Cell Death Detection ELISA was used to detect DNA fragmentation, a hallmark of apoptosis. HGECs were challenged with live and heat-killed P. gingivalis 33277 at MOI:10 and MOI:100 for 4, 24, and 48 hours. Negative control was unchallenged HGECs in media. Positive control was HGECs challenged with camptothecin 4 μg/ml. Values represent the means ± SD of at least two experiments. Statistical comparisons are to the unchallenged negative control cells (* P < 0.05, ** P < 0.01).