Neutrophil phagocyte oxidase activity controls invasive fungal growth and inflammation in zebrafish

Abstract

Neutrophils are primary cells of the innate immune system that generate reactive oxygen species (ROS) and mediate host defense. Deficient phagocyte NADPH oxidase (PHOX) function leads to chronic granulomatous disease (CGD) that is characterized by invasive infections including those by the generally non-pathogenic fungus Aspergillus nidulans. The role of neutrophil ROS in this specific host-pathogen interaction remains unclear. Here, we exploit the optical transparency of zebrafish to image the effects of neutrophil ROS on invasive fungal growth and neutrophil behavior in response to Aspergillus nidulans. In a wild-type host, A. nidulans germinates rapidly and elicits a robust inflammatory response with efficient fungal clearance. PHOX-deficient larvae have increased susceptibility to invasive A. nidulans infection despite robust neutrophil infiltration. Expression of p22phox specifically in neutrophils does not affect fungal germination but instead limits the area of fungal growth and excessive neutrophil inflammation and is sufficient to restore host survival in p22phox-deficient larvae. These findings suggest that neutrophil ROS limits invasive fungal growth and has immunomodulatory activities that contribute to the specific susceptibility of PHOX-deficient hosts to invasive A. nidulans infection.

Functional Characterization of Clinical Isolates of the Opportunistic Fungal Pathogen Aspergillus nidulans

“…having investigated the genetic and metabolic features of A. nidulans clinical strains, isolated from CGD and non-CGD patients, in the context of stress responses encountered during human host infection as well as during interactions with host immune responses (18)(19)(20)(21).…”

Functional characterization of clinical isolates of the opportunistic fungal pathogenAspergillus nidulans

“…Furthermore, the immune system of each animal was manipulated in order to give rise to either immunocompetent, CGD or neutropenic/neutrophilic models. As with patients, CGD models of both mice (19) and zebrafish (21) are very susceptible to A. nidulans infections. In both immunocompetent- and CGD-type zebrafish and mice, no difference in virulence between the A. nidulans clinical isolates and the reference strain was observed (Fig.…”

“…Infection with A. nidulans is prevalent in patients with chronic granulomatous disease (CGD) and isolates have mainly been characterized in the context of this disorder (14, 15). Studies on A. nidulans virulence have been carried out in CGD models (animal and cell culture) and virulence characteristics have been compared to the primary human opportunistic fungus A. fumigatus (20,21,45,46). A. fumigatus infection biology and characterization of strains that were isolated from immunocompromised patients with different conditions have received considerable attention in recent years (24,37,47), whereas similar studies into other pathogenic Aspergillus spp.…”

“…We evaluated strain virulence in an established zebrafish-aspergillosis model (72 Wild-type larvae were used as an immunocompetent model. Larvae with a dominant negative Rac2D57N mutation in neutrophils (mpx:rac2D57N) (Rosowski et al, 2017) were used as a model of leukocyte adhesion deficiency, where neutrophils do not reach the site of infection, and p22 phox _deficient larvae (p22 phox (sa11798 ) were used as a CGD model (21).…”

“…Hence, A. nidulans infections have been studied mainly in the context of CGD although this fungal species can also be virulent in non-CGD, immunocompromised patients (18). In comparison to A. fumigatus, investigations into A. nidulans isolate virulence have been neglected with very few studies having investigated the genetic and metabolic features of A. nidulans clinical strains, isolated from CGD and non-CGD patients, in the context of stress responses encountered during human host infection as well as when interacting with host immune responses (18–21).…”