Leishmania amazonensis: the phagocytosis of amastigotes by macrophages

In the present study, we examine the cell biology of Leishmania amastigote uptake by mammalian cells and compare this process to the phagocytosis of IgG-opsonized erythrocytes. We report that many aspects of amastigote uptake into macrophages resemble classical receptor-mediated phagocytosis. Parasite uptake requires energy expenditure by macrophages but not by parasites. Treating macrophages to prevent either energy metabolism or actin polymerization prevents amastigote uptake. The uptake of amastigotes by macrophages involves the colocalization of f-actin, paxillin, and talin to phagocytic cups that are formed around amastigotes during internalization. Treatment of macrophages with genestein, to inhibit protein phosphorylation, prevents amastigote uptake, indicating that this process, like receptor-mediated phagocytosis, depends on protein tyrosine phosphorylation. However, the amount and the pattern of protein tyrosine phosphorylation observed during amastigote uptake by macrophages is reduced relative to that observed during IgG-erythrocyte phagocytosis. The uptake of viable, but not heat-killed amastigotes, is associated with a decrease in the intensity of several specific macrophage proteins that are phosphorylated on tyrosine residues. In summary, although many features of amastigote uptake by macrophages resemble classical receptor-mediated phagocytosis, differences in macrophage protein phosphorylation during amastigote phagocytosis may contribute to the unique aspects of amastigote uptake and intracellular survival in macrophages.