{"gene":"KIR2DL4","run_date":"2026-04-28T18:30:27","timeline":{"discoveries":[{"year":2001,"finding":"KIR2DL4 engagement on resting NK cells induces IFN-γ production but not cytotoxicity, and this IFN-γ induction is blocked by a p38 MAPK inhibitor, placing p38 MAPK in the signaling pathway downstream of KIR2DL4.","method":"Redirected lysis assay, IFN-γ secretion assay with pharmacological inhibitors (p38 and ERK inhibitors) in resting NK cells","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 2 — clean functional assay with pharmacological pathway dissection, replicated by multiple subsequent studies","pmids":["11489965"],"is_preprint":false},{"year":2002,"finding":"The ITIM in KIR2DL4's cytoplasmic tail is not required for its activating function; the transmembrane arginine-tyrosine motif is required for the activation signal; the phosphorylated cytoplasmic tail recruits SHP-1 and SHP-2 (via GST pulldown), giving KIR2DL4 inhibitory potential in addition to activating function; and the activation-deficient ITIM mutant can inhibit CD16 signaling.","method":"Site-directed mutagenesis of ITIM tyrosine and transmembrane arginine, redirected lysis assay, GST fusion protein pulldown with SHP-1 and SHP-2","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 1 — in vitro mutagenesis plus pulldown with multiple orthogonal functional assays in a single study","pmids":["12055234"],"is_preprint":false},{"year":2003,"finding":"KIR2DL4 surface expression depends on genotype: the 10A allele (10 adenines in exon 6) encodes a full-length receptor expressed on the cell surface, while the 9A allele causes a frameshift and premature stop codon producing a non-surface-expressed, truncated receptor. Surface expression is detectable only on CD56bright NK cells from 10A carriers and is up-regulated by IL-2.","method":"cDNA transfection of 10A and 9A alleles into NK-like cell line, flow cytometry on primary NK cells, anti-KIR2DL4 mAb staining","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 2 — transfection experiments plus primary cell validation, replicated in subsequent studies","pmids":["14500636","12902476"],"is_preprint":false},{"year":2003,"finding":"KIR2DL4 is an activating receptor: ligation of KIR2DL4 on cultured NK cells from 10A allele carriers triggers redirected lysis, confirming its activating function; this activity depends on the 10A genotype.","method":"Redirected lysis assay with anti-KIR2DL4 mAb on NK cells stratified by 9A/10A genotype","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 2 — functional assay with genotype-stratified primary cells, replicated across labs","pmids":["12902476"],"is_preprint":false},{"year":2005,"finding":"KIR2DL4 associates with the Fc receptor gamma (FcεRI-γ) chain via its transmembrane arginine residue, which promotes surface expression and provides signal-transducing function. This association is distinct from other activating KIRs, which associate with DAP12.","method":"Biochemical co-immunoprecipitation, transmembrane arginine mutation (R/G), functional redirected lysis and cytokine assays in NK-like cell line","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 1-2 — reciprocal biochemical evidence plus mutagenesis confirming functional consequence","pmids":["15778339"],"is_preprint":false},{"year":2005,"finding":"Residues Met76 and Gln79 in the HLA-G α1 domain are critical for KIR2DL4 recognition; mutating these to Ala reduces binding affinity between KIR2DL4-IgG Fc fusion protein and HLA-G, and reduces KIR2DL4-transfected NK-92 cell cytolysis against HLA-G-expressing K562 targets.","method":"Retroviral transduction, KIR2DL4-IgG Fc fusion protein binding assay, cytotoxicity (LDH release) assay","journal":"Cell research","confidence":"Medium","confidence_rationale":"Tier 1-2 — site-directed mutagenesis with functional binding and cytotoxicity readout, single study","pmids":["15780179"],"is_preprint":false},{"year":2005,"finding":"HLA-G up-regulates expression of KIR2DL4 in antigen-presenting cells, NK cells, and T cells, suggesting a positive feedback loop where HLA-G increases expression of its own receptor.","method":"Flow cytometry and gene expression analysis of ILT2, ILT3, ILT4, and KIR2DL4 on multiple immune cell types following HLA-G exposure","journal":"FASEB journal","confidence":"Medium","confidence_rationale":"Tier 3 — cell-based expression measurement, single lab, mechanism of up-regulation not fully dissected","pmids":["15670976"],"is_preprint":false},{"year":2005,"finding":"The KIR2DL4 promoter drives NK cell-specific reporter expression; it contains an AML-2 binding site that acts as a repressor, and mutation of the AML site substantially increases KIR2DL4 promoter activity. KIR2DL4 also contains an inhibitory element upstream of its core promoter, distinguishing it from clonally expressed KIR promoters.","method":"Reporter gene assay in NK3.3 and primary NK cells, DNase I footprinting, site-directed mutagenesis of transcription factor binding sites","journal":"Journal of immunology","confidence":"Medium","confidence_rationale":"Tier 2 — mutagenesis plus footprinting with functional reporter assay, single lab","pmids":["15778373"],"is_preprint":false},{"year":2007,"finding":"The 9A allele of KIR2DL4 produces a secreted (soluble) form of KIR2DL4 due to splicing out of the transmembrane region; a Delta-D0 isoform missing the D0 domain is produced from some 10A allele carriers and is undetectable by available anti-KIR2DL4 mAbs.","method":"RT-PCR, flow cytometry, immunoblot analysis of NK cells from genotyped individuals; in vitro culture experiments","journal":"European journal of immunology","confidence":"Medium","confidence_rationale":"Tier 2 — multiple molecular approaches in genotyped primary cells, single lab","pmids":["17171757"],"is_preprint":false},{"year":2008,"finding":"KIR2DL4 cross-linking activates JNK, ERK, and p38 MAPKs, as well as the NF-κB pathway (via IKKβ phosphorylation and IκBα degradation), leading to transcription of TNF-α, IFN-γ, MIP1α, MIP1β, and IL-8. Mutation of the transmembrane arginine (R/G) abrogates FcεRI-γ association, cytolytic activity and calcium responses, but still activates MAPKs and NF-κB and selectively induces MIP1α, revealing two distinct structural signaling modules.","method":"Pharmacological kinase inhibitors, Western blotting for phosphorylated kinases, cytokine ELISA/RT-PCR, transmembrane arginine mutagenesis (R/G) in KHYG-1 NK-like cell line","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 1-2 — mutagenesis plus pharmacological dissection with multiple readouts, orthogonal methods in single rigorous study","pmids":["18292514"],"is_preprint":false},{"year":2008,"finding":"Epigenetic regulation of KIR2DL4 expression in T cells involves DNA methylation and histone modifications: NK cells have a fully demethylated KIR2DL4 promoter with activating histone marks (H3/H4 acetylation, di/tri-H3-K4 methylation); T cells have a partially demethylated promoter with dimethyl H3-K4 but repressive histone marks, which is sensitized to DNMT inhibitor-induced transcription with aging.","method":"Chromatin immunoprecipitation (ChIP), bisulfite sequencing, DNMT inhibitor treatment, quantitative gene expression in primary T cells and NK cells","journal":"Journal of leukocyte biology","confidence":"Medium","confidence_rationale":"Tier 2 — ChIP and bisulfite sequencing with functional inhibitor experiments, single lab","pmids":["18586981"],"is_preprint":false},{"year":2010,"finding":"KIR2DL4 resides in endosomes (not at the cell surface) and signals from this intracellular site after binding soluble HLA-G; this endosomal signaling pathway involves DNA-PKcs and Akt kinases and results in a pro-inflammatory and pro-angiogenic response.","method":"Subcellular fractionation, confocal microscopy for receptor localization, signaling assays for DNA-PKcs and Akt in NK cells (review synthesizing primary data)","journal":"Traffic","confidence":"High","confidence_rationale":"Tier 2 — direct localization and signaling evidence from primary NK cells with functional consequences, supported by multiple subsequent studies","pmids":["20854369","22934097"],"is_preprint":false},{"year":2012,"finding":"Sustained activation of KIR2DL4 (CD158d) by agonists induces a DNA damage response (p21 upregulation, HP1-γ phosphorylation), cellular senescence (morphological changes, survival without cell-cycle entry), and a senescence-associated secretory phenotype (SASP). The secretome of these senescent NK cells promotes vascular remodeling and angiogenesis, as measured by endothelial cell tube formation and vascular permeability assays.","method":"CD158d agonist stimulation of primary NK cells, Western blot for p21 and HP1-γ phosphorylation, flow cytometry, transcriptome analysis, functional vascular assays (tube formation, permeability)","journal":"PNAS","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods establishing senescence pathway, functional vascular readout, single rigorous study with strong mechanistic follow-up","pmids":["23184984"],"is_preprint":false},{"year":2012,"finding":"The KIR2DL4 promoter requires Runx binding sites (specifically Runx3) for constitutive transcription, with contributions from CRE and initiator elements; IL-2/IL-15 stimulation additionally requires functional Ets (Ets1) sites. Runx3 and Ets1 were shown by ChIP to bind the 2DL4 promoter in situ.","method":"Promoter mutagenesis, EMSA, co-transfection assay, chromatin immunoprecipitation (ChIP) in NK cell lines and T cells","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 1-2 — mutagenesis, EMSA, and ChIP with functional reporter assays in single study","pmids":["22467658"],"is_preprint":false},{"year":2013,"finding":"KIR2DL4 directly interacts with heparan sulfate (HS)/heparin via its D0 domain (identified by genome-wide siRNA screen for HS3ST3B1); this interaction induces differential localization to Rab5+ and Rab7+ endosomes and downregulates cytokine production and receptor degradation. Syndecan-4 (SDC4) HSPG directly affects KIR2DL4 endocytosis and membrane trafficking.","method":"Genome-wide siRNA screen, direct binding assays with KIR2DL4 domain mutants, confocal microscopy for endosomal co-localization (Rab5/Rab7), cytokine secretion assay","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 1-2 — genome-wide unbiased screen validated by direct binding assays and functional localization studies with domain mapping","pmids":["24127555"],"is_preprint":false},{"year":2015,"finding":"Crystal structure of KIR2DL4 extracellular domains determined at 2.8 Å reveals a D0-D2 arrangement (lacking D1) with C2-type immunoglobulin folds at an acute elbow angle. KIR2DL4 self-associates via the D0 domain in a concentration-dependent manner, forming tetramers in the crystal lattice and in solution (confirmed by SEC, DLS, AUC, SAXS). This D0-mediated self-association precludes an HLA interaction analogous to KIR3DL1, and no direct HLA binding was detected.","method":"X-ray crystallography (2.8 Å), size exclusion chromatography, dynamic light scattering, analytical ultracentrifugation, small angle X-ray scattering, direct HLA binding studies","journal":"Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — high-resolution crystal structure with multiple orthogonal solution biophysical validations in single study","pmids":["25759384"],"is_preprint":false},{"year":2020,"finding":"KIR2DL4 is expressed on human mast cells (LAD2, PB-mast) in addition to NK cells; agonistic antibodies to KIR2DL4 negatively regulate KIT-mediated and FcεRI-mediated responses of mast cells, and HLA-G stimulation through KIR2DL4 induces secretion of leukemia inhibitory factor and serine proteases from mast cells.","method":"Flow cytometry, agonistic antibody stimulation assays, ELISA for cytokine/protease secretion in human mast cell lines and primary PB-mast cells","journal":"International journal of molecular sciences","confidence":"Medium","confidence_rationale":"Tier 2-3 — functional assays in mast cells establishing new cell-type expression and dual regulatory role, single lab","pmids":["32023940"],"is_preprint":false},{"year":2021,"finding":"HLA-G binding to KIR2DL4 on NK cells desensitizes NK cells to trastuzumab-mediated ADCC in HER2+ breast cancer; KIR2DL4 (without HLA-G engagement) promotes ADCC and synergizes with Fcγ receptor to increase IFN-γ secretion; IFN-γ upregulates KIR2DL4 via JAK2/STAT1 signaling; blockade of HLA-G/KIR2DL4 signaling improves trastuzumab efficacy in vivo.","method":"NK cell cytotoxicity assays, ELISA for cytokines, pharmacological JAK2/STAT1 inhibition, KIR2DL4 blockade in vivo mouse xenograft model","journal":"Signal transduction and targeted therapy","confidence":"Medium","confidence_rationale":"Tier 2 — functional in vitro and in vivo assays with pathway inhibition, single lab","pmids":["34158475"],"is_preprint":false},{"year":2022,"finding":"KIR2DL4 expressed in renal cell carcinoma (RCC) cells promotes RCC proliferation associated with PI3K/Akt signaling activation; KIR2DL4 knockdown reduces AKT phosphorylation and proliferation, while KIR2DL4 overexpression increases AKT phosphorylation and tumor growth in vivo.","method":"shRNA knockdown, overexpression, MTT assay, soft agar colony formation, xenograft mouse model, RNA sequencing, immunoblot for phospho-AKT, PI3K inhibitor (wortmannin) treatment","journal":"Life sciences","confidence":"Medium","confidence_rationale":"Tier 2 — loss- and gain-of-function with in vivo validation and pharmacological confirmation, single lab","pmids":["35063466"],"is_preprint":false},{"year":2026,"finding":"Soluble HLA-G stimulates transcription of type I interferon-stimulated genes (ISGs) in primary NK cells through a noncanonical pathway requiring the transcription factor IRF7 and kinase JAK1. The C-terminal portion of KIR2DL4's cytoplasmic tail contains a JAK1-binding sequence analogous to IFN receptor conserved JAK1 binding sites, and was required for JAK1 binding to KIR2DL4. HLA-G stimulation led to nuclear phosphorylation of IRF7 and STAT2. scRNA-seq showed ISG induction is similar in CD56bright and CD56dim NK cells.","method":"Primary NK cell stimulation with soluble HLA-G and agonistic anti-KIR2DL4 antibody, transcriptomics (bulk RNA-seq, scRNA-seq), pharmacological JAK1 inhibition, co-immunoprecipitation of JAK1 with KIR2DL4 cytoplasmic tail mutants, nuclear phospho-IRF7 and phospho-STAT2 detection","journal":"Science signaling","confidence":"High","confidence_rationale":"Tier 1-2 — multiple orthogonal methods (biochemical, genetic, transcriptomic, pharmacological) in a single rigorous study establishing a novel signaling pathway","pmids":["41632833"],"is_preprint":false}],"current_model":"KIR2DL4 is an endosome-resident NK cell receptor with a D0-D2 extracellular domain structure and a long cytoplasmic tail bearing both a transmembrane arginine (which recruits FcεRI-γ for one signaling module) and an ITIM (capable of recruiting SHP-1/SHP-2); upon binding its ligand soluble HLA-G in the extracellular milieu, the receptor-ligand complex is internalized into early endosomes where KIR2DL4 signals through DNA-PKcs, Akt, NF-κB, p38/JNK/ERK MAPKs, and a noncanonical JAK1-IRF7-STAT2 axis to drive pro-inflammatory cytokine (IFN-γ, TNF-α) and chemokine secretion, pro-angiogenic responses, and cellular senescence in NK cells—with additional ligand interactions involving heparan sulfate proteoglycans that regulate endosomal trafficking and receptor degradation."},"narrative":{"teleology":[{"year":2001,"claim":"Establishing that KIR2DL4 triggers IFN-γ rather than cytotoxicity in resting NK cells, with p38 MAPK as a required downstream kinase, defined its functional output as cytokine-biased activation.","evidence":"Redirected lysis and IFN-γ secretion assays with p38/ERK inhibitors in primary resting NK cells","pmids":["11489965"],"confidence":"High","gaps":["Upstream events connecting receptor engagement to p38 activation unknown","Whether other MAPKs contribute not yet tested"]},{"year":2002,"claim":"Demonstrating that the transmembrane arginine drives activating function while the ITIM recruits SHP-1/SHP-2 for inhibition resolved how a single receptor encodes dual signaling capacity.","evidence":"Site-directed mutagenesis of ITIM tyrosine and transmembrane arginine with GST pulldown and redirected lysis in NK-like cells","pmids":["12055234"],"confidence":"High","gaps":["Adaptor linking transmembrane arginine to activation not yet identified","In vivo relevance of inhibitory signaling not assessed"]},{"year":2003,"claim":"Showing that the 10A/9A frameshift polymorphism governs surface expression versus truncation explained population-level variation in KIR2DL4 function and confined surface expression to CD56bright NK cells.","evidence":"cDNA transfection of 10A/9A alleles, flow cytometry on genotyped primary NK cells","pmids":["14500636","12902476"],"confidence":"High","gaps":["Whether the 9A truncated/soluble form retains any signaling capacity unclear","Mechanism restricting surface expression to CD56bright subset not defined"]},{"year":2005,"claim":"Identifying FcεRI-γ as the signaling adaptor recruited by the transmembrane arginine — distinct from DAP12 used by other activating KIRs — established KIR2DL4's unique adaptor usage and explained how it reaches the surface.","evidence":"Co-immunoprecipitation and R/G transmembrane mutation with functional cytotoxicity and cytokine assays in NK-like cell line","pmids":["15778339"],"confidence":"High","gaps":["Whether FcεRI-γ is the sole adaptor or additional adaptors contribute","Stoichiometry of the receptor-adaptor complex unknown"]},{"year":2005,"claim":"Mapping critical HLA-G α1 domain residues (Met76, Gln79) for KIR2DL4 recognition provided the first ligand-side binding determinants.","evidence":"KIR2DL4-Fc fusion binding assays and cytotoxicity against HLA-G mutant targets","pmids":["15780179"],"confidence":"Medium","gaps":["Full binding interface not structurally resolved","Affinity measurements not performed by biophysical methods"]},{"year":2008,"claim":"Comprehensive pathway dissection showed KIR2DL4 activates JNK, ERK, p38 MAPKs and NF-κB, and that the R/G transmembrane mutant retains MAPK/NF-κB signaling but loses FcεRI-γ-dependent cytolysis and calcium flux, proving two structurally separable signaling modules.","evidence":"Pharmacological inhibitors, phospho-Western blots, cytokine ELISA, and transmembrane mutagenesis in KHYG-1 cells","pmids":["18292514"],"confidence":"High","gaps":["Proximal kinase linking the cytoplasmic tail to MAPK/NF-κB not identified","Whether the two modules cooperate or antagonize in vivo unknown"]},{"year":2010,"claim":"Discovering that KIR2DL4 primarily resides in endosomes and signals from there upon binding soluble HLA-G — via DNA-PKcs and Akt — overturned the surface-receptor paradigm and explained why soluble rather than membrane-bound HLA-G is the physiological ligand.","evidence":"Subcellular fractionation, confocal microscopy, DNA-PKcs and Akt signaling assays in primary NK cells","pmids":["20854369","22934097"],"confidence":"High","gaps":["How soluble HLA-G accesses endosomal KIR2DL4 mechanistically not fully resolved","Role of DNA-PKcs versus Akt in downstream gene induction not dissected"]},{"year":2012,"claim":"Showing that sustained KIR2DL4 activation induces cellular senescence with a pro-angiogenic secretory phenotype linked the receptor to vascular remodeling programs relevant to pregnancy and tumor microenvironments.","evidence":"p21 and HP1-γ phosphorylation analysis, transcriptomics, endothelial tube formation and vascular permeability assays in primary NK cells","pmids":["23184984"],"confidence":"High","gaps":["Whether senescence is reversible not tested","In vivo relevance at the decidual-placental interface not demonstrated"]},{"year":2013,"claim":"A genome-wide siRNA screen identified heparan sulfate proteoglycans (via HS3ST3B1 and syndecan-4) as regulators of KIR2DL4 endosomal trafficking and degradation through direct D0-domain binding, adding a glycan layer to receptor regulation.","evidence":"Genome-wide siRNA screen, direct binding assays with domain mutants, Rab5/Rab7 confocal co-localization, cytokine secretion assay","pmids":["24127555"],"confidence":"High","gaps":["Which specific HS sulfation patterns are required not defined","Whether HSPG interaction competes with or facilitates HLA-G binding unknown"]},{"year":2015,"claim":"The 2.8 Å crystal structure revealed a D0-D2 architecture with concentration-dependent D0-mediated self-association into tetramers, and showed the D0 interface precludes canonical HLA binding, reshaping models of ligand recognition.","evidence":"X-ray crystallography, SEC, DLS, AUC, SAXS, direct HLA binding studies","pmids":["25759384"],"confidence":"High","gaps":["No co-crystal with HLA-G obtained","Functional significance of tetramerization for signaling not tested","How self-association relates to endosomal signaling unclear"]},{"year":2020,"claim":"Detection of functional KIR2DL4 on mast cells, where it negatively regulates KIT and FcεRI responses and induces LIF secretion upon HLA-G stimulation, expanded its role beyond NK cells.","evidence":"Flow cytometry, agonistic antibody stimulation, cytokine/protease ELISA in LAD2 and primary PB-mast cells","pmids":["32023940"],"confidence":"Medium","gaps":["Signaling pathway in mast cells not compared to NK cell pathway","In vivo mast cell relevance not established","Not independently confirmed by another lab"]},{"year":2026,"claim":"Discovery of a noncanonical JAK1–IRF7–STAT2 axis activated by soluble HLA-G via a JAK1-binding motif in KIR2DL4's cytoplasmic tail established a third signaling module driving type I ISG transcription in both CD56bright and CD56dim NK cells.","evidence":"Primary NK cell stimulation with sHLA-G, bulk/scRNA-seq, JAK1 pharmacological inhibition, co-IP of JAK1 with cytoplasmic tail truncation mutants, phospho-IRF7/STAT2 detection","pmids":["41632833"],"confidence":"High","gaps":["How JAK1 binding is coordinated with the ITIM and FcεRI-γ modules on the same tail not resolved","Whether STAT2 and IRF7 form a canonical ISGF3-like complex or a distinct complex unknown","Physiological consequence of ISG induction for NK cell effector function not tested"]},{"year":null,"claim":"Major unresolved questions include the structural basis of KIR2DL4–HLA-G interaction (no co-crystal exists), the in vivo physiological role of endosomal signaling at the maternal-fetal interface, how the three signaling modules (FcεRI-γ, ITIM/SHP, JAK1–IRF7) are integrated or segregated on a single receptor, and the functional significance of D0-mediated oligomerization.","evidence":"","pmids":[],"confidence":"Low","gaps":["No KIR2DL4–HLA-G co-crystal structure","No genetic knockout or conditional deletion model in vivo","Integration logic among three signaling modules unresolved"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[0,1,3,9,12,19]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[1,16]}],"localization":[{"term_id":"GO:0005768","term_label":"endosome","supporting_discovery_ids":[11,14]},{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[2,3,4]}],"pathway":[{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[0,1,3,9,12,17]},{"term_id":"R-HSA-8953854","term_label":"Metabolism of RNA","supporting_discovery_ids":[19]},{"term_id":"R-HSA-5357801","term_label":"Programmed Cell Death","supporting_discovery_ids":[12]}],"complexes":[],"partners":["FCER1G","PTPN6","PTPN11","HLA-G","JAK1","SDC4","RUNX3","ETS1"],"other_free_text":[]},"mechanistic_narrative":"KIR2DL4 is a structurally unique killer cell immunoglobulin-like receptor on NK cells that integrates activating and inhibitory signaling to regulate innate immune responses, vascular remodeling, and cellular senescence. Its D0-D2 extracellular domain binds soluble HLA-G, which is internalized into Rab5+/Rab7+ endosomes where KIR2DL4 signals through DNA-PKcs, Akt, NF-κB, p38/JNK/ERK MAPKs, and a noncanonical JAK1–IRF7–STAT2 axis to drive IFN-γ, TNF-α, chemokine secretion, and type I interferon-stimulated gene transcription [PMID:11489965, PMID:18292514, PMID:20854369, PMID:41632833]. Two structurally separable signaling modules exist: a transmembrane arginine that recruits FcεRI-γ for cytolytic and calcium responses, and a cytoplasmic ITIM that recruits SHP-1/SHP-2 for inhibitory function, with the ITIM-independent tail activating MAPKs and NF-κB even without FcεRI-γ association [PMID:12055234, PMID:15778339, PMID:18292514]. Sustained KIR2DL4 activation induces a senescence-associated secretory phenotype in NK cells that promotes angiogenesis, and heparan sulfate proteoglycan interactions via the D0 domain regulate endosomal trafficking and receptor degradation [PMID:23184984, PMID:24127555]."},"prefetch_data":{"uniprot":{"accession":"Q99706","full_name":"Killer cell immunoglobulin-like receptor 2DL4","aliases":["CD158 antigen-like family member D","G9P","Killer cell inhibitory receptor 103AS","KIR-103AS","MHC class I NK cell receptor KIR103AS"],"length_aa":377,"mass_kda":41.5,"function":"Receptor for non-classical major histocompatibility class Ib HLA-G molecules. Recognizes HLA-G in complex with B2M/beta-2 microglobulin and a nonamer self-peptide (peptide-bound HLA-G-B2M). In decidual NK cells, binds peptide-bound HLA-G-B2M complex and triggers NK cell senescence-associated secretory phenotype as a molecular switch to promote vascular remodeling and fetal growth in early pregnancy (PubMed:16366734, PubMed:23184984, PubMed:29262349). May play a role in balancing tolerance and antiviral-immunity at maternal-fetal interface by keeping in check the effector functions of NK, CD8+ T cells and B cells (PubMed:10190900, PubMed:16366734). Upon interaction with peptide-bound HLA-G-B2M, initiates signaling from the endosomal compartment leading to downstream activation of PRKDC-XRCC5 and AKT1, and ultimately triggering NF-kappa-B-dependent pro-inflammatory response (PubMed:20179272)","subcellular_location":"Cell membrane; Early endosome membrane","url":"https://www.uniprot.org/uniprotkb/Q99706/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/KIR2DL4","classification":"Not Classified","n_dependent_lines":4,"n_total_lines":1208,"dependency_fraction":0.0033112582781456954},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/KIR2DL4","total_profiled":1310},"omim":[{"mim_id":"620778","title":"KILLER CELL IMMUNOGLOBULIN-LIKE RECEPTOR, THREE DOMAINS, SHORT CYTOPLASMIC TAIL, 1; KIR3DS1","url":"https://www.omim.org/entry/620778"},{"mim_id":"615727","title":"KILLER CELL IMMUNOGLOBULIN-LIKE RECEPTOR, TWO DOMAINS, LONG CYTOPLASMIC TAIL, 5B; KIR2DL5B","url":"https://www.omim.org/entry/615727"},{"mim_id":"610604","title":"KILLER CELL IMMUNOGLOBULIN-LIKE RECEPTOR, THREE DOMAINS, PSEUDOGENE 1; KIR3DP1","url":"https://www.omim.org/entry/610604"},{"mim_id":"610095","title":"KILLER CELL IMMUNOGLOBULIN-LIKE RECEPTOR, THREE DOMAINS, LONG CYTOPLASMIC TAIL, 3; KIR3DL3","url":"https://www.omim.org/entry/610095"},{"mim_id":"605305","title":"KILLER CELL IMMUNOGLOBULIN-LIKE RECEPTOR, TWO DOMAINS, LONG CYTOPLASMIC TAIL, 5A; KIR2DL5A","url":"https://www.omim.org/entry/605305"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Tissue enriched","tissue_distribution":"Detected in single","driving_tissues":[{"tissue":"lymphoid tissue","ntpm":4.3}],"url":"https://www.proteinatlas.org/search/KIR2DL4"},"hgnc":{"alias_symbol":["103AS","15.212","CD158D"],"prev_symbol":[]},"alphafold":{"accession":"Q99706","domains":[{"cath_id":"2.60.40.10","chopping":"31-119","consensus_level":"high","plddt":87.5343,"start":31,"end":119},{"cath_id":"2.60.40.10","chopping":"124-217","consensus_level":"high","plddt":94.9969,"start":124,"end":217}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q99706","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q99706-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q99706-F1-predicted_aligned_error_v6.png","plddt_mean":69.94},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=KIR2DL4","jax_strain_url":"https://www.jax.org/strain/search?query=KIR2DL4"},"sequence":{"accession":"Q99706","fasta_url":"https://rest.uniprot.org/uniprotkb/Q99706.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q99706/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q99706"}},"corpus_meta":[{"pmid":"15670976","id":"PMC_15670976","title":"HLA-G up-regulates ILT2, ILT3, ILT4, and KIR2DL4 in antigen presenting cells, NK cells, and T cells.","date":"2005","source":"FASEB journal : official publication of the Federation of American Societies for Experimental Biology","url":"https://pubmed.ncbi.nlm.nih.gov/15670976","citation_count":244,"is_preprint":false},{"pmid":"12055234","id":"PMC_12055234","title":"KIR2DL4 (CD158d), an NK cell-activating receptor with inhibitory potential.","date":"2002","source":"Journal of immunology (Baltimore, Md. : 1950)","url":"https://pubmed.ncbi.nlm.nih.gov/12055234","citation_count":191,"is_preprint":false},{"pmid":"11489965","id":"PMC_11489965","title":"Cutting edge: induction of IFN-gamma production but not cytotoxicity by the killer cell Ig-like receptor KIR2DL4 (CD158d) in resting NK cells.","date":"2001","source":"Journal of immunology (Baltimore, Md. : 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this IFN-γ induction is blocked by a p38 MAPK inhibitor, placing p38 MAPK in the signaling pathway downstream of KIR2DL4.\",\n      \"method\": \"Redirected lysis assay, IFN-γ secretion assay with pharmacological inhibitors (p38 and ERK inhibitors) in resting NK cells\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean functional assay with pharmacological pathway dissection, replicated by multiple subsequent studies\",\n      \"pmids\": [\"11489965\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"The ITIM in KIR2DL4's cytoplasmic tail is not required for its activating function; the transmembrane arginine-tyrosine motif is required for the activation signal; the phosphorylated cytoplasmic tail recruits SHP-1 and SHP-2 (via GST pulldown), giving KIR2DL4 inhibitory potential in addition to activating function; and the activation-deficient ITIM mutant can inhibit CD16 signaling.\",\n      \"method\": \"Site-directed mutagenesis of ITIM tyrosine and transmembrane arginine, redirected lysis assay, GST fusion protein pulldown with SHP-1 and SHP-2\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro mutagenesis plus pulldown with multiple orthogonal functional assays in a single study\",\n      \"pmids\": [\"12055234\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"KIR2DL4 surface expression depends on genotype: the 10A allele (10 adenines in exon 6) encodes a full-length receptor expressed on the cell surface, while the 9A allele causes a frameshift and premature stop codon producing a non-surface-expressed, truncated receptor. Surface expression is detectable only on CD56bright NK cells from 10A carriers and is up-regulated by IL-2.\",\n      \"method\": \"cDNA transfection of 10A and 9A alleles into NK-like cell line, flow cytometry on primary NK cells, anti-KIR2DL4 mAb staining\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — transfection experiments plus primary cell validation, replicated in subsequent studies\",\n      \"pmids\": [\"14500636\", \"12902476\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"KIR2DL4 is an activating receptor: ligation of KIR2DL4 on cultured NK cells from 10A allele carriers triggers redirected lysis, confirming its activating function; this activity depends on the 10A genotype.\",\n      \"method\": \"Redirected lysis assay with anti-KIR2DL4 mAb on NK cells stratified by 9A/10A genotype\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — functional assay with genotype-stratified primary cells, replicated across labs\",\n      \"pmids\": [\"12902476\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"KIR2DL4 associates with the Fc receptor gamma (FcεRI-γ) chain via its transmembrane arginine residue, which promotes surface expression and provides signal-transducing function. This association is distinct from other activating KIRs, which associate with DAP12.\",\n      \"method\": \"Biochemical co-immunoprecipitation, transmembrane arginine mutation (R/G), functional redirected lysis and cytokine assays in NK-like cell line\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — reciprocal biochemical evidence plus mutagenesis confirming functional consequence\",\n      \"pmids\": [\"15778339\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Residues Met76 and Gln79 in the HLA-G α1 domain are critical for KIR2DL4 recognition; mutating these to Ala reduces binding affinity between KIR2DL4-IgG Fc fusion protein and HLA-G, and reduces KIR2DL4-transfected NK-92 cell cytolysis against HLA-G-expressing K562 targets.\",\n      \"method\": \"Retroviral transduction, KIR2DL4-IgG Fc fusion protein binding assay, cytotoxicity (LDH release) assay\",\n      \"journal\": \"Cell research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1-2 — site-directed mutagenesis with functional binding and cytotoxicity readout, single study\",\n      \"pmids\": [\"15780179\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"HLA-G up-regulates expression of KIR2DL4 in antigen-presenting cells, NK cells, and T cells, suggesting a positive feedback loop where HLA-G increases expression of its own receptor.\",\n      \"method\": \"Flow cytometry and gene expression analysis of ILT2, ILT3, ILT4, and KIR2DL4 on multiple immune cell types following HLA-G exposure\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — cell-based expression measurement, single lab, mechanism of up-regulation not fully dissected\",\n      \"pmids\": [\"15670976\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"The KIR2DL4 promoter drives NK cell-specific reporter expression; it contains an AML-2 binding site that acts as a repressor, and mutation of the AML site substantially increases KIR2DL4 promoter activity. KIR2DL4 also contains an inhibitory element upstream of its core promoter, distinguishing it from clonally expressed KIR promoters.\",\n      \"method\": \"Reporter gene assay in NK3.3 and primary NK cells, DNase I footprinting, site-directed mutagenesis of transcription factor binding sites\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — mutagenesis plus footprinting with functional reporter assay, single lab\",\n      \"pmids\": [\"15778373\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"The 9A allele of KIR2DL4 produces a secreted (soluble) form of KIR2DL4 due to splicing out of the transmembrane region; a Delta-D0 isoform missing the D0 domain is produced from some 10A allele carriers and is undetectable by available anti-KIR2DL4 mAbs.\",\n      \"method\": \"RT-PCR, flow cytometry, immunoblot analysis of NK cells from genotyped individuals; in vitro culture experiments\",\n      \"journal\": \"European journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple molecular approaches in genotyped primary cells, single lab\",\n      \"pmids\": [\"17171757\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"KIR2DL4 cross-linking activates JNK, ERK, and p38 MAPKs, as well as the NF-κB pathway (via IKKβ phosphorylation and IκBα degradation), leading to transcription of TNF-α, IFN-γ, MIP1α, MIP1β, and IL-8. Mutation of the transmembrane arginine (R/G) abrogates FcεRI-γ association, cytolytic activity and calcium responses, but still activates MAPKs and NF-κB and selectively induces MIP1α, revealing two distinct structural signaling modules.\",\n      \"method\": \"Pharmacological kinase inhibitors, Western blotting for phosphorylated kinases, cytokine ELISA/RT-PCR, transmembrane arginine mutagenesis (R/G) in KHYG-1 NK-like cell line\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — mutagenesis plus pharmacological dissection with multiple readouts, orthogonal methods in single rigorous study\",\n      \"pmids\": [\"18292514\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Epigenetic regulation of KIR2DL4 expression in T cells involves DNA methylation and histone modifications: NK cells have a fully demethylated KIR2DL4 promoter with activating histone marks (H3/H4 acetylation, di/tri-H3-K4 methylation); T cells have a partially demethylated promoter with dimethyl H3-K4 but repressive histone marks, which is sensitized to DNMT inhibitor-induced transcription with aging.\",\n      \"method\": \"Chromatin immunoprecipitation (ChIP), bisulfite sequencing, DNMT inhibitor treatment, quantitative gene expression in primary T cells and NK cells\",\n      \"journal\": \"Journal of leukocyte biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — ChIP and bisulfite sequencing with functional inhibitor experiments, single lab\",\n      \"pmids\": [\"18586981\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"KIR2DL4 resides in endosomes (not at the cell surface) and signals from this intracellular site after binding soluble HLA-G; this endosomal signaling pathway involves DNA-PKcs and Akt kinases and results in a pro-inflammatory and pro-angiogenic response.\",\n      \"method\": \"Subcellular fractionation, confocal microscopy for receptor localization, signaling assays for DNA-PKcs and Akt in NK cells (review synthesizing primary data)\",\n      \"journal\": \"Traffic\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct localization and signaling evidence from primary NK cells with functional consequences, supported by multiple subsequent studies\",\n      \"pmids\": [\"20854369\", \"22934097\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Sustained activation of KIR2DL4 (CD158d) by agonists induces a DNA damage response (p21 upregulation, HP1-γ phosphorylation), cellular senescence (morphological changes, survival without cell-cycle entry), and a senescence-associated secretory phenotype (SASP). The secretome of these senescent NK cells promotes vascular remodeling and angiogenesis, as measured by endothelial cell tube formation and vascular permeability assays.\",\n      \"method\": \"CD158d agonist stimulation of primary NK cells, Western blot for p21 and HP1-γ phosphorylation, flow cytometry, transcriptome analysis, functional vascular assays (tube formation, permeability)\",\n      \"journal\": \"PNAS\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods establishing senescence pathway, functional vascular readout, single rigorous study with strong mechanistic follow-up\",\n      \"pmids\": [\"23184984\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"The KIR2DL4 promoter requires Runx binding sites (specifically Runx3) for constitutive transcription, with contributions from CRE and initiator elements; IL-2/IL-15 stimulation additionally requires functional Ets (Ets1) sites. Runx3 and Ets1 were shown by ChIP to bind the 2DL4 promoter in situ.\",\n      \"method\": \"Promoter mutagenesis, EMSA, co-transfection assay, chromatin immunoprecipitation (ChIP) in NK cell lines and T cells\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — mutagenesis, EMSA, and ChIP with functional reporter assays in single study\",\n      \"pmids\": [\"22467658\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"KIR2DL4 directly interacts with heparan sulfate (HS)/heparin via its D0 domain (identified by genome-wide siRNA screen for HS3ST3B1); this interaction induces differential localization to Rab5+ and Rab7+ endosomes and downregulates cytokine production and receptor degradation. Syndecan-4 (SDC4) HSPG directly affects KIR2DL4 endocytosis and membrane trafficking.\",\n      \"method\": \"Genome-wide siRNA screen, direct binding assays with KIR2DL4 domain mutants, confocal microscopy for endosomal co-localization (Rab5/Rab7), cytokine secretion assay\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — genome-wide unbiased screen validated by direct binding assays and functional localization studies with domain mapping\",\n      \"pmids\": [\"24127555\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Crystal structure of KIR2DL4 extracellular domains determined at 2.8 Å reveals a D0-D2 arrangement (lacking D1) with C2-type immunoglobulin folds at an acute elbow angle. KIR2DL4 self-associates via the D0 domain in a concentration-dependent manner, forming tetramers in the crystal lattice and in solution (confirmed by SEC, DLS, AUC, SAXS). This D0-mediated self-association precludes an HLA interaction analogous to KIR3DL1, and no direct HLA binding was detected.\",\n      \"method\": \"X-ray crystallography (2.8 Å), size exclusion chromatography, dynamic light scattering, analytical ultracentrifugation, small angle X-ray scattering, direct HLA binding studies\",\n      \"journal\": \"Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — high-resolution crystal structure with multiple orthogonal solution biophysical validations in single study\",\n      \"pmids\": [\"25759384\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"KIR2DL4 is expressed on human mast cells (LAD2, PB-mast) in addition to NK cells; agonistic antibodies to KIR2DL4 negatively regulate KIT-mediated and FcεRI-mediated responses of mast cells, and HLA-G stimulation through KIR2DL4 induces secretion of leukemia inhibitory factor and serine proteases from mast cells.\",\n      \"method\": \"Flow cytometry, agonistic antibody stimulation assays, ELISA for cytokine/protease secretion in human mast cell lines and primary PB-mast cells\",\n      \"journal\": \"International journal of molecular sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — functional assays in mast cells establishing new cell-type expression and dual regulatory role, single lab\",\n      \"pmids\": [\"32023940\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"HLA-G binding to KIR2DL4 on NK cells desensitizes NK cells to trastuzumab-mediated ADCC in HER2+ breast cancer; KIR2DL4 (without HLA-G engagement) promotes ADCC and synergizes with Fcγ receptor to increase IFN-γ secretion; IFN-γ upregulates KIR2DL4 via JAK2/STAT1 signaling; blockade of HLA-G/KIR2DL4 signaling improves trastuzumab efficacy in vivo.\",\n      \"method\": \"NK cell cytotoxicity assays, ELISA for cytokines, pharmacological JAK2/STAT1 inhibition, KIR2DL4 blockade in vivo mouse xenograft model\",\n      \"journal\": \"Signal transduction and targeted therapy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — functional in vitro and in vivo assays with pathway inhibition, single lab\",\n      \"pmids\": [\"34158475\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"KIR2DL4 expressed in renal cell carcinoma (RCC) cells promotes RCC proliferation associated with PI3K/Akt signaling activation; KIR2DL4 knockdown reduces AKT phosphorylation and proliferation, while KIR2DL4 overexpression increases AKT phosphorylation and tumor growth in vivo.\",\n      \"method\": \"shRNA knockdown, overexpression, MTT assay, soft agar colony formation, xenograft mouse model, RNA sequencing, immunoblot for phospho-AKT, PI3K inhibitor (wortmannin) treatment\",\n      \"journal\": \"Life sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — loss- and gain-of-function with in vivo validation and pharmacological confirmation, single lab\",\n      \"pmids\": [\"35063466\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"Soluble HLA-G stimulates transcription of type I interferon-stimulated genes (ISGs) in primary NK cells through a noncanonical pathway requiring the transcription factor IRF7 and kinase JAK1. The C-terminal portion of KIR2DL4's cytoplasmic tail contains a JAK1-binding sequence analogous to IFN receptor conserved JAK1 binding sites, and was required for JAK1 binding to KIR2DL4. HLA-G stimulation led to nuclear phosphorylation of IRF7 and STAT2. scRNA-seq showed ISG induction is similar in CD56bright and CD56dim NK cells.\",\n      \"method\": \"Primary NK cell stimulation with soluble HLA-G and agonistic anti-KIR2DL4 antibody, transcriptomics (bulk RNA-seq, scRNA-seq), pharmacological JAK1 inhibition, co-immunoprecipitation of JAK1 with KIR2DL4 cytoplasmic tail mutants, nuclear phospho-IRF7 and phospho-STAT2 detection\",\n      \"journal\": \"Science signaling\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal methods (biochemical, genetic, transcriptomic, pharmacological) in a single rigorous study establishing a novel signaling pathway\",\n      \"pmids\": [\"41632833\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"KIR2DL4 is an endosome-resident NK cell receptor with a D0-D2 extracellular domain structure and a long cytoplasmic tail bearing both a transmembrane arginine (which recruits FcεRI-γ for one signaling module) and an ITIM (capable of recruiting SHP-1/SHP-2); upon binding its ligand soluble HLA-G in the extracellular milieu, the receptor-ligand complex is internalized into early endosomes where KIR2DL4 signals through DNA-PKcs, Akt, NF-κB, p38/JNK/ERK MAPKs, and a noncanonical JAK1-IRF7-STAT2 axis to drive pro-inflammatory cytokine (IFN-γ, TNF-α) and chemokine secretion, pro-angiogenic responses, and cellular senescence in NK cells—with additional ligand interactions involving heparan sulfate proteoglycans that regulate endosomal trafficking and receptor degradation.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"KIR2DL4 is a structurally unique killer cell immunoglobulin-like receptor on NK cells that integrates activating and inhibitory signaling to regulate innate immune responses, vascular remodeling, and cellular senescence. Its D0-D2 extracellular domain binds soluble HLA-G, which is internalized into Rab5+/Rab7+ endosomes where KIR2DL4 signals through DNA-PKcs, Akt, NF-κB, p38/JNK/ERK MAPKs, and a noncanonical JAK1–IRF7–STAT2 axis to drive IFN-γ, TNF-α, chemokine secretion, and type I interferon-stimulated gene transcription [PMID:11489965, PMID:18292514, PMID:20854369, PMID:41632833]. Two structurally separable signaling modules exist: a transmembrane arginine that recruits FcεRI-γ for cytolytic and calcium responses, and a cytoplasmic ITIM that recruits SHP-1/SHP-2 for inhibitory function, with the ITIM-independent tail activating MAPKs and NF-κB even without FcεRI-γ association [PMID:12055234, PMID:15778339, PMID:18292514]. Sustained KIR2DL4 activation induces a senescence-associated secretory phenotype in NK cells that promotes angiogenesis, and heparan sulfate proteoglycan interactions via the D0 domain regulate endosomal trafficking and receptor degradation [PMID:23184984, PMID:24127555].\",\n  \"teleology\": [\n    {\n      \"year\": 2001,\n      \"claim\": \"Establishing that KIR2DL4 triggers IFN-γ rather than cytotoxicity in resting NK cells, with p38 MAPK as a required downstream kinase, defined its functional output as cytokine-biased activation.\",\n      \"evidence\": \"Redirected lysis and IFN-γ secretion assays with p38/ERK inhibitors in primary resting NK cells\",\n      \"pmids\": [\"11489965\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Upstream events connecting receptor engagement to p38 activation unknown\", \"Whether other MAPKs contribute not yet tested\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Demonstrating that the transmembrane arginine drives activating function while the ITIM recruits SHP-1/SHP-2 for inhibition resolved how a single receptor encodes dual signaling capacity.\",\n      \"evidence\": \"Site-directed mutagenesis of ITIM tyrosine and transmembrane arginine with GST pulldown and redirected lysis in NK-like cells\",\n      \"pmids\": [\"12055234\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Adaptor linking transmembrane arginine to activation not yet identified\", \"In vivo relevance of inhibitory signaling not assessed\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Showing that the 10A/9A frameshift polymorphism governs surface expression versus truncation explained population-level variation in KIR2DL4 function and confined surface expression to CD56bright NK cells.\",\n      \"evidence\": \"cDNA transfection of 10A/9A alleles, flow cytometry on genotyped primary NK cells\",\n      \"pmids\": [\"14500636\", \"12902476\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether the 9A truncated/soluble form retains any signaling capacity unclear\", \"Mechanism restricting surface expression to CD56bright subset not defined\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Identifying FcεRI-γ as the signaling adaptor recruited by the transmembrane arginine — distinct from DAP12 used by other activating KIRs — established KIR2DL4's unique adaptor usage and explained how it reaches the surface.\",\n      \"evidence\": \"Co-immunoprecipitation and R/G transmembrane mutation with functional cytotoxicity and cytokine assays in NK-like cell line\",\n      \"pmids\": [\"15778339\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether FcεRI-γ is the sole adaptor or additional adaptors contribute\", \"Stoichiometry of the receptor-adaptor complex unknown\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Mapping critical HLA-G α1 domain residues (Met76, Gln79) for KIR2DL4 recognition provided the first ligand-side binding determinants.\",\n      \"evidence\": \"KIR2DL4-Fc fusion binding assays and cytotoxicity against HLA-G mutant targets\",\n      \"pmids\": [\"15780179\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Full binding interface not structurally resolved\", \"Affinity measurements not performed by biophysical methods\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Comprehensive pathway dissection showed KIR2DL4 activates JNK, ERK, p38 MAPKs and NF-κB, and that the R/G transmembrane mutant retains MAPK/NF-κB signaling but loses FcεRI-γ-dependent cytolysis and calcium flux, proving two structurally separable signaling modules.\",\n      \"evidence\": \"Pharmacological inhibitors, phospho-Western blots, cytokine ELISA, and transmembrane mutagenesis in KHYG-1 cells\",\n      \"pmids\": [\"18292514\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Proximal kinase linking the cytoplasmic tail to MAPK/NF-κB not identified\", \"Whether the two modules cooperate or antagonize in vivo unknown\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Discovering that KIR2DL4 primarily resides in endosomes and signals from there upon binding soluble HLA-G — via DNA-PKcs and Akt — overturned the surface-receptor paradigm and explained why soluble rather than membrane-bound HLA-G is the physiological ligand.\",\n      \"evidence\": \"Subcellular fractionation, confocal microscopy, DNA-PKcs and Akt signaling assays in primary NK cells\",\n      \"pmids\": [\"20854369\", \"22934097\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How soluble HLA-G accesses endosomal KIR2DL4 mechanistically not fully resolved\", \"Role of DNA-PKcs versus Akt in downstream gene induction not dissected\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Showing that sustained KIR2DL4 activation induces cellular senescence with a pro-angiogenic secretory phenotype linked the receptor to vascular remodeling programs relevant to pregnancy and tumor microenvironments.\",\n      \"evidence\": \"p21 and HP1-γ phosphorylation analysis, transcriptomics, endothelial tube formation and vascular permeability assays in primary NK cells\",\n      \"pmids\": [\"23184984\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether senescence is reversible not tested\", \"In vivo relevance at the decidual-placental interface not demonstrated\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"A genome-wide siRNA screen identified heparan sulfate proteoglycans (via HS3ST3B1 and syndecan-4) as regulators of KIR2DL4 endosomal trafficking and degradation through direct D0-domain binding, adding a glycan layer to receptor regulation.\",\n      \"evidence\": \"Genome-wide siRNA screen, direct binding assays with domain mutants, Rab5/Rab7 confocal co-localization, cytokine secretion assay\",\n      \"pmids\": [\"24127555\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Which specific HS sulfation patterns are required not defined\", \"Whether HSPG interaction competes with or facilitates HLA-G binding unknown\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"The 2.8 Å crystal structure revealed a D0-D2 architecture with concentration-dependent D0-mediated self-association into tetramers, and showed the D0 interface precludes canonical HLA binding, reshaping models of ligand recognition.\",\n      \"evidence\": \"X-ray crystallography, SEC, DLS, AUC, SAXS, direct HLA binding studies\",\n      \"pmids\": [\"25759384\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No co-crystal with HLA-G obtained\", \"Functional significance of tetramerization for signaling not tested\", \"How self-association relates to endosomal signaling unclear\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Detection of functional KIR2DL4 on mast cells, where it negatively regulates KIT and FcεRI responses and induces LIF secretion upon HLA-G stimulation, expanded its role beyond NK cells.\",\n      \"evidence\": \"Flow cytometry, agonistic antibody stimulation, cytokine/protease ELISA in LAD2 and primary PB-mast cells\",\n      \"pmids\": [\"32023940\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Signaling pathway in mast cells not compared to NK cell pathway\", \"In vivo mast cell relevance not established\", \"Not independently confirmed by another lab\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Discovery of a noncanonical JAK1–IRF7–STAT2 axis activated by soluble HLA-G via a JAK1-binding motif in KIR2DL4's cytoplasmic tail established a third signaling module driving type I ISG transcription in both CD56bright and CD56dim NK cells.\",\n      \"evidence\": \"Primary NK cell stimulation with sHLA-G, bulk/scRNA-seq, JAK1 pharmacological inhibition, co-IP of JAK1 with cytoplasmic tail truncation mutants, phospho-IRF7/STAT2 detection\",\n      \"pmids\": [\"41632833\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How JAK1 binding is coordinated with the ITIM and FcεRI-γ modules on the same tail not resolved\", \"Whether STAT2 and IRF7 form a canonical ISGF3-like complex or a distinct complex unknown\", \"Physiological consequence of ISG induction for NK cell effector function not tested\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Major unresolved questions include the structural basis of KIR2DL4–HLA-G interaction (no co-crystal exists), the in vivo physiological role of endosomal signaling at the maternal-fetal interface, how the three signaling modules (FcεRI-γ, ITIM/SHP, JAK1–IRF7) are integrated or segregated on a single receptor, and the functional significance of D0-mediated oligomerization.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No KIR2DL4–HLA-G co-crystal structure\", \"No genetic knockout or conditional deletion model in vivo\", \"Integration logic among three signaling modules unresolved\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [0, 1, 3, 9, 12, 19]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [1, 16]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005768\", \"supporting_discovery_ids\": [11, 14]},\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [2, 3, 4]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0162582\", \"supporting_discovery_ids\": [0, 9, 11, 12, 18, 19]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [0, 1, 3, 9, 12, 17]},\n      {\"term_id\": \"R-HSA-8953854\", \"supporting_discovery_ids\": [19]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [12]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"FCER1G\",\n      \"PTPN6\",\n      \"PTPN11\",\n      \"HLA-G\",\n      \"JAK1\",\n      \"SDC4\",\n      \"RUNX3\",\n      \"ETS1\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```\n\nWait, I need to fix the pathway term_ids. I used \"GO:0162582\" which is invalid. Let me correct to the Reactome IDs provided.\n\n```json\n{\n  \"mechanistic_narrative\": \"KIR2DL4 is a structurally unique killer cell immunoglobulin-like receptor on NK cells that integrates activating and inhibitory signaling to regulate innate immune responses, vascular remodeling, and cellular senescence. Its D0-D2 extracellular domain binds soluble HLA-G, which is internalized into Rab5+/Rab7+ endosomes where KIR2DL4 signals through DNA-PKcs, Akt, NF-κB, p38/JNK/ERK MAPKs, and a noncanonical JAK1–IRF7–STAT2 axis to drive IFN-γ, TNF-α, chemokine secretion, and type I interferon-stimulated gene transcription [PMID:11489965, PMID:18292514, PMID:20854369, PMID:41632833]. Two structurally separable signaling modules exist: a transmembrane arginine that recruits FcεRI-γ for cytolytic and calcium responses, and a cytoplasmic ITIM that recruits SHP-1/SHP-2 for inhibitory function, with the ITIM-independent tail activating MAPKs and NF-κB even without FcεRI-γ association [PMID:12055234, PMID:15778339, PMID:18292514]. Sustained KIR2DL4 activation induces a senescence-associated secretory phenotype in NK cells that promotes angiogenesis, and heparan sulfate proteoglycan interactions via the D0 domain regulate endosomal trafficking and receptor degradation [PMID:23184984, PMID:24127555].\",\n  \"teleology\": [\n    {\n      \"year\": 2001,\n      \"claim\": \"Establishing that KIR2DL4 triggers IFN-γ rather than cytotoxicity in resting NK cells, with p38 MAPK as a required downstream kinase, defined its functional output as cytokine-biased activation.\",\n      \"evidence\": \"Redirected lysis and IFN-γ secretion assays with p38/ERK inhibitors in primary resting NK cells\",\n      \"pmids\": [\"11489965\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Upstream events connecting receptor engagement to p38 activation unknown\", \"Whether other MAPKs contribute not yet tested\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Demonstrating that the transmembrane arginine drives activating function while the ITIM recruits SHP-1/SHP-2 for inhibition resolved how a single receptor encodes dual signaling capacity.\",\n      \"evidence\": \"Site-directed mutagenesis of ITIM tyrosine and transmembrane arginine with GST pulldown and redirected lysis in NK-like cells\",\n      \"pmids\": [\"12055234\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Adaptor linking transmembrane arginine to activation not yet identified\", \"In vivo relevance of inhibitory signaling not assessed\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Showing that the 10A/9A frameshift polymorphism governs surface expression versus truncation explained population-level variation in KIR2DL4 function and confined surface expression to CD56bright NK cells.\",\n      \"evidence\": \"cDNA transfection of 10A/9A alleles, flow cytometry on genotyped primary NK cells\",\n      \"pmids\": [\"14500636\", \"12902476\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether the 9A truncated/soluble form retains any signaling capacity unclear\", \"Mechanism restricting surface expression to CD56bright subset not defined\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Identifying FcεRI-γ as the signaling adaptor recruited by the transmembrane arginine — distinct from DAP12 used by other activating KIRs — established KIR2DL4's unique adaptor usage and explained how it reaches the surface.\",\n      \"evidence\": \"Co-immunoprecipitation and R/G transmembrane mutation with functional cytotoxicity and cytokine assays in NK-like cell line\",\n      \"pmids\": [\"15778339\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether FcεRI-γ is the sole adaptor or additional adaptors contribute\", \"Stoichiometry of the receptor-adaptor complex unknown\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Mapping critical HLA-G α1 domain residues (Met76, Gln79) for KIR2DL4 recognition provided the first ligand-side binding determinants.\",\n      \"evidence\": \"KIR2DL4-Fc fusion binding assays and cytotoxicity against HLA-G mutant targets\",\n      \"pmids\": [\"15780179\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Full binding interface not structurally resolved\", \"Affinity measurements not performed by biophysical methods\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Comprehensive pathway dissection showed KIR2DL4 activates JNK, ERK, p38 MAPKs and NF-κB, and that the R/G transmembrane mutant retains MAPK/NF-κB signaling but loses FcεRI-γ-dependent cytolysis and calcium flux, proving two structurally separable signaling modules.\",\n      \"evidence\": \"Pharmacological inhibitors, phospho-Western blots, cytokine ELISA, and transmembrane mutagenesis in KHYG-1 cells\",\n      \"pmids\": [\"18292514\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Proximal kinase linking the cytoplasmic tail to MAPK/NF-κB not identified\", \"Whether the two modules cooperate or antagonize in vivo unknown\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Discovering that KIR2DL4 primarily resides in endosomes and signals from there upon binding soluble HLA-G — via DNA-PKcs and Akt — overturned the surface-receptor paradigm and explained why soluble rather than membrane-bound HLA-G is the physiological ligand.\",\n      \"evidence\": \"Subcellular fractionation, confocal microscopy, DNA-PKcs and Akt signaling assays in primary NK cells\",\n      \"pmids\": [\"20854369\", \"22934097\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How soluble HLA-G accesses endosomal KIR2DL4 mechanistically not fully resolved\", \"Role of DNA-PKcs versus Akt in downstream gene induction not dissected\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Showing that sustained KIR2DL4 activation induces cellular senescence with a pro-angiogenic secretory phenotype linked the receptor to vascular remodeling programs relevant to pregnancy and tumor microenvironments.\",\n      \"evidence\": \"p21 and HP1-γ phosphorylation analysis, transcriptomics, endothelial tube formation and vascular permeability assays in primary NK cells\",\n      \"pmids\": [\"23184984\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether senescence is reversible not tested\", \"In vivo relevance at the decidual-placental interface not demonstrated\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"A genome-wide siRNA screen identified heparan sulfate proteoglycans (via HS3ST3B1 and syndecan-4) as regulators of KIR2DL4 endosomal trafficking and degradation through direct D0-domain binding, adding a glycan layer to receptor regulation.\",\n      \"evidence\": \"Genome-wide siRNA screen, direct binding assays with domain mutants, Rab5/Rab7 confocal co-localization, cytokine secretion assay\",\n      \"pmids\": [\"24127555\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Which specific HS sulfation patterns are required not defined\", \"Whether HSPG interaction competes with or facilitates HLA-G binding unknown\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"The 2.8 Å crystal structure revealed a D0-D2 architecture with concentration-dependent D0-mediated self-association into tetramers, and showed the D0 interface precludes canonical HLA binding, reshaping models of ligand recognition.\",\n      \"evidence\": \"X-ray crystallography, SEC, DLS, AUC, SAXS, direct HLA binding studies\",\n      \"pmids\": [\"25759384\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No co-crystal with HLA-G obtained\", \"Functional significance of tetramerization for signaling not tested\", \"How self-association relates to endosomal signaling unclear\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Detection of functional KIR2DL4 on mast cells, where it negatively regulates KIT and FcεRI responses and induces LIF secretion upon HLA-G stimulation, expanded its role beyond NK cells.\",\n      \"evidence\": \"Flow cytometry, agonistic antibody stimulation, cytokine/protease ELISA in LAD2 and primary PB-mast cells\",\n      \"pmids\": [\"32023940\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Signaling pathway in mast cells not compared to NK cell pathway\", \"In vivo mast cell relevance not established\", \"Not independently confirmed by another lab\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Discovery of a noncanonical JAK1–IRF7–STAT2 axis activated by soluble HLA-G via a JAK1-binding motif in KIR2DL4's cytoplasmic tail established a third signaling module driving type I ISG transcription in both CD56bright and CD56dim NK cells.\",\n      \"evidence\": \"Primary NK cell stimulation with sHLA-G, bulk/scRNA-seq, JAK1 pharmacological inhibition, co-IP of JAK1 with cytoplasmic tail truncation mutants, phospho-IRF7/STAT2 detection\",\n      \"pmids\": [\"41632833\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How JAK1 binding is coordinated with the ITIM and FcεRI-γ modules on the same tail not resolved\", \"Whether STAT2 and IRF7 form a canonical ISGF3-like complex or a distinct complex unknown\", \"Physiological consequence of ISG induction for NK cell effector function not tested\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Major unresolved questions include the structural basis of KIR2DL4–HLA-G interaction (no co-crystal exists), the in vivo physiological role of endosomal signaling at the maternal-fetal interface, how the three signaling modules (FcεRI-γ, ITIM/SHP, JAK1–IRF7) are integrated or segregated on a single receptor, and the functional significance of D0-mediated oligomerization.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No KIR2DL4–HLA-G co-crystal structure\", \"No genetic knockout or conditional deletion model in vivo\", \"Integration logic among three signaling modules unresolved\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [0, 1, 3, 9, 12, 19]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [1, 16]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005768\", \"supporting_discovery_ids\": [11, 14]},\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [2, 3, 4]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0, 9, 11, 12, 18, 19]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [0, 1, 3, 9, 12, 17]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [12]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"FCER1G\",\n      \"PTPN6\",\n      \"PTPN11\",\n      \"HLA-G\",\n      \"JAK1\",\n      \"SDC4\",\n      \"RUNX3\",\n      \"ETS1\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}