Initiation and regulation of T-cell responses in tuberculosis.

Tuberculosis (TB) poses a great challenge to immunologists, as it represents a chronic infection characterized by persistence of the pathogen despite development of antigen-specific immune responses. Among the characteristics of adaptive immune responses to Mycobacterium tuberculosis is a delay in the onset of detectable T-cell responses, in both humans and experimental animals. Recent studies have revealed mechanisms that contribute to this delay, including pathogen inhibition of apoptosis, delayed migration of dendritic cells from the lungs to the local lymph node, and influence of regulatory T cells. In addition, novel features of M. tuberculosis antigen-specific T-cell differentiation have been discovered, which reveal pathways that limit and promote immune control of infection. Taken together, these results highlight the need for additional basic research and provide optimism for the development of TB vaccines with greater efficacy.

Cloning and characterization of aspartate-beta-semialdehyde dehydrogenase from Mycobacterium tuberculosis H37 Rv.

AIMS: To clone and characterize the aspartate-beta-semialdehyde dehydrogenase of Mycobacterium tuberculosis H37Rv. METHODS AND RESULTS: The asd gene of M. tuberculosis H37Rv was cloned in pGEM-T Easy vector, subcloned in expression vector pQE30 having a T5 promoter, and overexpressed in Escherichia coli. The ASD enzyme was expressed to levels of 40% but was found to be inactive. Functional ASD was obtained by altering induction and growth conditions and the enzyme was purified to near homogeneity using nickel-nitrilotriacetic acid (Ni-NTA) affinity chromatography. The K(m) and V(max) values for the three substrates L-ASA, NADP and Pi, the turnover number and specific activity of the enzyme were determined. CONCLUSIONS: Functional ASD enzyme of M. tuberculosis was obtained by gene cloning and protein purification using affinity chromatography. The K(cat) and specific activity of the enzyme were 8.49 s(-1) and 13.4 micromol min(-1) microg(-1) respectively. SIGNIFICANCE AND IMPACT OF THE STUDY: The ASD enzyme is a validated drug target. We characterized this enzyme from M. tuberculosis and future work would focus on deducing the three-dimensional structure of the enzyme and design of inhibitors, which could be used as drugs against TB.