Human serum albumin and the enigma of chronic hepatitis type B

Antibodies to polymerized albumin in woodchuck hepatitis virus infection

Polymerized human serum albumin may play a role in the entry of hepatitis B virus into hepatocytes, and antibodies to polyalbumin that frequently appear during acute hepatitis may aid the process of viral clearance. We developed an enzyme-linked immunosorbent assay for antibodies to polymerized woodchuck albumin to enable us to evaluate further the role of these antibodies in an animal model system. Sera from 17 uninfected adult woodchucks and 8 newborns showed no binding to control plates coated with woodchuck transferrin, woodchuck albumin, or polymerized human serum albumin. One of 8 newborn animals demonstrated a significant antibody titer to polymerized woodchuck albumin, and 16 of 17 adults without evidence of prior woodchuck hepatitis virus infection had measurable serum antibody titers. Antibodies to polymerized woodchuck albumin could be adsorbed by prior incubation with the antigen. In 2 animals subjected to experimental infection, significant rises in polyalbumin antibody were seen. When 4 adult woodchucks were immunized with woodchuck polyalbumin, significant increases in antibody titer were observed in 2 of the 4 animals. Of the 4 immunized and 4 controls subsequently challenged with woodchuck hepatitis virus, 7 became viremic and all 8 developed antibody to woodchuck hepatitis virus core antigen. We conclude that naturally occurring antibodies to polymerized woodchuck albumin are observed in most adult woodchucks in the absence of woodchuck hepatitis virus infection and do not seem to confer immunity against infection with this virus.

Properties of a recombinant yeast-derived hepatitis B surface antigen containing S, preS2 and preS1 antigenic domains

Yeast cells have been engineered to express mixed HBsAg particles containing the S and a modified large (L*) protein. Their construction resulted in reduced protease sensitivity, reduced glycosylation and complete inactivation of the polymerized human albumin binding site. The particles exposed the S, preS1 and preS2 antigenic determinants and induced an immune response against the three domains. Highly purified preparations have been obtained and are presently being tested in human volunteers.

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.

Regulation of the immune response to hepatitis B virus and human serum albumin. III. Induction of anti-albumin antibody secretion in vitro by C-gene-derived proteins in peripheral B cells from chronic carriers of HBsAg

The circulatory pool of B cells from the majority (11/13) of chronic hepatitis B surface antigen (HBsAg) carriers contained sensitized B cells with the capacity to secrete IgG antibodies with specificity for human serum albumin (HSA), when stimulated with E. coli-derived core protein at low concentrations in vitro. The IgG anti-HSA secretion was dependent upon and regulated by T cells, and optimal secretion was obtained at T/B-cell ratios of 1.0-4.0, varying for different individuals. The level of anti-HSA secretion was higher for patients with on-going viral replication as assessed by hepatitis B virus (HBV)-DNA in serum. Culture supernatants containing anti-HSA antibodies also contained anti-HBc antibodies, as detected by enzyme-linked immunosorbent assay (ELISA) where the solid phase was charged with E. coli-derived core protein, or the synthetic peptides corresponding to the 75-84 and 132-147 sequences in the C region of HBV. In contrast, IgG anti-HBc (E. coli-derived), but no anti-HSA or anti-HBc 75-84, 132-147 antibodies, were detected at similar T/B-cell ratios in cell cultures from 5/6 individuals with naturally acquired immunity to hepatitis B. These data indicate that peripheral B cells from the majority of HB-immune donors are sensitized to unique (e.g. non-albumin associated) structures in the nucleocapsid of HBV, while B cells in the majority of chronic HBsAg carriers are sensitized to linear C-gene-derived structures in association with the host 'self'-component HSA.

Immunogenicity and safety in newborns of a new recombinant hepatitis B vaccine containing the S and pre-S2 antigens

A study to evaluate the safety and immunogenicity of a recombinant hepatitis B vaccine containing the S and pre-S2 antigens (GenHevac B Pasteur) was conducted in healthy newborn infants. All infants received 20 micrograms of vaccine within 24 h of birth and at 1 and 2 months with a booster injection at month 12. The vaccine was administered alone in 19 infants born to low risk mothers, i.e. surface antigen (HBsAg)-negative and antibody to the core antigen (Anti-HBc)-positive mothers. The vaccine was administered in combination with 100 IU hepatitis B immune globulin (HBIg) at birth and 1 month in 18 infants born to high risk mothers, i.e. HBsAg positive mothers. In the group not receiving HBIg, the anti-HBs seroconversion rate at the 10 mIU ml-1 threshold was 50% 1 month after the first injection. In both groups, the anti-HBs seroconversion rates were 100% 1 month after the third injection and greater than 85% 1 month after the second injection. After the booster injection greater than 90% of the infants had an anti-HBs titre greater than 1000 mIU ml-1 which will probably provide them with adequate protection for several years. The kinetics of the anti-pre-S2 response was similar to that of the anti-HBs response and 100% of infants in both groups had seroconverted 1 month after the second injection of the vaccine. The side effects were scarce, all mild and transient.(ABSTRACT TRUNCATED AT 250 WORDS)

Elimination of circulatory IgM anti-HSA precedes anti-HBe seroconversion in patients with CAH type B

The presence of IgM and IgA antibodies with specificity for human serum albumin (HSA) were consecutively analyzed in serum samples from four patients with biopsy verified CAH type B during seroconversion in the HBe/anti-HBe antigen system. Circulatory IgM anti-HSA antibodies were present during HBe antigenemia. The antibody titers fluctuated, decreased, and were finally lost from the circulation. After the disappearance of IgM anti-HSA antibodies, seroconversion to anti-HBe reactivity occurred and a quiescent phase of the disease was established, as judged by normalization of transaminases and absence of circulatory HBV-DNA. IgA anti-HSA antibodies persisted in the circulation after the elimination of IgM anti-HSA and seroconversion to anti-HBe reactivity. For one of the patients, a dramatic increase in titers was followed by elimination of IgA anti-HSA and seroconversion to anti-HBs. The data indicate that the host "self"-component HSA, when associated with "foreign" HBe or HBs antigenic structures, elicit immune responses to HSA, preventing the adequate development of anti-HBe and anti-HBs. The cessation of anti-HSA reactivity, however, seemed to permit subsequent sensitization to HBe and HBs antigenic determinants, as detected by the presence of circulatory antibodies.

Regulation of the immune response to hepatitis B virus and human serum albumin. II. Spontaneous secretion of antibodies with specificity for albumin in patients with chronic hepatitis B virus infection

Peripheral B and T cells sensitized to human serum albumin (HSA) were found in a cohort of patients chronically infected with hepatitis B virus (HBV). Throughout this study, two groups of symptomatic chronic hepatitis B surface antigen (HBsAg) carriers could be distinguished, characterized by divergent T-cell regulation of the spontaneous IgG anti-HSA secretion. Patients in a quiescent phase of the disease [patients with chronic persistent hepatitis B (CPH), anti-HBe reactivity and absence of viral replication, group A] had circulatory in vivo HBsAg-HSA preactivated B cells with the capacity to secrete spontaneously IgG antibodies with specificity for HSA when isolated and cultured. The addition of autologous T lymphocytes at a T/B-cell ratio of 8.0 suppressed the spontaneous anti-HSA secretion. In contrast, patients in an active stage of the disease exhibited in vivo preactivated T cells exerting helper cell functions on the spontaneous IgG anti-HSA secretion. Memory T cells, sensitized to low concentrations of HBsAg-HSA with disparate regulatory functions, were also detectable in the two groups of patients.

Absence of pre-S2 antibodies in natural hepatitis B virus infection

Antibodies to the host "self" component human serum albumin (HSA) and to its receptor are induced by the pre-S2 encoded aminoacid sequence (120-145) of the middle surface protein on the hepatitis B virus (HBV) particle and are produced as part of the immune response during acute HBV-infection. The antibodies disappeared rapidly during the convalescence phase and were not detectable in patients with naturally acquired immunity to HB. These data raise questions about the importance of anti-pre-S2 antibodies for long-term protection against HBV-infection. The coexistence of HBV-DNA with antibodies to native HSA (nHSA) in 13/16 patients with biopsy proven liver disease and of HBV-DNA with anti-pre-S2 in 10/13 patients argues against the attribution of virus eliminating properties to antibodies directed against pre-S2 determinants. In fact circulating anti-nHSA and anti-pre-S2 persisted in 16/17 and 13/17 patients, respectively, with major HBV-induced liver disease but not in symptomless HBsAg carriers. This finding suggests that continuous production of antibodies against the "self" component HSA and/or its receptor structures are associated with the pathogenesis of chronic HBV-induced liver disease. Pre-S2 coded peptide sequences should thus not be incorporated into HB vaccines.