, 18]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [18, 16]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [12, 8]},\n      {\"term_id\": \"GO:0001618\", \"supporting_discovery_ids\": [0, 11]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 3, 11]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [16, 9]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [5, 12, 14, 18]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [8, 13, 18]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [10, 16, 24]}\n    ],\n    \"complexes\": [\n      \"CD5-CK2 complex\",\n      \"CK2-CD5-BLNK-STAT3 complex (CLL)\",\n      \"CD5 Y429 signalosome (c-Cbl/CIN85/CRKL/UBASH3A/SHIP1)\"\n    ],\n    \"partners\": [\n      \"CD72\",\n      \"CSNK2B\",\n      \"LCK\",\n      \"CBL\",\n      \"SH3KBP1\",\n      \"CRKL\",\n      \"BLNK\",\n      \"STAT3\"\n    ],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"tie","faith_supported":9,"faith_total":9,"faith_pct":100.0}}