HIGH PREVALENCE OF NATURAL ANTIBODIES AGAINST PLASMODIUM-FALCIPARUM 83-KILODALTON APICAL MEMBRANE ANTIGEN (PF83/AMA-1) AS DETECTED BY CAPTURE-ENZYME-LINKED IMMUNOSORBENT-ASSAY USING FULL-LENGTH BACULOVIRUS RECOMBINANT PF83/AMA-1

The 83-kilodalton (kD) apical membrane antigen of Plasmodium falciparum (PF83/AMA-1) is a potential asexual blood stage vaccine component. This antigen has been expressed as a full-length nonfusion, recombinant baculovirus protein (PF83-7G8-1) using the authentic predicted signal peptide for appropriate postsynthetic routing. When purified by a novel high-performance, ion exchange chromatography (HPIEC) method, PF83-7G8-1 induced polyclonal antibodies in rats that immunoprecipitated bath 83- and 66-kD forms of PF83/AMA-1 from S-35-methionine metabolically labeled parasite extracts. Using HPIEC-purified PF83-7G8-1 in combination with a rat monoclonal antibody against the highly conserved carboxy-terminal (CT) region of PF83/AMA-1, we developed a CT-capture-enzyme-linked immunosorbent assay to measure naturally acquired responses against the entire PF83/AMA-1 molecule. Analysis of populations from villages in Guinea-Bissau and in an area of high malarial transmission in Senegal demonstrated a very high prevalence (94-100%) of naturally acquired serum IgG responses to PF83/AMA-1. Analysis of these natural responses showed that PF83/AMA-1 may be a well-recognized asexual parasite antigen. A statistically significant age-related change in antibody levels to PF83/AMA-1 was observed in Guinea-Bissau. No such correlation was observed in the Senegalese population, although an age-related antibody response was seen for total parasite antigen. No significant correlation was observed between PF83/AMA-1 responses and the parameters of parasite load and malaria-related fever.