FIG 4.
sCD4 activation of HIV-1YU2 Env variants with alterations of the gp41 ectodomain. Effect of soluble CD4 on HIV-1 infection of CD4-negative, CCR5-expressing cells. Recombinant luciferase-expressing HIV-1 with the indicated HIV-1 Env variants were normalized by reverse transcriptase activity and incubated with serial dilutions of sCD4 at 37°C for 1 h prior to infection of Cf2Th-CCR5 cells. The level of infection is reported in relative light units (RLU). For each data point, the infection was performed in quadruplicate; data shown are representative of those obtained in at least two independent experiments.