IL17A and asthma: Transforming growth factor β (TGF-β), mainly responsible for bronchial hyperreactivity and the structural changes of the bronchial wall in asthma and other various conditions, is produced by the activated Treg cells, and Treg cells also promote Th17 cells differentiation via TGF-β, and transfer of Treg cells enhanced Th17 cells (IL-17) production is associated with the systemic autoimmune disease in the animal model [9].