Objective: To study nitric oxide (NO) production and cytokine expression by macrophages infected by M. tuberculosis H(37)R(v), and to compare the difference between dead and live M. tuberculosis in the induction of immune responses, and thus to show if dead bacteria could be a possible candidate for new vaccines.
Methods: Reverse transcription-polymerase chain reaction (RT-PCR) and ELISA were used to measure the production of NO and cytokines in macrophages infected by H(37)R(v).
Results: Macrophages infected by viable M. tuberculosis produced more NO, IL-1, IL-12, IL-18, TNF-alpha and inducible nitric oxide synthases (iNOS), as compared with macrophages infected by dead bacteria. The number of bacteria was also an important factor determining the production of NO and cytokines.
Conclusions: Viable M. tuberculosis H(37)R(v) can induce the activation of macrophages and the production of more NO and cytokines which play important roles in the host immune response. Heat-killed M. tuberculosis H(37)R(v) failed to induce activation of macrophages and the production of NO and cytokines, which makes it unlikely to be a candidate for vaccine development.