IL9 and colitis: In both IBD patients and mice with experimental colitis, claudin-8 is downregulated by hyperactivation of IL-23/miR-223 (116) and IL-9/miR21 (117) pathways, causing inflammation-induced intestinal mucosal damage and retardation of mucosal healing, while IL-9/STAT5 pathway activation may also account for bowel epithelial inflammation (118).