Dysbiosis of the intestinal fungal microbiota increases lung resident group 2 innate lymphoid cells and is associated with enhanced asthma severity in mice and humans

BACKGROUND: The gut-lung axis is the concept that alterations of gut microbiota communities can influence immune function in the lungs. While studies have explored the relationship between intestinal bacterial dysbiosis and asthma development, less is understood about the impact of commensal intestinal fungi on asthma severity and control and underlying mechanisms by which this occurs. METHODS: Wild-type mice were treated with Cefoperazone to deplete gut bacteria and administered Candida albicans or water through gavage. Mice were then sensitized to house dust mite (HDM) and their lungs were analyzed for changes in immune response. Humans with asthma were recruited and stool samples were analyzed for Candida abundance and associations with asthma severity and control. RESULTS: Mice with intestinal Candida dysbiosis had enhanced Th2 response after airway sensitization with HDM, manifesting with greater total white cell and eosinophil counts in the airway, and total IgE concentrations in the serum. Group 2 innate lymphoid cells (ILC2) were more abundant in the lungs of mice with Candida gut dysbiosis, even when not sensitized to HDM, suggesting that ILC2 may be important mediators of the enhanced Th2 response. These effects occurred with no detectable increased Candida in the lung by culture or rtPCR suggesting gut-lung axis interactions were responsible. In humans with asthma, enhanced intestinal Candida burden was associated with the risk of severe asthma exacerbation in the past year, independent of systemic antibiotic and glucocorticoid use. CONCLUSIONS: Candida gut dysbiosis may worsen asthma control and enhance allergic airway inflammation, potentially mediated by ILC2. Further studies are necessary to examine whether microbial dysbiosis can drive difficult-to-control asthma in humans and to better understand the underlying mechanisms.