Fig. 1

Flow cytometric analysis of apoptosis in RAW264.1 macrophages infected with WT S. Typhimurium, ΔsseK3 mutant, or complemented strains. RAW264.1 macrophages were incubated for 4 h with WT S. Typhimurium, ΔsseK3 mutant, or sseK3 complemented strains. Apoptosis was assessed using Annexin V-FITC/PI double staining. (a) Representative dot plots showing Annexin V-FITC /PI staining. The upper left quadrant (Q1) contains the necrotic (Annexin V-FITC−/PI+) population, the upper right quadrant (Q2) contains the late apoptotic (Annexin V-FITC+/PI+) population, and the lower right quadrant (Q3) contains the early apoptotic (Annexin V-FITC+/PI-) population. The lower left quadrant (Q4) contains the healthy (double negative) population. (b) Percentage of apoptosis in cells exposed to different bacteria determined by flow cytometric analysis. After 4 h of incubation, the apoptosis rate in the ΔsseK3 mutant group was significantly lower than that in the WT and sseK3-complemented groups (***P < 0.001). Data from three independent experiments were used to determine percentage of apoptotic cells. Error bars indicate the SD from three independent experiments