A working model for P. gingivalis-activated apoptosis in HGF cells. Note that this is a highly reductive and simplified model showing only the major signaling events and that the intermediate steps are mostly omitted for space (details in Results and Discussion). In general, the P. gingivalis-activated molecules shown in this paper are displayed more prominently. The ER stress and Fas pathways were not activated. Whether the gingipains activate caspase-3 in vivo remains a question. The box on the left lists the major anti-apoptotic molecules activated early in infection, and the box on the right shows the pro-apoptotic molecules activated later. The two sets of forces are mutually antagonistic and thus, the balance shifts from anti- to pro-apoptosis as infection progresses.