Parasitized erythrocyte antigens and thrombospondin adhesion in the immunology and pathogenesis of falciparum malaria

Abstract

Falciparum-parasitized erythrocytes develop new antigens on the erythrocyte surface. Both antimalarial antibody and thrombospondin bind to surface antigens or ligands on the surface of the infected red cell. Diverse antigens may be involved in parasite evasion of host immunity, but conserved molecules may be required for pathogenesis. There is a high degree of antigenic diversity at the infected erythrocyte surface among isolates. This diversity may underlie the potential of falciparum malaria to repeatedly reinfect the same person. There is also evidence for an antigenically conserved, possibly functionally conserved, determinant on the infected red cell surface. Antibody to a conserved determinant on the infected red cell surface may be associated with immunity to falciparum malaria. A conserved membrane surface determinant may be involved in parasitized erythrocyte sequestration. Thrombospondin binding in vitro is specific to mature trophozoites and schizonts, the same stages which sequester in vivo. Specific adhesion to thrombospondin is common among laboratory strains of falciparum-parasitized erythrocytes bearing knobs and among all isolates of falciparum tested. The numbers of parasitized erythrocytes bound to thrombospondin in vitro increases with parasitemia. Specific binding of parasitized erythrocytes to an endothelial receptor and to thrombospondin, which itself interacts with clotting factors, may play a role in sequestration and vascular obstruction.