cytochalasin-d and Leishmaniasis

Visceral leishmaniasis is a vector-borne disease caused by an obligate intracellular protozoan parasite Leishmania donovani. The molecular mechanism involved in internalization of Leishmania is poorly understood. The entry of Leishmania involves interaction with the plasma membrane of host cells. We have previously demonstrated the requirement of host membrane cholesterol in the binding and internalization of L. donovani into macrophages. In the present work, we explored the role of the host actin cytoskeleton in leishmanial infection. We observed a dose-dependent reduction in the attachment of Leishmania promastigotes to host macrophages upon destabilization of the actin cytoskeleton by cytochalasin D. This is accompanied by a concomitant reduction in the intracellular amastigote load. We utilized a recently developed high resolution microscopy-based method to quantitate cellular F-actin content upon treatment with cytochalasin D. A striking feature of our results is that binding of Leishmania promastigotes and intracellular amastigote load show close correlation with cellular F-actin level. Importantly, the binding of Escherichia coli remained invariant upon actin destabilization of host cells, thereby implying specific involvement of the actin cytoskeleton in Leishmania infection. To the best of our knowledge, these novel results constitute the first comprehensive demonstration on the specific role of the host actin cytoskeleton in Leishmania infection. Our results could be significant in developing future therapeutic strategies to tackle leishmaniasis.

Topics: Actin Cytoskeleton; Actins; Animals; Cells, Cultured; Cytochalasin D; Leishmania donovani; Leishmaniasis; Macrophages; Mice; Microscopy, Fluorescence; Nucleic Acid Synthesis Inhibitors

Leishmania are flagellated protozoan parasites which, in their amastigote stages, survive and multiply within phagolysosome-like parasitophorous vacuoles (PV) of mammalian macrophages (MO). This study develops an earlier ultrastructural, incidental observation that zymosan particles (Z) were transferred to the PV of macrophages infected with Leishmania amazonensis. In the present report, a pulse-chase light microscopic assay was used to delineate several features of the Z transfer. The assay reflects both the movement of internalized particles to a position adjoining a PV, and their delivery to the vacuoles. Transfer was selective, in the sense that Z, beta-glucan or heat-killed yeast particles were transferred, whereas latex beads, aldehyde-fixed, or immunoglobulin G-coated erythrocytes were not. This selectivity may be related to the high density of carbohydrate ligands displayed on the surface of yeast-derived particles, to ligand resistance to lysosomal degradation or to signals encoded in the cytosolic tails of the receptors involved in particle recognition. A few Z particles could be found within PV after 1 h of incubation with infected MO, but chase periods of several hours at 34 degrees C were required for particle transfer to the PV in a substantial proportion of the MO. Ammonium chloride, chloroquine, or monensin, compounds which increase the pH in acidified compartments, substantially enhanced the transfer of Z particles. Finally, transfer was inhibited by cytochalasin D, but was unaffected by the antitubulin nocodazole. Although it is not yet known if particle transfer occurs by fusion of donor vesicles with PV or by interiorization of the former into the latter, the model described should be useful in the study of the interactions between large phagocytic vesicles and the modulation of those interactions by cellular, parasitic, and environmental signals.

Topics: Ammonium Chloride; Animals; Cells, Cultured; Chloroquine; Cytochalasin D; Hydrogen-Ion Concentration; Kinetics; Leishmaniasis; Macrophages; Male; Mice; Mice, Inbred BALB C; Microscopy, Electron; Monensin; Temperature; Vacuoles; Zymosan