FIGURE 3.

Streptolysin O is necessary and sufficient for GAS-induced macrophage apoptosis. A, screen of isogenic GAS virulence factor mutants reveals SLO is necessary for induction of macrophage apoptosis. B, single gene complementation of SLO rescues the mutant, and SLO confers to L. lactis (LL) the ability to induce macrophage apoptosis. C, streptococcal NADase (nga) plays a contributory, but not sufficient, role in induction of macrophage apoptosis. D, purified recombinant SLO induces dose-dependent macrophage apoptosis, which can be enhanced by the addition of bacterial components. t = 4 h for all experiments. *** = p < 0.0005. All experiments were performed in triplicate and repeated three times. MOI, multiplicity of infection. SLS, streptolysin S.