Hepatitis C: virus, host, disease

Hepatic NK cell-mediated hypersensitivity to ConA-induced liver injury in mouse liver expressing hepatitis C virus polyprotein

The role of hepatic NK cells in the pathogenesis of HCV-associated hepatic failure is incompletely understood. In this study, we investigated the effect of HCV on ConA-induced immunological hepatic injury and the influence of HCV on hepatic NK cell activation in the liver after ConA administration. An immunocompetent HCV mouse model that encodes the entire viral polyprotein in a liver-specific manner based on hydrodynamic injection and φC31o integrase was used to study the role of hepatic NK cells. Interestingly, the frequency of hepatic NK cells was reduced in HCV mice, whereas the levels of other intrahepatic lymphocytes remained unaltered. Next, we investigated whether the reduction in NK cells within HCV mouse livers might elicit an effect on immune-mediated liver injury. HCV mice were subjected to acute liver injury models upon ConA administration. We observed that HCV mice developed more severe ConA-induced immune-mediated hepatitis, which was dependent on the accumulated intrahepatic NK cells. Our results indicated that after the administration of ConA, NK cells not only mediated liver injury through the production of immunoregulatory cytokines (IFN-γ, TNF-α and perforin) with direct antiviral activity, but they also killed target cells directly through the TRAIL/DR5 and NKG2D/NKG2D ligand signaling pathway in HCV mice. Our findings suggest a critical role for NK cells in oversensitive liver injury during chronic HCV infection.

Activation of Vgamma9Vdelta2 T cells by non-peptidic antigens induces the inhibition of subgenomic HCV replication

Hepatitis C virus (HCV) has evolved complex strategies to evade host immune responses and establish chronic infection. Since human Vγ9Vδ2 T lymphocytes play a critical role in the immune response against viruses, we analyzed their antiviral functions on Huh7 hepatoma cells carrying the subgenomic HCV replicon (Rep60 cells). In a transwell culture system, Rep60 cells were co-cultured with either PBMCs or highly purified γδ T cells stimulated by non-peptidic antigens. Vγ9Vδ2 T cell activation was associated with a dramatic reduction of HCV RNA levels. Neutralizing antibodies targeting IFN-γ revealed a critical role for this cytokine in the inhibition of HCV replication. Interestingly, drugs already in clinical use, such as Phosphostim and Zoledronate, known to activate γδ T cells, were shown to induce the inhibition of HCV replication mediated by Vγ9Vδ2 T cells of HCV patients. Our data suggest that the therapeutic activation of Vγ9Vδ2 T lymphocytes may represent an additional strategy to inhibit HCV replication and to restore a T_h1-oriented immune response in HCV-infected patients.