ASSESSMENT OF THE HUMORAL IMMUNE-RESPONSE AGAINST PLASMODIUM-FALCIPARUM RHOPTRY-ASSOCIATED PROTEIN-1 AND PROTEIN-2

Naturally occurring antibody responses to Plasmodium falciparum rhoptr y-associated proteins 1 and 2 (RAP-1 and RAP-2) were measured with rec ombinant and parasite-derived forms of the antigens, For comparative p urposes, responses to multiple forms of three other malarial antigens were also examined. The sera of 100 Papua New Guineans were screened f or antibodies, Eighty-six and 82% of individuals over 30 years of age had antibodies that recognized parasite-derived RAP-1 and RAP-2, respe ctively, Importantly, we found that recombinant and native antigens sh are linear epitopes seen by the human immune system; thus, the recombi nant proteins may be adequate human immunogens. However, antibodies af finity purified on recombinant RAP-1 reacted with other antigens in ad dition to parasite-derived RAP-I, Thus, the antigenicity of RAP-I may have been overestimated previously, The recognition of RAP-1 and RAP-2 correlated with age and with the recognition of recombinant forms of the ring-infected erythrocyte surface antigen, merozoite surface prote in 1, and merozoite surface antigen 2 (MSA2) antigens. Antibodies to t hese antigens appear to be generated in response to the total exposure to malaria of the host, Antibodies to conserved regions of MSA2 had s tronger correlations with both age and the recognition of other antige ns than did the full-length recombinant MSA2 molecule, In contrast to results with the other antigens, there was no significant difference i n the ages of individuals with a certain antibody titer to the full-le ngth recombinant or parasite-derived MSA2 molecule, but antibodies to these two antigens did correlate with parasitemia. For all antigens te sted, antibody levels after two infections can approach the peak level s of antibodies obtained in immune individuals.