Presence of antibodies to the polymerase gene product(s) of hepatitis B and woodchuck hepatitis virus in natural and experimental infections

Antibodies against synthetic peptides derived from the polymerase gene of the hepatitis B virus (HBV) were present in 80% of renal dialysis patients infected with HBV and in woodchucks infected with woodchuck hepatitis virus (WHV). Polymerase antibody (anti-pol) appeared as the earliest marker of both HBV and WHV infections in approximately half of the individuals tested, suggesting that these antibodies were generated following early viral replication in the liver during the incubation period and prior to the appearance of virus in the blood. Many HBV- or WHV-infected individuals negative for surface antigen throughout infection also had anti-pol, but anti-pol appeared only after anti-surface, anti-core and/or anti-e. The presence of anti-pol did not correlate with other serologic markers of HBV or WHV infection, nor did it correlate with histologically confirmed hepatitis in woodchucks. However, there was a significant correlation between the presence of anti-pol and elevated liver enzyme levels in the sera of renal dialysis patients. In several cases, anti-pol was the sole marker of infection, suggesting that underlying infection and low levels of virus replication were present. Most individuals with anti-pol had antibodies to one of the three synthetic peptides, suggesting it may be immunodominant in natural infections. In human populations, groups with a high frequency of HBV infection have a high frequency of polymerase antibodies, and groups with a low frequency of HBV infection have a low frequency of polymerase antibodies. A standard assay for the detection of polymerase antibodies is described, and possible clinical applications are discussed.

A newly identified hepatitis B type virus in tree squirrels

Virus-associated particles have been isolated from the livers of three common gray tree squirrels (Sciurus carolinensis pennsylvanicus) that have histological evidence of hepatitis. Two of these livers were also positive by orcein staining, suggesting the presence of surface antigen in the cytoplasm of hepatocytes. Fractionation of these particles by CsCl density equilibrium gradient centrifugation and assay of the fractions for surface antigen, core antigen, and DNA polymerase activities demonstrate the presence of all three at an approximate density peak of 1.27. Electron microscopic examination of purified virus preparations showed spherical particles with a mean diameter of 25 nm. Initial characterization of the DNA polymerase product by gel electrophoresis showed a single DNase I sensitive band, migrating slightly faster than the woodchuck hepatitis virus DNA polymerase product. The presence of apparently cross-reacting antibodies was demonstrated by purified hepatitis B surface and/or core antigens binding to some squirrel sera in solid phase assays. Infected tree squirrels appear to lack detectable antigen in their sera. These results suggest that the tree squirrels studied are chronic carriers of a hepatitis B type virus. The host-virus interaction described herein may be useful in understanding the chronic carrier state associated with hepatitis B in man.

Products of the "X" gene in hepatitis B and related viruses

The X region in hepatitis B virus DNA potentially encodes a polypeptide 154 amino acids in length. Two synthetic peptides spanning residues 100 to 115 (peptide 99) and 115 to 131 (peptide 100) in a hydrophilic domain within the carboxy terminal third of the proposed gene product were made and used to raise peptide antisera in rabbits. Such antisera specifically bound to X reactive determinants in liver-derived core antigen particles from humans (HBcAg), ducks (DHBcAg), ground squirrels (GSHcAg) and woodchucks (WHcAg) at each step of core antigen purification. This reactivity was blocked by addition of excess synthetic peptide, and neither sera were reactive with other purified antigens such as HBsAg. Individual polypeptides associated with these core particles were also reactive by Western blotting. These findings suggest that X reactive determinants are present in the core particles of hepatitis B virus and related viruses, and that one or more core-associated polypeptides may have both X and core antigenic determinants. The possible significance of these observations upon the genetic organization and expression of the X gene is discussed.

Major polypeptide of duck hepatitis B surface antigen particles

The 40- to 50-nm pleomorphic particles found in the sera of domestic Pekin ducks infected with duck hepatitis B virus were purified by rate zonal and isopycnic centrifugation. Sodium dodecyl sulfate-polyacrylamide gel electrophoretic polypeptide analysis of these particles, called duck hepatitis B surface antigen particles, revealed the major component to be a single 17,500-dalton polypeptide. This result is in contrast to polypeptide analyses of the surface antigens of related mammalian viruses, including hepatitis B, in which a major doublet of polypeptides is seen with molecular weights ranging from 23,000 to 29,000. Tryptic maps of 17,500-dalton polypeptide resembled that of the major non-glycosylated polypeptide of the adw subtype of hepatitis B surface antigen. A serological assay for antibody to the purified duck virus particles is also described.

The nature of polypeptides larger in size than the major surface antigen components of hepatitis b and like viruses in ground squirrels, woodchucks, and ducks

The relationships of various polypeptides associated with hepatitis B surface antigen (HBsAg), ground squirrel hepatitis surface antigen (GSHsAg), woodchuck hepatitis surface antigen (WHsAg), and duck hepatitis B surface antigen (DHBsAg) were studied by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and tryptic peptide mapping. Analysis of independent antigen isolates by SDS-PAGE resulted in bands consistently observed at 24,000, 28,000, 32,000, 43,000, and 50,000 Da with HBsAg; at 22,000, 25,000, 35,000, 37,000, 39,000, and 42,000 Da with GSHsAg and WHsAg; and at 18,500, 30,000, and 38,500, Da with DHBsAg. Comparison of the major polypeptide pair from the mammalian viruses by tryptic peptide mapping suggests more than a single point of glycosylation or other post-translational modification(s) in some paired comparisons and/or heterogeneity in glycosylation in others. Comparison of the major component of each mammalian virus (HBsAg p24, GSHsAg p22, or WHsAg p22), or the major polypeptide of DHBsAg (p18.5), with their respective larger polypeptides by peptide mapping indicated that one or more of the larger components in each virus shares extensive homology with the appropriate major component. Further, these larger components possess additional spots, interpreted as additional primary sequences, which were not found in the map of the appropriate major component. Collectively, the results suggest that a number of surface antigen-associated polypeptides may be partially encoded for by the pre-S gene region known to exist in hepatitis B virus (HBV) and woodchuck hepatitis virus (WHV), and likely to exist in ground squirrel hepatitis virus (GSHV) and duck hepatitis B virus (DHBV) DNA.

Core particles of hepatitis B virus and ground squirrel hepatitis virus. I. Relationship between hepatitis B core antigen- and ground squirrel hepatitis core antigen-associated polypeptides by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and tryptic peptide mapping

The relationships among the core antigen polypeptides of hepatitis B virus (HBV) and ground squirrel hepatitis virus (GSHV) were studied using sodium dodecyl sulfate-polyacrylamide gel electrophoresis and tryptic peptide mapping. The major core antigen polypeptides of liver-derived HBV (p22) and GSHV (p20.5) shared 56% of the spots in their peptide maps. Comparison of hepatitis B core antigen (HBcAg) p19 or ground squirrel hepatitis core antigen (GSHcAg) p16.5 with their respective major polypeptides indicated that these components probably resulted from cleavage of the major polypeptide of each virus. Other polypeptides smaller than the major component of each virus were often faint on polyacrylamide gels and probably resulted from the cleavage or degradation of components larger than p22 of HBcAg or p20.5 of GSHcAg, since their peptide maps contained spots unique to these high-molecular-weight components. p26 of GSHcAg and p27.5 of HBcAg shared approximately two-thirds of the spots on their peptide maps with those of their respective major core polypeptides. Furthermore, p37.5 of GSHcAg and p40 of HBcAg shared about 60% homology with their respective major polypeptides, and also shared many of the spots that were unique to p26 of GSHcAg or p27.5 of HBcAg but were not found in the peptide map of their respective core antigen polypeptides. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis bands larger than 40,000 daltons were variably present, and peptide mapping indicated that these were aggregates of various smaller core antigen-associated polypeptides. The results suggest that p40 of HBcAg and p37.5 of GSHcAg are the largest unique polypeptides in these core particles, and that they are encoded for by the genome of each virus. That a subset of the spots unique to p40 or p37.5 was also found in p27.5 of HBcAg or p26 of GSHcAg, respectively, as compared to the major core polypeptides, also suggests that p27.5 and p26 are unique proteins encoded by the genome of each virus. It is proposed that the core antigen gene of each virus is larger than that which would encode the major polypeptide of each virus, and that the genetic organizations of the core genes of HBV and GSHV are very similar.

Core particles of hepatitis B virus and ground squirrel hepatitis virus. II. Characterization of the protein kinase reaction associated with ground squirrel hepatitis virus and hepatitis B virus

The recently described protein kinase activity in hepatitis B virus core antigen particles (Albin and Robinson, J. Virol. 34:297-302, 1980) has been demonstrated here in the liver-derived core particles of ground squirrel hepatitis virus. Both protein kinase activities were initially associated with DNA polymerase-positive heavy core particles in CsCl density equilibrium gradients and shifted to polymerase-negative cores during the course of purification. The major core-associated polypeptide of each virus was the dominant species labeled. A variable number of other polypeptide species were also labeled by this reaction. Tryptic peptide mapping of both major and minor phosphorylated polypeptides of each virus resulted in similar patterns, suggesting that many of the sites of phosphorylation were the same in the components of each core particle. Hydrolysis of these phosphorylated core particles revealed a major phosphoamino acid as serine and a minor phosphoamino acid as threonine. The products of the protein kinase reaction in both human hepatitis B and ground squirrel hepatitis virus core particles, then, share many characteristics. The possible function(s) of this protein kinase activity is discussed in the light of similarly characterized activities in other animal viruses.

Antigenic and structural relationships of the surface antigens of hepatitis B virus, ground squirrel hepatitis virus, and woodchuck hepatitis virus

The surface antigens of human hepatitis B (HBsAg), ground squirrel hepatitis (GSHsAg), and woodchuck hepatitis (WHsAg) viruses were compared serologically, and their major polypeptides were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and tryptic peptide mapping. Results showed that both GSHsAg and WHsAg are antigenically cross-reactive, that their major pairs of polypeptides have identical mobilities on sodium dodecyl sulfate gels, and that the major polypeptides of GSHsAg and WHsAg migrate faster in sodium dodecyl sulfate-polyacrylamide gel electrophoresis than do the corresponding bands of HBsAg. The peptide maps of the major (P-22) surface antigen polypeptides of GSHsAg and WHsAg showed that they shared over half of their spots. Peptide mapping of HBsAg subtypes indicated a close relationship between the major polypeptides (P-24) of adw and adr and a more distal relationship to ayw. Only about 25% of the spots shared by the combined HBsAg subtypes were also found in the peptide maps of GSHsAg and WHsAg, indicating at least some structural homology among the major polypeptides of the human and animal virus surface antigen particles. This is also reflected in the serological cross-reactivity among HBsAg, GSHsAg, and WHsAg. Further, the detection of ground squirrel and woodchuck antigens by Ausria II radioimmunoassay, combined with peptide mapping data indicating the common origin of these viruses, suggests that the common a determinant is shared by each and is restricted to approximately 25% of the sequences in their major polypeptides.

Structural relationships between the surface antigens of ground squirrel hepatitis virus and human hepatitis B virus

Several physical, chemical, and serological properties of surface antigen particles from ground squirrel hepatitis virus (GSHsAg) and human hepatitis B virus (HBsAg) were compared. GSHsAg and HBsAg particles were purified from positive sera by gel chromatography and isopycnic centrifugation. Both antigens consisted mainly of spherical particles with an average diameter of approximately 20 nm and a buoyant density in CsCl of approximately 1.19 g/ml. Their UV absorption spectra indicated the presence of more tryptophane than tyrosine and the absence of detectable nucleic acid. GSHsAg was found to contain two major polypeptides of approximately 23,000 and 27,000 daltons, with electrophoretic migration rates distinctly faster than those of the two major polypeptides of HBsAg particles. After radiolabeling of purified antigen preparations with Bolton-Hunter reagent, the two major polypeptides of GSHsAg showed almost identical tryptic peptide maps. The tryptic peptide map of the major polypeptide from GSHsAg contained 13 of 37 spots also present in the map of the major HBsAg polypeptide, and 13 of 27 spots in the map of the major HBsAg polypeptide were also present in the map of the major GSHsAg polypeptide. This suggests considerable sequence homology between the major surface antigen polypeptides of the two viruses. However, there was only a weak serological cross-reactivity between antigens of the two viruses. Using an anti-HBs-containing serum with a relatively strong cross-reactivity, GSHsAg was found to consist of at least two antigenically different subspecies. The more strongly cross-reacting from had a slightly higher buoyant density than the other antigenic form.