Inhibition of Intrahepatic Gamma Interferon Production by Hepatitis C Virus Nonstructural Protein 5A in Transgenic Mice

Abstract

Hepatitis C virus (HCV) utilizes strategies to suppress or evade the host immune response for establishment of persistent infection. We have shown previously that HCV nonstructural protein 5A (NS5A) impairs tumor necrosis factor alpha (TNF-␣)-mediated apoptosis. In this study, we have examined the immunomodulatory role of HCV NS5A protein in transgenic mouse (NS5A-Tg) liver when mice were challenged with an unrelated hepatotropic adenovirus as a nonspecific stimulus. Hepatotropic adenovirus was introduced intravenously into NS5A-Tg mice and control mice, and virus clearance from liver was compared over a time course of 3 weeks. The differential mRNA expression levels of 84 cytokine-related genes, signal pathway molecules, transcription factors, and cell surface molecules were determined using real-time reverse transcription-PCR array. NS5A-Tg mice failed to clear adenovirus from liver up to 3 weeks postinfection while control mice cleared virus within 1 to 2 weeks. Subsequent study revealed that gamma interferon (IFN-␥) expression is inhibited at both the mRNA and protein levels in NS5A-Tg mice, and an inverse expression of transcription factors Gata-3 and Tbx21 is observed. However, TNF-␣ mRNA and protein expression were elevated in both NS5A-Tg and control mice. Together, our results suggested that HCV NS5A acts as an immunomodulator by inhibiting IFN-␥ production and may play an important role toward establishment of chronic HCV infection.

Dendritic cells in hepatitis C infection: can they (help) win the battle?

“…Further, the HCV Tg mice have impaired expression of MHC class I molecules, due to defective transport to the cellular membrane. In contrast, the total amount of cellular MHC class I molecules, and the expression of class II MHC and other cellular receptors, including co-stimulatory molecules (B7-1 and B7-2), CD40, CD11c, and ICAM-1 in HCV-Tg mice is comparable to controls [101][102][103][104][105][106][107]. Interestingly, HCV core protein is co-localized with cytosoltrapped MHC class I molecules and this intracellular trap is unique to DCs, as MHC-class I traffic in isolated hepatocytes of HCV-Tg mice is normal [107].…”

“…Several transgenic (Tg) mouse lines expressing HCV proteins have been developed and are suitable for the investigation of antiviral immunity [100][101][102][103][104][105][106][107]. Similar to MDCs from patients with chronic HCV infection and DCexpressing HCV proteins, immature DCs from HCV transgenic mouse proteins had impaired allostimulatory capacity [102].…”

Induction and Evasion of Innate Antiviral Responses by Hepatitis C Virus

“…Data indicating an association between sequence polymorphisms in NS5A and treatment outcome support a role for NS5A in IFN antagonism in vivo (97). Transgenic mice expressing NS5A also show defective PKR, IFN-␤, and 2Ј,5Ј-oligoadenylate synthetase responses to virus infection and are slow in clearing adenovirus from the liver due to impaired IFN-␥ expression (98,99). It is possible that enhanced intrahepatic expression of USP18 (15,16) could also blunt IFN responses through its ISG15-deconjugating activity (100).…”

T Helper Type 1/T Helper Type 17-Related Cytokines in Chronic Hepatitis C Patients before and after Interferon and Ribavirin Therapy

“…Mild deficiencies include the failure to produce certain cytokines while the more severe ones include deficiency in cytokine production [20] and inhibition of intrahepatic IFN-␥ production by HCV NS5A as seen in transgenic mice [21] . Defective IFN-␥ production by peripheral blood mononuclear cells from HCV-infect- ed patients in response to nonstructural protein 4 is another example of the severe deficiencies [22] .…”