Kinetics of apoptosis and caspase activation following P. gingivalis infection. HGF monolayers were infected with wild type (WT) or triple gingipain mutant P. gingivalis and harvested at indicated times for the following assays as described under Experimental Procedures. (A) DNA fragmentation assay using the "Cell Death Detection ELISA" (Roche); (B) Caspase-3 activity assay in cell lysates; (C) Immunoblot detection of activated (cleaved) caspases in HGF cells infected with WT, with Sp1 serving as a control for equal protein loading; note the absence of activated caspases-8, -10, -12. (D) Immunoblot detection of α-spectrin fragments in infected HGF cells; the full-length 240 kDa spectrin and the caspase-specific 120 kDa product bands are so marked. In A and B, the standard error bars are from three experiments.