FIG 2.

Secreted effectors play no role in protecting S. Typhimurium from PMNs. (A) Whole bacteria were added to PMN cultures and incubated for 6 h, but no increase in caspase-3 activity was observed in PMNs upon addition of the different strains. (B) Bacterial supernatants cleared of bacteria by filtration and equilibrated to ensure identical protein content were added to PMN cultures and left for 6 h. The SL1344 strain expressing SipA showed no increased induction of caspase-3 activation compared to the ΔSipA strain. However, an unexplained statistically significant and reproducible reduction in caspase-3 levels in ΔSPI-1-treated PMNs was observed. The data presented are representative of three independent experiments, and statistically significant differences are denoted (**, P < 0.01; ***, P < 0.001).