Mya Muthig

Document Type

Honors Thesis

Major

Microbiology

Advisor(s)

Robert Wheeler

Committee Members

Melody Neely, Suzanne Angeli

Graduation Year

May, 2025

Publication Date

2025

Abstract

C. albicans is a human commensal that can cause superficial and systemic infections like candidemia, when it spreads to the bloodstream. One of the ways that this fungus is able to evade immune responses is by limiting phagocytosis of host immune cells. Phagocytosis is a process performed by innate immune cells, such as macrophages and neutrophils, which kill invading pathogens by engulfing them. These immune cells generate reactive oxygen species (ROS) during phagocytosis through the NADPH oxidase complex (NOX2). It is known that C. albicans can evade phagocytosis in multiple ways such as hyphal formation and masking pathogen-associated molecular patterns but its specific fungal factors that help it inhibit ROS production are not certain. Evidence suggests that the gene NMD5 may play a role in this process but whether or not this is its primary function or if it also contributes to virulence through other mechanisms is unknown. To assess the roles of nmd5p, a Zebrafish model can be employed because of their similarities to human innate immune cells (particularly their macrophages and neutrophils). Chronic granulomatous disease (CGD) is a genetic disorder characterized by an increased susceptibility to life-threatening bacterial and fungal infections. This defect in the immune system is caused by a mutation in one of the NOX2 components and reduces the amount of ROS produced. CGD can be mimicked in Zebrafish using a morpholino oligosaccharide to block the production of one of these NOX2 components. Since this can be modeled in zebrafish and is known for blocking phagocytosis, it was used in order to study the role of the NMD5 gene in C. albicans. NMD5 was recently found to be required for virulence and early immune evasion in zebrafish. If NMD5 functions solely to inhibit phagocytosis, then in a model where phagocytosis is already impaired, a nmd5Δ/Δ mutant strain should exhibit virulence similar to wild-type Candida. We tested this using a NOX2 knockdown, where reduced phagocytic activity mimics a compromised immune response. We found that the nmd5Δ/Δ mutant strain did produce similar virulence to the wild-type strain when NOX2 was knocked down. When phagocytosis was already blocked, losing NMD5 did not reduce virulence and therefore suggests its main role is phagocytosis inhibition. This research highlights the exciting discovery of a potential new gene in Candida virulence and immune evasion.

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