Mice deficient for granulocyte-macrophage colony-stimulating factor (GM-CSF(-/-)) are highly susceptible to infection with Mycobacterium tuberculosis, and clinical data have shown that anti-GM-CSF neutralizing antibodies can lead to increased susceptibility to tuberculosis in otherwise healthy people. GM-CSF activates human and murine macrophages to inhibit intracellular M. tuberculosis growth. We have previously shown that GM-CSF produced by iNKT cells inhibits growth of M. tuberculosis However, the more general role of T cell-derived GM-CSF during infection has not been defined and how GM-CSF activates macrophages to inhibit bacterial growth is unknown. Here we demonstrate that, in addition to nonconventional T cells, conventional T cells also produce GM-CSF during M. tuberculosis infection. Early during infection, nonconventional iNKT cells and gammadelta T cells are the main source of GM-CSF, a role subsequently assumed by conventional CD4(+) T cells as the infection progresses. M. tuberculosis-specific T cells producing GM-CSF are also detected in the peripheral blood of infected people. Under conditions where nonhematopoietic production of GM-CSF is deficient, T cell production of GM-CSF is protective and required for control of M. tuberculosis infection. However, GM-CSF is not required for T cell-mediated protection in settings where GM-CSF is produced by other cell types. Finally, using an in vitro macrophage infection model, we demonstrate that GM-CSF inhibition of M. tuberculosis growth requires the expression of peroxisome proliferator-activated receptor gamma (PPARgamma). Thus, we identified GM-CSF production as a novel T cell effector function. These findings suggest that a strategy augmenting T cell production of GM-CSF could enhance host resistance against M. tuberculosisIMPORTANCEMycobacterium tuberculosis is the bacterium that causes tuberculosis, the leading cause of death by any infection worldwide. T cells are critical components of the immune response to Mycobacterium tuberculosis While gamma interferon (IFN-gamma) is a key effector function of T cells during infection, a failed phase IIb clinical trial and other studies have revealed that IFN-gamma production alone is not sufficient to control M. tuberculosis In this study, we demonstrate that CD4(+), CD8(+), and nonconventional T cells produce GM-CSF during Mycobacterium tuberculosis infection in mice and in the peripheral blood of infected humans. Under conditions where other sources of GM-CSF are absent, T cell production of GM-CSF is protective and is required for control of infection. GM-CSF activation of macrophages to limit bacterial growth requires host expression of the transcription factor PPARgamma. The identification of GM-CSF production as a T cell effector function may inform future host-directed therapy or vaccine designs.

Interferon-gamma Release Assays (IGRAs) significantly increases the possibility for early diagnosis of tuberculosis, but IGRAs alone cannot discriminate active TB from LTBI. Therefore, fast and reliable discrimination of active tuberculosis, especially bacteriology negative tuberculosis, from LTBI is a great necessity. Here we established an assay based on flow cytometric multiparameter assay assessing expression of CD161 along with CD3, CD4, and CD8, whereby a set of indices formulated by the percentages of CD3(+)CD161(+), CD3(+)CD4(+)CD161(+) and CD3(+)CD8(+)CD161(+) T cells multiplied with lymphocyte/monocyte ratio were established. Application of the CD3(+)CD8(+)CD161(+) index to compare a cohort of active tuberculosis with a cohort of LTBI or health control yielded 0.7662 (95% confidence interval [CI] 0.6559-0.8552) or 0.7922 (95% CI 0.6846-0.8763) for sensitivity and 0.9048 (95% CI 0.8209-0.9580) or 0.8939 (95% CI 0.8392-0.9349) for specificity when the TB cohort was AFB(+); the corresponding results were 0.7481 (95% CI 0.6648-0.8198) or 0.7557 (95% CI 0.6730-0.8265) for sensitivity and 0.8571 (95% CI 0.7637-0.9239) or 0.8603 (95% CI 0.8008-0.9075) for specificity when the TB cohort was AFB(-). Our results reveal that in combination with IGRAs, CD161-based indices provide a novel, fast diagnostic solution addressing the limitation of current tuberculosis diagnostics.