Toxoplasmosis and the host-parasite relationship in murine schistosomiasis mansoni.

Infection with Toxoplasma gondii has been shown to suppress markedly the in vitro splenic lymphocyte response to nonspecific mitogens and the in vivo antibody response to sheep red blood cells. The effect of toxoplasmosis on an in vivo cell-mediated response, granuloma formation around Schistosoma mansoni eggs, was examined in the present study. The granulomas were markedly suppressed from two to 20 weeks after infection with T. gondii. In subsequent experiments the effect of toxoplasmosis-induced immunosuppression on the development of hepatosplenic schistosomiasis was evaluated. Mice with the combined infections had markedly smaller hepatic granulomas and lower mean portal pressures than those infected with S. mansoni alone. Although the prevalence of esophageal varices in the mice with schistosomiasis alone was 60%, there was no visible collateral circulation in the animals with both infections.