TJP1 and colitis: In support of this hypothesis, several authors have reported that colonization of germ-free mice with Bacteroides thetaiotaomicron or Escherichia coli Nissle 1917 (EcN) led to up-regulation of genes that encode for proteins involved in maintaining adhesion between intestinal epithelial cells, such as small proline-rich protein-2 (sprr2a) and zonula occludens-1 (ZO-1), respectively, which for EcN was proved to result in decreased intestinal permeability when colitis mouse model was treated with this bacterium (86, 87).