DEPRESSED IMMUNITY TO A SALMONELLA-TYPHIMURIUM VACCINE IN MICE EXPERIMENTALLY PARASITIZED BY TAENIA-CRASSICEPS

To assess the immunological status of mice parasitized with Taenia cra ssiceps metacestodes. 6-month old female BALB/c mice experimentally pa rasitized with T. crassiceps and immunized with Salmonella typhimurium antigens were infected with S. typhimurium virulent bacilli (1.6 x LD 50). Both T. crassiceps-parasitized and immunized and parasitized mice showed a very high susceptibility to infection ( * P < 0.01) with hi gher bacteremia than control and immunized-control animals and produce d a reduced IgG response to S. typhimurium antigens ( P < 0.05). This indicates that T. crassiceps is able to preclude development of immun ity to S. typhimurium, because appropriate antibody production to a he terologous antigenic stimulus did not take place, and the bacteremia r esults suggest the parasitosis altered the mononuclear phagocyte syste m. It has been demonstrated that Taenia solium metacestodes produce a small RNA molecule in culture which suppresses humoral and cellular re sponses against homologous antigens in mice. We propose that T. crassi ceps may be actively synthesizing such a factor, apart from other simu ltaneously acting immunomodulatory mechanisms, to induce an immunosupp ressed state favorable to its development in the host. (C) 1998 Elsevi er Science B.V.