Temperature dependency for survival of Mycobacterium leprae in macrophages.

Hansen's disease is caused by an infection with an intracellular pathogen, Mycobacterium leprae, which mainly inhabits macrophages and Schwann cells. However, little is known about the survival or growth mechanisms of the bacilli in mouse and human macrophages. In the present study, by using radiorespirometry analysis for the evaluation of the viability of M.leprae, we observed that in vitro incubation of M.leprae-infected macrophages at 35°C was more growth permissive than at 37°C, and supplementation with the immunosuppressive cytokine IL-10 supported the survival of the bacilli in the macrophages for 3 weeks, whereas viability of the bacilli was gradually lost if cultured without IL-10. In human macrophages, M.leprae retained its viability when cultured at 35°C for at least 4 weeks without IL-10. However, the viability of M.leprae was almost lost within 2 weeks if cultured at 37°C. These data suggest that temperature is a crucial factor for the survival of M.leprae in host cells.