KIR3DL2

KIR3DL2 is a three-domain immunoglobulin-like killer cell receptor expressed on NK cells and subsets of CD4 T cells that integrates recognition of classical MHC class I molecules, non-classical HLA free heavy chain forms, and microbial CpG DNA to regulate innate and adaptive immune responses. KIR3DL2 binds HLA-A3 and HLA-A11 in a peptide-dependent manner, with single amino acid substitutions at position 8 of the nonamer peptide critically affecting recognition, while it preferentially binds HLA-B27 free heavy chain homodimers (B27₂) in a peptide-independent manner via its D0 domain, triggering inhibition of IFN-γ production, promotion of KIR3DL2⁺ lymphocyte survival, and expansion of IL-17-producing CD4 T cells linked to spondyloarthritis pathogenesis (PMID:15162437, PMID:17407096, PMID:25582852, PMID:21248258). KIR3DL2 also functions as a cell-surface receptor for CpG oligodeoxynucleotides, binding them through its D0 domain and co-internalizing to deliver CpG DNA to TLR9 in early endosomes; this CpG engagement discriminates self-derived from pathogen-derived DNA sequences and, in malignant Sézary T cells, induces caspase-dependent apoptosis with STAT3 dephosphorylation (PMID:20147700, PMID:34760351, PMID:25007046). KIR3DL2 is aberrantly expressed on malignant T cells in cutaneous T-cell lymphoma and adult T-cell leukemia/lymphoma following HTLV-1-driven promoter hypomethylation, making it a therapeutic target for antibody-dependent cellular cytotoxicity (PMID:35687761, PMID:25361998).

1. 2003 Medium

   Initial functional studies asked whether KIR3DL2 delivers canonical inhibitory signals on CTL, and unexpectedly found that antibody cross-linking of KIR3DL2 on tumor-specific CTL clones produced neither inhibitory nor activating effects on cytotoxicity or cytokine output, raising the question of context-dependent signaling.

   Evidence Anti-KIR3DL2 antibody cross-linking with ⁵¹Cr-release cytotoxicity and IFN-γ assays on primary human CTL clones

   PMID:14562047

   Open questions at the time

   • Single lab observation; absence of effect may reflect insufficient cross-linking or cell-type-specific signaling
   • No direct assessment of ITIM phosphorylation or SHP recruitment
2. 2004 High

   Establishing ligand specificity, KIR3DL2*001 was shown to bind HLA-A3 and HLA-A11 in a peptide-dependent manner, with residue 8 of the nonamer peptide critically determining recognition, defining KIR3DL2 as a peptide-selective MHC class I receptor.

   Evidence HLA tetramer binding to KIR3DL2*001 transfectants with systematic peptide substitution analysis

   PMID:15162437

   Open questions at the time

   • Structural basis of peptide selectivity unresolved
   • Allelic variation in KIR3DL2 recognition not systematically explored
3. 2005 Medium

   Functional consequences of KIR3DL2 engagement were demonstrated when B27₂ homodimer-expressing cells protected KIR3DL2⁺ NK cells from apoptosis and enhanced their cytotoxicity, establishing a survival-promoting role for this receptor-ligand interaction in spondyloarthritis patients.

   Evidence Annexin V/7-AAD apoptosis and ⁵¹Cr-release cytotoxicity assays with SpA patient NK cells co-cultured with B27₂-expressing cells

   PMID:16255049

   Open questions at the time

   • Signaling pathway downstream of survival effect not identified
   • Single disease cohort studied
4. 2007 High

   A major advance was the discovery that HLA-B27 free heavy chain homodimers bind KIR3DL2 in a peptide-independent manner — fundamentally different from conventional HLA recognition — and that this ligation inhibits NK and T cell IFN-γ production, providing a mechanistic link between HLA-B27 and immune dysregulation.

   Evidence Tetramer binding to transfectants, peptide analogue studies, and functional IFN-γ secretion assays

   PMID:17407096

   Open questions at the time

   • Structural basis of peptide-independent recognition unresolved
   • Relative contribution of monomeric vs. dimeric FHC unclear
5. 2009 High

   Structural and mutagenesis work on KIR2DS4 identified that a proline-valine motif at positions 71–72, acquired by gene conversion from KIR3DL2, confers HLA-A*11 specificity, thereby mapping key specificity-determining residues in the KIR3DL2 binding surface.

   Evidence Crystal structure of KIR2DS4, swap mutagenesis of positions 71–72, and functional NK cell activation assays

   PMID:19858347

   Open questions at the time

   • No crystal structure of KIR3DL2 itself in complex with HLA ligand
   • Role of these residues in B27₂ recognition not tested
6. 2010 High

   KIR3DL2 was discovered to function beyond MHC recognition as a direct receptor for CpG oligodeoxynucleotides, binding CpG DNA via its D0 domain, co-internalizing with it, and shuttling it to TLR9 in early endosomes to trigger IFN-γ release — establishing a novel innate sensing role.

   Evidence Soluble receptor binding assay, D0 domain mutant analysis, confocal co-localization of CpG ODN and KIR3DL2, and cytokine secretion assays in NK cells

   PMID:20147700

   Open questions at the time

   • Structural basis of CpG–D0 interaction not determined
   • Whether CpG binding and HLA binding are mutually exclusive unknown
7. 2011 High

   The disease-relevant downstream consequence of KIR3DL2–B27₂ interaction was established: B27₂-expressing APCs drive survival, proliferation, and IL-17 production by KIR3DL2⁺ CD4 T cells, which express IL-23R, linking this pathway directly to Th17 expansion in spondyloarthritis.

   Evidence Co-culture of KIR3DL2⁺ CD4 T cells with B27₂-expressing APCs, flow cytometry for IL-23R, and IL-17 cytokine measurement across patient cohorts

   PMID:21248258

   Open questions at the time

   • Intracellular signaling cascade connecting KIR3DL2 ligation to IL-17 transcription not defined
   • Whether ITIM motifs are required for Th17 expansion not tested
8. 2013 High

   Quantitative comparison established that B27 free heavy chains bind KIR3DL2 more strongly than HLA-A3, with greater receptor phosphorylation and functional output, and that the disease-associated B*27:05 allele forms more surface dimers and stimulates KIR3DL2 more effectively than the non-disease-associated B*27:09, providing a molecular explanation for differential disease risk.

   Evidence Tetramer binding, KIR3DL2Fc pulldown, phosphorylation assays, reporter cell IL-2 production, and allele-specific dimer quantification

   PMID:23440420 PMID:23804219

   Open questions at the time

   • Affinity measurements in solution (SPR/ITC) not reported
   • Contribution of cis vs. trans B27₂ engagement in vivo unknown
9. 2014 Medium

   Two studies expanded the functional repertoire: CpG ODN engagement of KIR3DL2 on malignant Sézary T cells induces receptor internalization, STAT3 dephosphorylation, and caspase-dependent apoptosis, while an anti-KIR3DL2 antibody (IPH4102) mediates ADCC and phagocytosis against CTCL cells, validating KIR3DL2 as a therapeutic target in T-cell lymphoma.

   Evidence CpG ODN treatment with caspase inhibitor and STAT3 immunoblot in Sézary cells; ADCC/phagocytosis assays and mouse xenograft with IPH4102

   PMID:25007046 PMID:25361998

   Open questions at the time

   • Mechanism linking STAT3 dephosphorylation to apoptosis induction not delineated
   • Whether CpG-induced apoptosis occurs in non-malignant KIR3DL2⁺ cells not addressed
10. 2015 High

    Domain-level mapping through mutagenesis demonstrated that the D0 domain of KIR3DL2 is central to preferential B27₂ binding, with computational modeling predicting asymmetric contacts of D0 and D1 with both B27 heavy chains in the homodimer — the most detailed structural model of this interaction to date.

    Evidence Site-directed mutagenesis of KIR3DL2 Ig domains, functional reporter assays, and computational docking model

    PMID:25582852

    Open questions at the time

    • No experimental crystal or cryo-EM structure of the KIR3DL2–B27₂ complex
    • Contribution of individual D0 residues to CpG binding vs. B27₂ binding not dissected
11. 2021 Medium

    CpG DNA sensing by KIR3DL2 was shown to be sequence-specific, with human-genome-prevalent CpG sequences delivering inhibitory signals and parasite-genome-prevalent sequences activating NK cytotoxicity and IFN-γ production, suggesting KIR3DL2 discriminates self-DNA from pathogen DNA.

    Evidence Comparative genomic CpG analysis with functional lysis and IFN-γ assays in KIR3DL2⁺ NKL cells

    PMID:34760351

    Open questions at the time

    • Single cell line (NKL); not confirmed in primary NK cells
    • Structural basis of sequence-specific CpG discrimination unknown
    • In vivo relevance of DNA sensing in infection not tested
12. 2022 Medium

    HTLV-1 infection was found to drive KIR3DL2 surface expression on CD4⁺ T cells through promoter hypomethylation rather than Tax-mediated transactivation, and anti-KIR3DL2 antibody (lacutamab) killed primary ATL cells via ADCC, establishing KIR3DL2 as a target in HTLV-1-driven malignancy.

    Evidence PrimeFlow RNA co-detection, in vitro HTLV-1 infection, methylation profiling, and ex vivo ADCC assay on primary ATL cells

    PMID:35687761

    Open questions at the time

    • Epigenetic mechanism of promoter demethylation not fully characterized
    • Whether KIR3DL2 has a functional role in HTLV-1 pathogenesis beyond serving as a surface marker is unclear

• A high-resolution experimental structure of KIR3DL2 in complex with B27₂ homodimers or CpG DNA is still lacking, and the intracellular signaling pathways downstream of KIR3DL2 ligation — particularly how the same receptor can mediate inhibitory signaling, survival, IL-17 induction, or apoptosis depending on ligand and cell context — remain poorly defined.
• No crystal or cryo-EM structure of KIR3DL2 with any ligand
• Signaling intermediates linking ITIM phosphorylation to Th17 expansion or CpG-induced apoptosis not identified
• Whether CpG and HLA binding sites on D0 overlap is unknown