Killer cell inhibitory receptors specific for HLA-C and HLA-B identified by direct binding and by functional transfer

AbstractAn inhibitory signal is delivered to natural killer (NK) cells and a subset of cytotoxic T cells upon recognition of HLA class 1 molecules on target cells. We demonstrate that soluble forms of killer cell inhibitory receptors (KIR) bind directly and specifically to HLA-C alleles on transfected cells. Furthermore, transfer of individual KIR Into NK clones reconstituted recognition of HLA-C on target cells, leading to inhibition of lysis. Using such functional reconstitution, a related KIR that confers specificity for some HLA-B alleles was also identified. These KIR share conserved tyrosine phosphorylation motifs in their cytoplasmic tails. Thus, a single receptor in NK cells provides both specificity for HLA class I on target cells and the Inhibitory signal that prevents lysis

Recruitment of Tyrosine Phosphatase HCP by the Killer Cell Inhibitory Receptor

AbstractCytolysis of target cells by natural killer (NK) cells and by some cytotoxic T cells occurs unless prevented by inhibitory receptors that recognize MHC class I on target cells. Human NK cells express a p58 inhibitory receptor specific for HLA-C. We report association of the tyrosine phosphatase HCP with the p58 receptor in NK cells. HCP association was dependent on tyrosine phosphorylation of p58. Phosphotyrosyl peptides corresponding to the p58 tail bound and activated HCP in vitro. Furthermore, introduction of an inactive mutant HCP into an NK cell line prevented the p58-mediated inhibition of target cell lysis. These data imply that the inhibitory function of p58 is dependent on its tyrosine phosphorylation and on recruitment and activation of HCP

Adaptive NK cells in people exposed to Plasmodium falciparum correlate with protection from malaria

How antibodies naturally acquired during Plasmodium falciparum infection provide clinical immunity to blood-stage malaria is unclear. We studied the function of natural killer (NK) cells in people living in a malaria-endemic region of Mali. Multi-parameter flow cytometry revealed a high proportion of adaptive NK cells, which are defined by the loss of transcription factor PLZF and Fc receptor γ-chain. Adaptive NK cells dominated antibody-dependent cellular cytotoxicity responses, and their frequency within total NK cells correlated with lower parasitemia and resistance to malaria. P. falciparum–infected RBCs induced NK cell degranulation after addition of plasma from malaria-resistant individuals. Malaria-susceptible subjects with the largest increase in PLZF-negative NK cells during the transmission season had improved odds of resistance during the subsequent season. Thus, antibody-dependent lysis of P. falciparum–infected RBCs by NK cells may be a mechanism of acquired immunity to malaria. Consideration of antibody-dependent NK cell responses to P. falciparum antigens is therefore warranted in the design of malaria vaccines

Activation of NK Cells by an Endocytosed Receptor for Soluble HLA-G

Signaling from endosomes is emerging as a mechanism by which selected receptors provide sustained signals distinct from those generated at the plasma membrane. The activity of natural killer (NK) cells, which are important effectors of innate immunity and regulators of adaptive immunity, is controlled primarily by receptors that are at the cell surface. Here we show that cytokine secretion by resting human NK cells is induced by soluble, but not solid-phase, antibodies to the killer cell immunoglobulin-like receptor (KIR) 2DL4, a receptor for human leukocyte antigen (HLA)-G. KIR2DL4 was constitutively internalized into Rab5-positive compartments via a dynamin-dependent process. Soluble HLA-G was endocytosed into KIR2DL4–containing compartments in NK cells and in 293T cells transfected with KIR2DL4. Chemokine secretion induced by KIR2DL4 transfection into 293T cells occurred only with recombinant forms of KIR2DL4 that trafficked to endosomes. The profile of genes up-regulated by KIR2DL4 engagement on resting NK cells revealed a proinflammatory/proangiogenic response. Soluble HLA-G induced secretion of a similar set of cytokines and chemokines. This unique stimulation of resting NK cells by soluble HLA-G, which is endocytosed by KIR2DL4, implies that NK cells may provide useful functions at sites of HLA-G expression, such as promotion of vascularization in maternal decidua during early pregnancy

The Direct Binding of a p58 Killer Cell Inhibitory Receptor to Human Histocompatibility Leukocyte Antigen (HLA)-Cw4 Exhibits Peptide Selectivity

Natural killer (NK) cells in mice and humans express a number of structurally diverse receptors that inhibit target cell lysis upon recognition of major histocompatibility complex (MHC) class I molecules expressed on targets. The contribution of peptide to the structural features of class I required for NK cell inhibition appears to vary depending on the type of receptor engaged. Thus, while there is no peptide specificity in NK inhibition mediated by Ly-49A in the mouse, human histocompatibility antigen (HLA)-B*2705–specific NK clones displayed selectivity for peptides. In this report, we examine the role of peptide in the recognition of HLA-C by the defined killer cell inhibitory receptor (KIR) cl42 with established specificity for HLA-Cw4. Binding of soluble KIR cl42 molecules to HLA-Cw4 expressed on transporter associated with antigen presentation (TAP)-deficient RMA-S cells occurred only upon exogenous peptide loading. Moreover, there was peptide selectivity in that certain substitutions at positions 7 and 8 of the nonamer peptide QYDDAVYKL abolished Cw4 interaction with KIR cl42 despite similar surface expression of HLA-C. The specificity of this direct interaction between peptideloaded HLA-Cw4 on RMA-S cells and soluble KIR cl42 correlated with recognition by NK clones in that they were inhibited only by HLA-Cw4 loaded with the appropriate peptides