The exit of Trypanosoma cruzi from the phagosome is inhibited by raising the pH of acidic compartments.

Abstract

The protozoan parasite Trypanosoma cruzi can infect many distinct mammalian cell types. The parasites enter cells through the formation of phagocytic vacuoles, but later are found free in the cytosol, where they multiply as amastigotes. Using transmission electron microscopy we found that within 2 h after infection 70% of the parasites, including examples of both mammalian forms (trypomastigotes and amastigotes), were inside partially disrupted vacuoles or free in the cytosol. We demonstrated that the pH of vacuoles containing recently interiorized parasites is acidic, through immunocytochemical localization of the acidotropic compound DAMP (18) in their interior. Increasing the vacuolar pH with chloroquine, ammonium chloride, methylamine, or monensin significantly inhibited the escape of the parasites into the cytosol. These results are compatible with the hypothesis that an acid-active hemolysin of T. cruzi (15) might be involved in the escape mechanism.

The use of confocal laser scanning microscopy to analyze the process of parasitic protozoon-host cell interaction

“…It is important to point out, however, that in the case of T. cruzi this membrane has a short life span since it is completely lysed a few hours after its formation (12)(13)(14).…”

“…For some parasites, such as T. gondii, a special PV which does not fuse with components of the endo-lysosomal pathway of the host cell is an ideal site for parasite replication (8)(9)(10)(11). Other parasites, such as T. cruzi, must lyse the membrane lining the PV and enter into direct contact with the cytoplasmic structures of the host cell in order to start the process of division (12)(13)(14). Despite the importance of the PV, little information is available about the basic aspects related to its formation.…”

Morphological comparison of axenic amastigogenesis of trypomastigotes and metacyclic forms of Trypanosoma cruzi

“…Flagellated trypomastigotes are ingested by vertebrate cells through a process referred to as parasite-directed endocytosis (Burleigh & Andrews 1995) with formation of a parasitecontaining endocytic vacuole which fuse with lysosomes from the host cell (Carvalho & De Sousa 1989, Tardieux et al 1992. Within 2 h after infection, the trypomastigotes can leave the acidic environment as a phagosome before the transformation into amastigotes is completed (Ley et al 1990) and enter the slightly alkaline environment of the cytoplasm, where they multiply as aflagellate amastigotes (Burleigh & Andrews 1995). These early events appear to occur at different rates depending on the type of vertebrate cells studied.…”

A century of research: what have we learned about the interaction of Trypanosoma cruzi with host cells?

“…So far, TcTOX activity has been observed in ex-. So far, TcTOX activity has been observed in extracellular amastigotes (Ley et al 1990 Recent work has shown that the kinetics of endosomal and lysosomal marker accumulation, and their subsequent loss -indicative of parasite escape into the cytoplasm -is not correlated with either the infective form or phylogenetic group of the parasite tested under these particular conditions (Fernandes et al 200�b).…”

“…Once inside the host cells, trypomastigotes and amastigotes secrete TcTOX, a complement 9 (C9) factor-related molecule that, at low pH, will destroy the PV membrane and allow the parasite access to the cytosol (�ndrews & Whitlow 1989, �ndrews 1990, �ndrews et al 1990, Ley et al 1990, Manning-Cela et al 2001. Raising the intracellular pH with weak bases affects MT invasion and substantially delays escape from the PV, increasing the latency from about 2-10 h. By contrast, the kinetics of amastigote invasion and escape are not affected by this treatment (Stecconi- Silva et al 200�).…”