CLDN2 and inflammatory bowel disease: The pro-inflammatory cytokines IFN-γ, IL-6 and TNF- α were shown to be involved in the pathogenesis of inflammatory bowel disease [46,47,48], and the pro-inflammatory cytokine TNF-α also induces the up-regulation of the tight junction protein Claudin-2, which has been shown to contribute to the intestinal epithelial barrier dysfunction in inflammatory bowel disease [45,49].