. . . . . . . "HIV-1 Vpr downregulates the expression of surface CD4 receptors in Jurkat T cells" . "HIV-1 Vpr increases expression of Nef protein from integrase-defective HIV-1. The Vpr-mediated expression of Nef from IN-minus HIV-1 results in CD4 downregulation" . "HIV-1 Nef-Vpr fusion proteins are efficiently incorporated into HIV-1 particles and possess CD4 downregulation activity in target cells" . "downregulates" .