Production of infectious hepatitis delta virus in vitro and neutralization with antibodies directed against hepatitis B virus pre-S antigens

Role of the large hepatitis B virus envelope protein in infectivity of the hepatitis delta virion

The hepatitis delta virus (HDV) is coated with large (L), middle (M), and small (S) envelope proteins encoded by coinfecting hepatitis B virus (HBV). To study the role of the HBV envelope proteins in the assembly and infectivity of HDV, we produced three types of recombinant particles in Huh7 cells by transfection with HBV DNA and HDV cDNA: (i) particles with an envelope containing the S HBV envelope protein only, (ii) particles with an envelope containing S and M proteins, and (iii) particles with an envelope containing S, M, and L proteins. Although the resulting S-, SM-, and SML-HDV particles contained both hepatitis delta antigen and HDV RNA, only particles coated with all three envelope proteins (SML) showed evidence of infectivity in an in vitro culture system susceptible to HDV infection. We concluded that the L HBV envelope protein, and more specifically the pre-S1 domain, is important for infectivity of HDV particles and that the M protein, which has been reported to bear a site for binding to polymerized albumin in the pre-S2 domain, is not sufficient for infectivity. Our data also show that the helper HBV is not required for initiation of HDV infection. The mechanism by which the L protein may affect HDV infectivity is discussed herein.

In vitro culture systems for hepatitis B and delta viruses

The development of tissue culture technology has led to invaluable information in many fields of modern virology. Until recently, the lack of an in vitro culture system for the hepatitis B virus (HBV) was a considerable impediment to the study of its life cycle at the cellular and molecular levels. However, it did not prevent its isolation and molecular cloning. Such has been the case also for the hepatitis delta virus (HDV), the genome of which was cloned and sequenced before its replication could be observed in cultured cells. In recent years, tissue culture systems for HBV and HDV have been developed progressively by the identification of permissive, established cell lines for production of virions and susceptible primary hepatocyte cultures for infection assays. I will briefly review here the recent experiments that have contributed to replicate HBV and HDV in cell culture systems.

Virological and serological aspects of hepatitis B and the delta agent

The hepatitis B virus (HBV) belongs to a group of viruses termed hepadnaviruses. The 3.2 kb genome encodes for a variety of proteins involved in viral replication (p-gene), transactivation (x-gene), or encodes for structural proteins (c- and s-genes). Several viral and non-viral functions determine the clinical course of HBV infection. The hepatitis D virus resembles a viroid and requires the HBV as a helper virus. The interaction between the viruses is not well understood. More information on the interaction between the human host and viruses is needed to help improve the treatment.