KIR3DL2

KIR3DL2 is a three-domain killer immunoglobulin-like receptor expressed on NK cells and T-cell subsets that operates as a ligand-discriminating cell-surface receptor coupling recognition of HLA class I and CpG-DNA to control of effector cytokine output and lymphocyte survival (PMID:15162437, PMID:20147700, PMID:23440420). It binds HLA-A3 and HLA-A11 in a peptide-dependent manner, with peptide residue 8 critical for recognition (PMID:15162437), but engages β2m-free HLA-B27 free heavy chains and disulfide-bonded B27 homodimers more strongly and in a peptide-sequence-independent fashion, contacts mediated preferentially by the D0 domain together with complementary D1/D2 interactions across both heavy chains (PMID:23440420, PMID:25582852). B27 free heavy-chain engagement drives greater receptor phosphorylation and signaling than HLA-A3 and promotes survival of KIR3DL2+ NK and CD4 T cells, whereas heterotrimeric class I ligation inhibits IFN-γ production (PMID:17407096, PMID:23440420). Through its D0 domain KIR3DL2 also binds CpG oligodeoxynucleotides, co-internalizing and shuttling them to early endosomes for TLR9 engagement, and discriminates self-DNA from pathogen DNA in a sequence-specific manner to set IFN-γ and cytotoxic responses (PMID:20147700, PMID:34760351). These activities link the receptor to disease: stronger KIR3DL2–B27 free heavy-chain interaction expands IL-23R-bearing, IL-17-producing Th17 cells in spondyloarthritis (PMID:21248258, PMID:23804219), and on malignant Sézary T cells CpG engagement triggers caspase-dependent apoptosis coupled to STAT3 dephosphorylation (PMID:25007046), making KIR3DL2 an actionable target for antibody-mediated killing of cutaneous T-cell lymphoma (PMID:25361998).

1. 2003 Medium

   Established that KIR3DL2 engagement does not necessarily deliver inhibitory signals in all T-cell contexts, complicating the simple inhibitory-receptor model.

   Evidence antibody crosslinking on tumor-infiltrating CD8+ CTL clones with cytotoxicity and IFN-γ readouts

   PMID:14562047

   Open questions at the time

   • Negative finding in one CTL context only
   • Did not identify physiological ligand driving signaling
   • No biochemical signaling characterized
2. 2004 High

   Defined the first physiological HLA ligands of KIR3DL2 and the peptide-dependence of recognition, answering what classical class I molecules the receptor reads.

   Evidence HLA tetramer staining of KIR3DL2 transfectants with peptide analogue substitution

   PMID:15162437

   Open questions at the time

   • Functional consequence of A3/A11 binding not established here
   • Affinity relative to other ligands unknown
   • No structural interface defined
3. 2005 Medium

   Showed that KIR3DL2–B27 homodimer interaction promotes NK cell survival in spondyloarthritis, linking the receptor to a disease-relevant ligand.

   Evidence co-culture of patient NK cells with B27₂-expressing cell line; apoptosis and activation-marker assays

   PMID:16255049

   Open questions at the time

   • Did not resolve signaling mechanism of survival
   • Single patient-cell context
   • Causal role in disease not proven
4. 2007 High

   Demonstrated that β2m-free HLA-B27 heavy-chain homodimers are peptide-sequence-independent ligands of KIR3DL2 that inhibit IFN-γ, distinguishing this binding mode from peptide-dependent heterotrimer recognition.

   Evidence KIR transfectant binding with loaded vs unloaded B27 tetramers; NK IFN-γ functional assays

   PMID:17407096

   Open questions at the time

   • Domain basis of dimer binding not mapped
   • Did not quantify ligand hierarchy
   • Signaling downstream of inhibition uncharacterized
5. 2010 High

   Revealed a non-HLA ligand class, showing KIR3DL2 binds CpG ODN via its D0 domain and delivers it to endosomal TLR9, defining a receptor role in innate DNA sensing.

   Evidence soluble receptor binding, D0 domain-deletion mutagenesis, confocal co-localization, IFN-γ assays

   PMID:20147700

   Open questions at the time

   • Sequence selectivity of CpG binding not defined here
   • Physiological source of CpG ligand unaddressed
   • Relationship to HLA-binding function unclear
6. 2011 Medium

   Connected the KIR3DL2–B27 dimer axis to Th17 biology, showing it drives IL-17 production and IL-23R expression in CD4 T cells relevant to spondyloarthritis.

   Evidence co-culture of KIR3DL2+ CD4 T cells with B27₂-APCs; intracellular cytokine staining

   PMID:21248258

   Open questions at the time

   • Signaling pathway linking receptor to IL-17 not resolved
   • In vitro system only
   • Causal contribution to clinical disease not established
7. 2013 High

   Quantified the ligand hierarchy and signaling consequences, establishing that B27 free heavy chain binds more strongly than HLA-A3 and drives greater phosphorylation, IL-2 output, and lymphocyte survival.

   Evidence tetramer binding, KIR3DL2-Fc pulldown, KIR3DL2-CD3ε reporter assays, phosphorylation and survival assays

   PMID:23440420

   Open questions at the time

   • Endogenous signaling adaptors not identified
   • Structural interface predicted not solved
   • Link between phosphorylation and survival mechanistically incomplete
8. 2013 Medium

   Provided a molecular basis for differential disease association by linking allele-specific B27 dimer/FHC formation to differential KIR3DL2 stimulation.

   Evidence comparison of HLA-B*27:05 vs B*27:09 dimer formation, reporter and NK survival assays

   PMID:23804219

   Open questions at the time

   • Direct genetic disease causation not tested
   • Mechanism of differential dimer formation not the focus
   • Single in vitro system
9. 2014 Medium

   Mapped the apoptotic consequence of CpG engagement in malignant cells, showing KIR3DL2 ligation triggers caspase-dependent death and STAT3 dephosphorylation in Sézary cells.

   Evidence internalization assays, caspase-inhibitor rescue, STAT3 phosphorylation western blot, apoptosis assays

   PMID:25007046

   Open questions at the time

   • Signaling link between receptor and STAT3 not defined
   • Restricted to Sézary cell context
   • Endogenous CpG trigger in vivo unknown
10. 2014 Medium

    Validated KIR3DL2 as a therapeutic target, demonstrating that an anti-KIR3DL2 antibody mediates ADCC/phagocytosis and tumor control in CTCL models.

    Evidence in vitro ADCC/phagocytosis with primary Sézary cells; mouse xenograft model

    PMID:25361998

    Open questions at the time

    • Single antibody/agent tested
    • Mechanism of selective tumor expression not addressed
    • Clinical efficacy not established here
11. 2015 Medium

    Resolved the structural basis of preferential B27 dimer binding, identifying D0 as central and defining complementary D0/D1 contacts across both heavy chains.

    Evidence site-directed mutagenesis of receptor domains, functional binding assays, computational interface modeling

    PMID:25582852

    Open questions at the time

    • Model not validated by experimental structure
    • Contact residues inferred from modeling
    • Single lab
12. 2021 Medium

    Established sequence-specific self/non-self DNA discrimination, showing genome-common CpG drives inhibition while parasite-prevalent CpG drives activation.

    Evidence CpG-DNA uptake, IFN-γ and cytotoxicity assays with defined sequences, genomic bioinformatic survey

    PMID:34760351

    Open questions at the time

    • Molecular basis of sequence discrimination not solved
    • NKL cell line model only
    • In vivo relevance to anti-parasite immunity untested

• How KIR3DL2 integrates opposing inhibitory versus activating outcomes across its HLA and CpG ligands at the level of cytoplasmic signaling adaptors remains unresolved.
• No experimental structure of any ligand complex
• Cytoplasmic signaling adaptors and ITIM/ITAM usage not directly characterized in corpus
• Mechanism switching between inhibition and activation undefined