Extracellular amastigotes of Trypanosoma cruzi are potent inducers of phagocytosis in mammalian cells

Summary The protozoan parasite Trypanosoma cruzi, the aetiological agent of Chagas' disease, has two infective life cycle stages, trypomastigotes and amastigotes. While trypomastigotes actively enter mammalian cells, highly infective extracellular amastigotes (type I T. cruzi) rely on actin-mediated uptake, which is generally inefficient in non- professional phagocytes. We found that extra- cellular amastigotes (EAs) of T. cruzi G strain (type I), but not Y strain (type II), were taken up 100-fold more efficiently than inert particles. Mammalian cell lines showed levels of parasite uptake comparable to macrophages, and extensive actin recruitment and polymerization was observed at the site of entry. EA uptake was not dependent on parasite- secreted molecules and required the same molecu- lar machinery utilized by professional phagocytes during large particle phagocytosis. Transcriptional silencing of synaptotagmin VII and CD63 signifi- cantly inhibited EA internalization, demonstrating that delivery of supplemental lysosomal mem- brane to form the phagosome is involved in parasite uptake. Importantly, time-lapse live imag- ing using fluorescent reporters revealed phago- some-associated modulation of phosphoinositide metabolism during EA uptake that closely resem- bles what occurs during phagocytosis by macro- phages. Collectively, our results demonstrate that T. cruzi EAs are potent inducers of phagocytosis in non-professional phagocytes, a process that may facilitate parasite persistence in infected hosts.