Role of the mononuclear phagocytic system in the immune and nonspecific clearance of Trypanosoma cruzi bloodstream trypomastigotes.

1. The removal of T. cruzi bloodstream trypomastigotes (BTRYS) from the circulation is mediated mostly by the mononuclear phagocytic system (MPS). In the present study we investigated the nonspecific and the immune clearance of BTRYS in groups of 4 mice whose MPS activity was either enhanced by BCG treatment or depressed by silica treatment. 2. Treatment with BCG resulted in a significant increase in the nonspecific clearance of both carbon particles (100% after 6 min) and BTRYS (60% after 5 min) 28 days after BCG treatment but there was no change in the immune clearance of the parasites. 3. Pretreatment of the animals with silica induced a significant reduction of the colloidal carbon clearance (80% less than control 15 min later) but did not alter the nonspecific or the immune clearance of BTRYS. 4. We conclude that the removal of the opsonized parasites from the circulation is due to a mechanism different from that of the nonspecific clearance.