P294 - Control of interleukin-17 production in inflammatory bowel disease

Abstract

Loss of an immunological tolerance towards non-pathogenic luminal antigens is a key element in the pathogenesis of inflammatory bowel disease. Regulatory T cells (Tregs) are crucially involved in the induction and maintenance of this tolerance. Mice kept under germ-free conditions fail to induce an immunological tolerance in the gut. Intestinal epithelial cells (IECs) stimulate CD4+ Tregs dependent on MHC II. The corresponding MHC II-related processing of luminal antigens was shown to occur in multivesicular bodies (MVB). We hypothesised that the lack of tolerance induction in germfree mice might rely on defects in the MHC II-associated antigen presentation by IECs. To unravel the basic processes of the immunological homeostasis in the gut, we studied the influence of the bacterial flora on trafficking of luminal antigens into MHC II-enriched compartments responsible for antigen processing and presentation. NMRI mice were kept germ-free or conventionally colonised. Bacteria were specified in feces alliquots using 16S rRNA analysis. The results were correlated with the RDP II data base. The endocytic route of luminally applied ovalbumin (OVA) in IECs and associations with the MHC II pathway were visualised using fluorescenceand electron-microscopy. Colonised mice revealed a physiological murine flora without detection of any pathogen. IECs of the jejunum, ileum and colon lacked expression of MHC II and invariant chain (Ii) in germ-free mice. After colonisation both molecules were expressed in IECs of the jejunum and ileum, but not within the colon. While MHC II was seen within the endocytic pathway and at the basolateral membranes, Ii expression was restricted to the endocytic pathway. The majority of both antigens concentrated in MVB. In germ-free mice luminally applied OVA was only faintly detected within compartments of the endocytic tract after periods of up to two hours. In contrast colonised mice showed a significant increased uptake of OVA throughout the endocytic route (p = 0.001). Of note OVA accumulated within MHC II-enriched MVB in these mice. The bacterial colonisation of the gut seems to be essential for the MHC II-dependent antigen presentation by IECs. The physiological flora is responsible for the constitutive expression of MHC II and related molecules in IECs and a sufficient antigen delivery in processing-relevant compartments. Our data indicate that defects in the MHC II-associated antigen handling in IECs might contribute to the failure of germ-free mice in tolerance induction and support a regulatory function of these cells in the intestinal homeostasis. P294 Control of interleukin-17 production in inflammatory bowel disease L. Rovedatti1 *, A. Di Sabatino1, T. Kudo2, M. Sarra3, D. Rampton4, C.H. Knowles5, N. Sengupta5, G. Monteleone3, G.R. Corazza1, T.T. MacDonald2. 1First Department of Medicine, S. Matteo Hospital, University of Pavia, Pavia, Italy, 2Centre for Infectious Disease, Institute of Cell and Molecular Science, Barts and the London School of Medicine and Dentistry, London, United Kingdom, 3Department of Internal Medicine, University Tor Vergata, Rome, Italy, 4Centre for Gastroenterology, Institute of Cell and Molecular Science, Barts and the London School of Medicine and Dentistry, London, United Kingdom, 5Centre for Academic Surgery, Institute of Cell and Molecular Science, Barts and the London School of Medicine and Dentistry, London, United Kingdom