Surface charge on Plasmodium knowlesi and P. coatneyi-infected red cells of Macaca mulatta

Abstract

Red cells infected by Plasmodium falciparum, P. coatneyi, and P. knowlesi adhere to venous endothelium. The possible role of red cell surface charge in the adhesiveness was investigated. The electrophoretic mobility of red cells from monkeys infected by P. knowlesi and P. coatneyi was not significantly different from mobilities determined before infection. When the infected red cells were concentrated by density gradient, they still showed normal electrophoretic mobility. Surface charge distribution was studied by binding positively charged ferric oxide hydrosols to glutaraldehyde-fixed red cells. Colloid binding was similar between the red cells infected with P. knowlesi and P. coatneyi and the uninfected red cells. Furthermore, knoblike membrane protrusions on red cells infected by P. coatneyi showed similar colloid binding as adjacent membranes. Therefore, neither the net surface charge nor the charge distribution on the red cell surface was altered by these infections. The knoblike protrusions in P. coatneyi-infected red cells have radii of curvature of 28–98 nm. Since these low radii would theoretically allow two similarly curved surfaces to approach within 0.5–1.0 nm of each other, knoblike protrusions may form the basis of adhesion. Knoblike protrusions of P. falciparum-infected red cells have similar dimensions and are the apparent site of attachment to venous endothelium.