Binding of Leishmania promastigotes to macrophages

Leishmania tropica promastigotes are easily attached to and engulfed by C₃H peritoneal macrophages in vitro at 37°C. Different sugars at 0.3-0.5 M inhibited in vitro the attachment of L. tropica promastigotes to C₃H peritoneal macrophages with lactose (Gal-β [1→4]Glc) being the most efficient. Inhibition of attachment is also affected by pre-treatment of promastigotes with galactose oxidase. Oligosaccharides extending from promastigote and amastigote cell surfaces contain an important proportion of non-reducing galactose as does the carbohydrate-rich factor (EF) excreted by promastigotes of L. tropica and L. donovani. This study suggests that Leishmania, an obligatory intracellular parasite, uses as a means of entering the host cell a cellular mechanism similar to that used in the removal of damaged cells from blood circulation. This mechanism is assumed to take advantage of the exposed sugars, particularly the exposed non-reducing galactose, on the parasite surface during the stage of attachment. Once the parasite is inside the cell, the EF it produces might have a protective function, being inhibitory to some of the host cell lysosomal enzymes.