Interferon-γ-dependent immune responses contribute to the pathogenesis of sclerosing cholangitis in mice

Abstract

Background and aims: Primary sclerosing cholangitis (PSC) is an idiopathic, chronic cholestatic liver disorder characterized by biliary inflammation and fibrosis. Increased numbers of intrahepatic interferon-γ- (IFNγ) producing lymphocytes have been documented in patients with PSC, yet their functional role remains to be determined.

Methods: Liver tissue samples were collected from patients with PSC. The contribution of lymphocytes to liver pathology was assessed in Mdr2^-/- x Rag1^-/- mice, which lack T and B cells, and following depletion of CD90.2⁺ or natural killer (NK)p46⁺ cells in Mdr2^-/- mice. Liver pathology was also determined in Mdr2^-/- x Ifng^-/- mice and following anti-IFNγ antibody treatment of Mdr2^-/- mice. Immune cell composition was analysed by multi-colour flow cytometry. Liver injury and fibrosis were determined by standard assays.

Results: Patients with PSC showed increased IFNγ serum levels and elevated numbers of hepatic CD56^bright NK cells. In Mdr2^-/- mice, hepatic CD8⁺ T cells and NK cells were the primary source of IFNγ. Depletion of CD90.2⁺ cells reduced hepatic Ifng expression, NK cell cytotoxicity and liver injury similar to Mdr2^-/- x Rag1^-/- mice. Depletion of NK cells resulted in reduced CD8⁺ T cell cytotoxicity and liver fibrosis. The complete absence of IFNγ in Mdr2^-/-x Ifng^-/- mice reduced NK cell and CD8⁺ T cell frequencies expressing the cytotoxic effector molecules granzyme B and TRAIL and prevented liver fibrosis. The antifibrotic effect of IFNγ was also observed upon antibody-dependent neutralisation in Mdr2^-/- mice.

Conclusion: IFNγ changed the phenotype of hepatic CD8⁺ T cells and NK cells towards increased cytotoxicity and its absence attenuated liver fibrosis in chronic sclerosing cholangitis. Therefore, unravelling the immunopathogenesis of PSC with a particular focus on IFNγ might help to develop novel treatment options.

Lay summary: Primary sclerosing cholangitis (PSC) is a chronic cholestatic liver disease characterized by biliary inflammation and fibrosis, whose current medical treatment is hardly effective. We observed an increased interferon (IFN)-γ response in patients with PSC and in a mouse model of sclerosing cholangitis. IFNγ changed the phenotype of hepatic CD8⁺ T lymphocytes and NK cells towards increased cytotoxicity, and its absence decreased liver cell death, reduced frequencies of inflammatory macrophages in the liver and attenuated liver fibrosis. Therefore, IFNγ-dependent immune responses may disclose checkpoints for future therapeutic intervention strategies in sclerosing cholangitis.

Keywords: Fibrosis; Lymphocyte cytotoxicity; Mdr2 knockout; NK cells; Natural killer; PSC; Primary sclerosing cholangitis; TRAIL.