P028 A pathogenic role of activated mucosal-associated invariant T cells in an animal model of Inflammatory Bowel Disease

Background It is known that the mucosal-associated invariant T (MAIT) cells are the innate-like T cells that are restricted by the major histocompatibility complex-related molecule 1 (MR1), and that these cells express a semi-invariant T cell receptor. We have previously reported that the activation status of the circulating MAIT cells in patients with Ulcerative Colitis (UC) is associated with disease activity, and these cells infiltrate the inflamed colonic mucosa. These findings imply that MAIT cells are involved in the pathogenesis of Inflammatory Bowel Disease (IBD). However, the role of MAIT cells in the setting of IBD has not been revealed. Therefore, we investigated the role of MAIT cells in an animal model of UC. Methods To this end, we utilized MR1 deficient mice (MR1-/-), which lack MAIT cells, and isobutyl 6-formyl pterin (i6-FP), which is a synthetic antagonistic MR1 ligand. MR1-/- on the C57BL/6 background, their littermate wild-type controls, and C57BL/6 mice were sensitized by rectal administration of oxazolone to induce colitis. These were then administered an oral i6-FP. Splenocytes (SPL) and colonic lamina propria lymphocytes (LPL) were isolated from mice receiving i6-FP to measure cytokine production. MR1-/-, i6-FP-treated mice and their controls were orally administered FITC-dextran to analyze intestinal permeability. The peripheral blood mononuclear cells (PBMC) from the patients with UC were also isolated to study the effect of i6-FP on cytokine production by MAIT cells. Results MR1 deficiency or i6-FP treatment resulted in reduced severity of oxazolone-induced colitis. Mice treated with i6-FP resulted in reduced MAIT cell production of pro-inflammatory cytokines such as IFN-g and TNF in both SPL and colonic LPL. Similar results were also observed in PBMC isolated from the patients with UC when incubated with i6-FP. Although MR1 deficiency resulted in increased intestinal permeability, i6-FP administration did not affect gut integrity in mice. Conclusion The current studies indicate that MAIT cells have a pathogenic role in colitis and suppressing activation of these cells may reduce the severity of colitis without affecting gut integrity. Thus, MAIT cells may be potential therapeutic targets for IBD including UC.