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Interleukin-17A ( IL-17A), a pro-inflammatory cytokine acting on neutrophil recruitment, is known to play an important role during Mycobacterium tuberculosis infection, but the role of IL-17 A receptor signalling in immune defence against this intracellular pathogen remains poorly documented. Here we have analysed this signalling using C57 BL/6 mice genetically inactivated in the IL-17 receptor A subunit ( IL-17 RA−/−). Although early after infection bacterial growth was controlled to the same extent as in wild-type mice, IL-17 RA−/− mice were defective in exerting long-term control of M. tuberculosis infection, as demonstrated by a progressively increasing pulmonary bacterial burden and shortened survival time. Compared with infected wild-type mice, IL-17 RA−/− mice showed impaired recruitment of neutrophils to the lungs at the early but not the late stage of infection. Pulmonary tumour necrosis factor-α, IL-6 and particularly IL-10 levels were decreased in the absence of IL-17 RA signalling, whereas IL-1β was increased. CD4+-mediated and γδ-mediated IL-17 A production was dramatically increased in IL-17 RA−/− mice (confirming part of their phenotype), whereas production of interferon-γ and expression of the bactericidal enzyme inducible nitric oxide synthase were not affected. Collectively, our data suggest that early but not late neutrophil recruitment is essential for IL-17 A-mediated long-term control of M. tuberculosis infection and that a functional interferon-γ response is not sufficient to control M. tuberculosis growth when the IL-17 RA pathway is deficient. As treatment of auto-immune diseases with anti- IL-17 A antibodies is actually being tested in clinical studies, our data suggest that caution should be taken with respect to possible reactivation of tuberculosis. [ABSTRACT FROM AUTHOR]