The preS1 domain of hepatitis B virus and IgA cross-react in their binding to the hepatocyte surface

Using a solid-phase assay we have demonstrated specific competition between the preS1 sequence of hepatitis B virus and human IgA in their binding to isolated normal human liver plasma membranes, suggesting molecular mimicry. Monoclonal and polyclonal antibodies raised against virus and IgA epitopes were used to detect and map immunological cross-reactivity to the virus sequence involved in liver cell binding. These findings suggest the existence of a common receptor or of closely related receptors for the attachment of HBV and IgA to human liver cells.

Activation of multidrug resistance (P-glycoprotein) mdr3/mdr1a gene during the development of hepatocellular carcinoma in hepatitis B virus transgenic mice

The expression of multidrug resistance (mdr) genes was investigated in the livers of transgenic mice that express the human hepatitis B virus large envelope polypeptide under the transcriptional control of a liver-specific promoter. These mice develop a storage disease due to the accumulation of a nonsecretable form of hepatitis B surface antigen in the hepatocyte. Liver cell injury is followed by a hepatocellular proliferative response, dysplasia, microscopic nodular hyperplasia, and finally hepatocellular carcinoma. The expression of mdr1, mdr2, and mdr3 genes was analyzed in livers at different stages of the disease by RNase protection assay, Western blot, and immunohistochemistry. RNase protection assay revealed that mdr3 mRNA expression was moderately increased in tissue with microscopic nodular hyperplasia and significantly overexpressed in hepatocellular carcinoma but undetectable in earlier stages of the disease. Western blot using isoform-specific anti-mdr3 antibody demonstrated that the expression of mdr3 protein reflected the steady-state level of mdr3 mRNA. Immunohistochemical analyses using anti-mdr3 isoform-specific antibody and monoclonal antibody C219, which recognizes all the three mdr isoforms, demonstrated selective overexpression in preneoplastic foci during the stage of microscopic nodular hyperplasia as well as in neoplastic hepatocytes in hepatocellular carcinoma. No consistent activation of mdr1 and mdr2 (but occasional coactivation with mdr1) genes during hepatocarcinogenesis was observed. Our results suggest that the hepatocellular mdr3-specific activation mechanism is associated with the late events of hepatocarcinogenesis in this model. The predictable kinetics of mdr gene expression in this transgenic tumor model suggest that it is suitable for future studies of the mechanism of mdr gene activation and the possible pharmacological consequences for mdr3 gene expression of hepatocellular carcinoma.

Expression of HBsAg and HBcAg in liver tissue: correlation with disease activity

The patterns of Hepatitis B surface antigen (HBsAg) and Hepatitis B core antigen (HBcAg) expression were studied in liver biopsies taken from 41 patients with chronic HBV disease. Immunohistochemical methods were used on deparaffinized sections for the identification of HBsAg and HBcAg in liver tissue. Twenty-one of the 41 cases (51.2%) were classified as inactive liver disease and 20 (48.8%) as active liver disease. In liver biopsies with inactive disease, HBsAg demonstrated varying types of cytoplasmic expression in a rather high number of hepatocytes distributed mainly in clusters, while HBcAg was rarely expressed in liver nuclei. On the other hand, in liver biopsies with active disease HBsAg was characterized by a diffuse cytoplasmic expression in a few discrete hepatocytes, while HBcAg was expressed in the nuclei of the hepatocytes in 70% of the cases and in half of the positive cases it was also detected in the cytoplasm. In conclusion, HBsAg expression in a few scattered hepatocytes correlates with active liver disease and positive HBcAg, while varying HBsAg cytoplasmic expression in a rather high number of clustered hepatocytes is related to chronic inactive liver disease and negative expression of HBcAg.

Hepatitis B virus DNA in peripheral-blood mononuclear cells in chronic hepatitis B after HBsAg clearance

In this study, peripheral-blood mononuclear cells from patients with chronic hepatitis B and spontaneous or therapy-induced disappearance of HBsAg were examined for HBV DNA. Samples were evaluated by in situ hybridization and polymerase chain reaction both before and after clearance of HBsAg. By in situ hybridization, positive signals were observed in 2 of 13 samples collected after HBsAg loss, in 8 of 15 samples before HBsAg loss and in 0 of 4 control patients without serological markers of active or prior HBV infection. When polymerase chain reaction analyses were performed, HBV DNA was detected in 5 of 12 HBsAg-negative samples and 10 of 15 HBsAg-positive samples from the study group. Testing of mononuclear cells after disappearance of HBsAg revealed that two of eight patients were HBV DNA positive by in situ hybridization and by polymerase chain reaction, whereas two additional patients were positive by polymerase chain reaction alone. Mononuclear cell-associated HBV DNA was detected between 2 and 9 mo after the disappearance of circulating HBsAg by in situ hybridization and as long as 4 yr later by polymerase chain reaction. These data indicate that patients who have undergone HBsAg seroconversion may nonetheless harbor HBV DNA in their peripheral-blood mononuclear cells for prolonged periods.

Processing of hepatitis B virus surface antigen expressed by recombinant Oka varicella vaccine virus

We have constructed a recombinant Oka varicella vaccine virus expressing hepatitis B virus (HBV) surface antigen (HBsAg). HBsAg was synthesized as 26K and 30K proteins in infected cells and secreted into the culture supernatant as 30K and 35K proteins. Inhibitors and glycosidase treatments, and pulse-chase labelling experiments, revealed the glycosylation process of HBsAg. The latter was synthesized as a non-glycosylated 26K protein and subjected to N-linked glycosylation to form a 30K protein with high mannose glycans. Three species of dimers composed of 26K and 30K subunits were then formed with disulphide bonds. Both subunits of the dimers were further subjected to O-linked glycosylation and conversion from high mannose glycans to complex glycans followed by sialylation. Three species of dimers composed of 30K and 35K subunits were secreted into the culture supernatant as HBsAg particles. HBsAg was synthesized, glycosylated with both N- and O-linked glycans, sialylated, and then secreted into the culture supernatant within 1 h. These modifications of HBsAg by glycans might stabilize its structure and enhance its immunogenicity as a live HBV vaccine.

Receptor for pre-S1(21-47) component of hepatitis B virus on the liver cell: role in virus cell interaction

Attachment of hepatitis B virus to a hepatoblastoma cell line (HepG2) was examined using a synthetic peptide corresponding to the pre-S1 (21-47) region of the envelope protein. Scatchard analysis revealed a single class binding site of Kd 104 +/- 27 nM/l and 5.4 +/- 1.2 x 10(5) sites per cell. Competition of HBV with pre-S1 peptides was dose dependent, and demonstrated it as the dominant binding site. In view of the suggested sequence homology between the peptide and IgA, cross-competition studies were carried out. The results indicate no direct role of IgA receptor in HBV binding. The receptor for the pre-S1 peptide was identified as a single major peptide of molecular weight 31 kD using in-situ ligand receptor crosslinking.

Transferrin receptor mediates uptake and presentation of hepatitis B envelope antigen by T lymphocytes

Human activated T lymphocytes expressing class II molecules are able to present only complex antigens that bind to their own surface receptors, and thus can be captured, internalized, and processed through the class II major histocompatibility complex processing pathway. We have used the antigen-presenting T cell system to identify the viral receptor used by hepatitis B virus (HBV) to enter cells, as well as the sequence of HB envelope antigen (HBenvAg) involved in this interaction. Results show that both CD4+ and CD8+ T clones can process and present HBenvAg to class II-restricted cytotoxic T lymphocytes and that the CD71 transferrin receptor (TfR) is involved in efficient HBenvAg uptake by T cells. Moreover, we provide evidence that the HBenvAg sequence interacting with the T cell surface is contained within the pre-S2 region. Since TfR is also expressed on hepatocytes, it might represent a portal of cellular entry for HBV infection. This system of antigen presentation by T cells may serve as a model to study both lymphocyte receptors used by lymphocytotropic viruses and viral proteins critical to bind them.

Functional study of hepatitis delta virus large antigen in packaging and replication inhibition: role of the amino-terminal leucine zipper

The large hepatitis delta antigen (HDAg) has been found to be essential for the assembly of the hepatitis delta virion. Furthermore, in a cotransfection experiment, the large HDAg itself, without the hepatitis delta virus (HDV) genome and small HDAg, could be packaged into hepatitis B surface antigen (HBsAg) particles. By deletion analysis, it was shown that the amino-terminal leucine zipper domain was dispensable for packaging. The large HDAg could also help in copackaging of the small HDAg into HBsAg particles without the need for HDV RNA. This process was probably mediated through direct interaction of the two HDAgs as a mutated large HDAg whose leucine zipper domain was deleted such that it could not help in copackaging of the small HDAg. This mutated large HDAg did not suppress HDV replication, suggesting that this effect is probably also via protein interaction. These results indicated that functional domains of the large HDAg responsible for packaging with HBsAg particles and for the trans-negative effect on HDV replication can be separated.

Preferential ribosomal scanning is involved in the differential synthesis of the hepatitis B viral surface antigens from subgenomic transcripts

The envelope of the hepatitis B virus (HBV) is composed of three species of proteins, the large (L), middle (M), and major (S) surface proteins (HBsAgs), each of different molecular weights but sharing a common C-terminus. These three HBsAgs, encoded by two species of viral subgenomic transcripts (2.1 and 2.4 kb), which have a heterogenous 5'-terminus, appear in different amounts in both the 42-nm virions and the 22-nm subviral particles. To investigate the involvement of translational control in the differential expression of the L, M, and S proteins, we tested the translational capability of 2.1- and 2.4-kb transcripts in in vitro translation and of 2.1-kb transcripts in in vivo transfection experiments. Results of in vitro translation indicated that a large amount of the L protein and a very small amount of the M and S proteins were synthesized from the 2.4-kb mRNA. Translation of the 2.1-kb mRNA resulted in a 4:1 ratio of the S protein to the M protein. In contrast, translation of a similar 2.1-kb mRNA containing an optimal initiation context (5'-ACCATGG-3') of the pre-S2 region resulted in a reversed ratio, four times as much M protein as S protein. This result was also obtained by transfection of hepatoma cells with plasmid DNAs containing the mutated sequence (5'-ACCATGG-3') of the pre-S2 region. In considering these results, the production of a large amount of the L protein from the 2.4-kb mRNA and the determination of the level of the M protein by the context of translational initiation, we suggest that a preferential translational initiation is involved in the expression of differential amounts of the L, M, and S proteins.

PreS1-specific binding proteins as potential receptors for hepatitis B virus in human hepatocytes

Cellular receptors play an important role in viral pathogenesis. Until now, there has been no reliable information on the receptor(s) for hepatitis B virus (HBV). Therefore, we attempted to identify specific receptors in human hepatocytes using an immunological approach. Anti-idiotypic (Ab2) antibodies were raised in rabbits against our monoclonal antibody (MAb1) F35.25. MAb1 F35.25 (i) recognized the hepatocyte receptor binding site on HBV (located between amino acid residues 21 and 47 of the preS1 sequence) and (ii) blocked the attachment of preS1-positive HBV particles to human hepatocytes. The presence of Ab2 antibodies in rabbit sera was determined by the ability of antisera to inhibit Id (Ab1)/antigen (HBV) recognition. Affinity-purified Ab2 IgGs to F35.25 represented an internal image for the preS1 domain 12-53. Our present studies indicate that Ab2 IgGs to F35.25 (i) recognized the membrane-associated structure of the preS1-specific HBV receptor in a HepG2 cell binding assay, as visualized by immunoenzymatic staining; (ii) strongly bound to a major 35-kDa component and to three other related proteins of 50, 43, and 40 kDa in extracts of HepG2 cells; and (iii) reacted with several soluble and membrane-associated proteins in normal human liver cells. The binding was insensitive to reduction. All preS1 binding proteins were V8 protease sensitive and endoglycosidase H resistant. The 35-kDa species was trypsin resistant and generated a band of 32 kDa by endoglycosidase F treatment. Together, our results suggest that the identified preS1-specific binding proteins may be involved in the putative complex structure of the hepatocyte receptor for HBV.

Search for hepatitis B virus cell receptors reveals binding sites for interleukin 6 on the virus envelope protein

The major target organ for hepatitis B virus (HBV) is the liver. However, cells other than hepatocytes, including peripheral blood lymphocytes and monocytes, may become infected with HBV. The cell receptor binding site was assigned to the preS(21-47) segment of the HBV envelope protein. HBV receptors were detected on human liver and hepatoma cells, on B lymphocytes, and, as shown here, on monocytes, and T cell lines, activated by Escherichia coli lipopolysaccharide and concanavalin A, respectively. The cell receptors for HBV have not been characterized until now. The detection of HBV receptors and their "activation antigen" characteristic on distinct cells suggested paths for identification of the receptors with already defined cell surface proteins. This search revealed that interleukin 6 contains recognition sites for the preS(21-47) sequence and mediates HBV-cell interactions. Thus, HBV belongs to a group of viruses utilizing cytokines or cytokine receptors for replication and interference with the host immune system.

Translational modulation in hepatitis B virus preS-S open reading frame expression

A series of hepatitis B virus open reading frame (ORF) preS-S variants, including mutants in which the relative order of the in-frame start codons (AUG1, AUG2 and AUG3) and nearby sequences had been altered, was expressed both in vivo (in HepG2 hepatoblastoma cells) and in vitro (by T7 promoter-driven transcription followed by translation in a rabbit reticulocyte lysate). The ratio of the synthesis of the large, middle (M) and major (S) proteins or their chimeric counterparts was analysed to study the translational regulation of ORF expression. As expected on the basis of the ribosome scanning model, the AUG sequence context was found to be a prominent factor in determining the different translational behaviour of the two preS-S-specific mRNAs of 2.4 kb (predominantly translated from AUG1) and 2.1 kb (which includes AUG2 and/or AUG3 and can be translated from either). Results from both experimental systems suggested that initiation at internal AUGs in the 2.4 kb RNA is possible. In experiments in vitro, preS-S mutants bearing lesions in a region 5' to AUG2, which has been implicated in AUG2/AUG3 cis repression, showed no increase in the utilization of internal AUGs. In addition, the chimeric envelope polypeptides produced in transfected HepG2 cells in this study were informative with respect to preS-mediated endoplasmic retention: replacement of the preS2 N terminus with that from preS1 generated a chimeric M protein that was glycosylated within the putative preS1 retention sequence ad was not secreted. Thus, the preS1 retention sequence most likely acts inside the lumen of endoplasmic reticulum and its function is insensitive to glycosylation. A similar element might be active at the N terminus of M protein.

Deletion and insertion mutants of HBsAg particles

We have found previously that hybrid 22-nm HBsAg particles can be created by insertion of short antigenic sequences into the HBV major envelope protein. We have now performed a detailed deletion mutagenesis of the S gene of HBV encoding HBsAg. Deletion of the 51 C-terminal amino acids including most of the third and all of the fourth hydrophobic domain of the S protein did not affect particle assembly and secretion. However, secretion of 22-nm particles was abolished by minor deletions in the N-terminal region. Insertion and deletion/substitution mutants carrying a poliovirus epitope at the N-terminus and the preS1 region at the C-terminus have been characterized.

Production of hepatitis B virion-like particles in yeast

We constructed a yeast strain that simultaneously expresses four genes encoding the major S, middle S, large S hepatitis B viral envelope proteins and the core protein under the control of the yeast glyceraldehyde-3-phosphate dehydrogenase promoter and terminator. The lysate from this cell line, examined by immunological, physicochemical methods and electron microscopy, was found to contain spherical particles with a diameter of about 40 nm and a density of 1.25 g/ml. These particles reacted with anti-envelope antibodies, but not with anti-core antibodies. However, core antigenicity appeared upon treatment with 3% Nonidet P-40 that eliminates an outer envelope. These observations suggest production of a virion-like complex structure, or at least its DNA-less analog, consisting of core particle enveloped by antibody-reactive envelope. Such a structure was made only when all the four gene products were synthesized in a yeast cell. This system may be useful for the study of virus structure and assembly, and for improved vaccine development.

The large form of hepatitis delta antigen is crucial for assembly of hepatitis delta virus

The virions of hepatitis delta virus (HDV) contain two species of HDV-specific protein, a large and a small form of hepatitis delta antigen (HDAg). We examined the role of individual HDAgs in virion assembly in cotransfection experiments. First, we constructed a replication-competent HDV mutant expressing only the small HDAg. When cotransfected with a plasmid expressing hepatitis B virus surface antigens to the HuH-7 cells, the mutant did not produce HDV virions, whereas the wild-type HDV clone did. Therefore, though the small HDAg is important for viral replication and is incorporated into the virus, the small-form delta antigen by itself is insufficient for virion formation. When the system was co-transfected with an additional plasmid providing the large HDAg, the HDV virion was then recovered. There was also evidence suggesting that the large HDAg could be copackaged into the HBsAg particles, without the presence of the HDV genome and the small HDAg. The results indicate a crucial role of the large HDAg in HDV assembly.

Preferential expression of the large hepatitis B virus surface antigen gene by an adenovirus-hepatitis B virus recombinant

Using an adenovirus-hepatitis B virus (HBV) recombinant, expression of the HBV surface antigen (HBsAg) genes was examined in various cell lines using S1 nuclease mapping and radioimmunoassay. The steady-state level of the 2.4 kb RNA encoding the large HBsAg was much greater than, or the same as, that of the 2.0 kb RNA, encoding the middle and major HBsAgs, in primate cells, but was negligible in non-primate cells, as is the case in most expression systems. According to the amount of 2.4 kb RNA expressed, cells were classified into three groups: those in which (1) the amount of 2.4 kb RNA was much greater than that of 2.0 kb RNA (HepG2 and JHH-4), (2) the amount of 2.4 kb RNA was the same as that of 2.0 kb (Hul-1, HeLa and other non-hepatic primate cells), and (3) the amount of 2.4 kb RNA was less than one-tenth of that of 2.0 kb RNA (rodent cells). Radioimmunoassay revealed that most HBsAg is located intracellularly in primate cells, but is secreted into the culture medium of rodent cells. The expression of 2.4 kb RNA was unaffected by an inhibitor of DNA synthesis in HepG2 cells, which are of human liver origin, whereas it was strongly inhibited in human non-hepatic HeLa cells.

Defective immune adherence and elimination of hepatitis B surface antigen/antibody complexes in patients with mixed essential cryoglobulinemia type II

Mixed essential cryoglobulinemia type II (monoclonal Ig/polyclonal IgG) is characterized by systemic vasculitis caused by the deposition of circulating immune reactants that include the monoclonal component. Such reactants may include immune complexes (IC) formed from exogenous Ag. IC binding to E C receptor type 1 appears to play a role in transport and buffering of such IC (immune adherence: IA). To define the mechanisms responsible for immune deposition, 7 patients with cryoglobulinemia type II (IgM kappa/polyclonal IgG) and 14 normal volunteers were injected i.v. with hepatitis B surface Ag/antibody complexes. Two minutes after injection, only 19.4% (mean) of the circulating complexes were bound to E in patients as compared with 63.1% in normal subjects. This IA correlated directly with C4 and inversely with the IgM rheumatoid factor (RF) titer. Disappearance of IC was faster in patients (mean elimination rate: 15.7%/min) than in normal subjects (9.3%). In vitro experiments demonstrated that C depletion, interference with IC opsonization by monoclonal IgM RF, and decreased binding of opsonized IC in the presence of monoclonal RF are each associated with decreased IA. These observations suggest that, in patients with cryoglobulinemia type II, monoclonal IgM RF and low C contribute to reducing IA of circulating IC that might be rapidly trapped in tissues, resulting in injury.

Mutational analysis of hepatitis B surface antigen particle assembly and secretion

Cells infected with hepatitis B virus produce both virions and 20-nm subviral (surface antigen or HBsAg) particles; the latter are composed of viral envelope proteins and host-derived lipid. Although hepatitis B virus encodes three envelope proteins (L, M, and S), all of the information required to produce an HBsAg particle resides within the S protein. This polypeptide spans the bilayer at least twice and contains three hydrophobic regions, two of which are known to harbor topogenic signal sequences that direct this transmembrane orientation. We have examined the effects of mutations in these and other regions of the S protein on particle assembly and export. Lesions in the N terminal signal sequence (signal I) can still insert into the endoplasmic reticulum bilayer but do not participate in any of the subsequent steps in assembly. Deletion of the major internal signal (signal II) completely destabilizes the chain. Deletion of the C-terminal hydrophobic domain results in a stable, glycosylated, but nonsecreted chain. However, when coexpressed with wild-type S protein this mutant polypeptide can be incorporated into particles and secreted, indicating that the chain is still competent for some of the distal steps in particle assembly. The correct transmembrane disposition of the N terminus of the molecule is important for particle formation: addition of a heterologous (globin) domain to this region impairs secretion, but the defect can be corrected by provision of an N-terminal signal sequence that restores the proper topology of this region. The resulting chimeric chain is assembled into subviral particles that are secreted with normal efficiency.

Myristylation is involved in intracellular retention of hepatitis B virus envelope proteins

The envelope of hepatitis B virus contains three related proteins, one of which is myristylated. The nonmyristylated small and middle protein are assembled into empty envelope particles which are secreted from cells, whereas the myristylated large envelope protein is mainly found in complete virions and is not secreted in the absence of the nucleocapsid. The block to secretion can be partially overcome by mutation or deletion of the myristylation site. Creation of a myristyl attachment site in the small protein impairs the secretion of empty envelope particles but not their intracellular assembly. Myristylation may therefore play a crucial role in hepatitis B virus replication by channeling the envelope proteins into complete viral particles.

[An immunohistopathological study on intrahepatic distribution of HBeAga/b in biopsied chronic type B hepatitis]

In order to evaluate the role of a expression of HBV-associated, we investigated histological and cytological distribution of HBeAga, HBeAgb, and HBcAg by immunoperoxidase procedure using monochronal antibodies. Materials submitted for this study were needle biopsied specimens obtained from 41 chronic carriers and serial paraffin sections were used for the immunohistological study. The localization of HBeAga/b antigens was limited in hepatocellular nuclei, and hepatocellular cytoplasm was HBeAg negative, HBeAg was detected in 11 cases (33%) of 33 cases with chronic active hepatitis (CAH) and in 5 cases (63%) of 8 cases with chronic inactive hepatitis (CIH). Among the HBeAg positive 16 cases, HBeAgb was demonstrated in 15 cases, however, HBeAga was revealed only each one case of CAH and CIH, respectively. Most of HBeAg positive cells were distributed in the peripheral zone of the hepatic lobules while the positive cells were found in central to midzonal zones of 3 cases CAH and one case of CIH. All in histopathologically HBeAga/b positive cases were also HBeAg positive serologically. On the other hand, in HBeAg sero-positive patients, histological positive rate of HBeAga/b was in 33% in CAH and 50% in CIH.

Mechanism, kinetics, and role of duck hepatitis B virus e-antigen expression in vivo

No duck hepatitis B virus (DHBV) pre-C transcript has been identified so far, and neither the interrelationship of e-antigen (DHBeAg) with the expression of other viral antigens or virus replication nor its function is known. In this study we identified in infected livers a minor transcript from which the precursor protein of DHBeAg could be synthesized. Mutation of the first AUG on this transcript abolished expression of DHBeAg. DHBV genomes containing this mutation were infectious in Pekin ducks, the kinetics of pre-S envelope protein expression and virus secretion were not significantly different from wild-type, and the mutant genomes did not revert to wild-type to a detectable level after several passages. In contrast to pre-S protein, the level of DHBeAg in the serum was independent of the level of viremia, accumulated gradually to a high and constant level after a lag phase, and was also easily detectable in a mixed infection containing less than 0.1% of wild-type in a pre-C mutant virus containing inoculum. These data indicate that precore protein is synthesized from a minor pre-C mRNA with translation initiation at the pre-C AUG codon, and leads to high levels of DHBeAg rather late in infection. High levels of DHBeAg can even be produced efficiently by a very small subpopulation of wild-type virus in a mixed infection with predominantly pre-C mutant virus. Lack of DHBeAg appears to have no effect on DHBV viability and kinetics of virus secretion into the bloodstream when ducklings are infected with the pre-C AUG mutant virus a few days after birth.

Differentiating effect of sodium butyrate on human hepatoma cell lines PLC/PRF/5, HCC-M and HCC-T

The in vitro effect of sodium butyrate (SB) on human hepatoma cell lines PLC/PRF/5, HCC-M and HCC-T was investigated. SB was added at the non-toxic but cytostatic concentration of 1 mM. In all these cell lines, SB reduced cell proliferation and changed the morphology of the cells into a fibroblast-like shape. In PLC/PRF/5, alpha-fetoprotein production and c-myc expression were inhibited. In contrast, gene expression of albumin, one of the normal liver-cell products, and that of integrated hepatitis B virus genome, was increased. In HCC-M and HCC-T, c-myc expression, which was enhanced in the naive state, was reduced. In HCC-M, fos expression was inhibited but the expression of N- and K-ras genes did not change. SB seemed to induce normal or mature properties of hepatocytes in human hepatoma cell lines.

Immune complex binding efficiency of erythrocyte complement receptor 1 (CR1)

C3b-coated immune complexes adhere to the complement receptor 1 (CR1, CD35) on human erythrocytes. This multi-valent binding might be favoured by the known clustering of CR1 and by the multiple C3b-binding sites on each CR1. The size of the CR1 clusters correlates directly with the number of CR1/erythrocytes, and the different structural CR1 alleles bear between two and five C3b-binding sites. Using radiolabelled hepatitis B surface antigen-antibody complexes, we investigated whether CR1 numbers and structural alleles modulate the ability of erythrocytes to bind immune complexes, and assessed if any reorganization of immune complexes takes place at the erythrocyte surface after the initial binding reaction. The binding efficiency (immune complexes/CR1) correlated with CR1 number as determined by the maximal binding at 4 degrees C, the kinetics of binding at 37 degrees C, and the binding in the presence of excess immune complexes and of immune complexes of small size. Binding efficiencies were similar for erythrocytes with low CR1 from normal subjects and patients with AIDS or SLE. A monoclonal antibody blocking the C3b-binding sites (3D9) of CR1 interfered with binding efficiency at a lower concentration on cells bearing low CR1 numbers, suggesting that CR1 clustering is essential. The larger alleles of CR1 (DD and BB) were more efficient than AA alleles. The distribution of immune complexes, visualized by immunofluorescence, was heterogeneous on erythrocytes: about two out of three cells bore between one and 12 immune complexes. No visible immune complex reorganization took place after initial binding, as prefixed erythrocytes displayed the same immune complex distribution and number/erythrocytes as unfixed erythrocytes. The contribution of CR1 alleles in immune complex binding efficiency was confirmed by morphological analysis. These results demonstrate that immune adherence efficiency is the resultant of the CR1 clustering, as well as the particular alleles carried by erythrocytes. Moreover, there is little or no immune complexes surface reorganization after the initial binding reaction.

Clearance of neonatal antiHBc following hepatitis B vaccination: relationship to antiHBs levels

The persistence of antiHBc following hepatitis B virus (HBV) infection is sometimes regarded as evidence of a past infection, and the antiHBc inhibition of T-cell cytotoxic killing of HBV may be one way of tolerance leading to the carrier state. A model for studying the possibility of an immune tolerance occurring in the human situation was to observe the natural clearance rate of total antiHBc in babies who have acquired naturally maternal transferred antibodies, and to compare antiHBcIgG clearance and development of hepatitis B surface antigenaemia with the level of antibody to HBsAg (antiHBs), which is normally known to be virucidal. Two hundred and ninety-one normal infants who received hepatitis B vaccination in 1984 were followed and studied at six months, one, two and four years. AntiHBc was not found in any control infants born of HBsAg negative mothers. One child became antiHBc positive at four years reflecting acquired infection when antiHBs level had fallen to 36 mIU per ml. AntiHBc cleared in 66% of HBsAg pos./'e' neg. children at one year and completely by two years. In contrast, antiHBc clearance in children born of HBsAg pos./'e' pos. was inversely related to the antiHBs levels. Those with antiHBs levels over 50 mIU per ml cleared antiHBc more rapidly and were HBsAg negative, whereas in 28/49 (57%) HBs antigenaemia were associated more often with antiHBs under 10 mIU per ml and in 2/43 (5%) at levels between 11 to 50 mIU per ml. Two children who had later developed HBs antigenaemia in the presence of antiHBs after responding to earlier passive-active immunisation, suggest either defective antiHBs and/or the development of mutants or variants.(ABSTRACT TRUNCATED AT 250 WORDS)