The Role of IFNγ in the Immune Pathogenesis of Primary Sclerosing Cholangitis

Primary sclerosing cholangitis (PSC) is a chronic cholestatic liver disease characterized by inflammation and concentric fibrosis of the hepatic bile ducts. High levels of Interferon-γ (IFNγ) and IFNγ-induced chemokines have been detected in liver tissue and plasma of PSC patients. Aim of this study is to analyze the role of IFNγ-producing or IFNγ-activated cells in the immune pathogenesis of PSC. Therefore, IFNγ was neutralized in multidrug resistance protein 2 knockout (Mdr2 ^-/-) mice, a mouse model that resembles human PSC. Additionally, since T cells are one of the major producers of IFNγ, Mdr2 ^-/- mice were treated with anti-Thy1.2 antibody to deplete CD90.2 cells which are mainly T cells.

Mdr2 ^-/- mice (10 weeks old) were treated with anti-IFNγ or anti-Thy1.2 antibody twice a week for 2 weeks. Histological analysis of H&E stained liver tissue sections allowed the examination of inflammation and fibrosis. The cytotoxic potential of hepatic non-parenchymal cells (NPCs) were analysed via flow cytometry after restimulation with PMA/Ionomycin. Real time RT-PCR was applied to examine the gene expression of targets involved in the IFNγ signaling pathway. In addition to that, a bead-based multiplex assay was used to investigate the cytokine secretion after treatment.

Neutralization of IFNγ in Mdr2 ^-/- mice attenuated fibrotic remodeling indicated by reduced hydroxyproline level and hepatic mRNA expression of ColA1T3. The treatment with anti-IFNγ also resulted in reduced frequencies of IFNγ producing NK cells and CD8 T cells with reduced cytotoxic potential. Flow cytometry data showed a significant increase in the numbers of CD11b myeloid cells and Ly6G granulocytes in anti-IFNγ treated mice compared to the control group. In case of the Ly6G cells this can be explained by absence of IFNγ-mediated suppression of granulocyte recruitment. Depletion of CD90.2 cells with anti-Thy1.2 antibody in Mdr2 ^-/- mice showed a successful reduction of CD4, CD8 T cells and NKT cells. This correlated with the hepatic mRNA expression of IFNγ, which was significantly reduced in anti-Thy1.2 treated mice. Plasma ALT levels were significantly reduced in anti-Thy1.2 treated mice compared to IgG treated mice, indicating reduced tissue damage. Pro-inflammatory cytokines like TNFα, IL-17a and IFNγ were significantly reduced in the anti-Thy1.2 treated mice compared to the control group.

Overall the data suggests, that T cells and NK cells are one of the major producers of IFNγ in Mdr2 ^-/- mice and are involved in the immune pathogenesis of PSC. Further experiments will be performed to further elucidate the role of IFNγ in PSC.