CLDN2 and inflammatory bowel disease: Taken together, whereas the increase of claudin-2 in pleural inflammation indicates a separate regulatory pathway which has been reported for inflammatory bowel diseases, the general reduction of tightening proteins in inflamed pleura also points at a mechanism reported in a mouse lung inflammation model, which is not even based on an increase of claudin-2, but a universal decrease of tight junction proteins which may less specifically perturb the epithelial barrier.