Glycophorins and red cell invasion by Plasmodium falciparum

The major red cell sialoglycoproteins, the glycophorins, play a central role in the invasion of human red cells by Plasmodium falciparum. En(a-) cells deficient in glycophorin A (alpha) and S-s-U- cells deficient in glycophorin B (delta) are relatively resistant to invasion, while trypsin treatment of S-s-U- cells, which removes most of the remaining sialoglycoprotein, renders these cells almost totally resistant to invasion. Parasites inside these glycophorin-deficient cells develop normally. Invasion of erythroid precursors in vitro by merozoites of P. falciparum parallels the appearance of glycophorins on the surface of these nucleated cells, even though parasites fail to develop inside them. However, another type of cell from an erythroleukaemic line (K562) which expresses glycophorins on its surface is resistant to invasion. Furthermore, the observed increased invasion of young cells as opposed to an older cell population is not related quantitatively to the presence of glycophorins on the cell surface. Thus, although the role of glycophorins is both specific and important in the invasion of cells by P. falciparum, it is clearly only part of a complex process.