{"gene":"KIR2DS2","run_date":"2026-06-10T02:59:49","timeline":{"discoveries":[{"year":2003,"finding":"Crystal structure of KIR2DS2 at 2.3-Å resolution revealed that despite 99% extracellular amino acid identity with inhibitory KIR2DL2, activating KIR2DS2 does not bind HLA-Cw3; subtle displacements of two residues (Tyr45 and Gln71) account for the loss of HLA-C recognition compared to KIR2DL2.","method":"X-ray crystallography (2.3 Å structure) combined with KIR tetramer binding assays","journal":"The Journal of experimental medicine","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structure plus functional tetramer binding validation in a single rigorous study","pmids":["12668644"],"is_preprint":false},{"year":2000,"finding":"KIR2DS2 transduces activating signals through association with the DAP12 adaptor polypeptide via a charged lysine residue in its transmembrane domain; a naturally occurring mutant with six non-conservative mutations in the transmembrane exon, including disruption of this lysine, showed sharply reduced DAP12 association and failed to trigger NK cell activation.","method":"Sequence analysis of natural mutant cDNA, co-transfection experiments assessing DAP12 association, functional NK cytotoxicity assays","journal":"European journal of immunology","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — co-transfection reconstitution with mutagenesis (natural mutant) plus functional cytotoxicity readout in a single study","pmids":["11169398"],"is_preprint":false},{"year":2017,"finding":"KIR2DS2 directly recognizes viral peptides derived from conserved flaviviral superfamily 2 RNA helicase motif 1b region (including an 'MCHAT' motif present in 61 of 63 flaviviruses) presented by HLA-C*0102, leading to NK cell activation; an HCV helicase peptide (LNPSVAATL) also binds HLA-C*0102 and activates NK cells via KIR2DS2. KIR2DS2 was sufficient to inhibit HCV and dengue virus replication in the context of HLA-C*0102.","method":"Peptide-HLA binding assays, NK cell activation assays, endogenous antigen presentation, viral replication inhibition assays","journal":"Science immunology","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (peptide binding, NK activation, endogenous presentation, viral replication inhibition) in a single rigorous study","pmids":["28916719"],"is_preprint":false},{"year":2017,"finding":"KIR2DS2 recognizes a β2-microglobulin-independent ligand expressed on cancer cell lines, distinct from classical HLA-C1 or C2 group ligands; siRNA knockdown of β2-microglobulin reducing class I H chain expression by >97% did not reduce KIR2DS2 reporter responses, and anti-HLA class I antibodies did not block KIR2DS2 recognition of cancer cells. Trogocytosis indicated formation of KIR2DS2 ligand-specific immunological synapses.","method":"KIR2DS2 reporter cell assays, siRNA knockdown of β2-microglobulin, antibody blocking assays, trogocytosis analysis","journal":"Journal of immunology (Baltimore, Md. : 1950)","confidence":"High","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (reporter cells, siRNA knockdown, Ab blocking, trogocytosis) in single study","pmids":["28202613"],"is_preprint":false},{"year":2022,"finding":"Crystal structure of KIR2DS2 in complex with HLA-C*0102 at 2.5-Å resolution revealed that KIR2DS2 can bind HLA-C*0102 and HLA-A*1101 in two different orientations; Tyr45 in KIR2DS2 (vs. Phe45 in inhibitory KIRs) distinguishes the binding mode and affinity between activating and inhibitory KIRs; a conserved 'AT' motif in the peptide mediates recognition and determines peptide specificity.","method":"X-ray crystallography (2.5 Å complex structure)","journal":"Immunology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — crystal structure of the complex with functional interpretation; single lab but direct structural evidence","pmids":["34967442"],"is_preprint":false},{"year":2013,"finding":"KIR2DS2+ KIR2DL2- NK cell clones were C1-reactive (activated by C1 HLA-C alleles) irrespective of HLA-C environment; however, when KIR2DS2 and KIR2DL2 are co-expressed on the same NK cell, KIR2DL2-mediated inhibition overrides KIR2DS2-mediated activation. In contrast, KIR2DS2 and KIR2DL1 had an additive enhancing effect on NK responses against C1C1 targets.","method":"NK cell clone functional assays (co-culture with HLA-typed target cells), KIR genotype–phenotype analysis in 159 donors","journal":"Journal of immunology (Baltimore, Md. : 1950)","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional NK clone assays with defined HLA targets in a large cohort; single lab","pmids":["24078689"],"is_preprint":false},{"year":2012,"finding":"KIR2DS2, despite 99% extracellular identity with inhibitory KIR2DL2, was selected for lost recognition of HLA-C; the activating receptor was specifically selected to NOT bind the C1 epitope of HLA-C that its inhibitory counterpart KIR2DL2/3 recognizes.","method":"Comparative genetics, KIR tetramer binding (referenced from structural study), evolutionary analysis","journal":"Frontiers in immunology","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — evolutionary/genetic inference supported by tetramer binding data referenced from prior structural work; review synthesis","pmids":["23189078"],"is_preprint":false},{"year":2004,"finding":"Simultaneous engagement of KIR2DL3 and KIR2DS2 on the same NK cell clone was investigated using redirected killing assays with the combination of GL183 and novel ECM41 (KIR2DL3-specific) monoclonal antibodies, allowing dissection of their opposing inhibitory vs. activating functions on NK cells co-expressing both receptors.","method":"Generation of KIR2DL3-specific monoclonal antibody (ECM41), redirected killing assays with mAb combinations, NK clone surface expression analysis","journal":"International immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — novel mAb generation with functional redirected killing assays; single lab, two orthogonal approaches","pmids":["15314042"],"is_preprint":false},{"year":2011,"finding":"KIR2DS2*005 is a fusion gene resulting from unequal crossing-over between KIR2DS2 and KIR2DS3 within a 400 bp region of identity in intron 6; the encoded protein retains the KIR2DS2 ectodomain but has KIR2DS3 transmembrane and cytoplasmic regions. KIR2DS2*005 is expressed on the surface of NK and T lymphocytes, confirmed with two monoclonal antibodies.","method":"cDNA sequencing, recombination mapping, population genetics, dual monoclonal antibody surface expression analysis","journal":"Genes and immunity","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — molecular characterization with sequencing plus functional surface expression confirmation; single lab","pmids":["21593779"],"is_preprint":false},{"year":2012,"finding":"KIR2DS2 promoter contains a CpG island spanning from -160 to +26 with six cytosine sites; promoter hypomethylation at this CpG island is associated with increased KIR2DS2 mRNA expression, and frequency of unmethylated sites increased after hematopoietic cell transplantation, suggesting epigenetic regulation of KIR2DS2 expression.","method":"Sodium bisulfite treatment of genomic DNA, sequencing for CpG methylation, mRNA quantitative PCR","journal":"Human immunology","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, single method (bisulfite sequencing), small sample (n=20), correlational rather than causal","pmids":["22939905"],"is_preprint":false},{"year":2014,"finding":"KIR2DS2+ NK cell subpopulations showed enhanced cytotoxicity against glioblastoma (GBM) cells, retaining high CD69 and CD16 expression and producing more CD107a and granzyme A upon GBM contact; NK cell-mediated GBM killing depended on NKG2D ligand expression on GBM cells and was partially abrogated by NKG2D antibody blockade, indicating KIR2DS2 marks functionally activated NK cells whose killing is co-mediated by NKG2D.","method":"FACS sorting of KIR2DS2+ NK cell subpopulations, cytotoxicity assays in vitro, antibody blocking of NKG2D, in vivo GBM xenograft in NOD/SCID mice","journal":"Journal of immunology (Baltimore, Md. : 1950)","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — FACS-sorted subpopulations, in vitro functional assays, antibody blocking, and in vivo xenograft; single lab, multiple methods","pmids":["25381437"],"is_preprint":false},{"year":2022,"finding":"KIR2DS2high NK cells show enhanced spontaneous cytotoxic activation against malignant B cell lines, liver cancer cell lines, and primary CLL cells; KIR2DS2high NK cells have increased surface CD16 expression and enhanced ADCC in response to rituximab and obinutuzumab. Bulk RNA sequencing and single-cell RNA sequencing of KIR2DS2+ NK cells confirmed upregulation of NK-mediated cytotoxicity, translation, and FCGR gene pathways.","method":"Flow cytometry, bulk RNA sequencing, single-cell RNA sequencing, NK cell activation assays with tumor targets and therapeutic antibodies","journal":"Journal of immunology (Baltimore, Md. : 1950)","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (flow cytometry, bulk and scRNA-seq, functional assays); single lab","pmids":["35768150"],"is_preprint":false}],"current_model":"KIR2DS2 is an activating NK cell receptor that signals through association of its charged transmembrane lysine with the DAP12 adaptor; despite 99% extracellular identity with inhibitory KIR2DL2, structural differences at Tyr45 and Gln71 abolish classical HLA-Cw3 binding, while the complex structure with HLA-C*0102 reveals that Tyr45 (vs. Phe45 in inhibitory KIRs) and a conserved peptide 'AT' motif govern its distinct, restricted C1-group specificity; KIR2DS2 directly recognizes conserved flaviviral helicase peptides (including an 'MCHAT' motif) presented by HLA-C*0102 to activate NK cells and inhibit viral replication, and also recognizes a second, β2-microglobulin-independent ligand on cancer cells; when co-expressed with KIR2DL2, inhibitory signaling dominates, but KIR2DS2 marks NK cells with enhanced cytotoxicity against tumors partly co-mediated by NKG2D, and its expression is epigenetically regulated by CpG promoter methylation."},"narrative":{"mechanistic_narrative":"KIR2DS2 is an activating NK cell receptor that couples antigen recognition at the cell surface to NK cell cytotoxicity, signaling through the charged lysine in its transmembrane domain that recruits the DAP12 adaptor; a natural mutant disrupting this lysine loses DAP12 association and fails to trigger activation [PMID:11169398]. Despite 99% extracellular identity with the inhibitory receptor KIR2DL2, KIR2DS2 does not bind HLA-Cw3, a divergence traced structurally to displacements at Tyr45 and Gln71 and interpreted as evolutionary selection for loss of C1 epitope recognition by the activating receptor [PMID:12668644, PMID:23189078]. The complex structure with HLA-C*0102 shows that Tyr45 (versus Phe45 in inhibitory KIRs) dictates a distinct binding mode and that a conserved peptide 'AT' motif governs peptide-specific recognition [PMID:34967442]. Functionally, KIR2DS2 directly recognizes conserved flaviviral superfamily 2 RNA helicase peptides (an 'MCHAT' motif) and an HCV helicase peptide presented by HLA-C*0102, activating NK cells and being sufficient to inhibit HCV and dengue virus replication [PMID:28916719], and it additionally recognizes a β2-microglobulin-independent ligand on cancer cells distinct from classical HLA-C ligands [PMID:28202613]. KIR2DS2-mediated activation is integrated with co-expressed receptors: KIR2DL2 inhibition overrides it while KIR2DL1 is additive [PMID:24078689], and KIR2DS2+ NK cells display enhanced cytotoxicity against tumors, co-mediated by NKG2D and associated with elevated CD16 and ADCC [PMID:25381437, PMID:35768150].","teleology":[{"year":2000,"claim":"Established how KIR2DS2 converts ligand engagement into an activating signal, resolving why an inhibitory-like ectodomain produces stimulatory output.","evidence":"Sequence analysis of a natural transmembrane mutant, DAP12 co-transfection association, and NK cytotoxicity assays","pmids":["11169398"],"confidence":"High","gaps":["Downstream DAP12 signaling intermediates not mapped in this study","Did not define the physiological ligand driving activation"]},{"year":2003,"claim":"Explained at atomic resolution why activating KIR2DS2 fails to bind HLA-Cw3 despite near-identical ectodomain to inhibitory KIR2DL2, localizing the difference to two residues.","evidence":"2.3-Å X-ray crystal structure plus KIR tetramer binding assays","pmids":["12668644"],"confidence":"High","gaps":["Did not identify a positive ligand for KIR2DS2","Functional consequence of altered binding for NK activation not tested here"]},{"year":2012,"claim":"Framed the loss of HLA-C binding as an evolutionary selection event rather than a degenerate accident, positioning KIR2DS2 as deliberately diverged from its inhibitory counterpart.","evidence":"Comparative genetics and evolutionary analysis with referenced tetramer binding data (review synthesis)","pmids":["23189078"],"confidence":"Medium","gaps":["Inference rests on referenced prior structural/binding data","Does not establish the selective pressure or true activating ligand"]},{"year":2013,"claim":"Defined how KIR2DS2 activation is integrated with co-expressed inhibitory and activating KIRs on the same NK cell, addressing the net functional output.","evidence":"NK clone functional assays against HLA-typed targets and KIR genotype–phenotype analysis in 159 donors","pmids":["24078689"],"confidence":"Medium","gaps":["Molecular basis of inhibitory dominance not resolved","C1-reactivity readout did not identify the activating ligand at the molecular level"]},{"year":2017,"claim":"Identified a physiological activating ligand—conserved flaviviral helicase peptides presented by HLA-C*0102—and linked KIR2DS2 recognition to antiviral control.","evidence":"Peptide-HLA binding, NK activation, endogenous presentation, and HCV/dengue replication inhibition assays","pmids":["28916719"],"confidence":"High","gaps":["In vivo relevance during human infection not established","Affinity and structural basis of peptide recognition addressed only later"]},{"year":2017,"claim":"Revealed a second, β2-microglobulin-independent ligand on cancer cells, distinguishing tumor recognition from classical HLA-C peptide presentation.","evidence":"KIR2DS2 reporter assays, β2-microglobulin siRNA knockdown, anti-class I antibody blocking, and trogocytosis analysis","pmids":["28202613"],"confidence":"High","gaps":["Molecular identity of the non-classical ligand not determined","Binding affinity and structural basis of this interaction unknown"]},{"year":2022,"claim":"Provided the structural rationale for KIR2DS2 peptide-specific recognition of HLA-C*0102, pinpointing Tyr45 and a peptide 'AT' motif as determinants of binding mode and specificity.","evidence":"2.5-Å X-ray crystal structure of the KIR2DS2–HLA-C*0102 complex","pmids":["34967442"],"confidence":"High","gaps":["Functional impact of the two binding orientations on signaling not tested","Does not address the non-HLA cancer ligand"]},{"year":2014,"claim":"Showed KIR2DS2 marks functionally activated NK cells with enhanced antitumor cytotoxicity that is co-dependent on NKG2D ligands.","evidence":"FACS-sorted KIR2DS2+ NK subsets, in vitro cytotoxicity, NKG2D antibody blockade, and in vivo GBM xenografts","pmids":["25381437"],"confidence":"Medium","gaps":["Cannot separate direct KIR2DS2 signaling from NKG2D contribution","Whether KIR2DS2 itself engaged a GBM ligand not defined"]},{"year":2022,"claim":"Extended the antitumor phenotype across multiple malignancies and tied KIR2DS2 expression to elevated CD16 and antibody-dependent cytotoxicity transcriptional programs.","evidence":"Flow cytometry, bulk and single-cell RNA-seq, and NK activation assays with tumor targets and therapeutic antibodies","pmids":["35768150"],"confidence":"Medium","gaps":["Causal mechanism linking KIR2DS2 to CD16/FCGR upregulation not established","Correlative association between KIR2DS2 expression and cytotoxic state"]},{"year":2012,"claim":"Linked KIR2DS2 surface expression to epigenetic control via promoter CpG methylation, addressing how its variegated expression is regulated.","evidence":"Bisulfite sequencing of a promoter CpG island and mRNA qPCR (n=20)","pmids":["22939905"],"confidence":"Low","gaps":["Correlational, not causal; no methylation manipulation to demonstrate control","Small sample size","Mechanism connecting demethylation to transcription not defined"]},{"year":2011,"claim":"Characterized a recombinant KIR2DS2*005 fusion allele, defining allelic diversity at the locus and its effect on receptor architecture.","evidence":"cDNA sequencing, recombination mapping, population genetics, and dual-antibody surface expression analysis","pmids":["21593779"],"confidence":"Medium","gaps":["Functional signaling consequence of the swapped transmembrane/cytoplasmic regions not tested","Ligand recognition by the fusion protein not assessed"]},{"year":null,"claim":"The molecular identity of the β2-microglobulin-independent cancer ligand and the in vivo contribution of KIR2DS2 to antiviral and antitumor immunity remain unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["Non-classical cancer ligand not biochemically identified","Causal mechanism linking KIR2DS2 to CD16/ADCC programs unknown","In vivo human relevance of helicase-peptide recognition untested"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[1,2,3]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[1]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[1,8]}],"pathway":[{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[1,2,10]}],"complexes":[],"partners":["DAP12","HLA-C","NKG2D"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P43631","full_name":"Killer cell immunoglobulin-like receptor 2DS2","aliases":["CD158 antigen-like family member J","NK receptor 183 ActI","Natural killer-associated transcript 5","NKAT-5","p58 natural killer cell receptor clone CL-49","p58 NK receptor CL-49"],"length_aa":304,"mass_kda":33.5,"function":"Receptor on natural killer (NK) cells for HLA-C alleles. Does not inhibit the activity of NK cells","subcellular_location":"Cell membrane","url":"https://www.uniprot.org/uniprotkb/P43631/entry"},"depmap":{"release":"DepMap","has_data":false,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/KIR2DS2"},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/KIR2DS2","total_profiled":1310},"omim":[{"mim_id":"604956","title":"KILLER CELL IMMUNOGLOBULIN-LIKE RECEPTOR, TWO DOMAINS, SHORT CYTOPLASMIC TAIL, 5; KIR2DS5","url":"https://www.omim.org/entry/604956"},{"mim_id":"604955","title":"KILLER CELL IMMUNOGLOBULIN-LIKE RECEPTOR, TWO DOMAINS, SHORT CYTOPLASMIC TAIL, 4; KIR2DS4","url":"https://www.omim.org/entry/604955"},{"mim_id":"604954","title":"KILLER CELL IMMUNOGLOBULIN-LIKE RECEPTOR, TWO DOMAINS, SHORT CYTOPLASMIC TAIL, 3; KIR2DS3","url":"https://www.omim.org/entry/604954"},{"mim_id":"604953","title":"KILLER CELL IMMUNOGLOBULIN-LIKE RECEPTOR, TWO DOMAINS, SHORT CYTOPLASMIC TAIL, 2; KIR2DS2","url":"https://www.omim.org/entry/604953"},{"mim_id":"604142","title":"TYRO PROTEIN TYROSINE KINASE-BINDING PROTEIN; TYROBP","url":"https://www.omim.org/entry/604142"}],"hpa":{"profiled":false,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"","tissue_distribution":"","driving_tissues":[],"url":"https://www.proteinatlas.org/search/KIR2DS2"},"hgnc":{"alias_symbol":["cl-49","nkat5","183ActI","CD158J"],"prev_symbol":[]},"alphafold":{"accession":"P43631","domains":[{"cath_id":"2.60.40.10","chopping":"24-121","consensus_level":"high","plddt":93.9281,"start":24,"end":121},{"cath_id":"2.60.40.10","chopping":"127-220","consensus_level":"high","plddt":95.3312,"start":127,"end":220}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P43631","model_url":"https://alphafold.ebi.ac.uk/files/AF-P43631-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P43631-F1-predicted_aligned_error_v6.png","plddt_mean":80.62},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=KIR2DS2","jax_strain_url":"https://www.jax.org/strain/search?query=KIR2DS2"},"sequence":{"accession":"P43631","fasta_url":"https://rest.uniprot.org/uniprotkb/P43631.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P43631/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P43631"}},"corpus_meta":[{"pmid":"23189078","id":"PMC_23189078","title":"Diverse 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individual.","date":"2021","source":"HLA","url":"https://pubmed.ncbi.nlm.nih.gov/34155832","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":15927,"output_tokens":3387,"usd":0.049293,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":10869,"output_tokens":3415,"usd":0.06986,"stage2_stop_reason":"end_turn"},"total_usd":0.119153,"stage1_batch_id":"msgbatch_01BbTCMyrRPyhtEq6b1MdwCN","stage2_batch_id":"msgbatch_011dEed5bbxYvTAaQWKJevxu","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2003,\n      \"finding\": \"Crystal structure of KIR2DS2 at 2.3-Å resolution revealed that despite 99% extracellular amino acid identity with inhibitory KIR2DL2, activating KIR2DS2 does not bind HLA-Cw3; subtle displacements of two residues (Tyr45 and Gln71) account for the loss of HLA-C recognition compared to KIR2DL2.\",\n      \"method\": \"X-ray crystallography (2.3 Å structure) combined with KIR tetramer binding assays\",\n      \"journal\": \"The Journal of experimental medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structure plus functional tetramer binding validation in a single rigorous study\",\n      \"pmids\": [\"12668644\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"KIR2DS2 transduces activating signals through association with the DAP12 adaptor polypeptide via a charged lysine residue in its transmembrane domain; a naturally occurring mutant with six non-conservative mutations in the transmembrane exon, including disruption of this lysine, showed sharply reduced DAP12 association and failed to trigger NK cell activation.\",\n      \"method\": \"Sequence analysis of natural mutant cDNA, co-transfection experiments assessing DAP12 association, functional NK cytotoxicity assays\",\n      \"journal\": \"European journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — co-transfection reconstitution with mutagenesis (natural mutant) plus functional cytotoxicity readout in a single study\",\n      \"pmids\": [\"11169398\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"KIR2DS2 directly recognizes viral peptides derived from conserved flaviviral superfamily 2 RNA helicase motif 1b region (including an 'MCHAT' motif present in 61 of 63 flaviviruses) presented by HLA-C*0102, leading to NK cell activation; an HCV helicase peptide (LNPSVAATL) also binds HLA-C*0102 and activates NK cells via KIR2DS2. KIR2DS2 was sufficient to inhibit HCV and dengue virus replication in the context of HLA-C*0102.\",\n      \"method\": \"Peptide-HLA binding assays, NK cell activation assays, endogenous antigen presentation, viral replication inhibition assays\",\n      \"journal\": \"Science immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (peptide binding, NK activation, endogenous presentation, viral replication inhibition) in a single rigorous study\",\n      \"pmids\": [\"28916719\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"KIR2DS2 recognizes a β2-microglobulin-independent ligand expressed on cancer cell lines, distinct from classical HLA-C1 or C2 group ligands; siRNA knockdown of β2-microglobulin reducing class I H chain expression by >97% did not reduce KIR2DS2 reporter responses, and anti-HLA class I antibodies did not block KIR2DS2 recognition of cancer cells. Trogocytosis indicated formation of KIR2DS2 ligand-specific immunological synapses.\",\n      \"method\": \"KIR2DS2 reporter cell assays, siRNA knockdown of β2-microglobulin, antibody blocking assays, trogocytosis analysis\",\n      \"journal\": \"Journal of immunology (Baltimore, Md. : 1950)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (reporter cells, siRNA knockdown, Ab blocking, trogocytosis) in single study\",\n      \"pmids\": [\"28202613\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Crystal structure of KIR2DS2 in complex with HLA-C*0102 at 2.5-Å resolution revealed that KIR2DS2 can bind HLA-C*0102 and HLA-A*1101 in two different orientations; Tyr45 in KIR2DS2 (vs. Phe45 in inhibitory KIRs) distinguishes the binding mode and affinity between activating and inhibitory KIRs; a conserved 'AT' motif in the peptide mediates recognition and determines peptide specificity.\",\n      \"method\": \"X-ray crystallography (2.5 Å complex structure)\",\n      \"journal\": \"Immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — crystal structure of the complex with functional interpretation; single lab but direct structural evidence\",\n      \"pmids\": [\"34967442\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"KIR2DS2+ KIR2DL2- NK cell clones were C1-reactive (activated by C1 HLA-C alleles) irrespective of HLA-C environment; however, when KIR2DS2 and KIR2DL2 are co-expressed on the same NK cell, KIR2DL2-mediated inhibition overrides KIR2DS2-mediated activation. In contrast, KIR2DS2 and KIR2DL1 had an additive enhancing effect on NK responses against C1C1 targets.\",\n      \"method\": \"NK cell clone functional assays (co-culture with HLA-typed target cells), KIR genotype–phenotype analysis in 159 donors\",\n      \"journal\": \"Journal of immunology (Baltimore, Md. : 1950)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional NK clone assays with defined HLA targets in a large cohort; single lab\",\n      \"pmids\": [\"24078689\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"KIR2DS2, despite 99% extracellular identity with inhibitory KIR2DL2, was selected for lost recognition of HLA-C; the activating receptor was specifically selected to NOT bind the C1 epitope of HLA-C that its inhibitory counterpart KIR2DL2/3 recognizes.\",\n      \"method\": \"Comparative genetics, KIR tetramer binding (referenced from structural study), evolutionary analysis\",\n      \"journal\": \"Frontiers in immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — evolutionary/genetic inference supported by tetramer binding data referenced from prior structural work; review synthesis\",\n      \"pmids\": [\"23189078\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Simultaneous engagement of KIR2DL3 and KIR2DS2 on the same NK cell clone was investigated using redirected killing assays with the combination of GL183 and novel ECM41 (KIR2DL3-specific) monoclonal antibodies, allowing dissection of their opposing inhibitory vs. activating functions on NK cells co-expressing both receptors.\",\n      \"method\": \"Generation of KIR2DL3-specific monoclonal antibody (ECM41), redirected killing assays with mAb combinations, NK clone surface expression analysis\",\n      \"journal\": \"International immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — novel mAb generation with functional redirected killing assays; single lab, two orthogonal approaches\",\n      \"pmids\": [\"15314042\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"KIR2DS2*005 is a fusion gene resulting from unequal crossing-over between KIR2DS2 and KIR2DS3 within a 400 bp region of identity in intron 6; the encoded protein retains the KIR2DS2 ectodomain but has KIR2DS3 transmembrane and cytoplasmic regions. KIR2DS2*005 is expressed on the surface of NK and T lymphocytes, confirmed with two monoclonal antibodies.\",\n      \"method\": \"cDNA sequencing, recombination mapping, population genetics, dual monoclonal antibody surface expression analysis\",\n      \"journal\": \"Genes and immunity\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — molecular characterization with sequencing plus functional surface expression confirmation; single lab\",\n      \"pmids\": [\"21593779\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"KIR2DS2 promoter contains a CpG island spanning from -160 to +26 with six cytosine sites; promoter hypomethylation at this CpG island is associated with increased KIR2DS2 mRNA expression, and frequency of unmethylated sites increased after hematopoietic cell transplantation, suggesting epigenetic regulation of KIR2DS2 expression.\",\n      \"method\": \"Sodium bisulfite treatment of genomic DNA, sequencing for CpG methylation, mRNA quantitative PCR\",\n      \"journal\": \"Human immunology\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, single method (bisulfite sequencing), small sample (n=20), correlational rather than causal\",\n      \"pmids\": [\"22939905\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"KIR2DS2+ NK cell subpopulations showed enhanced cytotoxicity against glioblastoma (GBM) cells, retaining high CD69 and CD16 expression and producing more CD107a and granzyme A upon GBM contact; NK cell-mediated GBM killing depended on NKG2D ligand expression on GBM cells and was partially abrogated by NKG2D antibody blockade, indicating KIR2DS2 marks functionally activated NK cells whose killing is co-mediated by NKG2D.\",\n      \"method\": \"FACS sorting of KIR2DS2+ NK cell subpopulations, cytotoxicity assays in vitro, antibody blocking of NKG2D, in vivo GBM xenograft in NOD/SCID mice\",\n      \"journal\": \"Journal of immunology (Baltimore, Md. : 1950)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — FACS-sorted subpopulations, in vitro functional assays, antibody blocking, and in vivo xenograft; single lab, multiple methods\",\n      \"pmids\": [\"25381437\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"KIR2DS2high NK cells show enhanced spontaneous cytotoxic activation against malignant B cell lines, liver cancer cell lines, and primary CLL cells; KIR2DS2high NK cells have increased surface CD16 expression and enhanced ADCC in response to rituximab and obinutuzumab. Bulk RNA sequencing and single-cell RNA sequencing of KIR2DS2+ NK cells confirmed upregulation of NK-mediated cytotoxicity, translation, and FCGR gene pathways.\",\n      \"method\": \"Flow cytometry, bulk RNA sequencing, single-cell RNA sequencing, NK cell activation assays with tumor targets and therapeutic antibodies\",\n      \"journal\": \"Journal of immunology (Baltimore, Md. : 1950)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (flow cytometry, bulk and scRNA-seq, functional assays); single lab\",\n      \"pmids\": [\"35768150\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"KIR2DS2 is an activating NK cell receptor that signals through association of its charged transmembrane lysine with the DAP12 adaptor; despite 99% extracellular identity with inhibitory KIR2DL2, structural differences at Tyr45 and Gln71 abolish classical HLA-Cw3 binding, while the complex structure with HLA-C*0102 reveals that Tyr45 (vs. Phe45 in inhibitory KIRs) and a conserved peptide 'AT' motif govern its distinct, restricted C1-group specificity; KIR2DS2 directly recognizes conserved flaviviral helicase peptides (including an 'MCHAT' motif) presented by HLA-C*0102 to activate NK cells and inhibit viral replication, and also recognizes a second, β2-microglobulin-independent ligand on cancer cells; when co-expressed with KIR2DL2, inhibitory signaling dominates, but KIR2DS2 marks NK cells with enhanced cytotoxicity against tumors partly co-mediated by NKG2D, and its expression is epigenetically regulated by CpG promoter methylation.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"KIR2DS2 is an activating NK cell receptor that couples antigen recognition at the cell surface to NK cell cytotoxicity, signaling through the charged lysine in its transmembrane domain that recruits the DAP12 adaptor; a natural mutant disrupting this lysine loses DAP12 association and fails to trigger activation [#1]. Despite 99% extracellular identity with the inhibitory receptor KIR2DL2, KIR2DS2 does not bind HLA-Cw3, a divergence traced structurally to displacements at Tyr45 and Gln71 and interpreted as evolutionary selection for loss of C1 epitope recognition by the activating receptor [#0, #6]. The complex structure with HLA-C*0102 shows that Tyr45 (versus Phe45 in inhibitory KIRs) dictates a distinct binding mode and that a conserved peptide 'AT' motif governs peptide-specific recognition [#4]. Functionally, KIR2DS2 directly recognizes conserved flaviviral superfamily 2 RNA helicase peptides (an 'MCHAT' motif) and an HCV helicase peptide presented by HLA-C*0102, activating NK cells and being sufficient to inhibit HCV and dengue virus replication [#2], and it additionally recognizes a β2-microglobulin-independent ligand on cancer cells distinct from classical HLA-C ligands [#3]. KIR2DS2-mediated activation is integrated with co-expressed receptors: KIR2DL2 inhibition overrides it while KIR2DL1 is additive [#5], and KIR2DS2+ NK cells display enhanced cytotoxicity against tumors, co-mediated by NKG2D and associated with elevated CD16 and ADCC [#10, #11].\",\n  \"teleology\": [\n    {\n      \"year\": 2000,\n      \"claim\": \"Established how KIR2DS2 converts ligand engagement into an activating signal, resolving why an inhibitory-like ectodomain produces stimulatory output.\",\n      \"evidence\": \"Sequence analysis of a natural transmembrane mutant, DAP12 co-transfection association, and NK cytotoxicity assays\",\n      \"pmids\": [\"11169398\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Downstream DAP12 signaling intermediates not mapped in this study\", \"Did not define the physiological ligand driving activation\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Explained at atomic resolution why activating KIR2DS2 fails to bind HLA-Cw3 despite near-identical ectodomain to inhibitory KIR2DL2, localizing the difference to two residues.\",\n      \"evidence\": \"2.3-Å X-ray crystal structure plus KIR tetramer binding assays\",\n      \"pmids\": [\"12668644\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not identify a positive ligand for KIR2DS2\", \"Functional consequence of altered binding for NK activation not tested here\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Framed the loss of HLA-C binding as an evolutionary selection event rather than a degenerate accident, positioning KIR2DS2 as deliberately diverged from its inhibitory counterpart.\",\n      \"evidence\": \"Comparative genetics and evolutionary analysis with referenced tetramer binding data (review synthesis)\",\n      \"pmids\": [\"23189078\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Inference rests on referenced prior structural/binding data\", \"Does not establish the selective pressure or true activating ligand\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Defined how KIR2DS2 activation is integrated with co-expressed inhibitory and activating KIRs on the same NK cell, addressing the net functional output.\",\n      \"evidence\": \"NK clone functional assays against HLA-typed targets and KIR genotype–phenotype analysis in 159 donors\",\n      \"pmids\": [\"24078689\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular basis of inhibitory dominance not resolved\", \"C1-reactivity readout did not identify the activating ligand at the molecular level\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Identified a physiological activating ligand—conserved flaviviral helicase peptides presented by HLA-C*0102—and linked KIR2DS2 recognition to antiviral control.\",\n      \"evidence\": \"Peptide-HLA binding, NK activation, endogenous presentation, and HCV/dengue replication inhibition assays\",\n      \"pmids\": [\"28916719\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo relevance during human infection not established\", \"Affinity and structural basis of peptide recognition addressed only later\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Revealed a second, β2-microglobulin-independent ligand on cancer cells, distinguishing tumor recognition from classical HLA-C peptide presentation.\",\n      \"evidence\": \"KIR2DS2 reporter assays, β2-microglobulin siRNA knockdown, anti-class I antibody blocking, and trogocytosis analysis\",\n      \"pmids\": [\"28202613\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular identity of the non-classical ligand not determined\", \"Binding affinity and structural basis of this interaction unknown\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Provided the structural rationale for KIR2DS2 peptide-specific recognition of HLA-C*0102, pinpointing Tyr45 and a peptide 'AT' motif as determinants of binding mode and specificity.\",\n      \"evidence\": \"2.5-Å X-ray crystal structure of the KIR2DS2–HLA-C*0102 complex\",\n      \"pmids\": [\"34967442\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional impact of the two binding orientations on signaling not tested\", \"Does not address the non-HLA cancer ligand\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Showed KIR2DS2 marks functionally activated NK cells with enhanced antitumor cytotoxicity that is co-dependent on NKG2D ligands.\",\n      \"evidence\": \"FACS-sorted KIR2DS2+ NK subsets, in vitro cytotoxicity, NKG2D antibody blockade, and in vivo GBM xenografts\",\n      \"pmids\": [\"25381437\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Cannot separate direct KIR2DS2 signaling from NKG2D contribution\", \"Whether KIR2DS2 itself engaged a GBM ligand not defined\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Extended the antitumor phenotype across multiple malignancies and tied KIR2DS2 expression to elevated CD16 and antibody-dependent cytotoxicity transcriptional programs.\",\n      \"evidence\": \"Flow cytometry, bulk and single-cell RNA-seq, and NK activation assays with tumor targets and therapeutic antibodies\",\n      \"pmids\": [\"35768150\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Causal mechanism linking KIR2DS2 to CD16/FCGR upregulation not established\", \"Correlative association between KIR2DS2 expression and cytotoxic state\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Linked KIR2DS2 surface expression to epigenetic control via promoter CpG methylation, addressing how its variegated expression is regulated.\",\n      \"evidence\": \"Bisulfite sequencing of a promoter CpG island and mRNA qPCR (n=20)\",\n      \"pmids\": [\"22939905\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Correlational, not causal; no methylation manipulation to demonstrate control\", \"Small sample size\", \"Mechanism connecting demethylation to transcription not defined\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Characterized a recombinant KIR2DS2*005 fusion allele, defining allelic diversity at the locus and its effect on receptor architecture.\",\n      \"evidence\": \"cDNA sequencing, recombination mapping, population genetics, and dual-antibody surface expression analysis\",\n      \"pmids\": [\"21593779\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional signaling consequence of the swapped transmembrane/cytoplasmic regions not tested\", \"Ligand recognition by the fusion protein not assessed\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The molecular identity of the β2-microglobulin-independent cancer ligand and the in vivo contribution of KIR2DS2 to antiviral and antitumor immunity remain unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Non-classical cancer ligand not biochemically identified\", \"Causal mechanism linking KIR2DS2 to CD16/ADCC programs unknown\", \"In vivo human relevance of helicase-peptide recognition untested\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [1, 2, 3]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [1]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [1, 8]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [1, 2, 10]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"DAP12\", \"HLA-C\", \"NKG2D\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":5,"faith_total":5,"faith_pct":100.0}}