Expression and immune recognition of conserved alleles of Plasmodium falciparum variant antigens.

An important factor in the pathogenicity of P. falciparum, the causing agent of malaria is the expression of highly polymorphic antigens encoded by the multigene families var and rif. The extreme polymorphism of these genes in strains from different geographical regions is in contrast with the observation of a number of conserved alleles found in Amazonian isolates. The humoral response against these proteins is considered an important factor in the immunity against symptomatic infection in áreas with high transmission. We measured the antibody response against recombinant PfEMP1 and RIFIN antigens and detected low responsiveness of symptomatic and asymptomatic malaria infected individuals. These responses were not only weak when compared to the anti-merozoite surface protein 1 response, but also ceased rapidly after the removal of circulating parasites. On the basis of these results, the response against DBLa seems to be dependent on the presence of parasites and not important for the observed protection against symptomatic infection in hypoendemic settings. (AU)