Invasion-Inhibitory Antibodies Inhibit Proteolytic Processing of Apical Membrane Antigen 1 of Plasmodium falciparum Merozoites

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 100; no. 21; pp. 12295 - 12300
• Main Authors: Dutta, Sheetij, Haynes, J. David, Moch, J. Kathleen, Barbosa, Arnoldo, Lanar, David E.
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 14.10.2003; National Acad Sciences
• Subjects: Animals; Antibodies; Antibodies, Protozoan - metabolism; Antigen Presentation - drug effects; Antigens; Antigens, Protozoan - immunology; Antigens, Protozoan - metabolism; Antiserum; Biological Sciences; Chelating Agents - pharmacology; In Vitro Techniques; Malaria Vaccines - immunology; Malaria Vaccines - metabolism; Medical research; Membrane Proteins - immunology; Membrane Proteins - metabolism; Membranes; Merozoites; Models, Immunological; Parasites; Parasitism; Plasmodium falciparum - growth & development; Plasmodium falciparum - immunology; Plasmodium falciparum - metabolism; Protease inhibitors; Protease Inhibitors - pharmacology; Protein Processing, Post-Translational - drug effects; Proteins; Protozoan Proteins - immunology; Protozoan Proteins - metabolism; Rabbits; Recombinant Proteins - immunology; Recombinant Proteins - metabolism; Schizonts
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.2032858100

Apical membrane antigen 1 (AMA-1) is a promising vaccine candidate for Plasmodium falciparum malaria. Antibodies against AMA-1 of P. falciparum (PfAMA-1) interrupt merozoite invasion into RBCs. Initially localized within the apical complex, PfAMA-1 is proteolytically processed and redistributed circumferentially on merozoites at about the time of their release and invasion into RBCs. An 83-kDa precursor form of PfAMA-1 is processed to 66-kDa and then to 48- and 44-kDa products. We show that, even at low concentrations, IgG antibodies against correctly folded recombinant PfAMA-1 cross-linked and trapped the 52-, 48-, and 44-kDa proteolytic products on merozoites. These products are normally shed into the culture medium. At higher concentrations antibodies inhibited invasion into RBCs and caused a reduction in the amount of 44- and 48-kDa products, both on merozoites and in the culture medium. A corresponding increase also occurred in the amount of the 66- and 52-kDa forms detected on the merozoites. These antibodies also prevented circumferential redistribution of AMA-1. In contrast, monovalent invasion-inhibitory Fab fragments caused accumulation of 66- and 52-kDa forms, with no cross-linking, trapping, or prevention of redistribution. Antibodies at low concentrations can be used as trapping agents for intermediate and soluble forms of AMA-1 and are useful for studying proteolytic processing of AMA-1. With this technique, it was confirmed that protease inhibitor chymostatin and Ca2+chelators can inhibit the breakdown of the 66-kDa form. We propose that antibodies to AMA-1 capable of inhibiting erythrocyte invasion act by disrupting proteolytic processing of AMA-1.