FIG. 4.

HCV infectivity is resistant to acidic pH. (A) HCV or SIN was diluted in citric acid buffer (15 mM citric acid, 150 mM NaCl) at pH 7 (white bars) or pH 5 (black bars) for 10 min at 37°C. Samples were then neutralized and used to infect Huh-7.5 cells. Samples were harvested at 24 h (SIN) or 48 h (HCV) for luciferase assays. Values, expressed as percentages of pH 7 RLU, are the combined data from two independent experiments done in triplicate; error bars represent standard errors of the means. (B) Huh-7.5 cells were treated with bafilomycin A1 (+Baf) (25 nM) and then were infected with HCV (black bars) or SIN (white bars) at 4°C for 2 h. Cells were washed to remove unbound virus and then washed with citric acid buffer at pH 7 or 5. Cells were incubated in the presence of bafilomycin A1 for 24 h when they were harvested for luciferase assays. Luciferase activity from untreated cells washed with the pH 7 buffer (−Baf/pH 7) was expressed as 100 percent. Values are the combined data from two independent experiments done in triplicate; error bars represent standard errors of the means.