B-cell transinfection is an active cellular process. (A) Untreated, gamma-irradiated, and paraformaldehyde-fixed CD40L/IL-4–stimulated L3055-Bcl-2 (□) and PBMC-derived () B cells were incubated with JFH-1 and cocultured with Huh-7.5 cells, and transinfection was quantified. Stimulated L3055-Bcl-2 (□) or PBMC-derived () B cells were incubated with increasing concentrations of Bafilomycin A1, which prevents endosome acidification for 1 hour at 37°C and incubated with JFH-1 for 2 hours at 37°C immediately (B) or after a 12-hour recovery period (C). B cells were cocultured with Huh-7.5 cells and transinfection quantified. Error bars represent the SD of FFUs per 10⁶ B cells from 3 replicate infections.