Modulation of CD4 by chimeras between HIV-1 and SIVcpz/gor Vpus. (A) FACS analysis of 293T cells co-transfected with a CD4 expression vector and pCGCG plasmids expressing eGFP alone (eGFPonly) or together with the indicated vpu alleles. A construct expressing NL4-3 Vpu was used as a positive control. (B-D) Levels of CD4 surface expression in (B) 293T, (C) HeLa and (D) TZM-bl cells in the presence of the indicated vpu alleles are compared to those measured in the absence of Vpu (100%). Values give averages (±SEM) derived from three to five independent experiments. The same ranges of eGFP expression were used in all calculations. (E, F) Correlation between CD4 cell surface levels on 293T and (E) HeLa or (F) TZM-bl cells. (G, H) Correlation between CD4 and tetherin cell surface levels on (G) 293T cells and (H) TZM-bl and HeLa cells.