IL9 and asthma: Early studies in patients with mild asthma have shown that CD4+ T cells favour Th2 type immune responses in BALF, lung tissue, and blood, and secrete large amounts of cytokines, such as IL‐4, IL‐5, IL‐13 and IL‐9, while Th1‐type cytokines such as IFN‐γ, IL‐2 and IL‐12 are reduced.22, 23