An increased expression of IL-9, IRF4, Smad2, Smad3, IL-17A, IL-6, IL-4, IL-10, IL-13, IL-21, IFN-γ, TGF-β, TNF-α, IRF4, and PU.1 was observed in colonic biopsies of patients with ulcerative colitis (UC), and IL-9 expression was related to the expression of IRF4, Smad2, Smad3, IL-6, IL-13, and IL-17A (79, 80). Here, IL9 is linked to ulcerative colitis.