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 falciparu m (PF83/AMA-1) is a potential asexual blood stage vaccine component. T his 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 nov el high-performance, ion exchange chromatography (HPIEC) method, PF83- 7G8-1 induced polyclonal antibodies in rats that immunoprecipitated ba th 83- and 66-kD forms of PF83/AMA-1 from S-35-methionine metabolicall y labeled parasite extracts. Using HPIEC-purified PF83-7G8-1 in combin ation with a rat monoclonal antibody against the highly conserved carb oxy-terminal (CT) region of PF83/AMA-1, we developed a CT-capture-enzy me-linked immunosorbent assay to measure naturally acquired responses against the entire PF83/AMA-1 molecule. Analysis of populations from v illages 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 para site antigen. A statistically significant age-related change in antibo dy levels to PF83/AMA-1 was observed in Guinea-Bissau. No such correla tion was observed in the Senegalese population, although an age-relate d antibody response was seen for total parasite antigen. No significan t correlation was observed between PF83/AMA-1 responses and the parame ters of parasite load and malaria-related fever.