Schistosoma mansoniinfection reduces the protective efficacy of BCG vaccination against virulentMycobacterium tuberculosis

We hypothesized that the ability of BCG vaccination to protect againstMycobacterium tuberculosisis less in hosts exposed to chronic helminthes infection compared to unexposed individuals. To test this hypothesis we evaluated the efficacy of BCG vaccination in protecting againstM. tuberculosischallenge inSchistosoma mansonipre-infected mice by analyzing their ability to limit the replication of TB bacilli in the lung and liver and the histology of lung sections. The results show that BCG vaccinated mice with priorS. mansoniinfection show significantly higher number of colony forming units of TB bacilli as well as significant reduction in air exchange area in the lung compared to controls. In addition, spleen cells fromS. mansoniinfected mice were found to produce significantly less IFN-γ and nitric oxide when stimulated in vitro with PPD and several fold higher soluble egg antigen (SEA) and Concanavalin A induced IL-4 and IL-5 secretion. Taken together, our data show thatS. mansoniinfection reduces the protective efficacy of BCG vaccination againstM. tuberculosispossibly by attenuation of protective immune responses to mycobacterial antigens and/or by polarizing the general immune responses to the Th2 profile.