Induction of crisis forms in cultured Plasmodium falciparum with human immune serum from Sudan.

Serums from 90 individuals from three areas in Sudan were tested for inhibitory activity against cultures of Plasmodium falciparum. In addition to inhibitory activity against merozoite invasion, all of the serums demonstrated, in varying degrees, the ability to retard intraerythrocyte development, leading to crisis forms and parasite deterioration. These retardation factors could be removed by absorption of immune serum with parasite-infected erythrocytes and were demonstrable in purified immunoglobulin fractions. Serum from donors in hypoendemic Khartoum did not retard parasite development.