HLA-F on Autologous HIV-Infected Cells Activates Primary NK Cells Expressing the Activating Killer Immunoglobulin-Like Receptor KIR3DS1.

HIV-exposed seronegative homozygotes have a reduced risk of HIV infection. HLA-F is the ligand for the activating NK cell receptor (NKR) KIR3DS1. HLA-F is expressed on HIV-infected CD4 T cells. Coculture of sorted, HIV-infected CD4 (siCD4) T cells with NK cells activated a higher frequency of KIR3DS1 than KIR3DS1 NK cells from homozygotes to elicit anti-HIV functions such as CCL4, gamma interferon (IFN-γ), and CD107a expression. This was the case whether KIR3DS1 NK cells were analyzed inclusively or exclusively by gating out NK cells coexpressing the NKRs, KIR2DL1/L2/L3, 3DL2, KIR2DS1/S2/S3/S5, NKG2A, and ILT2. Blocking the interaction of HLA-F on siCD4 cells with KIR3DS1 on exclusively gated KIR3DS1 NK cells with KIR3DS1-Fc chimeric protein or an HLA-F-specific monoclonal antibody reduced the frequency of activated KIR3DS1 cells compared to that under control conditions. KIR3DS1 NK cell activation by HIV-infected CD4 cells may underlie the reduced risk of KIR3DS1 homozygotes to HIV infection. This study investigated a mechanism that may underly epidemiological studies showing that carriage of the homozygous genotype is more frequent among HIV-exposed seronegative subjects than among HIV-susceptible individuals. Carriage of this genotype is associated with a reduced risk of HIV infection. The protective mechanism involves the interaction of HLA-F on CD4 cells infected with replication-competent HIV with the activating NK receptor, KIR3DS1. This interaction leads to the activation of KIR3DS1 NK cells for secretion of cytokines and chemokines with anti-HIV activity. Among these is CCL4, which binds and blocks CCR5, the coreceptor for HIV entry of HIV into new target cells. In the setting of an exposure to HIV, incoming HIV-infected cells expressing HLA-F rapidly activate KIR3DS1 NK cells to elicit anti-HIV activity. Exclusive gating strategies and blocking experiments support the notion that the HLA-F/KIR3DS1 interaction is sufficient to activate NK cell functions.