{"gene":"RAET1E","run_date":"2026-04-28T19:45:45","timeline":{"discoveries":[{"year":2003,"finding":"ULBP4 (RAET1E) is a functional ligand for the NKG2D/DAP10 receptor complex on human NK cells; transduction of ULBP4 into EL4 cells confers NKG2D binding and mediates increased NK cytotoxic activity. Unlike other ULBPs (GPI-linked), ULBP4 contains predicted transmembrane and cytoplasmic domains.","method":"Recombinant NKG2D binding assay; transduction of ULBP4 into EL4 cells followed by NK cytotoxicity assay","journal":"Biochemical and biophysical research communications","confidence":"High","confidence_rationale":"Tier 2 — functional receptor-ligand interaction established by binding assay and cytotoxicity assay, foundational paper with 158 citations","pmids":["12732206"],"is_preprint":false},{"year":2003,"finding":"Letal (RAET1E/ULBP4) is the first human transmembrane NKG2D ligand lacking an immunoglobulin-like alpha-3 ectodomain; engagement of Letal simultaneously with TCR stimulation induces CD8+ T cell proliferation, IL-2 and IFN-γ secretion, and NK/CD8+ cell-mediated killing of cancer cells.","method":"In vitro T cell stimulation assay, NK/CD8+ cytotoxicity assay, mRNA expression analysis","journal":"Cancer biology & therapy","confidence":"Medium","confidence_rationale":"Tier 2 — functional assays with defined cellular phenotype; moderate evidence from single lab","pmids":["14508119"],"is_preprint":false},{"year":2004,"finding":"Letal (RAET1E/ULBP4) engagement induces costimulatory effects in CD8+CD28- tumor-infiltrating lymphocytes, increases Glut-1 expression and glucose uptake, protects CD8+ T cells from cisplatin-induced killing, and downregulates Fas expression rendering cells resistant to FasL-induced apoptosis.","method":"Ex vivo stimulation of tumor-infiltrating lymphocytes, glucose uptake assay, Fas/FasL apoptosis assay, flow cytometry","journal":"Cancer research","confidence":"Medium","confidence_rationale":"Tier 2 — multiple functional readouts from ex vivo experiments in a single study","pmids":["15026360"],"is_preprint":false},{"year":2007,"finding":"RAET1E produces a soluble 35-kDa isoform (RAET1E2) lacking the transmembrane region via alternative splicing in tumor cells. Soluble RAET1E2 downregulates surface NKG2D expression on NK-92 cells and markedly reduces NK cytotoxicity toward tumor cells, constituting an immune escape mechanism.","method":"RT-PCR identification of alternatively spliced transcript; recombinant RAET1E2 protein treatment of NK-92 cells; flow cytometry for NKG2D expression; NK cytotoxicity assay; gene transfection into COS-7 cells","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1-2 — multiple orthogonal methods (molecular cloning, recombinant protein, functional assays) in a single study; 67 citations","pmids":["17470428"],"is_preprint":false},{"year":2009,"finding":"ULBP4 (RAET1E) binds directly to TCRγ9/δ2 and activates γδ T cells through both TCRγδ and NKG2D receptors; immobilized soluble ULBP4 induces proliferation of Vδ2+ T cells, Th1 cytokine secretion, and cytolytic activity toward ULBP4-transfected targets.","method":"Binding assay with soluble chimeric TCRγ9/δ2 protein; TCR-negative Jurkat cell transfection with TCRγ9/δ2; blocking antibody epistasis; T cell proliferation and cytotoxicity assays","journal":"Blood","confidence":"High","confidence_rationale":"Tier 1-2 — direct binding demonstrated with recombinant chimeric protein, functional validation by receptor transfection and blocking antibodies; 141 citations","pmids":["19436053"],"is_preprint":false},{"year":2013,"finding":"Mouse Raet1e functions as an atherosclerosis-modifying gene; aortic overexpression of Raet1e in F1.Apoe−/− mice decreased atherosclerosis, placing Raet1e as the causal gene underlying the Ath11 10b locus. Raet1e is expressed in lesional aortic endothelial cells and macrophage-rich regions.","method":"Subcongenic mapping; transgene-induced aortic overexpression; promoter reporter luciferase assay; aortic gene expression comparison between congenic strains","journal":"Circulation research","confidence":"High","confidence_rationale":"Tier 2 — genetic epistasis via subcongenic analysis confirmed by transgenic rescue experiment and promoter functional assay","pmids":["23948654"],"is_preprint":false},{"year":2018,"finding":"Cellular processing of ULBP4 gives rise to mature ULBP4 glycoproteins distinct from previous reports, and ULBP4 undergoes proteolytic release generating soluble forms; ULBP4 is distinct from other ULBP family members in its processing and membrane anchoring via a transmembrane domain rather than GPI linkage.","method":"Biochemical characterization of cellular processing; proteolytic shedding assay; glycoprotein analysis","journal":"Frontiers in immunology","confidence":"Medium","confidence_rationale":"Tier 2 — experimental evidence for proteolytic release and atypical processing; single lab","pmids":["29651291"],"is_preprint":false},{"year":2019,"finding":"ULBP-4 is constitutively expressed on monocytes and this expression regulates NKG2D expression levels on NK cells.","method":"Flow cytometry of primary monocytes and NK cells; co-culture experiments","journal":"Blood advances","confidence":"Low","confidence_rationale":"Tier 3 — single study, single lab; subsequent paper disputed monocyte ULBP4 expression entirely","pmids":["31097432"],"is_preprint":false},{"year":2021,"finding":"Soluble ULBP4 enhances GM-CSF and IFN-γ production by CD8+ T lymphocytes and increases their motility, favoring kinapse-like behavior when cultured with human astrocytes; a shed 25-kDa form is elevated in CSF of female MS patients.","method":"In vitro treatment of primary human CD8+ T cells with soluble ULBP4; cytokine measurement; live cell motility assay with astrocyte co-culture; Western blot of CSF","journal":"Neurology(R) neuroimmunology & neuroinflammation","confidence":"Medium","confidence_rationale":"Tier 2 — multiple functional readouts with primary human cells; single lab","pmids":["34873031"],"is_preprint":false},{"year":2021,"finding":"ULBP4 is NOT expressed by human peripheral blood monocytes or PAMP-activated monocytes; a commercial antibody previously used to detect ULBP4 on monocytes has non-ULBP4-specific binding activity, invalidating earlier reports of constitutive monocyte ULBP4 expression.","method":"RT-PCR for ULBP4 transcripts; flow cytometry with validated antibodies; antibody specificity controls in ULBP4-knockout cells","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 — antibody validation with knockout controls, multiple methods; single lab contradicting a prior claim","pmids":["33556116"],"is_preprint":false}],"current_model":"RAET1E (ULBP4) is a transmembrane MHC class I-related glycoprotein that serves as a stress-induced ligand for the NKG2D/DAP10 activating receptor on NK cells, CD8+ T cells, and γδ T cells, as well as a direct ligand for TCRγ9/δ2; it can be alternatively spliced to produce a soluble isoform (RAET1E2) that downregulates NKG2D on NK cells and suppresses anti-tumor cytotoxicity, and is proteolytically shed from the cell surface, while in mouse models it functions as an atheroprotective gene expressed in aortic endothelial cells and macrophages."},"narrative":{"teleology":[{"year":2003,"claim":"Identification of RAET1E as a functional NKG2D ligand established that the ULBP family includes a transmembrane member capable of activating NK cell cytotoxicity, resolving whether additional human NKG2D ligands existed beyond the known GPI-anchored ULBPs and MICs.","evidence":"Recombinant NKG2D binding assay and NK cytotoxicity assay using ULBP4-transduced EL4 cells","pmids":["12732206","14508119"],"confidence":"High","gaps":["Crystal structure of ULBP4–NKG2D complex not determined","Physiological regulation of RAET1E surface expression undefined","Relative contribution of NKG2D versus other receptors in vivo unknown"]},{"year":2004,"claim":"Demonstration that RAET1E costimulates CD8+CD28− tumor-infiltrating lymphocytes—enhancing glucose uptake, protecting from cisplatin-induced death, and downregulating Fas—revealed a metabolic and survival-reprogramming function beyond simple cytotoxicity activation.","evidence":"Ex vivo stimulation of TILs with Letal/ULBP4; glucose uptake, Fas expression, and apoptosis assays","pmids":["15026360"],"confidence":"Medium","gaps":["Signaling pathway linking NKG2D engagement to Glut-1 upregulation not defined","In vivo relevance of TIL costimulation by ULBP4 not tested","Whether other NKG2D ligands produce identical metabolic effects unclear"]},{"year":2007,"claim":"Discovery of a soluble splice isoform (RAET1E2) that downregulates NKG2D and suppresses NK cytotoxicity identified a tumor immune-evasion mechanism intrinsic to the RAET1E locus, answering how tumors might exploit NKG2D ligand biology without requiring shedding enzymes.","evidence":"RT-PCR cloning of RAET1E2 transcript; recombinant soluble RAET1E2 treatment of NK-92 cells; flow cytometry and cytotoxicity assays","pmids":["17470428"],"confidence":"High","gaps":["Prevalence of RAET1E2 splice variant across tumor types not systematically assessed","Mechanism of NKG2D internalization/degradation upon soluble ULBP4 binding not elucidated","Whether RAET1E2 also engages TCRγδ unknown"]},{"year":2009,"claim":"Demonstration that ULBP4 directly binds TCRγ9/δ2 and activates γδ T cells through both TCR and NKG2D established RAET1E as a dual-receptor ligand, expanding its immunological function beyond the NKG2D axis.","evidence":"Binding assay with soluble chimeric TCRγ9/δ2; Jurkat cell transfection with TCRγδ; blocking antibody epistasis; Vδ2+ T cell proliferation and cytotoxicity assays","pmids":["19436053"],"confidence":"High","gaps":["Structural basis of ULBP4–TCRγ9/δ2 interaction unknown","Relative affinity of ULBP4 for NKG2D versus TCRγδ not quantified","In vivo contribution of γδ T cell activation by ULBP4 not demonstrated"]},{"year":2013,"claim":"Genetic mapping and transgenic rescue in mice identified Raet1e as the causal atheroprotective gene at the Ath11 10b locus, revealing an unexpected cardiovascular role for an NKG2D ligand beyond cancer immunosurveillance.","evidence":"Subcongenic mapping in Apoe−/− mice; transgene-induced aortic Raet1e overexpression; promoter luciferase assay","pmids":["23948654"],"confidence":"High","gaps":["Mechanism by which Raet1e reduces atherosclerosis (NKG2D-dependent or independent) not established","Whether human RAET1E has analogous vascular expression and function unknown","Immune cell types mediating the atheroprotective effect not identified"]},{"year":2018,"claim":"Biochemical characterization showed that mature ULBP4 glycoprotein undergoes proteolytic shedding from the cell surface, establishing an additional post-translational route—besides alternative splicing—for generating soluble ULBP4 that could modulate NKG2D signaling.","evidence":"Biochemical glycoprotein analysis and proteolytic shedding assay of ULBP4-expressing cells","pmids":["29651291"],"confidence":"Medium","gaps":["Identity of the protease(s) responsible for ULBP4 shedding not determined","Functional comparison of shed versus splice-derived soluble ULBP4 not performed","In vivo serum levels and clearance of shed ULBP4 not measured"]},{"year":2021,"claim":"Soluble ULBP4 was shown to stimulate CD8+ T cell cytokine production and motility in the CNS context, and a shed 25-kDa form was elevated in CSF of female MS patients, linking RAET1E to neuroinflammation; simultaneously, the prior report of constitutive ULBP4 expression on monocytes was refuted by antibody validation with knockout controls.","evidence":"Primary CD8+ T cell functional assays with soluble ULBP4; astrocyte co-culture motility imaging; CSF Western blot from MS patients; RT-PCR and flow cytometry with ULBP4-knockout validation cells","pmids":["34873031","33556116"],"confidence":"Medium","gaps":["Source of shed ULBP4 in the CNS not identified","Whether elevated CSF ULBP4 is causally related to MS pathology versus a bystander marker unclear","Antibody reagent issues highlight need for independent validation of ULBP4 tissue expression reports"]},{"year":null,"claim":"Key unresolved questions include the structural basis of ULBP4 recognition by both NKG2D and TCRγδ, the identity of sheddases acting on ULBP4, the signaling pathways downstream of ULBP4-mediated T cell costimulation, and whether the atheroprotective function of Raet1e translates to human cardiovascular biology.","evidence":"","pmids":[],"confidence":"Low","gaps":["No crystal structure of ULBP4 alone or in complex with NKG2D or TCRγδ","Sheddase identity unknown","Human vascular expression and cardiovascular relevance not established"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0048018","term_label":"receptor ligand activity","supporting_discovery_ids":[0,1,4]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[3,8]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[0,1,6]},{"term_id":"GO:0005576","term_label":"extracellular region","supporting_discovery_ids":[3,6,8]}],"pathway":[{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[0,1,2,4]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[3,5]}],"complexes":[],"partners":["KLRK1","HCST","TRDV2","TRGV9"],"other_free_text":[]},"mechanistic_narrative":"RAET1E (ULBP4) is a stress-induced, transmembrane MHC class I-related glycoprotein that activates innate and adaptive immune effector cells by engaging the NKG2D/DAP10 activating receptor on NK cells and CD8+ T cells, and by directly binding TCRγ9/δ2 on γδ T cells [PMID:12732206, PMID:19436053]. Unlike other ULBP family members that are GPI-anchored, RAET1E possesses a transmembrane domain and undergoes proteolytic shedding to generate soluble forms; an alternatively spliced soluble isoform (RAET1E2) downregulates NKG2D on NK cells and suppresses antitumor cytotoxicity, constituting an immune evasion mechanism [PMID:17470428, PMID:29651291]. RAET1E engagement costimulates CD8+CD28− tumor-infiltrating lymphocytes by increasing glucose uptake and conferring resistance to Fas-mediated and cisplatin-induced apoptosis [PMID:15026360]. In mouse models, the ortholog Raet1e functions as an atheroprotective gene expressed in aortic endothelial cells and macrophages, and transgenic overexpression reduces atherosclerosis in Apoe−/− mice [PMID:23948654]."},"prefetch_data":{"uniprot":{"accession":"Q8TD07","full_name":"Retinoic acid early transcript 1E","aliases":["Lymphocyte effector toxicity activation ligand","NKG2D ligand 4","N2DL-4","NKG2DL4","RAE-1-like transcript 4","UL16-binding protein 4"],"length_aa":263,"mass_kda":30.1,"function":"Binds and activates the KLRK1/NKG2D receptor, mediating natural killer cell cytotoxicity","subcellular_location":"Secreted","url":"https://www.uniprot.org/uniprotkb/Q8TD07/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/RAET1E","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/RAET1E","total_profiled":1310},"omim":[{"mim_id":"611817","title":"KILLER CELL LECTIN-LIKE RECEPTOR, SUBFAMILY K, MEMBER 1; KLRK1","url":"https://www.omim.org/entry/611817"},{"mim_id":"609244","title":"RETINOIC ACID EARLY TRANSCRIPT 1G; RAET1G","url":"https://www.omim.org/entry/609244"},{"mim_id":"609243","title":"RETINOIC ACID EARLY TRANSCRIPT 1E; RAET1E","url":"https://www.omim.org/entry/609243"},{"mim_id":"605699","title":"UL16-BINDING PROTEIN 3; ULBP3","url":"https://www.omim.org/entry/605699"},{"mim_id":"605698","title":"UL16-BINDING PROTEIN 2; ULBP2","url":"https://www.omim.org/entry/605698"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Focal adhesion sites","reliability":"Supported"},{"location":"Cytosol","reliability":"Additional"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in some","driving_tissues":[{"tissue":"cervix","ntpm":14.5},{"tissue":"esophagus","ntpm":37.6},{"tissue":"vagina","ntpm":18.1}],"url":"https://www.proteinatlas.org/search/RAET1E"},"hgnc":{"alias_symbol":["LETAL","bA350J20.7","ULBP4"],"prev_symbol":[]},"alphafold":{"accession":"Q8TD07","domains":[{"cath_id":"3.30.500.10","chopping":"50-202","consensus_level":"high","plddt":92.0922,"start":50,"end":202}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q8TD07","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q8TD07-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q8TD07-F1-predicted_aligned_error_v6.png","plddt_mean":81.62},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=RAET1E","jax_strain_url":"https://www.jax.org/strain/search?query=RAET1E"},"sequence":{"accession":"Q8TD07","fasta_url":"https://rest.uniprot.org/uniprotkb/Q8TD07.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q8TD07/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q8TD07"}},"corpus_meta":[{"pmid":"12732206","id":"PMC_12732206","title":"ULBP4 is a novel ligand for human NKG2D.","date":"2003","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/12732206","citation_count":158,"is_preprint":false},{"pmid":"19436053","id":"PMC_19436053","title":"The NKG2D ligand ULBP4 binds to TCRgamma9/delta2 and induces cytotoxicity to tumor cells through both TCRgammadelta and NKG2D.","date":"2009","source":"Blood","url":"https://pubmed.ncbi.nlm.nih.gov/19436053","citation_count":141,"is_preprint":false},{"pmid":"17470428","id":"PMC_17470428","title":"RAET1E2, a soluble isoform of the UL16-binding protein RAET1E produced by tumor cells, inhibits NKG2D-mediated NK cytotoxicity.","date":"2007","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/17470428","citation_count":67,"is_preprint":false},{"pmid":"15026360","id":"PMC_15026360","title":"Ovarian carcinoma expresses the NKG2D ligand Letal and promotes the survival and expansion of CD28- antitumor T cells.","date":"2004","source":"Cancer research","url":"https://pubmed.ncbi.nlm.nih.gov/15026360","citation_count":61,"is_preprint":false},{"pmid":"14508119","id":"PMC_14508119","title":"Letal, A tumor-associated NKG2D immunoreceptor ligand, induces activation and expansion of effector immune cells.","date":"2003","source":"Cancer biology & therapy","url":"https://pubmed.ncbi.nlm.nih.gov/14508119","citation_count":47,"is_preprint":false},{"pmid":"29651291","id":"PMC_29651291","title":"Cutting an NKG2D Ligand Short: Cellular Processing of the Peculiar Human NKG2D Ligand ULBP4.","date":"2018","source":"Frontiers in immunology","url":"https://pubmed.ncbi.nlm.nih.gov/29651291","citation_count":20,"is_preprint":false},{"pmid":"23948654","id":"PMC_23948654","title":"Altered expression of Raet1e, a major histocompatibility complex class 1-like molecule, underlies the atherosclerosis modifier locus Ath11 10b.","date":"2013","source":"Circulation research","url":"https://pubmed.ncbi.nlm.nih.gov/23948654","citation_count":20,"is_preprint":false},{"pmid":"11412876","id":"PMC_11412876","title":"Inflammatory polyradiculoneuropathy with spinal cord involvement and lethal [correction of letal] outcome after hepatitis B vaccination.","date":"2001","source":"Journal of the neurological sciences","url":"https://pubmed.ncbi.nlm.nih.gov/11412876","citation_count":16,"is_preprint":false},{"pmid":"34873031","id":"PMC_34873031","title":"Stress Signal ULBP4, an NKG2D Ligand, Is Upregulated in Multiple Sclerosis and Shapes CD8+ T-Cell Behaviors.","date":"2021","source":"Neurology(R) neuroimmunology & neuroinflammation","url":"https://pubmed.ncbi.nlm.nih.gov/34873031","citation_count":13,"is_preprint":false},{"pmid":"26519211","id":"PMC_26519211","title":"Characterization of 5' promoter and exon 1-3 polymorphism of the RAET1E gene.","date":"2015","source":"Human immunology","url":"https://pubmed.ncbi.nlm.nih.gov/26519211","citation_count":8,"is_preprint":false},{"pmid":"22845659","id":"PMC_22845659","title":"Three novel allelic variants of the RAET1E/ULBP4 gene in humans.","date":"2012","source":"Tissue antigens","url":"https://pubmed.ncbi.nlm.nih.gov/22845659","citation_count":8,"is_preprint":false},{"pmid":"31097432","id":"PMC_31097432","title":"Constitutive expression of ULBP-4 on monocytes regulates NK cell NKG2D expression.","date":"2019","source":"Blood advances","url":"https://pubmed.ncbi.nlm.nih.gov/31097432","citation_count":7,"is_preprint":false},{"pmid":"21553130","id":"PMC_21553130","title":"ULBP4/RAET1E is highly polymorphic in the Old World monkey.","date":"2011","source":"Immunogenetics","url":"https://pubmed.ncbi.nlm.nih.gov/21553130","citation_count":7,"is_preprint":false},{"pmid":"24849594","id":"PMC_24849594","title":"Further polymorphism of the RAET1E/ULBP4 gene in humans.","date":"2014","source":"Tissue 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Journal of legal medicine","url":"https://pubmed.ncbi.nlm.nih.gov/883421","citation_count":1,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":9986,"output_tokens":2454,"usd":0.033384},"stage2":{"model":"claude-opus-4-6","input_tokens":5818,"output_tokens":2544,"usd":0.139035},"total_usd":0.172419,"stage1_batch_id":"msgbatch_01SUR8NDzVrNmyszWyJeCct7","stage2_batch_id":"msgbatch_01G7Yfutko3cDWzejrwH5AMx","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2003,\n      \"finding\": \"ULBP4 (RAET1E) is a functional ligand for the NKG2D/DAP10 receptor complex on human NK cells; transduction of ULBP4 into EL4 cells confers NKG2D binding and mediates increased NK cytotoxic activity. Unlike other ULBPs (GPI-linked), ULBP4 contains predicted transmembrane and cytoplasmic domains.\",\n      \"method\": \"Recombinant NKG2D binding assay; transduction of ULBP4 into EL4 cells followed by NK cytotoxicity assay\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — functional receptor-ligand interaction established by binding assay and cytotoxicity assay, foundational paper with 158 citations\",\n      \"pmids\": [\"12732206\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Letal (RAET1E/ULBP4) is the first human transmembrane NKG2D ligand lacking an immunoglobulin-like alpha-3 ectodomain; engagement of Letal simultaneously with TCR stimulation induces CD8+ T cell proliferation, IL-2 and IFN-γ secretion, and NK/CD8+ cell-mediated killing of cancer cells.\",\n      \"method\": \"In vitro T cell stimulation assay, NK/CD8+ cytotoxicity assay, mRNA expression analysis\",\n      \"journal\": \"Cancer biology & therapy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — functional assays with defined cellular phenotype; moderate evidence from single lab\",\n      \"pmids\": [\"14508119\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Letal (RAET1E/ULBP4) engagement induces costimulatory effects in CD8+CD28- tumor-infiltrating lymphocytes, increases Glut-1 expression and glucose uptake, protects CD8+ T cells from cisplatin-induced killing, and downregulates Fas expression rendering cells resistant to FasL-induced apoptosis.\",\n      \"method\": \"Ex vivo stimulation of tumor-infiltrating lymphocytes, glucose uptake assay, Fas/FasL apoptosis assay, flow cytometry\",\n      \"journal\": \"Cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple functional readouts from ex vivo experiments in a single study\",\n      \"pmids\": [\"15026360\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"RAET1E produces a soluble 35-kDa isoform (RAET1E2) lacking the transmembrane region via alternative splicing in tumor cells. Soluble RAET1E2 downregulates surface NKG2D expression on NK-92 cells and markedly reduces NK cytotoxicity toward tumor cells, constituting an immune escape mechanism.\",\n      \"method\": \"RT-PCR identification of alternatively spliced transcript; recombinant RAET1E2 protein treatment of NK-92 cells; flow cytometry for NKG2D expression; NK cytotoxicity assay; gene transfection into COS-7 cells\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal methods (molecular cloning, recombinant protein, functional assays) in a single study; 67 citations\",\n      \"pmids\": [\"17470428\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"ULBP4 (RAET1E) binds directly to TCRγ9/δ2 and activates γδ T cells through both TCRγδ and NKG2D receptors; immobilized soluble ULBP4 induces proliferation of Vδ2+ T cells, Th1 cytokine secretion, and cytolytic activity toward ULBP4-transfected targets.\",\n      \"method\": \"Binding assay with soluble chimeric TCRγ9/δ2 protein; TCR-negative Jurkat cell transfection with TCRγ9/δ2; blocking antibody epistasis; T cell proliferation and cytotoxicity assays\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — direct binding demonstrated with recombinant chimeric protein, functional validation by receptor transfection and blocking antibodies; 141 citations\",\n      \"pmids\": [\"19436053\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Mouse Raet1e functions as an atherosclerosis-modifying gene; aortic overexpression of Raet1e in F1.Apoe−/− mice decreased atherosclerosis, placing Raet1e as the causal gene underlying the Ath11 10b locus. Raet1e is expressed in lesional aortic endothelial cells and macrophage-rich regions.\",\n      \"method\": \"Subcongenic mapping; transgene-induced aortic overexpression; promoter reporter luciferase assay; aortic gene expression comparison between congenic strains\",\n      \"journal\": \"Circulation research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis via subcongenic analysis confirmed by transgenic rescue experiment and promoter functional assay\",\n      \"pmids\": [\"23948654\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Cellular processing of ULBP4 gives rise to mature ULBP4 glycoproteins distinct from previous reports, and ULBP4 undergoes proteolytic release generating soluble forms; ULBP4 is distinct from other ULBP family members in its processing and membrane anchoring via a transmembrane domain rather than GPI linkage.\",\n      \"method\": \"Biochemical characterization of cellular processing; proteolytic shedding assay; glycoprotein analysis\",\n      \"journal\": \"Frontiers in immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — experimental evidence for proteolytic release and atypical processing; single lab\",\n      \"pmids\": [\"29651291\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"ULBP-4 is constitutively expressed on monocytes and this expression regulates NKG2D expression levels on NK cells.\",\n      \"method\": \"Flow cytometry of primary monocytes and NK cells; co-culture experiments\",\n      \"journal\": \"Blood advances\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — single study, single lab; subsequent paper disputed monocyte ULBP4 expression entirely\",\n      \"pmids\": [\"31097432\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Soluble ULBP4 enhances GM-CSF and IFN-γ production by CD8+ T lymphocytes and increases their motility, favoring kinapse-like behavior when cultured with human astrocytes; a shed 25-kDa form is elevated in CSF of female MS patients.\",\n      \"method\": \"In vitro treatment of primary human CD8+ T cells with soluble ULBP4; cytokine measurement; live cell motility assay with astrocyte co-culture; Western blot of CSF\",\n      \"journal\": \"Neurology(R) neuroimmunology & neuroinflammation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple functional readouts with primary human cells; single lab\",\n      \"pmids\": [\"34873031\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"ULBP4 is NOT expressed by human peripheral blood monocytes or PAMP-activated monocytes; a commercial antibody previously used to detect ULBP4 on monocytes has non-ULBP4-specific binding activity, invalidating earlier reports of constitutive monocyte ULBP4 expression.\",\n      \"method\": \"RT-PCR for ULBP4 transcripts; flow cytometry with validated antibodies; antibody specificity controls in ULBP4-knockout cells\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — antibody validation with knockout controls, multiple methods; single lab contradicting a prior claim\",\n      \"pmids\": [\"33556116\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"RAET1E (ULBP4) is a transmembrane MHC class I-related glycoprotein that serves as a stress-induced ligand for the NKG2D/DAP10 activating receptor on NK cells, CD8+ T cells, and γδ T cells, as well as a direct ligand for TCRγ9/δ2; it can be alternatively spliced to produce a soluble isoform (RAET1E2) that downregulates NKG2D on NK cells and suppresses anti-tumor cytotoxicity, and is proteolytically shed from the cell surface, while in mouse models it functions as an atheroprotective gene expressed in aortic endothelial cells and macrophages.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"RAET1E (ULBP4) is a stress-induced, transmembrane MHC class I-related glycoprotein that activates innate and adaptive immune effector cells by engaging the NKG2D/DAP10 activating receptor on NK cells and CD8+ T cells, and by directly binding TCRγ9/δ2 on γδ T cells [PMID:12732206, PMID:19436053]. Unlike other ULBP family members that are GPI-anchored, RAET1E possesses a transmembrane domain and undergoes proteolytic shedding to generate soluble forms; an alternatively spliced soluble isoform (RAET1E2) downregulates NKG2D on NK cells and suppresses antitumor cytotoxicity, constituting an immune evasion mechanism [PMID:17470428, PMID:29651291]. RAET1E engagement costimulates CD8+CD28− tumor-infiltrating lymphocytes by increasing glucose uptake and conferring resistance to Fas-mediated and cisplatin-induced apoptosis [PMID:15026360]. In mouse models, the ortholog Raet1e functions as an atheroprotective gene expressed in aortic endothelial cells and macrophages, and transgenic overexpression reduces atherosclerosis in Apoe−/− mice [PMID:23948654].\",\n  \"teleology\": [\n    {\n      \"year\": 2003,\n      \"claim\": \"Identification of RAET1E as a functional NKG2D ligand established that the ULBP family includes a transmembrane member capable of activating NK cell cytotoxicity, resolving whether additional human NKG2D ligands existed beyond the known GPI-anchored ULBPs and MICs.\",\n      \"evidence\": \"Recombinant NKG2D binding assay and NK cytotoxicity assay using ULBP4-transduced EL4 cells\",\n      \"pmids\": [\"12732206\", \"14508119\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Crystal structure of ULBP4–NKG2D complex not determined\",\n        \"Physiological regulation of RAET1E surface expression undefined\",\n        \"Relative contribution of NKG2D versus other receptors in vivo unknown\"\n      ]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Demonstration that RAET1E costimulates CD8+CD28− tumor-infiltrating lymphocytes—enhancing glucose uptake, protecting from cisplatin-induced death, and downregulating Fas—revealed a metabolic and survival-reprogramming function beyond simple cytotoxicity activation.\",\n      \"evidence\": \"Ex vivo stimulation of TILs with Letal/ULBP4; glucose uptake, Fas expression, and apoptosis assays\",\n      \"pmids\": [\"15026360\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Signaling pathway linking NKG2D engagement to Glut-1 upregulation not defined\",\n        \"In vivo relevance of TIL costimulation by ULBP4 not tested\",\n        \"Whether other NKG2D ligands produce identical metabolic effects unclear\"\n      ]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Discovery of a soluble splice isoform (RAET1E2) that downregulates NKG2D and suppresses NK cytotoxicity identified a tumor immune-evasion mechanism intrinsic to the RAET1E locus, answering how tumors might exploit NKG2D ligand biology without requiring shedding enzymes.\",\n      \"evidence\": \"RT-PCR cloning of RAET1E2 transcript; recombinant soluble RAET1E2 treatment of NK-92 cells; flow cytometry and cytotoxicity assays\",\n      \"pmids\": [\"17470428\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Prevalence of RAET1E2 splice variant across tumor types not systematically assessed\",\n        \"Mechanism of NKG2D internalization/degradation upon soluble ULBP4 binding not elucidated\",\n        \"Whether RAET1E2 also engages TCRγδ unknown\"\n      ]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Demonstration that ULBP4 directly binds TCRγ9/δ2 and activates γδ T cells through both TCR and NKG2D established RAET1E as a dual-receptor ligand, expanding its immunological function beyond the NKG2D axis.\",\n      \"evidence\": \"Binding assay with soluble chimeric TCRγ9/δ2; Jurkat cell transfection with TCRγδ; blocking antibody epistasis; Vδ2+ T cell proliferation and cytotoxicity assays\",\n      \"pmids\": [\"19436053\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Structural basis of ULBP4–TCRγ9/δ2 interaction unknown\",\n        \"Relative affinity of ULBP4 for NKG2D versus TCRγδ not quantified\",\n        \"In vivo contribution of γδ T cell activation by ULBP4 not demonstrated\"\n      ]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Genetic mapping and transgenic rescue in mice identified Raet1e as the causal atheroprotective gene at the Ath11 10b locus, revealing an unexpected cardiovascular role for an NKG2D ligand beyond cancer immunosurveillance.\",\n      \"evidence\": \"Subcongenic mapping in Apoe−/− mice; transgene-induced aortic Raet1e overexpression; promoter luciferase assay\",\n      \"pmids\": [\"23948654\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Mechanism by which Raet1e reduces atherosclerosis (NKG2D-dependent or independent) not established\",\n        \"Whether human RAET1E has analogous vascular expression and function unknown\",\n        \"Immune cell types mediating the atheroprotective effect not identified\"\n      ]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Biochemical characterization showed that mature ULBP4 glycoprotein undergoes proteolytic shedding from the cell surface, establishing an additional post-translational route—besides alternative splicing—for generating soluble ULBP4 that could modulate NKG2D signaling.\",\n      \"evidence\": \"Biochemical glycoprotein analysis and proteolytic shedding assay of ULBP4-expressing cells\",\n      \"pmids\": [\"29651291\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Identity of the protease(s) responsible for ULBP4 shedding not determined\",\n        \"Functional comparison of shed versus splice-derived soluble ULBP4 not performed\",\n        \"In vivo serum levels and clearance of shed ULBP4 not measured\"\n      ]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Soluble ULBP4 was shown to stimulate CD8+ T cell cytokine production and motility in the CNS context, and a shed 25-kDa form was elevated in CSF of female MS patients, linking RAET1E to neuroinflammation; simultaneously, the prior report of constitutive ULBP4 expression on monocytes was refuted by antibody validation with knockout controls.\",\n      \"evidence\": \"Primary CD8+ T cell functional assays with soluble ULBP4; astrocyte co-culture motility imaging; CSF Western blot from MS patients; RT-PCR and flow cytometry with ULBP4-knockout validation cells\",\n      \"pmids\": [\"34873031\", \"33556116\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Source of shed ULBP4 in the CNS not identified\",\n        \"Whether elevated CSF ULBP4 is causally related to MS pathology versus a bystander marker unclear\",\n        \"Antibody reagent issues highlight need for independent validation of ULBP4 tissue expression reports\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include the structural basis of ULBP4 recognition by both NKG2D and TCRγδ, the identity of sheddases acting on ULBP4, the signaling pathways downstream of ULBP4-mediated T cell costimulation, and whether the atheroprotective function of Raet1e translates to human cardiovascular biology.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"No crystal structure of ULBP4 alone or in complex with NKG2D or TCRγδ\",\n        \"Sheddase identity unknown\",\n        \"Human vascular expression and cardiovascular relevance not established\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0048018\", \"supporting_discovery_ids\": [0, 1, 4]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [3, 8]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 1, 6]},\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [3, 6, 8]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [0, 1, 2, 4]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [3, 5]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"KLRK1\",\n      \"HCST\",\n      \"TRDV2\",\n      \"TRGV9\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}