MAIT cells ameliorate liver fibrosis by enhancing the cytotoxicity of NK cells in cholestatic murine models

Abstract Background and aims Mucosal‐associated invariant T (MAIT) cells are innate‐like lymphocytes that display a critical role in various liver diseases. However, the role of MAIT cells in cholestatic liver fibrogenesis remains obscure. Our study aims to assess the contribution of MAIT cells and underlying mechanisms during this process. Methods Cholestatic murine models using MAIT cell‐deficient (MR1 − / − ) and wild‐type (WT) mice were established by feeding a 0.1% 3,5‐diethoxycarbonyl‐1,4‐dihydrocollidine (DDC)‐enriched diet or bile duct ligation (BDL). Liver samples were collected to determine the severity of fibrosis. Lymphocytes of the liver were isolated for analysing the phenotype and function of MAIT cells. Cell co‐culture experiments were performed to investigate the cross‐talk between MAIT and NK cells. Results Liver MAIT cells were more activated with increased cytokines in cholestatic mice models than in control mice, although their frequency was decreased. MAIT cell deficiency led to severe liver inflammation and fibrosis with more activated HSCs in cholestatic mice. In addition, MR1 − / − mice had an increased frequency of NK cells with higher expression of stimulatory receptors relative to WT mice. Paradoxically, activated MAIT cells significantly promoted the anti‐fibrotic ability of NK cells by enhancing their cytotoxicity against HSCs in co‐culture experiments. Importantly, this effect depended on direct cell–cell contact and TNF‐α produced by MAIT cells. Conclusion Our findings indicate that MAIT cells ameliorate cholestatic liver fibrosis by enhancing the cytotoxicity of NK cells against HSCs. An in‐depth understanding of the MAIT cell‐mediated regulatory effect will provide more valuable immunotherapy strategies to treat liver fibrosis.