Effect of antithymocyte serum on experimental toxoplasmosis in mice.

The effect of antithymocyte serum (ATS) on mice infected with high-virulent or low-virulent strains of Toxoplasma gondii was studied. Treatment with ATS reduced the survival time of mice infected with high-virulent Toxoplasma and aggravated the disease; treatment prolonged parasitemia in animals infected with low-virulent Toxoplasma. Although ATS adversely affected the humoral antibody response, its main effect on toxoplasmosis was probably due to depression of cell-mediated immunity. ATS appeared to be able to activate chronic Toxoplasma infection, but this effect was much less pronounced than that on acquisition of immunity. The results suggest that Toxoplasma infection should be routinely looked for in patients treated with antilymphocyte serum.