FIG. 6.

Preincubation of E/T cells at 31.5°C before transfer to 37°C results in reduced susceptibility to inhibition by T20 peptide. Serial dilutions of T20 were added to E/T cells that were incubated at 37°C (▪) or preincubated with the inhibitor for 60 min at 31.5°C and then transferred to 37°C (⧫) or preincubated without the inhibitor at 31.5°C for 60 min. T20 was added to these cells at the time of transfer to 37°C (▴). Syncytia were scored 3 h (89.6 Env) or 4 h (IIIB Env) after transfer to 37°C. The data are plotted as percent inhibition of syncytia in control cultures (medium control) as a function of the inhibitor dose. Three wells per group were set up in all experiments, and the standard deviations did not exceed 15% of the means. The ID₅₀ values calculated from the curves were as follows: 89.6 Env, 11 ng/ml (▪), 1.5 ng/ml (⧫), and 250 ng/ml (▴); IIIB Env, 5.2 ng/ml (▪), 0.4 ng/ml (⧫), and 190 ng/ml (▴).