Objectives: In autoimmune liver diseases, necrotic hepatocytes release IL-33, which activates ST2 receptor-expressing group 2 innate lymphoid cells (ILC2) and regulatory T cells (Tregs). We have previously shown that hepatic ILC2s aggravate liver injury. However, IL-33 pre-treatment ameliorated immune-mediated hepatitis. Further, IL-33-activated ILC2 and Tregs express amphiregulin (AREG). Since AREG is linked with tissue repair and immunosuppression, we now investigated the immunoregulatory role of the IL-33/AREG axis in immune-mediated hepatitis.

Methods: C57BL/6 (WT) and Areg-/- mice received concanavalin A (ConA) to induce acute immune-mediated hepatitis. To study IL-33-mediated immunosuppression mice received IL-33 on three consecutive days before ConA challenge.

Results: In acute liver inflammation, Il33 and Areg expression was elevated in the liver with Areg being the most up-regulated EGFR ligand. More precisely, we found that AREG expression was induced in ILC2 and ST2+ Tregs. IL­?33 pre-treatment prevented acute hepatitis and resulted in strong AREG expression by ILC2 and ST2+ Tregs. Interestingly, IL-33 reinforced the immunosuppressive function of ST2+ Tregs, exhibiting a high potential to protect from immune-mediated hepatitis. Areg-/- mice developed more severe immune-mediated hepatitis, accompanied with stronger activation and IL-13 expression of ILC2 and a reduced frequency of ST2+ Tregs in the liver. In vitro, exogenous AREG suppressed IL-13 expression by hepatic ILC2s, but induced activation, expansion and AREG expression in ST2+ Tregs. We further demonstrated that Tregs from Areg-/- mice were impaired in their ability to suppress activation of CD4+ T cells in vitro.

Conclusion: We here describe an immunoregulatory role of the IL-33/AREG axis in acute immune-mediated hepatitis, in which AREG suppresses the activation of ILC2s while maintaining ST2+ Tregs and reinforcing their immunosuppressive capacity in liver inflammation.