Caspase-3, 8, and 9 activity was therefore measured at different time points (Fig. 2), and was much lower in the mock group than in the infection groups (ΔsseK3 mutant, WT, and sseK3-complemented groups), indicating that S. Typhimurium infection could stimulate the activity of caspase-3, 8, and 9 in macrophages. Here, CASP3 is linked to infection.