Candida spp. suppress neutrophil reactive nitrogen species to evade killing

Candida albicans is a human commensal that can cause life-threatening invasive infection in immunocompromised individuals. Human immunity to C. albicans infection is thought to be largely dependent on neutrophil reactive oxygen and nitrogen species (ROS/RNS) generation by neutrophils. Despite this, our understanding of innate immune killing and escape by C. albicans is primarily studied in macrophages and the precise mechanisms of evasion are unclear in neutrophils. Here we sought to determine the importance of neutrophil reactive nitrogen species (RNS) production during C. albicans infection in vivo. Using a zebrafish model, we found that C. albicans rapidly downregulated neutrophil RNS below basal levels during the first day post infection, a time at which neutrophil RNS is upregulated in bacterial infections as an important host-defense mechanism, indicating fungal evasion of host neutrophils. We confirmed downregulation of RNS in human primary neutrophils and with clinical Candida spp. isolates, including emerging human pathogens C. auris and C. glabrata. Using a zebrafish arginase 2 transgenic line and a C. albicans car1Δ mutant, we show that both host and fungal arginase contribute the reduction in neutrophil RNS. Despite pathogen downregulation, upregulation of neutrophil RNS via Hypoxia inducible factor (Hif)-1α stabilisation, was sufficient to improve C. albicans infection survival, dependent on the presence of neutrophils and Nitric oxide synthase 2 (Nos2). Finally, restoration of neutrophil RNS, via Hif-1α stabilisation, was synergistic with clinically relevant antifungal treatment, increasing survival and clearance of C. albicans infections. Together, these data demonstrate that restoration of the neutrophil RNS response in C. albicans infection improves infection outcomes, highlighting the potential of targeting Hif-1α and RNS in host directed therapies against fungal infections.