Animal models for the study of hepatitis B virus infection

Even with an effective vaccine, an estimated 240 million people are chronically infected with hepatitis B virus （HBV） worldwide. Current antiviral therapies, including interferon and nucleot（s）ide analogues, rarely cure chronic hepatitis B. Animal models are very crucial for understanding the pathogenesis of chronic hepatitis B and developing new therapeutic drugs or strategies. HBV can only infect humans and chimpanzees, with the use of chimpanzees in HBV research strongly restricted. Thus, most advances in HBV research have been gained using mouse models with HBV replication or infection or models with HBV-related hepadnaviral infection. This review summarizes the animal models currently available for the study of HBV infection.

Molecular Cloning,Characterization and Expression Analysis of Woodchuck Retinoic Acid-Inducible GeneⅠ

Cytosolic retinoic acid-inducible gene I（RIG-I） is an important innate immune RNA sensor and can induce antiviral cytokines, e.g., interferon-β（IFN-β）. Innate immune response to hepatitis B virus（HBV） plays a pivotal role in viral clearance and persistence. However, knowledge of the role that RIG-I plays in HBV infection is limited. The woodchuck is a valuable model for studying HBV infection. To characterize the molecular basis of woodchuck RIG-I（w RIG-I）, we analyzed the complete coding sequences（CDSs） of w RIG-I, containing 2778 base pairs that encode 925 amino acids. The deduced w RIG-I protein was 106.847 k D with a theoretical isoelectric point（p I） of 6.07, and contained three important functional structures [caspase activation and recruitment domains（CARDs）, DEx D/H-box helicases, and a repressor domain（RD）]. In woodchuck fibroblastoma cell line（WH12/6）, w RIG-I-targeted small interfering RNA（si RNA） down-regulated RIG-I and its downstrean effector–IFN-β transcripts under RIG-I＇ ligand, 5＇-ppp double stranded RNA（ds RNA） stimulation. We also measured m RNA levels of w RIG-I in different tissues from healthy woodchucks and in the livers from woodchuck hepatitis virus（WHV）-infected woodchucks. The basal expression levels of w RIG-I were abundant in the kidney and liver. Importantly, w RIG-I was significantly up-regulated in acutely infected woodchuck livers, suggesting that RIG-I might be involved in WHV infection. These results may characterize RIG-I in the woodchuck model, providing a strong basis for further study on RIG-I-mediated innate immunity in HBV infection.

Asymptomatic Hepadnaviral Persistence and Its Consequences in the Woodchuck Model of Occult Hepatitis B Virus Infection

Woodchuck hepatitis virus (WHV) is molecularly and pathogenically closely related to hepatitis B virus (HBV).Both viruses display tropism towards hepatocytes and cells of the immune system and cause similar liver pathology,where acute hepatitis can progress to chronic hepatitis and to hepatocellular carcinoma (HCC).Two forms of occult hepadnaviral persistence were identified in the woodchuck-WHV model:secondary occult infection (SOI) and primary occult infection (POI).SOI occurs after resolution of a serologically apparent infection with hepatitis or after subclinical serologically evident virus exposure.POI is caused by small amounts of virus and progresses without serological infection markers,but the virus genome and its replication are detectable in the immune system and with time in the liver.SOI can be accompanied by minimal hepatitis,while the hallmark of POI is normal liver morphology.Nonetheless,HCC develops in about 20% of animals with SOI or POI within 3 to 5 years.The virus persists throughout the lifespan in both SOI and POI at serum levels rarely greater than 100 copies/mL,causes hepatitis and HCC when concentrated and administered to virus-na(i)ve woodchucks.SOI is accompanied by virusspecific T and B cell immune responses,while only virusspecific T cells are detected in POI.SOI coincides with protection against reinfection,while POI does not and hepatitis develops after challenge with liver pathogenic doses >1000 virions.Both SOI and POI are associated with virus DNA integration into the liver and the immune system genomes.Overall,SOI and POI are two distinct forms of silent hepadnaviral persistence that share common characteristics.Here,we review findings from the woodchuck model and discuss the relevant observations made in human occult HBV infection (OBI).