IL-17F, rather than IL-17A, underlies airway inflammation in a steroid-insensitive toluene diisocyanate-induced asthma model.

Steroid insensitivity constitutes a major problem for asthma management. Toluene diisocyanate (TDI) is one of the leading allergens of asthma that induces both T-helper Th2 and Th17 responses, and is often associated with poor responsiveness to steroid treatment in the clinic. We sought to evaluate the effects of inhaled and systemic steroids on a TDI-induced asthma model and to find how interleukin (IL)-17A and IL-17F function in this model. BALB/c mice were exposed to TDI for generating an asthma model and were treated with inhaled fluticasone propionate, systemic prednisone, anti-IL-17A, anti-IL-17F, recombinant IL-17A or IL-17F. Both fluticasone propionate and prednisone showed no effects on TDI-induced airway hyperresponsiveness (AHR), bronchial neutrophilia and eosinophilia, and epithelial goblet cell metaplasia. TDI-induced Th2 and Th17 signatures were not suppressed by fluticasone propionate or prednisone. Treatment with anti-IL-17A after TDI exposure led to increased AHR, aggravated mucus production and airway eosinophil recruitment, accompanied by amplified Th2 responses, whereas anti-IL-17F ameliorated TDI-induced AHR and airway neutrophilia, with decreased Th17 responses. Recombinant IL-17A and IL-17F showed opposite effects to the monoclonal antibodies. IL-17A and IL-17F exert distinct biological effects during airway inflammation of a TDI-induced asthma model, which is unresponsive to both inhaled and systemic steroids.