Expression of strain-specific surface antigens on Plasmodium falciparum-infected erythrocytes.

Antigenic determinants present on the surface of squirrel monkey erythrocytes infected with late developmental stages of P. falciparum were recognized through their ability to bind antibodies present in the serum of immune monkeys. Two different assays were used to demonstrate the presence of these antigenic determinants on the cell surface: the fluorescent labelling of intact cells in suspensions and the binding to protein A-Sepharose. Such determinants appear to be strain-specific and have, for a given strain, a variable expression according to whether the parasites are taken from intact or splenectomized animals or whether they have been grown in vitro.