Selective internalization of choline-phospholipids in Plasmodium falciparum parasitized human erythrocytes

We have incubated control and Plasmodium falciparum parasitized human erythrocytes with lipid vesicles containing radiolabeled long-chain phosphatidylcholine and sphingomyelin, in the presence of a nonspecific lipid transfer protein. Most of the radiolabeled phospholipids were, immediately thereafter, available for extracellular phospholipases, suggesting that uptake of vesicles as such did not occur. In time, the amount of phosphatidylcholine inserted in the outer leaflet of the host cell membrane of parasitized erythrocytes decreased, indicating that phosphatidylcholine was being internalized in parasitized erythrocytes. The exclusion of sphingomyelin from the internalization process suggests that the removal of phosphatidylcholine from the outer leaflet of the erythrocyte membrane is caused by transbilayer migration, rather than by endocytosis. The extent of phosphatidylcholine internalization indicates that part of it does not remain in the inner leaflet of the host cell membrane, but is taken up by the intraerythrocytic parasite. Individual phosphatidylcholine species, containing 16:0/18:1-, 16:0/18:2- and 16:0/20:4-fatty acids, showed similar extents of internalization, after being incorporated in parasitized erythrocytes by a phosphatidylcholine specific transfer protein.