Although the exchange of metabolites between the intraerythrocytic malaria parasite and the external medium has been studied extensively, the transport of molecules across the erythrocyte cytoplasmic membrane and cytoplasm and the parasitophorous vacuolar membrane needs to be investigated more fully to be completely understood. Recently, the concept of the parasitophorous duct, establishing a continuity between the environment and the vacuolar space surrounding the intraerythrocytic parasite, has been suggested to provide an explanation of how macromolecules can cross two membranes in a cell devoid of an endocytic system. This concept is highly controversial and has been suspected to be an in vitro artefact. In this article, Bruno Pouvelle and Jürg Gysin present evidence of the existence of the parasitophorous duct in Saimiri monkey Plasmodium falciparum- and P. vivax-infected erythrocytes, with a series of ex vivo experiments showing stage and species dependent variations of the characteristics of this structure.
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Plug for the parasitophorous duct: a solution of two conundra.
Malar J
October 2020
Department of Pathology, Faculty of Medicine Ramathibodi Hospital, Mahidol University, Rama 6 Road, Bangkok, 10400, Thailand.
Background: We present two conundra in the biology of intraerythrocytic malaria parasite: how an apparent open parasitophorous duct provide direct access of only a select set of serum proteins to the parasitophorous vacuole, and how proteases mediate membrane lysis to allow merozoite egress.
Solution: We posit the existence of a parasitophorous vacuolar duct plug that is originally formed from a tight junction (or parts thereof) between merozoite apical surface and red blood cell plasma membrane, which by moving over the parasite surface towards the posterior end draws the parasite into the host cell interior, and by remaining at the passage orifice provides a location of transporter(s) for import of serum proteins into parasitophorous vacuole and an opening for merozoite egress upon its dissolution/dismantling through protease(s) action.
Conclusion: This notion obviates the need of a distinct intact parasitophorous vacuolar membrane, which in the proposed model is an extension of the red blood cell membrane but still forms an intracellular compartment for parasite growth and development.
Presence of the parasitophorous duct in Plasmodium falciparum and P. vivax parasitized Saimiri monkey red blood cells.
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Unité de Parasitologie Expérimentale, Institut Pasteur de Lyon, Domaine du Poirier, 69210 Lentilly, France.
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Department of Pathology, Anatomy and Cell Biology, Jefferson Medical College, Philadelphia, PA 19107, USA.
We have previously provided evidence for a pathway in Plasmodium falciparum-infected erythrocytes, coined the parasitophorous duct pathway, which provides serum (macro)molecules direct access to intraerythrocytic parasites . The present study addresses the purity of the fluorescent macromolecules used to define the duct pathway and provides ultrastructural evidence for its presence. The fluorescent tracers used to characterize transport remain intact during their incubation with infected erythrocytes.
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