title: Invasion-inhibitory antibodies inhibit proteolytic processing of apical membrane antigen 1 of Plasmodium falciparum merozoites.
abstract: 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.
authors.affiliation: Department of Immunology, Walter Reed Army Institute of Research, Silver Spring, MD 20910, USA. sheetij.dutta@na.amedd.army.mil
authors.forename: Sheetij
authors.initials: S
authors.lastname: Dutta
authors.forename: J David
authors.initials: JD
authors.lastname: Haynes
authors.forename: J Kathleen
authors.initials: JK
authors.lastname: Moch
authors.forename: Arnoldo
authors.initials: A
authors.lastname: Barbosa
authors.forename: David E
authors.initials: DE
authors.lastname: Lanar
mesh_terms: D000818:Animals; D000913:Antibodies, Protozoan / Q000378:metabolism*; D017951:Antigen Presentation / Q000187:drug effects; D000953:Antigens, Protozoan / Q000276:immunology* / Q000378:metabolism*; D002614:Chelating Agents / Q000494:pharmacology; D066298:In Vitro Techniques; D017780:Malaria Vaccines / Q000276:immunology / Q000378:metabolism; D008565:Membrane Proteins / Q000276:immunology* / Q000378:metabolism*; D018448:Models, Immunological; D010963:Plasmodium falciparum / Q000254:growth & development / Q000276:immunology* / Q000378:metabolism; D011480:Protease Inhibitors / Q000494:pharmacology; D011499:Protein Processing, Post-Translational / Q000187:drug effects; D015800:Protozoan Proteins / Q000276:immunology* / Q000378:metabolism*; D011817:Rabbits; D011994:Recombinant Proteins / Q000276:immunology / Q000378:metabolism
chemical_list: D000913:Antibodies, Protozoan; D000953:Antigens, Protozoan; D002614:Chelating Agents; D017780:Malaria Vaccines; D008565:Membrane Proteins; D011480:Protease Inhibitors; D015800:Protozoan Proteins; D011994:Recombinant Proteins; C090077:apical membrane antigen I, Plasmodium