Intestinal barrier dysfunction is linked to human IBD and contributes to progression of experimental, immune-mediated colitis. Claudin family tight junction proteins are critical determinants of epithelial paracellular permeability and barrier function. Expression of one of these, claudin-2, a pore-forming claudin, is specifically upregulated in IBD. We have shown that claudin-2 overexpression or, conversely, channel inhibition, augment or attenuate, respectively, immune-mediated colitis severity.