Ultrastructural evidence for a parasitophorous duct in human erythrocytes infected with malaria parasites

Abstract

The human malaria parasite, Plasmodium falciparum, spends all but a few minutes of its 48 hour asexual life cycle in host erythrocytes (RBC). Models of the host-parasite complex, obtained by transmission and freeze-fracture electron microscopy, suggest that the intraerythrocytic parasite is contained in a continous, sealed vacuole (PVM). The parasite has an obligate nutritional requirement for serum fatty acids, lipids and proteins. Since mature erythrocytes do not endocytose, a long standing enigma has been the mechanism by which intracellular parasites obtain access to these (macro)molecules. Using a variety of fluorescent labeled macromolecules and confocal fluorescence microscopy (CFIM), we demonstrated that macromolecules in serum did not cross the erythrocyte or PVM, but rather gained direct access to the aqueous space surrounding the parasite through a parasitophorous duct. Being limited by the resolution of the light microscope, we initiated TEM investigations to identify the duct at the ultrastructural level.