47–49 The interaction between T cells and macrophages

is known to be critical for prevention of bacterial growth.50–53 However, it is not clear how various M. tuberculosis proteins can trigger the Th1 response. Several factors, such as the affinity between the T-cell receptor (TCR) and peptide–MHC ligand, peptide ligand density and costimulatory signalling during T-cell activation, can play important roles NSC 683864 cell line in the regulation of the Th1/Th2 T-cell response.11,12,54–57 Cytokines induced during innate activation of macrophages have also been shown to be extremely important in controlling the Th1/Th2 balance. For example, induction of IL-12 or TNF-α can trigger a Th1 response;58,59 however, if more IL-10 is produced, the response is likely to be biased towards the Th2 type response.60,61 It has been shown that various M. tuberculosis

secretory proteins bind to a specific receptor on macrophages and influence the downstream signalling cascades and the induction of pro-inflammatory cytokines.62 Although up-regulation of iNOS expression and NO production during infection with M. tuberculosis is well known, very few studies have actually identified the M. tuberculosis proteins directly involved in the up-regulation of the iNOS gene. Our study indicates that rRv2626c affects the macrophage-signalling cascades Ruxolitinib order and up-regulates iNOS induction and NO production mainly by increasing NF-κB activity. Interestingly, flow cytometry data indicate that Rv2626c binds to the macrophage surface with high affinity and specificity. It is possible that the specific binding of Rv2626c on the macrophage surface causes modulation of the downstream signalling pathways triggering NF-κB signalling, which results in increased induction of iNOS23 as well as the cytokines TNF-α63 and IL-12.64 Although the exact beneficial role of iNOS/NO in anti-mycobacterial Rho killing has not been uniformly elucidated,65 studies have confirmed that iNOS/NO is crucial in limiting bacterial growth.66,67 Similarly, the role of TNF-α in TB is paradoxical because, although there is evidence of its protective role,68 it can play a part in the tissue damage that

characterizes human disease.68 A recent study also indicates that M. tuberculosis activates TNF-α production to induce apoptosis of macrophages.62 Our study clearly demonstrates that the secretory M. tuberculosis Rv2626c protein induces pro-inflammatory responses by modulating the expression of iNOS and increasing the secretion of IL-12 and TNF-α, which may play an important role in the initiation of the adaptive immune response in the host. Mycobacterium tuberculosis proteins that induce the Th1 response have been used as targets for subunit vaccines. For example, use of the mycobacterial 30-kDa major secretory protein (antigen 85B, Ag85B) was found to protect animals from M. tuberculosis infection by inducing a Th1-dominant response.