Oxidative Stress Responses to the Fungal Allergen Alternaria Mediate IL-33 Secretion By Airway Epithelial Cells and Type 2 Immunity in the Airways

Rationale: While IL-33 likely plays a key role in type 2 immune responses in the airways, our knowledge of the mechanisms involved in production and secretion of IL-33 is limited.  Oxidative stress regulates  many biological and pathological conditions. The goal of this project was to investigate the role of oxidative stress in IL-33 secretion and type 2 immune responses induced by the common environmental allergen Alternaria.

Methods: Normal human bronchial epithelial (NHBE) cells were cultured with Alternaria extract. Naïve Balb/c mice were intranasally exposed to Alternaria extract once or several times.  Pharmacologic inhibitors and gene knockout mice were used to dissect the mechanisms.

Results: Exposure of NHBE cells to Alternaria induced production of reactive oxygen species (ROS) within 15 minutes and extracellular secretion of IL-33 within 60 minutes.  ROS scavengers, such as reduced glutathione (GSH) and N-acetyl-cysteine (NAC), inhibited IL-33 secretion.  When naïve mice were exposed intranasally to Alternaria, they produced type 2 cytokines (e.g. IL-33, IL-5, IL-13) followed by development of eosinophilic inflammation.  These pathological changes were prevented by administering ROS scavengers or pretreating animals with the antioxidant bardoxolone methyl (CDDO-Me).  Finally, mice deficient in Nrf2 (a key transcription factor regulating expression of anti-oxidant molecules) showed enhanced eosinophilic airway inflammation when exposed to Alternaria.

Conclusions: Oxidative stress plays important roles in regulating secretion of IL-33 by airway epithelial cells and in mediating eosinophilic airway inflammation induced by exposure to allergens.  The potential roles for antioxidants in the treatment of asthma and allergic airway diseases need to be carefully re-evaluated.