Advanced label-free optical technologies such as multiphoton microscopy and Raman spectroscopy hold great potential for a characterization of mucosal inflammation in vivo. Using these approaches, we will evaluate optical properties of epithelial barrier function and dysfunction as well as consequences of epithelial barrier defects including immune cell infiltration and bacterial translocation in preclinical colitis models ex vivo and in vivo. Based on these studies, project C01 will further develop advanced optical technologies for the in vivo evaluation of mucosal inflammation in human IBD.