Effect of exposure times and pH values on SE mediated enhancement of HIV infection. (A) Effect of pre-incubation time on SE-mediated HIV infection enhancement. R5 HIV-1 was mixed with the indicated concentrations of SE, incubated for the various time periods, and 20 μl of the virus stocks was used to infect 280 μl TZM-bl cell cultures in triplicates. Values in all panels give averages ± SD (n = 3) measured 3 days after virus exposure. (B) The SE/virus mixture was incubated for 10 min at RT, and 20 μl were added to 280 μl TZM-bl cells. After different time points, the supernatant was removed, and fresh DMEM was added for further culture. The star indicates high cytotoxicity. (C) Virus stocks of R5 HIV-1 treated with the indicated concentrations of SE were used to infect TZM-bl cultures adjusted to the indicated pH values. After two hours of virus exposure, the virus stocks were removed, and the cells were cultured in fresh medium under neutral pH conditions. Higher or lower pH values could not be analyzed as they were cytotoxic. Both panels give average values ± SD (n = 3). (D) Virus stocks adjusted to the indicated pH values were either treated with PBS or with various concentrations of SE and subsequently used to infect TZM-bl indicator cells. (E) TZM-bl cells were incubated with either PBS or 10% cervico vaginal lavage (CLF) and infected with medium or 10% SE treated HIV-1. Infection rates were determined 3 dpi.