Regulation of interferon-induced major histocompatibility complex class i expression by hepatitis C virus

Abstract

Hepatitis C virus (HCV) is a positive-sense, single-stranded RNA virus that is characterized by hepatotropism. A diverse range of cytokines are produced in response to HCV infection, and they induce amplification or transition of further immune responses. Virus-specific cytotoxic T cell responses are vital for the successful clearance of HCV infection. Major histocompatibility complex (MHC) class I is a key molecule for the recognition of virus-infected cells by cytotoxic T cells, and its expression is increased by type I or type II interferons (IFNs). In order to escape the virus-specific cytotoxic T cell responses, viruses have developed specialized mechanisms that subvert the antigen processing and presentation machinery. Yet, the effect of HCV infection on the expression of MHC class I is not well understood. Recently, an in vitro cell culture system for HCV (HCVcc) infection has been developed using the HCV genotype 2a JFH-1 strain. This system mimics the complete viral life cycle, thus providing an opportunity to address many aspects of the HCV life cycle and host-virus interactions, including its effect on MHC class I expression, in a more physiological condition. The production and infection of HCVcc in vitro each require quantification of infectious HCV virions. For this purpose, a focus-forming assay of HCV virions is typically performed by immunostaining HCV antigens with fluorochrome-conjugated specific antibodies and subsequent fluorescence microscopical observation. However, manual counting of foci by fluorescence microscopical observation is inconvenient and labor-consuming, and can yield biased results. In the first part of the study, therefore, we established in vitro HCVcc system and developed and optimized a method of colorimetric focus-forming assay and image analysis, using an ELISpot reader for convenient and objective quantification of HCV virions. In the second part of the study, we addressed whether HCV infection alters the expression ...