Potentiation of autoimmune response in rats infected with Toxoplasma gondii.

The influence that an infection with Toxoplasma gondii in thymus proximity produces on the autoimmune response was studied. Rats infected with 3 X 10(3) trophozoites of T. gondii in thymus proximity were immunized with 5 mg/ml of chemically modified rat male accessory glands saline extract (MRAG) and/or human serum albumin (HSA) emulsified in complete Freund's adjuvant (CFA) at 6 days after infection. A second immunization was performed 30 days later. Four experimental groups were made: group 1-rats were immunized with MRAG-CFA and HSA-CFA; group 2-rats were infected and immunized with MRAG-CFA and HSA-CFA; group 3-rats were infected and immunized with MRAG-CFA; group 4-rats were infected and immunized with HSA-CFA. The cellular immune response was evaluated at 15 days after first immunization by delayed type hypersensitivity (DTH) test and the humoral response was studied by passive haemagglutination test at 45 days after first immunization. The results indicate that the cellular and humoral immune response against MRAG were significantly potentiated in infected rats (p less than 0.02, p less than 0.05, respectively). The response to HSA did not show significant differences between the infected and uninfected groups. Concomitantly, the histopathological alterations produced by T. gondii in thymus gland were studied at 6 and 52 days after infection. Cortical depletion and presence of parasites in the thymic cortex were detected in both cases. Involution thymic was demonstrated in infected rats killed at 52 days after infection. The possible participation of the thymus gland in the enhancement of the autoimmune response to MRAG is discussed.