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Regulation of transcription of the HBV genome seems to differ among HBV genomes derived from different genotypes. These differences in transcriptional control among HBV genotypes may be the molecular basis for differences in the clinical course among HBV genotypes.

In chronically infected patients, hepatitis B virus (HBV) particles reach numbers as large as >10⁹ genome equivalents (GE)/ml of serum. However, expression of infectious HBV particles in cell culture only yields 10⁵–10⁶ GE/ml, which is insufficient for many studies. HBV transcription and possibly replication is dependent on hepatocyte-specific differentiation. Thus, we tested several cell culture parameters that have been reported to enhance the expression of hepatocyte-specific markers, such as growth on different extracellular matrices, different cell culture media, low concentrations of fetal calf serum (FCS) and the addition of dimethyl sulfoxide (DMSO) to the medium. Lower concentrations of FCS, growth on collagen and inclusion of DMSO in the medium only moderately enhanced HBV production in vitro when applied individually. However, combinations of these parameters optimised cell culture conditions and reproducibly increased the release of HBV particles about 100-fold to titres >10⁸ GE/ml of culture medium.

Stable expression of HBx leads to deregulation of apoptosis induced by UV irradiation depending on the cell line used. In an immortalized hepatocyte line HBx acted anti-apoptotic whereas expression in a carcinoma derived hepatocyte line HBx enhanced apoptosis.

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