Formation and Modification of the Parasitophorous Vacuole Occupied by Toxoplasma Gondii

Abstract

Toxoplasma tachyzoites are able to actively invade and survive within specialized vacuoles in a wide range of vertebrate host cells. The parasite enters a vacuole that is derived from the plasma membrane by invagination, yet these vacuoles differ from standard phagocytic compartments in several respects. The Toxoplasma-containing vacuole, or parasitophorous vacuole (PV), resists acidification [Sibley et al., 1985b] and fusion with lysosomes [Jones and Hirsch 1972]. These vacuoles also resist fusion with vesicles containing soluble tracers for fluid phase endocytosis including Lucifer yellow [Joiner et al., 1990] and with vesicles containing permanent labels such as acridine orange that accumulate in acidic compartments [Sibley et al., 1985a]. While the PV is inert with respect to interactions with the host-cell endocytic network, events within the vacuole are dynamic. During invasion and vacuole formation, the parasite secretes a number of proteins from specialized storage organelles called rhoptries and dense granules. The contents of these secretory organelles are targetted to different sites within the vacuole including the vacuolar membrane and the intravacuolar network that forms a membranous interface within the vacuole [Sibley et al., 1986].