Natural selection on apical membrane antigen-1 of Plasmodium falciparum.

The Apical Membrane Antigen-1 (AMA-1) is a protein localized in the apical organelles of the merozoite, one of the stages in the life cycle of malaria parasites (Plasmodium spp.) that infects the vertebrate host. This antigen, which is encoded by a single polymorphic locus, plays a role in evading immune detection and mediating invasion into target host cells. We found evidence of positive Darwinian selection on immunogenic regions of P. falciparum AMA-1 favoring genetic diversity in the T-cell epitopes and in regions likely to interact with host antibodies. These results support the hypothesis that polymorphism at the AMA-1 locus in maintained by balancing selection arising from host immune recognition.