The immunopathology of Schistosoma mansoni granulomas in human colonic schistosomiasis.

The immunopathology of Schistosoma mansoni infection was studied in colonic biopsies obtained from 14 patients with established schistosomiasis. The characteristic lesions of this parasitic infection are mainly induced by the presence of living eggs in the tissue. Different types of lesions can be present simultaneously. The earliest lesions contain T-lymphocytes as well as accessory cells around living eggs. They transform into granulomas composed of eosinophils, T-lymphocytes, a few B-lymphocytes and large mononuclear cells expressing major histocompatibility (MHC) class II antigens. These cells are also Mac 387 positive. This means that they are monocytes/macrophages freshly recruited from the blood. In other, probably older, granulomas, MHC class II positive cells tend to disappear and the centrally located multinucleated giant cells are negative for antibodies directed against MHC class II antigens. It appears thus that the composition of the granulomas in schistosomiasis is variable. The lesions may have characteristics of cell-mediated immunity and/or of a foreign-body reaction. Contrary to what is often seen in Crohn's disease or intestinal tuberculosis no major hyperplasia of the lymphoid tissue is observed in the colon in association with S. mansoni infection.