SummaryInflammatory bowel diseases are characterized by a deregulated immune response targeting the gut bacterial flora. Mucosal-associated invariant T (MAIT) cells are major histocompatibility complex (MHC) class Ib-restricted innate-like lymphocytes with anti-bacterial functions. They display an effector/memory phenotype and are found in large numbers in the blood, mucosae and liver. They have also been implicated in inflammatory diseases such as multiple sclerosis. Therefore, we aimed to analyse the possible involvement of MAIT cells in Crohn's disease (CD) and ulcerative colitis (UC). To this end, a phenotypical and functional analysis of MAIT cells isolated from the blood of healthy subjects, CD and UC patients was undertaken. MAIT cells were also quantified in ileal biopsies of CD patients. The frequency of blood MAIT cells was specifically reduced in IBD patients compared with healthy donors, whereas it was dramatically greater in the inflamed versus healthy tissue. MAIT cells were activated as they expressed significantly more the Ki67 antigen, and this was accompanied by phenotypical changes such as increased expression of natural killer (NK)G2D and B and T lymphocyte attenuator (BTLA). Finally, in-vitroactivated MAIT cells from CD and UC patients secreted significantly more interleukin (IL)-17, together with a decreased interferon (IFN)-γ in CD but an increased IL-22 in UC. These data show that MAIT cells are activated in IBD, which results in an increased recruitment towards the inflamed tissues, an altered phenotype and a switch in the pattern of cytokine secretion. This is the first demonstration that MAIT cells are immune players in IBD, whose precise functions in this context need to be addressed.

SUMMARY BackgroundRecently, a new enteropathy has been described: olmesartan-associated enteropathy. However, the association has been questioned: a phase 3 trial and a cohort study found no association between gastrointestinal events and olmesartan.

In this population-based study, CD and UC incidences increased dramatically in adolescents across a 24-year span, suggesting that one or more strong environmental factors may predispose this population to IBD.

Extraintestinal manifestations occurred at lower frequency in elderly-onset compared with pediatric-onset patients. In both age populations, presence of EIM at diagnosis independently increased the need for corticosteroid and immunosuppressive treatment.

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