Persistent Hepatitis B Viral Replication in a FVB/N Mouse Model: Impact of Host and Viral Factors

The mechanism underlying the chronicity of hepatitis B virus (HBV) infection has long been an interesting question. However, this mechanism remains unclear largely due to the lack of an animal model that can support persistent HBV replication and allow for the investigation of the relevant immune responses. In this study, we used hydrodynamic injection to introduce HBV replicon DNA into the livers of three different mouse strains: BALB/c, C57BL/6, and FVB/N. Interestingly, we found that an HBV clone persistently replicated in the livers of FVB/N mice for up to 50 weeks but was rapidly cleared from the livers of BALB/c and C57BL/6 mice. Flow cytometric analysis and quantitative reverse transcription PCR analysis of the mouse livers indicated that after DNA injection, FVB/N mice had few intrahepatic activated cytotoxic T lymphocytes (CTLs) and produced low levels of alanine aminotransferase, interferon (IFN)-γ, tumor necrosis factor (TNF)-α, and the CXCL9 and CXCL10 chemokines. These findings were in sharp contrast with those observed in BALB/c and C57BL/6 mice, reflecting a strong correlation between the degree of liver inflammation and viral clearance. Mutational analysis further demonstrated that a change of Asn-214 to Ser-214 in the HBV surface antigen rendered the persistent HBV clone clearable in FVB/N mice, which was accompanied by increased levels of activated CTL and upregulated expression of IFN-γ, CXCL9, and CXCL10 in the livers. These results indicate that the heterogeneity of the host factors and viral sequences may influence the immune responses against HBV. An inadequate activation of immune or inflammatory responses can lead to persistent HBV replication in vivo.乙型肝炎病毒（hepatitis B virus, HBV）感染慢性化的潜在机制长期以来均为学界关注的重要科学问题。然而，由于缺乏能够支持HBV持续复制并可用于相关免疫应答研究的动物模型，该机制至今仍未完全阐明。本研究采用水动力注射法，将HBV复制子DNA导入BALB/c、C57BL/6及FVB/N三种不同品系小鼠的肝脏。值得注意的是，我们发现某一HBV克隆可在FVB/N小鼠肝脏中持续复制长达50周，却能快速从BALB/c与C57BL/6小鼠的肝脏中被清除。对小鼠肝脏组织开展流式细胞术分析（flow cytometric analysis）与定量逆转录PCR（quantitative reverse transcription PCR）后发现，DNA注射后，FVB/N小鼠肝内活化的细胞毒性T淋巴细胞（cytotoxic T lymphocytes, CTLs）数量极少，且丙氨酸氨基转移酶（alanine aminotransferase, ALT）、干扰素（interferon, IFN）-γ、肿瘤坏死因子（tumor necrosis factor, TNF）-α以及趋化因子CXCL9、CXCL10的表达水平均较低。上述结果与BALB/c及C57BL/6小鼠的观测结果形成鲜明对比，提示肝脏炎症程度与病毒清除效率之间存在显著相关性。突变分析进一步证实，将HBV表面抗原中第214位的天冬酰胺突变为丝氨酸后，该持续性HBV克隆可在FVB/N小鼠体内被清除，同时伴随肝内活化CTL数量增加，以及IFN-γ、CXCL9、CXCL10的表达水平上调。本研究结果表明，宿主因子与病毒序列的异质性可能影响机体抗HBV免疫应答，免疫或炎症应答激活不足可导致HBV在体内持续复制。