Studies on the role of red blood cell glycoproteins as receptors for invasion by Plasmodium falciparum merozoites

The mechanism of invasion of human red blood cells by Plasmodium falciparum merozoites has been studied by several indirect methods. Red blood cells of the S+s+U+ and S−s−U− blood group phenotypes were trypsin treated and their susceptibility to invasion measured. Trypsin-treated S+s+U+ cells lack the portion of glycophorin A which bears the MN blood group determinants but possess glycophorin B, whereas trypsin-treated S−s−U− cells lack both the glycophorin A MN determinants and the glycophorin B molecule. Since the treated S−s−U− cells showed an even greater loss in susceptibility to invasion than the treated S+s+U+ cells, we conclude that glycophorin B does have a role in merozoite recognition, although it appears less important than glycophorin A. Attempts to decrease invasion by pretreatment with glycosidases were unsuccessful, except for the previously reported effect of neuraminidase. N-acetyl-D-glucosamine decreases the appearance of ring-stage parasites after in vitro reinvasion of P. falciparum. However, the persistence of intact and lysed schizont-infected cells when N-acetyl-D-glucosamine was present, several hours after disappearance of these cells from control cultures, leads us to conclude that this sugar has a deleterious effect on terminal stages of parasite maturation. It is therefore not possible to conclude that N-acetyl-D-glucosamine inhibits merozoite attachment and reinvasion specifically by competition for the receptor.