One fate of epimastigote forms of Trypanosoma cruzi injected in mice. An ultrastructural study.

Recently, we suggested that epimastigote forms of Trypanosoma cruzi are cleared from circulation of mice by a mechanism independent of lysis and that platelets play an important role in this process. These observations prompted us to look at the fate of epimastigotes in the lung, liver, and spleen of mice injected intravenously with these parasite forms. Using transmission electron microscopy, we observed clumps of epimastigotes and platelets in direct contact with phagocytes in the lumen of capillaries. However, the platelets and parasites were probably separated before phagocytosis because only parasites were found inside the phagocytes. Indeed, most of the phagocytes, although containing epimastigotes in different stages of disintegration, contained no platelets. The removal of parasites from platelets was probably mediated by phagocytes through a mechanism similar to the removal of bacteria from the surface of erythrocytes in humans. These observations suggest that the nonvirulence of T. cruzi epimastigotes in mice is not due to lysis but probably to the inability of these parasite forms to escape destruction by the phagocytes.