Proinflammatory cytokines are critical mediators that control Mycobacterium tuberculosis (Mtb) growth during active tuberculosis (ATB). To further inhibit bacterial proliferation in diseased individuals, drug inhibitors of cell wall synthesis such as isoniazid (INH) areemployed. However, whether INH presents an indirect effect on bacterial growth by regulating host cytokines during ATB is not well known. To examine this hypothesis, we used an in vitro human granuloma system generated with primary leukocytes from healthy donors adapted to model ATB. Intense Mtb proliferation in cell cultures was associated with monocyte/macrophage activation and secretion of IL-1β and TNF. Treatment with INH significantly reduced Mtb survival, but altered neither T-cell-mediated Mtb killing, nor production of IL-1β and TNF. However, blockade of both IL-1R1 and TNF signaling rescued INH-induced killing, suggesting synergistic roles of these cytokines in mediating control of Mtb proliferation. Additionally, mycobacterial killing by INH was highly dependent upon drug activation by the pathogen catalase-peroxidase KatG and involved a host PI3K-dependent pathway. Finally, experiments using coinfected (KatG-mutated and H37Rv strains) cells suggested that active INH does not directly enhance host-mediated killing of Mtb. Our results thus indicate that Mtb-stimulated host IL-1 and TNF have potential roles in TB chemotherapy.Keywords: Human r IL-1 r TNF r Isoniazid r Leukocytes r Mycobacterium tuberculosis Additional supporting information may be found in the online version of this article at the publisher's web-site IntroductionUpon Mycobacterium tuberculosis (Mtb) exposure, it is estimated that 5-10% of human subjects will develop active tuberculosis Correspondence: Prof. André Báfica e-mail: andre.bafica@ufsc.br (TB) [1], which is characterized by intense pathogen proliferation associated with cellular activation and cell death. Cellular structures known as necrotic granulomas may promote bacterial dissemination and enhance Mtb transmission [2,3]. On the other hand, counter balance is supported by host recognition of Mtb, which induces cytokines such as IL-1β and TNF [4,5], two potent inflammatory mediators that suppress Mtb growth [4,6]. It has C 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.eji-journal.eu Eur. J. Immunol. 2016. 46: 1936-1947 Immunity to infection 1937 been shown that these cytokines regulate intracellular bacterial growth in human macrophages, whether by recruitment of antimicrobial effector molecules [7] or induction of apoptotic cell death [8]. In conjunction with 9], IL-1β, and TNF can provide signals to help differentiation and antigen presentation by macrophages [6,10,11]. Moreover, the adverse outcome of latent TB reactivation observed in clinical trials with anti-TNF therapies, additionally confirmed the essential role of TNF for controlling Mtb growth in humans [12]. In addition to antibiotics, which are major therapeutic tools to promote further suppression of mycobacterial growth [13], host-targeted i...