Abstract
The cytoadhesion of Plasmodium falciparum-infected erythrocytes (IEs) to the endothelial cells lining the microvasculature, clogging the microvessels of various organs, is a key event in the pathogenesis of certain severe forms of malaria, such as cerebral malaria and pulmonary edema. Studies aiming to identify possible correlations between the severity of clinical cases and the presence of particular cytoadhesion phenotypes have been largely unsuccessful. One of the possible reasons for this failure is that some of the key receptors and/or mechanisms involved have yet to be identified. By combining IE selection, cell transfection, and adhesion inhibition assays, we identified a new cytoadhesion receptor, neural cell adhesion molecule (NCAM). NCAM is a member of the immunoglobulin superfamily and has nonpolysialylated and polysialylated isoforms, the latter being rare in adults. The nonpolysialylated form is present on the surfaces of endothelial cells in the microvessels of various organs in which IE sequestration occurs. We found that multiphenotypic IEs interacted with nonpolysialylated NCAM and with another, as yet unidentified receptor. These IEs also displayed cytoadhesion in flow conditions, presenting the unique ability to form adherent macroaggregates composed of hundreds of IEs. These features may act as virulence factors, increasing the capacity of IEs to clog microvessels via receptor synergy and macroaggregate formation, thereby facilitating the pathogenesis of severe forms of malaria.