Mechanisms involved in protective immune response generated by secretory proteins of Mycobacterium habana against experimental tuberculosis

Abstract

Live mycobacteria secrete a number of unique proteins early in their multiplication which are important for both the pathogenesis and the stimulation of specific host responses. We have investigated the mechanisms by which the host mounts immune response against tuberculosis after vaccination with secretory proteins (SP) of a vaccine candidate Mycobacterium habana TMC 5135. Mice vaccinated with SP of 10th day growth of M. habana, either alone or emulsified in Freund's incomplete adjuvant (FIA) possessed antituberculous resistance and cellular immune responses against M. tuberculosis H37Rv. These proteins induced a significant cutaneous delayed type hypersensitivity response in guinea pigs vaccinated with heat killed M. tuberculosis H37Rv, which was equivalent to that observed with a standard purified protein derivative (PPD). The splenocytes of these guinea pigs have shown higher proliferative response after stimulation with SP than with PPD. The SP + FIA immunization has been found to exert maximum prophylactic effect by potentiating both the oxygen dependent arms and enzymatic activities of macrophages. Macrophages from mice vaccinated with SP of M. habana produced enhanced levels of interleukin (IL)-2, interleukin-12 and interferon (IFN)- γ. The protective as well as cell mediated immune responses were upregulated in SP immunized animals when compared to whole cell (M. habana) vaccinated animals. SDS-PAGE of SP from M. habana showed the prominent bands of 60, 32, 31 and 30 kDa. Furthermore, the western analysis of SP with pulmonary tuberculosis patient's serum has revealed the presence of immunoreactive antigens of 36, 35, 33/32 kDa. Overall study demonstrated that the secretory antigens released by actively growing M. habana bacilli could activate different arms of effective immune response.