Antibody to the receptor for polymerized human serum albumin in acute and persistent infection with hepatitis B virus

Both middle and large envelope proteins can mediate neutralization of hepatitis B virus infectivity by anti-preS2 antibodies: escape by naturally occurring preS2 deletions

Hepatitis B virus (HBV) expresses co-terminal large (L), middle (M), and small (S) envelope proteins containing preS1/preS2/S, preS2/S, and S domain alone, respectively. S and preS1 domains mediate sequential virion attachment to heparan sulfate proteoglycans and sodium taurocholate cotransporting polypeptide (NTCP), respectively, which can be blocked by anti-S and anti-preS1 antibodies. How anti-preS2 antibodies neutralize HBV infectivity remains enigmatic. The late stage of chronic HBV infection often selects for mutated preS2 translation initiation codon to prevent M protein expression, or in-frame preS2 deletions to shorten both L and M proteins. When introduced to infectious clone of genotype C or D, both M-minus mutations and most 5' preS2 deletions sustained virion production. Such mutant progeny viral particles were infectious in NTCP-reconstituted HepG2 cells. Neutralization experiments were performed on the genotype D clone. Although remaining susceptible to anti-preS1 and anti-S neutralizing antibodies, M-minus mutants were only partially neutralized by two anti-preS2 antibodies tested while preS2 deletion mutants were resistant. By infection experiments using viral particles with lost versus increased M protein expression, or a neutralization escaping preS2 deletion only present on L or M protein, we found that both full-length L and M proteins contributed to virus neutralization by the two anti-preS2 antibodies. Thus, immune escape could be a driving force for the selection of M-minus mutations, and especially preS2 deletions. The fact that both L and M proteins could mediate neutralization by anti-preS2 antibodies may shed light on the underlying molecular mechanism.IMPORTANCEThe large (L), middle (M), and small (S) envelope proteins of hepatitis B virus (HBV) contain preS1/preS2/S, preS2/S, and S domain alone, respectively. The discovery of heparan sulfate proteoglycans and sodium taurocholate cotransporting polypeptide (NTCP) as the low- and high-affinity HBV receptors could explain neutralizing potential of anti-S and anti-preS1 antibodies, respectively, but how anti-preS2 neutralizing antibodies work remains enigmatic. In this study, we found two M-minus mutants in the context of genotype D partially escaped two anti-preS2 neutralizing antibodies in NTCP-reconstituted HepG2 cells, while several naturally occurring preS2 deletion mutants escaped both antibodies. By point mutations to eliminate or enhance M protein expression, and by introducing preS2 deletion selectively to L or M protein, we found binding of anti-preS2 antibodies to both L and M proteins contributed to neutralization of wild-type HBV infectivity. Our finding may shed light on the possible mechanism(s) whereby anti-preS2 antibodies neutralize HBV infectivity.

Quasispecies variant of pre-S/S gene in HBV-related hepatocellular carcinoma with HBs antigen positive and occult infection

Background

Hepatocellular carcinoma (HCC) can develop in patients who are negative for the hepatitis B surface antigen (HBsAg) in serum but positive for hepatitis B virus (HBV) DNA in the liver, referred to as occult HBV infection (OBI). Previous reports showed that HBV variants in OBI-related HCC are different from those in HBsAg-positive HCC. In the present study, HBV quasispecies based on the pre-S/S gene in OBI-related HCC patients were examined by high throughput sequencing and compared with those in HBsAg-positive HCC.

Methods

Nineteen tissue samples (9 OBI-related and 10 HBsAg-positive non-cancerous tissues) were collected at the time of surgery at Kobe University Hospital. The quasispecies with more than 1% variation in the pre-S/S region were isolated and analysed by ultra-deep sequencing.

Results

There were no significant differences in the major HBV populations, which exhibit more than 20% variation within the entire pre-S/S region, between OBI-related HCC and HBsAg-positive HCC. However, the prevalences of major populations with pre-S2 region mutations and of minor populations with polymerized human serum albumin-binding domain mutations were significantly higher in OBI-related HCC than in HBsAg-positive HCC. Moreover, the major variant populations associated with the B-cell epitope, located within the pre-S1 region, and the a determinant domain, located in the S region, were detected frequently in HBsAg-positive HCC. The minor populations of variants harbouring the W4R, L30S, Q118R/Stop, N123D and S124F/P mutations in the pre-S region and the L21F/S and L42F/S mutations in the S region were detected more frequently in OBI-related HCC than in HBsAg-positive HCC.

Conclusions

Ultra-deep sequencing revealed that the B-cell epitope domain in the pre-S1 region and alpha determinant domain in the S region were variable in HBsAg-positive HCC, although the quasispecies associated with the pre-S2 region were highly prevalent in OBI-related HCC.

Trial registration

Ref: R000034382/UMIN000030113; Retrospectively registered 25 November 2017.

Hepatitis B vaccine containing surface antigen and selected preS1 and preS2 sequences. 1. Safety and immunogenicity in young, healthy adults

The safety and immunogenicity of a yeast-derived recombinant hepatitis B virus (HBV) vaccine containing surface antigen (S) and selected preS1 and preS2 sequences (S-L*) were compared with those of a vaccine prepared with S alone (Engerix-B). S-L* consisted of composite particles containing S and L* at a ratio of 70/30. L* encompassed amino acid residues 12-52 of preS1 residues 133-145 of preS2, and the entire S domain. A total of 100 healthy, HBV-seronegative, young adults were randomized to receive 20 micrograms/dose of either S-L* or Engerix-B under double-blind conditions according to a 0-, 1-, 2-, 12-month schedule. In vivo humoral and in vitro lymphoproliferative responses to S and preS regions were monitored. Addition of the selected preS sequences to S did not enhance the in vivo humoral anti-HBs response but improved the in vitro stimulating capacity of the antigen (L*) in S-L* primed subjects.

Effects of acyclovir and vidarabin 5'-monophosphate on anti-duck hepatitis B virus in an in vitro culture system

Various anti-viral agents, e.g., interferon, have recently been used for the treatment of viral hepatitis. In the present study, duck hepatitis B virus (DHBV) was cultured in vitro and the anti-DHBV effects of acyclovir (ACV) and vidarabin 5'-monophosphate (VMP) were studied. The portal perfusion method was applied to the livers of 7-day-old white ducks weighing 100 g, bred in Japan, and hepatocytes were infected with DHBV in vitro. Duck hepatocytes infected with DHBV were cultured in medium containing ACV or VMP, and the anti-DHBV effects of these drugs were assessed by determining DHBV-DNA and duck hepatitis B surface antigen in the medium. Both ACV and VMP had anti-DHBV effects when used immediately after infection; however, both drugs were ineffective in hepatocytes obtained from a DHBV carrier duck. In conclusion, the anti-DHBV effects of these drugs were very limited. However, this culture system appears to be useful for studies of hepatitis virus and anti-viral drugs.

Improved immunogenicity in mice of a mammalian cell-derived recombinant hepatitis B vaccine containing pre-S1 and pre-S2 antigens as compared with conventional yeast-derived vaccines

The widely used hepatitis B virus (HBV) vaccines consist of the small hepatitis B surface (SHBs) protein produced in transfected yeast cells. The frequency of non-responders, especially among immunocompromised patients, has increased the demand for a more immunogenic vaccine. We evaluated the immunogenicity of recombinant HBs 20 nm particles secreted by transfected Chinese hamster ovary (CHO) cells, Bio-Hep-B (BioTechnology General Ltd, Israel), and compared it with yeast-derived vaccines. The CHO-derived vaccine contains the small hepatitis B surface antigen (SHBs protein) as the major component, as well as the middle HBs (MHBs, pre-S2) and the large HBs (LHBs, pre-S1) antigens. Nine groups of ten female Balb/c mice, 4-6 weeks old, were injected once intraperitoneally (i.p.) with 0.09, 0.27 or 0.81 micrograms of each of three vaccines: Bio-Hep-B or two conventional yeast-derived recombinant vaccines, Engerix-B (SmithKline Beecham, Belgium) and H-B-Vax II (Merck, Sharp & Dohme, USA) containing only non-glycosylated SHBs antigen. After 30 days, 40% of the mice injected with 0.09 microgram Bio-Hep-B had seroconverted, but none of the mice receiving the same dose of the other vaccines. The immunogenic dose in 50% of the mice at day 14 after injection was 0.13 microgram for Bio-Hep-B, but over 0.81 microgram for the other two vaccines. Mice of the strain B10/M (which are unresponsive to SHBs and MHBs antigens at the T-cell level) developed 100-fold higher anti-HBs titres after immunization with 1 microgram of Bio-Hep-B i.p., as compared with mice receiving the same amount of yeast-derived HBsAg vaccines.(ABSTRACT TRUNCATED AT 250 WORDS)

Naturally occurring escape mutants of hepatitis B virus with various mutations in the S gene in carriers seropositive for antibody to hepatitis B surface antigen

Hepatitis B virus (HBV) DNA was extracted from sera of six carriers with hepatitis B e antigen as well as antibody to hepatitis B surface antigen and sequenced within the pre-S regions and the S gene. HBV DNA clones from five of these carriers had point mutations in the S gene, resulting in conversion from Ile-126 or Thr-126 of the wild-type virus to Ser-126 or Asn-126 in three carriers and conversion from Gly-145 to Arg-145 in three of them; clones with Asn-126 or Arg-145 were found in one carrier. All 12 clones from the other carrier had an insertion of 24 bp encoding an additional eight amino acids between Thr-123 and Cys-124. In addition, all or at least some of the HBV DNA clones from these carriers had in-phase deletions in the 5' terminus of the pre-S2 region. These results indicate that HBV escape mutants with mutations in the S gene affecting the expression of group-specific determinants would survive in some carriers after they seroconvert to antibody against surface antigen. Carriers with HBV escape mutants may transmit HBV either by donation of blood units without detectable surface antigen or through community-acquired infection, which would hardly be prevented by current hepatitis B immuneglobulin or vaccines.

Amniocentesis in mothers who are hepatitis B virus carriers does not expose the infant to an increased risk of hepatitis B virus infection

Sixty-seven pairs of mothers with hepatitis B virus (HBV) surface antigen (HBsAg) and their infants were divided into two study groups to determine the effect of amniocentesis on intrauterine HBV infection. In the first study group (35 pairs), the infant's HBsAg status in cord blood was studied and the results were compared with those obtained in the cord blood from 65 infants born to HBsAg-positive women who did not have an amniocentesis. In the second study group (32 pairs), the HBV status of the infants was studied at the age of three months to five years and compared with the HBV status of 3,454 infants in the National HBV Prevention Program. In the first study group, one sample (2.9%) was weakly positive for HBsAg; while in the first control group, two (3.1%) were positive. In the second study group, three (10%) infants were positive for HBsAg. The failure rates of immunoprophylaxis in the second study and control groups were similar (9.4% vs 11% for HBsAg carrier mothers; 30% vs 14% for HBe antigen-positive carrier mothers). This suggested that genetic amniocentesis did not increase the risk of intrauterine HBV infection.

Significance of measurement of pre-S2 antigen for the prevention of vertical transmission of hepatitis B virus in infants born to HBsAg carrier mothers

The significance of pre-S2 antigen (pre-S2 Ag) as a marker of hepatitis B virus (HBV) infection, especially in infants born to HBsAg carrier mothers who are HBeAg-negative or HBeAg-positive, was evaluated. Pre-S2 Ag was measured by enzyme immunoassay. HBsAg carrier mothers who were HBeAg-negative and HBeAb-positive were divided into two groups: group A, mothers whose infants were not infected with HBV (n = 10) and group B, mothers whose infants were infected with HBV (n = 13). Absorption rates of pre-S2 Ag in group A and B were 0.09 +/- 0.04 and 1.36 +/- 0.95, respectively. The values for pre-S2 Ag in group B were significantly higher than those in group A. Values for pre-S2 Ag among HBsAg carrier mothers who were HBeAg-positive and HBeAb-negative were also measured by reverse passive hemagglutination. In the same way, HBsAg carrier mothers who were HBeAg-positive and HBeAb-negative were divided into two groups: group C, mothers whose infants did not become HBsAg carriers (n = 15) and group D, mothers whose infants became HBsAg carriers (n = 11). The titers of pre-S2 Ag (reverse passive hemagglutination) in group C and D were 2(5.75) +/- 1.68 and 2(10.45 +/- 1.69), respectively. The values for pre-S2 Ag in group D were significantly higher than those in group C. The values for pre-S2 Ag as markers of infectivity became higher with increasing amounts of HBV-DNA.(ABSTRACT TRUNCATED AT 250 WORDS)

Immunogenicity and safety of a recombinant hepatitis B vaccine produced in mammalian cells and containing the S and the preS2

A group of 273 health care workers, at risk of HBV infection, underwent vaccination with recombinant HBsAg produced in mammalian cells and containing protein sequences coded by both the S and pre-S2 regions (Genhevac B). Preliminary results show that a very early pre-S2 response occurred which may be useful in post-exposure prophylaxis. This observation, in addition to reduced influence by the vaccination protocol, provides grounds for optimism in spite of the fact that the efficiency spectrum of this vaccine was not superior to that of recombinant vaccines produced in yeast.

Prognostic significance of pre-S2 antigen and antibody in fulminant hepatitis B. Evidence for heterogeneous serological responses

Serial sera were collected prospectively and from early on in the clinical course of ten patients with fulminant hepatitis B. These were analysed for HBV DNA (dot-blot technique), HBsAg, HBeAg, pre-S2-Ag and their respective antibodies. Two patterns emerged in nine of the patients. The first and well-recognised pattern of rapid clearance of antigens and appearance of antibodies was seen in four patients, all of whom survived. The second pattern seen in five patients was one of persistence of HBsAg and pre-S2 antigen and failure to detect antibodies but only one patient survived. The first pattern may reflect a more rapid cessation of virus replication and this may favour liver cell regeneration and recovery. In contrast, the second pattern may indicate continuing virus replication and liver cell damage which could contribute to the high mortality in some patients with fulminant hepatitis B.

Significance of natural polymerized albumin and its receptor in hepatitis B infection of hepatocytes

Lack of information regarding the presence of native albumin polymer in serum and its structural similarity to the one produced by glutaraldehyde treatment casts doubt on the postulate that hepatitis B virus attachment to hepatocytes is mediated through polymerized albumin. We used a sandwich enzyme-linked immunosorbent assay with murine monoclonal antibodies raised against glutaraldehyde-polymerized albumin to detect native albumin polymer in human serum and its cross-reactivity with other albumin polymers. Presence of polymerized albumin receptor on the HepG2 cell was studied by radioreceptor assay. Purified hepatitis B virus and synthetic peptide analogous to part of pre-S2 sequence (120-145) were used to study polymerized albumin-dependent attachment of the virus to HepG2 cells. Antibodies raised against pre-S2 peptide were used to inhibit the pre-S2 and hepatitis B virus attachment to HepG2 cells. Glutaraldehyde-treated polymerized albumin was found to be immunologically cross-reactive with native albumin polymer. Its levels were found to be significantly raised in sera of patients with liver diseases. Polymerized albumin has specific saturable receptor on HepG2 cells with two classes of binding sites of different equilibrium dissociation constant (Kd1 = (16 +/- 9.6)pmol/L and Kd2 = (1,019 +/- 172)pmol/L. Albumin monomer was unable to compete for the polymerized albumin receptor sites on HepG2 cells. Anti-pre-S2 antibodies inhibit hepatitis B virus and pre-S2 binding to hepatocyte by 40% and 70%, respectively. Added extraneous polymerized albumin and the antibody against it did not interfere with virus attachment to HepG2 cells.

A biphasic pattern of anti-pre-S responses in acute hepatitis B virus infection

The clinical relevance of the immune response to the translation products of the pre-S1 and pre-S2 regions of hepatitis B virus was examined by testing sequential serum samples from 17 patients with acute self-limited hepatitis B and from two patients in whom chronic liver disease developed. Anti-pre-S antibodies were determined by enzyme immunoassays based on the inhibition of binding of monoclonal antibodies to epitopes in the pre-S1 and pre-S2 sequence. In acute, self-limited infection, anti-pre-S antibodies appeared in a biphasic pattern. The early antibodies were detected at the time of clinical signs of acute disease when HBsAg and often HBeAg were present, but hepatitis B virus DNA was no longer detectable in serum. Anti-pre-S levels then fell, but subsequently reappeared as the late antibody during the recovery phase, after development of anti-HBe, but before anti-HBs. Anti-pre-S responses were detected in 15 of 17 patients who recovered (88.2%) and in both patients with acute hepatitis B virus infection evolving to chronic liver disease. Although the early antibodies to pre-S1 and pre-S2 proteins appeared at the time of decreasing levels of infectious virus in serum in cases of self-limited infection, these antibodies also were transiently or continuously present with high levels of serum hepatitis B virus DNA in patients in whom chronic hepatitis B infection developed. Thus the anti-pre-S response in acute hepatitis is not a prognostic marker for clinical resolution.(ABSTRACT TRUNCATED AT 250 WORDS)

Fine specificity of human antibody response to the PreS1 domain of hepatitis B virus

The preS1 domain of hepatitis B virus envelope proteins contains a site of attachment to the hepatocyte membrane that has been shown to evoke virus-neutralizing antibodies. Using synthetic peptides, we have examined kinetics and specificity of the anti-body response to preS1 during acute and chronic HBV infection. Antibodies against two continuous B cell epitopes, p (21-32) and p (32-47), which overlap with the virus receptor for hepatocytes, were detected in 17 (28%) and 28 (47%) patients, respectively, of 60 patients who were tested during acute hepatitis B. Serial testing demonstrated these anti-preS1 specificities in more than 50% of patients who became virus free. By contrast, five patients with chronic evolution of hepatitis B and 61 of 66 patients with an established chronic HBV infection were negative, independent of serological profile and liver disease activity. Fifteen (22.7%) patients with chronic hepatitis B were positive for antibody to the C-terminus p (94-117) preS1 sequence that, unlike the acute-phase anti-(21-32) and anti-(32-47) reactivities, did not behave as a virus-precipitating antibody. Acute-phase sera were found to also contain virus-precipitating antibodies directed against conformational preS1 epitopes. These results indicate that the preS1 site, which contains the binding activity for the hepatocyte membrane, elicits an early antibody response during acute hepatitis B. A defect in such antibody repertoire may participate in the chronicity process as a result of continuing reinfection of hepatocytes by circulating virions.

Significance of anti-pre-S antibodies in patients with fulminant hepatic failure

Anti-pre-S antibody was tested in 38 sera from patients with fulminant hepatitis (positive for HBsAg and/or IgM anti-HBc) using a specific solid phase enzyme linked immunosorbent assay (ELISA). Anti-pre-S activity was detected in 50 percent sera samples positive for HBsAg but negative for IgM anti-HBc. There were 12.5% sera positive for both HBsAg as well as IgM anti-HBc and 75% sera negative for HBsAg but positive for IgM anti-HBc. The prevalence of HBV-specific DNA-polymerase activity was high in all the three groups whereas anti-HBs positivity was low. Anti-pre-S activity was observed both in the presence as well as in the absence of DNA-polymerase activity. High-anti-pre-S level in fulminant hepatitis B patients was assumed to be implicated in the fast clearance of HBsAg from circulation.

Polymerized albumin binding to serum in various liver diseases: its significance and relation to hepatitis B virus infection

Sensitive and specific enzyme-linked immunosorbent assays (ELISA) were developed to detect separately the binding of polymerized human serum albumin (PHSA) to its antibody (A-PHSA) and to the hepatitis B surface antigen (HBsAg). A-PHSA was not detected in normal serum, whereas more than one-third to about half of sera from patients with acute liver cell injury showed this antibody. Frequency of A-PHSA positivity was low in chronic liver diseases, being relatively higher in those with continuing liver injury. A-PHSA detection was not related to seropositivity for HBsAg. PHSA binding of HBsAg positive sera showed a higher frequency of positivity in chronic carriers than acute hepatitis B. Of 172 asymptomatic HBsAg carriers, PHSA binding was demonstrated in 25 (15%), the frequency being significantly high if HBeAg was also present (84%). Binding was infrequent in sera having anti-HBe (2.9%) and in those negative for both HBeAg and anti-HBe (2.7%). Binding of HBsAg to PHSA was significantly higher than to human serum albumin (HSA). Immunoblotting of separated HBsAg components showed PHSA binding specifically to the high molecular weight peptide. PHSA binding in HBsAg positive serum may indicate the latter's infectivity as detected in a study of maternal-fetal transmission, where it demonstrates 100% infectivity in HBsAg and HBeAg positive mothers. PHSA possibly mediates the attachment of the HBV to the hepatocyte and a competitive binding between A-PHSA with HBsAg for PHSA may modulate the course of HBV infection.

Expression of pre-S2 region of hepatitis B surface antigen in Escherichia coli

We constructed a recombinant plasmid that can express the entire pre-S2 sequence of hepatitis B surface antigen (HBsAg) as a fusion protein in E. coli. The hybrid protein, which comprises the bacterial TrpLE protein and the pre-S2 sequence, was the prominent protein that was found in cell extracts. As determined by immune blot analysis, this protein reacted with human HBV convalescent sera, as well as with sera from animals immunized with either purified HBsAg or isolated polypeptides containing pre-S2. It bound specifically to 125I-polymerized human albumin cross-linked with glutaraldehyde but not to 125I-monomeric human albumin. A novel adjuvant formulation was used in place of Freund's adjuvant to immunize guinea pigs with the recombinant product. The antisera obtained from serial bleedings were found to react with HBsAg of both d and y subtypes. These antisera were also shown to react solely with HBsAg polypeptides which contain of HBsAg to solid-phase polymerized the binding of HBsAg to solid-phase polymerized human albumin.

Changes in serum levels of hepatitis B virus markers after interferon treatment

The effect of interferon (IFN) treatment on serum levels of pre-S antigens [pre-S(1) antigen, pre-S(2) antigen, polymerized human serum albumin receptor (pAR)] which are coded by the pre-S region of hepatitis B virus DNA (HBV-DNA), and HBV-markers was analyzed in 23 patients with chronic hepatitis B. One year after IFN treatment, 4 patients (Group C) became HBeAg negative. Six patients (Group B) transiently became HBeAg-negative, but reverted to HBeAg positive. Thirteen patients (Group A) remained HBeAg positive. All of the patients remained HBsAg-positive. Initiation of IFN treatment was rapidly followed by reduction or loss of DNA-P in the serum whether the patients became HBeAg negative or remained positive, and whether serum transaminase (S-GPT) levels became normal or not after IFN treatment. Group C patients, in whom pre-S antigens decreased rapidly during IFN treatment and disappeared before S-GPT levels normalized, became HBeAg negative one year after IFN treatment. Anti-pAR was detected in three out of these 4 patients. In contrast, Group A and Group B patients, in whom pre-S antigens decreased slowly during IFN treatment and did not disappear in spite of those patients being transiently negative for HBeAg and DNA-P, remained HBeAg positive with elevated S-GPT levels one year after IFN treatment. Anti-pAR was almost undetectable. These results suggest that testing for pre-S antigens is more useful for determining the prognosis of patients with chronic hepatitis B treated with IFN than testing for HBsAg, HBeAg and DNA-P.

Identification of an attachment site for human liver plasma membranes on hepatitis B virus particles

The surface antigen of hepatitis B virus (HBsAg) exposes three protein domains: preS1, preS2, and S. In a previous study we have shown that preS1 sequences expressed in transfected yeast cells bind specifically to plasma membranes of human liver. In this study we show that purified virus particles from a virus carrier bind also specifically to such membranes. Subviral HBsAg filaments which are rich in preS1 bind well too, while HBsAg 20-nm particles which contain small amounts of preS1 bind to a much lesser degree. The binding can be inhibited by a monoclonal antibody which recognizes a sequential epitope between amino acids 27 and 49 of the preS1 domain.

The preS1 antigen of hepatitis B virus is highly immunogenic at the T cell level in man

14 hepatitis B vaccine recipients who showed high titers of anti-hepatitis B surface antibodies in serum after booster immunization with a polyvalent hepatitis B surface antigen vaccine that contained trace amounts of hepatitis B virus (HBV) preS1 and preS2 envelope antigens were studied for their in vitro T cell response to these antigens. All 14 subjects displayed a significant proliferative T cell response to the S/p25 envelope region encoded polypeptide; 8 also responded to preS1, while only 1 showed a significant level of T cell proliferation to preS2. Limiting dilution analysis demonstrated that the frequency of preS-specific T cells in two of these vaccine recipients was higher than that of S/p25-specific T cells. T cell cloning was then performed and a total of 29 HBV envelope antigen-reactive CD4+ cloned lines were generated from two preS-responsive vaccines. 21 of these lines were S/p25 specific, 7 preS1 specific, and 1 preS2 specific. Taken together, all these results suggest that the preS1 antigen may function as a strong T cell immunogen in man.

Human liver plasma membranes contain receptors for the hepatitis B virus pre-S1 region and, via polymerized human serum albumin, for the pre-S2 region

Hepatitis B virus particles contain three related viral envelope proteins, the small, middle, and large S (surface) proteins. All three proteins contain the small S amino acid sequence at their carboxyl terminus. It is not clear which of these S proteins functions as the viral attachment protein, binding to a target cell receptor and initiating infection. In this report, recombinant hepatitis B surface antigen (rHBsAg) particles, which contain only virus envelope proteins, were radioactively labeled, and their attachment to human liver membranes was examined. Only the rHBsAg particles containing the large S protein were capable of directly attaching to liver plasma membranes. The attachment was saturable and could be prevented by competition with unlabeled particles or by a monoclonal antibody specific for the large S protein. In the presence of polymerized human serum albumin, both large and middle S protein-containing rHBsAg particles were capable of attaching to the liver plasma membranes. Small S protein-containing rHBsAg particles were not able to attach even in the presence of polymerized human serum albumin. These results indicate that the large S protein may be the viral attachment protein for hepatocytes, binding directly to liver plasma membranes by its unique amino-terminal (pre-S1) sequence. These results also indicate that polymerized human serum albumin or a similar molecule could act as an intermediate receptor, attaching to liver plasma membranes and to the amino acid sequence (pre-S2) shared by the middle and large S proteins but not contained in the small S protein.

The multiple-indicator dilution technique for characterization of normal and retrograde flow in once-through rat liver perfusions

The technique of normal and retrograde rat liver perfusion has been widely used to probe zonal differences in drug-metabolizing activities. The validity of this approach mandates the same tissue spaces being accessed by substrates during both normal and retrograde perfusions. Using the multiple-indicator dilution technique, we presently examine the extent to which retrograde perfusion alters the spaces accessible to noneliminated references. A bolus dose of 51Cr-labeled red blood cells, 125I-albumin, 14C-sucrose and 3H2O was injected into the portal (normal) or hepatic (retrograde) vein of rat livers perfused at 10 ml per min per liver. The outflow perfusate was serially collected over 220 sec to characterize the transit times and the distribution spaces of the labels. During retrograde perfusion, red blood cells, albumin and sucrose profiles peaked later and lower than during normal perfusion, whereas the water curves were similar. The transit times of red blood cells, albumin and sucrose were longer (p less than 0.005), whereas those for water did not change. Consequently, retrograde flow resulted in significantly larger sinusoidal blood volumes (45%), albumin Disse space (42%) and sucrose Disse space (25%) than during normal flow, whereas the distribution spaces for total and intracellular water remained unaltered. The distension of the vascular tree was confirmed by electron microscopy, by which occasional isolated foci of widened intercellular recesses and spaces of Disse were observed. Cellular ultrastructure was otherwise unchanged, and there was no difference found between normal and retrograde perfusion for bile flow rates, AST release, perfusion pressure, oxygen consumption and metabolic removal of ethanol, a substrate with flow-limited distribution, which equilibrates rapidly with cell water (hepatic extraction ratios were virtually identical: normal vs. retrograde, 0.50 vs. 0.48 at 6 to 7.4 mM input concentration). These findings suggest that the functional and metabolic capacities of the liver remain unperturbed during retrograde perfusion, rendering the technique suitable for the investigation of zonal differences in drug-metabolizing enzymes.

Treatment of acute and chronic viral hepatitis

Over the 12 years since the first introduction of interferon for the treatment of chronic hepatitis B, progress has apparently been slow. Nevertheless, it now appears that at least one third of chronic hepatitis virus carriers, particularly those with more severe disease, and a similar, perhaps greater, proportion of those with chronic parenteral non-A, non-B hepatitis, can be successfully treated with alpha-interferon. In the not too distant future, controlled trials of alpha-interferons in these situations will be complete and they will be a yardstick by which other future therapies can be judged. Already a number of trials are in progress to determine which agents might, in addition to interferon, augment the response rates. The situation clinically is analogous to that for tuberculosis in the 1950s and for cancer chemotherapy only a decade or so ago. The prospects of prevention of the progression to cirrhosis, and perhaps in the long term reduction in the incidence of hepatocellular carcinoma, are exciting, and with the introduction of a number of new cytokines available through recombinant technology, each with novel antiviral activities, the future prospects are exciting indeed.

Anti-pre-S antibodies in different groups of patients with hepatitis B virus infection

The anti-pre-S antibody in the samples of sera from normal healthy persons and patients with different clinical types of liver diseases due to hepatitis B virus (HBV) infection was detected by a newly established enzyme-linked immunosorbent assay technique. This test is a blocking assay where anti-pre-S antibody in the patient's serum blocks subsequent addition of horse radish peroxidase-labelled polymerized human serum albumin (pHSA) to the pHSA-receptor site of HBsAg molecules fixed on a solid surface. Anti-pre-S activity was not detected in any from 95 healthy persons who were negative for all HBV-markers or from 105 healthy HBV carriers. In 12 sera from HBV vaccine recipients, anti-pre-S activity was noted in higher proportions compared with anti-HBs, after both the second and third doses of vaccine. Anti-pre-S activity was detected in small proportions of HBsAg positive sera from acute viral hepatitis (4.2%) and chronic active hepatitis (10%). In subacute viral hepatitis patients, the anti-pre-S antibody was totally absent. However, anti-pre-S activity was recorded in high proportions of HBsAg-positive sera from patients with cirrhosis of liver (57.2%) and fulminant hepatitis (41.6%). The anti-pre-S antibodies were assumed to be implicated in the clearance of HBV particles from circulation without causing tissue damage.

Antibodies to translation products of the pre-S1 and pre-S2 regions of the envelope gene of hepatitis B virus in fulminant hepatitis B

Sera from 11 patients with fulminant hepatitis B were tested for antibodies to translation products of the pre-S1 and pre-S2 regions of hepatitis B virus of IgM, IgA and IgG classes, as well as of IgA1, IgA2 and SIgA, with solid-phase enzyme immunoassays using native viral polypeptides. Antibodies to pre-S1 region product of IgM and/or IgA class were detected invariably in six patients who still had detectable hepatitis B surface antigen in serum at the time of clinical presentation. The remaining five patients who had lost HBsAg at presentation had antibodies to pre-S region products of various immunoglobulin classes in higher titers. The five patients with fulminant hepatitis without HBsAg had higher levels of IgA antibodies to pre-S region products than the seven patients with nonfulminant acute hepatitis B who had lost HBsAg: IgA antibody to pre-S1 region product (75.6 +/- 63.8 vs. 2.9 +/- 3.2, p less than 0.01) and IgA antibody to pre-S2 region product (28.9 +/- 25.3 vs. 4.2 +/- 6.9, p less than 0.01). IgA antibodies to pre-S1 and pre-S2 region products were invariably polymeric in fulminant hepatitis B. These findings are compatible with the hypothesis that a heightened humoral antibody response to pre-S1 and pre-S2 region products occurs early during the course of fulminant hepatitis B, participating in severe hepatic injury and early clearance of virus characteristic of this disease.

Cellular immune response to hepatitis B virus antigens. An overview

It has been suggested that the cellular immune response to HBV antigens is responsible for hepatocellular injury in acute and chronic hepatitis B. However, definitive immunological studies have so far been hampered by the lack of appropriate model systems to study HBV antigen-specific T cells. The availability of highly purified and recombinant HBV antigens and of experimental techniques to maintain in continuous growth antigen-specific T cells derived not only from the peripheral blood but also from the liver should allow a better understanding of the fine immunopathogenetical mechanisms involved in viral clearance and liver damage. Whether some important biological characteristics of HBV antigens described in the mouse system, such as the high immunogenicity of the pre-S antigens and the capacity of the nucleocapsid of HBV to be a T cell-dependent and -independent antigen, are relevant to the immunopathogenesis of liver damage during natural HBV infection in man remains to be evaluated.

Antibody response to pre-S2 and hepatitis B virus induced liver damage

Antibodies to the pre-S2 encoded sequence of the hepatitis B virus (HBV) envelope were detected in 83% of patients recovering from acute hepatitis B. Such antibodies were absent in cases showing chronic evolution and were found in less than 10% of chronic hepatitis B cases, with no relation to liver disease activity. In acute infection anti-pre-S2 became detectable when maximum liver damage had already occurred and was still detectable in 30% of the cases tested 5-7 years after recovery, as well as in 40% of healthy individuals with naturally acquired immunity to HBV. 10 out of 20 recipients of a plasma-derived, pre-S2-containing, HB vaccine acquired anti-pre-S2 and had no evidence of concurrent liver damage or of autoimmune reactions to human albumin or of suppression of the anti-HBs response. These findings indicate that the antibody response to pre-S2 is a marker of HBV clearance and has no role in the pathogenesis of HBV-related liver damage.

Methods for the study of pre-S proteins of hepatitis B virus and their antibodies: pathogenetic and clinical implications

The envelope gene of hepatitis B virus (HBV) consists of a large open reading frame which codes 3 different polypeptides by the variable use of 3 contiguous regions: the pre-S1, pre-S2 and S regions. The protein coded by the entire sequence (L protein) is identified by its unique pre-S1 epitopes and has a role in virus assembly and secretion. Pre-S1 antigens are expressed preferentially on virions and are less abundant, but present, on subviral particles. The pre-S2 sequence contains a species-specific receptor for polyalbumin, which has been implicated in virus binding to hepatocytes. Methods have been recently developed to measure pre-S1 and pre-S2 levels in serum and available data indicate that these assays may be useful in prognostic assessment of acute hepatitis B and to measure virus replication in chronic infection, although further studies are certainly needed to define specificity and sensitivity compared to conventional HBV markers. Both pre-S1 and pre-S2 are highly immunogenic and elicit anti-pre-S antibodies. Methods for detection of anti-pre-S in human sera have proved difficult to be developed due to unspecific reaction of serum components with pre-S sequences and epitope variability of the immune response in humans. Anti-pre-S2 seems a marker of recovery from acute infection, while evidence of its involvement in liver damage is weak. Both anti-pre-S2 and anti-pre-S1, but we have limited information on the latter, may be involved in virus neutralization. These issues are particularly relevant for future HB vaccine development, as it is proposed that inclusion of strategic pre-S sequences could increase efficacy.

Antibodies to polymerized human serum albumin in acute and chronic liver disease

Since antibodies to polyalbumin have been noted to occur in patients with hepatitis or cirrhosis, we investigated sera from 219 patients with a variety of acute and chronic liver diseases with and without HBsAg using an ELISA. The prevalence of circulating polyalbumin antibodies was shown to be significantly increased over that of healthy controls (6.7%) in patients with autoimmune chronic active hepatitis (67%), acute viral hepatitis (41%) and fulminant hepatic necrosis (38%), but such antibodies were absent in chronic hepatitis B patients and other liver diseases. Serial studies in acute hepatitis showed evidence of antibodies early in the course of illness with disappearance prior to full recovery. In acute hepatitis B, the presence of polyalbumin antibodies was significantly associated with female sex (p less than 0.01), 3-fold higher transaminase levels and shorter duration of clinical illness (less than 4 weeks in all cases). Polyalbumin antibodies appear to be associated with diseases characterized by active hepatocyte necrosis. Since they are evident early in acute hepatitis B when complexes of polyalbumin and virus are likely, these antibodies may play an adjunctive role to other hepatitis B-related antibodies in the clearance of hepatitis B virus infection.

Detection of antibodies against pre-S1 proteins in sera of patients with hepatitis B virus (HBV) infection

Pre-S1 (large S) proteins are components of the envelope of HBV. The presence of pre-S1 proteins is correlated with viral replication. To test sera of patients with HBV infection for the presence of antibodies against pre-S1 proteins (anti-pre-S1), an E. coli extract containing a pre-S fusion protein covering the greater part of the pre-S1 region was subjected to Western blotting and probed with sera of patients. Anti-pre-S1 was present in the sera of all 4 patients with acute self-limited HBV infection and in the sera of 3 patients with a fulminant course. The antibodies could not be detected in the sera of 6 patients with acute HBV infection entering chronicity, in the sera from 10 HBsAg carriers or in the sera of 25 patients with chronic liver disease, positive for HBsAg and antibodies to hepatitis Delta virus. In an additional study, anti-pre-S1 could not be found in 11 sera from 12 patients with previous HBV infection, positive for anti-HBs and anti-HBc. Antibodies to pre-S1 proteins appear at the early stage of acute resolving HBV infection and seem to play a role in the elimination of the virus. The antibodies are absent in the sera of patients with acute HBV infection entering a chronic course and in the sera of chronic HBsAg-carriers.

Synthesis in yeast of hepatitis B virus surface antigen modified P31 particles by gene modification

The pre-S2 portion of hepatitis B virus surface antigen P31 gene was modified to make gene products resistant to trypsin-like proteases in Saccharomyces cerevisiae. The coding sequence for 6 amino acids (Ser44 - Thr49) including Arg48 was removed, and the altered gene was inserted into an expression vector. The modified HBsAg P31 (M-P31c) gene products, consisting of GP37 and GP34, formed particles having both HBsAg antigenicity and polymerized-albumin receptor activity. Since the M-P31c particles can elicite two kinds of protective antibodies against hepatitis B virus, anti-S and anti-pre-S2 antibodies, the M-P31c particles are expected to be potentially effective to S-nonresponders.