Time-course induction of apoptosis by wild-type and attenuated strains of rubella virus.

The time-course of rubella virus (RV)-induced apoptosis was studied in RK13 cells. DEVD-specific caspase activity assay and Western blotting for caspase-3 were used to determine the time-course of caspase activation and demonstrated that RV-induced apoptotic changes occur as early as 12 h post-infection (p.i.). Caspase activity followed a cyclic pattern, as seen with apoptotic-inducing drugs, with maximum activity detected at 72 h p.i. Apoptosis caused by wild-type (RN) and attenuated vaccine (Cendehill) strains of RV was compared by TUNEL staining, counting dead floating cells and DNA fragmentation analysis. Although the amount of apoptosis due to the wild-type strain was marginally greater, this was probably due to its faster growth rate.