KLRD1 and HIV-1 infection: Thus, the interaction between KIR3DS1 and HLA-F upregulated on HIV-1–infected cells may have similarities to the well-reported upregulation of stress ligands such as ULPBs and MIC-A/MIC-B in HIV-1 infection, which are in turn recognized by the activating NK-cell receptor NKG2D (43).