Adherence of Erythrocytes during Exflagellation of Plasmodium falciparum Microgametes Is Dependent on Erythrocyte Surface Sialic Acid and Glycophorins

By T. J. Templeton, D. Keister, O. Muratova, J. Procter, D. Kaslow. 1998

Malaria male gametocytes within a newly ingested infected blood meal in the mosquito midgut emerge from erythrocytes and extrude approximately eight flagellar microgametes in a process termed exflagellation. In culture, and in blood removed from infected patients, emerging microgametes avidly adhere to neighboring uninfected and infected erythrocytes, as well as to emerged female macrogametes, creating “exflagellation centers”. The mechanism of erythrocyte adherence is not known nor has it been determined for what purpose microgametes may bind to erythrocytes. The proposition of a function underlying erythrocyte adherence is supported by the observation of species-specificity in adhesion: microgametes of the human malaria Plasmodium falciparum can bind human erythrocytes but not chicken erythrocytes, whereas avian host Plasmodium gallinaceum microgametes bind chicken but not human erythrocytes. In this study we developed a binding assay in which normal, enzyme-treated, variant or null erythrocytes are identified by a cell surface fluorescent label and assayed for adherence to exflagellating microgametes. Neuraminidase, trypsin or ficin treatment of human erythrocytes eliminated their ability to adhere to Plasmodium falciparum microgametes, suggesting a role of sialic acid and one or more glycophorins in the binding to a putative gamete receptor. Using nulls lacking glycophorin A [En(a−)], glycophorin B (S−s−U−) or a combination of glycophorin A and B (Mk/Mk) we showed that erythrocytes lacking glycophorin B retain the ability to bind but a lack of glycophorin A reduced adherence by exflagellating microgametes. We propose that either the sialic acid moiety of glycophorins, predominantly glycophorin A, or a more complex interaction involving the glycophorin peptide backbone, is the erythrocyte receptor for adhesion to microgametes.

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Citations in the corpus

Analysis of the Plasmodium falciparum proteome by high-accuracy mass spectrometry (2002, background): “The male gamete has been shown to bind to sialic acid on erythrocytes through a lectin-like activit”
Malaria transmission‐blocking antigen, Pfs230, mediates human red blood cell binding to exflagellating male parasites and oocyst production (2006, background): “One possibility that has been suggested is that the male/RBC interaction is involved in microgamete release or movement through the blood meal (Carter and Graves, 1988; Templeton et al., 1998).”
Three Members of the 6-cys Protein Family of Plasmodium Play a Role in Gamete Fertility (2010, background): “falciparum, indicate that P230 not only plays a role in gamete-gamete interactions but male gamete interactions with erythrocytes may be required for gamete maturation resulting in an optimal fertilisation capacity [27,62].”