IL13 and colitis: Elevated secretion of IL-13 is tightly associated with the expression of TL1A in the transgenic mouse model described above [19, 20], and the fourth European Crohn's and Colitis Organisation (ECCO) guidelines state that the TGF-β1/Smad3 pathway activated by IL-13 is a central process in the formation of intestinal fibrosis [21].