Interactions between macrophagelike cells and Leishmania braziliensis in vitro.

The interaction between macrophagelike cells (P388D murine tumor cells) and Leishmania braziliensis panamensis promastigotes was studied in vitro under various conditions by light and electron microscopy. When the macrophagelike cells and L braziliensis promastigate were incubated together for 2 minutes, 90% of the promastigotes were attached to the macrophagelike cells by the tip of the flagella. The macrophagelike cells did not form pseudopods or aggregated microfilaments around the inserted flagellum. After a 5-minute incubation period, the parasites attached to the macrophagelike cells did not show preferred orientation. At this time, numerous pseudopods and aggregated microfilaments of the macrophagelike cells were seen around the invading parasites. When the relationship between the cytochalasin B-treated promastigotes and the macrophagelike cells were examined, no interaction of the promastigote flagella with macrophagelike cells was observed at 2 minutes. After a 5-minute incubation period, 50% of the attached parasites adhered to a macrophagelike cell without any particular orientation. When the interaction between the promastigotes and cytochalasin B-treated macrophagelike cells were examined, the cytochalasin B-treated cells showed fewer pseudopods than the untreated cells, and the number of parasites attached to them was reduced considerably after a 5-minute incubation period. This data demonstrated, for the first time, that the mode of entry by Leishmania promastigotes into macrophagelike cells is dependent on the activation of the macrophagelike cells following the attachment of Leishmania promastigotes.