Clinical implications of hepatitis B virus envelope protein variation.

The envelope proteins of hepatitis B virus are highly conserved. They are involved in viral attachment to hepatocytes, virion assembly and secretion and induction of humoral and T-cell immune responses. The major neutralisation epitope is located within the S protein and is conformation dependent, probably due to the formation of disulphide bridges. Variation in the envelope proteins of hepatitis B virus has been described in vaccinees and in patients receiving monoclonal and polyclonal antibody therapy. These arise through point mutations in the surface gene and appear to be selected by the immune response. The emergence of such variants has clinical relevance, in particular with regard to vaccine failure and diagnostic difficulties.