Glycolipid anchorage of Plasmodium falciparum surface antigens

Human red blood cells (RBC) were infected with the malarial parasite Plasmodium falciparum, the anchoring of schizont proteins to RBC membranes by glycoinositol phospholipids was demonstrated by three criteria: (1) metabolic incorporation of 3H-ethanolamine and 3H-myristate into the protein; (2) release of 35S-methionine-labelled protein into the supernatant after incubation with phosphatidylinositol-specific phospholipase C; and (3) the exposure of a glycoinositol phosphate epitope on the methionine-labelled protein following phospholipase C cleavage. Labelled proteins were analysed by immunoprecipitation, polyacrylamide gel electrophoresis in sodium dodecylsulphate and gel fluorography. Several candidate proteins were observed when each criteria was investigated. Among these, 3 proteins which met all three criteria were identified by immunoprecipitation with monospecific sera or monoclonal antibodies. These included 3 possible vaccine candidates, the p190 major surface antigen, the p76 serine protease and the p71 protein which is thought to be a member of the family of heat-shock Hsp70 proteins.