Effect of the strain of Toxoplasma gondii on the development of toxoplasmic encephalitis in mice treated with antibody to interferon-gamma.

To examine whether differences observed in the development of toxoplasmic encephalitis between strains of Toxoplasma gondii are determined by the numbers of cysts occurring in the brain, C57BL/10 mice were infected with ten cysts of the ME49, Beverley, or C56 strain of the parasite. At 10 weeks after infection, the numbers of cysts and inflammatory changes in the brains of the mice were examined in each of the experimental groups. The ME49 strain formed significantly more cysts than did the other two strains, with no difference in the number of cysts being noted between the Beverley and C56 strains. Mice infected with the ME49 strain showed infiltration of inflammatory mononuclear cells in both the meninges and the parenchyma of their brains, whereas mice infected with the Beverley or C56 strain showed no inflammatory changes in their brains. Treatment of mice with a monoclonal antibody to interferon-gamma (IFN-gamma) once weekly for 3 weeks beginning at 10 weeks after infection augmented the inflammatory changes in the brains of mice infected with each strain. However, the intensity of the inflammatory changes differed significantly between the mice, depending on the strain of T. gondii with which they were infected. Mice infected with the ME49 strain showed the most remarkable inflammatory changes in their brains. Mice infected with the Beverley strain developed foci of acute inflammation in their brains after treatment with an antibody to IFN-gamma.(ABSTRACT TRUNCATED AT 250 WORDS)