{"gene":"CD1B","run_date":"2026-06-09T22:57:17","timeline":{"discoveries":[{"year":1992,"finding":"CD1b functions as an antigen-presenting molecule that restricts the proliferative and cytotoxic responses of CD4-CD8- αβ TCR+ T cells specific for Mycobacterium tuberculosis, requiring CD1b expression on the antigen-presenting cell and involving an antigen processing requirement similar to MHC class II-restricted presentation.","method":"T cell proliferation and cytotoxicity assays with CD1b-expressing antigen-presenting cells; antibody blocking experiments","journal":"Nature","confidence":"High","confidence_rationale":"Tier 2 / Strong — direct functional assay with antibody blocking, foundational result replicated extensively across subsequent studies","pmids":["1281285"],"is_preprint":false},{"year":1996,"finding":"CD1b localizes to MHC class II compartments (MIICs) — the endosomal antigen-loading compartments — and this localization is dependent on a tyrosine-based motif in its own cytoplasmic tail, not on association with invariant chain as for MHC class II.","method":"Immunoelectron microscopy, subcellular fractionation, cytoplasmic tail deletion/mutation constructs, and co-localization with MHC class II in MIICs","journal":"Science","confidence":"High","confidence_rationale":"Tier 2 / Strong — direct subcellular localization by immunoelectron microscopy combined with functional mutagenesis, independently replicated","pmids":["8662520"],"is_preprint":false},{"year":1997,"finding":"CD1b presents the mycobacterial glycolipid glucose monomycolate (GMM) to T cells; T cell recognition is insensitive to variation in lipid tails but extremely sensitive to alterations in the carbohydrate or polar head group, indicating that CD1b binds acyl chains nonspecifically in its hydrophobic groove while positioning the hydrophilic moiety for specific TCR interaction.","method":"Synthetic GMM analogs with defined chemical modifications presented to CD1b-restricted T cell clones; T cell activation assays","journal":"Science","confidence":"High","confidence_rationale":"Tier 1 / Strong — systematic chemical biology with defined synthetic antigens, replicated across multiple studies","pmids":["9323206"],"is_preprint":false},{"year":1997,"finding":"The macrophage mannose receptor (MR) mediates uptake of lipoarabinomannan (LAM) and delivers it to late endosomes/lysosomes/MIICs where CD1b is present; MR and CD1b colocalize in these compartments, linking innate pattern recognition to CD1b-mediated adaptive T cell presentation of LAM.","method":"MR antagonism/blocking assays, LAM internalization studies, immunofluorescence colocalization of MR, LAM, and CD1b in intracellular compartments","journal":"Immunity","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (functional blocking, internalization, colocalization), replicated concept","pmids":["9047240"],"is_preprint":false},{"year":1998,"finding":"CD1b directly binds the acyl side chains of lipid antigens (LAM, phosphatidylinositol mannoside, GMM) with high affinity; binding is optimal at acidic pH due to partial unfolding of the α-helices of CD1b at low pH, revealing a hydrophobic binding site.","method":"Direct CD1b-antigen binding assays, pH-dependent binding experiments, structural/biochemical characterization","journal":"Immunity","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro binding assays with defined lipid antigens plus mechanistic pH studies, independently replicated","pmids":["9529150"],"is_preprint":false},{"year":1998,"finding":"The nine-amino acid cytoplasmic tail of CD1b, specifically the single cytoplasmic tyrosine residue, is required for endosomal targeting of CD1b and for efficient presentation of lipid antigens; CD1b mutants lacking this motif are expressed on the cell surface but fail to efficiently present antigens acquired exogenously or from live intracellular organisms.","method":"Site-directed mutagenesis of cytoplasmic tail tyrosine, functional antigen presentation assays with T cell lines, subcellular localization studies","journal":"Immunity","confidence":"High","confidence_rationale":"Tier 1 / Strong — mutagenesis with functional readout, independently replicated and mechanistically consistent with localization data","pmids":["9529151"],"is_preprint":false},{"year":1999,"finding":"Nascent CD1b heavy chains interact with the ER chaperones calnexin and calreticulin prior to β2-microglobulin binding; prevention of these chaperone interactions leads to proteasome- and mannosidase-dependent degradation of CD1b; β2-microglobulin rescues chaperone-unassociated CD1b from degradation.","method":"Co-immunoprecipitation of CD1b with calnexin/calreticulin, glucosidase inhibitor (castanospermine) treatment, proteasome inhibitor experiments, β2-microglobulin rescue assays in β2m-deficient cells","journal":"International immunology","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal co-IP with chaperones, multiple orthogonal inhibitor approaches, functional rescue experiment","pmids":["10508179"],"is_preprint":false},{"year":2000,"finding":"Self-glycosphingolipids (e.g., GM1 ganglioside) bind to CD1b on the cell surface at neutral pH and are recognized without internalization or processing; binding is highly reversible and other ceramide-containing glycosphingolipids can displace GM1, acting as competitive blockers. This contrasts with the endosomal loading pathway used for exogenous mycobacterial lipids.","method":"Cell surface CD1b-lipid binding assays at neutral pH, soluble GM1-CD1b complex T cell stimulation, competitive displacement assays, inhibitor studies","journal":"Immunity","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods including soluble complex formation, competitive displacement, and functional T cell assays","pmids":["10981968"],"is_preprint":false},{"year":2000,"finding":"TCR interactions with CD1b occur on the membrane-distal aspects over the α1 and α2 domain helices; TCRs bind in a diagonal orientation relative to the longitudinal axes of the α-helices, making contacts with both helices and bound antigen simultaneously, similar to but distinct from TCR-MHC interactions.","method":"Epitope-specific antibody panel mapping and site-specific CD1b mutants tested for T cell recognition","journal":"Journal of Immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — mutagenesis panel with functional T cell readout, single lab study","pmids":["11035089"],"is_preprint":false},{"year":2002,"finding":"Newly synthesized CD1b is transported rapidly to the cell surface from the Golgi and then enters the endocytic system via AP-2-dependent internalization at the plasma membrane, followed by a second sorting event (possibly involving AP-3) that delivers it to MIICs; this trafficking pathway via the cell surface is important for efficient lipid antigen presentation.","method":"Pulse-chase experiments, AP-2 dominant-negative inhibition, inhibitor studies, functional antigen presentation assays","journal":"The EMBO Journal","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal approaches (pulse-chase, dominant-negative AP-2, functional assays) in a single detailed study","pmids":["11847129"],"is_preprint":false},{"year":2002,"finding":"Lipid chain length determines whether CD1b-mediated antigen presentation occurs via endosomal or cell-surface pathways: long-chain (C80) GMM antigens require delivery of CD1b and antigen to late endosomes over several hours, while short-chain (C32) analogs are presented rapidly by cell-surface CD1b. Dendritic cells preferentially present long-chain glycolipids due to efficient endosomal delivery.","method":"Synthetic GMM analogs of defined chain lengths, endosomal inhibitors, comparison of professional vs. nonprofessional APCs, intracellular trafficking studies","journal":"Nature Immunology","confidence":"High","confidence_rationale":"Tier 2 / Strong — systematic chemical biology with defined antigens and multiple cell types, endosomal inhibitor studies provide mechanistic validation","pmids":["11938350"],"is_preprint":false},{"year":2004,"finding":"Saposin C (SAP-C) is required for CD1b-mediated lipid antigen presentation: SAP-C-deficient fibroblasts expressing CD1b fail to activate lipid-specific T cells, and this is rescued by reconstitution with SAP-C but not other SAPs. SAP-C directly interacts with CD1b (demonstrated by co-precipitation), colocalizes with lipid antigen in lysosomal compartments, and efficiently extracts lipid antigen from membranes.","method":"SAP-deficient fibroblast reconstitution, co-immunoprecipitation of SAP-C with CD1b, liposome lipid extraction assays, immunofluorescence colocalization","journal":"Nature Immunology","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (genetic reconstitution, co-IP, biochemical extraction, colocalization), highly cited mechanistic study","pmids":["14716313"],"is_preprint":false},{"year":2008,"finding":"pH-dependent ionic tethers in the CD1b heavy chain (residues D60, E62) connect the rigid α1 helix to flexible regions of the α2 helix and the 50-60 loop; disruption of these tethers by acidic pH or mutation increases lipid association and dissociation with CD1b and preferentially promotes presentation of antigens with bulky lipid tails, functioning as molecular switches that respond to pH during endosomal recycling.","method":"Molecular dynamics modeling, mutagenesis of D60/E62, lipid binding assays at varying pH, functional antigen presentation assays","journal":"Immunity","confidence":"High","confidence_rationale":"Tier 1 / Moderate — mutagenesis combined with in vitro binding assays and structural modeling, single lab with multiple orthogonal methods","pmids":["18538591"],"is_preprint":false},{"year":2011,"finding":"CD1b uses endogenous scaffold lipids (specifically deoxyceramides and diacylglycerols identified by lipidomics) seated below the antigen in its large groove; these scaffolds lack hydrophilic head groups and function to augment presentation of small glycolipid antigens, enabling CD1b to present antigens with an unusually broad range of chain lengths.","method":"Comparative lipidomics of CD1 proteins, crystal structure analysis of CD1b with scaffold lipids, functional antigen presentation assays with scaffold lipids","journal":"PNAS","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structure plus lipidomics plus functional antigen presentation assays, multiple orthogonal methods","pmids":["22087000"],"is_preprint":false},{"year":2011,"finding":"A crystal structure of CD1b bound to mycobacterial diacylsulfoglycolipid (at 1.9 Å) reveals that antigen binding causes repositioning of endogenous spacer lipids (diradylglycerols) within the groove, F' pocket closure, and extensive rearrangement of residues exposed to TCRs, including reduction of A' pocket capacity and incomplete embedding of the methyl-ramified phthioceranoyl chain — explaining why hydrophobic tail modifications are critical for T cell recognition.","method":"1.9 Å crystal structure of CD1b-diacylsulfoglycolipid complex, site-directed mutagenesis, functional T cell stimulation assays","journal":"PNAS","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structure plus mutagenesis with functional validation","pmids":["22006319"],"is_preprint":false},{"year":2012,"finding":"CD1e functions as a lipid transfer protein that assists α-mannosidase-dependent processing of hexamannosylated phosphatidylinositol mannosides (PIM6) for CD1b presentation; CD1e selectively assists digestion of PIM6 species according to acylation degree and transfers only diacylated PIM from membranes to CD1b.","method":"Lipid transfer assays from donor to acceptor liposomes, membrane-to-CD1b transfer assays, enzymatic digestion assays with defined PIM substrates","journal":"Journal of Biological Chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — reconstituted in vitro lipid transfer assays with defined substrates plus functional T cell readout","pmids":["22782895"],"is_preprint":false},{"year":2016,"finding":"Crystal structure of a GEM TCR bound to CD1b presenting glucose-6-O-monomycolate (GMM) shows the GEM TCR docks centrally above CD1b with the conserved TCR α-chain extensively contacting both CD1b and the glucose moiety of GMM; both TCR α- and β-chains act as 'tweezers' to grip the glucose head group, creating highly specific mycobacterial glycolipid recognition.","method":"Crystal structure of GEM TCR-CD1b-GMM ternary complex, mutagenesis of TCR contact residues, functional T cell assays with tuberculosis patient cells","journal":"Nature Communications","confidence":"High","confidence_rationale":"Tier 1 / Strong — ternary complex crystal structure combined with mutagenesis and patient T cell validation","pmids":["27807341"],"is_preprint":false},{"year":2019,"finding":"CD1b-autoreactive T cells recognize common self-phospholipids (phosphatidylcholine, phosphatidylinositol, phosphatidylethanolamine) via a 'lateral escape channel' in the TCR that shunts phospholipid head groups sideways along the CD1b-TCR interface without contacting the TCR; the TCR recognition site contacts the phosphate neck region common to all major self-phospholipids but absent in sphingolipids, explaining broad cross-reactivity.","method":"Crystal structure of TCR-CD1b-phosphatidylcholine complex, T cell activation assays with diverse phospholipids","journal":"Nature Communications","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structure of ternary complex with multiple functional T cell activation assays","pmids":["30610190"],"is_preprint":false},{"year":2020,"finding":"Human γδ T cells with Vδ1-containing TCRs recognize CD1b by at least two distinct mechanisms: some require lipid antigen, others do not; CD1b specificity is mediated by the Vδ1 chain (demonstrated by chain swap experiments); one Vδ1+Vγ4+ TCR shows dual reactivity to CD1b and butyrophilin-like proteins.","method":"CD1b tetramers, TCR chain swap experiments, CD1b blocking assays, multiple donor analysis","journal":"PNAS","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — tetramer staining plus chain swap experiments, single lab, multiple donors","pmids":["32868441"],"is_preprint":false},{"year":2022,"finding":"Crystal structure (1.9 Å) of CD1b presenting self-phosphatidylinositol-C34:1 with an endogenous scaffold lipid, and (2.4 Å) of this complex bound to the autoreactive BC8B αβ TCR; TCR contacts both the phosphoinositol headgroup and glycerol neck via antigen remodeling within CD1b; alanine scanning mutagenesis identified Glu-80 of CD1b as critical for TCR binding; both CD1b α1 and α2 domains modulate the interaction.","method":"1.9 Å and 2.4 Å crystal structures, alanine scanning mutagenesis, surface plasmon resonance","journal":"Journal of Biological Chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — two crystal structures with mutagenesis and SPR binding measurements in a single study","pmids":["36587766"],"is_preprint":false},{"year":2000,"finding":"CD1b-restricted T cell recognition of GMM requires a precise stereospecific epitope: the exact glucose structure, stereochemistry of the mycolate lipid, and the linkage between carbohydrate and lipid are all required; mycobacteria generate antigenic GMM by coupling mycobacterial mycolates to host-derived glucose, creating an epitope formed by interaction of host and pathogen biosynthetic pathways.","method":"TCR α/β chain transfection reconstitution of GMM recognition, chemical characterization of GMM produced in infected tissue, mycobacterial mutant and in vivo infection studies","journal":"Journal of Experimental Medicine","confidence":"High","confidence_rationale":"Tier 2 / Strong — TCR reconstitution plus chemical analysis of natural antigen, in vivo infection confirmation, multiple orthogonal methods","pmids":["11015438"],"is_preprint":false},{"year":2000,"finding":"CD1b and CD1c traffic to different intracellular compartments: CD1b accumulates predominantly in lysosomal MHC class II compartments (MIICs), while CD1c accumulates in early/late endosomes. CD1b-mediated antigen presentation requires endosomal acidification and endosomal localization of CD1b, while CD1c-mediated presentation does not require these.","method":"Subcellular fractionation, immunofluorescence in dendritic cells, endosomal acidification inhibitors, cytoplasmic tail deletion mutants, functional antigen presentation assays","journal":"Journal of Experimental Medicine","confidence":"High","confidence_rationale":"Tier 2 / Strong — compartment-specific localization with functional inhibitor studies and mutant constructs, multiple orthogonal methods","pmids":["10899914"],"is_preprint":false},{"year":2000,"finding":"GPI-anchored CD1b (CD1b.DAF) is less efficient than native CD1b in antigen presentation, demonstrating that the CD1b cytoplasmic tail-dependent endosomal trafficking pathway is required for optimal antigen loading, distinct from CD1c which maintains presentation capacity when GPI-reanchored.","method":"GPI-reanchored CD1b chimeric constructs, phospholipase C sensitivity assay confirming GPI modification, T cell cytotoxicity and cytokine release functional assays","journal":"Journal of Immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — engineered chimeric constructs with functional readout, single lab study","pmids":["10903726"],"is_preprint":false},{"year":2011,"finding":"CD1b-GMM fluorescent tetramers bind αβ TCRs directly (blocked by recombinant clonotypic TCR comprised of TRAV17 and TRBV4-1), proving a cognate mechanism of CD1b-glycolipid complex recognition by the TCR; nearly all CD1b tetramer-detected cells express CD4 co-receptor, contrary to prior emphasis on CD8+ and DN clones.","method":"Fluorescent CD1b tetramer staining, recombinant TCR blocking, polyclonal T cell sorting and functional activation, ex vivo analysis from TB-infected donors","journal":"Journal of Experimental Medicine","confidence":"High","confidence_rationale":"Tier 2 / Strong — recombinant TCR blocking proves cognate mechanism, ex vivo human donors, multiple orthogonal methods","pmids":["21807869"],"is_preprint":false},{"year":2015,"finding":"CD1b-autoreactive T cells recognize CD1b-phospholipid complexes via αβ TCRs; phosphatidylglycerol (PG) is the immunodominant self-lipid antigen; T cells do not discriminate mammalian from bacterial PG, suggesting recognition of infection- or stress-associated lipids. Identified using CD1b dextramers.","method":"CD1b polyvalent dextramer staining, mass spectrometry identification of lipid antigens, T cell activation assays scanning major phospholipid classes","journal":"PNAS","confidence":"High","confidence_rationale":"Tier 2 / Strong — mass spectrometry antigen identification plus functional T cell assays with defined lipids, multiple orthogonal methods","pmids":["26621732"],"is_preprint":false}],"current_model":"CD1b is a non-polymorphic MHC class I-like antigen-presenting molecule that binds diverse lipid and glycolipid antigens (including mycobacterial GMM, LAM, sulfoglycolipids, and self-phospholipids) via a large hydrophobic groove (containing an A' pocket, C' pocket, F' pocket, and T' tunnel) that accommodates acyl chains while positioning polar head groups for TCR contact; it traffics from the ER (where it associates with calnexin/calreticulin chaperones and β2-microglobulin) to MHC class II compartments (MIICs)/lysosomes via a tyrosine-based endocytosis motif in its cytoplasmic tail, requires the lipid transfer protein saposin C for lysosomal antigen loading, uses scaffold lipids (deoxyceramides/diacylglycerols) to accommodate antigens of varying size, and is regulated by pH-dependent ionic tethers that control groove conformation during endosomal recycling, collectively enabling presentation of both foreign mycobacterial lipids and self-phospholipids to diverse αβ and γδ T cell populations."},"narrative":{"mechanistic_narrative":"CD1b is a non-polymorphic MHC class I-like antigen-presenting molecule that displays lipid and glycolipid antigens to T cells, functioning as a bridge between innate lipid recognition and adaptive cellular immunity, most prominently against Mycobacterium tuberculosis [PMID:1281285, PMID:9323206]. Its hydrophobic groove binds the acyl chains of antigens such as glucose monomycolate (GMM), lipoarabinomannan, phosphatidylinositol mannosides, and sulfoglycolipids nonspecifically while positioning the polar head group for TCR contact, so that T cell recognition is exquisitely sensitive to the carbohydrate/head group yet tolerant of lipid-tail variation [PMID:9323206, PMID:9529150, PMID:22006319]. To accommodate antigens of widely varying size, CD1b seats endogenous scaffold lipids (deoxyceramides, diacylglycerols/diradylglycerols) beneath the bound antigen, and antigen capture triggers F' pocket closure and remodeling of the residues exposed to the TCR [PMID:22087000, PMID:22006319]. Maturation begins in the ER, where nascent heavy chains engage calnexin and calreticulin before β2-microglobulin assembly, with failure of these interactions routing CD1b to proteasomal/mannosidase-dependent degradation [PMID:10508179]. A tyrosine-based motif in its short cytoplasmic tail directs CD1b through AP-2-dependent internalization from the cell surface into MHC class II compartments/lysosomes, an acidic environment required for loading exogenous mycobacterial lipids; pH-dependent ionic tethers (D60, E62) act as conformational switches that open the groove for bulky-tailed antigens during endosomal recycling [PMID:8662520, PMID:9529151, PMID:11847129, PMID:18538591, PMID:10899914]. Lysosomal antigen loading further depends on the lipid transfer protein saposin C, which binds CD1b and extracts antigen from membranes, while CD1e assists α-mannosidase processing and transfer of PIM species [PMID:14716313, PMID:22782895]. CD1b-lipid complexes are recognized by diverse αβ TCRs in a diagonal, antigen-contacting docking mode — including conserved 'GEM' TCRs that grip the GMM glucose like tweezers — and also by Vδ1+ γδ T cells [PMID:11035089, PMID:27807341, PMID:32868441, PMID:21807869]. Beyond foreign lipids, CD1b presents self-phospholipids (phosphatidylglycerol, phosphatidylcholine, phosphatidylinositol, phosphatidylethanolamine) to autoreactive T cells, which engage the conserved phosphate/glycerol neck region via a lateral escape channel that shunts head groups sideways, explaining broad cross-reactivity [PMID:30610190, PMID:36587766, PMID:26621732].","teleology":[{"year":1992,"claim":"Established that CD1b is itself an antigen-presenting molecule, defining a presentation system parallel to but distinct from classical MHC.","evidence":"T cell proliferation/cytotoxicity assays against M. tuberculosis with CD1b-expressing APCs and antibody blocking","pmids":["1281285"],"confidence":"High","gaps":["Antigen identity unknown at this point","Did not establish lipid versus peptide nature of presented antigen"]},{"year":1996,"claim":"Resolved where CD1b loads antigen and how it gets there, showing it uses its own tail-encoded sorting signal rather than the invariant chain used by MHC class II.","evidence":"Immunoelectron microscopy, subcellular fractionation, and cytoplasmic tail mutants localizing CD1b to MIICs","pmids":["8662520"],"confidence":"High","gaps":["Adaptor machinery reading the motif not yet identified","Route from Golgi to MIIC not resolved"]},{"year":1997,"claim":"Identified a defined mycobacterial glycolipid (GMM) as antigen and revealed the head-group-specific, tail-permissive logic of recognition that defines CD1b binding.","evidence":"Synthetic GMM analogs with defined modifications tested on CD1b-restricted T cell clones","pmids":["9323206"],"confidence":"High","gaps":["Structural basis of groove binding not yet visualized","How acyl chains are accommodated unknown"]},{"year":1997,"claim":"Connected innate pattern recognition to CD1b presentation by showing the mannose receptor delivers LAM into CD1b-containing compartments.","evidence":"MR blocking, LAM internalization, and immunofluorescence colocalization of MR/LAM/CD1b","pmids":["9047240"],"confidence":"High","gaps":["Whether MR is the sole uptake route unknown","Loading step within lysosome not defined"]},{"year":1998,"claim":"Provided direct biochemical and pH-dependent mechanism for antigen capture, showing CD1b binds acyl chains and unfolds at acidic pH to expose its hydrophobic site.","evidence":"Direct CD1b-lipid binding assays and pH-dependent binding/structural characterization","pmids":["9529150"],"confidence":"High","gaps":["Atomic-resolution groove architecture not yet solved","Accessory loading factors not identified"]},{"year":1998,"claim":"Pinpointed the single cytoplasmic tyrosine as the functional determinant linking endosomal targeting to efficient antigen presentation.","evidence":"Site-directed mutagenesis of the tail tyrosine with presentation and localization readouts","pmids":["9529151"],"confidence":"High","gaps":["Surface-loaded antigens still presentable, leaving the boundary between pathways open","Sorting adaptors not yet defined"]},{"year":1999,"claim":"Defined the ER assembly and quality-control pathway, showing chaperone engagement and β2m assembly are required to escape degradation.","evidence":"Co-IP with calnexin/calreticulin, glucosidase/proteasome inhibitors, and β2m rescue in deficient cells","pmids":["10508179"],"confidence":"High","gaps":["Whether lipid is loaded in the ER not addressed","Timing of scaffold lipid acquisition unknown"]},{"year":2000,"claim":"Distinguished a neutral-pH, surface, processing-independent route for self-glycosphingolipids from the endosomal route for foreign lipids.","evidence":"Surface CD1b-lipid binding at neutral pH, soluble GM1-CD1b complex T cell stimulation, and competitive displacement","pmids":["10981968"],"confidence":"High","gaps":["Physiological relevance of surface self-lipid display unclear","TCR contribution to self-lipid discrimination not resolved"]},{"year":2000,"claim":"Mapped the geometry of TCR engagement, establishing diagonal docking over the α1/α2 helices contacting both helices and antigen.","evidence":"Epitope-specific antibody mapping and site-specific CD1b mutants tested for T cell recognition","pmids":["11035089"],"confidence":"Medium","gaps":["Single-lab mutagenesis without a co-crystal structure","Diversity of docking modes across TCRs not addressed"]},{"year":2000,"claim":"Showed the natural GMM epitope is a host-pathogen hybrid requiring stereospecific coupling of pathogen mycolate to host glucose.","evidence":"TCR chain transfection reconstitution, chemical analysis of natural GMM, and in vivo infection studies","pmids":["11015438"],"confidence":"High","gaps":["Generality across mycobacterial lipids unknown","Enzymes generating the epitope not identified here"]},{"year":2000,"claim":"Demonstrated compartment-specialized trafficking, contrasting lysosomal CD1b (acidification-dependent) with endosomal CD1c.","evidence":"Subcellular fractionation, acidification inhibitors, tail mutants, and presentation assays in dendritic cells","pmids":["10899914"],"confidence":"High","gaps":["Mechanistic basis of differential sorting between CD1 isoforms not resolved"]},{"year":2000,"claim":"Confirmed the requirement of tail-driven endosomal recycling for optimal loading using GPI-reanchoring that bypasses the tail.","evidence":"GPI-reanchored CD1b.DAF chimeras with PLC sensitivity controls and functional T cell assays","pmids":["10903726"],"confidence":"Medium","gaps":["Single-lab engineered-construct study","Residual presentation mechanism by GPI-anchored CD1b not defined"]},{"year":2002,"claim":"Defined the full itinerary, showing CD1b reaches the surface first then enters via AP-2 with a second AP-3-linked sort to MIICs.","evidence":"Pulse-chase, dominant-negative AP-2, inhibitors, and functional presentation assays","pmids":["11847129"],"confidence":"High","gaps":["Direct demonstration of AP-3 involvement incomplete","Recycling kinetics not fully quantified"]},{"year":2002,"claim":"Linked antigen lipid chain length to the route of presentation, explaining why long-chain antigens need endosomal delivery.","evidence":"Synthetic GMM analogs of defined chain lengths with endosomal inhibitors and APC comparisons","pmids":["11938350"],"confidence":"High","gaps":["Structural basis for chain-length-dependent loading not resolved here"]},{"year":2004,"claim":"Identified saposin C as the lysosomal lipid-loading cofactor that extracts antigen from membranes and physically engages CD1b.","evidence":"SAP-deficient fibroblast reconstitution, co-IP with CD1b, liposome extraction, and colocalization","pmids":["14716313"],"confidence":"High","gaps":["Stoichiometry/structure of the CD1b-saposin C interaction unknown","Whether other lipid transfer proteins contribute not resolved"]},{"year":2008,"claim":"Revealed pH-responsive ionic tethers (D60/E62) acting as molecular switches that gate groove flexibility and bulky-tail loading during endosomal recycling.","evidence":"Molecular dynamics, D60/E62 mutagenesis, pH-varied binding, and presentation assays","pmids":["18538591"],"confidence":"High","gaps":["In situ confirmation of pH-driven conformational change in cells limited","Single-lab structural modeling"]},{"year":2011,"claim":"Established that endogenous scaffold lipids fill the groove beneath antigen, enabling presentation across a broad antigen size range.","evidence":"Comparative lipidomics, crystal structure of CD1b with scaffold lipids, and presentation assays","pmids":["22087000"],"confidence":"High","gaps":["How scaffold lipids are selected and exchanged in cells not defined"]},{"year":2011,"claim":"Provided atomic-level mechanism for tail sensitivity, showing antigen binding repositions spacer lipids, closes the F' pocket, and remodels TCR-exposed residues.","evidence":"1.9 Å crystal structure of CD1b-diacylsulfoglycolipid with mutagenesis and T cell assays","pmids":["22006319"],"confidence":"High","gaps":["Conformational dynamics during loading inferred from static structure"]},{"year":2011,"claim":"Proved cognate αβ TCR recognition of CD1b-GMM by tetramer and recombinant TCR blocking, and reassigned the dominant responding population toward CD4+ cells.","evidence":"CD1b-GMM tetramer staining, clonotypic TCR blocking, and ex vivo TB donor analysis","pmids":["21807869"],"confidence":"High","gaps":["Functional consequence of CD4 co-receptor usage not defined"]},{"year":2012,"claim":"Defined CD1e as a processing/transfer accessory that prepares PIM6 antigens by acylation-selective digestion and transfer to CD1b.","evidence":"Reconstituted lipid transfer and enzymatic digestion assays with defined PIM substrates plus T cell readout","pmids":["22782895"],"confidence":"High","gaps":["Whether CD1e acts on antigens beyond PIM not addressed here"]},{"year":2015,"claim":"Established that CD1b presents self-phospholipids, with phosphatidylglycerol immunodominant and no mammalian/bacterial discrimination, implicating stress/infection-associated self-lipid recognition.","evidence":"CD1b dextramer staining, mass spectrometry antigen ID, and phospholipid-scanning T cell assays","pmids":["26621732"],"confidence":"High","gaps":["In vivo trigger for autoreactivity not defined","Structural basis of cross-reactivity not yet shown here"]},{"year":2016,"claim":"Defined the structural basis of conserved GEM TCR recognition, showing dual-chain 'tweezer' gripping of the GMM glucose for high mycobacterial specificity.","evidence":"GEM TCR-CD1b-GMM ternary crystal structure, mutagenesis, and TB patient T cell assays","pmids":["27807341"],"confidence":"High","gaps":["Why GEM TCR usage recurs across donors not mechanistically explained"]},{"year":2019,"claim":"Explained broad self-phospholipid cross-reactivity via a lateral escape channel that shunts head groups while the TCR reads the conserved phosphate neck.","evidence":"Crystal structure of TCR-CD1b-phosphatidylcholine with phospholipid-scanning activation assays","pmids":["30610190"],"confidence":"High","gaps":["Frequency and physiological role of such autoreactive cells not defined"]},{"year":2020,"claim":"Extended CD1b recognition to γδ T cells, showing Vδ1-mediated, variably lipid-dependent reactivity and overlap with butyrophilin-like recognition.","evidence":"CD1b tetramers, TCR chain-swap experiments, and blocking across multiple donors","pmids":["32868441"],"confidence":"Medium","gaps":["No co-crystal structure of γδ TCR-CD1b","Antigen requirements for lipid-independent recognition undefined"]},{"year":2022,"claim":"Provided structural definition of autoreactive αβ TCR engagement of a self-phosphatidylinositol complex, identifying CD1b Glu-80 as a key TCR-contact residue.","evidence":"1.9/2.4 Å crystal structures, alanine-scanning mutagenesis, and SPR","pmids":["36587766"],"confidence":"High","gaps":["Thymic selection and in vivo role of these autoreactive cells not addressed"]},{"year":null,"claim":"How CD1b antigen presentation is dysregulated in disease and how the surface self-lipid display versus lysosomal foreign-lipid loading pathways are integrated in vivo remain unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No timeline disease-causation study","In vivo balance between self and foreign lipid presentation undefined","Regulation of scaffold lipid exchange in cells not established"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0008289","term_label":"lipid binding","supporting_discovery_ids":[2,4,7,13,14]},{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[0,8,16,17]},{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[13,14]}],"localization":[{"term_id":"GO:0005764","term_label":"lysosome","supporting_discovery_ids":[1,11,21]},{"term_id":"GO:0005768","term_label":"endosome","supporting_discovery_ids":[9,21]},{"term_id":"GO:0005783","term_label":"endoplasmic reticulum","supporting_discovery_ids":[6]},{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[7,9,22]}],"pathway":[{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[0,2,23,24]},{"term_id":"R-HSA-9609507","term_label":"Protein localization","supporting_discovery_ids":[1,5,9,21]}],"complexes":[],"partners":["B2M","CANX","CALR","PSAP","CD1E"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P29016","full_name":"T-cell surface glycoprotein CD1b","aliases":[],"length_aa":333,"mass_kda":36.9,"function":"Antigen-presenting protein that binds self and non-self lipid and glycolipid antigens and presents them to T-cell receptors on natural 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similar to MHC class II-restricted presentation.\",\n      \"method\": \"T cell proliferation and cytotoxicity assays with CD1b-expressing antigen-presenting cells; antibody blocking experiments\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — direct functional assay with antibody blocking, foundational result replicated extensively across subsequent studies\",\n      \"pmids\": [\"1281285\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"CD1b localizes to MHC class II compartments (MIICs) — the endosomal antigen-loading compartments — and this localization is dependent on a tyrosine-based motif in its own cytoplasmic tail, not on association with invariant chain as for MHC class II.\",\n      \"method\": \"Immunoelectron microscopy, subcellular fractionation, cytoplasmic tail deletion/mutation constructs, and co-localization with MHC class II in MIICs\",\n      \"journal\": \"Science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — direct subcellular localization by immunoelectron microscopy combined with functional mutagenesis, independently replicated\",\n      \"pmids\": [\"8662520\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"CD1b presents the mycobacterial glycolipid glucose monomycolate (GMM) to T cells; T cell recognition is insensitive to variation in lipid tails but extremely sensitive to alterations in the carbohydrate or polar head group, indicating that CD1b binds acyl chains nonspecifically in its hydrophobic groove while positioning the hydrophilic moiety for specific TCR interaction.\",\n      \"method\": \"Synthetic GMM analogs with defined chemical modifications presented to CD1b-restricted T cell clones; T cell activation assays\",\n      \"journal\": \"Science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — systematic chemical biology with defined synthetic antigens, replicated across multiple studies\",\n      \"pmids\": [\"9323206\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"The macrophage mannose receptor (MR) mediates uptake of lipoarabinomannan (LAM) and delivers it to late endosomes/lysosomes/MIICs where CD1b is present; MR and CD1b colocalize in these compartments, linking innate pattern recognition to CD1b-mediated adaptive T cell presentation of LAM.\",\n      \"method\": \"MR antagonism/blocking assays, LAM internalization studies, immunofluorescence colocalization of MR, LAM, and CD1b in intracellular compartments\",\n      \"journal\": \"Immunity\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (functional blocking, internalization, colocalization), replicated concept\",\n      \"pmids\": [\"9047240\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"CD1b directly binds the acyl side chains of lipid antigens (LAM, phosphatidylinositol mannoside, GMM) with high affinity; binding is optimal at acidic pH due to partial unfolding of the α-helices of CD1b at low pH, revealing a hydrophobic binding site.\",\n      \"method\": \"Direct CD1b-antigen binding assays, pH-dependent binding experiments, structural/biochemical characterization\",\n      \"journal\": \"Immunity\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro binding assays with defined lipid antigens plus mechanistic pH studies, independently replicated\",\n      \"pmids\": [\"9529150\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"The nine-amino acid cytoplasmic tail of CD1b, specifically the single cytoplasmic tyrosine residue, is required for endosomal targeting of CD1b and for efficient presentation of lipid antigens; CD1b mutants lacking this motif are expressed on the cell surface but fail to efficiently present antigens acquired exogenously or from live intracellular organisms.\",\n      \"method\": \"Site-directed mutagenesis of cytoplasmic tail tyrosine, functional antigen presentation assays with T cell lines, subcellular localization studies\",\n      \"journal\": \"Immunity\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — mutagenesis with functional readout, independently replicated and mechanistically consistent with localization data\",\n      \"pmids\": [\"9529151\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"Nascent CD1b heavy chains interact with the ER chaperones calnexin and calreticulin prior to β2-microglobulin binding; prevention of these chaperone interactions leads to proteasome- and mannosidase-dependent degradation of CD1b; β2-microglobulin rescues chaperone-unassociated CD1b from degradation.\",\n      \"method\": \"Co-immunoprecipitation of CD1b with calnexin/calreticulin, glucosidase inhibitor (castanospermine) treatment, proteasome inhibitor experiments, β2-microglobulin rescue assays in β2m-deficient cells\",\n      \"journal\": \"International immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal co-IP with chaperones, multiple orthogonal inhibitor approaches, functional rescue experiment\",\n      \"pmids\": [\"10508179\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"Self-glycosphingolipids (e.g., GM1 ganglioside) bind to CD1b on the cell surface at neutral pH and are recognized without internalization or processing; binding is highly reversible and other ceramide-containing glycosphingolipids can displace GM1, acting as competitive blockers. This contrasts with the endosomal loading pathway used for exogenous mycobacterial lipids.\",\n      \"method\": \"Cell surface CD1b-lipid binding assays at neutral pH, soluble GM1-CD1b complex T cell stimulation, competitive displacement assays, inhibitor studies\",\n      \"journal\": \"Immunity\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods including soluble complex formation, competitive displacement, and functional T cell assays\",\n      \"pmids\": [\"10981968\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"TCR interactions with CD1b occur on the membrane-distal aspects over the α1 and α2 domain helices; TCRs bind in a diagonal orientation relative to the longitudinal axes of the α-helices, making contacts with both helices and bound antigen simultaneously, similar to but distinct from TCR-MHC interactions.\",\n      \"method\": \"Epitope-specific antibody panel mapping and site-specific CD1b mutants tested for T cell recognition\",\n      \"journal\": \"Journal of Immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — mutagenesis panel with functional T cell readout, single lab study\",\n      \"pmids\": [\"11035089\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Newly synthesized CD1b is transported rapidly to the cell surface from the Golgi and then enters the endocytic system via AP-2-dependent internalization at the plasma membrane, followed by a second sorting event (possibly involving AP-3) that delivers it to MIICs; this trafficking pathway via the cell surface is important for efficient lipid antigen presentation.\",\n      \"method\": \"Pulse-chase experiments, AP-2 dominant-negative inhibition, inhibitor studies, functional antigen presentation assays\",\n      \"journal\": \"The EMBO Journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal approaches (pulse-chase, dominant-negative AP-2, functional assays) in a single detailed study\",\n      \"pmids\": [\"11847129\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Lipid chain length determines whether CD1b-mediated antigen presentation occurs via endosomal or cell-surface pathways: long-chain (C80) GMM antigens require delivery of CD1b and antigen to late endosomes over several hours, while short-chain (C32) analogs are presented rapidly by cell-surface CD1b. Dendritic cells preferentially present long-chain glycolipids due to efficient endosomal delivery.\",\n      \"method\": \"Synthetic GMM analogs of defined chain lengths, endosomal inhibitors, comparison of professional vs. nonprofessional APCs, intracellular trafficking studies\",\n      \"journal\": \"Nature Immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — systematic chemical biology with defined antigens and multiple cell types, endosomal inhibitor studies provide mechanistic validation\",\n      \"pmids\": [\"11938350\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Saposin C (SAP-C) is required for CD1b-mediated lipid antigen presentation: SAP-C-deficient fibroblasts expressing CD1b fail to activate lipid-specific T cells, and this is rescued by reconstitution with SAP-C but not other SAPs. SAP-C directly interacts with CD1b (demonstrated by co-precipitation), colocalizes with lipid antigen in lysosomal compartments, and efficiently extracts lipid antigen from membranes.\",\n      \"method\": \"SAP-deficient fibroblast reconstitution, co-immunoprecipitation of SAP-C with CD1b, liposome lipid extraction assays, immunofluorescence colocalization\",\n      \"journal\": \"Nature Immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (genetic reconstitution, co-IP, biochemical extraction, colocalization), highly cited mechanistic study\",\n      \"pmids\": [\"14716313\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"pH-dependent ionic tethers in the CD1b heavy chain (residues D60, E62) connect the rigid α1 helix to flexible regions of the α2 helix and the 50-60 loop; disruption of these tethers by acidic pH or mutation increases lipid association and dissociation with CD1b and preferentially promotes presentation of antigens with bulky lipid tails, functioning as molecular switches that respond to pH during endosomal recycling.\",\n      \"method\": \"Molecular dynamics modeling, mutagenesis of D60/E62, lipid binding assays at varying pH, functional antigen presentation assays\",\n      \"journal\": \"Immunity\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — mutagenesis combined with in vitro binding assays and structural modeling, single lab with multiple orthogonal methods\",\n      \"pmids\": [\"18538591\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"CD1b uses endogenous scaffold lipids (specifically deoxyceramides and diacylglycerols identified by lipidomics) seated below the antigen in its large groove; these scaffolds lack hydrophilic head groups and function to augment presentation of small glycolipid antigens, enabling CD1b to present antigens with an unusually broad range of chain lengths.\",\n      \"method\": \"Comparative lipidomics of CD1 proteins, crystal structure analysis of CD1b with scaffold lipids, functional antigen presentation assays with scaffold lipids\",\n      \"journal\": \"PNAS\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structure plus lipidomics plus functional antigen presentation assays, multiple orthogonal methods\",\n      \"pmids\": [\"22087000\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"A crystal structure of CD1b bound to mycobacterial diacylsulfoglycolipid (at 1.9 Å) reveals that antigen binding causes repositioning of endogenous spacer lipids (diradylglycerols) within the groove, F' pocket closure, and extensive rearrangement of residues exposed to TCRs, including reduction of A' pocket capacity and incomplete embedding of the methyl-ramified phthioceranoyl chain — explaining why hydrophobic tail modifications are critical for T cell recognition.\",\n      \"method\": \"1.9 Å crystal structure of CD1b-diacylsulfoglycolipid complex, site-directed mutagenesis, functional T cell stimulation assays\",\n      \"journal\": \"PNAS\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structure plus mutagenesis with functional validation\",\n      \"pmids\": [\"22006319\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"CD1e functions as a lipid transfer protein that assists α-mannosidase-dependent processing of hexamannosylated phosphatidylinositol mannosides (PIM6) for CD1b presentation; CD1e selectively assists digestion of PIM6 species according to acylation degree and transfers only diacylated PIM from membranes to CD1b.\",\n      \"method\": \"Lipid transfer assays from donor to acceptor liposomes, membrane-to-CD1b transfer assays, enzymatic digestion assays with defined PIM substrates\",\n      \"journal\": \"Journal of Biological Chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — reconstituted in vitro lipid transfer assays with defined substrates plus functional T cell readout\",\n      \"pmids\": [\"22782895\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Crystal structure of a GEM TCR bound to CD1b presenting glucose-6-O-monomycolate (GMM) shows the GEM TCR docks centrally above CD1b with the conserved TCR α-chain extensively contacting both CD1b and the glucose moiety of GMM; both TCR α- and β-chains act as 'tweezers' to grip the glucose head group, creating highly specific mycobacterial glycolipid recognition.\",\n      \"method\": \"Crystal structure of GEM TCR-CD1b-GMM ternary complex, mutagenesis of TCR contact residues, functional T cell assays with tuberculosis patient cells\",\n      \"journal\": \"Nature Communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — ternary complex crystal structure combined with mutagenesis and patient T cell validation\",\n      \"pmids\": [\"27807341\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"CD1b-autoreactive T cells recognize common self-phospholipids (phosphatidylcholine, phosphatidylinositol, phosphatidylethanolamine) via a 'lateral escape channel' in the TCR that shunts phospholipid head groups sideways along the CD1b-TCR interface without contacting the TCR; the TCR recognition site contacts the phosphate neck region common to all major self-phospholipids but absent in sphingolipids, explaining broad cross-reactivity.\",\n      \"method\": \"Crystal structure of TCR-CD1b-phosphatidylcholine complex, T cell activation assays with diverse phospholipids\",\n      \"journal\": \"Nature Communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structure of ternary complex with multiple functional T cell activation assays\",\n      \"pmids\": [\"30610190\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Human γδ T cells with Vδ1-containing TCRs recognize CD1b by at least two distinct mechanisms: some require lipid antigen, others do not; CD1b specificity is mediated by the Vδ1 chain (demonstrated by chain swap experiments); one Vδ1+Vγ4+ TCR shows dual reactivity to CD1b and butyrophilin-like proteins.\",\n      \"method\": \"CD1b tetramers, TCR chain swap experiments, CD1b blocking assays, multiple donor analysis\",\n      \"journal\": \"PNAS\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — tetramer staining plus chain swap experiments, single lab, multiple donors\",\n      \"pmids\": [\"32868441\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Crystal structure (1.9 Å) of CD1b presenting self-phosphatidylinositol-C34:1 with an endogenous scaffold lipid, and (2.4 Å) of this complex bound to the autoreactive BC8B αβ TCR; TCR contacts both the phosphoinositol headgroup and glycerol neck via antigen remodeling within CD1b; alanine scanning mutagenesis identified Glu-80 of CD1b as critical for TCR binding; both CD1b α1 and α2 domains modulate the interaction.\",\n      \"method\": \"1.9 Å and 2.4 Å crystal structures, alanine scanning mutagenesis, surface plasmon resonance\",\n      \"journal\": \"Journal of Biological Chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — two crystal structures with mutagenesis and SPR binding measurements in a single study\",\n      \"pmids\": [\"36587766\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"CD1b-restricted T cell recognition of GMM requires a precise stereospecific epitope: the exact glucose structure, stereochemistry of the mycolate lipid, and the linkage between carbohydrate and lipid are all required; mycobacteria generate antigenic GMM by coupling mycobacterial mycolates to host-derived glucose, creating an epitope formed by interaction of host and pathogen biosynthetic pathways.\",\n      \"method\": \"TCR α/β chain transfection reconstitution of GMM recognition, chemical characterization of GMM produced in infected tissue, mycobacterial mutant and in vivo infection studies\",\n      \"journal\": \"Journal of Experimental Medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — TCR reconstitution plus chemical analysis of natural antigen, in vivo infection confirmation, multiple orthogonal methods\",\n      \"pmids\": [\"11015438\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"CD1b and CD1c traffic to different intracellular compartments: CD1b accumulates predominantly in lysosomal MHC class II compartments (MIICs), while CD1c accumulates in early/late endosomes. CD1b-mediated antigen presentation requires endosomal acidification and endosomal localization of CD1b, while CD1c-mediated presentation does not require these.\",\n      \"method\": \"Subcellular fractionation, immunofluorescence in dendritic cells, endosomal acidification inhibitors, cytoplasmic tail deletion mutants, functional antigen presentation assays\",\n      \"journal\": \"Journal of Experimental Medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — compartment-specific localization with functional inhibitor studies and mutant constructs, multiple orthogonal methods\",\n      \"pmids\": [\"10899914\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"GPI-anchored CD1b (CD1b.DAF) is less efficient than native CD1b in antigen presentation, demonstrating that the CD1b cytoplasmic tail-dependent endosomal trafficking pathway is required for optimal antigen loading, distinct from CD1c which maintains presentation capacity when GPI-reanchored.\",\n      \"method\": \"GPI-reanchored CD1b chimeric constructs, phospholipase C sensitivity assay confirming GPI modification, T cell cytotoxicity and cytokine release functional assays\",\n      \"journal\": \"Journal of Immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — engineered chimeric constructs with functional readout, single lab study\",\n      \"pmids\": [\"10903726\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"CD1b-GMM fluorescent tetramers bind αβ TCRs directly (blocked by recombinant clonotypic TCR comprised of TRAV17 and TRBV4-1), proving a cognate mechanism of CD1b-glycolipid complex recognition by the TCR; nearly all CD1b tetramer-detected cells express CD4 co-receptor, contrary to prior emphasis on CD8+ and DN clones.\",\n      \"method\": \"Fluorescent CD1b tetramer staining, recombinant TCR blocking, polyclonal T cell sorting and functional activation, ex vivo analysis from TB-infected donors\",\n      \"journal\": \"Journal of Experimental Medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — recombinant TCR blocking proves cognate mechanism, ex vivo human donors, multiple orthogonal methods\",\n      \"pmids\": [\"21807869\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"CD1b-autoreactive T cells recognize CD1b-phospholipid complexes via αβ TCRs; phosphatidylglycerol (PG) is the immunodominant self-lipid antigen; T cells do not discriminate mammalian from bacterial PG, suggesting recognition of infection- or stress-associated lipids. Identified using CD1b dextramers.\",\n      \"method\": \"CD1b polyvalent dextramer staining, mass spectrometry identification of lipid antigens, T cell activation assays scanning major phospholipid classes\",\n      \"journal\": \"PNAS\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — mass spectrometry antigen identification plus functional T cell assays with defined lipids, multiple orthogonal methods\",\n      \"pmids\": [\"26621732\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"CD1b is a non-polymorphic MHC class I-like antigen-presenting molecule that binds diverse lipid and glycolipid antigens (including mycobacterial GMM, LAM, sulfoglycolipids, and self-phospholipids) via a large hydrophobic groove (containing an A' pocket, C' pocket, F' pocket, and T' tunnel) that accommodates acyl chains while positioning polar head groups for TCR contact; it traffics from the ER (where it associates with calnexin/calreticulin chaperones and β2-microglobulin) to MHC class II compartments (MIICs)/lysosomes via a tyrosine-based endocytosis motif in its cytoplasmic tail, requires the lipid transfer protein saposin C for lysosomal antigen loading, uses scaffold lipids (deoxyceramides/diacylglycerols) to accommodate antigens of varying size, and is regulated by pH-dependent ionic tethers that control groove conformation during endosomal recycling, collectively enabling presentation of both foreign mycobacterial lipids and self-phospholipids to diverse αβ and γδ T cell populations.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"CD1b is a non-polymorphic MHC class I-like antigen-presenting molecule that displays lipid and glycolipid antigens to T cells, functioning as a bridge between innate lipid recognition and adaptive cellular immunity, most prominently against Mycobacterium tuberculosis [#0, #2]. Its hydrophobic groove binds the acyl chains of antigens such as glucose monomycolate (GMM), lipoarabinomannan, phosphatidylinositol mannosides, and sulfoglycolipids nonspecifically while positioning the polar head group for TCR contact, so that T cell recognition is exquisitely sensitive to the carbohydrate/head group yet tolerant of lipid-tail variation [#2, #4, #14]. To accommodate antigens of widely varying size, CD1b seats endogenous scaffold lipids (deoxyceramides, diacylglycerols/diradylglycerols) beneath the bound antigen, and antigen capture triggers F' pocket closure and remodeling of the residues exposed to the TCR [#13, #14]. Maturation begins in the ER, where nascent heavy chains engage calnexin and calreticulin before β2-microglobulin assembly, with failure of these interactions routing CD1b to proteasomal/mannosidase-dependent degradation [#6]. A tyrosine-based motif in its short cytoplasmic tail directs CD1b through AP-2-dependent internalization from the cell surface into MHC class II compartments/lysosomes, an acidic environment required for loading exogenous mycobacterial lipids; pH-dependent ionic tethers (D60, E62) act as conformational switches that open the groove for bulky-tailed antigens during endosomal recycling [#1, #5, #9, #12, #21]. Lysosomal antigen loading further depends on the lipid transfer protein saposin C, which binds CD1b and extracts antigen from membranes, while CD1e assists α-mannosidase processing and transfer of PIM species [#11, #15]. CD1b-lipid complexes are recognized by diverse αβ TCRs in a diagonal, antigen-contacting docking mode — including conserved 'GEM' TCRs that grip the GMM glucose like tweezers — and also by Vδ1+ γδ T cells [#8, #16, #18, #23]. Beyond foreign lipids, CD1b presents self-phospholipids (phosphatidylglycerol, phosphatidylcholine, phosphatidylinositol, phosphatidylethanolamine) to autoreactive T cells, which engage the conserved phosphate/glycerol neck region via a lateral escape channel that shunts head groups sideways, explaining broad cross-reactivity [#17, #19, #24].\",\n  \"teleology\": [\n    {\n      \"year\": 1992,\n      \"claim\": \"Established that CD1b is itself an antigen-presenting molecule, defining a presentation system parallel to but distinct from classical MHC.\",\n      \"evidence\": \"T cell proliferation/cytotoxicity assays against M. tuberculosis with CD1b-expressing APCs and antibody blocking\",\n      \"pmids\": [\"1281285\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Antigen identity unknown at this point\", \"Did not establish lipid versus peptide nature of presented antigen\"]\n    },\n    {\n      \"year\": 1996,\n      \"claim\": \"Resolved where CD1b loads antigen and how it gets there, showing it uses its own tail-encoded sorting signal rather than the invariant chain used by MHC class II.\",\n      \"evidence\": \"Immunoelectron microscopy, subcellular fractionation, and cytoplasmic tail mutants localizing CD1b to MIICs\",\n      \"pmids\": [\"8662520\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Adaptor machinery reading the motif not yet identified\", \"Route from Golgi to MIIC not resolved\"]\n    },\n    {\n      \"year\": 1997,\n      \"claim\": \"Identified a defined mycobacterial glycolipid (GMM) as antigen and revealed the head-group-specific, tail-permissive logic of recognition that defines CD1b binding.\",\n      \"evidence\": \"Synthetic GMM analogs with defined modifications tested on CD1b-restricted T cell clones\",\n      \"pmids\": [\"9323206\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of groove binding not yet visualized\", \"How acyl chains are accommodated unknown\"]\n    },\n    {\n      \"year\": 1997,\n      \"claim\": \"Connected innate pattern recognition to CD1b presentation by showing the mannose receptor delivers LAM into CD1b-containing compartments.\",\n      \"evidence\": \"MR blocking, LAM internalization, and immunofluorescence colocalization of MR/LAM/CD1b\",\n      \"pmids\": [\"9047240\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether MR is the sole uptake route unknown\", \"Loading step within lysosome not defined\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"Provided direct biochemical and pH-dependent mechanism for antigen capture, showing CD1b binds acyl chains and unfolds at acidic pH to expose its hydrophobic site.\",\n      \"evidence\": \"Direct CD1b-lipid binding assays and pH-dependent binding/structural characterization\",\n      \"pmids\": [\"9529150\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Atomic-resolution groove architecture not yet solved\", \"Accessory loading factors not identified\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"Pinpointed the single cytoplasmic tyrosine as the functional determinant linking endosomal targeting to efficient antigen presentation.\",\n      \"evidence\": \"Site-directed mutagenesis of the tail tyrosine with presentation and localization readouts\",\n      \"pmids\": [\"9529151\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Surface-loaded antigens still presentable, leaving the boundary between pathways open\", \"Sorting adaptors not yet defined\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Defined the ER assembly and quality-control pathway, showing chaperone engagement and β2m assembly are required to escape degradation.\",\n      \"evidence\": \"Co-IP with calnexin/calreticulin, glucosidase/proteasome inhibitors, and β2m rescue in deficient cells\",\n      \"pmids\": [\"10508179\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether lipid is loaded in the ER not addressed\", \"Timing of scaffold lipid acquisition unknown\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Distinguished a neutral-pH, surface, processing-independent route for self-glycosphingolipids from the endosomal route for foreign lipids.\",\n      \"evidence\": \"Surface CD1b-lipid binding at neutral pH, soluble GM1-CD1b complex T cell stimulation, and competitive displacement\",\n      \"pmids\": [\"10981968\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physiological relevance of surface self-lipid display unclear\", \"TCR contribution to self-lipid discrimination not resolved\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Mapped the geometry of TCR engagement, establishing diagonal docking over the α1/α2 helices contacting both helices and antigen.\",\n      \"evidence\": \"Epitope-specific antibody mapping and site-specific CD1b mutants tested for T cell recognition\",\n      \"pmids\": [\"11035089\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab mutagenesis without a co-crystal structure\", \"Diversity of docking modes across TCRs not addressed\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Showed the natural GMM epitope is a host-pathogen hybrid requiring stereospecific coupling of pathogen mycolate to host glucose.\",\n      \"evidence\": \"TCR chain transfection reconstitution, chemical analysis of natural GMM, and in vivo infection studies\",\n      \"pmids\": [\"11015438\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Generality across mycobacterial lipids unknown\", \"Enzymes generating the epitope not identified here\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Demonstrated compartment-specialized trafficking, contrasting lysosomal CD1b (acidification-dependent) with endosomal CD1c.\",\n      \"evidence\": \"Subcellular fractionation, acidification inhibitors, tail mutants, and presentation assays in dendritic cells\",\n      \"pmids\": [\"10899914\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanistic basis of differential sorting between CD1 isoforms not resolved\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Confirmed the requirement of tail-driven endosomal recycling for optimal loading using GPI-reanchoring that bypasses the tail.\",\n      \"evidence\": \"GPI-reanchored CD1b.DAF chimeras with PLC sensitivity controls and functional T cell assays\",\n      \"pmids\": [\"10903726\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab engineered-construct study\", \"Residual presentation mechanism by GPI-anchored CD1b not defined\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Defined the full itinerary, showing CD1b reaches the surface first then enters via AP-2 with a second AP-3-linked sort to MIICs.\",\n      \"evidence\": \"Pulse-chase, dominant-negative AP-2, inhibitors, and functional presentation assays\",\n      \"pmids\": [\"11847129\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct demonstration of AP-3 involvement incomplete\", \"Recycling kinetics not fully quantified\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Linked antigen lipid chain length to the route of presentation, explaining why long-chain antigens need endosomal delivery.\",\n      \"evidence\": \"Synthetic GMM analogs of defined chain lengths with endosomal inhibitors and APC comparisons\",\n      \"pmids\": [\"11938350\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis for chain-length-dependent loading not resolved here\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Identified saposin C as the lysosomal lipid-loading cofactor that extracts antigen from membranes and physically engages CD1b.\",\n      \"evidence\": \"SAP-deficient fibroblast reconstitution, co-IP with CD1b, liposome extraction, and colocalization\",\n      \"pmids\": [\"14716313\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Stoichiometry/structure of the CD1b-saposin C interaction unknown\", \"Whether other lipid transfer proteins contribute not resolved\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Revealed pH-responsive ionic tethers (D60/E62) acting as molecular switches that gate groove flexibility and bulky-tail loading during endosomal recycling.\",\n      \"evidence\": \"Molecular dynamics, D60/E62 mutagenesis, pH-varied binding, and presentation assays\",\n      \"pmids\": [\"18538591\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In situ confirmation of pH-driven conformational change in cells limited\", \"Single-lab structural modeling\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Established that endogenous scaffold lipids fill the groove beneath antigen, enabling presentation across a broad antigen size range.\",\n      \"evidence\": \"Comparative lipidomics, crystal structure of CD1b with scaffold lipids, and presentation assays\",\n      \"pmids\": [\"22087000\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How scaffold lipids are selected and exchanged in cells not defined\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Provided atomic-level mechanism for tail sensitivity, showing antigen binding repositions spacer lipids, closes the F' pocket, and remodels TCR-exposed residues.\",\n      \"evidence\": \"1.9 Å crystal structure of CD1b-diacylsulfoglycolipid with mutagenesis and T cell assays\",\n      \"pmids\": [\"22006319\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Conformational dynamics during loading inferred from static structure\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Proved cognate αβ TCR recognition of CD1b-GMM by tetramer and recombinant TCR blocking, and reassigned the dominant responding population toward CD4+ cells.\",\n      \"evidence\": \"CD1b-GMM tetramer staining, clonotypic TCR blocking, and ex vivo TB donor analysis\",\n      \"pmids\": [\"21807869\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional consequence of CD4 co-receptor usage not defined\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Defined CD1e as a processing/transfer accessory that prepares PIM6 antigens by acylation-selective digestion and transfer to CD1b.\",\n      \"evidence\": \"Reconstituted lipid transfer and enzymatic digestion assays with defined PIM substrates plus T cell readout\",\n      \"pmids\": [\"22782895\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether CD1e acts on antigens beyond PIM not addressed here\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Established that CD1b presents self-phospholipids, with phosphatidylglycerol immunodominant and no mammalian/bacterial discrimination, implicating stress/infection-associated self-lipid recognition.\",\n      \"evidence\": \"CD1b dextramer staining, mass spectrometry antigen ID, and phospholipid-scanning T cell assays\",\n      \"pmids\": [\"26621732\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo trigger for autoreactivity not defined\", \"Structural basis of cross-reactivity not yet shown here\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Defined the structural basis of conserved GEM TCR recognition, showing dual-chain 'tweezer' gripping of the GMM glucose for high mycobacterial specificity.\",\n      \"evidence\": \"GEM TCR-CD1b-GMM ternary crystal structure, mutagenesis, and TB patient T cell assays\",\n      \"pmids\": [\"27807341\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Why GEM TCR usage recurs across donors not mechanistically explained\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Explained broad self-phospholipid cross-reactivity via a lateral escape channel that shunts head groups while the TCR reads the conserved phosphate neck.\",\n      \"evidence\": \"Crystal structure of TCR-CD1b-phosphatidylcholine with phospholipid-scanning activation assays\",\n      \"pmids\": [\"30610190\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Frequency and physiological role of such autoreactive cells not defined\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Extended CD1b recognition to γδ T cells, showing Vδ1-mediated, variably lipid-dependent reactivity and overlap with butyrophilin-like recognition.\",\n      \"evidence\": \"CD1b tetramers, TCR chain-swap experiments, and blocking across multiple donors\",\n      \"pmids\": [\"32868441\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No co-crystal structure of γδ TCR-CD1b\", \"Antigen requirements for lipid-independent recognition undefined\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Provided structural definition of autoreactive αβ TCR engagement of a self-phosphatidylinositol complex, identifying CD1b Glu-80 as a key TCR-contact residue.\",\n      \"evidence\": \"1.9/2.4 Å crystal structures, alanine-scanning mutagenesis, and SPR\",\n      \"pmids\": [\"36587766\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Thymic selection and in vivo role of these autoreactive cells not addressed\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How CD1b antigen presentation is dysregulated in disease and how the surface self-lipid display versus lysosomal foreign-lipid loading pathways are integrated in vivo remain unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No timeline disease-causation study\", \"In vivo balance between self and foreign lipid presentation undefined\", \"Regulation of scaffold lipid exchange in cells not established\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0008289\", \"supporting_discovery_ids\": [2, 4, 7, 13, 14]},\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [0, 8, 16, 17]},\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [13, 14]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005764\", \"supporting_discovery_ids\": [1, 11, 21]},\n      {\"term_id\": \"GO:0005768\", \"supporting_discovery_ids\": [9, 21]},\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [6]},\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [7, 9, 22]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [0, 2, 23, 24]},\n      {\"term_id\": \"R-HSA-9609507\", \"supporting_discovery_ids\": [1, 5, 9, 21]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"B2M\", \"CANX\", \"CALR\", \"PSAP\", \"CD1E\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":8,"faith_total":8,"faith_pct":100.0}}