Innate mucosal-associated invariant T (MAIT) cells are activated in inflammatory bowel diseases

Abstract

Inflammatory 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-vitro-activated 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.

Keywords: MHC class I-like; immune system; inflammatory bowel diseases; innate T cells.

© 2014 British Society for Immunology.

Figures

Figure 1

Blood mucosal-associated invariant T (MAIT) cells are less abundant in Crohn's disease (CD) and ulcerative colitis (UC). The proportion of blood MAIT and γδ T cells in CD, UC and healthy donors was analysed by flow cytometry. (a) Total MAIT cells are defined as T cell receptor (TCR)γδ- Vα7.2+CD161hi cells, γδ T cells as CD3+TCRγδ+ cells. One representative example for each group is shown. (b) Percentage of MAIT cells (left panel) or γδ T cells (right panel) [analysed as in (a)] among CD3+ T cells, in healthy donors (n = 46), CD (n = 31) and UC (n = 9) patients. Statistical analysis of mean ± standard error of the mean (s.e.m.). **P < 0·05; ***P < 0·005.

Figure 2

CD8+ mucosal-associated invariant T (MAIT) cells are specifically decreased in blood of inflammatory bowel diseases (IBD) patients. The proportion of CD8+, CD4+ and CD4–CD8– [double-negative (DN)] blood MAIT cells were analysed in IBD versus healthy donors. (a) One representative example per group of the proportion of CD8+, CD4+ and DN cells among CD3+Vα7.2+CD161hi MAIT cells. (b) Percentage of CD8+ (left), CD4+ (middle) and DN (right) MAIT cells among CD3+ T cells in the blood of healthy, Crohn's disease (CD) and ulcerative colitis (UC) patients. Data are analysed from the same set of patients as in Fig. 1. Statistical analysis of mean ± standard error of the mean (s.e.m.). **P < 0·05; *** P < 0·005.

Figure 3

Mucosal-associated invariant T (MAIT) cells accumulation in the inflamed ileon of patients with Crohn's disease (CD). Ileal biopsies of patients with CD were triple-stained with interleukin (IL)-18Rα (green), anti-CD3 (red) and anti-Vα7.2 (magenta) antibodies. This staining strategy allows the identification of CD3+Vα7.2+IL18Rα+ MAIT cells . (a) Representative example of MAIT cells in the inflamed (upper panel) versus healthy ileum (lower panel). The right panel demonstrates triple staining of analysed MAIT cells. (b) Percentage of MAIT cells [analysed as in (a)] among total CD3+ T cells in the inflamed versus healthy ileum of CD patients. The left panel shows the mean ± standard error of the mean (s.e.m.). of the percentage of MAIT cells among T cells in healthy versus injured ileum of 11 CD patients. The right panel shows the paired data obtained for each patient analysed. Analyses were performed with the ×63 objective of a LSM 710 confocal microscope (Zeiss).

Figure 4

Blood mucosal-associated invariant T (MAIT) cells are more proliferative in Crohn's disease (CD) and ulcerative colitis (UC). (a) Representative Ki67 intracellular staining of MAIT cells (analysed as in Fig. 1) among total CD3+, CD8+ or double-negative (DN) T cells from healthy donors, CD and UC patients. (b) Percentage of proliferating (Ki67+) MAIT cells analysed as in (a) in the different groups (controls n = 6, CD n = 6, UC n = 2). Statistical analysis of mean ± standard error of the mean (s.e.m.). **P < 0·05.

Figure 5

Blood mucosal-associated invariant T (MAIT) cells from inflammatory bowel diseases (IBD) patients up-regulate natural killer (NK)G2D and B and T lymphocyte attenuator (BTLA) expression. (a,c) Representative example of NKG2D (a) and BTLA (c) expression by total, CD8+ or double-negative (DN) MAIT cells among healthy donors, Crohn's disease (CD) and ulcerative colitis (UC) patients. The dotted lines represent staining with an isotype-matched control. (b,d) Percentages of NKG2D-positive (b) and BTLA-positive (d) MAIT cells among the different groups (controls n = 23, CD n = 28, UC n = 12). Statistical analysis of mean ± standard error of the mean (s.e.m.). ***P < 0·005.

Figure 6

Altered and distinct pattern of cytokine secretion by blood mucosal-associated invariant T (MAIT) from Crohn's disease (CD) and ulcerative colitis (UC) patients. CD3+Vα7.2+CD161hi blood MAIT cells from healthy donors (n = 5), CD (n = 8) and UC (n = 6) patients were fluorescence activated cell sorted (FACS) with a purity >95%; 105 sorted cells were plated and stimulated for 36 h with phorbol myristate acetate (PMA) and ionomycin. The amount of 13 different cytokines in the cell culture supernatants was quantified by a multiplex bead-based assay. Results for interleukin (IL)-2, tumour necrosis factor (TNF)α, interferon (IFN)-γ, IL-17 and IL-22 are shown. Statistical analysis of mean ± standard error of the mean (s.e.m.). *P < 0·05.