(A) Human THP-1 cells were infected with M. tuberculosis (H37Rv), ΔsecA2, and complemented ΔsecA2 (ΔsecA2-C) strains at an MOI of 10. Cells were stained after 48 and 72 hours for TUNEL or for caspase activation using FLICA probes and analyzed by FACS. Representative histograms of staining with TUNEL or a polycaspase-specific probe (fluorescein-VAD-FMK) at 48 hours are shown (open histogram, uninfected; filled histogram, infected with H37Rv or ΔsecA2 as indicated). Quantitation by FACS of cells positive for TUNEL or for active caspase-8, caspase-9, or polycaspase is summarized. Data shown are from the time points for peak signal detection (48 hours for TUNEL and polycaspase, 72 hours for caspase-8 and 9). (B) TUNEL staining of mouse BMMs 72 hours after infection with indicated bacterial strains. Staining was quantitated by FACS as in A. (C) TUNEL staining of THP-1 cells infected with the indicated bacteria for 48 hours in the absence or presence of caspase-3–specific inhibitor (Z-DEVD-FMK). *P < 0.001 compared to no inhibitor (1-way ANOVA, Bonferroni post-test). (D) Filtrates from cultures of H37Rv, ΔsecA2 mutant, or ΔsecA2-αsodA were analyzed for SodA activity (left). Graph shows mean and range for duplicate samples, with SodA activity normalized to the level of WT (H37Rv). ^†Below detection level. The ΔsecA2-αsodA showed restoration of SodA activity in the culture filtrate and also reversed the TUNEL⁺ cell death induced by ΔsecA2 in THP-1 cells infected for 48 hours at an MOI of 10:1 (right).