Analysis of the high molecular weight rhoptry complex ofPlasmodium falciparumusing monoclonal antibodies

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Abstract
SUMMARY: Twenty-one monoclonal antibodies, obtained after immunization of mice with erythrocytic stages ofPlasmodium falciparum, produced a double dot image in IFA. Immunoelectronmicroscopy indicated that the mAbs reacted with the rhoptries. Rhoptries are pear-shaped apical organelles, believed to be involved in invasion of the host cell by the parasite. The mAbs all immunoprecipitated the high molecular weight antigen complex. 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 recognized by some of the mAbs. The epitopes defined by the mAbs were present in most of the 40P. falciparumstrains or isolates studied by IFA. Interestingly, the mAbs also reacted with high titres onP. vivaxandP. ovale, but produced images that did not indicate an apical location. The mAbs failed to react on the non-human malaria parasites studied,P. cynomolgiandP. inui. OnP. bergheiorP. chabaudiparasites, only 5 mAbs gave a positive reaction, labelling a large network outside the parasite. Finally, the mAbs did not react withP. falciparumsporozoites, indicating that the rhoptries of merozoites and sporozoites, the two invasive stages of the malaria life-cycle are equipped with distinct sets of proteins.