Perforation of the host cell plasma membrane during Toxoplasma invasion requires rhoptry exocytosis

Abstract

Toxoplasma gondii is an obligate intracellular parasite. Proteins released during host cell invasion from apical secretory organelles known as rhoptries are delivered into the host cell cytosol to perform functions critical for parasite survival and virulence. How these effector proteins move across the host cell plasma membrane is unknown but may involve a previously noted temporary loss of host cell plasma membrane barrier integrity. Here, we use high-speed, multi-wavelength fluorescence imaging to spatially monitor the barrier integrity of the host cell plasma membrane, in real time, during invasion. The data reveal that early in invasion the parasite creates a transient perforation in the host cell membrane. The perforation occurs at the point on the host membrane in contact with the parasite’s apical end. Parasites depleted of any of five proteins known to be required for rhoptry exocytosis are unable to perforate the host cell membrane. These data suggest a model in which perforating agents stored within rhoptries are released onto the host cell at the initiation of invasion to create a conduit for the delivery of rhoptry effector proteins.