The results of in vitro studies using cell culture models have shown that the expression of claudin-2, but not that of the other members of the claudin family, is stimulated by proinflammatory cytokines such as interleukin-6 (IL-6) or interleukin-13 (IL-13) [22,23], both of which are involved in the pathogenesis of IBD [14,22,23,24]. Here, IL13 is linked to inflammatory bowel disease.