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 the downregulation of RNS in human primary neutrophils and with clinical Candida isolates, including emerging human pathogens Candida auris and Candida glabrata. Inducible nitric oxide synthase (iNOS; Nos2 in zebrafish), the enzyme responsible for RNS production, competes with the arginase enzyme for a shared substrate, L-arginine. Using a zebrafish arginase2 transgenic line and a C. albicans car1Δ mutant, we showed that both host and fungal arginase contribute to the reduction in neutrophil RNS. Despite pathogen downregulation, upregulation of neutrophil RNS via hypoxia-inducible factor 1α (Hif-1α) stabilization was sufficient to improve host survival following C. albicans infection. Inhibition of Nos2 blocked the host protective effect of Hif-1α stabilization. Finally, restoration of neutrophil RNS via Hif-1α stabilization was additive to 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.IMPORTANCECandida albicans is a fungus that normally lives harmlessly in the human body but can cause life-threatening infections in people with weakened immune systems. A key part of the body's defense against this fungus is neutrophils, immune cells that kill microbes using toxic molecules. However, how Candida avoids neutrophil defense is not well understood. Here, we used zebrafish and human immune cells to show that Candida suppresses an important neutrophil defense, reactive nitrogen species (RNS), during infection. Unlike bacteria, which trigger RNS, Candida reduces these protective molecules to below normal levels, helping its survival. This effect was also observed with other disease-causing Candida species. We went on to show that both the host and Candida contribute to this suppression. Importantly, boosting the neutrophil response improved survival and helped clear infection, especially when combined with standard antifungal drugs. These findings suggest new ways to support the immune system alongside existing treatments.