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Title: Macrophages facilitate the excystation and differentiation of Toxoplasma gondii sporozoites into tachyzoites following oocyst internalization

item FREPPEL, WESLEY - Aix-Marseille University
item PUECH, PIERRE-HENRI - Aix-Marseille University
item FERGUSON, DAVID - Oxford Radcliffe Hospitals
item AZAS, NADINE - Aix-Marseille University
item Dubey, Jitender
item AURELIEN, DUMETRE - Aix-Marseille University

Submitted to: Nature Scientific Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/30/2016
Publication Date: 9/13/2016
Citation: Freppel, W., Puech, P., Ferguson, D.J., Azas, N., Dubey, J.P., Aurelien, D. 2016. Macrophages facilitate the excystation and differentiation of Toxoplasma gondii sporozoites into tachyzoites following oocyst internalization. Nature Scientific Reports. 6:e33654.

Interpretive Summary: Human toxoplasmosis, caused by single-celled parasite, Toxoplasma gondii, accounts for an estimated one-fifth of all diagnosed foodborne infections in the United States, and one fifth of the economic costs attributable to any foodborne pathogen. Pregnant women and their fetuses are exposed to elevated health risks. The ingestion of under cooked infected meat is considered an important source of toxoplasmosis in humans. Poultry is important in the transmission of Toxoplasma both as direct source of infection for humans, and indirectly as prey for the reservoir host, cats. Cats can excrete millions of environmentally resistant stage (oocyst) in their feces. Humans can acquire toxoplasmosis by ingesting food and water contaminated with oocysts. It is uncertain if oocysts can be aerosolized and be infectious to people by inhalation or by direct contamination of eyes. In the present paper authors found that oocysts can be ingested and disrupted by macrophages and the encysted parasites released from the oocyst can be infectious. The findings suggest that people can become infected with T. gondii not only by ingestion but also by inhalation. These results will be useful for public health workers, veterinarians, and parasitologists.

Technical Abstract: Toxoplasma gondii is a common parasite of humans and domestic animals, which is transmitted via oocysts in cat faeces or tissue cysts in contaminated meat. The oocyst and sporocyst walls are multilayered polymeric structures that protect the infective sporozoites from deleterious physical and chemical attacks including disinfectants. Upon oocyst acquisition, the resilient features of these walls are abolished to let the sporozoites excyst and invade host cells following a process that remains poorly understood. Given the resistance of the oocyst wall to digestive enzymes and the ability of oocysts to cause parenteral infections, this study investigated the possible contribution of macrophages in supporting sporozoite excystation following oocyst internalization. By using single cell micromanipulations and real-time and time-point imaging techniques, we demonstrated that RAW macrophages could interact with oocysts within minutes, irrespective of the oocyst surface structure, and engulfed most of them within 4 h, involving remodeling of the macrophage actin cytoskeleton. After 24h of coincubation in physiological conditions, internalized oocysts were associated to macrophage acidic compartments and showed evidences of wall disruption. Free sporozoites were observed in macrophages containing oocyst remnants or in new macrophages, giving rise to dividing tachyzoites. All together, these results highlight an unexpected role of host phagocytic cells in processing T. gondii oocysts and open new perspectives to identify chemical factors that lead to oocyst wall disruption under physiological conditions.