Iron induces Aspergillus proteases in cystic fibrosis allergic bronchopulmonary aspergillosis

RATIONALE: Allergic bronchopulmonary aspergillosis (ABPA) is a hypersensitivity disease triggered by inhaled Aspergillus -fumigatus (Af) spores (i.e., conidia), in persons with cystic fibrosis (CF). High iron levels have been commonly described in CF respiratory secretions. Af proteases cause a severe allergic immune response, leading to pulmonary exacerbations and progressive lung function decline. The stimuli that promote Af proteases in ABPA are poorly understood. OBJECTIVES: Determine if airway iron is a critical factor in CF-ABPA by regulating fungal protease production. METHODS: We used transcriptomics and proteomics to investigate the role of iron in stimulating the production of Af proteases and evaluated the impact of these iron-induced Af proteases on the Th2 immune response in CF bronchial epithelial (CFBE) cells and in a CF-ABPA mouse model. MEASUREMENTS AND MAIN RESULTS: Transcriptional analysis showed a significant upregulation of Af proteases with exposure to iron and a downregulation with iron chelation. This finding was validated in secretome studies showing that Af-culture filtrates (Af-cf) from iron-exposed conidia contained significantly higher levels of 14 proteases compared to controls. Exposure to iron-primed Af-cf increased the production of Th2 promoting cytokines (IL-33, IL-25 and TSLP) in CFBE cells compared to the wild type cells. In vivo, inoculation of CF mice with iron-primed Af conidia led to higher levels of serum IgE and Th2 cytokines (IL-4, IL-5, IL-9, IL-13) in lung tissue. CONCLUSIONS: These findings suggest that airway iron is a potent stimulus for Af proteases and represents a modifiable risk factor and potential therapeutic target for CF-ABPA.