The role of the IL23/IL17 pathway in inflammatory bowel disease

Abstract

The aetiology of IBD is unknown, but available evidence suggests that an aberrant immune response towards the commensal microbial flora is responsible for intestinal inflammation in genetically susceptible individuals. Studies from animal models of intestinal inflammation have greatly advanced our understanding of the immunological basis of IBD. However, translation of results from animal research into human studies is essential in order to improve treatment options and patient quality of life. In this thesis we present the successful introduction of translational studies on human tissue in our laboratory. In particular, we evaluated the role of the IL23/IL17 pathway in the human immune response and its role in IBD. IL23-driven inflammation has been primarily linked to its activity on Th-17 cells; however, work from our laboratory has identified a novel population of IL23-responsive ILC, which are responsible for innate colitis in mice. Here we have analyzed the role of IL23-responsive innate cells in IBD. Our results show increased expression of Th-17 signature genes amongst intestinal CD3- cells in patients with IBD. Furthermore, we observed a marked and selective increase in IL17 producing CD56- ILC in the inflamed intestine of patients with CD. ILC may contribute to intestinal inflammation through secretion of cytokines, such as IL17A and IL17F, and recruitment of other inflammatory cells, representing a novel tissue-specific target for the treatment of IBD. In addition, we present here our preliminary data on the characterization of human intestinal and systemic DC populations. In particular, we aimed to evaluate if in the context of the intestinal microenvironment DC develop specific regulatory features, as observed in murine CD103+ DC. We show that human intestinal DC populations exhibit specific regulatory properties, such as expression of genes associated with TGF-β and RA activity. Furthermore, CD103+ DC are present in the human gut and are characterized by tolerogenic markers. Remarkably, patients with IBD have reduced frequencies of intestinal CD103+ DC, which display a more pro-inflammatory phenotype. Alteration in DC subset composition and functional activity may result in a distort balance between immune effector and regulatory responses, promoting the development of intestinal inflammation.EThOS - Electronic Theses Online ServiceGBUnited Kingdo