ANALYSIS OF THE HIGH-MOLECULAR-WEIGHT RHOPTRY COMPLEX OF PLASMODIUM-FALCIPARUM USING MONOCLONAL-ANTIBODIES

Twenty-one monoclonal antibodies, obtained after immunization of mice with erythrocytic stages of Plasmodium falciparum, produced a double d ot image in IFA. Immunoelectronmicroscopy indicated that the mAbs reac ted with the rhoptries. Rhoptries are pear-shaped apical organelles, b elieved to be involved in invasion of the host cell by the parasite. T he mAbs all immunoprecipitated the high molecular weight antigen compl ex. Some mAbs recognized on immunoblots only 1 protein of this complex , whereas others reacted with RhopH1 and RhopH3, or RhopH2 and RhopH3 or with the 3 proteins. An additional antigen of 52 kDa was also recog nized by some of the mAbs. The epitopes defined by the mAbs were prese nt in most of the 40 P. falciparum strains or isolates studied by IFA. Interestingly, the mAbs also reacted with high titres on P. vivax and P. ovale, but produced images that did not indicate an apical locatio n. The mAbs failed to react on the non-human malaria parasites studied , P. cynomolgi and P. inui. On P. berghei or P. chabaudi parasites, on ly 5 mAbs gave a positive reaction, labelling a large network outside the parasite. Finally, the mAbs did not react with P. falciparum sporo zoites, indicating that the rhoptries of merozoites and sporozoites, t he two invasive stages of the malaria life-cycle are equipped with dis tinct sets of proteins.