In vitro parasite-monocyte interactions in human leishmaniasis. Evidence for an active role of the parasite in attachment.

Leishmania are obligate intracellular parasites of mononuclear phagocytes in the mammalian host. To more clearly define features of the early events in host-parasite interaction, human monocytes were so-cultured with Leishmania tropica amastigotes in vitro. Infection of monocytes was time dependent and inhibited at 4 degrees C and in the presence of cytochalasin B. Pretreatment of amastigotes with cytochalasins prevented their attachment to normal monocytes. Untreated amastigotes attached normally but could not enter cytochalasin-pretreated monocytes. This suggests that amastigotes actively participate in attachment but require host cell participation for interiorization.