PVR and HIV infectious disease: It has been shown that HIV infection reduces the expression of MICA, ULBP1 and ULBP2 via inhibition by Nef [29], downregulates the co-activating ligand NK, T and B cell antigen (NTB-A) via inhibition by Vpu [32,33] and downregulates the DNAM-1 ligand poliovirus receptor (PVR) via inhibition by both Nef and Vpu [30,31].