RELATIONSHIP BETWEEN HUMORAL RESPONSE TO PLASMODIUM-FALCIPARUM MEROZOITE SURFACE ANTIGEN-2 AND MALARIA MORBIDITY IN A HIGHLY ENDEMIC AREA OF PAPUA-NEW-GUINEA

The prevalence and concentration of antibodies to merozoite surface an tigen-2 (MSA-2) were measured in blood samples collected during a cros s-sectional survey. Antibodies were measured by enzyme-linked immunoso rbent assay using two recombinant proteins that closely approximated t he full-length mature MSA-2 polypeptides expressed by the Plasmodium f alciparum isolate FC27 and the cloned line 3D7 and that were represent ative of the dimorphic forms of MSA-2. Antibodies were also measured t o a form of the 3D7 MSA-2 lacking the central repetitive sequences (d3 D7). High antibody prevalence was observed to all three antigens: the overall prevalence of Ige to FC27, 3D7, and d3D7 was 91%, 90%, and 90% , respectively. The majority of individuals greater than or equal to 5 years of age had antibodies to both forms of MSA-2. The geometric mea n antibody units increased with age with a plateau being reached by 15 -20 years of age. There was a significant positive association of anti body prevalence with both the presence of the parasite and an enlarged spleen in children. This study provides the first evidence that antib odies against nonrepeat regions of MSA-2 are associated with fewer fev er episodes and less anemia, both known to be indicators of malaria mo rbidity.