{"gene":"CD86","run_date":"2026-06-09T22:57:18","timeline":{"discoveries":[{"year":1993,"finding":"CD86 (B7-2) was cloned as a counter-receptor for CD28 and CTLA-4; it costimulates IL-2 production and T cell proliferation, and unlike B7-1, its mRNA is constitutively expressed in unstimulated B cells.","method":"Molecular cloning, cDNA transfection, functional T cell proliferation assay, IL-2 secretion assay","journal":"Science","confidence":"High","confidence_rationale":"Tier 1 / Strong — molecular cloning with functional reconstitution, replicated in both human and murine systems (PMID:7694363 and PMID:7504059)","pmids":["7694363","7504059"],"is_preprint":false},{"year":1994,"finding":"Human CD86 binds CD28 and CTLA-4 with similar overall avidity to CD80 but with distinct kinetics: CD86-CTLA-4 complexes dissociate 5- to 8-fold faster than CD80-CTLA-4 complexes, and CD86 is unable to bind the CTLA4Ig Y100A mutant (>200-fold less than CD80), demonstrating that CD80 and CD86 use different binding determinants on CTLA-4.","method":"Cell-binding assays, CTLA4Ig competition, dissociation kinetics measurement, mutant CTLA4Ig binding experiments","journal":"Immunity","confidence":"High","confidence_rationale":"Tier 1 / Strong — multiple orthogonal binding assays with mutagenesis, single rigorous study","pmids":["7534620"],"is_preprint":false},{"year":1994,"finding":"CD86 expression is rapidly induced on the surface of B cells after BCR (Ig receptor) engagement, whereas B7-1 is not upregulated under the same conditions; BCR-induced CD86 costimulates T cell proliferation in a CD28-dependent manner independent of B7-1.","method":"Flow cytometry on normal and BCR-transgenic B cells, functional CD28-blocking experiments, anti-IgM or antigen stimulation","journal":"Journal of Immunology","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple B cell systems, CD28-blocking controls, replicated functional readout","pmids":["7519638"],"is_preprint":false},{"year":1994,"finding":"The serologically defined CD86 differentiation antigen (recognized by mAbs FUN-1 and BU-63) is identical to B7-2/B70; FUN-1 completely blocks the costimulatory activity of B7-2 in functional assays.","method":"cDNA transfection into cells, antibody binding, functional costimulation block assay","journal":"Blood","confidence":"High","confidence_rationale":"Tier 1 / Strong — direct functional identity established by transfection and antibody blocking","pmids":["7520767"],"is_preprint":false},{"year":1994,"finding":"B7-1 and B7-2 can be independently regulated by the same stimulus on B cells (LPS or anti-IgD-dextran): B7-2 expression is significantly higher than B7-1 at all time points assayed, and blocking B7-2 inhibits TCR-dependent T cell proliferation and cytokine production without affecting early TCR signaling (CD69 or IL-2Rα induction).","method":"Flow cytometry, antibody blocking in T cell proliferation and cytokine assays, B cell stimulation experiments","journal":"Journal of Experimental Medicine","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple cell types, multiple stimuli, orthogonal functional readouts","pmids":["7519245"],"is_preprint":false},{"year":1995,"finding":"B7-2 (CD86), but not B7-1, preferentially costimulates the initial production of IL-4, particularly in naive T cells; repetitive costimulation with B7-2 results in moderate IL-4 and IL-2, whereas B7-1 drives high IL-2 and low IL-4, demonstrating that the two ligands direct distinct Th differentiation outcomes.","method":"In vitro T cell stimulation with B7-transfected CHO cells, cytokine ELISA/bioassay, CD45RA+ naive T cell differentiation assays","journal":"Immunity","confidence":"High","confidence_rationale":"Tier 2 / Strong — direct comparison of B7-1 vs B7-2 transfectants in naive and memory T cell subsets, multiple cytokine readouts","pmids":["7538442"],"is_preprint":false},{"year":1995,"finding":"Anti-B7-1 treatment skews toward Th2 (generating IL-4-producing T cells that can transfer protection from EAE), whereas anti-B7-2 treatment increases EAE severity; these effects require initial cytokine secretion since co-treatment with anti-IL-4 prevents disease amelioration by anti-B7-1.","method":"In vivo antibody blockade in EAE model, adoptive transfer of T cell clones, cytokine neutralization","journal":"Cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — in vivo epistasis with adoptive transfer and cytokine neutralization controls","pmids":["7534215"],"is_preprint":false},{"year":1996,"finding":"Constitutive B7.2 transgene expression on B cells is sufficient to prevent Fas-mediated deletion of self-reactive B cells and trigger extensive T cell-dependent clonal expansion and autoantibody secretion, demonstrating that repression of B7.2 is critical for Fas-mediated peripheral B cell tolerance.","method":"B7.2 transgenic mice, adoptive transfer, Fas-deficient comparison, anti-B7.2 blocking, T cell-dependent B cell expansion assay","journal":"Journal of Experimental Medicine","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic gain-of-function with transgene plus loss-of-function controls, multiple mechanistic readouts","pmids":["9705947"],"is_preprint":false},{"year":1999,"finding":"Either B7-1 or B7-2 alone (without both) is sufficient to produce the lymphoproliferative phenotype in CTLA-4-deficient mice; eliminating both B7-1 and B7-2 completely abrogates lymphoproliferation, demonstrating overlapping and CD28-dependent functions of the two ligands in vivo.","method":"Genetic epistasis — B7-1/B7-2 double knockout bred onto CTLA-4-deficient background, lymphocyte activation and organ infiltration assessment","journal":"Journal of Experimental Medicine","confidence":"High","confidence_rationale":"Tier 2 / Strong — rigorous genetic epistasis with compound knockout mice, replicated phenotypic readouts","pmids":["9892625"],"is_preprint":false},{"year":2003,"finding":"The crystal structure of the receptor-binding (IgV-type) domain of human B7-2 at 2.7 Å resolution reveals that unliganded B7-2 is monomeric in solution and in crystalline form, whereas B7-1 dimerizes through hydrophobic contacts; the B7-2 dimer observed in the B7-2/CTLA-4 complex has a hydrophilic interface, providing a structural basis for preventing B7-1/B7-2 heterodimers and for differential signaling.","method":"X-ray crystallography at 2.7 Å resolution, solution state analysis","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 / Moderate — crystal structure with mechanistic interpretation, single study","pmids":["12606712"],"is_preprint":false},{"year":2005,"finding":"Using photobleaching-based FRET, B7-2 exists as a monomer on the cell surface whereas B7-1 exists predominantly as dimers; mutations in B7-1 dimer interface convert it to a monomeric surface state, validating the crystallographic dimer interface and showing that B7-1 and B7-2 do not form hetero-oligomers.","method":"Photobleaching-based FRET (pbFRET) on live cells, site-directed mutagenesis of B7-1 dimer interface","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 / Strong — live-cell FRET combined with mutagenesis to validate crystal structure interface","pmids":["16221763"],"is_preprint":false},{"year":1996,"finding":"Five single amino acid substitutions within the MYPPPY domain of CTLA-4 modestly affect CD80 binding but each completely abrogates CD86 binding, demonstrating that CD80 and CD86 bind with different kinetics and utilize distinct but overlapping sites on CTLA-4; additionally, the V domain of CD86 (but not CD80) alone is sufficient for CTLA-4 binding.","method":"Site-directed mutagenesis of CTLA-4, surface plasmon resonance (SPR) kinetics, transfectant binding assays","journal":"Journal of Immunology","confidence":"High","confidence_rationale":"Tier 1 / Strong — systematic mutagenesis with SPR kinetics, two independent papers confirming differential CTLA-4 binding","pmids":["8557978","8609386"],"is_preprint":false},{"year":1999,"finding":"CD80 engagement of CD28 (and anti-CD28 mAb) induces robust tyrosine phosphorylation of CD28 itself and enhanced PI3K association with CD28, whereas CD86 engagement fails to induce detectable CD28 tyrosyl phosphorylation or PI3K association under the same conditions; both ligands equivalently phosphorylate CBL and VAV and activate NFAT.","method":"Tyrosine phosphorylation assays of CD28, PI3K co-immunoprecipitation with CD28, NFAT reporter assay, cytokine ELISA in Jurkat and primary human T cells stimulated with CHO-CD80 vs CHO-CD86 transfectants","journal":"Journal of Biological Chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — direct biochemical signaling comparison with multiple orthogonal methods in the same study","pmids":["9915850"],"is_preprint":false},{"year":2004,"finding":"Ligation of B7-1/B7-2 on dendritic cells by CTLA-4/CD28 expressed on T cells is obligately required to trigger functional IDO (indoleamine 2,3-dioxygenase) activity; disrupting this interaction leaves IDO inactive, and direct antibody-mediated cross-linking of B7-1/B7-2 fully restores IDO activity; only CD4+ T cells trigger IDO activation.","method":"IDO activity assay on human monocyte-derived DCs, antibody blocking of B7-1/B7-2 or CTLA-4/CD28, direct Ab cross-linking of B7 molecules, CD4/CD8 T cell subset experiments","journal":"Journal of Immunology","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple blocking and reconstitution experiments with functional IDO readout, single lab with orthogonal methods","pmids":["15034022"],"is_preprint":false},{"year":2004,"finding":"CD86 and CD80 have opposing functions on dendritic cells in regulating Treg suppression: blocking CD86 potently enhances Treg suppression, whereas blocking CD80 impairs Treg suppression; CD80 and CD86 expression ratio on DCs changes during maturation and correlates with Treg suppressive capacity.","method":"Antibody blocking of CD86 and CD80 in alloantigen DC-T cell suppression assays, flow cytometry of DC maturation states","journal":"Journal of Immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — functional blocking assays, single lab, limited mechanistic depth on the molecular basis","pmids":["14978077"],"is_preprint":false},{"year":2001,"finding":"The KSHV viral protein K5 (but not K3) selectively enhances endocytosis of ICAM-1 and B7-2 from the surface of B cells, without affecting B7-1; this K5-induced downregulation is reversed by a dominant-negative dynamin mutant, demonstrating enhanced endocytosis as the mechanism; K5-transfected B cells show substantially impaired ability to induce T cell activation.","method":"K5/K3 cDNA transfection in BJAB cells, flow cytometry of surface markers, dominant-negative dynamin co-expression rescue, T cell activation assay","journal":"Journal of Clinical Investigation","confidence":"High","confidence_rationale":"Tier 1 / Moderate — mechanistic rescue with dominant-negative dynamin, functional consequence demonstrated, single lab with multiple orthogonal methods","pmids":["11413168"],"is_preprint":false},{"year":2003,"finding":"Iris pigment epithelial (IPE) cells constitutively express CD86 on their surface, and this CD86 enables them to contact-inhibit T cells by directly engaging CTLA-4 on T cells; blocking CD86 (anti-CD86 or CD86/CD80 KO IPE) or CTLA-4 (CTLA4Ig or CTLA-4 KO T cells) abrogates IPE-mediated T cell suppression, whereas CD28 KO T cells are still suppressed.","method":"Flow cytometry of IPE surface markers, antibody blocking, CD80/CD86 double KO and CTLA-4/CD28 KO mice, in vitro T cell suppression assay","journal":"Journal of Experimental Medicine","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple genetic KOs combined with antibody blocking, defines CD86-CTLA-4 as the specific suppressive axis","pmids":["12835481"],"is_preprint":false},{"year":2009,"finding":"Direct engagement of B7-2 (CD86) on B cells promotes IgG secretion by already class-switched B cells in a B7-1/2-on-B-cell-specific manner; B7-2 engagement induces expression of XBP-1 and spliced XBP1 (indicating increased protein synthesis) and this effect is independent of effects on T cell activation or germinal center formation.","method":"Mixed bone marrow irradiation chimeras lacking B7-1/2 only on B cells, in vitro B7-2 engagement of class-switched B cells, ELISA for IgG/IgM, XBP-1 expression analysis by RT-PCR","journal":"Journal of Immunology","confidence":"High","confidence_rationale":"Tier 2 / Strong — cell-intrinsic role established by chimeric mice plus in vitro mechanism, orthogonal readouts","pmids":["19933871"],"is_preprint":false},{"year":2012,"finding":"Prohibitin (Phb)1 and Phb2 bind to CD86 via tyrosine-containing transmembrane adaptor interactions; CD40 priming increases Phb1/2 expression and their association with CD86. Both Phb1/2 and the CD86 cytoplasmic domain (including serine/threonine PKC phosphorylation sites) are required for CD86-induced IκBα phosphorylation and NF-κB activation leading to Oct-2 and IgG1 upregulation; only Phb1/2 (not cytoplasmic domain) are required for CD86-induced PLCγ2 and PKCα/βII phosphorylation.","method":"Proteomics-based pulldown/co-IP of CD86-interacting proteins, shRNA knockdown of Phb1/2, CD86 cytoplasmic domain truncation and site-directed mutagenesis, phosphorylation assays, IgG1 ELISA and mRNA quantification","journal":"Journal of Immunology","confidence":"High","confidence_rationale":"Tier 1 / Strong — proteomics identification combined with shRNA, mutagenesis, and phosphorylation assays in a single rigorous study","pmids":["23241883"],"is_preprint":false},{"year":2011,"finding":"Toxoplasma gondii upregulates B7-2 (but not B7-1) on macrophages through a JNK (Jun N-terminal kinase)-dependent but MyD88/TRIF-independent mechanism; parasite invasion is required; this induction occurs at the transcript level; T. gondii-infected macrophages stimulate naive T cell proliferation in a B7-2-dependent manner; the same JNK-dependent mechanism operates in human monocytes.","method":"Infection of bone marrow-derived macrophages and human monocytes, MAPK inhibitor panel (JNK, ERK, p38), RT-PCR, flow cytometry, T cell proliferation blocking assays, genome-wide transcriptional analysis","journal":"Infection and Immunity","confidence":"High","confidence_rationale":"Tier 2 / Strong — pharmacological dissection of MAPK pathway, replicated in mouse and human cells, functional blocking confirmation","pmids":["21911468"],"is_preprint":false},{"year":2020,"finding":"Tet2 and Tet3 DNA demethylases in B cells are required for downregulation of CD86 following chronic self-antigen exposure; in Tet2/Tet3-deficient B cells, CD86 fails to be repressed because HDAC1 and HDAC2 accumulate less at the Cd86 locus; anti-CD86 blockade restricts (though does not completely prevent) the aberrant T and B cell activation and lupus-like disease caused by Tet2/Tet3 deficiency.","method":"Conditional Tet2/Tet3 double-knockout in B cells, ChIP for HDAC1/HDAC2 at Cd86 locus, anti-CD86 antibody blockade, flow cytometry, autoantibody measurement","journal":"Nature Immunology","confidence":"High","confidence_rationale":"Tier 2 / Strong — conditional genetic KO with ChIP-based mechanistic demonstration, functional rescue with anti-CD86","pmids":["32572241"],"is_preprint":false},{"year":2022,"finding":"CTLA-4 targets both CD80 and CD86 for destruction via transendocytosis, but CD86 results in a distinct fate: in the presence of CD86, CTLA-4 detaches in a pH-dependent manner and recycles back to the cell surface to permit further transendocytosis rounds, whereas CD80 keeps CTLA-4 ligand-bound leading to ubiquitylation and lysosomal degradation; clinically relevant autoimmune disease mutations selectively disrupt CD86 transendocytosis by affecting either CTLA-4 recycling or CD86 binding.","method":"Transendocytosis assays, pH-dependent dissociation experiments, ubiquitylation and endosomal trafficking analysis, analysis of clinical CTLA-4 mutations","journal":"Nature Immunology","confidence":"High","confidence_rationale":"Tier 1 / Strong — mechanistic dissection with multiple orthogonal methods and clinically validated mutations, single rigorous study","pmids":["35999394"],"is_preprint":false},{"year":2016,"finding":"Bacterial superantigens bind directly to B7-2 (CD86) at its homodimer interface using the same 12-aa β-strand-hinge-α-helix domain they use to bind CD28, thereby bridging and potentiating the B7-2/CD28 interaction; B7-2 dimer interface mimetic peptides competitively block superantigen binding to B7-2 and CD28, attenuate cytokine overexpression, and protect mice from lethal superantigen challenge.","method":"Direct binding assays of superantigens to cell-surface B7-2 and CD28, peptide competition assays, cytokine production assays, in vivo lethal challenge model","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Strong — direct binding to B7-2 demonstrated, competitive peptide inhibition, in vivo rescue, multiple orthogonal methods","pmids":["27708164"],"is_preprint":false},{"year":2002,"finding":"BCR stimulation and β2-adrenergic receptor (β2AR) stimulation cooperate to regulate B7-2 (CD86) expression on B cells; β2AR stimulation enhances BCR-induced CD86 by increasing B7-2 mRNA stability, NF-κB nuclear binding, and NF-κB-dependent transcription through PKA-, PKC-, and MAPK-dependent mechanisms.","method":"In vitro B cell stimulation with BCR and β2AR agonists, mRNA stability assay, NF-κB EMSA and reporter assay, kinase inhibitor panel","journal":"Journal of Immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple signaling pathway inhibitors and transcription factor assays, single lab, limited mutagenesis","pmids":["12055247"],"is_preprint":false},{"year":2011,"finding":"B7-2 (but not B7-1) expression specifically on follicular B cells is required for maintenance of the follicular T helper (TFH) cell phenotype and germinal center B cell development; bidirectional interactions between CD28 on activated T cells and B7-2 on follicular B cells are essential, as shown by mixed adoptive transfer experiments.","method":"B7-2 KO and B7-1 KO mouse infection model (vaccinia virus), mixed adoptive transfer of B7-2-deficient B cells, flow cytometry of TFH and GC B cells, neutralizing antibody titers","journal":"Journal of Immunology","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic KO combined with mixed adoptive transfer to define cell-intrinsic requirement, multiple functional readouts","pmids":["21441451"],"is_preprint":false},{"year":2012,"finding":"Induced regulatory T cells (iTregs) acquire both CD80 and CD86 from mature dendritic cells via trogocytosis; CD86 is acquired to a higher extent than CD80; iTregs that acquired CD86 show higher activation markers and enhanced suppressive function compared to those that did not; this trogocytosis occurs independently of CTLA-4, CD28, and PD-L1.","method":"Flow cytometry and confocal fluorescence microscopy of iTreg-DC co-cultures, DKO (CD80/CD86 double KO) iTregs used as recipients, suppression assays","journal":"Cellular & Molecular Immunology","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — direct visualization plus functional suppression assay, single lab, mechanism of trogocytosis not molecularly dissected","pmids":["22307040"],"is_preprint":false},{"year":2017,"finding":"CD86 (B7.2) functions as a co-receptor for lymphotropic hepatitis C virus (HCV) B-cell infection; cDNA library screening identified CD86 as specific to the lymphotropic HCV strain; silencing CD86 reduces B-cell infection; HCV infection via CD86 inhibits memory B-cell recall responses.","method":"cDNA library screening, infectious clone/chimeric virus system, CD86 silencing/knockdown, B cell infection assays, memory B cell recall function assay","journal":"Nature Communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — cDNA library screen with functional validation by silencing, single lab","pmids":["28067225"],"is_preprint":false},{"year":1997,"finding":"CD28 surface levels are differentially downregulated by B7-1 and B7-2: B7-1 engagement is considerably more effective at downregulating CD28 than B7-2 engagement, indicating a differential functional effect on activated T cells.","method":"Flow cytometry of CD28 surface expression on T cells after stimulation with B7-1 or B7-2 transfectants","journal":"Transplantation","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single method (flow cytometry), single lab, no molecular mechanism identified","pmids":["9392322"],"is_preprint":false},{"year":1995,"finding":"CD86 expressed on vascular endothelial cells costimulates allogeneic CD4+ T cells; blocking anti-CD86 mAb inhibits this proliferative response and induces alloantigen-specific T cell anergy, whereas CD80 is undetectable on endothelial cells even after IFN-γ treatment.","method":"Flow cytometry of HUVEC and MVEC, antibody blocking of allogeneic MLR, CD28-dependent anergy induction","journal":"International Immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — antibody blocking with functional anergy readout, two endothelial cell types tested, single lab","pmids":["7495740"],"is_preprint":false},{"year":1999,"finding":"Human CD80 and CD86 expressed on murine B16 melanoma cells trigger NK cell-mediated cytotoxicity; this triggering is independent of CD28 and CTLA-4 (not detected on the NK cell lines tested), suggesting NK cells use distinct receptors to interact with CD80/CD86.","method":"Transfection of CD80/CD86 into B16 melanoma, NK cell cytotoxicity assay, antibody blocking, flow cytometry for CD28/CTLA-4 on NK cells","journal":"Journal of Immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — direct lysis assay with blocking confirmation, but receptor identity on NK cells not established","pmids":["10510357"],"is_preprint":false},{"year":2013,"finding":"CD86 expressed on activated NK cells serves as an activating receptor: CTLA4Ig ligation of CD86 on NK cells increases expression of CD107a and perforin and enhances NK cell killing of tumor targets; blocking CD86 on a CD86-high human NK cell line inhibits the CTLA4Ig-enhanced killing.","method":"NK depletion experiments in vivo, flow cytometry for CD86 on activated NK cells, CD107a/perforin upregulation assay, NK cytotoxicity assay with anti-CD86 blocking","journal":"PloS One","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo and in vitro complementary experiments, antibody blocking, single lab","pmids":["24349559"],"is_preprint":false},{"year":2021,"finding":"Pomalidomide (Pom) reverses KSHV-induced downregulation of B7-2 on primary effusion lymphoma (PEL) cells through a cereblon-dependent mechanism involving PI3K signaling; restoration of B7-2 on PEL cells leads to increased T cell activation and NK-mediated cytotoxicity; Pom-resistant cells with ~90% reduction in cereblon no longer upregulate B7-2, and cereblon-knockout cells behave similarly.","method":"Pom treatment of PEL cells, cereblon KO and Pom-resistant cell line generation, surface B7-2 flow cytometry, T cell activation and NK cytotoxicity assays, PI3K inhibitor experiments","journal":"PLoS Pathogens","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — cereblon KO and resistant line convergently support mechanism, functional downstream consequences shown, single lab","pmids":["33411730"],"is_preprint":false}],"current_model":"CD86 (B7-2) is a monomeric IgV-type cell-surface costimulatory ligand constitutively expressed on antigen-presenting cells that binds CD28 and CTLA-4 with fast on/off kinetics (using distinct but overlapping sites from CD80), triggers CD28-mediated T cell costimulation (with preferential induction of IL-4/Th2 responses relative to CD80), delivers reverse signaling into B cells through prohibitin-1/2 adaptors to activate NF-κB and promote IgG secretion, is selectively targeted for transendocytosis by CTLA-4 with subsequent recycling of CTLA-4 back to the cell surface, is transcriptionally repressed on self-reactive B cells by Tet2/Tet3-mediated chromatin modification (via HDAC1/2 recruitment), and is upregulated on macrophages in response to Toxoplasma gondii via a JNK-dependent pathway; superantigens potentiate T cell activation by simultaneously engaging CD86 and CD28 at their homodimer interfaces, while viral proteins (KSHV K5) and regulatory T cells actively remove CD86 from APC surfaces by enhanced endocytosis and trogocytosis, respectively."},"narrative":{"mechanistic_narrative":"CD86 (B7-2) is a monomeric IgV-type cell-surface costimulatory ligand on antigen-presenting cells that, together with the related CD80, engages CD28 and CTLA-4 on T cells to deliver the second signal required for productive T cell activation, IL-2 production, and proliferation [PMID:7694363, PMID:7504059, PMID:7519245]. Unlike CD80, its mRNA is constitutively expressed and rapidly induced on B cells following BCR engagement, allowing CD28-dependent costimulation independently of CD80 [PMID:7694363, PMID:7504059, PMID:7519638]. CD86 binds CD28 and CTLA-4 with avidity comparable to CD80 but with markedly faster dissociation kinetics and through distinct, only partially overlapping binding determinants — it is uniquely sensitive to CTLA-4 MYPPPY-domain substitutions and to the CTLA4Ig Y100A mutation, and its V domain alone suffices for CTLA-4 binding [PMID:7534620, PMID:8557978, PMID:8609386]. Structurally CD86 is monomeric in solution and on the cell surface, in contrast to dimeric CD80, a difference that underlies their non-overlapping oligomeric behavior and differential signaling [PMID:12606712, PMID:16221763]. Functionally CD80 and CD86 are not redundant: CD86 preferentially costimulates early IL-4 production and Th2-skewed differentiation, and engagement of CD28 by CD86 fails to induce the CD28 tyrosine phosphorylation and PI3K recruitment elicited by CD80 [PMID:7538442, PMID:7534215, PMID:9915850]. In vivo, CD86 and CD80 have overlapping CD28-dependent roles, since either ligand alone supports the lymphoproliferative phenotype of CTLA-4-deficient mice while loss of both abolishes it [PMID:9892625]. CD86 is selectively targeted by CTLA-4 transendocytosis, but in a fate distinct from CD80: CTLA-4 detaches from CD86 in a pH-dependent manner and recycles to the surface, and clinically relevant autoimmune CTLA-4 mutations selectively disrupt this CD86 transendocytosis [PMID:35999394]. Beyond its forward costimulatory ligand role, CD86 transmits reverse signals into B cells through prohibitin-1/2 transmembrane adaptors and its cytoplasmic PKC phosphorylation sites, driving IκBα phosphorylation, NF-κB activation, Oct-2 and XBP-1 induction, and IgG secretion by class-switched B cells [PMID:19933871, PMID:23241883]. CD86 expression is tightly controlled: it is repressed on self-reactive B cells through Tet2/Tet3-dependent recruitment of HDAC1/2 to the Cd86 locus to enforce peripheral tolerance, and its failed repression causes autoantibody production and lupus-like disease [PMID:9705947, PMID:32572241]. Pathogens manipulate CD86 — Toxoplasma gondii upregulates it on macrophages via a JNK-dependent pathway, KSHV K5 selectively drives its dynamin-dependent endocytosis to impair T cell activation, and bacterial superantigens bridge CD86 and CD28 at their dimer interfaces to potentiate cytokine storm [PMID:21911468, PMID:11413168, PMID:27708164].","teleology":[{"year":1993,"claim":"Establishing CD86 as a distinct CD28/CTLA-4 counter-receptor answered whether B cells possess a constitutive costimulatory ligand separate from CD80.","evidence":"Molecular cloning with cDNA transfection and functional T cell proliferation/IL-2 assays in human and murine systems","pmids":["7694363","7504059"],"confidence":"High","gaps":["Did not resolve why constitutive vs inducible expression matters functionally","No structural or kinetic distinction from CD80 yet"]},{"year":1994,"claim":"Kinetic and mutagenesis analysis showed CD86 binds CD28/CTLA-4 through distinct determinants and with faster dissociation than CD80, establishing that the two ligands are biochemically non-equivalent.","evidence":"Cell-binding assays, CTLA4Ig competition, dissociation kinetics, and Y100A mutant CTLA4Ig binding","pmids":["7534620"],"confidence":"High","gaps":["Functional consequence of faster off-rate not yet defined","Binding-site architecture not visualized structurally"]},{"year":1994,"claim":"Demonstrating BCR-inducible, CD80-independent CD86 expression and its serological identity to B7-2/B70 unified the antigen nomenclature and located CD86 in B cell activation.","evidence":"Flow cytometry on BCR-transgenic B cells, CD28-blocking functional assays, and antibody (FUN-1/BU-63) blocking with cDNA transfectants","pmids":["7519638","7520767","7519245"],"confidence":"High","gaps":["Transcriptional control of inducibility not defined","Whether differential regulation alters T cell outcome unaddressed"]},{"year":1995,"claim":"Showing CD86 preferentially drives early IL-4 and Th2 differentiation while anti-B7 blockade alters EAE severity established functional divergence of CD80 and CD86 in directing T helper outcomes.","evidence":"B7-transfected CHO costimulation of naive T cells with cytokine readouts, and in vivo EAE antibody blockade with adoptive transfer and IL-4 neutralization","pmids":["7538442","7534215"],"confidence":"High","gaps":["Molecular basis of the Th2 bias unresolved","Whether bias reflects kinetics, oligomeric state, or signaling unknown"]},{"year":1996,"claim":"Mapping CTLA-4 substitutions that abolish CD86 but not CD80 binding, and finding the CD86 V domain alone is sufficient, pinpointed distinct overlapping binding sites on CTLA-4.","evidence":"Site-directed CTLA-4 mutagenesis with SPR kinetics and transfectant binding assays","pmids":["8557978","8609386"],"confidence":"High","gaps":["Co-crystal of the CD86/CTLA-4 interface not yet available","Functional consequence of distinct sites unaddressed"]},{"year":1996,"claim":"Forced constitutive B7-2 on B cells preventing Fas-mediated deletion of self-reactive B cells established that CD86 repression is required for peripheral B cell tolerance.","evidence":"B7.2 transgenic mice with adoptive transfer, Fas-deficient comparison, and anti-B7.2 blocking","pmids":["9705947"],"confidence":"High","gaps":["Mechanism enforcing CD86 repression unknown","Whether forward or reverse CD86 signaling drives the phenotype unclear"]},{"year":1999,"claim":"Genetic epistasis and signaling comparison showed CD86 and CD80 have overlapping CD28-dependent functions in vivo yet differ in CD28 phosphorylation/PI3K recruitment, defining redundancy at the phenotypic level and divergence at the biochemical level.","evidence":"B7-1/B7-2 double knockout on CTLA-4-deficient background, plus CD28 phosphorylation, PI3K co-IP, and NFAT assays comparing CD80 vs CD86 transfectants","pmids":["9892625","9915850"],"confidence":"High","gaps":["How differential CD28 phosphorylation maps to distinct outcomes unresolved","Contribution of CD86 reverse signaling not separated"]},{"year":2003,"claim":"Crystallography and live-cell FRET established that CD86 is monomeric whereas CD80 is dimeric, providing a structural basis for their differential signaling and the absence of heterodimers.","evidence":"X-ray crystallography of the CD86 IgV domain at 2.7 Å and photobleaching FRET on live cells with dimer-interface mutagenesis","pmids":["12606712","16221763"],"confidence":"High","gaps":["Direct link from oligomeric state to signaling output not demonstrated","Stoichiometry of CD86 in receptor-bound state in situ unclear"]},{"year":2003,"claim":"Identifying CD86 as the costimulatory ligand mediating IDO induction in DCs and contact-inhibition by epithelial cells extended CD86 function to CTLA-4-dependent immune suppression.","evidence":"IDO activity assays with B7/CTLA-4 blocking and cross-linking, and IPE-T cell suppression assays using CD80/CD86 and CTLA-4/CD28 knockouts","pmids":["15034022","12835481"],"confidence":"High","gaps":["Signaling pathway into DCs downstream of CD86 ligation not detailed","Relative roles of CD80 vs CD86 in IDO not fully separated"]},{"year":2004,"claim":"Opposing roles of CD86 and CD80 on DCs in Treg suppression indicated their expression ratio tunes regulatory output.","evidence":"Antibody blocking of CD86 vs CD80 in alloantigen DC-T suppression assays with DC maturation profiling","pmids":["14978077"],"confidence":"Medium","gaps":["Molecular basis of opposing effects not defined","Single-lab functional blocking without genetic confirmation"]},{"year":2009,"claim":"Demonstrating that CD86 engagement on class-switched B cells drives IgG secretion and XBP-1 induction established a cell-intrinsic reverse-signaling role independent of T cell help.","evidence":"Mixed bone marrow chimeras lacking B7 only on B cells, in vitro CD86 engagement, IgG ELISA, and XBP-1 RT-PCR","pmids":["19933871"],"confidence":"High","gaps":["Cytoplasmic signaling machinery not yet identified at this stage","Physiological ligand engaging CD86 in vivo unclear"]},{"year":2011,"claim":"Defining the prohibitin-1/2 / cytoplasmic-domain axis and follicular B cell requirement explained how CD86 reverse signaling activates NF-κB and supports germinal center/TFH biology.","evidence":"Proteomic CD86 pulldown with Phb1/2 shRNA, cytoplasmic domain mutagenesis and phosphorylation assays, plus B7-2 KO infection models with mixed adoptive transfer","pmids":["23241883","21441451"],"confidence":"High","gaps":["How prohibitins couple to PLCγ2/PKC mechanistically unresolved","Whether the same axis operates outside B cells unknown"]},{"year":2011,"claim":"Showing pathogen-driven and viral manipulation of CD86 surface levels (Toxoplasma JNK-dependent upregulation; KSHV K5 dynamin-dependent endocytosis) revealed CD86 as a contested node in host-pathogen conflict.","evidence":"Macrophage/monocyte infection with MAPK inhibitor panel and T cell blocking assays; K5/K3 transfection with dominant-negative dynamin rescue and T cell activation assays","pmids":["21911468","11413168"],"confidence":"High","gaps":["Transcription factors downstream of JNK at the Cd86 locus not identified","K5 substrate-recognition determinants on CD86 unmapped"]},{"year":2020,"claim":"Linking Tet2/Tet3 demethylases to HDAC1/2 recruitment at the Cd86 locus defined the epigenetic mechanism repressing CD86 on self-reactive B cells and its causal role in lupus-like autoimmunity.","evidence":"Conditional Tet2/Tet3 B cell knockout, HDAC1/2 ChIP at Cd86, anti-CD86 blockade, and autoantibody measurement","pmids":["32572241"],"confidence":"High","gaps":["How Tet enzymes direct HDAC recruitment to Cd86 mechanistically unclear","Anti-CD86 only partially rescued disease, leaving CD86-independent contributions"]},{"year":2022,"claim":"Resolving the distinct CTLA-4 transendocytosis fate of CD86 (pH-dependent CTLA-4 recycling vs CD80-driven degradation) and tying it to autoimmune CTLA-4 mutations explained ligand-specific control of CTLA-4 turnover.","evidence":"Transendocytosis assays, pH-dependent dissociation, ubiquitylation/endosomal trafficking analysis, and clinical CTLA-4 mutation analysis","pmids":["35999394"],"confidence":"High","gaps":["Structural basis of pH-dependent CD86/CTLA-4 detachment not solved","In vivo quantitative impact on T cell tolerance unclear"]},{"year":2016,"claim":"Showing that superantigens engage CD86 at its dimer interface to bridge CD28 identified CD86 as a direct target for toxin-driven cytokine storm and a therapeutic interception point.","evidence":"Direct binding of superantigens to surface B7-2 and CD28, peptide competition, cytokine assays, and lethal in vivo challenge with mimetic peptides","pmids":["27708164"],"confidence":"High","gaps":["Co-structure of the superantigen/CD86/CD28 ternary complex absent","Generality across superantigen families not fully tested"]},{"year":null,"claim":"How CD86's monomeric structure, fast binding kinetics, distinct CTLA-4 transendocytosis fate, and prohibitin-dependent reverse signaling are integrated to produce its non-redundant immunological outcomes remains unresolved.","evidence":"","pmids":[],"confidence":"High","gaps":["No unified model linking oligomeric state, kinetics, and signaling output","Receptors mediating CD86's CD28/CTLA-4-independent roles (e.g. on NK cells) unidentified","Structural basis of forward vs reverse signaling not solved"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0048018","term_label":"receptor ligand activity","supporting_discovery_ids":[0,1,4,11]},{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[17,18]},{"term_id":"GO:0001618","term_label":"virus receptor activity","supporting_discovery_ids":[26]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[2,9,10,15,21]}],"pathway":[{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[0,4,8,24]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[12,18]}],"complexes":[],"partners":["CD28","CTLA4","PHB1","PHB2"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P42081","full_name":"T-lymphocyte activation antigen CD86","aliases":["Activation B7-2 antigen","B70","BU63","CTLA-4 counter-receptor B7.2","FUN-1"],"length_aa":329,"mass_kda":37.7,"function":"Costimulatory molecule that belongs to the immunoglobulin superfamily that plays an important role in T-lymphocyte activation (PubMed:12196291, PubMed:7694363). Acts as the primary auxiliary signal augmenting the MHC/TCR signal in naive T-cells by acting as a ligand for the CD28 receptor which is constitutively expressed on the cell surface of T-cells (PubMed:12196291, PubMed:7694363). May play a critical role in the early events of T-cell activation and costimulation of naive T-cells, such as deciding between immunity and anergy that is made by T-cells within 24 hours after activation (PubMed:7527824). Also involved in the regulation of B cells function, plays a role in regulating the level of IgG(1) produced. Upon CD40 engagement, activates NF-kappa-B signaling pathway via phospholipase C and protein kinase C activation (By similarity). Also acts as an inhibitor of T-cell activation by acting as a ligand for CTLA4, a decoy receptor, thereby blocking CD28-mediated T-cell priming (PubMed:11279501) Interferes with the formation of CD86 clusters, and thus acts as a negative regulator of T-cell activation (Microbial infection) Acts as a receptor for adenovirus subgroup B","subcellular_location":"Cell membrane","url":"https://www.uniprot.org/uniprotkb/P42081/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/CD86","classification":"Not Classified","n_dependent_lines":5,"n_total_lines":1208,"dependency_fraction":0.0041390728476821195},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/CD86","total_profiled":1310},"omim":[{"mim_id":"620787","title":"T-CELL ACTIVATION INHIBITOR, MITOCHONDRIAL; TCAIM","url":"https://www.omim.org/entry/620787"},{"mim_id":"614372","title":"MANNOSE-BINDING LECTIN DEFICIENCY; MBLD","url":"https://www.omim.org/entry/614372"},{"mim_id":"613335","title":"MEMBRANE-ASSOCIATED RING-CH FINGER PROTEIN 8; MARCHF8","url":"https://www.omim.org/entry/613335"},{"mim_id":"613332","title":"MEMBRANE-ASSOCIATED RING-CH FINGER PROTEIN 2; MARCHF2","url":"https://www.omim.org/entry/613332"},{"mim_id":"613331","title":"MEMBRANE-ASSOCIATED RING-CH FINGER PROTEIN 1; MARCHF1","url":"https://www.omim.org/entry/613331"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Plasma membrane","reliability":"Supported"},{"location":"Centriolar satellite","reliability":"Additional"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"lymphoid tissue","ntpm":32.5}],"url":"https://www.proteinatlas.org/search/CD86"},"hgnc":{"alias_symbol":["B7.2","B7-2"],"prev_symbol":["CD28LG2"]},"alphafold":{"accession":"P42081","domains":[{"cath_id":"2.60.40.10","chopping":"27-134","consensus_level":"high","plddt":95.9491,"start":27,"end":134},{"cath_id":"2.60.40.10","chopping":"141-235","consensus_level":"high","plddt":90.8089,"start":141,"end":235}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P42081","model_url":"https://alphafold.ebi.ac.uk/files/AF-P42081-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P42081-F1-predicted_aligned_error_v6.png","plddt_mean":80.06},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=CD86","jax_strain_url":"https://www.jax.org/strain/search?query=CD86"},"sequence":{"accession":"P42081","fasta_url":"https://rest.uniprot.org/uniprotkb/P42081.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P42081/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P42081"}},"corpus_meta":[{"pmid":"7534215","id":"PMC_7534215","title":"B7-1 and B7-2 costimulatory molecules activate differentially the Th1/Th2 developmental pathways: application to autoimmune disease therapy.","date":"1995","source":"Cell","url":"https://pubmed.ncbi.nlm.nih.gov/7534215","citation_count":1500,"is_preprint":false},{"pmid":"7694363","id":"PMC_7694363","title":"Cloning of B7-2: a CTLA-4 counter-receptor that costimulates human T cell proliferation.","date":"1993","source":"Science (New York, N.Y.)","url":"https://pubmed.ncbi.nlm.nih.gov/7694363","citation_count":888,"is_preprint":false},{"pmid":"7534620","id":"PMC_7534620","title":"Human B7-1 (CD80) and B7-2 (CD86) bind with similar avidities but distinct kinetics to CD28 and CTLA-4 receptors.","date":"1994","source":"Immunity","url":"https://pubmed.ncbi.nlm.nih.gov/7534620","citation_count":808,"is_preprint":false},{"pmid":"7519245","id":"PMC_7519245","title":"Comparative analysis of B7-1 and B7-2 costimulatory ligands: expression and function.","date":"1994","source":"The Journal of experimental medicine","url":"https://pubmed.ncbi.nlm.nih.gov/7519245","citation_count":616,"is_preprint":false},{"pmid":"7532678","id":"PMC_7532678","title":"Differential effects of anti-B7-1 and anti-B7-2 monoclonal antibody treatment on the development of diabetes in the nonobese diabetic mouse.","date":"1995","source":"The Journal of experimental medicine","url":"https://pubmed.ncbi.nlm.nih.gov/7532678","citation_count":539,"is_preprint":false},{"pmid":"7538442","id":"PMC_7538442","title":"B7-1 and B7-2 do not deliver identical costimulatory signals, since B7-2 but not B7-1 preferentially costimulates the initial production of IL-4.","date":"1995","source":"Immunity","url":"https://pubmed.ncbi.nlm.nih.gov/7538442","citation_count":504,"is_preprint":false},{"pmid":"7500044","id":"PMC_7500044","title":"Expression of costimulatory molecules B7-1 (CD80), B7-2 (CD86), and interleukin 12 cytokine in multiple sclerosis lesions.","date":"1995","source":"The Journal of experimental medicine","url":"https://pubmed.ncbi.nlm.nih.gov/7500044","citation_count":385,"is_preprint":false},{"pmid":"7541819","id":"PMC_7541819","title":"Cellular interaction in germinal centers. 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retrovirally transduced melanoma cells: suppression by interleukin 10.","date":"1998","source":"British journal of cancer","url":"https://pubmed.ncbi.nlm.nih.gov/9652756","citation_count":32,"is_preprint":false},{"pmid":"11584372","id":"PMC_11584372","title":"Enhanced expression of B7-1, B7-2, and intercellular adhesion molecule 1 in sinusoidal endothelial cells by warm ischemia/reperfusion injury in rat liver.","date":"2001","source":"Hepatology (Baltimore, Md.)","url":"https://pubmed.ncbi.nlm.nih.gov/11584372","citation_count":32,"is_preprint":false},{"pmid":"9148019","id":"PMC_9148019","title":"Anomalous expression of costimulatory molecules B7-1, B7-2 and CD28 in primary biliary cirrhosis.","date":"1997","source":"Journal of hepatology","url":"https://pubmed.ncbi.nlm.nih.gov/9148019","citation_count":32,"is_preprint":false},{"pmid":"12372936","id":"PMC_12372936","title":"B7-1 (CD80) and B7-2 (CD 86) expression in human tubular epithelial cells in vivo and in 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Delivery of costimulatory signals from bystander professional antigen-presenting cells.","date":"1996","source":"The Journal of clinical endocrinology and metabolism","url":"https://pubmed.ncbi.nlm.nih.gov/8923872","citation_count":30,"is_preprint":false},{"pmid":"12798304","id":"PMC_12798304","title":"Dual expression of CD80 and CD86 produces a tumor vaccine superior to single expression of either molecule.","date":"2003","source":"Cellular immunology","url":"https://pubmed.ncbi.nlm.nih.gov/12798304","citation_count":29,"is_preprint":false},{"pmid":"9392322","id":"PMC_9392322","title":"Differential down-regulation of CD28 by B7-1 and B7-2 engagement.","date":"1997","source":"Transplantation","url":"https://pubmed.ncbi.nlm.nih.gov/9392322","citation_count":29,"is_preprint":false},{"pmid":"15797507","id":"PMC_15797507","title":"CD86 and beta2-adrenergic receptor stimulation regulate B-cell activity cooperatively.","date":"2005","source":"Trends in immunology","url":"https://pubmed.ncbi.nlm.nih.gov/15797507","citation_count":28,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":51349,"output_tokens":8150,"usd":0.138149,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":17767,"output_tokens":5602,"usd":0.114443,"stage2_stop_reason":"end_turn"},"total_usd":0.252592,"stage1_batch_id":"msgbatch_01ACAxJQabDsht39JXeWG22d","stage2_batch_id":"msgbatch_01QEU22A9U5sbPTgsMzTmvSf","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1993,\n      \"finding\": \"CD86 (B7-2) was cloned as a counter-receptor for CD28 and CTLA-4; it costimulates IL-2 production and T cell proliferation, and unlike B7-1, its mRNA is constitutively expressed in unstimulated B cells.\",\n      \"method\": \"Molecular cloning, cDNA transfection, functional T cell proliferation assay, IL-2 secretion assay\",\n      \"journal\": \"Science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — molecular cloning with functional reconstitution, replicated in both human and murine systems (PMID:7694363 and PMID:7504059)\",\n      \"pmids\": [\"7694363\", \"7504059\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"Human CD86 binds CD28 and CTLA-4 with similar overall avidity to CD80 but with distinct kinetics: CD86-CTLA-4 complexes dissociate 5- to 8-fold faster than CD80-CTLA-4 complexes, and CD86 is unable to bind the CTLA4Ig Y100A mutant (>200-fold less than CD80), demonstrating that CD80 and CD86 use different binding determinants on CTLA-4.\",\n      \"method\": \"Cell-binding assays, CTLA4Ig competition, dissociation kinetics measurement, mutant CTLA4Ig binding experiments\",\n      \"journal\": \"Immunity\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — multiple orthogonal binding assays with mutagenesis, single rigorous study\",\n      \"pmids\": [\"7534620\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"CD86 expression is rapidly induced on the surface of B cells after BCR (Ig receptor) engagement, whereas B7-1 is not upregulated under the same conditions; BCR-induced CD86 costimulates T cell proliferation in a CD28-dependent manner independent of B7-1.\",\n      \"method\": \"Flow cytometry on normal and BCR-transgenic B cells, functional CD28-blocking experiments, anti-IgM or antigen stimulation\",\n      \"journal\": \"Journal of Immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple B cell systems, CD28-blocking controls, replicated functional readout\",\n      \"pmids\": [\"7519638\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"The serologically defined CD86 differentiation antigen (recognized by mAbs FUN-1 and BU-63) is identical to B7-2/B70; FUN-1 completely blocks the costimulatory activity of B7-2 in functional assays.\",\n      \"method\": \"cDNA transfection into cells, antibody binding, functional costimulation block assay\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — direct functional identity established by transfection and antibody blocking\",\n      \"pmids\": [\"7520767\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"B7-1 and B7-2 can be independently regulated by the same stimulus on B cells (LPS or anti-IgD-dextran): B7-2 expression is significantly higher than B7-1 at all time points assayed, and blocking B7-2 inhibits TCR-dependent T cell proliferation and cytokine production without affecting early TCR signaling (CD69 or IL-2Rα induction).\",\n      \"method\": \"Flow cytometry, antibody blocking in T cell proliferation and cytokine assays, B cell stimulation experiments\",\n      \"journal\": \"Journal of Experimental Medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple cell types, multiple stimuli, orthogonal functional readouts\",\n      \"pmids\": [\"7519245\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"B7-2 (CD86), but not B7-1, preferentially costimulates the initial production of IL-4, particularly in naive T cells; repetitive costimulation with B7-2 results in moderate IL-4 and IL-2, whereas B7-1 drives high IL-2 and low IL-4, demonstrating that the two ligands direct distinct Th differentiation outcomes.\",\n      \"method\": \"In vitro T cell stimulation with B7-transfected CHO cells, cytokine ELISA/bioassay, CD45RA+ naive T cell differentiation assays\",\n      \"journal\": \"Immunity\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — direct comparison of B7-1 vs B7-2 transfectants in naive and memory T cell subsets, multiple cytokine readouts\",\n      \"pmids\": [\"7538442\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"Anti-B7-1 treatment skews toward Th2 (generating IL-4-producing T cells that can transfer protection from EAE), whereas anti-B7-2 treatment increases EAE severity; these effects require initial cytokine secretion since co-treatment with anti-IL-4 prevents disease amelioration by anti-B7-1.\",\n      \"method\": \"In vivo antibody blockade in EAE model, adoptive transfer of T cell clones, cytokine neutralization\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — in vivo epistasis with adoptive transfer and cytokine neutralization controls\",\n      \"pmids\": [\"7534215\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"Constitutive B7.2 transgene expression on B cells is sufficient to prevent Fas-mediated deletion of self-reactive B cells and trigger extensive T cell-dependent clonal expansion and autoantibody secretion, demonstrating that repression of B7.2 is critical for Fas-mediated peripheral B cell tolerance.\",\n      \"method\": \"B7.2 transgenic mice, adoptive transfer, Fas-deficient comparison, anti-B7.2 blocking, T cell-dependent B cell expansion assay\",\n      \"journal\": \"Journal of Experimental Medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic gain-of-function with transgene plus loss-of-function controls, multiple mechanistic readouts\",\n      \"pmids\": [\"9705947\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"Either B7-1 or B7-2 alone (without both) is sufficient to produce the lymphoproliferative phenotype in CTLA-4-deficient mice; eliminating both B7-1 and B7-2 completely abrogates lymphoproliferation, demonstrating overlapping and CD28-dependent functions of the two ligands in vivo.\",\n      \"method\": \"Genetic epistasis — B7-1/B7-2 double knockout bred onto CTLA-4-deficient background, lymphocyte activation and organ infiltration assessment\",\n      \"journal\": \"Journal of Experimental Medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — rigorous genetic epistasis with compound knockout mice, replicated phenotypic readouts\",\n      \"pmids\": [\"9892625\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"The crystal structure of the receptor-binding (IgV-type) domain of human B7-2 at 2.7 Å resolution reveals that unliganded B7-2 is monomeric in solution and in crystalline form, whereas B7-1 dimerizes through hydrophobic contacts; the B7-2 dimer observed in the B7-2/CTLA-4 complex has a hydrophilic interface, providing a structural basis for preventing B7-1/B7-2 heterodimers and for differential signaling.\",\n      \"method\": \"X-ray crystallography at 2.7 Å resolution, solution state analysis\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — crystal structure with mechanistic interpretation, single study\",\n      \"pmids\": [\"12606712\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Using photobleaching-based FRET, B7-2 exists as a monomer on the cell surface whereas B7-1 exists predominantly as dimers; mutations in B7-1 dimer interface convert it to a monomeric surface state, validating the crystallographic dimer interface and showing that B7-1 and B7-2 do not form hetero-oligomers.\",\n      \"method\": \"Photobleaching-based FRET (pbFRET) on live cells, site-directed mutagenesis of B7-1 dimer interface\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — live-cell FRET combined with mutagenesis to validate crystal structure interface\",\n      \"pmids\": [\"16221763\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"Five single amino acid substitutions within the MYPPPY domain of CTLA-4 modestly affect CD80 binding but each completely abrogates CD86 binding, demonstrating that CD80 and CD86 bind with different kinetics and utilize distinct but overlapping sites on CTLA-4; additionally, the V domain of CD86 (but not CD80) alone is sufficient for CTLA-4 binding.\",\n      \"method\": \"Site-directed mutagenesis of CTLA-4, surface plasmon resonance (SPR) kinetics, transfectant binding assays\",\n      \"journal\": \"Journal of Immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — systematic mutagenesis with SPR kinetics, two independent papers confirming differential CTLA-4 binding\",\n      \"pmids\": [\"8557978\", \"8609386\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"CD80 engagement of CD28 (and anti-CD28 mAb) induces robust tyrosine phosphorylation of CD28 itself and enhanced PI3K association with CD28, whereas CD86 engagement fails to induce detectable CD28 tyrosyl phosphorylation or PI3K association under the same conditions; both ligands equivalently phosphorylate CBL and VAV and activate NFAT.\",\n      \"method\": \"Tyrosine phosphorylation assays of CD28, PI3K co-immunoprecipitation with CD28, NFAT reporter assay, cytokine ELISA in Jurkat and primary human T cells stimulated with CHO-CD80 vs CHO-CD86 transfectants\",\n      \"journal\": \"Journal of Biological Chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — direct biochemical signaling comparison with multiple orthogonal methods in the same study\",\n      \"pmids\": [\"9915850\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Ligation of B7-1/B7-2 on dendritic cells by CTLA-4/CD28 expressed on T cells is obligately required to trigger functional IDO (indoleamine 2,3-dioxygenase) activity; disrupting this interaction leaves IDO inactive, and direct antibody-mediated cross-linking of B7-1/B7-2 fully restores IDO activity; only CD4+ T cells trigger IDO activation.\",\n      \"method\": \"IDO activity assay on human monocyte-derived DCs, antibody blocking of B7-1/B7-2 or CTLA-4/CD28, direct Ab cross-linking of B7 molecules, CD4/CD8 T cell subset experiments\",\n      \"journal\": \"Journal of Immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple blocking and reconstitution experiments with functional IDO readout, single lab with orthogonal methods\",\n      \"pmids\": [\"15034022\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"CD86 and CD80 have opposing functions on dendritic cells in regulating Treg suppression: blocking CD86 potently enhances Treg suppression, whereas blocking CD80 impairs Treg suppression; CD80 and CD86 expression ratio on DCs changes during maturation and correlates with Treg suppressive capacity.\",\n      \"method\": \"Antibody blocking of CD86 and CD80 in alloantigen DC-T cell suppression assays, flow cytometry of DC maturation states\",\n      \"journal\": \"Journal of Immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — functional blocking assays, single lab, limited mechanistic depth on the molecular basis\",\n      \"pmids\": [\"14978077\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"The KSHV viral protein K5 (but not K3) selectively enhances endocytosis of ICAM-1 and B7-2 from the surface of B cells, without affecting B7-1; this K5-induced downregulation is reversed by a dominant-negative dynamin mutant, demonstrating enhanced endocytosis as the mechanism; K5-transfected B cells show substantially impaired ability to induce T cell activation.\",\n      \"method\": \"K5/K3 cDNA transfection in BJAB cells, flow cytometry of surface markers, dominant-negative dynamin co-expression rescue, T cell activation assay\",\n      \"journal\": \"Journal of Clinical Investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — mechanistic rescue with dominant-negative dynamin, functional consequence demonstrated, single lab with multiple orthogonal methods\",\n      \"pmids\": [\"11413168\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Iris pigment epithelial (IPE) cells constitutively express CD86 on their surface, and this CD86 enables them to contact-inhibit T cells by directly engaging CTLA-4 on T cells; blocking CD86 (anti-CD86 or CD86/CD80 KO IPE) or CTLA-4 (CTLA4Ig or CTLA-4 KO T cells) abrogates IPE-mediated T cell suppression, whereas CD28 KO T cells are still suppressed.\",\n      \"method\": \"Flow cytometry of IPE surface markers, antibody blocking, CD80/CD86 double KO and CTLA-4/CD28 KO mice, in vitro T cell suppression assay\",\n      \"journal\": \"Journal of Experimental Medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple genetic KOs combined with antibody blocking, defines CD86-CTLA-4 as the specific suppressive axis\",\n      \"pmids\": [\"12835481\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Direct engagement of B7-2 (CD86) on B cells promotes IgG secretion by already class-switched B cells in a B7-1/2-on-B-cell-specific manner; B7-2 engagement induces expression of XBP-1 and spliced XBP1 (indicating increased protein synthesis) and this effect is independent of effects on T cell activation or germinal center formation.\",\n      \"method\": \"Mixed bone marrow irradiation chimeras lacking B7-1/2 only on B cells, in vitro B7-2 engagement of class-switched B cells, ELISA for IgG/IgM, XBP-1 expression analysis by RT-PCR\",\n      \"journal\": \"Journal of Immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — cell-intrinsic role established by chimeric mice plus in vitro mechanism, orthogonal readouts\",\n      \"pmids\": [\"19933871\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Prohibitin (Phb)1 and Phb2 bind to CD86 via tyrosine-containing transmembrane adaptor interactions; CD40 priming increases Phb1/2 expression and their association with CD86. Both Phb1/2 and the CD86 cytoplasmic domain (including serine/threonine PKC phosphorylation sites) are required for CD86-induced IκBα phosphorylation and NF-κB activation leading to Oct-2 and IgG1 upregulation; only Phb1/2 (not cytoplasmic domain) are required for CD86-induced PLCγ2 and PKCα/βII phosphorylation.\",\n      \"method\": \"Proteomics-based pulldown/co-IP of CD86-interacting proteins, shRNA knockdown of Phb1/2, CD86 cytoplasmic domain truncation and site-directed mutagenesis, phosphorylation assays, IgG1 ELISA and mRNA quantification\",\n      \"journal\": \"Journal of Immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — proteomics identification combined with shRNA, mutagenesis, and phosphorylation assays in a single rigorous study\",\n      \"pmids\": [\"23241883\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Toxoplasma gondii upregulates B7-2 (but not B7-1) on macrophages through a JNK (Jun N-terminal kinase)-dependent but MyD88/TRIF-independent mechanism; parasite invasion is required; this induction occurs at the transcript level; T. gondii-infected macrophages stimulate naive T cell proliferation in a B7-2-dependent manner; the same JNK-dependent mechanism operates in human monocytes.\",\n      \"method\": \"Infection of bone marrow-derived macrophages and human monocytes, MAPK inhibitor panel (JNK, ERK, p38), RT-PCR, flow cytometry, T cell proliferation blocking assays, genome-wide transcriptional analysis\",\n      \"journal\": \"Infection and Immunity\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — pharmacological dissection of MAPK pathway, replicated in mouse and human cells, functional blocking confirmation\",\n      \"pmids\": [\"21911468\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Tet2 and Tet3 DNA demethylases in B cells are required for downregulation of CD86 following chronic self-antigen exposure; in Tet2/Tet3-deficient B cells, CD86 fails to be repressed because HDAC1 and HDAC2 accumulate less at the Cd86 locus; anti-CD86 blockade restricts (though does not completely prevent) the aberrant T and B cell activation and lupus-like disease caused by Tet2/Tet3 deficiency.\",\n      \"method\": \"Conditional Tet2/Tet3 double-knockout in B cells, ChIP for HDAC1/HDAC2 at Cd86 locus, anti-CD86 antibody blockade, flow cytometry, autoantibody measurement\",\n      \"journal\": \"Nature Immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — conditional genetic KO with ChIP-based mechanistic demonstration, functional rescue with anti-CD86\",\n      \"pmids\": [\"32572241\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"CTLA-4 targets both CD80 and CD86 for destruction via transendocytosis, but CD86 results in a distinct fate: in the presence of CD86, CTLA-4 detaches in a pH-dependent manner and recycles back to the cell surface to permit further transendocytosis rounds, whereas CD80 keeps CTLA-4 ligand-bound leading to ubiquitylation and lysosomal degradation; clinically relevant autoimmune disease mutations selectively disrupt CD86 transendocytosis by affecting either CTLA-4 recycling or CD86 binding.\",\n      \"method\": \"Transendocytosis assays, pH-dependent dissociation experiments, ubiquitylation and endosomal trafficking analysis, analysis of clinical CTLA-4 mutations\",\n      \"journal\": \"Nature Immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — mechanistic dissection with multiple orthogonal methods and clinically validated mutations, single rigorous study\",\n      \"pmids\": [\"35999394\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Bacterial superantigens bind directly to B7-2 (CD86) at its homodimer interface using the same 12-aa β-strand-hinge-α-helix domain they use to bind CD28, thereby bridging and potentiating the B7-2/CD28 interaction; B7-2 dimer interface mimetic peptides competitively block superantigen binding to B7-2 and CD28, attenuate cytokine overexpression, and protect mice from lethal superantigen challenge.\",\n      \"method\": \"Direct binding assays of superantigens to cell-surface B7-2 and CD28, peptide competition assays, cytokine production assays, in vivo lethal challenge model\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — direct binding to B7-2 demonstrated, competitive peptide inhibition, in vivo rescue, multiple orthogonal methods\",\n      \"pmids\": [\"27708164\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"BCR stimulation and β2-adrenergic receptor (β2AR) stimulation cooperate to regulate B7-2 (CD86) expression on B cells; β2AR stimulation enhances BCR-induced CD86 by increasing B7-2 mRNA stability, NF-κB nuclear binding, and NF-κB-dependent transcription through PKA-, PKC-, and MAPK-dependent mechanisms.\",\n      \"method\": \"In vitro B cell stimulation with BCR and β2AR agonists, mRNA stability assay, NF-κB EMSA and reporter assay, kinase inhibitor panel\",\n      \"journal\": \"Journal of Immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple signaling pathway inhibitors and transcription factor assays, single lab, limited mutagenesis\",\n      \"pmids\": [\"12055247\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"B7-2 (but not B7-1) expression specifically on follicular B cells is required for maintenance of the follicular T helper (TFH) cell phenotype and germinal center B cell development; bidirectional interactions between CD28 on activated T cells and B7-2 on follicular B cells are essential, as shown by mixed adoptive transfer experiments.\",\n      \"method\": \"B7-2 KO and B7-1 KO mouse infection model (vaccinia virus), mixed adoptive transfer of B7-2-deficient B cells, flow cytometry of TFH and GC B cells, neutralizing antibody titers\",\n      \"journal\": \"Journal of Immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic KO combined with mixed adoptive transfer to define cell-intrinsic requirement, multiple functional readouts\",\n      \"pmids\": [\"21441451\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Induced regulatory T cells (iTregs) acquire both CD80 and CD86 from mature dendritic cells via trogocytosis; CD86 is acquired to a higher extent than CD80; iTregs that acquired CD86 show higher activation markers and enhanced suppressive function compared to those that did not; this trogocytosis occurs independently of CTLA-4, CD28, and PD-L1.\",\n      \"method\": \"Flow cytometry and confocal fluorescence microscopy of iTreg-DC co-cultures, DKO (CD80/CD86 double KO) iTregs used as recipients, suppression assays\",\n      \"journal\": \"Cellular & Molecular Immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — direct visualization plus functional suppression assay, single lab, mechanism of trogocytosis not molecularly dissected\",\n      \"pmids\": [\"22307040\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"CD86 (B7.2) functions as a co-receptor for lymphotropic hepatitis C virus (HCV) B-cell infection; cDNA library screening identified CD86 as specific to the lymphotropic HCV strain; silencing CD86 reduces B-cell infection; HCV infection via CD86 inhibits memory B-cell recall responses.\",\n      \"method\": \"cDNA library screening, infectious clone/chimeric virus system, CD86 silencing/knockdown, B cell infection assays, memory B cell recall function assay\",\n      \"journal\": \"Nature Communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — cDNA library screen with functional validation by silencing, single lab\",\n      \"pmids\": [\"28067225\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"CD28 surface levels are differentially downregulated by B7-1 and B7-2: B7-1 engagement is considerably more effective at downregulating CD28 than B7-2 engagement, indicating a differential functional effect on activated T cells.\",\n      \"method\": \"Flow cytometry of CD28 surface expression on T cells after stimulation with B7-1 or B7-2 transfectants\",\n      \"journal\": \"Transplantation\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single method (flow cytometry), single lab, no molecular mechanism identified\",\n      \"pmids\": [\"9392322\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"CD86 expressed on vascular endothelial cells costimulates allogeneic CD4+ T cells; blocking anti-CD86 mAb inhibits this proliferative response and induces alloantigen-specific T cell anergy, whereas CD80 is undetectable on endothelial cells even after IFN-γ treatment.\",\n      \"method\": \"Flow cytometry of HUVEC and MVEC, antibody blocking of allogeneic MLR, CD28-dependent anergy induction\",\n      \"journal\": \"International Immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — antibody blocking with functional anergy readout, two endothelial cell types tested, single lab\",\n      \"pmids\": [\"7495740\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"Human CD80 and CD86 expressed on murine B16 melanoma cells trigger NK cell-mediated cytotoxicity; this triggering is independent of CD28 and CTLA-4 (not detected on the NK cell lines tested), suggesting NK cells use distinct receptors to interact with CD80/CD86.\",\n      \"method\": \"Transfection of CD80/CD86 into B16 melanoma, NK cell cytotoxicity assay, antibody blocking, flow cytometry for CD28/CTLA-4 on NK cells\",\n      \"journal\": \"Journal of Immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — direct lysis assay with blocking confirmation, but receptor identity on NK cells not established\",\n      \"pmids\": [\"10510357\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"CD86 expressed on activated NK cells serves as an activating receptor: CTLA4Ig ligation of CD86 on NK cells increases expression of CD107a and perforin and enhances NK cell killing of tumor targets; blocking CD86 on a CD86-high human NK cell line inhibits the CTLA4Ig-enhanced killing.\",\n      \"method\": \"NK depletion experiments in vivo, flow cytometry for CD86 on activated NK cells, CD107a/perforin upregulation assay, NK cytotoxicity assay with anti-CD86 blocking\",\n      \"journal\": \"PloS One\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo and in vitro complementary experiments, antibody blocking, single lab\",\n      \"pmids\": [\"24349559\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Pomalidomide (Pom) reverses KSHV-induced downregulation of B7-2 on primary effusion lymphoma (PEL) cells through a cereblon-dependent mechanism involving PI3K signaling; restoration of B7-2 on PEL cells leads to increased T cell activation and NK-mediated cytotoxicity; Pom-resistant cells with ~90% reduction in cereblon no longer upregulate B7-2, and cereblon-knockout cells behave similarly.\",\n      \"method\": \"Pom treatment of PEL cells, cereblon KO and Pom-resistant cell line generation, surface B7-2 flow cytometry, T cell activation and NK cytotoxicity assays, PI3K inhibitor experiments\",\n      \"journal\": \"PLoS Pathogens\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — cereblon KO and resistant line convergently support mechanism, functional downstream consequences shown, single lab\",\n      \"pmids\": [\"33411730\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"CD86 (B7-2) is a monomeric IgV-type cell-surface costimulatory ligand constitutively expressed on antigen-presenting cells that binds CD28 and CTLA-4 with fast on/off kinetics (using distinct but overlapping sites from CD80), triggers CD28-mediated T cell costimulation (with preferential induction of IL-4/Th2 responses relative to CD80), delivers reverse signaling into B cells through prohibitin-1/2 adaptors to activate NF-κB and promote IgG secretion, is selectively targeted for transendocytosis by CTLA-4 with subsequent recycling of CTLA-4 back to the cell surface, is transcriptionally repressed on self-reactive B cells by Tet2/Tet3-mediated chromatin modification (via HDAC1/2 recruitment), and is upregulated on macrophages in response to Toxoplasma gondii via a JNK-dependent pathway; superantigens potentiate T cell activation by simultaneously engaging CD86 and CD28 at their homodimer interfaces, while viral proteins (KSHV K5) and regulatory T cells actively remove CD86 from APC surfaces by enhanced endocytosis and trogocytosis, respectively.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"CD86 (B7-2) is a monomeric IgV-type cell-surface costimulatory ligand on antigen-presenting cells that, together with the related CD80, engages CD28 and CTLA-4 on T cells to deliver the second signal required for productive T cell activation, IL-2 production, and proliferation [#0, #4]. Unlike CD80, its mRNA is constitutively expressed and rapidly induced on B cells following BCR engagement, allowing CD28-dependent costimulation independently of CD80 [#0, #2]. CD86 binds CD28 and CTLA-4 with avidity comparable to CD80 but with markedly faster dissociation kinetics and through distinct, only partially overlapping binding determinants \\u2014 it is uniquely sensitive to CTLA-4 MYPPPY-domain substitutions and to the CTLA4Ig Y100A mutation, and its V domain alone suffices for CTLA-4 binding [#1, #11]. Structurally CD86 is monomeric in solution and on the cell surface, in contrast to dimeric CD80, a difference that underlies their non-overlapping oligomeric behavior and differential signaling [#9, #10]. Functionally CD80 and CD86 are not redundant: CD86 preferentially costimulates early IL-4 production and Th2-skewed differentiation, and engagement of CD28 by CD86 fails to induce the CD28 tyrosine phosphorylation and PI3K recruitment elicited by CD80 [#5, #6, #12]. In vivo, CD86 and CD80 have overlapping CD28-dependent roles, since either ligand alone supports the lymphoproliferative phenotype of CTLA-4-deficient mice while loss of both abolishes it [#8]. CD86 is selectively targeted by CTLA-4 transendocytosis, but in a fate distinct from CD80: CTLA-4 detaches from CD86 in a pH-dependent manner and recycles to the surface, and clinically relevant autoimmune CTLA-4 mutations selectively disrupt this CD86 transendocytosis [#21]. Beyond its forward costimulatory ligand role, CD86 transmits reverse signals into B cells through prohibitin-1/2 transmembrane adaptors and its cytoplasmic PKC phosphorylation sites, driving I\\u03baB\\u03b1 phosphorylation, NF-\\u03baB activation, Oct-2 and XBP-1 induction, and IgG secretion by class-switched B cells [#17, #18]. CD86 expression is tightly controlled: it is repressed on self-reactive B cells through Tet2/Tet3-dependent recruitment of HDAC1/2 to the Cd86 locus to enforce peripheral tolerance, and its failed repression causes autoantibody production and lupus-like disease [#7, #20]. Pathogens manipulate CD86 \\u2014 Toxoplasma gondii upregulates it on macrophages via a JNK-dependent pathway, KSHV K5 selectively drives its dynamin-dependent endocytosis to impair T cell activation, and bacterial superantigens bridge CD86 and CD28 at their dimer interfaces to potentiate cytokine storm [#19, #15, #22].\",\n  \"teleology\": [\n    {\n      \"year\": 1993,\n      \"claim\": \"Establishing CD86 as a distinct CD28/CTLA-4 counter-receptor answered whether B cells possess a constitutive costimulatory ligand separate from CD80.\",\n      \"evidence\": \"Molecular cloning with cDNA transfection and functional T cell proliferation/IL-2 assays in human and murine systems\",\n      \"pmids\": [\"7694363\", \"7504059\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not resolve why constitutive vs inducible expression matters functionally\", \"No structural or kinetic distinction from CD80 yet\"]\n    },\n    {\n      \"year\": 1994,\n      \"claim\": \"Kinetic and mutagenesis analysis showed CD86 binds CD28/CTLA-4 through distinct determinants and with faster dissociation than CD80, establishing that the two ligands are biochemically non-equivalent.\",\n      \"evidence\": \"Cell-binding assays, CTLA4Ig competition, dissociation kinetics, and Y100A mutant CTLA4Ig binding\",\n      \"pmids\": [\"7534620\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional consequence of faster off-rate not yet defined\", \"Binding-site architecture not visualized structurally\"]\n    },\n    {\n      \"year\": 1994,\n      \"claim\": \"Demonstrating BCR-inducible, CD80-independent CD86 expression and its serological identity to B7-2/B70 unified the antigen nomenclature and located CD86 in B cell activation.\",\n      \"evidence\": \"Flow cytometry on BCR-transgenic B cells, CD28-blocking functional assays, and antibody (FUN-1/BU-63) blocking with cDNA transfectants\",\n      \"pmids\": [\"7519638\", \"7520767\", \"7519245\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Transcriptional control of inducibility not defined\", \"Whether differential regulation alters T cell outcome unaddressed\"]\n    },\n    {\n      \"year\": 1995,\n      \"claim\": \"Showing CD86 preferentially drives early IL-4 and Th2 differentiation while anti-B7 blockade alters EAE severity established functional divergence of CD80 and CD86 in directing T helper outcomes.\",\n      \"evidence\": \"B7-transfected CHO costimulation of naive T cells with cytokine readouts, and in vivo EAE antibody blockade with adoptive transfer and IL-4 neutralization\",\n      \"pmids\": [\"7538442\", \"7534215\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular basis of the Th2 bias unresolved\", \"Whether bias reflects kinetics, oligomeric state, or signaling unknown\"]\n    },\n    {\n      \"year\": 1996,\n      \"claim\": \"Mapping CTLA-4 substitutions that abolish CD86 but not CD80 binding, and finding the CD86 V domain alone is sufficient, pinpointed distinct overlapping binding sites on CTLA-4.\",\n      \"evidence\": \"Site-directed CTLA-4 mutagenesis with SPR kinetics and transfectant binding assays\",\n      \"pmids\": [\"8557978\", \"8609386\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Co-crystal of the CD86/CTLA-4 interface not yet available\", \"Functional consequence of distinct sites unaddressed\"]\n    },\n    {\n      \"year\": 1996,\n      \"claim\": \"Forced constitutive B7-2 on B cells preventing Fas-mediated deletion of self-reactive B cells established that CD86 repression is required for peripheral B cell tolerance.\",\n      \"evidence\": \"B7.2 transgenic mice with adoptive transfer, Fas-deficient comparison, and anti-B7.2 blocking\",\n      \"pmids\": [\"9705947\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism enforcing CD86 repression unknown\", \"Whether forward or reverse CD86 signaling drives the phenotype unclear\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Genetic epistasis and signaling comparison showed CD86 and CD80 have overlapping CD28-dependent functions in vivo yet differ in CD28 phosphorylation/PI3K recruitment, defining redundancy at the phenotypic level and divergence at the biochemical level.\",\n      \"evidence\": \"B7-1/B7-2 double knockout on CTLA-4-deficient background, plus CD28 phosphorylation, PI3K co-IP, and NFAT assays comparing CD80 vs CD86 transfectants\",\n      \"pmids\": [\"9892625\", \"9915850\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How differential CD28 phosphorylation maps to distinct outcomes unresolved\", \"Contribution of CD86 reverse signaling not separated\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Crystallography and live-cell FRET established that CD86 is monomeric whereas CD80 is dimeric, providing a structural basis for their differential signaling and the absence of heterodimers.\",\n      \"evidence\": \"X-ray crystallography of the CD86 IgV domain at 2.7 Å and photobleaching FRET on live cells with dimer-interface mutagenesis\",\n      \"pmids\": [\"12606712\", \"16221763\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct link from oligomeric state to signaling output not demonstrated\", \"Stoichiometry of CD86 in receptor-bound state in situ unclear\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Identifying CD86 as the costimulatory ligand mediating IDO induction in DCs and contact-inhibition by epithelial cells extended CD86 function to CTLA-4-dependent immune suppression.\",\n      \"evidence\": \"IDO activity assays with B7/CTLA-4 blocking and cross-linking, and IPE-T cell suppression assays using CD80/CD86 and CTLA-4/CD28 knockouts\",\n      \"pmids\": [\"15034022\", \"12835481\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Signaling pathway into DCs downstream of CD86 ligation not detailed\", \"Relative roles of CD80 vs CD86 in IDO not fully separated\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Opposing roles of CD86 and CD80 on DCs in Treg suppression indicated their expression ratio tunes regulatory output.\",\n      \"evidence\": \"Antibody blocking of CD86 vs CD80 in alloantigen DC-T suppression assays with DC maturation profiling\",\n      \"pmids\": [\"14978077\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular basis of opposing effects not defined\", \"Single-lab functional blocking without genetic confirmation\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Demonstrating that CD86 engagement on class-switched B cells drives IgG secretion and XBP-1 induction established a cell-intrinsic reverse-signaling role independent of T cell help.\",\n      \"evidence\": \"Mixed bone marrow chimeras lacking B7 only on B cells, in vitro CD86 engagement, IgG ELISA, and XBP-1 RT-PCR\",\n      \"pmids\": [\"19933871\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Cytoplasmic signaling machinery not yet identified at this stage\", \"Physiological ligand engaging CD86 in vivo unclear\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Defining the prohibitin-1/2 / cytoplasmic-domain axis and follicular B cell requirement explained how CD86 reverse signaling activates NF-κB and supports germinal center/TFH biology.\",\n      \"evidence\": \"Proteomic CD86 pulldown with Phb1/2 shRNA, cytoplasmic domain mutagenesis and phosphorylation assays, plus B7-2 KO infection models with mixed adoptive transfer\",\n      \"pmids\": [\"23241883\", \"21441451\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How prohibitins couple to PLCγ2/PKC mechanistically unresolved\", \"Whether the same axis operates outside B cells unknown\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Showing pathogen-driven and viral manipulation of CD86 surface levels (Toxoplasma JNK-dependent upregulation; KSHV K5 dynamin-dependent endocytosis) revealed CD86 as a contested node in host-pathogen conflict.\",\n      \"evidence\": \"Macrophage/monocyte infection with MAPK inhibitor panel and T cell blocking assays; K5/K3 transfection with dominant-negative dynamin rescue and T cell activation assays\",\n      \"pmids\": [\"21911468\", \"11413168\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Transcription factors downstream of JNK at the Cd86 locus not identified\", \"K5 substrate-recognition determinants on CD86 unmapped\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Linking Tet2/Tet3 demethylases to HDAC1/2 recruitment at the Cd86 locus defined the epigenetic mechanism repressing CD86 on self-reactive B cells and its causal role in lupus-like autoimmunity.\",\n      \"evidence\": \"Conditional Tet2/Tet3 B cell knockout, HDAC1/2 ChIP at Cd86, anti-CD86 blockade, and autoantibody measurement\",\n      \"pmids\": [\"32572241\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How Tet enzymes direct HDAC recruitment to Cd86 mechanistically unclear\", \"Anti-CD86 only partially rescued disease, leaving CD86-independent contributions\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Resolving the distinct CTLA-4 transendocytosis fate of CD86 (pH-dependent CTLA-4 recycling vs CD80-driven degradation) and tying it to autoimmune CTLA-4 mutations explained ligand-specific control of CTLA-4 turnover.\",\n      \"evidence\": \"Transendocytosis assays, pH-dependent dissociation, ubiquitylation/endosomal trafficking analysis, and clinical CTLA-4 mutation analysis\",\n      \"pmids\": [\"35999394\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of pH-dependent CD86/CTLA-4 detachment not solved\", \"In vivo quantitative impact on T cell tolerance unclear\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Showing that superantigens engage CD86 at its dimer interface to bridge CD28 identified CD86 as a direct target for toxin-driven cytokine storm and a therapeutic interception point.\",\n      \"evidence\": \"Direct binding of superantigens to surface B7-2 and CD28, peptide competition, cytokine assays, and lethal in vivo challenge with mimetic peptides\",\n      \"pmids\": [\"27708164\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Co-structure of the superantigen/CD86/CD28 ternary complex absent\", \"Generality across superantigen families not fully tested\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How CD86's monomeric structure, fast binding kinetics, distinct CTLA-4 transendocytosis fate, and prohibitin-dependent reverse signaling are integrated to produce its non-redundant immunological outcomes remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No unified model linking oligomeric state, kinetics, and signaling output\", \"Receptors mediating CD86's CD28/CTLA-4-independent roles (e.g. on NK cells) unidentified\", \"Structural basis of forward vs reverse signaling not solved\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0048018\", \"supporting_discovery_ids\": [0, 1, 4, 11]},\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [17, 18]},\n      {\"term_id\": \"GO:0001618\", \"supporting_discovery_ids\": [26]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [2, 9, 10, 15, 21]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [0, 4, 8, 24]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [12, 18]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"CD28\", \"CTLA4\", \"PHB1\", \"PHB2\"],\n    \"other_free_text\": []\n  }\n}\n```","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":10,"faith_total":10,"faith_pct":100.0}}