Woodchuck Gamma Interferon Upregulates Major Histocompatibility Complex Class I Transcription but Is Unable To Deplete Woodchuck Hepatitis Virus Replication Intermediates and RNAs in Persistently Infected Woodchuck Primary Hepatocytes

Gamma interferon (IFN-γ) is an important mediator with multiple functions in the host defense against viral infection. IFN-γ, in concert with tumor necrosis factor alpha (TNF-α), leads to a remarkable reduction of intrahepatic replication intermediates and specific mRNAs of hepatitis B virus (HBV) by a noncytolytic mechanism in the transgenic mouse model. Thus, it is rational to evaluate the potential value of IFN-γ for the treatment of chronic HBV infection. In the present study, we expressed recombinant woodchuck IFN-γ (wIFN-γ) in Escherichia coli and mammalian cells. wIFN-γ protected woodchuck cells against infection of murine encephalomyocarditis virus in a species-specific manner. It upregulated the mRNA level of the woodchuck major histocompatibility complex class I (MHC-I) heavy chain in permanent woodchuck WH12/6 cells and regulated differentially the gene expression. However, the level of the replication intermediates and specific RNAs of woodchuck hepatitis virus (WHV) in persistently WHV-infected primary woodchuck hepatocytes did not change despite a treatment with 1,000 U of wIFN-γ per ml or with a combination of wIFN-γ and woodchuck TNF-α. Rather, hepatocytes derived from chronic carriers had an elevated level of the MHC-I heavy-chain mRNAs, most probably due to the exposure to inflammatory cytokines in vivo. Treatment with high doses of wIFN-γ led to an abnormal cell morphology and loss of hepatocytes. Thus, wIFN-γ regulates the gene expression in woodchuck hepatocytes but could not deplete WHV replication intermediates and mRNAs in persistently infected hepatocytes. The cellular response to wIFN-γ may be changed in hepatocytes from chronically WHV-infected woodchucks. It should be clarified in the future whether the continuous exposure of hepatocytes to inflammatory cytokines or the presence of viral proteins leads to changes of the cellular response to wIFN-γ.

γ干扰素（Gamma interferon, IFN-γ）是宿主抗病毒感染防御过程中具有多重功能的重要介质。IFN-γ与肿瘤坏死因子α（tumor necrosis factor alpha, TNF-α）协同作用，可通过非溶细胞机制，显著降低转基因小鼠模型中乙型肝炎病毒（hepatitis B virus, HBV）的肝内复制中间体及特异性mRNA水平。因此，评估IFN-γ用于慢性HBV感染治疗的潜在价值具有合理性。本研究中，我们在大肠杆菌（Escherichia coli）与哺乳动物细胞中表达了重组土拨鼠γ干扰素（recombinant woodchuck IFN-γ, wIFN-γ）。wIFN-γ以种特异性方式保护土拨鼠细胞免受鼠脑心肌炎病毒（murine encephalomyocarditis virus）感染；其可上调永生化土拨鼠WH12/6细胞中土拨鼠主要组织相容性复合体I类（major histocompatibility complex class I, MHC-I）重链的mRNA水平，并对基因表达产生差异性调控。然而，在每毫升1000单位wIFN-γ单独处理，或wIFN-γ与土拨鼠TNF-α联合处理的情况下，持续感染土拨鼠肝炎病毒（woodchuck hepatitis virus, WHV）的原代土拨鼠肝细胞内，WHV的复制中间体及特异性RNA水平并未发生改变。相反，来自慢性感染携带者的肝细胞的MHC-I重链mRNA水平升高，这极有可能是体内暴露于炎性细胞因子所致。高剂量wIFN-γ处理会引发肝细胞形态异常及细胞丢失。综上，wIFN-γ可调控土拨鼠肝细胞的基因表达，但无法清除持续感染肝细胞内的WHV复制中间体与mRNA。慢性WHV感染土拨鼠的肝细胞对wIFN-γ的细胞应答可能发生了改变。未来仍需阐明，究竟是肝细胞持续暴露于炎性细胞因子，还是病毒蛋白的存在，导致了肝细胞对wIFN-γ的应答发生变化。