HIGH-LEVEL HEPATITIS-B VIRUS-REPLICATION IN TRANSGENIC MICE

Hepatitis B virus (HBV) transgenic mice whose hepatocytes replicate th e virus at levels comparable to that in the infected livers of patient s,vith chronic hepatitis have been produced, without any evidence of c ytopathology. High-level viral gene expression was obtained in the liv er and kidney tissues in three independent lineages. These animals wer e produced with a terminally redundant viral DNA construct (HBV 1.3) t hat starts just upstream of HBV enhancer I, extends completely around the circular viral genome, and ends just downstream of the unique poly adenylation site in HBV. In these animals, the viral mRNA is more abun dant in centrilobular hepatocytes than elsewhere in the hepatic lobule . High-level viral DNA replication occurs inside viral nucleocapsid pa rticles that preferentially form in the cytoplasm of these centrilobul ar hepatocytes, suggesting that an expression threshold must be reache d for nucleocapsid assembly and viral replication to occur. Despite th e restricted distribution of the viral replication machinery in centri lobular cytoplasmic nucleocapsids, nucleocapsid particles are detectab le in the vast majority of hepatocyte nuclei throughout the hepatic lo bule. The intranuclear nucleocapsid particles are empty, however, sugg esting that viral nucleocapsid particle assembly occurs independently in the nucleus and the cytoplasm of the hepatocyte and implying that c ytoplasmic nucleocapsid particles do not transport the viral genome ac ross the nuclear membrane into the nucleus during the viral life cycle , This model creates the opportunity to examine the influence of viral and host factors on HBV pathogenesis and replication and to assess th e antiviral potential of pharmacological agents and physiological proc esses, including the immune response.