FIG. 3.

CD4 dependence of chimeric viruses. U87-CD4-CXCR4 or -CCR5 cells at ∼20% confluency in 1-cm² wells were treated with anti-CD4 MAb 318 (1 μg/ml) prior to infection with 200 μl of each cell-free transfection supernatant (containing comparable levels of p24 antigen). Virus was left for 3 days to infect. Cells were then stained for intracellular gp120 antigen, and the number of blue foci per well was counted and expressed as percent neutralization. The coreceptor preference of each chimeric virus is distinguished.