title: Inhibition of Ca(2+) signaling by Mycobacterium tuberculosis is associated with reduced phagosome-lysosome fusion and increased survival within human macrophages.
abstract: 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.
authors.affiliation: Inflammation Program, University of Iowa and Veterans Affairs Medical Center, Iowa City, Iowa 52242, USA.
authors.forename: Z A
authors.initials: ZA
authors.lastname: Malik
authors.forename: G M
authors.initials: GM
authors.lastname: Denning
authors.forename: D J
authors.initials: DJ
authors.lastname: Kusner
mesh_terms: D000328:Adult; D000907:Antibodies, Bacterial / Q000276:immunology; D002118:Calcium / Q000378:metabolism; D020013:Calcium Signaling; D002478:Cells, Cultured; D003600:Cytosol / Q000378:metabolism; D006801:Humans; D008247:Lysosomes; D008264:Macrophages / Q000187:drug effects / Q000276:immunology / Q000378:metabolism / Q000382:microbiology*; D008561:Membrane Fusion; D009169:Mycobacterium tuberculosis / Q000276:immunology* / Q000502:physiology; D010587:Phagocytosis; D010588:Phagosomes; D017452:Receptors, IgG / Q000276:immunology; D015054:Zymosan / Q000494:pharmacology
chemical_list: D000907:Antibodies, Bacterial; D017452:Receptors, IgG; D015054:Zymosan; D002118:Calcium