An in Vitro Assay for Sequestration: Binding of Plasmodium falciparum‐Infected Erythrocytes to Formalin‐Fixed Endothelial Cells and Amelanotic Melanoma Cells1

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Abstract
Human erythrocytes infected with P. falciparum bind specifically to cultured endothelial cells and to a line of amelanotic melanoma cells. Endothelial cells and amelanotic melanoma cells were fixed in various ways and whether the fixed cells were still able to bind infected erythrocytes was determined. Only cells fixed with 1.0-2.5% formalin in phosphate-buffered saline continued to bind infected erythrocytes as well as unfixed cells. The mechanism of binding to fixed and unfixed cells appeared to be identical for the following reasons. First, erythrocytes infected by parasite strains that bound to unfixed cells also bound to fixed cells while those that did not bind to unfixed cells did not bind to fixed cells. Second, immune serum that inhibited binding to unfixed cells also inhibited binding to fixed cells. Third, EM showed that knobs were the points of attachment between infected erythrocytes and both fixed and unfixed melanoma cells. Fixed cells gave reproducible results over at least 2 mo. A simplified, reproducible assay for measuring binding of P. falciparum-infected erythrocytes to target cells was developed.