P064 EBI2 and oxysterols in the development of intestinal lymphoid structures and colitis
Wyss A.*1, Raselli T.1, Schmelczer G.1, Spalinger M.1, Atrott K.1, Frey-Wagner I.1, Sailer A.W.2, Rogler G.1, Misselwitz B.1
1University of Zurich, Zurich, Switzerland 2Novartis Institutes for BioMedical Research, Basel, Switzerland
Immunological mechanisms leading to gut inflammation in inflammatory bowel diseases remain insufficiently understood. The colon comprises two types of lymphoid structures, colonic patches (CLP) and solitary intestinal lymphoid tissues (SILT). The formation of gut lymphoid structures includes the interaction between a variety of chemotactic factors and their ligands. Epstein Barr virus induced gene 2 (EBI2) is a G-protein coupled receptor expressed on immune cells. The EBI2 ligand 7α,25-Dihydroxycholesterol is produced by two enzymes, CH25H and CYP7B1. EBI2 and its oxysterol ligand were shown to mediate migration, positioning and differentiation of B cells within secondary lymphoid organs. SILTs and EBI2 have not been implicated in the pathogenesis of colitis.
Using a whole mount approach the colons of EBI2–/– mice and wildtype littermates were stained to determine the number of B cell follicles. DSS colitis was induced by administration of 2–3% dextran sodium sulfate (DSS) for 7 days or 4 cycles of 7 days interspersed with 10 day recovery periods. To study the effect of EBI2 in the IL10 colitis model, EBI2–/– and IL10–/– mice were crossbred and examined after 200 days. T cell transfer colitis was induced by transfer of naïve T cells from wildtype or EBI2–/– mice to immunodeficient RAG2–/– mice.
EBI2–/– mice showed significantly less B cell follicles within the colon than littermate wildtype controls. The difference was restricted to smaller lymphoid structures, pointing to an anomaly in SILT development. Despite the defective colonic lymphoid tissue, loss of EBI2 did not affect the severity of acute or chronic DSS colitis. However, EBI2–/– mice did not show an increase in the number of lymphoid structures upon chronic inflammation, which we observed in wildtype controls. In acute and chronic DSS colitis, mRNA levels of CH25H and CYP7B1 were upregulated in the colon. A similar upregulation was found in rectal biopsies of ulcerative colitis patients, suggesting increased oxysterol production upon inflammation. Lack of EBI2 in IL10–/– mice leads to a later onset and a less severe colitis. Furthermore, transfer of T cells lacking EBI2 leads to a lower grade of inflammation in the transfer colitis model.
We could show that EBI2 is involved in the development of intestinal lymphoid tissue during homeostasis and after immunological challenge. Oxysterol production is likely increased in the inflamed gut and knockout of their receptor EBI2 affected the severity of colitis in experimental mouse models. These findings establish a role for EBI2 and oxysterols in the maturation of the gut immune system and in the pathophysiology of inflammatory bowel diseases.