Pathogenic Mycobacterium bovis strains differ in their ability to modulate the proinflammatory activation phenotype of macrophages

Abstract

BackgroundTuberculosis, caused by Mycobacterium tuberculosis or Mycobacterium bovis, remains one of the leading infectious diseases worldwide. The ability of mycobacteria to rapidly grow in host macrophages is a factor contributing to enhanced virulence of the bacteria and disease progression. Bactericidal functions of phagocytes are strictly dependent on activation status of these cells, regulated by the infecting agent and cytokines. Pathogenic mycobacteria can survive the hostile environment of the phagosome through interference with activation of bactericidal responses. To study the mechanisms employed by highly virulent mycobacteria to promote their intracellular survival, we investigated modulating effects of two pathogenic M. bovis isolates and a reference M. tuberculosis H37Rv strain, differing in their ability to multiply in macrophages, on activation phenotypes of the cells primed with major cytokines regulating proinflammatory macrophage activity.ResultsBone marrow- derived macrophages obtained from C57BL/6 mice were infected by mycobacteria after a period of cell incubation with or without treatment with IFN-γ, inducing proinflammatory type-1 macrophages (M1), or IL-10, inducing anti-inflammatory type-2 cells (M2). Phenotypic profiling of M1 and M2 was then evaluated. The M. bovis strain MP287/03 was able to grow more efficiently in the untreated macrophages, compared with the strains B2 or H37Rv. This strain induced weaker secretion of proinflammatory cytokines, coinciding with higher expression of M2 cell markers, mannose receptor (MR) and arginase-1 (Arg-1). Treatment of macrophages with IFN-γ and infection by the strains B2 and H37Rv synergistically induced M1 polarization, leading to high levels of inducible nitric oxide synthase (iNOS) expression, and reduced expression of the Arg-1. In contrast, the cells infected with the strain MP287/03 expressed high levels of Arg-1 which competed with iNOS for the common substrate arginine, leading to lower levels of NO production.ConclusionsThe data obtained demonstrated that the strain, characterized by increased growth in macrophages, down- modulated classical macrophage activation, through induction of an atypical mixed M1/M2 phenotype.

Pulmonary Infection with Hypervirulent Mycobacteria Reveals a Crucial Role for the P2X7 Receptor in Aggressive Forms of Tuberculosis

“…More precisely, cells from Beijing 1471 Mtb -infected C57BL/6 mice produced higher levels of IL-1β and IFNγ. In contrast, cells from MP287/03 Mbv -infected mice secreted comparatively lower levels of pro-inflammatory cytokines and higher levels of IL-10, which supports the notion that MP287/03 Mbv is a poor inducer of pro-inflammatory cytokines [38]. As observed for the composition of cellular infiltrates, the absence of P2X7R had different effects on the cytokine profiles induced by hypervirulent strains.…”

“…Thus, eATP induced the P2X7R-mediated killing of H37Rv Mtb bacilli and the P2X7R-mediated release of viable Beijing 1471 Mtb and MP287/03 Mbv bacilli. The resistance of these hypervirulent mycobacteria to intracellular killing has also been described following macrophage stimulation with IFNγ [37], [38] and can be attributed to the ability of pathogenic mycobacteria to block phagosome-lysosome fusion [57]. The moderate extent of tissue damage with consequently small amounts of eATP release and the susceptibility to eATP-induced intracellular killing explain, respectively, the lack of involvement or the protective role of P2X7R during the H37Rv Mtb infection [39], [40].…”

“…To investigate this possibility, we used murine models of pulmonary TB induced by intratracheal infections with the highly virulent isolates Mtb strain 1471 (Beijing genotype) and Mbv strain MP287/03. These mycobacterial strains were epidemiologically associated with outbreaks of TB in human and bovine populations, respectively, and showed high virulence in our previous in vitro studies [36], [37], [38]. In C57BL/6 mice that were infected with a low dose (approx.…”

Mycobacterium tuberculosis Strains of the Modern Sublineage of the Beijing Family Are More Likely To Display Increased Virulence than Strains of the Ancient Sublineage

“…The bone marrow-derived macrophages (BMDM) were obtained through the cultivation of bone marrow cells of C57BL/6 mice in Dulbecco's modified Eagle medium-nutrient mixture F-12 (DMEM/F12) complemented with 20% L929 cell-conditioned medium (as a source of macrophage colony-stimulating factor [M-CSF] to induce macrophage differentiation), as previously described (23). The cells were infected with the mycobacterial strains at a multiplicity of infection (MOI) of 1:1 bacterium/macrophage.…”

Function of microglia and macrophages in secondary damage after spinal cord injury

“…The properties of M2 macrophages are resolving/anti-inflammatory function, neuro/axonal-trophic support and scar-degrading capacities . Markers for M2 macrophages are arginase-1, Ym1, found in inflammatory zone 1 (FIZZ1), CD206, CD209, CD163, and mannose receptor (MR) and IL-1 receptor antagonist (IL-1Ra) ( Table 2) (Simmons and Seed, 1988;Ezekowitz et al, 1990;Law et al, 1993;Relloso et al, 2002;Menzies et al, 2010;Komori et al, 2011;Andrade et al, 2012;Rodriguez Guerrero et al, 2012;Varnum and Ikezu, 2012). Kigerl et al (2009) showed a comparatively smaller and transient M2 macrophage response in SCI, which probably explains the prolonged pro-inflammatory response, with detrimental effects on tissue viability if not terminated on time .…”