A Poison Capsule Defense

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Science  11 Jan 2002:
Vol. 295, Issue 5553, pp. 235
DOI: 10.1126/science.295.5553.235b

The soil fungus Cryptococcus neoformans can enter and persist within human macrophages, causing virulent infections if the person becomes immunocompromised. This fungus need not infect a vertebrate in order to complete its life cycle, so its pathogenicity is puzzling. A clue to its virulence may come from its life in soil, where predatory microorganisms, such as amoebas, are present.

Steenbergen et al. have discovered remarkable parallels between the defensive strategies used by C. neoformans when eaten by Acanthamoeba castellani and when surviving in human cells. Amoebas ingest the fungal cells, but the cells remain within vacuoles and produce a toxic polysaccharide, as they do when residing within macrophage vacuoles. The engulfed fungus possesses other unfriendly characteristics also exhibited during macrophage infection, and it ultimately kills its host amoeba, whose death releases vital nutrients. Other soil fungi, such as Histoplasma capsulatum, that cause potentially fatal human infections are probably similarly armed because they, too, must run the gauntlet of voracious amoebas. — CA

Proc. Natl. Acad. Sci. U.S.A.98, 15245 (2001).

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