Tregs protect against invariant NKT cell-mediated autoimmune colitis and hepatitis

Sensitivity and stability of Balb/c, C57BL/6J, and ICR mice to the acute liver injury induced by concanavalin A

Autoimmune hepatitis (AIH) is an autoimmune disease mediated by abnormal autoimmune. The pathogenesis and pathological manifestation of immune-mediated liver injury, induced by concanavalin A (ConA) in mice, closely parallel those observed in human AIH. However, the sensitivity and stability of mice to ConA vary depending on the strain and sex of the mice. Therefore, this study aimed to compare the sensitivity and stability of Balb/c, C57BL/6J, and ICR mice to ConA-induced acute liver injury. In this study, the mice in ConA group were injected with ConA (15 mg/kg·bw) via tail vein. After 8 h, the blood, liver, and spleen were collected for subsequent analysis. The liver index of Balb/c mice was increased (P < 0.05). Serum alanine aminotransferase (ALT), aspartate aminotransferase (AST), and lactate dehydrogenase (LDH) levels of male C57BL/6J mice in ConA-treated group were the highest among the three strains of mice, followed by female Balb/c mice (P < 0.05). After ConA challenge, ICR, Balb/c, and C57BL/6J mice (both male and female) appeared markedly inflammatory cell infiltration and hepatocyte necrosis. Furthermore, hemorrhagic necrosis is more severe in females than in males. Lastly, male C57BL/6J and female Balb/c mice had the lowest coefficient of variation in serum ALT, AST, and LDH activities, while female Balb/c mice had the minimum coefficient of variation of the liver index, suggesting that they have good stability to ConA. Altogether, our study found that Balb/c female and C57BL/6J male mice have high sensitivity and good stability to ConA challenge, which were suitable for mimicking the pathology of AIH in humans.

Regulatory T-cells: The Face-off of the Immune Balance

Regulatory T-cells (Tregs) play a crucial role in maintaining immune homeostasis, ensuring a balanced immune response. Tregs primarily operate in an antigen-specific fashion, facilitated by their distinct distribution within discrete niches. Tregs have been studied extensively, from their point of origin in the thymus origin to their fate in the periphery or organs. Signals received from antigen-presenting cells (APCs) stimulate Tregs to dampen inflammation. Almost all tumors are characterized by a pathological abundance of immune suppression in their microenvironment. Conversely, the lack thereof proves detrimental to immunological disorders. Achieving a balanced expression of Tregs in relation to other immune compartments is important in establishing an effective and adaptable immune tolerance towards cancer cells and autoantigens. In the context of cancer, it is essential to decrease the frequency of Tregs to overcome tumor suppression. A lower survival rate is associated with the presence of excessive exhausted effector immune cells and an increased frequency of regulatory cells. However, when it comes to treating graft rejection and autoimmune diseases, the focus lies on immune tolerance and the transfer of Tregs. Here, we explore the complex mechanisms that Tregs use in human disease to balance effector immune cells.

The ST2+ Treg/amphiregulin axis protects from immune-mediated hepatitis

Introduction

The alarmin IL-33 has been implicated in the pathology of immune-mediated liver diseases. IL-33 activates regulatory T cells (Tregs) and type 2 innate lymphoid cells (ILC2s) expressing the IL-33 receptor ST2. We have previously shown that endogenous IL-33/ST2 signaling activates ILC2s that aggravate liver injury in murine immune-mediated hepatitis. However, treatment of mice with exogenous IL-33 before induction of hepatitis ameliorated disease severity. Since IL-33 induces expression of amphiregulin (AREG) crucial for Treg function, we investigated the immunoregulatory role of the ST2+ Treg/AREG axis in immune-mediated hepatitis.

Methods

C57BL/6, ST2-deficient (Il1rl1-/-) and Areg-/- mice received concanavalin A to induce immune-mediated hepatitis. Foxp3Cre+ x ST2fl/fl mice were pre-treated with IL-33 before induction of immune-mediated hepatitis. Treg function was assessed by adoptive transfer experiments and suppression assays. The effects of AREG and IL-33 on ST2+ Tregs and ILC2s were investigated in vitro. Immune cell phenotype was analyzed by flow cytometry.

Results and discussion

We identified IL-33-responsive ST2+ Tregs as an effector Treg subset in the murine liver, which was highly activated in immune-mediated hepatitis. Lack of endogenous IL-33 signaling in Il1rl1-/- mice aggravated disease pathology. This was associated with reduced Treg activation. Adoptive transfer of exogenous IL-33-activated ST2+ Tregs before induction of hepatitis suppressed inflammatory T-cell responses and ameliorated disease pathology. We further showed increased expression of AREG by hepatic ST2+ Tregs and ILC2s in immune-mediated hepatitis. Areg-/- mice developed more severe liver injury, which was associated with enhanced ILC2 activation and less ST2+ Tregs in the inflamed liver. Exogenous AREG suppressed ILC2 cytokine expression and enhanced ST2+ Treg activation in vitro. In addition, Tregs from Areg-/- mice were impaired in their capacity to suppress CD4+ T-cell activation in vitro. Moreover, application of exogenous IL-33 before disease induction did not protect Foxp3Cre+ x ST2fl/fl mice lacking ST2+ Tregs from immune-mediated hepatitis. In summary, we describe an immunoregulatory role of the ST2+ Treg/AREG axis in immune-mediated hepatitis, in which AREG suppresses the activation of hepatic ILC2s while maintaining ST2+ Tregs and reinforcing their immunosuppressive capacity in liver inflammation.