Inhibition of fusion between Env(NYP)- and CD4/CCR5(Δ18)-expressing cells by Sch-C. The extent of fusion upon direct co-incubation at 37°C for 3 hr (filled circles) and after establishing 27°-TAS (open circles) was measured in the presence of different concentrations of Sch-C, as described in the legend to Figure 2. The TAS was created by a 2 hr pre-incubation at 27°C. This temperature was not permissive to fusion with cells expressing a low (R5d18.2, panel A) and relatively high (R5d18.23, panel B) level of the truncated CCR5. Inhibition of fusion by Sch-C added after creating 18°-TAS (2 hr at 18°C) with cells expressing a higher level of CCR5(Δ18) is shown by gray circles.