The Mycobacterium tuberculosis Early Secreted Antigenic Target of 6 kDa Inhibits T Cell Interferon-γ Production through the p38 Mitogen-activated Protein Kinase Pathway

We reported previously that the early secreted antigenic target of 6 kDa (ESAT-6) from Mycobacterium tuberculosis directly inhibits human T cell IFN-gamma production and proliferation in response to stimulation with anti-CD3 and anti-CD28. To determine the mechanism of this effect, we treated T cells with kinase inhibitors before stimulation with ESAT-6. Only the p38 MAPK inhibitor, SB203580, abrogated ESAT-6-mediated inhibition of IFN-gamma production in a dose-dependent manner. SB203580 did not reverse ESAT-6-mediated inhibition of IL-17 and IL-10 production, suggesting a specific effect of SB203580 on IFN-gamma production. SB203580 did not act through inhibition of AKT (PKB) as an AKT inhibitor did not affect ESAT-6 inhibition of T cell IFN-gamma production and proliferation. ESAT-6 did not reduce IFN-gamma production by expanding FoxP3(+) T regulatory cells. Incubation of T cells with ESAT-6 induced phosphorylation and increased functional p38 MAPK activity, but not activation of ERK or JNK. Incubation of peripheral blood mononuclear cells with ESAT-6 induced activation of p38 MAPK, and inhibition of p38 MAPK with SB203580 reversed ESAT-6 inhibition of M. tuberculosis-stimulated IFN-gamma production by peripheral blood mononuclear cells from subjects with latent tuberculosis infection. Silencing of p38 alpha MAPK with siRNA rendered T cells resistant to ESAT-6 inhibition of IFN-gamma production. Taken together, our results demonstrate that ESAT-6 inhibits T cell IFN-gamma production in a p38 MAPK-dependent manner.