Characterization of the antibody response against Plasmodium falciparum erythrocyte membrane protein 1 in human volunteers

The immune response against the Plasmodium falciparum variant surface antigen P. falciparum erythrocyte membrane protein 1 (PfEMP1) is a key component of clinical immunity against falciparum malaria. In this study, we used sera from human volunteers who had been infected with the P. falciparum 3D7 strain to investigate the development, specificity, and dynamics of anti-PfEMP1 antibodies measured against six different strain 3D7 Duff binding-like domain 1 alpha (DBL1 alpha) fusion proteins. We observed that a parasitemia of 20 to 200 infected erythrocytes per mu l was required to trigger an antibody response to DBL1 alpha and that antibodies against one DBL1 alpha variant cross-react with other DBL1 alpha variants. Both serum and purified immunoglobulin Gs (IgGs) were able to agglutinate infected erythrocytes, and purified anti-DBL1 alpha IgGs bound to the live infected red blood cell surface in a punctate surface pattern, confirming that the IgGs recognize native PfEMP1. Analysis of sera from tourists naturally infected with P.falciparum suggests that the anti-PfEMP1 antibodies often persisted for more than 100 days after a single infection. These results help to further our understanding of the development of acquired immunity to P. falciparum infections.