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Toxoplasma gondii invades host cells via two distinct mechanisms: phagocytosis and a unique energy-dependent process. This parasite causes toxoplasmosis by destroying infected cells after rapid multiplication.
Area of Science:
- Cell biology
- Parasitology
- Immunology
Background:
- Toxoplasma gondii is an obligate intracellular protozoal parasite causing toxoplasmosis.
- Infection involves both phagocytic and non-professional phagocytes, leading to cell destruction.
- Parasite multiplication within host cells is a key pathological event.
Purpose of the Study:
- To elucidate the distinct mechanisms of Toxoplasma gondii invasion into host cells.
- To understand the cellular and molecular processes involved in parasite entry.
- To identify factors modulating parasite invasion.
Main Methods:
- Comparative analysis of parasite invasion pathways.
- Investigation of cytochalasin-sensitive morphological changes during invasion.
- Examination of host cell membrane properties influencing entry.
Main Results:
- Two invasion mechanisms identified: phagocytosis and a novel, energy-dependent process.
- The novel invasion involves parasite apical pole-host cell membrane interaction.
- Host cell membrane composition and microviscosity modulate parasite entry.
Conclusions:
- Toxoplasma gondii employs diverse strategies to enter host cells.
- Parasite entry is an active, energy-requiring process involving cellular cooperation.
- Host cell factors significantly influence the efficiency of Toxoplasma gondii invasion.
Abstract:
Toxoplasma gondii, an obligate intracellular protozoal parasite, is the etiologic agent of toxoplasmosis. A main event in the pathologic course of this organism is the infection of both phagocytic cells and "nonprofessional phagocytes"--e.g., heart cells--and the subsequent destruction of these cells following massive multiplication of the parasite therein. There are two mechanisms of invasion. The parasite may enter a cell such as a macrophage by the well-known mechanism of phagocytosis without triggering its own death inside the cell. By the other process, communication of the parasite's apical pole and the host cell membrane may evoke a sequence of invasion steps different from that of phagocytosis. This invasion process involves the cooperation of the host cell and the parasite. The entry of the parasite is characteristically a rapid process that requires the input of energy by both of the cells involved. A series of cytochalasin-sensitive morphologic changes that are undergone by the parasite and the host cell lead to the interiorization of the parasite. Chemical factors, as well as membrane composition, microviscosity, and membrane structures on the host cell membrane, modulate the parasite's entry.