IL17A and inflammatory bowel disease: In particular, TNF-α plays a critical role in inflammatory bowel disease, where it can synergize with IFN-γ to regulate multiple tight-junction (TJ) proteins, including myosin light chain kinase, occludin, and ZO-1, as well as claudin-1 and claudin-2 (106, –, 109), which are also regulated by IL-17.