Toxoplasmosis in nude mice.

Immunity to the intracellular protozoan, Toxoplasma gondii, in mice is of the premunition type. Chemoprophylaxis with sulfadiazine normally permits mice to develop immunity to virulent organisms. However, nude (nu/nu) mice, which lack the thymus, failed to develop immunity to toxoplasma during 3 weeks of drug therapy while their hirsute littermates developed immunity during this period. When nude mice were injected intraperitoneally with thymus cells from hirsute littermates, they became able to develop immunity to toxoplasma during drug prophylaxis. The injection of bone marrow cells or high-titered specific antibody did not prolong survival after sulfadiazine was discontinued. Therefore, it appears that immunity to toxoplasma in mice is dependent upon active cellular immunity while the role of antibody is uncertain.