P. gingivalis infection induces cell apoptosis in bEnd.3 brain endothelial cells. (A) Cells are infected with either heat-killed or live P. gingivalis at an MOI of 500 for 90 min. After being replaced with fresh medium for 6, 12, or 24 h, nuclear condensation is determined by DAPI staining. Arrows indicate cells with a condensed nucleus. The scale bar represents 100 μm. (B) Cells are treated with various live bacteria (1, 50, 100 and 200 MOI) or heat-killed bacteria (500 MOI) for 90 min. Cell survival is stained with Annexin V FITC/PI after 24 h and analyzed with a flow cytometer (upper panel). The quantitative percentage of apoptotic cells is shown in the lower panel. Data are presented as mean values ± SEM (n = 4). Significant differences of the control or heat-killed P. gingivalis group are expressed as **, p < 0.01; ***, p < 0.001; NS, p > 0.05.