Macrophage PHOX Restricts Aspergillus fumigatus Germination and Hyphal Development Through ROS-Dependent Immunity

Abstract

Aspergillus fumigatus is a fungal pathogen that causes invasive disease in immunocompromised individuals. Innate immune cells, including macrophages and neutrophils, are essential for controlling A. fumigatus, but the mechanisms by which specific phagocytes control distinct stages of infection remain incompletely understood. In particular, the contribution of macrophage-derived reactive oxygen species (ROS) to conidial clearance and control of fungal germination and hyphae remains unclear. Here, we used larval zebrafish with mutation of p22, an essential subunit of the phagocyte NADPH oxidase (PHOX) complex, and neutrophil-deficiency, to define the role of macrophage-derived ROS during A. fumigatus infection. Mutation of p22 or pharmacological ROS scavenging increased host susceptibility, supporting a role for ROS in macrophage-mediated defense. However, macrophage ROS restricts fungal developmental progression rather than promoting clearance of conidia. Using {Delta}pksP conidia, we confirmed that fungal melanin limits the localization of p22 to phagosomes, but found no difference in conidial killing of {Delta}pksP conidia, supporting the finding that PHOX-generated ROS are not required for macrophage conidial killing. However, {Delta}pksP conidia have defective virulence only in ROS-producing larvae, as melanin inhibits ROS-mediated control of germination and hyphal growth. These findings identify macrophage PHOX activity as a stage-specific regulator of A. fumigatus infection that primarily restricts fungal developmental progression, while PksP-produced melanin promotes immune evasion by limiting macrophage ROS-dependent antifungal activity. These findings provide insight into how macrophages inhibit the transition from conidia to invasive fungal growth and how A. fumigatus evades this defense, with implications for understanding determinants of disease progression during invasive aspergillosis.