Cytoadherence of knobby and knoblessPlasmodium falciparum-infected erythrocytes

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Abstract
Cytoadherence ofPlasmodium falciparum-infected erythrocytes to melanoma cells was analysed using strains or isolates of parasites expressing or not expressing knobs (K+or K−phenotype) on the erythrocyte surface. Both K+and K−parasites had the capacity to cytoadhere to melanoma cells. Using a panel of melanoma cell lines with different surface expression of the cytoadherence receptors CD36, thrombospondin and ICAM-1 indicated that CD36 was the major receptor for parasites of both K+and K−phenotypes. Binding competition experiments between K+and K−-infected erythrocytes suggested that K+cytoadherence is of higher affinity than that of K−parasites. However, some K−cytoadherence was also found in isolates containing mixed populations of K+and K−parasites. The interaction of the two types of infected erythrocytes with melanoma cells also differed ultrastructurally, erythrocytes of K+phenotype showing intimate interdigitations with microvilli on the melanoma cells, while erythrocytes of K−phenotype displayed more separated interactions with fewer sites of contact and involving only a few melanoma cell microvilli. One and the same infected erythrocyte may co-express the ligand for CD36-mediated cytoadherence and the structures mediating binding of uninfected erythrocytes to form rosettes.