Hepatitis C virus non-structural 3/4A protein interferes with intrahepatic interferon-γ production

Background The non-structural (NS) 3/4A protease/helicase of the hepatitis C virus is known to modulate signalling pathways in the infected hepatocyte by cleaving CARD adaptor inducing IFN beta (Cardif), T-cell protein tyrosine phosphatase (TC-PTP) and TIR domain-containing adaptor inducing IFN beta (TRIF), but the effects of NS3/4A in vivo still remain unclear. Aim To investigate the influence of NS3/4A on intracellular and intercellular signalling in vivo by analysing the intrahepatic inflammatory response of naive, lipopolysaccharide (LPS)/D-galactosamine (D-galN) or tumour necrosis factor-alpha (TNF alpha)/D-galN-treated NS3/4A-transgenic (Tg) mice. Methods The intrahepatic immunity of naive and LPS/D-galN-or TNF alpha/D-galN-treated NS3/4A-Tg mice was determined using western blot, ELISA, real-time PCR, flow cytometry and survival monitoring. The injection of cytokines or antibodies against signalling components was performed to analyse the relevance of the respective pathways for the investigated issues. A Tg mouse lineage expressing an inactivated NS3/4A protease (NS3/4A(Ile1073Ala)-Tgs) was generated to examine if protective effects were NS3/4A protease dependent. Results The activation of hepatic signal transducer and activator of transcription 1 and 2 was impaired in NS3/4A-Tg mice after treatment with LPS/D-galN or TNF alpha/D-galN. This was paralleled by a reduction in hepatic interferon-g (IFN gamma). Reconstitution of IFN gamma reverted the resistance to LPS/TNF alpha in NS3/4A-Tg mice. Subsequently, blocking IFNg in vivo rendered wild-type mice resistant against treatment with LPS/TNF alpha. A new Tg mouse expressing an inactivated NS3/4A protease had the same phenotype as wild-type mice with respect to hepatic IFN gamma levels and sensitivity to LPS/D-galN. Finally, the chemokine profile was altered in the NS3/4A-Tg mice towards an anti-inflammatory state, which helps to explain the altered immune cell subsets and reduction in hepatic IFN gamma production. Conclusions Our data demonstrate that the NS3/4A protease reduces the intrahepatic production of IFN Omega and alters TNF alpha-mediated effects, thereby impairing the hepatic inflammatory response. This may contribute to viral persistence.