Mécanismes de subversion de l'immunité innée par le virus de l'Hépatite C (VHC)
Hepatitis C infection is a worldwide health problem since the risk to develop a persistent infection is relatively elevated (40 to 60%) and nearly half of the infected patients do not respond to the classical anti-HCV therapy based on a combination of PEG-IFNα and ribavirin. Viral persistence is based on powerful evasion strategies of the host’s innate immune system. In our study, we characterized antiviral response in primary human normal and chronically HCV-infected hepatocytes, a cutting-edge in our field due to the difficulty to isolate this particular cell type. In order to better define the antiviral response in freshly isolated human primary hepatocytes, we stimulated these cells with extracellular and intracellular dsRNA to trigger TLR3/TRIF and RIG-I-MDA5/CARDIF-mediated antiviral signaling pathways. By using qRT-PCR and microarray analysis, we report that both detection pathways are functional in normal human hepatocytes, their activation leading to the expression of both common (IFIT1, OASL, ISG15 and CXCL10) and specific genes (IL28A, IL28B and IL29), these last ones being a signature of the intracellular dsRNA-mediated pathway. HCV NS3/4A plays a key role in the viral polyprotein processing and upon viral RNA detection by interfering with the host’s antiviral signalling cascades. We report that major antiviral genes induction following activation of RIG-I mediated pathway are severely impaired in ectopically NS3/4A expressing normal hepatocytes due to CARDIF cleavage, but can be restored by specific NS3/4A inhibitor BILN2061. Our microarray analysis also revealed a role for NS3/4A following TRL3-mediated pathway activation on regulation of apoptosis and programmed cell death, which could be linked to strategies for the virus to persist in its host. Despite HCV strategies to circumvent the host’s immune defense system, we observed significant upregulation of ISGs and chemokines in liver biopsies and corresponding isolated hepatocytes from chronically HCV-infected patients. However, no type I and III interferon, neither key-antiviral genes (e.g., CCL5) were detected, underlying an ongoing –but inefficient- antiviral response unable to eradicate the virus. Moreover, we obtained significant inverse correlations between ISGs mRNAs and viral RNA in addition to CARDIF decrease, clearly unravelling efficient viral interfering strategies in a context of chronic HCV infection. This sustained -albeit incomplete- hepatic innate immune response is certainly associated to the failure of the classical IFN-based therapy in half of the infected patients and to the chronic inflammation causing liver damages and eventually leading to hepatocarcinoma which is often observed at late stage of the disease.
NS3/4A ISGs (Interferon Stimulated Genes) Hepatitis C Virus Primary Hepatocytes Viral Interference