Effect of sex hormones on the response of mice to infection with Toxoplasma gondii.

Groups of male and female mice were gonadectomized and some implanted with a pellet of hexoestrol. Half of the animals in each group, including controls, were infected with a low-virulence strain of Toxoplasma gondii. The animals were killed 6 weeks after infection. Gonadectomy increased the relative thymic weight in both sexes, but more so in the male, and the paracortical area of the lymph node was enlarged, as was the thymus-dependent area of the spleen. Hexoestrol administration induced almost complete thymic atrophy and partial involution of the peripheral lymphoid tissues. Greater resistance to toxoplasmic infection was found in the gonadectomized mice than in controls of both sexes, possibly due to a better cell-mediated immunity in the gonadectomized animals. Overwhelming toxoplasmosis with increased mortality was found in the hexoestrol-treated mice after infection, probably resulting from a depression of cell-mediated immunity caused by hexoestrol. It is postulated that the cellular immune response is of greater importance than the formation of antibody in resistance to toxoplasmic infection. The role of the thymolmphatic--sex hormonal interrelation on the age--sex differences seen in the incidence of toxoplasmic lymphadenopathy is also discussed.