SE enhances founder HIV infection and boosts HIV infection independently of the viral producer and target cell type. (A) Effect of SE on HIV particles carrying gp120/41 from founder viruses. Pseudotyped HIV-1 particles were generated by transient transfection of 293T cells with an env-defective HIV-1 NL4-3 backbone and plasmids expressing the Env proteins previously described (34). Virions were treated with medium, 10 μg/ml SEVI or 10% SE and used to infect TZM-bl cells. The inoculum was removed after 2 hrs and infection rates were determined 2 dpi. Shown are the average levels of triplicate TZM-bl cell infections ± SD. (B) Correlation between the magnitudes of SEVI and SE-mediated enhancement of HIV-1 pseudotype infection shown in Fig 4A. N-fold enhanced infection rates were calculated by dividing infection rates obtained in the presence of SEVI or SE by those of mock-treated virus infection. (C) SE enhances infection of testis derived HIV-1. X4 tropic HIV-1 IIIb and R5 tropic SF162 were harvested from infected testis tissue, treated with indicated concentrations of SE and used to infect TZM-bl cells. (D, E) SE enhances the infectiousness of HIV-1 for PBMCs and macrophages. Stocks of an R5-tropic HIV-1 NL4-3 V3 variant (92TH04.12) containing the luciferase reporter gene in place of nef were generated by transient transfection of 293T cells. Virus stocks were treated with the indicated concentrations of SE and used to infect PBMC (D) and macrophages (E). Similar results were obtained using various primary HIV-1 strains. (F) SE favours in trans-infection of T cells by viral particles bound to epithelial cells. CaSki cells derived from an epithelial cervical carcinoma were exposed to HIV-1 treated with SE or medium for 3 hrs. Subsequently, the virus inoculum was washed out and the cells were cocultivated with CEM-M7 cells for three days. Infection rates were determined by luciferase assay. The numbers above the bars indicate n-fold enhancement relative to the infectivity measured using PBS/medium-treated virus stocks.