In vitro cytoadherence of Plasmodium falciparum-infected erythrocytes to melanoma cells: factors affecting adhesion.

A reproducible and standardized assay for measuring the cytoadherence of knobby Plasmodium falciparum-infected red cells to amelanotic melanoma cells was developed. Adhesion was dependent on temperature, haematocrit, and parasitaemia. Addition of EDTA to the binding medium reduced adhesion. Removal of protease-sensitive molecules on the surface of the infected cell abolished cytoadherence, whereas removal of carbohydrate residues by treatment of cells with neuraminidase or galactosidase promoted adhesion. Calcium, magnesium, fibrinogen or fibronectin in the medium had no effect on adhesion nor was there any enhancement of adhesion by pre-loading infected cells with calcium. Serum was essential for good adhesion. Adhesion was species specific for target cells; human endothelial or amelanotic melanoma cells were suitable target cells whereas bovine cells were not. The amelanotic melanoma cell could be formalin-fixed and still retain its adhesion properties. The binding properties of formalin-fixed amelanotic melanoma cells were not identical to those of endothelial or unfixed target cells.