Role of the surface coat in in vitro attachment and phagocytosis of Plasmodium berghei by peritoneal macrophages.

Evidence is presented to indicate that Plasmodium berghei merozoites, but not trophozotites, have an antiphagocytic capsule. The capsule appears to form around the developing merozoties of the schizont in the parasitophorous vacuole. Serum from animals immune to P. berghei reacts with this capsule. After reaction with immune serum, the antiphagocytic action of the capsule is lost. By the process of binding serum protein, the capsule becomes electron dense and can be readily visuallzed as the surface coat by electron microscopy. At physiological temperatures, phagocytosis by macrophages rapidly follows adhesion of antibody-coated parasites. Both tight and loose phagosomes are formed.