Effect of sex hormones on the immune system of guinea-pigs and on the development of toxoplasmic lesions in non-lymphoid organs.

The role of cell-mediated immunity in the pathogenesis of toxoplasmic lesions in non-lymphoid organs and its significance in resistance to infection with Toxoplasma gondii were studied in guinea-pigs. Alteration of the sex hormonal environment in both sexes has significant effects on the immunological status of the guinea-pig, changing its reaction to toxoplasmic infection. Thus, gonadectomy appears to enhance delayed hypersensitivity, leading to a greater prominence of lesions in the non-lymphoid organs of gonadectomized male and female animals than in controls. This observation supports the possibility that delayed hypersensitivity plays a major role in the pathogenesis of non-lymphoid, toxoplasmic lesions. Hexoestrol administration for a long period of time induces complete thymic atrophy and severe involution of the thymus-dependent areas of the lymph nodes and spleen, leading to the suppression of cell-mediated immunity and overwhelming disease in those animals infected with Toxoplasma gondii, suggesting that cell-mediated immunity is of importance in resistance to toxoplasmic infection. In view of these findings, the difficulties in the treatment of non-lymphoid toxoplasmic lesions, such as ocular ones, by depressing cellular immunity, are discussed.