Sialic acid-dependent binding of Plasmodium falciparum merozoite surface antigen, Pf200, to human erythrocytes

Plasmodium falciparum merozoites, the extracellular stage of the erythrocytic cycle of the human malarial parasite, specifically invade human E. The major determinant of that specificity is the sialic acid residues of E glycophorin. In the present study we show that the merozoite surface Ag, Pf200 (m.w. 195,000 to 205,000), of two different isolates of P. falciparum, binds to the surface of human E but not E from other species not invaded by P. falciparum. Pf200 does not bind to neuraminidase-treated E, indicating the interaction is dependent on sialic acid residues. Binding is inhibited by soluble glycophorin and selective mAb against the glycosylated domain of glycophorin, but not by a mAb against the peptide domain of glycophorin. mAb.5B1 previously identified as reacting with Pf 200, blocks binding of the protein to the E. Binding between Pf200 and the E is not high affinity, as Pf200 can be released from the surface by 0.25 M NaCl.