Effect of Toxoplasma gondii on histopathology and histochemistry or reticuloendothelial system in experimental animals.

The effect of acute and chronic infections by Toxoplasma gondii on the spleen, thymus and liver of mice and rats, and on their antibody response has been studied. In acute infection while the splenic weight increased the thymic weight decreased. The histopathological studies demonstrated lymphocytic depletion of splenic follicles and thymic cortex. Numerous phagocytes and plasma cells were seen in the red pulp and thymic medulla. Vascular congestion and haemorrhages were marked. The liver cells showed degeneration which progressed from hydropic to fatty. The succinic dehydrogenase activity of damaged cells was decreased, while the phosphatase activity was increased. The parasites were seen in some liver cells. Marked cellular infiltration was observed around the blood vessels in the form of granulomata. The reticuloendothelial cells, Kupffer cells and phagocytes showed higher alkaline phosphatase activity. In chronic infection the thymus showed early lymphocytic depletion then returned to normal. The splenic weight was increased and the follicles were enlarged with the presence of immunoblasts in the germinal centres. The cords of the red pulp were thickened and contained numerous plasma cells. Most of the liver cells were normal with normal enzymatic activity but small foci of necrosis were seen. There was a gradual increase in antibody response in both acute and chronic infections. It was concluded from the results that acute infection mainly produced toxic effects, whereas chronic infection produced immunological responses.