Killer cell immunoglobulin-like receptor 3DL1-mediated recognition of human leukocyte antigen B.

Members of the killer cell immunoglobulin-like receptor (KIR) family, a large group of polymorphic receptors expressed on natural killer (NK) cells, recognize particular peptide-laden human leukocyte antigen (pHLA) class I molecules and have a pivotal role in innate immune responses. Allelic variation and extensive polymorphism within the three-domain KIR family (KIR3D, domains D0-D1-D2) affects pHLA binding specificity and is linked to the control of viral replication and the treatment outcome of certain haematological malignancies. Here we describe the structure of a human KIR3DL1 receptor bound to HLA-B*5701 complexed with a self-peptide. KIR3DL1 clamped around the carboxy-terminal end of the HLA-B*5701 antigen-binding cleft, resulting in two discontinuous footprints on the pHLA. First, the D0 domain, a distinguishing feature of the KIR3D family, extended towards ß2-microglobulin and abutted a region of the HLA molecule with limited polymorphism, thereby acting as an 'innate HLA sensor' domain. Second, whereas the D2-HLA-B*5701 interface exhibited a high degree of complementarity, the D1-pHLA-B*5701 contacts were suboptimal and accommodated a degree of sequence variation both within the peptide and the polymorphic region of the HLA molecule. Although the two-domain KIR (KIR2D) and KIR3DL1 docked similarly onto HLA-C and HLA-B respectively, the corresponding D1-mediated interactions differed markedly, thereby providing insight into the specificity of KIR3DL1 for discrete HLA-A and HLA-B allotypes. Collectively, in association with extensive mutagenesis studies at the KIR3DL1-pHLA-B*5701 interface, we provide a framework for understanding the intricate interplay between peptide variability, KIR3D and HLA polymorphism in determining the specificity requirements of this essential innate interaction that is conserved across primate species.

Cooperativity of HIV-Specific Cytolytic CD4 T Cells and CD8 T Cells in Control of HIV Viremia.

UNLABELLED: CD4+ T cells play a pivotal role in the control of chronic viral infections. Recently, nontraditional CD4+ T cell functions beyond helper effects have been described, and a role for cytolytic CD4+ T cells in the control of HIV infection has been suggested. We define here the transcriptional, phenotypic, and functional profiles of HIV-specific cytolytic CD4+ T cells. Fluidigm BioMark and multiparameter flow cytometric analysis of HIV-specific cytolytic CD4+ T cells revealed a distinct transcriptional signature compared to Th1 CD4+ cells but shared similar features with HIV-specific cytolytic CD8+ T cells. Furthermore, HIV-specific cytolytic CD4+ T cells showed comparable killing activity relative to HIV-specific CD8+ T cells and worked cooperatively in the elimination of virally infected cells. Interestingly, we found that cytolytic CD4+ T cells emerge early during acute HIV infection and tightly follow acute viral load trajectory. This emergence was associated to the early viral set point, suggesting an involvement in early control, in spite of CD4 T cell susceptibility to HIV infection. Our data suggest cytolytic CD4+ T cells as an independent subset distinct from Th1 cells that show combined activity with CD8+ T cells in the long-term control of HIV infection. IMPORTANCE: The ability of the immune system to control chronic HIV infection is of critical interest to both vaccine design and therapeutic approaches. Much research has focused on the effect of the ability of CD8+ T cells to control the virus, while CD4+ T cells have been overlooked as effectors in HIV control due to the fact that they are preferentially infected. We show here that a subset of HIV-specific CD4+ T cells cooperate in the cytolytic control of HIV replication. Moreover, these cells represent a distinct subset of CD4+ T cells showing significant transcriptional and phenotypic differences compared to HIV-specific Th1 cells but with similarities to CD8+ T cells. These findings are important for our understanding of HIV immunopathology.

Degenerate recognition of MHC class I molecules with Bw4 and Bw6 motifs by a killer cell Ig-like receptor 3DL expressed by macaque NK cells.

The killer cell Ig-like receptors (KIRs) expressed on the surface of NK cells recognize specific MHC class I (MHC-I) molecules and regulate NK cell activities against pathogen-infected cells and neoplasia. In HIV infection, survival is linked to host KIR and MHC-I genotypes. In the SIV macaque model, however, the role of NK cells is unclear due to the lack of information on KIR-MHC interactions. In this study, we describe, to our knowledge, the first in-depth characterization of KIR-MHC interactions in pigtailed macaques (Macaca nemestrina). Initially, we identified three distinct subsets of macaque NK cells that stained ex vivo with macaque MHC-I tetramers loaded with SIV peptides. We then cloned cDNAs corresponding to 15 distinct KIR3D alleles. One of these, KIR049-4, was an inhibitory KIR3DL that bound MHC-I tetramers and prevented activation, degranulation, and cytokine production by macaque NK cells after engagement with specific MHC-I molecules on the surface of target cells. Furthermore, KIR049-4 recognized a broad range of MHC-I molecules carrying not only the Bw4 motif, but also Bw6 and non-Bw4/Bw6 motifs. This degenerate, yet peptide-dependent, MHC reactivity differs markedly from the fine specificity of human KIRs.