Hepatitis C Virus Attenuates Interferon-Induced Major Histocompatibility Complex Class I Expression and Decreases CD8+ T Cell Effector Functions.

Background & Aims: Major histocompatibility complex (MHC) class I−restricted CD8⁺ T cells are required for clearance of hepatitis C virus (HCV) infection. MHC class I expression is up-regulated by type I and II interferons (IFNs). However, little is known about the effects of HCV infection on IFN-induced expression of MHC class I. Methods: We used the HCV cell culture system (HCVcc) with the genotype 2a Japanese fulminant hepatitis-1 strain to investigate IFN-induced expression of MHC class I and its regulatory mechanisms. HCVcc-infected Huh-7.5 cells were analyzed by flow cytometry, metabolic labeling, immunoprecipitation, and immunoblotting analyses. Protein kinase R (PKR) was knocked down with lentiviruses that express small hairpin RNAs. The functional effects of MHC class I regulation by HCV were demonstrated in co-culture studies, using HCV-specific CD8⁺ T cells. Results: Although the baseline level of MHC class I was not affected by HCV infection, IFN-induced expression of MHC class I was notably attenuated in HCV-infected cells. This was associated with replicating HCV RNA, not with viral protein. HCV infection reduced IFN-induced synthesis of MHC class I protein and induced phosphorylation of PKR and eIF2α. IFN-induced MHC class I expression was restored by small hairpin RNA-mediated knockdown of PKR in HCV-infected cells. Co-culture of HCV-specific CD8⁺ T cells and HCV-infected cells that expressed HLA-A2 demonstrated that HCV infection reduced the effector functions of HCV-specific CD8⁺ T cells; these functions were restored by small hairpin RNA-mediated knockdown of PKR. Conclusions: IFN-induced expression of MHC class I is attenuated in HCV-infected cells by activation of PKR, which reduces the effector functions of HCV-specific CD8⁺ T cells. This appears to be an important mechanism by which HCV circumvents antiviral adaptive immune responses. [Copyright &y& Elsevier]