FIG. 3.

The pore-forming toxin enhances the ability of L. pneumophila to induce apoptosis within U937 cells. The wild-type strain AA100, mutant GL208, and complemented GL208 were analyzed for their ability to induce apoptosis at the postexponential phase. The percentage of positive apoptotic cells was quantitated by TUNEL assay. Uninfected U937 cells (UI) were used as a control. The data are representative of three different experiments, and error bars represent the standard deviations of triplicate samples.