Plasmodium falciparum: surface modifications of infected erythrocytes from clinical isolates. Evidence of antigenic diversity using Venezuelan human malarial sera.

Infections of human erythrocytes with the mature asexual blood stages of Plasmodium falciparum result in antigenic changes in the host cell membrane that, by virtue of their position, length of exposure, and close association with functional changes critical to pathogenesis, are a potential important target for host effector mechanisms. These parasite-induced antigens expressed on the surface of infected erythrocytes have been shown to exhibit considerable polymorphism. An antibody-mediated agglutination assay using malaria serum samples from different regions of Venezuela has been developed to examine the extent of antigenic diversity of infected red blood cells (IRBC) taken from subjects with naturally acquired P. falciparum infections. An important humoral immune recognition of surface molecules from red blood cells infected with a wide variety of clinical isolates of P. falciparum was observed even when sera from individuals experiencing a single episode of malaria were used. A process of in vivo antigenic variation of surface molecules is postulated, since agglutination of IRBC was observed with acute heterologous but not autologous sera. When sera obtained from Amerindians inhabiting the Venezuelan Amazon were assayed, a strong immune response to different parasite isolates, including those of another geographic region, was observed, suggesting the recognition of highly conserved immunogenic parasitic epitopes in people exposed to multiple malaria infections.