CD4 and infection: To account for the HIV Nef-mediated downmodulation of CD4 in infected cells[34], we separately labelled CD4+ T cells and CD8+ T cells with CellTrace Violet dye (Vio) and CellTrace Red dye (Red), respectively, and prior to infection with a NL4-3 reporter virus expressing eGFP under control of the HIV- 1 LTR.