Recombinant duck interferon: a new reagent for studying the mode of interferon action against hepatitis B virus.

Although interferon is widely used to treat chronic hepatitis B virus infections, its mode of action against hepadnaviruses is largely unknown. This deficit is due mainly to the lack of suitable model systems. The duck system could not be used because purified duck interferon was not available in sufficient quantities. We have now cloned a DNA fragment that contains an intronless gene for duck interferon. The primary translation product consists of 191 amino acids, the N-terminal 30 residues of which constitute a signal peptide. Mature duck interferon is 50% identical to the recently cloned chicken interferon. Sequence homology to mammalian interferons is marginal, but conservation of four cysteine residues and inducibility by virus indicate a distant relationship between duck interferon and mammalian type I interferons. Purified recombinant duck interferon from Escherichia coli is biologically active: it activates the interferon-inducible Mx gene, prevents cell destruction by cytolytic RNA viruses, and has a strong inhibitory effect on duck hepatitis B virus in cultured primary duck hepatocytes. This new reagent should help to define the interferon-sensitive step of the hepadnavirus life cycle. Furthermore, the duck system can now be used for systematic studies of the in vivo effectiveness of interferon in chronic hepatitis B virus infections.