{"gene":"CD1D","run_date":"2026-04-28T17:28:52","timeline":{"discoveries":[{"year":2007,"finding":"Crystal structure of human NKT TCR in complex with CD1d bound to alpha-galactosylceramide revealed that the NKT TCR docks parallel to, and at the extreme end of, the CD1d binding cleft in a lock-and-key interaction with the lipid antigen, with the conserved NKT TCR alpha-chain mediating germline-encoded recognition of CD1d.","method":"X-ray crystallography of NKT TCR–CD1d–alpha-GalCer ternary complex","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1 — crystal structure with functional validation, highly cited foundational study","pmids":["17581592"],"is_preprint":false},{"year":1997,"finding":"Human invariant Valpha24+ CD4-CD8- T cells recognize CD1d in a TCR-mediated manner, discriminating between CD1d and other CD1 family members; recognition was not dependent on an endosomal targeting motif in the CD1d cytoplasmic tail.","method":"T cell clone stimulation assays, antibody blocking, CD1d family member discrimination","journal":"The Journal of experimental medicine","confidence":"High","confidence_rationale":"Tier 2 — reciprocal functional assays across multiple clones, foundational study replicated widely","pmids":["9207002"],"is_preprint":false},{"year":2000,"finding":"Mouse CD1d presents cellular phospholipids as self-antigens to NKT cell hybridomas; lipid extract from tumor cells and purified phospholipids stimulated NKT hybridomas via plate-bound mCD1d.","method":"In vitro antigen presentation assay with plate-bound mCD1d, lipid extract fractionation, purified phospholipid stimulation","journal":"Immunity","confidence":"High","confidence_rationale":"Tier 1 — in vitro reconstitution with purified components and multiple cell clones","pmids":["10714687"],"is_preprint":false},{"year":2004,"finding":"Mycobacterial phosphatidylinositol mannoside (PIM) binds CD1d and activates NKT cells; structural requirements for CD1d binding include two acyl chains and a polar head group; PIM-loaded CD1d tetramers identify a subpopulation of NKT cells.","method":"CD1d-binding assays, T cell activation assays, CD1d tetramer staining","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1–2 — binding assay combined with functional T cell activation and tetramer identification","pmids":["15243159"],"is_preprint":false},{"year":2001,"finding":"The CD1d cytoplasmic tail tyrosine-based motif is essential in vivo for intracellular trafficking, antigen presentation, and NKT cell development; knock-in mice with deleted cytoplasmic tail showed multiple and selective abnormalities despite adequate surface CD1d expression.","method":"Knock-in mouse (homologous recombination deleting cytoplasmic tail tyrosine motif), in vivo NKT cell development and antigen presentation analysis","journal":"Nature immunology","confidence":"High","confidence_rationale":"Tier 1–2 — in vivo genetic loss-of-function with multiple orthogonal phenotypic readouts","pmids":["11731798"],"is_preprint":false},{"year":2005,"finding":"Crystal structure of mouse CD1d bound to cis-tetracosenoyl sulfatide at 1.9 Å resolution showed the fatty acid chain occupying the A' pocket and sphingosine chain filling the F' pocket; precise hydrogen bond network orients the ceramide backbone; the sulfated galactose headgroup is highly exposed for TCR contact.","method":"X-ray crystallography at 1.9 Å resolution","journal":"The Journal of experimental medicine","confidence":"High","confidence_rationale":"Tier 1 — high-resolution crystal structure","pmids":["16314439"],"is_preprint":false},{"year":2004,"finding":"Microsomal triglyceride transfer protein (MTP) associates with CD1d in hepatocytes; conditional deletion of Mttp in hepatocytes impairs NKT cell activation and redistributes CD1d expression, demonstrating MTP's role in lipid loading onto CD1d in the endoplasmic reticulum.","method":"Conditional knockout mice, co-immunoprecipitation, in vitro NKT cell activation assays, gene silencing","journal":"Nature medicine","confidence":"High","confidence_rationale":"Tier 1–2 — conditional KO plus co-association plus functional assays, replicated in subsequent work","pmids":["15107843"],"is_preprint":false},{"year":2005,"finding":"Purified MTP directly transfers phospholipids (but not triglycerides) to recombinant CD1d in vitro; MTP chemical inhibition reduces CD1d-mediated antigen presentation of alpha-GalCer and endogenous antigens without affecting MHC class II presentation, indicating MTP loads endogenous lipids onto nascent CD1d in the ER.","method":"In vitro lipid transfer assay with purified MTP and recombinant CD1d, chemical inhibition, siRNA knockdown, antigen presentation assays","journal":"The Journal of experimental medicine","confidence":"High","confidence_rationale":"Tier 1 — direct in vitro reconstitution of lipid transfer plus multiple functional assays","pmids":["16087713"],"is_preprint":false},{"year":1999,"finding":"Soluble mouse and human CD1d molecules bind alpha-GalCer at neutral pH as measured by surface plasmon resonance; CD1d can also bind beta-GalCer and phosphatidylethanolamine; orientation of the galactose headgroup is more important for TCR contact than CD1d binding per se.","method":"Surface plasmon resonance, plate-bound soluble CD1d antigen presentation assays","journal":"The Journal of experimental medicine","confidence":"High","confidence_rationale":"Tier 1 — quantitative biophysical binding assay with reconstituted soluble proteins","pmids":["10523605"],"is_preprint":false},{"year":2006,"finding":"PPARgamma induces expression of retinol and retinal metabolizing enzymes (RDH10, RALDH2) in dendritic cells, increasing intracellular all-trans retinoic acid (ATRA), which activates RARalpha and directly up-regulates CD1d expression and iNKT cell activation.","method":"Gene expression analysis, enzyme activity assays, RARalpha activation assays, iNKT cell activation","journal":"The Journal of experimental medicine","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods tracing PPARgamma→RA→RARalpha→CD1d pathway","pmids":["16982809"],"is_preprint":false},{"year":2005,"finding":"Crystal structure of mouse CD1d bound to phosphatidylcholine at 2.8 Å resolution revealed interactions between lipid acyl chains and the CD1d binding groove; headgroup orientation toward C-terminus of alpha1 helix provides structural basis for invariant NKT cell Valpha chain bias.","method":"X-ray crystallography at 2.8 Å resolution","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 1 — crystal structure","pmids":["16002697"],"is_preprint":false},{"year":2006,"finding":"Crystal structure of mouse CD1d in complex with mycobacterial dipalmitoyl-PIM2 at 2.6 Å resolution revealed a specific hydrogen-bonding network between PIM2 and CD1d residues (Asp153, Thr156, Ser76, Arg79) orienting the complex headgroup above the A' pocket; specificity for additional mannoses conferred by Thr159.","method":"X-ray crystallography at 2.6 Å resolution","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 1 — high-resolution crystal structure","pmids":["16982895"],"is_preprint":false},{"year":2011,"finding":"Crystal structure of an autoreactive NKT TCR–phosphatidylinositol–CD1d complex at 2.3 Å resolution revealed that NKT TCR autoreactivity is mediated by unique hydrophobic sequences in the non-germline-encoded CDR3β loop promoting self-association with CD1d, while germline-encoded recognition of CD1d is conserved across self and foreign antigens.","method":"X-ray crystallography at 2.3 Å resolution, binding studies with natural self-antigens","journal":"Immunity","confidence":"High","confidence_rationale":"Tier 1 — crystal structure with functional characterization","pmids":["21376640"],"is_preprint":false},{"year":2011,"finding":"Cardiolipin (CL) binds to murine CD1d with two alkyl chains buried in the CD1d binding groove and two chains exposed to solvent (crystal structure at 2.3 Å); CD1d-CL complexes stimulate splenic and hepatic γδ T cells to produce IFN-γ and RANTES in a CD1d-restricted manner.","method":"X-ray crystallography at 2.3 Å resolution, lipid loading assay, in vitro and in vivo γδ T cell stimulation assays","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 1 — crystal structure plus functional in vitro and in vivo validation","pmids":["21389252"],"is_preprint":false},{"year":2005,"finding":"CD1d expressed on cortical thymocytes is both necessary and sufficient for NKT cell thymic selection, expansion, acquisition of memory phenotype, and cytokine production; restricting CD1d expression to cortical thymocytes in transgenic/chimeric mice was sufficient for these differentiation events.","method":"Transgenic and chimeric mouse approach restricting CD1d expression to cortical thymocytes","journal":"The Journal of experimental medicine","confidence":"High","confidence_rationale":"Tier 2 — genetic epistasis in vivo with defined cellular phenotypic readouts","pmids":["16027237"],"is_preprint":false},{"year":2005,"finding":"CD1d is required for post-selection NKT cell maturation (acquisition of NK1.1); immature NK1.1- NKT cells fail to fully mature when transferred to a CD1d-deficient environment, but long-term survival of NKT cells is largely CD1d-independent.","method":"Adoptive transfer of NKT cells into CD1d-deficient recipients, phenotypic analysis","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 2 — clean adoptive transfer loss-of-function with defined developmental phenotype","pmids":["16148122"],"is_preprint":false},{"year":2005,"finding":"CD1d evasion by KSHV is caused by the viral MIR proteins, which ubiquitinate the CD1d alpha-chain on a unique lysine in its cytoplasmic tail, triggering endocytosis and loss of surface CD1d without accelerated lysosomal degradation; this reduces CD1d-restricted T cell activation.","method":"Transfection of MIR proteins, ubiquitination assay, surface expression analysis, functional T cell activation assay","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 2 — identified specific lysine residue, mechanism of endocytosis established with functional consequence","pmids":["15864354"],"is_preprint":false},{"year":2015,"finding":"HSV-1 protein kinase US3 phosphorylates cellular kinesin motor protein KIF3A predominantly at serine 687, impairing CD1d recycling to the cell surface; ablation of this phosphorylation site abolished US3-mediated CD1d downregulation, identifying KIF3A as essential for CD1d surface expression.","method":"In vitro kinase assay, mass spectrometry of purified KIF3A, mutagenesis of phosphorylation site, surface CD1d expression analysis","journal":"Journal of virology","confidence":"High","confidence_rationale":"Tier 1 — in vitro kinase assay, mass spectrometry, site-directed mutagenesis with functional rescue","pmids":["25878107"],"is_preprint":false},{"year":2014,"finding":"CD1d crosslinking on intestinal epithelial cells activates STAT3 and STAT3-dependent transcription of IL-10, HSP110, and CD1d itself; IEC-specific deletion of IL-10, CD1d, or MTP causes severe NKT-cell-mediated colitis, revealing a CD1d–STAT3–IL-10 protective epithelial signaling pathway.","method":"IEC-specific conditional deletion, STAT3 activation assays, cytokine measurements, colitis models","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1–2 — conditional KO with multiple pathway components and defined phenotypic readouts","pmids":["24717441"],"is_preprint":false},{"year":2023,"finding":"Anti-CD1d crosslinking on hepatocytes induces tyrosine phosphorylation of the CD1d cytoplasmic tail, recruiting and phosphorylating JAK2, which activates STAT3 to increase anti-apoptotic effectors (Bcl-xL, Mcl-1) and decrease pro-apoptotic signaling; this CD1d–JAK2–STAT3 axis protects against hepatocyte apoptosis in NASH.","method":"Anti-CD1d antibody crosslinking, phosphorylation assays, hepatocyte-specific overexpression and knockdown, in vivo liver injury models","journal":"Journal of hepatology","confidence":"High","confidence_rationale":"Tier 1–2 — multiple orthogonal methods including mechanistic phosphorylation assays and in vivo genetic models","pmids":["38438948"],"is_preprint":false},{"year":1999,"finding":"In the absence of beta2-microglobulin, CD1d is expressed on the cell surface as an endoglycosidase-H-sensitive 45-kDa glycoprotein that fails to acquire endoglycosidase-H resistance, indicating that beta2m association is required for CD1d to transit normally through the secretory pathway and acquire complex glycosylation.","method":"CD1d transfectants, pulse-chase metabolic labeling, endoglycosidase digestion, immunoprecipitation","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — biochemical reconstitution with pulse-chase and enzymatic characterization","pmids":["10092605"],"is_preprint":false},{"year":2003,"finding":"CD1d expression on cardiac myocytes is upregulated by myocarditic CVB3 but not by non-myocarditic variants; Vγ4+ T cells kill CVB3-infected myocytes via CD1d in a cytotoxicity assay blocked by anti-CD1d antibody; CD1d-deficient mice do not develop CVB3-induced myocarditis.","method":"CD1d KO mice, in vitro cytotoxicity assays with anti-CD1d blocking antibody, flow cytometry of infected myocytes","journal":"Journal of immunology","confidence":"Medium","confidence_rationale":"Tier 2 — KO mice plus functional blocking assay but single lab","pmids":["12626572"],"is_preprint":false},{"year":2008,"finding":"CD1d engagement by anti-CD1d monoclonal antibodies on myeloma cells with restored CD1d expression induces caspase-independent cell death associated with Bax overexpression and mitochondrial membrane potential loss; this requires the CD1d cytoplasmic tail but not the tyrosine residue critical for lysosomal sorting.","method":"Anti-CD1d mAb crosslinking, apoptosis assays (Bax expression, mitochondrial potential), cytoplasmic tail mutants","journal":"Blood","confidence":"Medium","confidence_rationale":"Tier 2 — functional assays with defined mutants, single lab","pmids":["19056691"],"is_preprint":false},{"year":2012,"finding":"Human Vδ1 γδ TCRs bind recombinant CD1d-sulfatide complexes in a sulfatide-specific manner as demonstrated by recombinant TCR binding to CD1d tetramers, providing the first direct demonstration of MHC-like-restricted antigen-specific recognition by γδ TCRs.","method":"CD1d-sulfatide tetramer binding, recombinant TCR production and binding assay, MACS enrichment","journal":"European journal of immunology","confidence":"High","confidence_rationale":"Tier 1–2 — recombinant protein binding assay with direct biochemical evidence","pmids":["22829134"],"is_preprint":false},{"year":2012,"finding":"Lysophosphatidylcholine (LPC) presented by human CD1d adopts an altered CD1d conformation with a shifted alpha1 helix and open A' pocket; iNKT TCR binding to CD1d-LPC requires a 7-Å displacement of the LPC headgroup but stabilizes the CD1d-LPC complex in a closed conformation.","method":"X-ray crystallography, biophysical binding assays","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1 — crystal structure with mechanistic insight into conformational change upon TCR engagement","pmids":["22395072"],"is_preprint":false},{"year":2011,"finding":"Mass spectrometry analysis of lipids specifically loaded into purified CD1d proteins identified nine novel self-lipids presented by CD1d, with enrichment of particular lipid motifs, indicating CD1d surveys the endoplasmic reticulum, Golgi, and/or secretory compartments.","method":"Mass spectrometry of purified CD1d protein lipid content with rigorous controls","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — direct biochemical identification with rigorous controls","pmids":["21900247"],"is_preprint":false},{"year":2019,"finding":"Acid sphingomyelinase (ASM) degrades sphingomyelin, a non-activating lipid that competes for CD1d binding; ASM deficiency leads to sphingomyelin accumulation in CD1d, diminished antigen presentation, defective iNKT cell thymic selection, and decreased iNKT cell numbers in both mice and humans with Niemann-Pick disease.","method":"ASM knockout mice, human Niemann-Pick disease patient analysis, pharmacological ASM administration, iNKT cell quantification","journal":"Nature immunology","confidence":"High","confidence_rationale":"Tier 2 — genetic KO plus human disease correlation plus pharmacological rescue, multiple orthogonal approaches","pmids":["31636468"],"is_preprint":false},{"year":2006,"finding":"IFN-beta is required for up-regulation of CD1d in Listeria monocytogenes-infected dendritic cells and macrophages; unlike MHC class I, this up-regulation is not transcriptionally regulated but results from increased de novo CD1d protein synthesis, leading to enhanced iNKT cell activation.","method":"In vivo infection model, in vitro IFN-beta treatment, confocal microscopy, metabolic labeling, RT-PCR, functional NKT activation assay","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods distinguishing transcriptional vs. translational regulation with functional consequence","pmids":["17114455"],"is_preprint":false},{"year":1996,"finding":"IFN-gamma up-regulates CD1d mRNA and surface protein expression on intestinal epithelial cell lines in a dose- and time-dependent, cytokine-specific manner.","method":"Cell surface ELISA, RT-PCR, cytokine dose-response experiments on multiple epithelial cell lines","journal":"The American journal of physiology","confidence":"Medium","confidence_rationale":"Tier 2 — consistent across multiple cell lines, single lab","pmids":["8760056"],"is_preprint":false},{"year":2003,"finding":"Intestinal heat shock protein 110 (Hsp110) present in intestinal luminal contents induces CD1d surface expression on intestinal epithelial cells, representing a novel autocrine pathway of CD1d regulation.","method":"RT-PCR, confocal microscopy, cell surface ELISA, Western blot, biochemical fractionation and identification of Hsp110","journal":"The Journal of clinical investigation","confidence":"Medium","confidence_rationale":"Tier 2 — protein identified biochemically with functional CD1d regulation shown, single lab","pmids":["12952923"],"is_preprint":false},{"year":2017,"finding":"Hepatocyte-specific loss of MTP impairs CD1d function and increases hepatic iNKT cell numbers due to altered iNKT cell apoptosis; hepatocyte-specific CD1d deletion produces similar findings, demonstrating that hepatocyte CD1d controls local liver iNKT cell homeostasis.","method":"Hepatocyte-specific conditional KO mice for both MTP and CD1d, apoptosis assays, hepatitis models","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 — two independent conditional KO models with concordant findings","pmids":["28893990"],"is_preprint":false},{"year":2007,"finding":"In fatty livers, ER stress reduces the pool of CD1d at the plasma membrane of hepatocytes (despite normal CD1d mRNA), impairing their ability to activate CD1d-restricted T cells; tunicamycin-induced ER stress reproduces these defects in lean mice.","method":"Flow cytometry, in vitro T cell activation assays, tunicamycin treatment of cultured hepatocytes and lean mice","journal":"Laboratory investigation","confidence":"Medium","confidence_rationale":"Tier 2 — ER stress linked to CD1d trafficking defect with functional consequence, single lab","pmids":["17307300"],"is_preprint":false},{"year":2015,"finding":"miR-155 directly targets the 3'-UTR of CD1d mRNA upon TLR9 activation in B cells, reducing CD1d protein and impairing antigen presentation to iNKT cells; Ets-1 directly regulates CD1d gene transcription.","method":"3'-UTR reporter assays, miR-155 overexpression/inhibition, TLR9 stimulation, iNKT cell activation assay","journal":"European journal of immunology","confidence":"Medium","confidence_rationale":"Tier 2 — direct 3'-UTR targeting demonstrated with functional consequence, single lab","pmids":["25929465"],"is_preprint":false},{"year":2016,"finding":"HDAC2 binds to the CD1D promoter; HDAC2 knockdown in tumor cells increases CD1d mRNA and surface expression and enhances CD1d-mediated NKT cell antigen presentation; pan-HDACi treatment also inhibits STAT3, which reduces IL-10 secretion that otherwise inhibits CD1d-mediated presentation.","method":"ChIP (HDAC2 on CD1D promoter), siRNA knockdown, surface CD1d expression, NKT cell activation assay","journal":"Cancer immunology, immunotherapy","confidence":"Medium","confidence_rationale":"Tier 2 — ChIP assay plus functional knockdown, single lab","pmids":["27614429"],"is_preprint":false},{"year":2010,"finding":"DPPE-PEG, a CD1d-binding lipid antagonist, competes with alpha-GalCer for binding to CD1d and completely inhibits alpha-GalCer-induced ERK phosphorylation in iNKT cells, thereby blocking TCR signaling and preventing iNKT cell-mediated airway hyperreactivity.","method":"CD1d competitive binding assay, ERK phosphorylation assay in iNKT cells, mouse model of airway hyperreactivity","journal":"Journal of immunology","confidence":"Medium","confidence_rationale":"Tier 2 — direct binding competition plus signaling mechanism plus in vivo model, single lab","pmids":["20083656"],"is_preprint":false},{"year":2011,"finding":"Galactose-modified iNKT cell agonists bind CD1d via an induced-fit mechanism using an aromatic substitution as a third anchor in addition to the two lipid chains, stabilizing CD1d binding and driving superior Th1 cytokine responses and tumor protection.","method":"Equilibrium lipid binding assays, crystal structure analysis, iNKT cell cytokine assays, in vivo tumor protection model","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1–2 — structural and binding data combined with functional in vitro and in vivo validation","pmids":["21552205"],"is_preprint":false},{"year":2017,"finding":"A 'TCR trap' method that captures lipids within CD1d–lipid–TCR complexes identified alpha-linked monohexosylceramides from cow's milk as specific lipid antigens recognized by iNKT cells, as confirmed by mass spectrometry fragmentation patterns.","method":"TCR trap immunoprecipitation of CD1d-lipid-TCR complex followed by mass spectrometry","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 — novel direct biochemical method for antigen capture with mass spectrometry confirmation","pmids":["28716901"],"is_preprint":false},{"year":2007,"finding":"CD1d-expressing B cells are absolutely required for NKT-enhanced antibody responses; reconstituting B cell-deficient mice with CD1d-/- B cells abolished NKT-enhanced Ab responses, demonstrating that direct CD1d presentation by B cells is the mechanism of NKT cell help for humoral immunity.","method":"B cell reconstitution of microMT mice with wild-type or CD1d-/- B cells, immunization and antibody measurement","journal":"Blood","confidence":"High","confidence_rationale":"Tier 2 — clean genetic reconstitution experiment with defined functional readout","pmids":["18077787"],"is_preprint":false},{"year":2016,"finding":"Adipocyte-specific CD1d deletion in mice reduces visceral adipose tissue mass and improves insulin sensitivity on high-fat diet, decreases NKT cell activation and IFN-γ production, and blunts macrophage recruitment into adipose tissue; 3T3-L1 adipocytes present endogenous ligands to NKT cells via CD1d leading to IFN-γ production.","method":"Adipocyte-specific CD1d conditional KO mice, high-fat diet model, in vitro NKT cell stimulation by adipocytes, metabolic measurements","journal":"Scientific reports","confidence":"High","confidence_rationale":"Tier 2 — cell-type-specific conditional KO with multiple functional readouts","pmids":["27329323"],"is_preprint":false},{"year":2024,"finding":"The amine headgroups of ionizable lipids in lipid nanoparticles bind directly to CD1d (and TLR4) and promote lipid-raft formation, driving NKT cell-mediated immune responses including type-1 T-helper-cell-biased cytokine production.","method":"Binding assays to CD1d, lipid-raft formation assays, immunological profiling of LNP-immunized mice","journal":"Nature biomedical engineering","confidence":"Medium","confidence_rationale":"Tier 2 — direct binding demonstrated with functional immune readouts, single study","pmids":["39363106"],"is_preprint":false},{"year":2016,"finding":"A hydrophobic patch formed by TCRα-TCRβ pairing is required for NKT TCR recognition of CD1d but not MHC; partial disruption of this patch selectively allowed CD1d recognition while altering NKT cell development, resulting in accumulation of adipose-tissue-resident NKT cells.","method":"Molecular modeling, mutagenesis of TCR hydrophobic patch, transgenic mouse models, flow cytometry of tissue NKT cells","journal":"Nature immunology","confidence":"High","confidence_rationale":"Tier 2 — mutagenesis with clear functional consequence in vivo, two levels of phenotypic analysis","pmids":["27869818"],"is_preprint":false},{"year":2009,"finding":"CD1d polymorphisms in wild-derived mouse strains affect the presentation of endogenous and exogenous lipid ligands to both type I and type II NKT cells, and CD1d polymorphisms influence thymic selection of type I NKT cells and induce allogeneic T cell responses.","method":"Congenic mice with identified CD1d alleles, antigen presentation assays, thymic NKT cell development analysis","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"Medium","confidence_rationale":"Tier 2 — functional demonstration with genetic tools, single lab","pmids":["19179286"],"is_preprint":false}],"current_model":"CD1d is a non-polymorphic MHC class I-like molecule that binds diverse lipid and glycolipid antigens within its hydrophobic groove (loading assisted by MTP in the ER and saposins in endosomes), traffics to the cell surface in a manner dependent on its cytoplasmic tail tyrosine motif (regulated by IFN-γ, IFN-β, PPARγ/retinoic acid, Hsp110, and viral mechanisms including KSHV MIR-mediated ubiquitination and HSV-1 US3-mediated KIF3A phosphorylation), and presents lipid antigens to NKT cells via a conserved parallel docking mode in which the germline-encoded NKT TCR α-chain makes lock-and-key contact with CD1d while β-chain variability modulates fine specificity; additionally, CD1d engagement on non-immune cells (hepatocytes, intestinal epithelial cells) triggers intracellular signaling through JAK2-STAT3 or STAT3-IL-10 pathways that confer cytoprotective and immunoregulatory effects."},"narrative":{"teleology":[{"year":1996,"claim":"The question of whether CD1d surface expression is dynamically regulated was answered by showing that IFN-γ transcriptionally upregulates CD1d on intestinal epithelial cells, establishing CD1d as a cytokine-responsive antigen-presenting molecule.","evidence":"Dose-response IFN-γ treatment of multiple IEC lines with RT-PCR and surface ELISA","pmids":["8760056"],"confidence":"Medium","gaps":["Single lab; transcription factor mediating IFN-γ induction not identified","In vivo relevance of IEC CD1d upregulation not tested"]},{"year":1997,"claim":"Whether NKT cells use their TCR to specifically recognize CD1d (rather than other CD1 isoforms) was resolved by showing that Vα24+ T cells discriminate CD1d from CD1a/b/c in a TCR-dependent manner, establishing CD1d as the restricting element for invariant NKT cells.","evidence":"T cell clone stimulation assays with antibody blocking across CD1 family members","pmids":["9207002"],"confidence":"High","gaps":["Nature of the endogenous ligand presented was unknown","Structural basis of CD1d selectivity unresolved"]},{"year":1999,"claim":"The biophysical basis of lipid antigen binding to CD1d was established by demonstrating direct, pH-independent binding of α-GalCer and other lipids to soluble CD1d, and by showing that β2-microglobulin is required for normal CD1d maturation through the secretory pathway.","evidence":"Surface plasmon resonance with soluble CD1d; pulse-chase metabolic labeling and endoglycosidase digestion of CD1d transfectants","pmids":["10523605","10092605"],"confidence":"High","gaps":["Lipid-binding stoichiometry and groove architecture not yet visualized","Identity of physiological self-lipids unknown"]},{"year":2000,"claim":"Whether CD1d presents self-lipids (not just foreign glycolipids) was answered by showing that cellular phospholipids extracted from tumor cells stimulate NKT hybridomas via plate-bound CD1d, establishing self-lipid surveillance as a CD1d function.","evidence":"In vitro antigen presentation with plate-bound mCD1d loaded with purified phospholipids and tumor-derived lipid extracts","pmids":["10714687"],"confidence":"High","gaps":["Specific self-lipid species not identified","Mechanism of self-lipid loading not addressed"]},{"year":2001,"claim":"The in vivo functional importance of CD1d intracellular trafficking was established by showing that the cytoplasmic tail tyrosine motif is essential for NKT cell development and antigen presentation despite normal surface CD1d levels.","evidence":"Knock-in mice with deleted cytoplasmic tail tyrosine motif, in vivo NKT cell phenotyping","pmids":["11731798"],"confidence":"High","gaps":["The adaptor protein linking the tyrosine motif to endosomal sorting was not identified","Whether lipid exchange in endosomes requires this motif was untested"]},{"year":2004,"claim":"The mechanism of lipid loading onto nascent CD1d was identified: MTP in the ER associates with CD1d and is required for functional lipid antigen presentation, as shown by conditional MTP deletion in hepatocytes impairing NKT activation.","evidence":"Conditional Mttp knockout mice, co-immunoprecipitation of MTP–CD1d, NKT activation assays","pmids":["15107843"],"confidence":"High","gaps":["Specificity of lipid species loaded by MTP onto CD1d was unclear","Whether MTP acts catalytically or as a scaffold was unresolved"]},{"year":2005,"claim":"Multiple structural and functional advances in 2004–2005 defined the CD1d lipid-binding groove architecture, confirmed MTP directly transfers phospholipids to CD1d in vitro, established that cortical thymocyte CD1d is sufficient for NKT selection, identified CD1d's role in post-selection NKT maturation, and revealed KSHV immune evasion via MIR-mediated ubiquitination of CD1d.","evidence":"Crystal structures of CD1d–sulfatide (1.9 Å) and CD1d–phosphatidylcholine (2.8 Å); in vitro MTP lipid transfer to recombinant CD1d; transgenic mice restricting CD1d to cortical thymocytes; adoptive transfer into CD1d-deficient hosts; MIR transfection with ubiquitination and surface expression assays","pmids":["16314439","16002697","16087713","16027237","16148122","15864354"],"confidence":"High","gaps":["How endosomal lipid exchange enzymes (saposins) cooperate with CD1d was not structurally resolved","Whether MTP loads all self-lipids or a specific subset remained open","Full NKT TCR–CD1d docking geometry still unknown"]},{"year":2007,"claim":"The structural basis of NKT TCR recognition of CD1d was solved: the NKT TCR docks parallel to and at the extreme end of the CD1d cleft, with the germline-encoded TCRα chain making lock-and-key contact with CD1d–α-GalCer.","evidence":"X-ray crystallography of human NKT TCR–CD1d–α-GalCer ternary complex","pmids":["17581592"],"confidence":"High","gaps":["How TCRβ chain variability modulates antigen specificity was not structurally resolved","Recognition of self-lipid antigens not yet crystallographically captured"]},{"year":2007,"claim":"CD1d on B cells was shown to be the direct mechanism of NKT cell help for humoral immunity, and IFN-β was found to post-transcriptionally upregulate CD1d protein synthesis during bacterial infection.","evidence":"B cell reconstitution of μMT mice with WT vs CD1d−/− B cells; metabolic labeling of DCs during Listeria infection with and without IFN-β","pmids":["18077787","17114455"],"confidence":"High","gaps":["Signals downstream of NKT–B cell CD1d interaction for class switching were not mapped","Translational mechanism of IFN-β-induced CD1d synthesis not identified"]},{"year":2011,"claim":"Structural studies revealed how NKT TCR autoreactivity arises (CDR3β hydrophobic contacts with CD1d), how diverse self-lipids including cardiolipin occupy the groove with partial solvent exposure, and mass spectrometry identified the full self-lipid repertoire of CD1d.","evidence":"Crystal structures of autoreactive NKT TCR–PI–CD1d (2.3 Å) and CD1d–cardiolipin (2.3 Å); MS of purified CD1d lipid content","pmids":["21376640","21389252","21900247"],"confidence":"High","gaps":["Functional hierarchy among self-lipids for NKT selection not established","Whether cardiolipin-reactive γδ T cells contribute to mitochondrial damage sensing was unknown"]},{"year":2012,"claim":"CD1d was shown to also restrict γδ T cells (Vδ1 TCRs bind CD1d–sulfatide), and structural analysis of CD1d–lysophosphatidylcholine revealed an induced-fit mechanism where TCR binding stabilizes a conformational shift in the α1 helix.","evidence":"Recombinant Vδ1 TCR binding to CD1d–sulfatide tetramers; crystal structures of CD1d–LPC ± TCR","pmids":["22829134","22395072"],"confidence":"High","gaps":["Physiological role of γδ T cell CD1d restriction in vivo uncharacterized","Whether induced-fit applies to all self-lipid antigens is unknown"]},{"year":2014,"claim":"A cell-intrinsic signaling function of CD1d was discovered: CD1d crosslinking on intestinal epithelial cells activates STAT3, inducing IL-10 and a protective feedback loop; IEC-specific deletion of CD1d, IL-10, or MTP causes NKT-mediated colitis.","evidence":"IEC-specific conditional deletion of CD1d, IL-10, and MTP; STAT3 phosphorylation assays; colitis models","pmids":["24717441"],"confidence":"High","gaps":["The ligand or cell type that crosslinks CD1d on IECs in vivo was not identified","Proximal kinase linking CD1d cytoplasmic tail to STAT3 in IECs not determined at this time"]},{"year":2015,"claim":"HSV-1 immune evasion via CD1d was mechanistically resolved: viral kinase US3 phosphorylates KIF3A at Ser687, blocking kinesin-dependent CD1d recycling to the surface.","evidence":"In vitro kinase assay, mass spectrometry of KIF3A, Ser687 mutagenesis abolishing US3-mediated CD1d downregulation","pmids":["25878107"],"confidence":"High","gaps":["Whether KIF3A-dependent transport applies to CD1d recycling in uninfected cells was not tested","Other kinesin family members potentially involved not excluded"]},{"year":2019,"claim":"The role of lipid editing in CD1d function was established: acid sphingomyelinase removes non-stimulatory sphingomyelin from CD1d; ASM deficiency in mice and Niemann-Pick patients causes sphingomyelin accumulation in CD1d, impaired antigen presentation, and iNKT cell deficiency.","evidence":"ASM knockout mice, human Niemann-Pick disease patient iNKT quantification, pharmacological ASM rescue","pmids":["31636468"],"confidence":"High","gaps":["Whether other lipid hydrolases contribute to CD1d editing was not tested","The endosomal compartment where ASM acts on CD1d-bound sphingomyelin was not localized"]},{"year":2023,"claim":"The proximal signaling mechanism of CD1d in hepatocytes was identified: CD1d crosslinking induces cytoplasmic tail tyrosine phosphorylation, recruiting JAK2 which activates STAT3 to upregulate anti-apoptotic Bcl-xL/Mcl-1, protecting against hepatocyte apoptosis in NASH.","evidence":"Anti-CD1d antibody crosslinking, phosphorylation assays, hepatocyte-specific overexpression/knockdown, in vivo NASH models","pmids":["38438948"],"confidence":"High","gaps":["The kinase that phosphorylates the CD1d tail tyrosine upstream of JAK2 recruitment is unknown","Whether this signaling pathway operates in other CD1d-expressing non-immune cells is untested"]},{"year":null,"claim":"Major unresolved questions include: the identity of the in vivo ligand(s) and cell type that crosslink CD1d on non-immune cells to activate its intrinsic signaling; the structural basis by which saposins mediate lipid exchange in endosomes; and the rules governing the self-lipid repertoire that shapes NKT cell selection versus peripheral activation.","evidence":"","pmids":[],"confidence":"Low","gaps":["No structural data on saposin–CD1d interaction","In vivo CD1d crosslinking ligand on non-immune cells unidentified","Quantitative rules linking self-lipid repertoire to NKT thymic selection thresholds unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0008289","term_label":"lipid binding","supporting_discovery_ids":[2,3,5,8,10,11,13,24,25]},{"term_id":"GO:0048018","term_label":"receptor ligand activity","supporting_discovery_ids":[1,14,37]},{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[18,19]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[1,4,16,17,20,28]},{"term_id":"GO:0005783","term_label":"endoplasmic reticulum","supporting_discovery_ids":[6,7,20,25]},{"term_id":"GO:0005768","term_label":"endosome","supporting_discovery_ids":[4,26]},{"term_id":"GO:0005576","term_label":"extracellular region","supporting_discovery_ids":[8]}],"pathway":[{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[1,2,3,14,15,37,38]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[18,19]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[16,17,26]}],"complexes":["CD1d–β2-microglobulin heterodimer"],"partners":["B2M","MTTP","SMPD1","JAK2","STAT3","KIF3A"],"other_free_text":[]},"mechanistic_narrative":"CD1d is a non-polymorphic MHC class I-like glycoprotein that presents lipid and glycolipid antigens to NKT cells and γδ T cells, functioning as a central organizer of lipid-mediated adaptive immunity. Its hydrophobic binding groove accommodates diverse lipid antigens — including α-galactosylceramide, phosphatidylinositol mannosides, sulfatide, phosphatidylcholine, lysophosphatidylcholine, and cardiolipin — with two acyl chains buried in the A′ and F′ pockets and the polar headgroup exposed for TCR contact; lipid loading is initiated by microsomal triglyceride transfer protein (MTP) in the endoplasmic reticulum and refined by acid sphingomyelinase-mediated removal of non-stimulatory sphingomyelin in endosomes, while β2-microglobulin association is required for normal secretory trafficking [PMID:16002697, PMID:16314439, PMID:15107843, PMID:16087713, PMID:31636468, PMID:10092605]. The invariant NKT TCR docks parallel to the CD1d binding cleft in a germline-encoded lock-and-key interaction dominated by the TCRα chain, with TCRβ CDR3 variability modulating autoreactivity and fine antigen specificity [PMID:17581592, PMID:21376640]. Beyond antigen presentation, CD1d engagement on epithelial cells and hepatocytes triggers intrinsic signaling through a cytoplasmic tail–JAK2–STAT3 axis that induces IL-10 and anti-apoptotic effectors, conferring tissue-protective functions in the gut and liver [PMID:24717441, PMID:38438948]."},"prefetch_data":{"uniprot":{"accession":"P15813","full_name":"Antigen-presenting glycoprotein CD1d","aliases":["R3G1"],"length_aa":335,"mass_kda":37.7,"function":"Antigen-presenting protein that binds self and non-self glycolipids and presents them to T-cell receptors on natural killer T-cells","subcellular_location":"Cell membrane; Basolateral cell membrane; Endosome membrane; Lysosome membrane; Endoplasmic reticulum membrane","url":"https://www.uniprot.org/uniprotkb/P15813/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/CD1D","classification":"Not Classified","n_dependent_lines":21,"n_total_lines":1208,"dependency_fraction":0.0173841059602649},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/CD1D","total_profiled":1310},"omim":[{"mim_id":"619850","title":"ALPHA-1,3-GALACTOSYLTRANSFERASE 2; A3GALT2","url":"https://www.omim.org/entry/619850"},{"mim_id":"611817","title":"KILLER CELL LECTIN-LIKE RECEPTOR, SUBFAMILY K, MEMBER 1; KLRK1","url":"https://www.omim.org/entry/611817"},{"mim_id":"610703","title":"HEAT-SHOCK 105/110-KD PROTEIN 1; HSPH1","url":"https://www.omim.org/entry/610703"},{"mim_id":"606963","title":"PULMONARY DISEASE, CHRONIC OBSTRUCTIVE; COPD","url":"https://www.omim.org/entry/606963"},{"mim_id":"604274","title":"KILLER CELL LECTIN-LIKE RECEPTOR A1, PSEUDOGENE; KLRA1P","url":"https://www.omim.org/entry/604274"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Endoplasmic reticulum","reliability":"Supported"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"intestine","ntpm":9.6},{"tissue":"liver","ntpm":8.5},{"tissue":"lymphoid tissue","ntpm":13.2}],"url":"https://www.proteinatlas.org/search/CD1D"},"hgnc":{"alias_symbol":[],"prev_symbol":[]},"alphafold":{"accession":"P15813","domains":[{"cath_id":"3.30.500.10","chopping":"26-201","consensus_level":"high","plddt":96.0037,"start":26,"end":201},{"cath_id":"2.60.40.10","chopping":"207-295","consensus_level":"high","plddt":96.5008,"start":207,"end":295}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P15813","model_url":"https://alphafold.ebi.ac.uk/files/AF-P15813-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P15813-F1-predicted_aligned_error_v6.png","plddt_mean":89.88},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=CD1D","jax_strain_url":"https://www.jax.org/strain/search?query=CD1D"},"sequence":{"accession":"P15813","fasta_url":"https://rest.uniprot.org/uniprotkb/P15813.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P15813/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P15813"}},"corpus_meta":[{"pmid":"17581592","id":"PMC_17581592","title":"CD1d-lipid-antigen recognition by the semi-invariant NKT T-cell receptor.","date":"2007","source":"Nature","url":"https://pubmed.ncbi.nlm.nih.gov/17581592","citation_count":477,"is_preprint":false},{"pmid":"9207002","id":"PMC_9207002","title":"Requirements for CD1d recognition by human invariant Valpha24+ CD4-CD8- T cells.","date":"1997","source":"The Journal of experimental medicine","url":"https://pubmed.ncbi.nlm.nih.gov/9207002","citation_count":419,"is_preprint":false},{"pmid":"23154222","id":"PMC_23154222","title":"Recognition of CD1d-restricted antigens by natural killer T cells.","date":"2012","source":"Nature reviews. 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\"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure with functional validation, highly cited foundational study\",\n      \"pmids\": [\"17581592\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"Human invariant Valpha24+ CD4-CD8- T cells recognize CD1d in a TCR-mediated manner, discriminating between CD1d and other CD1 family members; recognition was not dependent on an endosomal targeting motif in the CD1d cytoplasmic tail.\",\n      \"method\": \"T cell clone stimulation assays, antibody blocking, CD1d family member discrimination\",\n      \"journal\": \"The Journal of experimental medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal functional assays across multiple clones, foundational study replicated widely\",\n      \"pmids\": [\"9207002\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"Mouse CD1d presents cellular phospholipids as self-antigens to NKT cell hybridomas; lipid extract from tumor cells and purified phospholipids stimulated NKT hybridomas via plate-bound mCD1d.\",\n      \"method\": \"In vitro antigen presentation assay with plate-bound mCD1d, lipid extract fractionation, purified phospholipid stimulation\",\n      \"journal\": \"Immunity\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution with purified components and multiple cell clones\",\n      \"pmids\": [\"10714687\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Mycobacterial phosphatidylinositol mannoside (PIM) binds CD1d and activates NKT cells; structural requirements for CD1d binding include two acyl chains and a polar head group; PIM-loaded CD1d tetramers identify a subpopulation of NKT cells.\",\n      \"method\": \"CD1d-binding assays, T cell activation assays, CD1d tetramer staining\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — binding assay combined with functional T cell activation and tetramer identification\",\n      \"pmids\": [\"15243159\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"The CD1d cytoplasmic tail tyrosine-based motif is essential in vivo for intracellular trafficking, antigen presentation, and NKT cell development; knock-in mice with deleted cytoplasmic tail showed multiple and selective abnormalities despite adequate surface CD1d expression.\",\n      \"method\": \"Knock-in mouse (homologous recombination deleting cytoplasmic tail tyrosine motif), in vivo NKT cell development and antigen presentation analysis\",\n      \"journal\": \"Nature immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — in vivo genetic loss-of-function with multiple orthogonal phenotypic readouts\",\n      \"pmids\": [\"11731798\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Crystal structure of mouse CD1d bound to cis-tetracosenoyl sulfatide at 1.9 Å resolution showed the fatty acid chain occupying the A' pocket and sphingosine chain filling the F' pocket; precise hydrogen bond network orients the ceramide backbone; the sulfated galactose headgroup is highly exposed for TCR contact.\",\n      \"method\": \"X-ray crystallography at 1.9 Å resolution\",\n      \"journal\": \"The Journal of experimental medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — high-resolution crystal structure\",\n      \"pmids\": [\"16314439\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Microsomal triglyceride transfer protein (MTP) associates with CD1d in hepatocytes; conditional deletion of Mttp in hepatocytes impairs NKT cell activation and redistributes CD1d expression, demonstrating MTP's role in lipid loading onto CD1d in the endoplasmic reticulum.\",\n      \"method\": \"Conditional knockout mice, co-immunoprecipitation, in vitro NKT cell activation assays, gene silencing\",\n      \"journal\": \"Nature medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — conditional KO plus co-association plus functional assays, replicated in subsequent work\",\n      \"pmids\": [\"15107843\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Purified MTP directly transfers phospholipids (but not triglycerides) to recombinant CD1d in vitro; MTP chemical inhibition reduces CD1d-mediated antigen presentation of alpha-GalCer and endogenous antigens without affecting MHC class II presentation, indicating MTP loads endogenous lipids onto nascent CD1d in the ER.\",\n      \"method\": \"In vitro lipid transfer assay with purified MTP and recombinant CD1d, chemical inhibition, siRNA knockdown, antigen presentation assays\",\n      \"journal\": \"The Journal of experimental medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct in vitro reconstitution of lipid transfer plus multiple functional assays\",\n      \"pmids\": [\"16087713\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"Soluble mouse and human CD1d molecules bind alpha-GalCer at neutral pH as measured by surface plasmon resonance; CD1d can also bind beta-GalCer and phosphatidylethanolamine; orientation of the galactose headgroup is more important for TCR contact than CD1d binding per se.\",\n      \"method\": \"Surface plasmon resonance, plate-bound soluble CD1d antigen presentation assays\",\n      \"journal\": \"The Journal of experimental medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — quantitative biophysical binding assay with reconstituted soluble proteins\",\n      \"pmids\": [\"10523605\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"PPARgamma induces expression of retinol and retinal metabolizing enzymes (RDH10, RALDH2) in dendritic cells, increasing intracellular all-trans retinoic acid (ATRA), which activates RARalpha and directly up-regulates CD1d expression and iNKT cell activation.\",\n      \"method\": \"Gene expression analysis, enzyme activity assays, RARalpha activation assays, iNKT cell activation\",\n      \"journal\": \"The Journal of experimental medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods tracing PPARgamma→RA→RARalpha→CD1d pathway\",\n      \"pmids\": [\"16982809\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Crystal structure of mouse CD1d bound to phosphatidylcholine at 2.8 Å resolution revealed interactions between lipid acyl chains and the CD1d binding groove; headgroup orientation toward C-terminus of alpha1 helix provides structural basis for invariant NKT cell Valpha chain bias.\",\n      \"method\": \"X-ray crystallography at 2.8 Å resolution\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure\",\n      \"pmids\": [\"16002697\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Crystal structure of mouse CD1d in complex with mycobacterial dipalmitoyl-PIM2 at 2.6 Å resolution revealed a specific hydrogen-bonding network between PIM2 and CD1d residues (Asp153, Thr156, Ser76, Arg79) orienting the complex headgroup above the A' pocket; specificity for additional mannoses conferred by Thr159.\",\n      \"method\": \"X-ray crystallography at 2.6 Å resolution\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — high-resolution crystal structure\",\n      \"pmids\": [\"16982895\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Crystal structure of an autoreactive NKT TCR–phosphatidylinositol–CD1d complex at 2.3 Å resolution revealed that NKT TCR autoreactivity is mediated by unique hydrophobic sequences in the non-germline-encoded CDR3β loop promoting self-association with CD1d, while germline-encoded recognition of CD1d is conserved across self and foreign antigens.\",\n      \"method\": \"X-ray crystallography at 2.3 Å resolution, binding studies with natural self-antigens\",\n      \"journal\": \"Immunity\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure with functional characterization\",\n      \"pmids\": [\"21376640\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Cardiolipin (CL) binds to murine CD1d with two alkyl chains buried in the CD1d binding groove and two chains exposed to solvent (crystal structure at 2.3 Å); CD1d-CL complexes stimulate splenic and hepatic γδ T cells to produce IFN-γ and RANTES in a CD1d-restricted manner.\",\n      \"method\": \"X-ray crystallography at 2.3 Å resolution, lipid loading assay, in vitro and in vivo γδ T cell stimulation assays\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure plus functional in vitro and in vivo validation\",\n      \"pmids\": [\"21389252\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"CD1d expressed on cortical thymocytes is both necessary and sufficient for NKT cell thymic selection, expansion, acquisition of memory phenotype, and cytokine production; restricting CD1d expression to cortical thymocytes in transgenic/chimeric mice was sufficient for these differentiation events.\",\n      \"method\": \"Transgenic and chimeric mouse approach restricting CD1d expression to cortical thymocytes\",\n      \"journal\": \"The Journal of experimental medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis in vivo with defined cellular phenotypic readouts\",\n      \"pmids\": [\"16027237\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"CD1d is required for post-selection NKT cell maturation (acquisition of NK1.1); immature NK1.1- NKT cells fail to fully mature when transferred to a CD1d-deficient environment, but long-term survival of NKT cells is largely CD1d-independent.\",\n      \"method\": \"Adoptive transfer of NKT cells into CD1d-deficient recipients, phenotypic analysis\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean adoptive transfer loss-of-function with defined developmental phenotype\",\n      \"pmids\": [\"16148122\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"CD1d evasion by KSHV is caused by the viral MIR proteins, which ubiquitinate the CD1d alpha-chain on a unique lysine in its cytoplasmic tail, triggering endocytosis and loss of surface CD1d without accelerated lysosomal degradation; this reduces CD1d-restricted T cell activation.\",\n      \"method\": \"Transfection of MIR proteins, ubiquitination assay, surface expression analysis, functional T cell activation assay\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — identified specific lysine residue, mechanism of endocytosis established with functional consequence\",\n      \"pmids\": [\"15864354\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"HSV-1 protein kinase US3 phosphorylates cellular kinesin motor protein KIF3A predominantly at serine 687, impairing CD1d recycling to the cell surface; ablation of this phosphorylation site abolished US3-mediated CD1d downregulation, identifying KIF3A as essential for CD1d surface expression.\",\n      \"method\": \"In vitro kinase assay, mass spectrometry of purified KIF3A, mutagenesis of phosphorylation site, surface CD1d expression analysis\",\n      \"journal\": \"Journal of virology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro kinase assay, mass spectrometry, site-directed mutagenesis with functional rescue\",\n      \"pmids\": [\"25878107\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"CD1d crosslinking on intestinal epithelial cells activates STAT3 and STAT3-dependent transcription of IL-10, HSP110, and CD1d itself; IEC-specific deletion of IL-10, CD1d, or MTP causes severe NKT-cell-mediated colitis, revealing a CD1d–STAT3–IL-10 protective epithelial signaling pathway.\",\n      \"method\": \"IEC-specific conditional deletion, STAT3 activation assays, cytokine measurements, colitis models\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — conditional KO with multiple pathway components and defined phenotypic readouts\",\n      \"pmids\": [\"24717441\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Anti-CD1d crosslinking on hepatocytes induces tyrosine phosphorylation of the CD1d cytoplasmic tail, recruiting and phosphorylating JAK2, which activates STAT3 to increase anti-apoptotic effectors (Bcl-xL, Mcl-1) and decrease pro-apoptotic signaling; this CD1d–JAK2–STAT3 axis protects against hepatocyte apoptosis in NASH.\",\n      \"method\": \"Anti-CD1d antibody crosslinking, phosphorylation assays, hepatocyte-specific overexpression and knockdown, in vivo liver injury models\",\n      \"journal\": \"Journal of hepatology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — multiple orthogonal methods including mechanistic phosphorylation assays and in vivo genetic models\",\n      \"pmids\": [\"38438948\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"In the absence of beta2-microglobulin, CD1d is expressed on the cell surface as an endoglycosidase-H-sensitive 45-kDa glycoprotein that fails to acquire endoglycosidase-H resistance, indicating that beta2m association is required for CD1d to transit normally through the secretory pathway and acquire complex glycosylation.\",\n      \"method\": \"CD1d transfectants, pulse-chase metabolic labeling, endoglycosidase digestion, immunoprecipitation\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — biochemical reconstitution with pulse-chase and enzymatic characterization\",\n      \"pmids\": [\"10092605\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"CD1d expression on cardiac myocytes is upregulated by myocarditic CVB3 but not by non-myocarditic variants; Vγ4+ T cells kill CVB3-infected myocytes via CD1d in a cytotoxicity assay blocked by anti-CD1d antibody; CD1d-deficient mice do not develop CVB3-induced myocarditis.\",\n      \"method\": \"CD1d KO mice, in vitro cytotoxicity assays with anti-CD1d blocking antibody, flow cytometry of infected myocytes\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — KO mice plus functional blocking assay but single lab\",\n      \"pmids\": [\"12626572\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"CD1d engagement by anti-CD1d monoclonal antibodies on myeloma cells with restored CD1d expression induces caspase-independent cell death associated with Bax overexpression and mitochondrial membrane potential loss; this requires the CD1d cytoplasmic tail but not the tyrosine residue critical for lysosomal sorting.\",\n      \"method\": \"Anti-CD1d mAb crosslinking, apoptosis assays (Bax expression, mitochondrial potential), cytoplasmic tail mutants\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — functional assays with defined mutants, single lab\",\n      \"pmids\": [\"19056691\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Human Vδ1 γδ TCRs bind recombinant CD1d-sulfatide complexes in a sulfatide-specific manner as demonstrated by recombinant TCR binding to CD1d tetramers, providing the first direct demonstration of MHC-like-restricted antigen-specific recognition by γδ TCRs.\",\n      \"method\": \"CD1d-sulfatide tetramer binding, recombinant TCR production and binding assay, MACS enrichment\",\n      \"journal\": \"European journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — recombinant protein binding assay with direct biochemical evidence\",\n      \"pmids\": [\"22829134\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Lysophosphatidylcholine (LPC) presented by human CD1d adopts an altered CD1d conformation with a shifted alpha1 helix and open A' pocket; iNKT TCR binding to CD1d-LPC requires a 7-Å displacement of the LPC headgroup but stabilizes the CD1d-LPC complex in a closed conformation.\",\n      \"method\": \"X-ray crystallography, biophysical binding assays\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure with mechanistic insight into conformational change upon TCR engagement\",\n      \"pmids\": [\"22395072\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Mass spectrometry analysis of lipids specifically loaded into purified CD1d proteins identified nine novel self-lipids presented by CD1d, with enrichment of particular lipid motifs, indicating CD1d surveys the endoplasmic reticulum, Golgi, and/or secretory compartments.\",\n      \"method\": \"Mass spectrometry of purified CD1d protein lipid content with rigorous controls\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct biochemical identification with rigorous controls\",\n      \"pmids\": [\"21900247\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Acid sphingomyelinase (ASM) degrades sphingomyelin, a non-activating lipid that competes for CD1d binding; ASM deficiency leads to sphingomyelin accumulation in CD1d, diminished antigen presentation, defective iNKT cell thymic selection, and decreased iNKT cell numbers in both mice and humans with Niemann-Pick disease.\",\n      \"method\": \"ASM knockout mice, human Niemann-Pick disease patient analysis, pharmacological ASM administration, iNKT cell quantification\",\n      \"journal\": \"Nature immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO plus human disease correlation plus pharmacological rescue, multiple orthogonal approaches\",\n      \"pmids\": [\"31636468\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"IFN-beta is required for up-regulation of CD1d in Listeria monocytogenes-infected dendritic cells and macrophages; unlike MHC class I, this up-regulation is not transcriptionally regulated but results from increased de novo CD1d protein synthesis, leading to enhanced iNKT cell activation.\",\n      \"method\": \"In vivo infection model, in vitro IFN-beta treatment, confocal microscopy, metabolic labeling, RT-PCR, functional NKT activation assay\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods distinguishing transcriptional vs. translational regulation with functional consequence\",\n      \"pmids\": [\"17114455\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"IFN-gamma up-regulates CD1d mRNA and surface protein expression on intestinal epithelial cell lines in a dose- and time-dependent, cytokine-specific manner.\",\n      \"method\": \"Cell surface ELISA, RT-PCR, cytokine dose-response experiments on multiple epithelial cell lines\",\n      \"journal\": \"The American journal of physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — consistent across multiple cell lines, single lab\",\n      \"pmids\": [\"8760056\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Intestinal heat shock protein 110 (Hsp110) present in intestinal luminal contents induces CD1d surface expression on intestinal epithelial cells, representing a novel autocrine pathway of CD1d regulation.\",\n      \"method\": \"RT-PCR, confocal microscopy, cell surface ELISA, Western blot, biochemical fractionation and identification of Hsp110\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — protein identified biochemically with functional CD1d regulation shown, single lab\",\n      \"pmids\": [\"12952923\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Hepatocyte-specific loss of MTP impairs CD1d function and increases hepatic iNKT cell numbers due to altered iNKT cell apoptosis; hepatocyte-specific CD1d deletion produces similar findings, demonstrating that hepatocyte CD1d controls local liver iNKT cell homeostasis.\",\n      \"method\": \"Hepatocyte-specific conditional KO mice for both MTP and CD1d, apoptosis assays, hepatitis models\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — two independent conditional KO models with concordant findings\",\n      \"pmids\": [\"28893990\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"In fatty livers, ER stress reduces the pool of CD1d at the plasma membrane of hepatocytes (despite normal CD1d mRNA), impairing their ability to activate CD1d-restricted T cells; tunicamycin-induced ER stress reproduces these defects in lean mice.\",\n      \"method\": \"Flow cytometry, in vitro T cell activation assays, tunicamycin treatment of cultured hepatocytes and lean mice\",\n      \"journal\": \"Laboratory investigation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — ER stress linked to CD1d trafficking defect with functional consequence, single lab\",\n      \"pmids\": [\"17307300\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"miR-155 directly targets the 3'-UTR of CD1d mRNA upon TLR9 activation in B cells, reducing CD1d protein and impairing antigen presentation to iNKT cells; Ets-1 directly regulates CD1d gene transcription.\",\n      \"method\": \"3'-UTR reporter assays, miR-155 overexpression/inhibition, TLR9 stimulation, iNKT cell activation assay\",\n      \"journal\": \"European journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct 3'-UTR targeting demonstrated with functional consequence, single lab\",\n      \"pmids\": [\"25929465\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"HDAC2 binds to the CD1D promoter; HDAC2 knockdown in tumor cells increases CD1d mRNA and surface expression and enhances CD1d-mediated NKT cell antigen presentation; pan-HDACi treatment also inhibits STAT3, which reduces IL-10 secretion that otherwise inhibits CD1d-mediated presentation.\",\n      \"method\": \"ChIP (HDAC2 on CD1D promoter), siRNA knockdown, surface CD1d expression, NKT cell activation assay\",\n      \"journal\": \"Cancer immunology, immunotherapy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — ChIP assay plus functional knockdown, single lab\",\n      \"pmids\": [\"27614429\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"DPPE-PEG, a CD1d-binding lipid antagonist, competes with alpha-GalCer for binding to CD1d and completely inhibits alpha-GalCer-induced ERK phosphorylation in iNKT cells, thereby blocking TCR signaling and preventing iNKT cell-mediated airway hyperreactivity.\",\n      \"method\": \"CD1d competitive binding assay, ERK phosphorylation assay in iNKT cells, mouse model of airway hyperreactivity\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct binding competition plus signaling mechanism plus in vivo model, single lab\",\n      \"pmids\": [\"20083656\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Galactose-modified iNKT cell agonists bind CD1d via an induced-fit mechanism using an aromatic substitution as a third anchor in addition to the two lipid chains, stabilizing CD1d binding and driving superior Th1 cytokine responses and tumor protection.\",\n      \"method\": \"Equilibrium lipid binding assays, crystal structure analysis, iNKT cell cytokine assays, in vivo tumor protection model\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — structural and binding data combined with functional in vitro and in vivo validation\",\n      \"pmids\": [\"21552205\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"A 'TCR trap' method that captures lipids within CD1d–lipid–TCR complexes identified alpha-linked monohexosylceramides from cow's milk as specific lipid antigens recognized by iNKT cells, as confirmed by mass spectrometry fragmentation patterns.\",\n      \"method\": \"TCR trap immunoprecipitation of CD1d-lipid-TCR complex followed by mass spectrometry\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — novel direct biochemical method for antigen capture with mass spectrometry confirmation\",\n      \"pmids\": [\"28716901\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"CD1d-expressing B cells are absolutely required for NKT-enhanced antibody responses; reconstituting B cell-deficient mice with CD1d-/- B cells abolished NKT-enhanced Ab responses, demonstrating that direct CD1d presentation by B cells is the mechanism of NKT cell help for humoral immunity.\",\n      \"method\": \"B cell reconstitution of microMT mice with wild-type or CD1d-/- B cells, immunization and antibody measurement\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean genetic reconstitution experiment with defined functional readout\",\n      \"pmids\": [\"18077787\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Adipocyte-specific CD1d deletion in mice reduces visceral adipose tissue mass and improves insulin sensitivity on high-fat diet, decreases NKT cell activation and IFN-γ production, and blunts macrophage recruitment into adipose tissue; 3T3-L1 adipocytes present endogenous ligands to NKT cells via CD1d leading to IFN-γ production.\",\n      \"method\": \"Adipocyte-specific CD1d conditional KO mice, high-fat diet model, in vitro NKT cell stimulation by adipocytes, metabolic measurements\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — cell-type-specific conditional KO with multiple functional readouts\",\n      \"pmids\": [\"27329323\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"The amine headgroups of ionizable lipids in lipid nanoparticles bind directly to CD1d (and TLR4) and promote lipid-raft formation, driving NKT cell-mediated immune responses including type-1 T-helper-cell-biased cytokine production.\",\n      \"method\": \"Binding assays to CD1d, lipid-raft formation assays, immunological profiling of LNP-immunized mice\",\n      \"journal\": \"Nature biomedical engineering\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct binding demonstrated with functional immune readouts, single study\",\n      \"pmids\": [\"39363106\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"A hydrophobic patch formed by TCRα-TCRβ pairing is required for NKT TCR recognition of CD1d but not MHC; partial disruption of this patch selectively allowed CD1d recognition while altering NKT cell development, resulting in accumulation of adipose-tissue-resident NKT cells.\",\n      \"method\": \"Molecular modeling, mutagenesis of TCR hydrophobic patch, transgenic mouse models, flow cytometry of tissue NKT cells\",\n      \"journal\": \"Nature immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — mutagenesis with clear functional consequence in vivo, two levels of phenotypic analysis\",\n      \"pmids\": [\"27869818\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"CD1d polymorphisms in wild-derived mouse strains affect the presentation of endogenous and exogenous lipid ligands to both type I and type II NKT cells, and CD1d polymorphisms influence thymic selection of type I NKT cells and induce allogeneic T cell responses.\",\n      \"method\": \"Congenic mice with identified CD1d alleles, antigen presentation assays, thymic NKT cell development analysis\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — functional demonstration with genetic tools, single lab\",\n      \"pmids\": [\"19179286\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"CD1d is a non-polymorphic MHC class I-like molecule that binds diverse lipid and glycolipid antigens within its hydrophobic groove (loading assisted by MTP in the ER and saposins in endosomes), traffics to the cell surface in a manner dependent on its cytoplasmic tail tyrosine motif (regulated by IFN-γ, IFN-β, PPARγ/retinoic acid, Hsp110, and viral mechanisms including KSHV MIR-mediated ubiquitination and HSV-1 US3-mediated KIF3A phosphorylation), and presents lipid antigens to NKT cells via a conserved parallel docking mode in which the germline-encoded NKT TCR α-chain makes lock-and-key contact with CD1d while β-chain variability modulates fine specificity; additionally, CD1d engagement on non-immune cells (hepatocytes, intestinal epithelial cells) triggers intracellular signaling through JAK2-STAT3 or STAT3-IL-10 pathways that confer cytoprotective and immunoregulatory effects.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"CD1d is a non-polymorphic MHC class I-like glycoprotein that presents lipid and glycolipid antigens to NKT cells and γδ T cells, functioning as a central organizer of lipid-mediated adaptive immunity. Its hydrophobic binding groove accommodates diverse lipid antigens — including α-galactosylceramide, phosphatidylinositol mannosides, sulfatide, phosphatidylcholine, lysophosphatidylcholine, and cardiolipin — with two acyl chains buried in the A′ and F′ pockets and the polar headgroup exposed for TCR contact; lipid loading is initiated by microsomal triglyceride transfer protein (MTP) in the endoplasmic reticulum and refined by acid sphingomyelinase-mediated removal of non-stimulatory sphingomyelin in endosomes, while β2-microglobulin association is required for normal secretory trafficking [PMID:16002697, PMID:16314439, PMID:15107843, PMID:16087713, PMID:31636468, PMID:10092605]. The invariant NKT TCR docks parallel to the CD1d binding cleft in a germline-encoded lock-and-key interaction dominated by the TCRα chain, with TCRβ CDR3 variability modulating autoreactivity and fine antigen specificity [PMID:17581592, PMID:21376640]. Beyond antigen presentation, CD1d engagement on epithelial cells and hepatocytes triggers intrinsic signaling through a cytoplasmic tail–JAK2–STAT3 axis that induces IL-10 and anti-apoptotic effectors, conferring tissue-protective functions in the gut and liver [PMID:24717441, PMID:38438948].\",\n  \"teleology\": [\n    {\n      \"year\": 1996,\n      \"claim\": \"The question of whether CD1d surface expression is dynamically regulated was answered by showing that IFN-γ transcriptionally upregulates CD1d on intestinal epithelial cells, establishing CD1d as a cytokine-responsive antigen-presenting molecule.\",\n      \"evidence\": \"Dose-response IFN-γ treatment of multiple IEC lines with RT-PCR and surface ELISA\",\n      \"pmids\": [\"8760056\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab; transcription factor mediating IFN-γ induction not identified\", \"In vivo relevance of IEC CD1d upregulation not tested\"]\n    },\n    {\n      \"year\": 1997,\n      \"claim\": \"Whether NKT cells use their TCR to specifically recognize CD1d (rather than other CD1 isoforms) was resolved by showing that Vα24+ T cells discriminate CD1d from CD1a/b/c in a TCR-dependent manner, establishing CD1d as the restricting element for invariant NKT cells.\",\n      \"evidence\": \"T cell clone stimulation assays with antibody blocking across CD1 family members\",\n      \"pmids\": [\"9207002\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Nature of the endogenous ligand presented was unknown\", \"Structural basis of CD1d selectivity unresolved\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"The biophysical basis of lipid antigen binding to CD1d was established by demonstrating direct, pH-independent binding of α-GalCer and other lipids to soluble CD1d, and by showing that β2-microglobulin is required for normal CD1d maturation through the secretory pathway.\",\n      \"evidence\": \"Surface plasmon resonance with soluble CD1d; pulse-chase metabolic labeling and endoglycosidase digestion of CD1d transfectants\",\n      \"pmids\": [\"10523605\", \"10092605\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Lipid-binding stoichiometry and groove architecture not yet visualized\", \"Identity of physiological self-lipids unknown\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Whether CD1d presents self-lipids (not just foreign glycolipids) was answered by showing that cellular phospholipids extracted from tumor cells stimulate NKT hybridomas via plate-bound CD1d, establishing self-lipid surveillance as a CD1d function.\",\n      \"evidence\": \"In vitro antigen presentation with plate-bound mCD1d loaded with purified phospholipids and tumor-derived lipid extracts\",\n      \"pmids\": [\"10714687\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Specific self-lipid species not identified\", \"Mechanism of self-lipid loading not addressed\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"The in vivo functional importance of CD1d intracellular trafficking was established by showing that the cytoplasmic tail tyrosine motif is essential for NKT cell development and antigen presentation despite normal surface CD1d levels.\",\n      \"evidence\": \"Knock-in mice with deleted cytoplasmic tail tyrosine motif, in vivo NKT cell phenotyping\",\n      \"pmids\": [\"11731798\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"The adaptor protein linking the tyrosine motif to endosomal sorting was not identified\", \"Whether lipid exchange in endosomes requires this motif was untested\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"The mechanism of lipid loading onto nascent CD1d was identified: MTP in the ER associates with CD1d and is required for functional lipid antigen presentation, as shown by conditional MTP deletion in hepatocytes impairing NKT activation.\",\n      \"evidence\": \"Conditional Mttp knockout mice, co-immunoprecipitation of MTP–CD1d, NKT activation assays\",\n      \"pmids\": [\"15107843\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Specificity of lipid species loaded by MTP onto CD1d was unclear\", \"Whether MTP acts catalytically or as a scaffold was unresolved\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Multiple structural and functional advances in 2004–2005 defined the CD1d lipid-binding groove architecture, confirmed MTP directly transfers phospholipids to CD1d in vitro, established that cortical thymocyte CD1d is sufficient for NKT selection, identified CD1d's role in post-selection NKT maturation, and revealed KSHV immune evasion via MIR-mediated ubiquitination of CD1d.\",\n      \"evidence\": \"Crystal structures of CD1d–sulfatide (1.9 Å) and CD1d–phosphatidylcholine (2.8 Å); in vitro MTP lipid transfer to recombinant CD1d; transgenic mice restricting CD1d to cortical thymocytes; adoptive transfer into CD1d-deficient hosts; MIR transfection with ubiquitination and surface expression assays\",\n      \"pmids\": [\"16314439\", \"16002697\", \"16087713\", \"16027237\", \"16148122\", \"15864354\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How endosomal lipid exchange enzymes (saposins) cooperate with CD1d was not structurally resolved\", \"Whether MTP loads all self-lipids or a specific subset remained open\", \"Full NKT TCR–CD1d docking geometry still unknown\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"The structural basis of NKT TCR recognition of CD1d was solved: the NKT TCR docks parallel to and at the extreme end of the CD1d cleft, with the germline-encoded TCRα chain making lock-and-key contact with CD1d–α-GalCer.\",\n      \"evidence\": \"X-ray crystallography of human NKT TCR–CD1d–α-GalCer ternary complex\",\n      \"pmids\": [\"17581592\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How TCRβ chain variability modulates antigen specificity was not structurally resolved\", \"Recognition of self-lipid antigens not yet crystallographically captured\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"CD1d on B cells was shown to be the direct mechanism of NKT cell help for humoral immunity, and IFN-β was found to post-transcriptionally upregulate CD1d protein synthesis during bacterial infection.\",\n      \"evidence\": \"B cell reconstitution of μMT mice with WT vs CD1d−/− B cells; metabolic labeling of DCs during Listeria infection with and without IFN-β\",\n      \"pmids\": [\"18077787\", \"17114455\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Signals downstream of NKT–B cell CD1d interaction for class switching were not mapped\", \"Translational mechanism of IFN-β-induced CD1d synthesis not identified\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Structural studies revealed how NKT TCR autoreactivity arises (CDR3β hydrophobic contacts with CD1d), how diverse self-lipids including cardiolipin occupy the groove with partial solvent exposure, and mass spectrometry identified the full self-lipid repertoire of CD1d.\",\n      \"evidence\": \"Crystal structures of autoreactive NKT TCR–PI–CD1d (2.3 Å) and CD1d–cardiolipin (2.3 Å); MS of purified CD1d lipid content\",\n      \"pmids\": [\"21376640\", \"21389252\", \"21900247\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional hierarchy among self-lipids for NKT selection not established\", \"Whether cardiolipin-reactive γδ T cells contribute to mitochondrial damage sensing was unknown\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"CD1d was shown to also restrict γδ T cells (Vδ1 TCRs bind CD1d–sulfatide), and structural analysis of CD1d–lysophosphatidylcholine revealed an induced-fit mechanism where TCR binding stabilizes a conformational shift in the α1 helix.\",\n      \"evidence\": \"Recombinant Vδ1 TCR binding to CD1d–sulfatide tetramers; crystal structures of CD1d–LPC ± TCR\",\n      \"pmids\": [\"22829134\", \"22395072\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physiological role of γδ T cell CD1d restriction in vivo uncharacterized\", \"Whether induced-fit applies to all self-lipid antigens is unknown\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"A cell-intrinsic signaling function of CD1d was discovered: CD1d crosslinking on intestinal epithelial cells activates STAT3, inducing IL-10 and a protective feedback loop; IEC-specific deletion of CD1d, IL-10, or MTP causes NKT-mediated colitis.\",\n      \"evidence\": \"IEC-specific conditional deletion of CD1d, IL-10, and MTP; STAT3 phosphorylation assays; colitis models\",\n      \"pmids\": [\"24717441\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"The ligand or cell type that crosslinks CD1d on IECs in vivo was not identified\", \"Proximal kinase linking CD1d cytoplasmic tail to STAT3 in IECs not determined at this time\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"HSV-1 immune evasion via CD1d was mechanistically resolved: viral kinase US3 phosphorylates KIF3A at Ser687, blocking kinesin-dependent CD1d recycling to the surface.\",\n      \"evidence\": \"In vitro kinase assay, mass spectrometry of KIF3A, Ser687 mutagenesis abolishing US3-mediated CD1d downregulation\",\n      \"pmids\": [\"25878107\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether KIF3A-dependent transport applies to CD1d recycling in uninfected cells was not tested\", \"Other kinesin family members potentially involved not excluded\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"The role of lipid editing in CD1d function was established: acid sphingomyelinase removes non-stimulatory sphingomyelin from CD1d; ASM deficiency in mice and Niemann-Pick patients causes sphingomyelin accumulation in CD1d, impaired antigen presentation, and iNKT cell deficiency.\",\n      \"evidence\": \"ASM knockout mice, human Niemann-Pick disease patient iNKT quantification, pharmacological ASM rescue\",\n      \"pmids\": [\"31636468\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether other lipid hydrolases contribute to CD1d editing was not tested\", \"The endosomal compartment where ASM acts on CD1d-bound sphingomyelin was not localized\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"The proximal signaling mechanism of CD1d in hepatocytes was identified: CD1d crosslinking induces cytoplasmic tail tyrosine phosphorylation, recruiting JAK2 which activates STAT3 to upregulate anti-apoptotic Bcl-xL/Mcl-1, protecting against hepatocyte apoptosis in NASH.\",\n      \"evidence\": \"Anti-CD1d antibody crosslinking, phosphorylation assays, hepatocyte-specific overexpression/knockdown, in vivo NASH models\",\n      \"pmids\": [\"38438948\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"The kinase that phosphorylates the CD1d tail tyrosine upstream of JAK2 recruitment is unknown\", \"Whether this signaling pathway operates in other CD1d-expressing non-immune cells is untested\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Major unresolved questions include: the identity of the in vivo ligand(s) and cell type that crosslink CD1d on non-immune cells to activate its intrinsic signaling; the structural basis by which saposins mediate lipid exchange in endosomes; and the rules governing the self-lipid repertoire that shapes NKT cell selection versus peripheral activation.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No structural data on saposin–CD1d interaction\", \"In vivo CD1d crosslinking ligand on non-immune cells unidentified\", \"Quantitative rules linking self-lipid repertoire to NKT thymic selection thresholds unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0008289\", \"supporting_discovery_ids\": [2, 3, 5, 8, 10, 11, 13, 24, 25]},\n      {\"term_id\": \"GO:0048018\", \"supporting_discovery_ids\": [1, 14, 37]},\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [18, 19]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [1, 4, 16, 17, 20, 28]},\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [6, 7, 20, 25]},\n      {\"term_id\": \"GO:0005768\", \"supporting_discovery_ids\": [4, 26]},\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [8]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [1, 2, 3, 14, 15, 37, 38]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [18, 19]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [16, 17, 26]}\n    ],\n    \"complexes\": [\n      \"CD1d–β2-microglobulin heterodimer\"\n    ],\n    \"partners\": [\n      \"B2M\",\n      \"MTTP\",\n      \"SMPD1\",\n      \"JAK2\",\n      \"STAT3\",\n      \"KIF3A\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}