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Ex Vivo Responses for Interferon‐gamma and Proinflammatory Cytokine Secretion to Low‐Molecular‐Weight Antigen MTB12 of Mycobacterium tuberculosis during Human Tuberculosis

MTB12 protein, also called CFP‐2, is a major and early secreted component of Mycobacterium tuberculosis. However, its role during mycobacterial infection has been poorly characterized. In this study, we purified the native MTB12 protein and investigated the profile of MTB12‐induced cytokines [interferon (IFN)‐γ, tumour necrosis factor (TNF)‐α and interleukin (IL)‐6], in early tuberculosis (TB) patients (n = 20) and healthy controls (n = 35). The cytokine profiles were compared with those induced by the 30‐kDa antigen (Ag). In healthy controls, MTB12‐induced IFN‐γ production was markedly decreased in peripheral blood mononuclear cells compared with 30‐kDa Ag‐induced IFN‐γ. In TB patients, the mean IFN‐γ level induced by MTB12 was lower than that induced by the 30‐kDa Ag, albeit the difference was not significant. After 2 months of anti‐TB therapy, both the MTB12‐ and 30‐kDa‐induced IFN‐γ levels were significantly increased in TB patients. MTB12‐induced TNF‐α and IL‐6 levels were prominently upregulated in monocyte‐derived macrophages from TB patients, but they were not significantly different from those induced by the 30‐kDa Ag. Further, the activation of p38 mitogen‐activated protein kinase and extracellular signal‐regulated kinase was required for the induction of TNF‐α and IL‐6 by MTB12, as well as by the 30‐kDa Ag. Collectively, these data suggest that the MTB12 protein plays an essential role for proinflammatory responses through the MAPK pathway during the early stages of human TB, even though its T‐cell immunoreactivity is weaker than that of the 30‐kDa Ag.