Th17 responses in chronic allergic airway inflammation abrogate regulatory T-cell-mediated tolerance and contribute to airway remodeling.

The role of T-helper type 17 (Th17) responses in airway remodeling in asthma is currently unknown. We demonstrate that both parenteral and mucosal allergen sensitization, followed by allergen inhalation, leads to Th17-biased lung immune responses. Unlike Th17 cells generated in vitro, lung Th17 cells did not produce tumor necrosis factor-α or interleukin (IL)-22. Eosinophilia predominated in acute inflammation, while neutrophilia and IL-17 increased in chronic disease. Allergen-induced tolerance involved Foxp3-, Helios-, and glycoprotein-A repetitions predominant-expressing regulatory T cells (Treg) and IL-10/interferon-γ priming. This Treg phenotype was altered in inflamed lungs and abrogated by inhalation of IL-17. Using Th17-deficient mice with genetic disruption of gp130 in T cells, we showed that Th17 cells induce airway remodeling independent of the Th2 response. All-trans retinoic acid administration ameliorated Th17-mediated disease and increased Treg activity, while dexamethasone inhibited eosinophilia but not neutrophilia, and enhanced Th17 development in vitro. Targeting the Th17/Treg axis might therefore be therapeutic in neutrophilic and glucocorticoid-refractory asthma.