Plasmodium falciparum: isolation of intact and erythrocyte-free trophozoites from sorbitol lysates.

An in vitro culture of Plasmodium falciparum (isolate FCUP-1/RSA) was arrested in the trophozoite stage with alpha-difluoromethylornithine (DFMO), followed by sorbitol treatment to liberate intracellular parasites from infected erythrocytes. Most of the unlysed erythrocytes and ghost membranes were removed by filtration, after agglutination with anti-erythrocyte monoclonal antibodies or wheat-germ agglutinin. A highly purified parasite preparation was obtained after chromatography on an immuno-affinity column consisting of polystyrene particles to which anti-erythrocyte monoclonal antibodies had been adsorbed. Isolated parasites were free of surrounding erythrocyte membranes and structurally intact as assessed by transmission electron microscopy, SDS-PAGE and ELISA.