{"gene":"CD1E","run_date":"2026-04-28T17:28:52","timeline":{"discoveries":[{"year":2000,"finding":"CD1e exists as multiple alternatively spliced isoforms in dendritic cells; isoforms with three alpha domains associate with beta2-microglobulin, accumulate in late Golgi and late endosomal compartments due to atypical dilysine motifs in the cytoplasmic tail, and are cleaved into stable soluble forms in late endosomes. CD1e does not transit through the plasma membrane.","method":"Transfection of isoform constructs, subcellular fractionation, immunofluorescence, biochemical characterization","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods (transfection, fractionation, imaging) with functional characterization of isoforms","pmids":["10948205"],"is_preprint":false},{"year":2005,"finding":"Soluble CD1e is required for efficient processing of mycobacterial hexamannosylated phosphatidyl-myo-inositols (PIM6) by lysosomal alpha-mannosidase; recombinant CD1e binds glycolipids and assists their digestion, acting as a glycolipid-editing factor that expands the repertoire of CD1b-presented antigens.","method":"T cell stimulation assays with CD1b-restricted T cells, recombinant CD1e glycolipid-binding assays, in vitro digestion assays with lysosomal alpha-mannosidase","journal":"Science","confidence":"High","confidence_rationale":"Tier 1–2 — in vitro reconstitution of processing activity with recombinant protein, functional T cell readout; highly cited foundational paper","pmids":["16311334"],"is_preprint":false},{"year":2005,"finding":"During dendritic cell maturation, CD1e is redistributed from the Golgi to late endosomes/lysosomes via sorting endosomes without passing through the plasma membrane; in mature DCs it localizes almost exclusively to lysosomes, where it is cleaved into a soluble form.","method":"Live-cell fluorescence microscopy, immunoelectron microscopy, pulse-chase biosynthesis experiments in immature and maturing DCs","journal":"Traffic","confidence":"High","confidence_rationale":"Tier 2 — direct localization by multiple imaging methods (light and electron microscopy) with functional context of maturation-linked redistribution","pmids":["15752135"],"is_preprint":false},{"year":2008,"finding":"The cytoplasmic tail of CD1e controls its intracellular trafficking: the C-terminal half mediates Golgi accumulation, and monoubiquitination of cytoplasmic lysines triggers exit from Golgi compartments and transport to lysosomes. Replacing all eight cytoplasmic lysines with arginines causes accumulation in TGN46+ compartments and surface expression; fusion of this mutant to ubiquitin restores normal lysosomal trafficking kinetics.","method":"Chimeric molecule expression, lysine-to-arginine mutagenesis, ubiquitin fusion constructs, immunofluorescence microscopy in transfected cells and DCs","journal":"Traffic","confidence":"High","confidence_rationale":"Tier 1–2 — mutagenesis combined with rescue experiments and multiple imaging readouts establishing mechanistic role of ubiquitination","pmids":["18208508"],"is_preprint":false},{"year":2008,"finding":"A naturally occurring CD1e variant with proline at position 194 (allele 4) fails to assist PIM6 presentation to CD1b-restricted T cells due to inefficient assembly and poor transport to late endosomal compartments.","method":"T cell stimulation assays, subcellular localization analysis of allelic variants in transfected cells and DCs","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 2 — functional assay (T cell stimulation) combined with mechanistic explanation (assembly/transport defect) for a defined mutant","pmids":["18325888"],"is_preprint":false},{"year":2011,"finding":"CD1e facilitates rapid formation of CD1-lipid complexes and accelerates their turnover, positively or negatively modulating lipid antigen presentation by CD1b, CD1c, and CD1d. In CD1e transgenic mouse antigen-presenting cells, lipid complexes assemble more efficiently and show faster turnover than in WT cells.","method":"T cell stimulation assays with CD1b/c/d-restricted T cells, CD1e transgenic mouse APCs, kinetic lipid-loading assays","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal assays (human cell, transgenic mouse, kinetic loading), replicated across different CD1 isoforms","pmids":["21844346"],"is_preprint":false},{"year":2011,"finding":"Crystal structure of human CD1e at 2.90-Å resolution reveals a groove with a wider portal (2 Å larger spacing between α1 and α2 helices) compared to other CD1 proteins, with no stable endogenous ligand density despite confirmed lipid binding by native mass spectrometry. CD1e mediates lipid transfer to CD1b and displacement of lipids from stable CD1b-antigen complexes in vitro, and lipid association/dissociation rates are considerably faster than with CD1b.","method":"X-ray crystallography, native mass spectrometry, in vitro lipid transfer assays, kinetic lipid association/dissociation measurements","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 — crystal structure with functional validation by native MS and in vitro lipid transfer reconstitution","pmids":["21788486"],"is_preprint":false},{"year":2012,"finding":"CD1e acts as a lipid transfer protein that selectively assists alpha-mannosidase-dependent digestion of PIM6 according to degree of acylation, and transfers only diacylated PIM from donor liposomes to acceptor liposomes and from membranes to CD1b.","method":"In vitro digestion assays with defined PIM species of varying acylation, liposome-to-liposome and membrane-to-CD1b lipid transfer assays with recombinant CD1e","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — reconstituted in vitro with defined substrates, demonstrating acylation-selective transfer activity","pmids":["22782895"],"is_preprint":false},{"year":2012,"finding":"LAPTM5 is a molecular partner of CD1e; the two proteins colocalize in trans-Golgi and late endosomal compartments, and their association occurs under physiological conditions and increases when lysosomal acidification is inhibited by bafilomycin. However, LAPTM5 does not control CD1e ubiquitination or generation of the soluble lysosomal CD1e form.","method":"Co-immunoprecipitation, colocalization by fluorescence microscopy, bafilomycin treatment, mass spectrometry identification of binding partner","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2–3 — partner identified by MS and confirmed by Co-IP/colocalization, but functional consequence of interaction not fully established","pmids":["22880058"],"is_preprint":false},{"year":2003,"finding":"Rhesus macaque CD1e shares the same intracellular localization and biochemical properties as human CD1e (Golgi in immature DCs, late endosomal cleavage to soluble form), demonstrating conservation of the unique intracellular trafficking pathway across primate evolution.","method":"Immunofluorescence microscopy and biochemical characterization of simian CD1e in dendritic cells","journal":"Immunogenetics","confidence":"Medium","confidence_rationale":"Tier 2 — direct localization and biochemical characterization in a primate ortholog confirming conserved mechanism","pmids":["12671734"],"is_preprint":false},{"year":2022,"finding":"CD1e and B2M (beta-2-microglobulin) interact directly, as demonstrated by surface plasmon resonance using cell-free synthesized proteins.","method":"Cell-free protein synthesis, Ni2+ affinity purification, surface plasmon resonance (SPR)","journal":"Protein expression and purification","confidence":"Medium","confidence_rationale":"Tier 2 — direct biophysical binding assay with purified proteins, but single method and limited mechanistic follow-up","pmids":["36460227"],"is_preprint":false}],"current_model":"CD1e is a unique intracellular CD1 family member expressed in dendritic cells that, after monoubiquitination-driven exit from the Golgi, traffics to lysosomes where it is cleaved into a soluble form; in lysosomes, soluble CD1e acts as a lipid-editing/transfer protein that binds glycolipids with fast on/off kinetics (facilitated by its unusually wide groove), selectively assists lysosomal alpha-mannosidase digestion of complex mycobacterial glycolipids (e.g., PIM6) in an acylation-dependent manner, and transfers lipid antigens to CD1b and other CD1 molecules, thereby modulating the repertoire and kinetics of CD1-restricted T cell responses."},"narrative":{"teleology":[{"year":2000,"claim":"Establishing that CD1e is an exclusively intracellular CD1 molecule answered the question of why no surface CD1e expression had been detected: alternatively spliced isoforms with three α-domains associate with β2-microglobulin but accumulate in late Golgi and late endosomes via atypical dilysine tail motifs, where they are cleaved into soluble forms, never reaching the plasma membrane.","evidence":"Transfection of isoform constructs, subcellular fractionation, immunofluorescence, and biochemical analysis in dendritic cells","pmids":["10948205"],"confidence":"High","gaps":["Protease responsible for endosomal cleavage to soluble form not identified","Function of alternatively spliced isoforms lacking full alpha domains unclear","Signal directing Golgi retention versus endosomal transit not fully defined"]},{"year":2003,"claim":"Conservation of CD1e's intracellular trafficking and cleavage in rhesus macaque dendritic cells established that this unique non-surface pathway is evolutionarily conserved across primates, strengthening the inference that it serves a selected function.","evidence":"Immunofluorescence and biochemical characterization of simian CD1e in dendritic cells","pmids":["12671734"],"confidence":"Medium","gaps":["Functional consequence of conservation not tested (no antigen presentation assay in macaque)","Whether non-primate mammals have a functional CD1e ortholog not addressed"]},{"year":2005,"claim":"Two key advances defined the cell biology and function of CD1e: live-cell and immunoelectron microscopy showed that DC maturation triggers CD1e redistribution from Golgi to lysosomes via sorting endosomes, and in vitro reconstitution demonstrated that soluble CD1e is required for lysosomal α-mannosidase to efficiently process PIM6, thereby expanding the CD1b-presented antigen repertoire.","evidence":"Live-cell fluorescence and immunoelectron microscopy of immature/mature DCs; recombinant CD1e glycolipid-binding assays and in vitro digestion assays with CD1b-restricted T cell readout","pmids":["15752135","16311334"],"confidence":"High","gaps":["Mechanism by which CD1e facilitates α-mannosidase activity not resolved at molecular level","Whether CD1e assists processing of non-PIM glycolipids not tested","In vivo relevance in intact organism not demonstrated"]},{"year":2008,"claim":"The molecular mechanism governing CD1e's unusual Golgi-to-lysosome trafficking was resolved: monoubiquitination of cytoplasmic tail lysines triggers exit from the Golgi, as shown by lysine-to-arginine mutagenesis causing Golgi retention and surface expression, rescued by ubiquitin fusion. A natural CD1e variant (Pro194) that fails to assemble properly and cannot reach lysosomes is functionally inactive in PIM6 presentation.","evidence":"Mutagenesis, ubiquitin-fusion rescue constructs, immunofluorescence in DCs; T cell stimulation assays and localization analysis of allelic variants","pmids":["18208508","18325888"],"confidence":"High","gaps":["E3 ubiquitin ligase responsible for CD1e monoubiquitination not identified","Whether the Pro194 variant has clinical immunological consequences in carriers unknown","Mechanism of CD1e cleavage in late endosomes still undefined"]},{"year":2011,"claim":"Structural and functional analyses revealed how CD1e acts as a lipid transfer protein: its crystal structure showed an unusually wide groove portal (2 Å wider than other CD1 proteins) with no stably bound endogenous lipid, and kinetic assays demonstrated fast lipid association/dissociation enabling CD1e to transfer lipids to CD1b and displace lipids from stable CD1b complexes. Transgenic mouse studies showed CD1e accelerates both formation and turnover of CD1b/c/d–lipid complexes, positively or negatively modulating antigen presentation.","evidence":"X-ray crystallography at 2.90 Å, native mass spectrometry, in vitro lipid transfer assays, CD1e transgenic mouse APC functional assays with CD1b/c/d-restricted T cells","pmids":["21788486","21844346"],"confidence":"High","gaps":["Structural basis for selectivity toward specific lipid substrates not defined","Whether CD1e interacts directly with other CD1 molecules during transfer not established","Negative modulation mechanism (accelerated turnover) not fully dissected"]},{"year":2012,"claim":"The lipid transfer specificity of CD1e was refined: it selectively assists α-mannosidase digestion and membrane-to-CD1b transfer of diacylated but not higher-acylated PIM species, establishing acylation state as a selectivity determinant. Separately, LAPTM5 was identified as a molecular partner of CD1e in the Golgi and late endosomes.","evidence":"In vitro digestion and liposome transfer assays with defined PIM species of varying acylation; Co-IP, colocalization, and MS identification of LAPTM5 interaction","pmids":["22782895","22880058"],"confidence":"High","gaps":["Functional role of LAPTM5–CD1e interaction remains undefined (LAPTM5 does not control CD1e ubiquitination or cleavage)","Structural basis for acylation-dependent selectivity not determined","Whether CD1e transfers non-PIM lipid antigens with similar selectivity not systematically tested"]},{"year":null,"claim":"Key unresolved questions include the identity of the protease that cleaves CD1e in lysosomes, the E3 ligase mediating its monoubiquitination, whether CD1e directly contacts other CD1 molecules during lipid transfer, and the in vivo immunological consequences of CD1e deficiency or polymorphism in infection or autoimmunity.","evidence":"","pmids":[],"confidence":"Low","gaps":["Protease responsible for lysosomal cleavage of CD1e unknown","E3 ubiquitin ligase for CD1e monoubiquitination not identified","No in vivo loss-of-function model in an organism with a complete CD1 system"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0008289","term_label":"lipid binding","supporting_discovery_ids":[1,6,7]},{"term_id":"GO:0140104","term_label":"molecular carrier activity","supporting_discovery_ids":[6,7]}],"localization":[{"term_id":"GO:0005794","term_label":"Golgi apparatus","supporting_discovery_ids":[0,2,3]},{"term_id":"GO:0005764","term_label":"lysosome","supporting_discovery_ids":[0,1,2,3,5]},{"term_id":"GO:0005768","term_label":"endosome","supporting_discovery_ids":[0,2]}],"pathway":[{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[1,5,7]}],"complexes":[],"partners":["B2M","CD1B","LAPTM5"],"other_free_text":[]},"mechanistic_narrative":"CD1e is a unique intracellular member of the CD1 lipid antigen-presenting family that functions as a lysosomal lipid-editing and transfer protein in dendritic cells, shaping the repertoire of glycolipid antigens presented by CD1b, CD1c, and CD1d molecules. Synthesized in the Golgi, CD1e traffics directly to lysosomes without transiting the plasma membrane; this routing is controlled by monoubiquitination of cytoplasmic tail lysines, and upon arrival in late endosomes/lysosomes, CD1e is proteolytically cleaved into a stable soluble form [PMID:10948205, PMID:15752135, PMID:18208508]. Soluble CD1e binds glycolipids with fast on/off kinetics — enabled by an unusually wide antigen-binding groove — and selectively assists lysosomal α-mannosidase in digesting complex mycobacterial phosphatidyl-myo-inositol mannosides (PIM6) in an acylation-dependent manner, while also transferring processed lipid antigens to CD1b [PMID:16311334, PMID:21788486, PMID:22782895]. By accelerating both CD1–lipid complex formation and turnover, CD1e positively or negatively modulates lipid antigen presentation across multiple CD1 isoforms, thereby tuning CD1-restricted T cell responses [PMID:21844346]."},"prefetch_data":{"uniprot":{"accession":"P15812","full_name":"T-cell surface glycoprotein CD1e, membrane-associated","aliases":["R2G1"],"length_aa":388,"mass_kda":43.6,"function":"T-cell surface glycoprotein CD1e, soluble binds diacetylated lipids, including phosphatidyl inositides and diacylated sulfoglycolipids, and is required for the presentation of glycolipid antigens on the cell surface. The membrane-associated form is not active","subcellular_location":"Lysosome lumen","url":"https://www.uniprot.org/uniprotkb/P15812/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/CD1E","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/CD1E","total_profiled":1310},"omim":[{"mim_id":"188411","title":"THYMOCYTE ANTIGEN CD1E; CD1E","url":"https://www.omim.org/entry/188411"},{"mim_id":"188370","title":"THYMOCYTE ANTIGEN CD1A; CD1A","url":"https://www.omim.org/entry/188370"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Golgi apparatus","reliability":"Supported"},{"location":"Nucleoli","reliability":"Additional"}],"tissue_specificity":"Tissue enriched","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"lymphoid tissue","ntpm":895.4}],"url":"https://www.proteinatlas.org/search/CD1E"},"hgnc":{"alias_symbol":[],"prev_symbol":[]},"alphafold":{"accession":"P15812","domains":[{"cath_id":"3.30.500.10","chopping":"37-207","consensus_level":"high","plddt":93.4626,"start":37,"end":207},{"cath_id":"2.60.40.10","chopping":"213-301","consensus_level":"high","plddt":96.116,"start":213,"end":301}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P15812","model_url":"https://alphafold.ebi.ac.uk/files/AF-P15812-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P15812-F1-predicted_aligned_error_v6.png","plddt_mean":81.5},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=CD1E","jax_strain_url":"https://www.jax.org/strain/search?query=CD1E"},"sequence":{"accession":"P15812","fasta_url":"https://rest.uniprot.org/uniprotkb/P15812.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P15812/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P15812"}},"corpus_meta":[{"pmid":"16311334","id":"PMC_16311334","title":"Assistance of microbial glycolipid antigen processing by CD1e.","date":"2005","source":"Science (New York, N.Y.)","url":"https://pubmed.ncbi.nlm.nih.gov/16311334","citation_count":194,"is_preprint":false},{"pmid":"10948205","id":"PMC_10948205","title":"Characterization of CD1e, a third type of CD1 molecule expressed in dendritic cells.","date":"2000","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/10948205","citation_count":71,"is_preprint":false},{"pmid":"15752135","id":"PMC_15752135","title":"The cellular pathway of CD1e in immature and maturing dendritic cells.","date":"2005","source":"Traffic (Copenhagen, Denmark)","url":"https://pubmed.ncbi.nlm.nih.gov/15752135","citation_count":56,"is_preprint":false},{"pmid":"21844346","id":"PMC_21844346","title":"Fine tuning by human CD1e of lipid-specific immune responses.","date":"2011","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/21844346","citation_count":55,"is_preprint":false},{"pmid":"21788486","id":"PMC_21788486","title":"Crystal structure of human CD1e reveals a groove suited for lipid-exchange processes.","date":"2011","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/21788486","citation_count":42,"is_preprint":false},{"pmid":"22782895","id":"PMC_22782895","title":"Deciphering the role of CD1e protein in mycobacterial phosphatidyl-myo-inositol mannosides (PIM) processing for presentation by CD1b to T lymphocytes.","date":"2012","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/22782895","citation_count":30,"is_preprint":false},{"pmid":"18325888","id":"PMC_18325888","title":"Cutting edge: a naturally occurring mutation in CD1e impairs lipid antigen presentation.","date":"2008","source":"Journal of immunology (Baltimore, Md. : 1950)","url":"https://pubmed.ncbi.nlm.nih.gov/18325888","citation_count":30,"is_preprint":false},{"pmid":"18838176","id":"PMC_18838176","title":"Susceptibility to Guillain-Barré syndrome is not associated with CD1A and CD1E gene polymorphisms.","date":"2008","source":"Journal of neuroimmunology","url":"https://pubmed.ncbi.nlm.nih.gov/18838176","citation_count":25,"is_preprint":false},{"pmid":"11019917","id":"PMC_11019917","title":"Identification of two novel human CD1E alleles.","date":"2000","source":"Tissue antigens","url":"https://pubmed.ncbi.nlm.nih.gov/11019917","citation_count":25,"is_preprint":false},{"pmid":"18208508","id":"PMC_18208508","title":"Control of the intracellular pathway of CD1e.","date":"2008","source":"Traffic (Copenhagen, Denmark)","url":"https://pubmed.ncbi.nlm.nih.gov/18208508","citation_count":15,"is_preprint":false},{"pmid":"21496400","id":"PMC_21496400","title":"CD1A and CD1E gene polymorphisms are associated with susceptibility to multiple sclerosis.","date":"2011","source":"International journal of immunopathology and pharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/21496400","citation_count":13,"is_preprint":false},{"pmid":"20954848","id":"PMC_20954848","title":"Association of CD1A +622 T/C, +737 G/C and CD1E +6129 A/G genes polymorphisms with multiple sclerosis.","date":"2010","source":"Immunological investigations","url":"https://pubmed.ncbi.nlm.nih.gov/20954848","citation_count":9,"is_preprint":false},{"pmid":"20136774","id":"PMC_20136774","title":"Polymorphism of human CD1a, CD1d, and CD1e in exon 2 in Chinese Han and She ethnic populations.","date":"2010","source":"Tissue antigens","url":"https://pubmed.ncbi.nlm.nih.gov/20136774","citation_count":8,"is_preprint":false},{"pmid":"37506141","id":"PMC_37506141","title":"STK11 mutation impacts CD1E expression to regulate the differentiation of macrophages in lung adenocarcinoma.","date":"2023","source":"Immunity, inflammation and 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with beta2-microglobulin, accumulate in late Golgi and late endosomal compartments due to atypical dilysine motifs in the cytoplasmic tail, and are cleaved into stable soluble forms in late endosomes. CD1e does not transit through the plasma membrane.\",\n      \"method\": \"Transfection of isoform constructs, subcellular fractionation, immunofluorescence, biochemical characterization\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (transfection, fractionation, imaging) with functional characterization of isoforms\",\n      \"pmids\": [\"10948205\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Soluble CD1e is required for efficient processing of mycobacterial hexamannosylated phosphatidyl-myo-inositols (PIM6) by lysosomal alpha-mannosidase; recombinant CD1e binds glycolipids and assists their digestion, acting as a glycolipid-editing factor that expands the repertoire of CD1b-presented antigens.\",\n      \"method\": \"T cell stimulation assays with CD1b-restricted T cells, recombinant CD1e glycolipid-binding assays, in vitro digestion assays with lysosomal alpha-mannosidase\",\n      \"journal\": \"Science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — in vitro reconstitution of processing activity with recombinant protein, functional T cell readout; highly cited foundational paper\",\n      \"pmids\": [\"16311334\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"During dendritic cell maturation, CD1e is redistributed from the Golgi to late endosomes/lysosomes via sorting endosomes without passing through the plasma membrane; in mature DCs it localizes almost exclusively to lysosomes, where it is cleaved into a soluble form.\",\n      \"method\": \"Live-cell fluorescence microscopy, immunoelectron microscopy, pulse-chase biosynthesis experiments in immature and maturing DCs\",\n      \"journal\": \"Traffic\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct localization by multiple imaging methods (light and electron microscopy) with functional context of maturation-linked redistribution\",\n      \"pmids\": [\"15752135\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"The cytoplasmic tail of CD1e controls its intracellular trafficking: the C-terminal half mediates Golgi accumulation, and monoubiquitination of cytoplasmic lysines triggers exit from Golgi compartments and transport to lysosomes. Replacing all eight cytoplasmic lysines with arginines causes accumulation in TGN46+ compartments and surface expression; fusion of this mutant to ubiquitin restores normal lysosomal trafficking kinetics.\",\n      \"method\": \"Chimeric molecule expression, lysine-to-arginine mutagenesis, ubiquitin fusion constructs, immunofluorescence microscopy in transfected cells and DCs\",\n      \"journal\": \"Traffic\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — mutagenesis combined with rescue experiments and multiple imaging readouts establishing mechanistic role of ubiquitination\",\n      \"pmids\": [\"18208508\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"A naturally occurring CD1e variant with proline at position 194 (allele 4) fails to assist PIM6 presentation to CD1b-restricted T cells due to inefficient assembly and poor transport to late endosomal compartments.\",\n      \"method\": \"T cell stimulation assays, subcellular localization analysis of allelic variants in transfected cells and DCs\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — functional assay (T cell stimulation) combined with mechanistic explanation (assembly/transport defect) for a defined mutant\",\n      \"pmids\": [\"18325888\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"CD1e facilitates rapid formation of CD1-lipid complexes and accelerates their turnover, positively or negatively modulating lipid antigen presentation by CD1b, CD1c, and CD1d. In CD1e transgenic mouse antigen-presenting cells, lipid complexes assemble more efficiently and show faster turnover than in WT cells.\",\n      \"method\": \"T cell stimulation assays with CD1b/c/d-restricted T cells, CD1e transgenic mouse APCs, kinetic lipid-loading assays\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal assays (human cell, transgenic mouse, kinetic loading), replicated across different CD1 isoforms\",\n      \"pmids\": [\"21844346\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Crystal structure of human CD1e at 2.90-Å resolution reveals a groove with a wider portal (2 Å larger spacing between α1 and α2 helices) compared to other CD1 proteins, with no stable endogenous ligand density despite confirmed lipid binding by native mass spectrometry. CD1e mediates lipid transfer to CD1b and displacement of lipids from stable CD1b-antigen complexes in vitro, and lipid association/dissociation rates are considerably faster than with CD1b.\",\n      \"method\": \"X-ray crystallography, native mass spectrometry, in vitro lipid transfer assays, kinetic lipid association/dissociation measurements\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure with functional validation by native MS and in vitro lipid transfer reconstitution\",\n      \"pmids\": [\"21788486\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"CD1e acts as a lipid transfer protein that selectively assists alpha-mannosidase-dependent digestion of PIM6 according to degree of acylation, and transfers only diacylated PIM from donor liposomes to acceptor liposomes and from membranes to CD1b.\",\n      \"method\": \"In vitro digestion assays with defined PIM species of varying acylation, liposome-to-liposome and membrane-to-CD1b lipid transfer assays with recombinant CD1e\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstituted in vitro with defined substrates, demonstrating acylation-selective transfer activity\",\n      \"pmids\": [\"22782895\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"LAPTM5 is a molecular partner of CD1e; the two proteins colocalize in trans-Golgi and late endosomal compartments, and their association occurs under physiological conditions and increases when lysosomal acidification is inhibited by bafilomycin. However, LAPTM5 does not control CD1e ubiquitination or generation of the soluble lysosomal CD1e form.\",\n      \"method\": \"Co-immunoprecipitation, colocalization by fluorescence microscopy, bafilomycin treatment, mass spectrometry identification of binding partner\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — partner identified by MS and confirmed by Co-IP/colocalization, but functional consequence of interaction not fully established\",\n      \"pmids\": [\"22880058\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Rhesus macaque CD1e shares the same intracellular localization and biochemical properties as human CD1e (Golgi in immature DCs, late endosomal cleavage to soluble form), demonstrating conservation of the unique intracellular trafficking pathway across primate evolution.\",\n      \"method\": \"Immunofluorescence microscopy and biochemical characterization of simian CD1e in dendritic cells\",\n      \"journal\": \"Immunogenetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct localization and biochemical characterization in a primate ortholog confirming conserved mechanism\",\n      \"pmids\": [\"12671734\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"CD1e and B2M (beta-2-microglobulin) interact directly, as demonstrated by surface plasmon resonance using cell-free synthesized proteins.\",\n      \"method\": \"Cell-free protein synthesis, Ni2+ affinity purification, surface plasmon resonance (SPR)\",\n      \"journal\": \"Protein expression and purification\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct biophysical binding assay with purified proteins, but single method and limited mechanistic follow-up\",\n      \"pmids\": [\"36460227\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"CD1e is a unique intracellular CD1 family member expressed in dendritic cells that, after monoubiquitination-driven exit from the Golgi, traffics to lysosomes where it is cleaved into a soluble form; in lysosomes, soluble CD1e acts as a lipid-editing/transfer protein that binds glycolipids with fast on/off kinetics (facilitated by its unusually wide groove), selectively assists lysosomal alpha-mannosidase digestion of complex mycobacterial glycolipids (e.g., PIM6) in an acylation-dependent manner, and transfers lipid antigens to CD1b and other CD1 molecules, thereby modulating the repertoire and kinetics of CD1-restricted T cell responses.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"CD1e is a unique intracellular member of the CD1 lipid antigen-presenting family that functions as a lysosomal lipid-editing and transfer protein in dendritic cells, shaping the repertoire of glycolipid antigens presented by CD1b, CD1c, and CD1d molecules. Synthesized in the Golgi, CD1e traffics directly to lysosomes without transiting the plasma membrane; this routing is controlled by monoubiquitination of cytoplasmic tail lysines, and upon arrival in late endosomes/lysosomes, CD1e is proteolytically cleaved into a stable soluble form [PMID:10948205, PMID:15752135, PMID:18208508]. Soluble CD1e binds glycolipids with fast on/off kinetics — enabled by an unusually wide antigen-binding groove — and selectively assists lysosomal α-mannosidase in digesting complex mycobacterial phosphatidyl-myo-inositol mannosides (PIM6) in an acylation-dependent manner, while also transferring processed lipid antigens to CD1b [PMID:16311334, PMID:21788486, PMID:22782895]. By accelerating both CD1–lipid complex formation and turnover, CD1e positively or negatively modulates lipid antigen presentation across multiple CD1 isoforms, thereby tuning CD1-restricted T cell responses [PMID:21844346].\",\n  \"teleology\": [\n    {\n      \"year\": 2000,\n      \"claim\": \"Establishing that CD1e is an exclusively intracellular CD1 molecule answered the question of why no surface CD1e expression had been detected: alternatively spliced isoforms with three α-domains associate with β2-microglobulin but accumulate in late Golgi and late endosomes via atypical dilysine tail motifs, where they are cleaved into soluble forms, never reaching the plasma membrane.\",\n      \"evidence\": \"Transfection of isoform constructs, subcellular fractionation, immunofluorescence, and biochemical analysis in dendritic cells\",\n      \"pmids\": [\"10948205\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Protease responsible for endosomal cleavage to soluble form not identified\",\n        \"Function of alternatively spliced isoforms lacking full alpha domains unclear\",\n        \"Signal directing Golgi retention versus endosomal transit not fully defined\"\n      ]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Conservation of CD1e's intracellular trafficking and cleavage in rhesus macaque dendritic cells established that this unique non-surface pathway is evolutionarily conserved across primates, strengthening the inference that it serves a selected function.\",\n      \"evidence\": \"Immunofluorescence and biochemical characterization of simian CD1e in dendritic cells\",\n      \"pmids\": [\"12671734\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Functional consequence of conservation not tested (no antigen presentation assay in macaque)\",\n        \"Whether non-primate mammals have a functional CD1e ortholog not addressed\"\n      ]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Two key advances defined the cell biology and function of CD1e: live-cell and immunoelectron microscopy showed that DC maturation triggers CD1e redistribution from Golgi to lysosomes via sorting endosomes, and in vitro reconstitution demonstrated that soluble CD1e is required for lysosomal α-mannosidase to efficiently process PIM6, thereby expanding the CD1b-presented antigen repertoire.\",\n      \"evidence\": \"Live-cell fluorescence and immunoelectron microscopy of immature/mature DCs; recombinant CD1e glycolipid-binding assays and in vitro digestion assays with CD1b-restricted T cell readout\",\n      \"pmids\": [\"15752135\", \"16311334\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Mechanism by which CD1e facilitates α-mannosidase activity not resolved at molecular level\",\n        \"Whether CD1e assists processing of non-PIM glycolipids not tested\",\n        \"In vivo relevance in intact organism not demonstrated\"\n      ]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"The molecular mechanism governing CD1e's unusual Golgi-to-lysosome trafficking was resolved: monoubiquitination of cytoplasmic tail lysines triggers exit from the Golgi, as shown by lysine-to-arginine mutagenesis causing Golgi retention and surface expression, rescued by ubiquitin fusion. A natural CD1e variant (Pro194) that fails to assemble properly and cannot reach lysosomes is functionally inactive in PIM6 presentation.\",\n      \"evidence\": \"Mutagenesis, ubiquitin-fusion rescue constructs, immunofluorescence in DCs; T cell stimulation assays and localization analysis of allelic variants\",\n      \"pmids\": [\"18208508\", \"18325888\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"E3 ubiquitin ligase responsible for CD1e monoubiquitination not identified\",\n        \"Whether the Pro194 variant has clinical immunological consequences in carriers unknown\",\n        \"Mechanism of CD1e cleavage in late endosomes still undefined\"\n      ]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Structural and functional analyses revealed how CD1e acts as a lipid transfer protein: its crystal structure showed an unusually wide groove portal (2 Å wider than other CD1 proteins) with no stably bound endogenous lipid, and kinetic assays demonstrated fast lipid association/dissociation enabling CD1e to transfer lipids to CD1b and displace lipids from stable CD1b complexes. Transgenic mouse studies showed CD1e accelerates both formation and turnover of CD1b/c/d–lipid complexes, positively or negatively modulating antigen presentation.\",\n      \"evidence\": \"X-ray crystallography at 2.90 Å, native mass spectrometry, in vitro lipid transfer assays, CD1e transgenic mouse APC functional assays with CD1b/c/d-restricted T cells\",\n      \"pmids\": [\"21788486\", \"21844346\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Structural basis for selectivity toward specific lipid substrates not defined\",\n        \"Whether CD1e interacts directly with other CD1 molecules during transfer not established\",\n        \"Negative modulation mechanism (accelerated turnover) not fully dissected\"\n      ]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"The lipid transfer specificity of CD1e was refined: it selectively assists α-mannosidase digestion and membrane-to-CD1b transfer of diacylated but not higher-acylated PIM species, establishing acylation state as a selectivity determinant. Separately, LAPTM5 was identified as a molecular partner of CD1e in the Golgi and late endosomes.\",\n      \"evidence\": \"In vitro digestion and liposome transfer assays with defined PIM species of varying acylation; Co-IP, colocalization, and MS identification of LAPTM5 interaction\",\n      \"pmids\": [\"22782895\", \"22880058\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Functional role of LAPTM5–CD1e interaction remains undefined (LAPTM5 does not control CD1e ubiquitination or cleavage)\",\n        \"Structural basis for acylation-dependent selectivity not determined\",\n        \"Whether CD1e transfers non-PIM lipid antigens with similar selectivity not systematically tested\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include the identity of the protease that cleaves CD1e in lysosomes, the E3 ligase mediating its monoubiquitination, whether CD1e directly contacts other CD1 molecules during lipid transfer, and the in vivo immunological consequences of CD1e deficiency or polymorphism in infection or autoimmunity.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"Protease responsible for lysosomal cleavage of CD1e unknown\",\n        \"E3 ubiquitin ligase for CD1e monoubiquitination not identified\",\n        \"No in vivo loss-of-function model in an organism with a complete CD1 system\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0008289\", \"supporting_discovery_ids\": [1, 6, 7]},\n      {\"term_id\": \"GO:0140104\", \"supporting_discovery_ids\": [6, 7]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005794\", \"supporting_discovery_ids\": [0, 2, 3]},\n      {\"term_id\": \"GO:0005764\", \"supporting_discovery_ids\": [0, 1, 2, 3, 5]},\n      {\"term_id\": \"GO:0005768\", \"supporting_discovery_ids\": [0, 2]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [1, 5, 7]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"B2M\",\n      \"CD1B\",\n      \"LAPTM5\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}