Participation of cell surface anionic sites in the interaction between Trypanosoma cruzi and macrophages

Cationized ferritin particles, which bind to cell surfaces, were used to analyse the role of cell surface anionic sites during the T. cruzi-macrophage interaction. Incubation of bloodstream trypomastigotes of T. cruzi with cationized ferritin before the interaction reduced significantly their surface charge, measured by determination of the cellular electrophoretic mobility, and increased markedly their ingestion by macrophages. The same treatment of cellular electrophoretic mobility, and increased markedly their ingestion by macrophages. The same treatment of cellular electrophoretic mobility, and increased markedly their ingestion by macrophages. The same treatment of epimastigotes interfered neither with the surface charge nor with their ingestion by macrophages. These results are discussed considering the presence of sialic acid on the surface of T. cruzi and the difference of the surface charge existant between epimastigote and trypomastigote forms. Incubation of the macrophages with cationized ferritin before interaction with T. cruzi markedly reduced the ingestion of epimastigotes and increased the ingestion of trypomastigotes. Macrophages labeled at 4 degrees C with cationized ferritin and then incubated in the presence of T. cruzi at 37 degrees C interiorized the anionic sites of the cell surface into endocytic vacuoles. However, no cationized ferritin particles were seen in association with the membrane of endocytic vacuoles containing parasites. Macrophages incubated at 37 degrees C in the presence of cationized ferritin or horseradish peroxidase, incorporated these proteins into cytoplasmic vacuoles. If these labeled macrophages were incubated in the presence of T. cruzi they ingested the parasites which could be seen within endocytic vacuoles. Cytoplasmic vacuoles labeled with horseradish peroxidase fused with all endocytic vacuoles containing T. cruzi. However, no fusion was observed of cytoplasmic vacuoles containing cationized ferritin particles with endocytic vacuoles containing parasites. These results, together with others reported previously, suggest that during the interaction of T. cruzi and macrophages cell surface anionic sites of both, cells and parasites, are involved.