Date of Award

8-2012

Level of Access Assigned by Author

Campus-Only Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biomedical Sciences

Advisor

Robert T. Wheeler

Second Committee Member

Carol H. Kim

Third Committee Member

John T. Singer

Abstract

Candida albicans is a human commensal and clinically important fungal pathogen that grows as both yeast and hyphal forms during human infection. Although Candida can cause cutaneous and mucosal disease, systemic infections cause the greatest mortality in hospitals. C. albicans in the blood or candidemia occurs primarily in immunocompromised patients, and the innate immune system plays a paramount role in immunity to disseminated infection. In vitro interactions between C. albicans and innate immune cells are dramatic, with neutrophils rapidly destroying yeast and macrophages rapidly being lysed by germinating hyphae. We have developed a zebrafish model of candidemia to probe the molecular nature of these interactions in the intact host. We show that infection of zebrafish larvae with as few as 10 yeast cells causes lethal disseminated disease that shares important traits with disseminated disease in mammals: dimorphic fungal growth, dependence on hyphal growth for virulence, and dependence on the phagocyte oxidase for immunity. Using fluorescently marked immune cells and fungi, we find that within macrophages, phagocytosed yeast can remain viable and even divide without germinating. In a similar fashion, although neutrophils kill yeast, the vast majority of Candida cells within neutrophils are viable. We visualized the cellular impact of loss of phagocyte oxidase activity on both host and pathogen, finding that it mediates the vast majority of oxidative stress in fungi while limiting both fungal proliferation and filamentous growth. This model promises to bridge the gap between in vitro and in vivo experiments by providing a means to non-invasively image infection.

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