Protection against experimental toxoplasmosis by adoptive immunotherapy.

The role of humoral and cell-mediated immunity against toxoplasmosis in experimentally infected guinea pigs was examined by using a syngeneic passive transfer system. Serum or spleen and lymph node cells from guinea pigs immune to infection with the RH strain of Toxoplasma gondii conferred partial protection against symptomatic disease in recipient guinea pigs. This result was based on the reduced dissemination or growth of T. gondii parasites from the primary inoculation site to various selected organ sites of the recipients of immune serum or cells. Similar levels of partial protection against disseminated toxoplasmosis occurred in animals infused with cell suspensions enriched for immune T cells, whereas treatment of immune cells with a monoclonal anti-guinea pig T cell antibody plus complement abolished their ability to transfer resistance. These findings provide substantial direct evidence implicating both cellular and humoral components of the immune response as important effector mechanisms in host resistance to toxoplasmosis.