Parasitophorous vacuoles of Leishmania amazonensis-infected macrophages maintain an acidic pH

Abstract

Leishmania amastigotes are intracellular protozoan parasites of mononuclear phagocytes which reside within parasitophorous vacuoles of phagolysosomal origin. The pH of these compartments was studied with the aim of elucidating strategies used by these microorganisms to evade the microbicidal mechanisms of their host cells. For this purpose, rat bone marrow-derived macrophages were infected with L. amazonensis amastigotes. Intracellular acidic compartments were localized by using the weak base 3-(2,4-dinitroanilino)-3'-amino-N-methyldipropylamine as a probe. This indicator, which can be detected by light microscopy by using immunocytochemical methods, mainly accumulated in perinuclear lysosomes of uninfected cells, whereas in infected cells, it was essentially localized in parasitophorous vacuoles, which thus appeared acidified. Phagolysosomal pH was estimated quantitatively in living cells loaded with the pH-sensitive endocytic tracer fluoresceinated dextran. After a 15to 20-h exposure, the tracer was mainly detected in perinuclear lysosomes and parasitophorous vacuoles of uninfected and infected macrophages, respectively. Fluorescence intensities were determined from digitized video images of single cells after processing and automatic subtraction of background. We found statistically different mean pH values of 5.17 to 5.48 for lysosomes and 4.74 to 5.26 for parasitophorous vacuoles. As for lysosomes of monensin-treated cells, the pH gradient of parasitophorous vacuoles collapsed after monensin was added. This very likely indicates that these vacuoles maintain an acidic internal pH by an active process. These results show that L. amazonensis amastigotes are acidophilic and opportunistic organisms and suggest that these intracellular parasites have evolved means for survival under these harsh conditions and have acquired plasma membrane components compatible with the environment.

Leishmania promastigotes require lipophosphoglycan to actively modulate the fusion properties of phagosomes at an early step of phagocytosis

“…Error bars indicate SEM. (Alexander and Vickerman, 1975;Chang and Dwyer, 1976;Shepherd et al, 1983;Rabinovitch et al, 1985;Antoine et al, 1990;Prina et al, 1990;Russell et al, 1992;Lang et al, 1994), which are hydrolase-enriched organelles arising from phagosome maturation (Desjardins, 1995;Haas, 1998). This clearly indicates that amastigotes are well adapted for survival within the harsh environment of phagolysosomes.…”

A Microbial Strategy to Multiply in Macrophages: The Pregnant Pause

“…Similarly, 2 days after entering macrophages, L. donovani amastigotes colocalize with rab7, LAMP-1, and cathepsins B, D, H, and L (35). As expected for lysosomal compartments, vacuoles harboring Leishmania amazonensis amastigotes are ϳpH 5.0 (36). The ability to culture amastigotes in broth will expedite analysis of the mechanisms that equip parasites to replicate in lysosomes (37).…”

Legionella pneumophila Replication Vacuoles Mature into Acidic, Endocytic Organelles

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