Inhibition of Ca(2+) Signaling by Mycobacterium tuberculosisIs Associated with Reduced Phagosome–Lysosome Fusion and Increased Survival within Human Macrophages

Complement receptor (CR)-mediated phagocytosis of Mycobacterium tuberculosis by macrophages results in intracellular survival, suggesting that M. tuberculosis interferes with macrophage microbicidal mechanisms. As increases in cytosolic Ca(2+) concentration ([Ca(2+)](c)) promote phagocyte antimicrobial responses, we hypothesized that CR phagocytosis of M. tuberculosis is accompanied by altered Ca(2+) signaling. Whereas the control complement (C)-opsonized particle zymosan (COZ) induced a 4.6-fold increase in [Ca(2+)](c) in human macrophages, no change in [Ca(2+)](c) occurred upon addition of live, C-opsonized virulent M. tuberculosis. Viability of M. tuberculosis and ingestion via CRs was required for infection of macrophages in the absence of increased [Ca(2+)](c), as killed M. tuberculosis or antibody (Ab)-opsonized, live M. tuberculosis induced elevations in [Ca(2+)](c) similar to COZ. Increased [Ca(2+)](c) induced by Ab-opsonized bacilli was associated with a 76% reduction in intracellular survival, compared with C-opsonized M. tuberculosis. Similarly, reversible elevation of macrophage [Ca(2+)](c) with the ionophore A23187 reduced intracellular viability by 50%. Ionophore-mediated elevation of [Ca(2+)](c) promoted the maturation of phagosomes containing live C-opsonized bacilli, as evidenced by acidification and accumulation of lysosomal protein markers. These data demonstrate that M. tuberculosis inhibits CR-mediated Ca(2+) signaling and indicate that this alteration of macrophage activation contributes to inhibition of phagosome–lysosome fusion and promotion of intracellular mycobacterial survival.