Effect of the antiphagocytic agent cytochalasin B on macrophage invasion by Leishmania mexicana promastigotes and Trypanosoma cruzi epimastigotes.

Unstimulated mouse peritoneal exudate cells were cultured on coverslips in Medium 199 containing 10 per cent (v/v) calf serum. Cytochalasin B dissolved in dimethyl sulphoxide (DMSO) and diluted in Medium 199 was added to cultures to give final concentrations of 1, 5 and 10 mug/ml. Equal numbers of Leishmania mexicana promastigotes, Trypanosoma cruzi epimastigotes and sheep red cells were added to 24 hr cultures incubated at 37 C. The macrophage monolayers were fixed and stained at various time intervals. L. mexicana promastigotes sheep red blood cells were found to attach to macrophages in the presence of the drug but did not enter the cells. When the medium containing the cytochalasin was replaced with normal medium phagocytosis of the adherent parasites and red cells followed rapidly. T. cruzi epimastigotes were found inside macrophages in both drug-treated and drug-free cultures although the number found to be intracellular in the latter was significantly greater. This study suggest that L. mexicana promastigotes enter macrophages by being phagocytosed, whereas T. cruzi epimastigotes can actively penetrate these cells.