Increased Expression of Interleukin-36, a Member of the Interleukin-1 Cytokine Family, in Inflammatory Bowel Disease

Background:Interleukin (IL)-36 (IL-36, IL-36, and IL-36) is a recently reported member of the IL-1 cytokine family. In this study, we investigated IL-36 expression in the inflamed mucosa of patients with inflammatory bowel disease and characterized the proinflammatory actions of IL-36 cytokines in human colonic epithelial cells.Methods:IL-36 mRNA expression was evaluated using real-time PCR. IL-36 protein expression was analyzed using immunoblotting and immunohistochemical technique. Intracellular signaling pathways were evaluated by immunoblotting and by specific siRNA-transfected cells.Results:The mRNA expression of IL-36 and IL-36, but not of IL-36, was enhanced in the inflamed mucosa of patients with inflammatory bowel disease, in particular, in ulcerative colitis. Immunohistochemical analysis showed that T cells, monocytes, and plasma cells are the source of IL-36 and IL-36 in colonic mucosa. DNA microarray analysis indicated that IL-36 induces the mRNA expression of CXC chemokines and acute phase proteins in intestinal epithelial cell line, HT-29 cells. IL-36 and IL-36 dose-dependently and time-dependently induced the mRNA and protein expression of CXC chemokines (CXCL1, CXCL2, CXCL3 etc.) in HT-29 and Widr cells. Stimulation with IL-36 and IL-36 assembled MyD88 adaptor proteins (MyD88, TRAF6, IRAK1, and TAK1) into a complex and induced the activation of NF-B and AP-1 and also the phosphorylation of MAPKs. MAPK inhibitors and siRNAs specific for NF-B and c-Jun AP-1 significantly reduced IL-36-induced CXC chemokine expression.Conclusions:IL-36 and IL-36 may play a proinflammatory role in the pathophysiology of inflammatory bowel disease through induction of CXC chemokines and acute phase proteins.