HIV infection remains a global health emergency that has caused around 36 million deaths. NK cells play an important role in the control of HIV-1 infections, and are able to detect and destroy infected cells using a large array of activating and inhibitory receptors, including KIRs. Here we demonstrate that CD155 serves as a functional interaction partner for the inhibitory NK cell receptor KIR2DL5, and that KIR2DL5+ NK cells are inhibited by CD155-expressing target cells. CD155 surface expression on HIV-1-infected CD4+ T cells was downregulated by the HIV-1 Nef protein, resulting in increased anti-viral activity of KIR2DL5+ NK cells through the loss of inhibitory signals. Taken together, these studies demonstrate functional consequences of the novel interaction between KIR2DL5 and CD155 for the antiviral activity of KIR2DL5+ NK cells during HIV-1 infection.