Date of Award

Summer 8-23-2019

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Biomedical Sciences

Advisor

Robert T. Wheeler

Second Committee Member

Clarissa Henry

Third Committee Member

Reeta Rao

Additional Committee Members

Julie Gosse

Paul Millard

Abstract

Candida yeasts are common commensals that can cause mucosal disease and life-threatening systemic infections. While many of the components required for defense against Candida albicans infection are well established, questions remain about how various host cells at mucosal sites assess threats and coordinate defenses to prevent normally commensal organisms from becoming pathogenic. Using two Candida species, C. albicans and C. parapsilosis, which differ in their abilities to damage epithelial tissues, we used traditional methods (pathogen CFU, host survival, and host cytokine expression) combined with high-resolution intravital imaging of transparent zebrafish larvae to illuminate host-pathogen interactions at the cellular level in the complex environment of a mucosal infection. In zebrafish, C. albicans grows as both yeast and epithelium-damaging filaments, activates the NF-kB pathway, evokes proinflammatory cytokines, and causes the recruitment of phagocytic immune cells. On the other hand, C. parapsilosis remains in yeast morphology and elicits the recruitment of phagocytes without inducing inflammation. High-resolution mapping of phagocyte-Candida interactions at the infection site revealed that neutrophils and macrophages attack both Candida species, regardless of the cytokine environment. Time-lapse monitoring of single-cell gene expression in transgenic reporter zebrafish revealed a partitioning of the immune response during C. albicans infection: the transcription factor NF-kB is activated largely in cells of the swimbladder epithelium, while the proinflammatory cytokine tumor necrosis factor alpha (TNF-a) is expressed in motile cells, mainly macrophages. Our results point to different host strategies for combatting pathogenic Candida species and separate signaling roles for host cell types.

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