The effect of S22 peptide on virus infectivity. A. Infections of HeLa-CD4 cells expressing CCR5(Δ18) (R5d18.23 cells, 6.6 × 104 coreceptors/cell) were carried out in the absence and the presence of varying concentrations of the S22 peptide (0, 25, 100, and 200 μM). The replication competent wild-type (open circles) or CCR5(Δ18)-adapted (filled circles) JRCSF isolates were tested. Infections performed in the presence of S22 were normalized to those obtained in cells expressing wild-type CCR5 in the absence of peptide. The graph shows a representative experiment performed in duplicate. Error bars are the range. B. Reconstruction of CCR5(Δ18) function by S22 peptide using a single-cycle infectivity assay. Infectivities of viruses pseudotyped with JRCSF wt (open squares) and S298N mutant (filled squares) were determined in the presence of varied concentrations of the sulfopeptide. Titers were normalized as in panel A. Data points represent averages of two experiments performed in duplicate. Error bars are SE. Note that the overall infectivity of pseudoviruses on these cells was much lower than those obtained for replication-competent viruses (panel B vs. panel A).