Reduced Numbers and Proapoptotic Features of Mucosal-associated Invariant T Cells as a Characteristic Finding in Patients with Inflammatory Bowel Disease

BACKGROUND Mucosal-associated invariant T (MAIT) cells are innate-like T cells involved in the homeostasis of mucosal immunity; however, their role in inflammatory bowel disease (IBD) is unclear. METHODS Flow cytometry was used to enumerate peripheral blood MAIT cells in 88 patients with ulcerative colitis (UC), 68 with Crohn's disease (CD), and in 57 healthy controls. Immunohistochemistry identified MAIT cells in intestinal tissue samples from patients with UC (n = 5) and CD (n = 10), and in control colon (n = 5) and small intestine (n = 9) samples. In addition, expression of activated caspases by MAIT cells in the peripheral blood of 14 patients with UC and 15 patients with CD, and 16 healthy controls was examined. RESULTS Peripheral blood analysis revealed that patients with IBD had significantly fewer MAIT cells than healthy controls (P < 0.0001). The number of MAIT cells in the inflamed intestinal mucosae of patients with UC and CD was also lower than that in control mucosae (P = 0.0079 and 0.041, respectively). The number of activated caspase-expressing MAIT cells in the peripheral blood of patients with UC and CD was higher than that in healthy controls (P = 0.0061 and 0.0075, respectively), suggesting that the reduced MAIT cell numbers in IBD are associated with an increased level of apoptosis among these cells. CONCLUSIONS The number of MAIT cells in the peripheral blood and inflamed mucosae of patients with UC and CD was lower than that in non-IBD controls. Also, MAIT cells from patients with IBD exhibited proapoptotic features. These data suggest the pathological involvement and the potential for therapeutic manipulation of these cells in patients with IBD.