Enhanced priming of adaptive immunity by a proapoptotic mutant of Mycobacterium tuberculosis
Joseph Hinchey, … , William R. Jacobs Jr., Steven A. Porcelli
Joseph Hinchey, … , William R. Jacobs Jr., Steven A. Porcelli
Published August 1, 2007
Citation Information: J Clin Invest. 2007;117(8):2279-2288. https://doi.org/10.1172/JCI31947.
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Research Article

Enhanced priming of adaptive immunity by a proapoptotic mutant of Mycobacterium tuberculosis

Abstract

The inhibition of apoptosis of infected host cells is a well-known but poorly understood function of pathogenic mycobacteria. We show that inactivation of the secA2 gene in Mycobacterium tuberculosis, which encodes a component of a virulence-associated protein secretion system, enhanced the apoptosis of infected macrophages by diminishing secretion of mycobacterial superoxide dismutase. Deletion of secA2 markedly increased priming of antigen-specific CD8+ T cells in vivo, and vaccination of mice and guinea pigs with a secA2 mutant significantly increased resistance to M. tuberculosis challenge compared with standard M. bovis bacille Calmette-Guérin vaccination. Our results define a mechanism for a key immune evasion strategy of M. tuberculosis and provide what we believe to be a novel approach for improving mycobacterial vaccines.

Authors

Joseph Hinchey, Sunhee Lee, Bo Y. Jeon, Randall J. Basaraba, Manjunatha M. Venkataswamy, Bing Chen, John Chan, Miriam Braunstein, Ian M. Orme, Steven C. Derrick, Sheldon L. Morris, William R. Jacobs Jr., Steven A. Porcelli

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Figure 1

Induction of caspase and SodA-dependent apoptosis in macrophages by infection with M. tuberculosis ΔsecA2.

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Induction of caspase and SodA-dependent apoptosis in macrophages by infe...
(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).