CASP3 and infection: Immunoblotting showed that in HeLa, Cal27, HN13, A549, and H1299 cells, both major biochemical markers of apoptosis, caspase-3 and PARP, were cleaved into smaller fragments in an infection time-dependent manner; in Huh7 and HepG2 cells, weak cleavage of PARP appeared at 24 h.p.i.; no cleavage of both biochemical markers was observed in 293T cells (Fig. 1c and Fig. S1C).