Type 1 interferon-induced IL-7 maintains CD8 ⁺ T-cell responses and homeostasis by suppressing PD-1 expression in viral hepatitis

Type 1 interferon (IFN-I) promotes antigen-presenting cell maturation and was recently shown to induce hepatic IL-7 production during infection. Herein, we further explored the underlying mechanisms used by IFN-I to orchestrate antiviral immune responses in the liver. Acute viral hepatitis was induced by i.v. injection of adenovirus (Ad) in IFN-α receptor knockout (IFNAR ^-/-) and control mice. To disrupt signaling, monoclonal antibodies (mAbs) against IL-7 receptor alpha (IL-7Rα) or PD-L1 were i.p. injected. We found that CD8 ⁺ T cells in IFNAR ^-/- mice were less effective than those in control mice. The reduced T-cell function was accompanied by increased levels of PD-1 expression, apoptosis and decreased IFN-γ production. The lack of IFN-I signaling also impaired the expression of accessory molecules in both intrahepatic dendritic cell (DCs) and hepatocytes. PD-L1 was comparably and highly expressed on hepatocytes in both IFNAR ^-/- and control mice. Injection of PD-L1-specific mAb in IFNAR ^-/- mice reversed the compromised immune responses in the liver. Further investigation showed that hepatic IL-7 elevation was less pronounced in IFNAR ^-/- mice compared to the controls. A treatment with recombinant IL-7 suppressed PD-1 expression on CD8 ⁺ T cells in vitro. Accordingly, blocking IL-7R signaling in vivo resulted in increased PD-1 expression on CD8 ⁺ T cells in Ad-infected mice. Collectively, the results suggest that IFN-I-induced hepatic IL-7 production maintains antiviral CD8 ⁺ T-cell responses and homeostasis by suppressing PD-1 expression in acute viral hepatitis.