The gut mucosa is constantly exposed to a huge burden of dietary antigens, diverse microorganisms and external compounds. Its ability to act as a barrier against the passage of potentially harmful molecules is therefore critical for normal homeostasis. Numerous studies have been shown that the barrier function of IBD patients is severely impaired. Yet, it remains unknown whether this dysfunction (‘leaky gut’) is a primary event in IBD or rather the consequence of ongoing mucosal inflammation. In our lab, we will use both in vivo (patients and family members), ex vivo (intestinal biopsies) and in vitro (intestinal cells) techniques to approach the intestinal barrier from different perspectives. Also the influence of genetic factors on intestinal permeability will be evaluated. This research will provide new insights in the pathophysiology of IBD, ultimately advancing the development of (diagnostic) markers and new therapeutic perspectives for IBD patients (e.g. barrier-restoring agents).