Structural alteration of the erythrocyte membrane during malarial parasite invasion and intraerythrocytic development.

Erythrocyte entry by malarial merozoites causes structural alteration of the erythrocyte membrane. First, entry into erythrocytes by merozoites requires the formation of a junction between the erythrocyte membrane and the apical end of the merozoite. Secondly, migration of the junction parallel to the long axis of the merozoite brings the merozoite into an invagination of the erythrocyte membrane. Freeze-fracture studies show that the junction consists of a narrow band of rhomboidally arrayed intramembrane particles (IMP) on the P face of the erythrocyte membrane and matching rhomboidally arrayed pits on the E face. IMP on the P face of the erythrocyte membrane disappear beyond this junction, resulting in the absence of IMP from the P face of the parasitophorous vacuole membrane which originated from the erythrocyte membrane. The erythrocyte membrane is sealed off by fusion of the junction at the posterior end of the merozoite in the fashion of an iris diaphragm. After completing its entry into the erythrocyte the merozoite is surrounded by a parasitophorous vacuole membrane which is different in its molecular organization from the original erythrocyte membrane. In addition, two types of erythrocyte membrane modification are induced by intraerythrocytic parasites. They include electron-dense protrusions called knobs and caveola-vesicle complexes along the erythrocyte membrane.