Role of inflammatory cells in Chagas' disease. II. Interactions of mouse macrophages and human monocytes with intracellular forms of Trypanosoma cruzi: uptake and mechanism of destruction.

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In this study we examined the kinetics of interaction between mouse peritoneal macrophages (MPH) or human blood monocytes (HBM) with intracellular (amastigote [AMA]) forms of Trypanosoma cruzi. In electron microscopy studies, AMA were seen bound to the surface of unelicited MPH after 5 min of interaction, i.e., when the first observations were made. Internalization was visible after 8 min, and the AMA were never seen outside of phagocytic vacuoles. Signs of AMA damage were first seen after 4 hr. Amastigote disintegration was commonly observed 12 hr after their initial contact with MPH. Similar results were obtained with HBM. These kinetic patterns of AMA uptake and destruction were in agreement with the results of quantitative assays in which the number of AMA contained by 200 MPH and the percentage of infected MPH were measured. The extent of the release of 3H-labeled materials from MPH that had phagocytosed [3H]AMA was approximately 10, 90, and 99% of the total ingested radioactivity after 4, 12, and 24 hr of incubation, respectively. A comparison of the kinetic patterns of MPH interaction with noninvasive AMA and invasive trypomastigote (TRY) forms showed that, after internalization, both the percentage of AMA-containing MPH and the number of AMA per 200 MPH declined dramatically over a 70-hr incubation period, whereas the percentage of MPH infected by the TRY remained virtually constant and the number of organisms per 200 cells increased markedly. This contrast indicated that the AMA had been destroyed, whereas the TRY had managed to survive, transform into AMA, and multiply within MPH. AMA killing by MPH involved H2O2 but not other intermediates of oxygen reduction, because it was inhibited by catalase but not by scavengers of O2, OH ., and 1O2. AMA lost their viability when incubated with glucose and glucose oxidase, confirming their sensitivity to H2O2. Thus, MPH and HBM have the potential for participating in the clearance of T. cruzi AMA from chagasic tissue lesions.