Cytoadhesion of Plasmodium falciparum ring-stage-infected erythrocytes.

A common pathological characteristic of Plasmodium falciparum infection is the cytoadhesion of mature-stage-infected erythrocytes (IE) to host endothelium and syncytiotrophoblasts. Massive accumulation of IE in the brain microvasculature or placenta is strongly correlated with severe forms of malaria. Extensive binding of IE to placental chondroitin sulfate A (CSA) is associated with physiopathology during pregnancy. The adhesive phenotype of IE correlates with the appearance of Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1) at the erythrocyte surface (approximately 16 h after merozoite invasion), so that only early blood-stage (ring-stage) IE appear in the peripheral blood. Here, we describe results that challenge the existing view of blood-stage IE biology by demonstrating the specific adhesion of IE, during the early ring-stage, to endothelial cell lines from the brain and lung and to placental syncytiotrophoblasts. Later, during blood-stage development of these IE, trophozoites switch to an exclusively CSA cytoadhesion phenotype. Therefore, adhesion to an individual endothelial cell or syncytiotrophoblast may occur throughout the blood-stage cycle, indicating the presence in malaria patients of noncirculating (cryptic) parasite subpopulations. We detected two previously unknown parasite proteins on the surface of ring-stage IE. These proteins disappear shortly after the start of PfEMP1-mediated adhesion.