Antibody responses to the repetitive Plasmodium falciparum antigen Pf332 in humans naturally primed to the parasite

Antibodies to the degenerate repeats of EB200, a part of the Plasmodium falciparum antigen Pf332, are protective in monkeys. To analyse the prevalence, magnitude and specificity of antibodies to EB200 in malaria-exposed humans, the IgG antibody reactivity with recombinant EB200 protein as well as with crude malaria antigen was determined in Senegalese donors (n = 100; 4-87 years). Antibody reactivity with EB200 was low or absent in children below 15 years but was prevalent and significantly higher in older donors. In comparison, all individuals displayed reactivity with a crude malaria antigen preparation, which also increased with age. The reactivity with the crude malaria antigen was correlated to the reactivity with EB200, suggesting that the low levels of IgG to EB200 found in some adult donors reflected a limited degree of recent exposure to parasites rather than a selective non-responsiveness to Pf332. Comparison of serological and clinical data showed that high levels of antibodies to crude malaria antigen and to EB200 were predictive of fewer future clinical attacks of malaria. A reactivity pattern very similar to that found in Senegalese donors was observed in Liberian adults where 80% of the sera showed reactivity with EB200 and all peptides were recognized by between 60 and 100% of the donors. This strong reactivity with EB200-derived overlapping peptides suggests that the epitopes in EB200, to a large extent, are linear. In the light of previous data on the parasite neutralizing capacity of antibodies to Pf332, the present results emphasize the potential interest of Pf332-derived sequences for inclusion in a subunit vaccine against P falciparum malaria.