Figure 3.

Nef proteins from HIV-1, HIV-2, and SIV down-modulate human CC- and CXC-CKRs. CHO cell lines, stably expressing the indicated receptors, were transfected with bicistronic expression constructs encoding GFP alone (control) or GFP together with one of the indicated lentiviral Nef proteins from either HIV-1 (SF2, NL4-3, and NA-7), HIV-2 (NEP), or SIV (Mac239). Twenty hours after transfection, steady-state cell surface levels of CKRs and CD4 were analyzed by flow cytometry after staining with either receptor-specific mAbs or the anti-HA-tag mAb. Relative cell surface levels were calculated as described in the legend to Figure 1, and values obtained for cells expressing GFP alone were set to 100%. Histogram bars represent the arithmetic means of triplicates + SD from two similar experiments.