HBsAg retention sensitizes the hepatocyte to injury by physiological concentrations of interferon-gamma

Complex HBV populations with mutations in core promoter, C gene, and pre-S region are associated with development of cirrhosis in long-term renal transplant recipients

Long-term immunosuppressed renal transplant recipients with chronic hepatitis B virus (HBV) infection often develop liver cirrhosis (LC) and end-stage liver disease (ESLD). This study investigated accumulation and persistence of specific HBV mutants in relation to the clinical course in these patients (n = 38; mean follow-up, 3.5 years). HBV was analyzed longitudinally via length polymorphism of polymerase chain reaction (PCR) fragments (median, 6.5 serum samples per patient) as well as by cloning and partial sequencing of 346 full-length HBV genomes. Fourteen patients (group 1) developed LC or died from ESLD, whereas 24 patients (group 2) showed no evidence of LC during follow-up. Development of LC and ESLD was associated with persistence of HBV mutant populations characterized by deletions/insertions in core promoter plus deletions in the C gene and/or deletions in the pre-S region (86% of group 1 vs. 17% of group 2; P <.0001). HBV without these mutations or with core promoter mutations alone were predominantly found in group 2 (14% of group 1 vs. 75% of group 2). In patients infected with core promoter mutants, the additional appearance and persistence of deletions in the C gene and/or the pre-S region were accompanied or followed by development of LC and ESLD. The mutations were distributed on individual genomes in various combinations, leading to a high complexity of the virus population. In conclusion, these data suggest that accumulation and persistence of specific HBV populations characterized by mutations in 3 subgenomic regions play a role in pathogenesis of LC and ESLD in long-term renal transplant recipients.

The effect of IFNgamma on the hepatocyte: cell cycle and apoptosis

The inflammatory cytokine interferon gamma (IFNgamma) can cause cell cycle arrest and apoptosis in the hepatocyte. Primarily these processes are protective but in chronic liver disease oncogenic mutations may prosper. IFNgamma signalling is discussed showing how p53 is induced to cause cell cycle arrest. While caspases are are known to be responsible for IFNgamma induced apoptosis, how they are activated is unclear. Potential mechanisms are reviewed.

Non-cytolytic inhibition of hepatitis B virus replication in human hepatocytes

BACKGROUND/AIMS

Interferon-gamma (IFN-gamma) has been shown to abolish hepatitis B virus (HBV) gene expression and replication in HBV transgenic mice without destroying infected hepatocytes. We investigated the characteristics of IFN-gamma induced non-cytolytic inhibition of viral replication in human HBV infection.

METHODS

We used an in vitro model where lymphocytes from 15 HBsAg positive patients were co-cultured with transfected hepatocytes supporting HBV replication. The effector and target cells were separated by a membrane, which allowed transfer of soluble factors only, to determine whether IFN-gamma produced from antigen-specific CD4+ T cells or mitogen stimulated lymphocytes inhibits HBV replication.

RESULTS

IFN-gamma produced following lymphocyte stimulation reduced cytoplasmic HBV DNA in the target cells. The degree of HBV DNA reduction correlated with the level of IFN-gamma in the supernatants. Further investigations using naturally infected human hepatocytes confirmed that recombinant IFN-gamma reduces HBV DNA and HBV RNA in these cells as well, in parallel with the induction of cellular interferon-responsive genes. This antiviral effect was without significant cytotoxicity and was more pronounced in hepatocytes from patients with low HBV replication.

CONCLUSIONS

These results provide direct evidence that IFN-gamma can inhibit both HBV transcription and replication in human hepatocytes without cell lysis.

Concerted action of the FasL/Fas and perforin/granzyme A and B pathways is mandatory for the development of early viral hepatitis but not for recovery from viral infection

Cytotoxic T lymphocytes (CTL) play a major role in the recovery from primary viral infections and the accompanying tissue injuries. However, it is unclear to what extent the two main cytolytic pathways, perforin-granzyme A and B exocytosis and Fas ligand (FasL)-Fas interaction, contribute to these processes. Here we have employed mouse strains with either spontaneous mutations or targeted gene defects in one or more components of either of the two cytolytic pathways to analyze the molecular basis of viral clearance and induction of hepatitis during lymphocytic choriomeningitis virus infection. Our results reveal that viral clearance is solely dependent on perforin but that virus-induced liver damage only occurs when both the FasL/Fas and the perforin pathways, including granzymes A and B, are simultaneously activated. The finding that development of hepatitis but not viral clearance is dependent on the concomitant activation of FasL-Fas and perforin-granzymes may be helpful in designing novel strategies to prevent hepatic failures during viral infections.

Activating immunity in the liver. I. Liver dendritic cells (but not hepatocytes) are potent activators of IFN-gamma release by liver NKT cells

A prominent subset of the hepatic innate immune system is alpha-galactosylceramide (alphaGalCer)-reactive, (CD4(+) and CD4(-)CD8(-)) CD1d-restricted NKT cells. We investigated in C57BL/6 (B6) mice which hepatic cell type stimulates hepatic NKT cell activation. Surface expression of CD1d but not CD40, CD80, or CD86 costimulator molecules was detected in hepatocytes. Pulsed in vitro or in vivo with alphaGalCer, hepatocytes triggered IL-4 release by liver NKT cells but required exogenous IL-12 to trigger IFN-gamma release by NKT cells. Liver dendritic cells (DC) isolated from nontreated mice showed low surface expression of MHC, CD1d, and CD40, CD80, or CD86 costimulator molecules that were strikingly up-regulated after alphaGalCer injection. Although liver CD11c(+) DC displayed lower CD1d surface expression than hepatocytes, they were potent stimulators of IFN-gamma and IL-4 release by liver NKT when pulsed with alphaGalCer in vitro or in vivo. Liver DC are thus potent stimulators of proinflammatory cytokine release by NKT cells, are activated themselves in the process of NKT cell activation, and express an activated phenotype after the NKT cell population is eliminated following alphaGalCer stimulation.

Pathomorphological Characteristics and Pathogenesis of Viral Hepatitis

Viral hepatitis (VH) is an inflammatory reaction of the liver to hepatotropic viruses. Acute VH can be classified according to the virus and type of necrosis. Chronic hepatitis (CH) might be active, persistent or lobular based on previous classification. More recently the grade (necroinflammatory activity) and stage (fibrosis and architectural distorsion) of CH have been distinguished and scored. Apoptosis and necrosis probably coexist in VH and contribute to hepatocyte death. Several "death factors", such as transforming growth factor b, Apo1/Fas and tumor necrosis factor play a role in the execution of cell death. Injury of hepatocytes during viral infection can occur as a direct effect of the virus or as a result of the host immune response. Expression of different viral antigens can be detected during VH and might be visualized. Phenotyping of the portal inflammatory cell infiltrate in CH has shown a T-cell zone comprised of CD4+ helper T cells and CD8+ supressor/cytotoxic T cells at the periphery of the lobules. The pathogenetic mechanisms responsible for the final outcome of viral infection depend on viral factors (such as genotype, mutation etc.), virus-host interaction, expression of viral protein, several cytokines etc. which finally lead to the well known histological alterations of viral hepatitis.

Effect of hepatocyte apoptosis induced by TNF-α on acute severe hepatitis in mouse models

AIM: To study the effect of hepatocyte apoptosis and necrosis induced by TNF-α on the pathogenesis of acute severe hepatitis (ASH).

METHODS: The model of ASH was prepared in D-galactosamine (GalN) sensitized BALB/c mice by injection of either endotoxin (ET) or tumor necrosis factor-α (TNF-α). Morphological changes of apoptotic hepatocytes were studied by both light and electron microscope and in site end labeling method (ISEL). Molecular biological changes of DNA ladder were observed by electrophoresis of extract from liver tissues. Biochemical changes were measured by alanine aminotransferase (ALT), aspartic aminotransferase (AST) and TNF-α. The relation between apoptosis and necrosis was evaluated simultaneously.

RESULTS: The sequence of hepatocyte apoptosis, necrosis, and final death from ASH was observed both in GalN/ET and GalN/TNF-α group. Apoptosis was prominent at 3.5 h and 6 h after injection of inducer, while necrosis became dominant at 9 h after challenge. The appearance of apoptosis was earlier in GalN/TNF-α group than that in GalN/ET group. Pretreatment of mice with antiTNF IgG1 may completely prevent the liver injury induced by GalN/ET.

CONCLUSION: TNF-α can cause liver damage by inducing hepatic apoptosis and necrosis in mice with endotoxemia.

Break of T cell ignorance to a viral antigen in the liver induces hepatitis

To study peripheral tolerance of CD8 T cells to a classically MHC-restricted peptide Ag expressed in hepatocytes, ALB1 transgenic (tg) mice expressing the CTL epitope GP33 of the lymphocytic choriomeningitis virus glycoprotein under control of the mouse albumin promoter were generated. ALB1 mice exclusively expressed the GP33 transgene in the liver and, at a 100- to 1000-fold lower level, in the thymus. TCR-tg mice specific for the GP33 epitope were used to directly follow GP33-specific T cells in vivo. These experiments revealed that 1) thymic expression of the GP33 transgene led to incomplete central deletion of TCR-tg cells; and 2) peripheral TCR-tg cells in ALB1 mice ignored the GP33 transgene expressed in hepatocytes. Ignorance of adoptively transferred TCR-tg cells in ALB1 mice was broken by infection with lymphocytic choriomeningitis virus, leading to induction of hepatitis in ALB1, but not in control, mice. Taken together, we have established a novel model of virus-induced CD8 T cell-mediated autoimmune hepatitis in mice and demonstrate that naive CD8 T cells may ignore Ags expressed in the liver.

Ongoing murine T1 or T2 immune responses to the hepatitis B surface antigen are excluded from the liver that expresses transgene-encoded hepatitis B surface antigen

Different protein- or DNA-based vaccination techniques are available that prime potent humoral and cellular, T1 or T2 immune responses to the hepatitis B surface Ag (HBsAg) in mice. T1 and T2 are immune responses with isotype profile indicating Th1 and Th2 immunoregulation. We tested whether HBsAg-specific immune responses can be established in transgenic mice that express HBsAg in the liver (HBs-tg mice) using either these different vaccination techniques or an adoptive transfer system. HBsAg-specific responses could not be primed in HBs-tg mice with the established, potent vaccine delivery techniques. In contrast, adoptive transfers of T1- and T2-type HBsAg-immune spleen cells into congenic HBs-tg hosts (that were not conditioned by pretreatment) suppressed HBsAg antigenemia and gave rise to HBsAg-specific serum Ab titers. The establishment of continuously rising anti-HBsAg serum Ab levels with alternative isotype profiles (reflecting T1 or T2 polarization) in transplanted HBs-tg hosts required donor CD4+ T cell-dependent restimulation of adoptively transferred immune cells by transgene-derived HBsAg. Injections of HBsAg-specific Abs into HBs-tg mice did not establish stable humoral immunity. The expanding T1 or T2 immune responses to HBsAg in HBs-tg hosts did not suppress transgene-directed HBsAg expression in the liver and did not induce liver injury. In addition to priming functional antiviral effector cells, the conditioning of the liver microenvironment to enable delivery of antiviral effector functions to this organ are therefore critical for effective antiviral defense. A major challenge in the development of a therapeutic vaccine against chronic hepatitis B or C virus infection is thus the efficient targeting of specifically induced immune effector specificities to the liver.

Immunopathogenesis of hepatitis B virus recurrence after liver transplantation

BACKGROUND AND AIMS

Hepatitis B virus (HBV) recurrence after orthotopic liver transplantation is associated with inflammatory graft changes, despite immunosuppression and donor/recipient HLA mismatch. We investigated whether immune mechanisms are involved in the pathogenesis of hepatitis B after liver transplantation.

METHODS

The virus-specific T helper (Th) cell response, activation of Th1/Th2 subpopulations, donor/recipient HLA, and expression of tumor necrosis factor (TNF)-alpha/TNF receptors were determined in 28 patients who underwent transplantation for HBV-related cirrhosis (17 with HBV recurrence and 11 without recurrence) in comparison to 30 nontransplant patients with chronic hepatitis B.

RESULTS

Orthotopic liver transplantation recipients with HBV recurrence showed significant hepatitis B core antigen-specific T-cell proliferation, comparable to nontransplant patients, which was not present in transplant recipients without recurrence. In addition, hepatic and serum interleukin (IL)-2, interferon-gamma, and TNF-alpha were enhanced, without changes in IL-4 and IL-10. Phenotypically, hepatic infiltrates in allografts with HBV recurrence were comprised of CD4+ lymphocytes and macrophages with a correlation between interferon-gamma- and TNF-alpha-producing cells and the degree of necroinflammatory activity. There was a marked up-regulation of both TNF-alpha receptors, significantly greater than in nontransplant patients.

CONCLUSIONS

These findings suggest that despite immunosuppression, HLA class I-independent immune mechanisms have a significant pathogenic role in liver damage associated with HBV recurrence after liver transplantation.

Lethal hepatic apoptosis mediated by tumor necrosis factor receptor, unlike Fas-mediated apoptosis, requires hepatocyte sensitization in mice

BACKGROUND/AIMS

Tumor necrosis factor a (TNF-alpha) and Fas ligand are apoptotic cell-death mediators that act by binding to their responsive receptors. The aims of this study were to assess the differences between liver cell deaths induced by TNF-alpha and anti-Fas antibody, and to investigate the mechanism by which GalN sensitizes the hepatocyte to injury by TNF-alpha.

METHODS

TNF-alpha or anti-Fas antibody was injected into BALB/c mice sensitized or unsensitized by D-galactosamine (GalN). Liver injury was assessed biochemically and histologically. The expressions of TNF receptor (TNFR)1 and TNFR2 mRNA in the liver were determined by Northern blot analysis. Nuclear factor-kappaB (NF-kappaB) DNA binding activity was determined by gel shift assay.

RESULTS

In GalN-sensitized mice, hepatocyte apoptosis and liver failure were observed after TNF-alpha injection, but neither occurred in unsensitized mice. Microscopically, GalN preceding TNF-alpha caused massive hemorrhagic liver damage with fragmented hepatocyte nuclei resembling effects of anti-Fas antibody, but GalN largely failed to sensitize to injury by this antibody. TNFR1 mRNA expression in the liver was upregulated within 3 h after GalN administration, and anti-TNFR1 antibody protected GalN-sensitized mice from hepatotoxic effects of TNF-alpha. GalN treatment failed to affect TNF-alpha-induced NF-kappaB activation.

CONCLUSIONS

Unlike Fas-related apoptosis, TNFR-mediated apoptosis requires hepatocyte sensitization involving TNFR1 upregulation.

Clearance of HCV RNA in a chronic hepatitis C virus-infected patient during acute hepatitis B virus superinfection

The routes of hepatitis B virus and hepatitis C virus transmission are quite similar and coexistence of both viruses in one patient is not a rare phenomenon. Until now, the natural course of liver diseases induced by coinfections has not been well documented and the mechanisms of interaction between the two viruses and the human host have not been fully clarified. We report the case of a patient suffering from chronic hepatitis due to hepatitis C virus who developed an acute hepatitis B virus superinfection. Serum hepatitis C virus ribonucleic acid became undetectable by reverse transcriptase/polymerase chain reaction at diagnosis of acute hepatitis B virus infection. At the same time, there was a striking increase in the serum concentrations of the antibodies against C22 and C33c hepatitis C virus antigens. Four months after clinical resolution of the acute hepatitis, hepatitis B surface antigen was undetectable in serum and three months later antibodies against hepatitis B surface antigen appeared. Two years after acute hepatitis B virus infection, the patient has had no relapse of markers for viral replication of hepatitis B virus. Transaminases are within the reference range and hepatitis C virus ribonucleic acid is undetectable in both serum and liver tissue. We hypothesize that acute hepatitis B virus infection stimulated a specific humoral response against hepatitis C virus as well as triggering non-specific defense mechanisms which finally eliminated both viruses.

A Critical Role for Antigen-Specific Th1 Cells in Acute Liver Injury in Mice

A novel liver injury model was established in mice by targeting of OVA-containing liposomes into the liver, followed by adoptive transfer of OVA-specific Th1 cells. Combined treatment of mice with OVA-containing liposomes and Th1 cell transfer caused an increase in serum transaminase activity that was paralleled with an elevation of serum IFN-γ levels. In sharp contrast, OVA-specific Th2 cell transfer resulted in an increase of serum IL-4 levels, but did not induce liver injury. Neither NK, NK T, nor CD8+ T cells were required for the Th1-induced liver injury. The liver injury was blocked by anti-IFN-γ mAb and anti-TNF-α mAb, but not by anti-Fas ligand mAb. The Fas/Fas ligand independency was also demonstrated using Fas-deficient lpr mice. These findings indicate that Th1 cells are the major effector cells in acute liver injury.

Utilization of transgenic mice replicating high levels of hepatitis B virus for antiviral evaluation of lamivudine

A recently developed transgenic mouse strain which expresses high levels of hepatitis B virus (HBV) was studied as a model for evaluation of potential chemotherapeutic agents. Lamivudine ([-]2'-deoxy-3'-thiacytidine), known to reduce hepatitis B viremia in human patients, and zidovudine (3'-azido-3'-deoxythymidine), previously shown to be ineffective for HBV infections in man, were used in parallel in this transgenic animal model. Orally administered lamivudine at dosages of 100, 50, and 25 mg/kg per day given once a day for 21 days significantly decreased serum and liver HBV DNA titers in a dose-responsive manner. Zidovudine (approximately 22 mg/kg per day) administered in the drinking water for 21 days was not effective in reducing these HBV parameters as compared to transgenic placebo-treated controls. The serum HBV DNA titers rebounded to high levels 1 week after cessation of lamivudine treatment. Male and female mice responded in a similar manner to these therapies. The results using this transgenic mouse model were similar to what would be predicted from treatment of HBV-infected human patients with lamivudine and zidovudine, and indicate these mice may be useful as a small animal chemotherapeutic model for study of potential HBV inhibitors.

IRF-1 is an essential mediator in IFN-gamma-induced cell cycle arrest and apoptosis of primary cultured hepatocytes

IFN-gamma induces cell cycle arrest and p53-independent apoptosis in primary cultured hepatocytes. However, it is not yet understood what molecules regulate the mechanism. We report here that interferon regulatory factor 1 (IRF-1) is an essential molecule in these phenomena. Hepatocytes from IRF-1-deficient mice were completely resistant to IFN-gamma in apoptosis indicated by three different hallmarks such as LDH release, DNA fragmentation and the activation of caspase-3 family. Caspase-1 expression was little detected in hepatocytes, and constitutive and IFN-gamma-induced mRNA expression of Fas or caspase-3 did not change in between wild type and IRF-1-deficient hepatocytes. Expression of IFN-gamma-inducible caspase, caspase-11, did not change either. Thus, it is unlikely that these molecules directly regulate the mechanisms. Interestingly, IRF-1-deficient hepatocytes were also resistant to IFN-gamma-induced cell cycle arrest despite IFN-gamma-induced cell cycle arrest and apoptosis are regulated by independent pathways. Results by Northern blot analysis showed that IFN-gamma-induced but not constitutive p53 mRNA expression was regulated by IRF-1. In fact, IFN-gamma did not induce cell cycle arrest in p53-deficient hepatocytes. Taken together, IRF-1 mediates IFN-gamma signaling into primary hepatocytes for cell cycle arrest via p53 expression and for apoptosis.

Acute liver injury following infection with a cytopathic strain of duck hepatitis B virus

A variant avian hepadnavirus that has been shown to destroy hepatocytes in vitro was found to be cytopathic in vivo. A single amino acid change of glycine to glutamic acid at position 133 (G133E) in the preS protein of duck hepatitis B virus (DHBV) caused an increase in the intranuclear pool of viral covalently closed circular DNA (cccDNA), resulting in a transient elevation of viral replication and eventual hepatocyte destruction. In vivo viral infection with the G133E virus was compared with infection with wild-type virus over a 72-day period. Birds were inoculated with virus at day 2 post-hatch to ensure a high percentage of infected hepatocytes and potential persistence of virus. Birds infected with the G133E virus had increased periportal cellular proliferation and numerous lysed apoptotic hepatocytes following 100% infection of hepatocytes. The liver damage within G133E virus-infected birds subsided over time, resulting in mild chronic hepatitis that was similar to that observed within wild-type virus-infected birds. The subsidence of liver damage in G133E virus-infected birds coincided with a reduction of viral cccDNA to wild-type virus levels in the liver. Our study indicates that maintenance of wild-type levels of viral cccDNA promotes persistence of virus infection by establishing a noncytopathic infection.

Functional analysis of HBV genomes from patients with fulminant hepatitis

Two previous case reports suggest that hepatitis B virus (HBV) core promoter variants with a high replication competence contribute to the pathogenesis of fulminant hepatitis B (FHB). We recently found in HBV genomes from patients with FHB an accumulation of mutations within the core promoter region. Therefore, the aim of this study was to investigate the phenotype of these HBV variants. Replication competence and expression of hepatitis B surface antigen (HBsAg) and hepatitis B e antigen (HBeAg) of viral genomes from seven patients with FHB and one patient with fulminant recurrent hepatitis after liver transplantation were analyzed by transfection experiments in human hepatoma cells. Compared with wild-type virus, the HBV variants from the seven patients with FHB produced similar or slightly lower levels of intracellular replicative intermediates and extracellular viral particles. In contrast, the HBV genomes from the patient with fulminant recurrent hepatitis synthesized and secreted significantly more HBV DNA. All genomes tested expressed similar or even higher levels of HBeAg compared with wild-type virus, except for those from four patients with a precore stop codon mutation in the respective dominant viral populations. The level of HBsAg produced by all variant genomes was similar or reduced compared with wild-type virus. These data indicate that in some cases HBV variants with enhanced replication competence and/or a defect in HBeAg expression may contribute to the development of FHB. However, neither phenotype is an essential prerequisite; thus, an additional role of other viral or host factors in the pathogenesis of FHB is suggested.

Dendritic Cell Immunization Breaks Cytotoxic T Lymphocyte Tolerance in Hepatitis B Virus Transgenic Mice

Hepatitis B virus (HBV) transgenic mice that are immunologically tolerant to HBV-encoded Ags represent a model of chronic HBV infection suitable for the development of therapeutic immunization strategies before testing in humans. Five lineages of HBV transgenic mice were immunized with plasmid DNA that encodes hepatitis B surface Ag (HBsAg) or with cytokine-activated bone marrow-derived dendritic cells (DCs) in an attempt to break tolerance to HBsAg at the B and T cell levels. DNA immunization stimulated an Ab response but not a cytotoxic T lymphocyte response to HBsAg in two of the five transgenic lineages studied. In contrast, infusion of activated transgenic or nontransgenic DCs stimulated a splenic CTL response in all three transgenic lineages immunized in this manner at precursor frequencies comparable to those in nontransgenic mice, indicating that DC function is normal, and HBsAg-specific CTLs are present but functionally silent in these transgenic animals. Importantly, none of the animals developed hepatitis or displayed suppressed viral gene expression or replication following either DNA immunization or DC administration even in the presence of anti-hepatitis B surface (HBs) Abs and HBs-specific CTLs. These results indicate that Ag presentation by cytokine-activated DCs can break tolerance and trigger an anti-viral CTL response in HBV transgenic mice, and they suggest that this strategy is more efficient than DNA immunization in this setting. Nonetheless, more efficient immunization strategies are needed to stimulate an immune response of sufficient quality and magnitude to achieve an immunotherapeutic antiviral effect.

Donor-recipient sharing of HLA class II alleles predicts earlier recurrence and accelerated progression of hepatitis C following liver transplantation

Both direct viral cytopathic effects and host immune responses appear to be important in the pathogenesis of hepatitis C virus (HCV) infection. Liver transplantation provides a means to explore the role of the immune system in the development of HCV-related liver damage through comparing the natural history of HCV in patients with different degrees of donor-recipient human leukocyte antigen (HLA) matching. We evaluated 36 patients with recurrent hepatitis C viremia following liver transplantation to determine whether hepatocellular injury or progression to bridging fibrosis occur more rapidly when donor and recipients share HLA alleles. HLA typing for the HLA-A and HLA-B loci was performed by serological techniques and PCR-based oligotyping was used to type alleles of the DRB1, DRB3, DQA1, and DQB1 loci. A median of eight liver biopsies, obtained during a median follow-up of 36 months, were reviewed per patient. Donor-recipient sharing of alleles of HLA-DQB1 or DRB1 was associated with more rapid development of recurrent hepatitis by univariate analysis (chi2=5.7, P=0.02 and chi2=5.54, P=0.02 respectively). However, only sharing of HLA-DRB1 alleles was identified as an independent predictor of reduced time to recurrent histologic injury by multivariate analysis (chi2 =5.74, P=0.02). Furthermore, sharing of HLA-DRB3 and histologic evidence of rejection were associated with more rapid progression to bridging fibrosis both by univariate methods (chi2=4.12, P=0.04 and chi2=4.66, P=0.03 respectively), and by multivariate analysis (chi2=13.01, P=0.001). These findings suggest that HLA class II-restricted immune responses may contribute to the pathogenesis of HCV-related liver injury in liver transplant recipients.

Aberrant expression of a cytokeratin in a subset of hepatocytes during chronic WHV infection

Chronic infection of woodchucks with woodchuck hepatitis virus (WHV) invariably leads, within 2-4 years, to the appearance of hepatocellular carcinoma (HCC). HCC is preceded by an extended period of chronic liver damage, probably resulting from the immune response to viral antigens. It may be that infection itself also induces changes in the hepatocyte population. To begin to identify some of the changes in the liver prior to the appearance of HCC, monoclonal antibodies (MAbs) were generated from mice immunized with hepatocytes from a woodchuck chronically infected with WHV or with a tumor lysate. Immunofluorescence microscopy was used to select MAbs that reacted with host markers whose patterns of expression would distinguish chronically infected from uninfected liver or from liver tumors. One of these MAbs (2F2) reacted strongly with a subset of hepatocytes in chronically infected liver; a similar staining pattern was not detected in uninfected or transiently infected liver. Evidence is presented that this strong staining reaction reflects the overexpression or accumulation of the hepatocyte-specific intermediate filament protein, cytokeratin K18, a protein previously implicated in cryptogenic cirrhosis of the liver in humans (Ku, N. O. , Wright, T. L., Terrault, N. A., Gish, R., and Omary, M. B. J. Clin. Invest. 99: 19-23, 1997). Double immunofluorescent staining with antibodies to K18 and M-envelope protein of WHV suggested that strong reactivity to K18 was limited to cells expressing high levels of one or both of the large viral-envelope proteins, M and L; however, high expression of these viral proteins was not always associated with a strong K18 staining reaction.

Cytokeratin expression is reduced in glycogenotic clear hepatocytes but increased in ground-glass cells in chronic human and woodchuck hepadnaviral infection

Hepatocytes of normal adult liver express cytokeratins (CKs) 8/18, but bile duct cells additionally contain CK7/19. We have previously demonstrated the frequent occurrence of foci of altered hepatocytes in association with hepatic tumors in humans and provided evidence for a preneoplastic nature of the focal lesions. In this study, we investigated the CK expression in both the preneoplastic lesions and extrafocal parenchyma. Sixty-seven explanted livers with cirrhosis or advanced fibrosis harboring preneoplastic focal lesions, with or without hepatitis B virus (HBV) infection, as well as 9 livers with HBV-associated fulminant hepatitis, were studied for the expression of CK7/8/14/18/19. Five livers from woodchucks infected with the woodchuck hepatitis virus (WHV) were also investigated. Glycogenotic clear hepatocytes were negative or weakly positive for CK8/18, while amphophilic hepatocytes were strongly positive for these CKs, the changes being associated with marked reduction and increase, respectively, of highly organized membranous components in their cytoplasm. This allows the distinct recognition of the clear-cell and clear-cell-dominant preneoplastic lesions in the human and woodchuck livers. In ground-glass hepatocytes expressing viral antigens, an unusual accumulation of CK8/18 was observed, but there was no evidence of preferential necrosis of ground-glass hepatocytes. Many CK7- and CK19-positive ductular (oval) cells were found in extrafocal liver tissue, but only rarely were they present within focal lesions.

The role of immune responses in the pathogenesis of hepatitis C virus infection

Hepatitis C virus (HCV) is notable for the high rate of chronic infection, which occurs in nearly all individuals who become infected. Liver biopsies from individuals with chronic HCV infection are notable for the presence of numerous mononuclear cells, at least some of which are CD4+ and CD8+ T lymphocytes. The immune response to HCV is polyclonal and multispecific, both in terms of antibody and cellular immune responses. Individuals who recover from acute HCV infection appear to have quantitatively more vigorous CD4+ proliferative responses against one or more HCV proteins compared with those individuals who develop chronic disease. CD8+ responses are less well characterized, in part because of the technical difficulties involved in isolating and characterizing these cells. HCV-specific CTL can be readily isolated from the liver and PBMC of chronically infected individuals, and recognize multiple epitopes. Even individuals with the same HLA type do not consistently recognize the same epitope. Thus, there does not appear to be an immunodominant response on the CD8+ level in this infection. CD8+ cells do appear to play some role in limiting viral replication. These responses are insufficient to eradicate virus completely, however, and may cause liver injury once chronic infection is established. Cytokines produced by both CD4+ and CD8+ cells may play an important role in both inhibiting viral replication and causing liver injury. A better understanding of the role of cellular immunity in the pathogenesis of HCV infection may aid in the development of vaccines and immunotherapeutic intervention strategies.

Induction of hepatocyte growth factor/scatter factor by interferon-gamma in human leukemia cells

Induction of hepatocyte growth factor/scatter factor (HGF/SF) may be one of the critical steps in organ regeneration, wound healing, and embryogenesis. We previously reported the production of HGF/SF from various human leukemia cell lines and a high level of the growth factor in blood and bone marrow plasma from patients with various types of leukemia. We determined here the effects of hematopoietic cytokines on HGF/SF production in human leukemia cell lines, KG-1, a myeloid cell line, and RPMI-8226, a B cell line. Interferon (IFN)-gamma remarkably stimulated HGF/SF production in both cell lines at concentrations of more than 0.1 or 1 IU/ml. IFN-alpha and IFN-beta were as effective as IFN-gamma in RPMI-8226 cells, but less than IFN-gamma in KG-1 cells. HGF/SF gene expression in KG-1 cells was also up-regulated by IFN-gamma. Granulocyte colony-stimulating factor (G-CSF), granulocyte/macrophage colony-stimulating factor (GM-CSF), interleukin (IL)-5 and IL-6 had no effect on HGF/SF production in the 2 leukemia cell lines. We also determined the effects of HGF/SF inducers known for human fibroblasts on the growth factor production in leukemia cells. Out of phorbol 12-myristate 13-acetate (PMA), cholera toxin, IL-1 beta, and tumor necrosis factor (TNF)-alpha, the former three were as effective as IFN-gamma in KG-1 cells, but only TNF-alpha stimulated HGF/SF production in RPMI-8226 cells, whose effect was less than those of IFN-alpha, IFN-beta, and IFN-gamma. The effect of IFN-gamma in KG-1 cells was synergistic with that of PMA. In contrast with the effect in leukemia cells, HGF/SF induction by IFN-gamma in human skin fibroblasts was much less than that by PMA or cholera toxin. These results indicated that IFN-gamma is a potent inducer of HGF/SF in human leukemia cells. This finding suggests the presence of a homeostatic control mechanism in liver regeneration and repair: hepatic injury, DNA synthesis inhibition, or apoptosis caused by IFN-gamma is subsequently overcome by cytokine-induced HGF/SF, a potent promoter of liver DNA synthesis.

Activation of hepatitis B virus S promoter by the viral large surface protein via induction of stress in the endoplasmic reticulum

Hepatitis B virus (HBV) codes for three forms of surface protein. The minor, large form is translated from transcripts specified by the preS1 promoter, while the middle and small forms are translated from transcripts specified by the downstream S promoter. When the large surface protein is overexpressed, the secretion of both subviral and virion particles is blocked within the secretory pathway. We show here that overexpression of the large surface protein leads to up to a 10-fold activation of the S promoter but not of an unrelated promoter. Neither the middle nor the small surface protein, nor a secretable form of the large surface protein, activates the S promoter, but agents that induce endoplasmic reticulum (ER) stress have an effect similar to that of the large surface protein. The large surface protein also activates the S promoter in the context of the entire viral genome. Therefore, it appears that HBV has evolved a feedback mechanism, such that ER stress induced by accumulation of the large surface protein increases the synthesis of the middle and small surface proteins, which in combination with the large surface protein can form mixed, secretable particles. In addition, like other agents that induce ER stress, the large surface protein can activate the cellular grp78 and grp94 promoters, raising the possibility that it may alter the physiology of the host cell.

Histopathology and pathobiology of hepatotropic virus-induced liver injury

The present report concerns current knowledge regarding immunopathogenesis that can be applied in the interpretation of histopathological changes in acute and chronic viral hepatitis. The histopathological features of viral hepatitis have not been changed and light microscopic examination remains essential for making a diagnosis and classification of chronic hepatitis and for the provision of objective parameters on grading and staging. However, new understanding and knowledge of viral pathogenesis, host immune responses, the biological behaviour of the causative viral agents and, in particular, viral interference in multiple hepatotropic viral infections must be taken into consideration in the interpretation of histopathological and immunopathological findings of liver tissues. This report also presents some histopathological analyses on multiple hepatotropic viral infections. It can be concluded that the diagnostic histological criteria for acute hepatitis remain applicable in such settings. However, the cause of acute flare up in chronic hepatitis could not be determined without clinical, virological and serological information. Routine histopathology cannot distinguish a new infection from an acute exacerbation due to a high level of viral replication or mutant virus. A repertoire of immunocytochemical stainings for viral antigens is helpful, but caution must be exercised in suggesting a specific viral aetiology due to the fact that suppression of pre-existing viral antigens can be pronounced when the new or concurrent infection is hepatitis C virus related.

Expression of a Schistosoma mansoni 28-kilodalton glutathione S-transferase in the livers of transgenic mice and its effect on parasite infection

Schistosomiasis is a debilitating tropical disease for which an effective vaccine is needed. A 28-kDa glutathione S-transferase from Schistosoma mansoni (Sm28GST) has been shown to induce protective immunity. Sm28GST possesses significant sequence identity to mammalian GST isoforms. In order to study self-reactivity in mice immunized with Sm28GST and the concomitant phenomena of immune tolerance and epitope suppression, as well as their consequences for the protective immunity induced by this vaccination, we developed transgenic (Tg) mice that express Sm28GST under the control of a part of the mouse transferrin gene promoter. A study of (P28)Tg mice showed that the expression of Sm28GST was strictly localized in pericentrolobular hepatocytes. No histological change, inflammatory infiltrates, or modification of seric L-aspartate: 2-oxoglutarate aminotransferase concentration was observed over an 18-month period, despite a cross-reactivity between Sm28GST and a mouse molecule of 30 kDa. The immunoglobulin G anti-Sm28GST response of (P28)Tg mice immunized with recombinant Sm28GST was lower (P < 0.001) than that observed in non-(P28)Tg littermates and inversely proportional of Sm28GST liver expression. The response of non-(P28)Tg mouse spleen cells to Sm28GST stimulation was greater (P < 0.01) than that observed with (P28)Tg mouse spleen cells. (P28)Tg mice infected with 40 S. mansoni furcocercariae harbored more worms (P < 0.05) than did non-(P28)Tg control mice. The increase in the level of infection in (P28)Tg mice was reflected in concomitant increases in the numbers of adult worms and schistosome eggs found in livers and intestines after whole-body perfusion at 56 days postinfection, but no relative increase in the fertility of individual female worms was observed. The results obtained argue for the involvement of Sm28GST in reducing levels of infection and support the view that this enzyme has a central role in the maintenance of parasite viability, at least during its migration through host tissues.

Role of sinusoidal endothelial cells of the liver in concanavalin A-induced hepatic injury in mice

CD4+ T lymphocytes have been identified as being responsible for organ damage in the murine model of experimental liver injury induced by intravenous injection of concanavalin A (Con A). Liver sinusoidal endothelial cells (SEC) and Kupffer's cells (KC) are among the first cells that come into contact with lymphocytes in the liver sinusoid. We aimed to investigate the respective role of these cell populations in the initial steps of T-cell-mediated liver injury in Con A-induced hepatitis. By electron microscopy, we could show that intravenously applied Con A bound predominantly to SEC but not to KC. KC depletion by gadolinium chloride treatment of mice did not result in protection from liver injury, indicating that KCs are not primarily involved in the generation of liver injury. We could show that a CD4+ T-cell line (LNC.2) displayed selective cytotoxicity toward SEC (>50%) but not KC (12%) or fibroblasts (5%) in the presence of Con A in vitro. Microscopic observation revealed that the SEC monolayer was rapidly destroyed by LnC2 in the presence of Con A. Specificity of the Con A-induced cytotoxicity was shown by the ability of a competitive ligand, methyl-alpha-D-mannopyranoside, to reduce T-cell-mediated cytotoxicity to SEC by more than 50%. Tumor necrosis factor alpha (TNF-alpha) was produced by LnC2 in high amounts after Con A stimulation (>6 ng/mL), but antiserum to TNF-alpha did not reduce LnC2-mediated cytotoxicity toward SEC. In conclusion, we could show for the first time that liver SECs have accessory function and are selectively destroyed by CD4+ T lymphocytes in the presence of Con A. We speculate that SEC damage is an early event in T-cell-mediated liver injury recruiting T lymphocytes from the sinusoidal circulation. Loss of the SEC barrier function then exposes underlying hepatocytes to further attack by activated T lymphocytes. These results offer a model of initiating events in T-cell-mediated liver diseases, such as viral or autoimmune hepatitis, and suggest an important role for sinusoidal endothelial cells.

Early graft loss secondary to massive hemorrhagic necrosis following orthotopic liver transplantation. Evidence for cytokine-mediated univisceral Shwartzman reaction

Massive hemorrhagic necrosis (MHN) of the liver following orthotopic liver transplantation (OLT) occurs infrequently during an otherwise uneventful recovery 1 week after OLT. It is characterized by fever and sudden deterioration of allograft function leading to failure in the absence of vascular thrombosis. The etiology is unknown, although it is usually preceded by some degree of allograft rejection. Between 6 and 8 days after OLT, four patients (out of 150) became febrile, hypotensive, and experienced a rapid rise in transaminases within 48 hr. Two patients had evidence of mild rejection; the other two had moderate to severe acute cellular rejection. All patients were ABO identical, crossmatch negative. Bolus steroids were given followed by OKT3 in the two patients with severe rejection. Although sepsis was suspected, antibiotic therapy did not ameliorate the clinical course. Each patient progressed to MHN with severe centrilobular necrosis and variable portal infiltrate. High levels of interferon-gamma and tumor necrosis factor-alpha occurred prior to the rise in transaminases in each MHN patient (155 +/- 39 pg/ml and 414 +/- 201 pg/ml, respectively) compared with levels in OLT patients with severe rejection (14 +/- 4 pg/ml and 26 +/- 5 pg/ml, respectively, P < 0.05). These data support the concept of a cytokine-mediated inflammatory response leading to a univisceral Shwartzman reaction in the transplanted liver. Early recognition of this syndrome and retransplantation are critical for survival.

Hepatitis B virus transgenic mice: models of viral immunobiology and pathogenesis

It should be apparent from the foregoing that the transgenic mouse model system has contributed substantially to our understanding of many aspects of HBV biology, immunobiology and pathogenesis in the past several years. We have learned that HBV can replicate within the mouse hepatocyte, as well as other mouse cell types, suggesting that there are probably no strong tissue or species specific constraints to viral replication once the viral genome enters the cell. However, the failure thus far to detect viral cccDNA in the hepatocyte nucleus in several independently derived transgenic lineages suggests that other, currently undefined, constraints on host range and tissue specificity may also be operative. Thanks to the transgenic mouse model we now understand the pathophysiological basis for HBsAg filament formation and ground glass cell production, and we have learned that at least this viral gene product can be toxic for the hepatocyte, first by compromising its ability to survive the hepatocytopathic effects of LPS and IFN alpha and eventually by causing it to die in the absence of any obvious exogenous stimulus. In recent studies, it has been shown that preformed nucleocapsid particles do not cross the nuclear membrane in either direction at least in the mouse hepatocyte. If this is confirmed, it will have two important implications: first, that nucleocapsid disassembly must occur in the cytoplasm before the nascent viral genome can enter the nucleus; second, that the intranuclear nucleocapsid particles are empty, and therefore serve no currently defined purpose in the viral life cycle. This should stimulate new interest in the analysis of the function of these particles that are a prominent feature of mammalian hepadnavirus infection. The transgenic mouse model has also established definitively that HBV-induced liver disease has an immunological basis, and that the class I-restricted CTL response plays a central role in this process. Additionally, the mouse studies have taught us that when the CTL recognize their target antigen on the hepatocytes they cause them to undergo apoptosis, forming the acidophilic, Councilman bodies that are characteristic of viral hepatitis. Further, we have learned that although the CTL initiate the liver disease, they actually contribute more to disease severity indirectly by recruiting antigen nonspecific effector cells into the liver than by directly killing the hepatocytes themselves. In addition, by releasing IFN gamma when they recognize antigen, the CTL can destroy enough of the liver to cause fulminant hepatitis in mice whose hepatocytes overproduce the large envelope protein and are hypersensitive to the cytopathic effects of this cytokine. We have also learned that the CTL are unable to recognize HBV-positive parenchymal cells outside of the liver, apparently because they cannot traverse the microvascular barriers that exist at most extrahepatic tissue sites. This important new discovery may permit the virus to survive a vigorous CTL response and contribute not only to the maintenance of memory T cells following acute hepatitis but also to serve as a reservoir to reseed the liver in patients with chronic hepatitis. The transgenic mouse model has also revealed that activated CTL and the cytokines they secrete can down-regulate HBV gene expression, and possibly even control viral replication, by noncytotoxic intracellular inactivation mechanisms involving the degradation of viral RNA and, perhaps, the degradation of viral nucleocapsids and replicative DNA intermediates without killing the cell. If HBV replication is indeed interrupted by this previously unsuspected activity, it could contribute substantially to viral clearance during acute infection when the immune response to HBV is vigorous. Alternatively, it could also contribute to viral persistence, by only partially down-regulating the virus during chronic infection when the immune response is weak.

Intracellular retention of surface protein by a hepatitis B virus mutant that releases virion particles

In the course of chronic infection, hepatitis B virus mutants can sometimes be found circulating in the serum as the predominant species. One class of such mutants contains in-frame deletions in the S promoter region. By transfecting hepatoma cells with wild-type or mutant viral genomic DNA, we have shown that one such mutant gives rise to extremely small amounts of S transcripts, as expected, and therefore expresses very little of the middle and small surface (viral envelope) proteins that are translated from these transcripts. In addition, this mutant gives rise to greater-than-wild-type levels of the preS1 transcripts, which are translated into the large surface protein. Because the large surface protein, unlike the other forms of surface protein, is incompetent for secretion, cells transfected with the mutant viral DNA contain large amounts of 20-nm particles within dilated perinuclear vesicles. Therefore, this and similar S promoter mutants may be one contributing factor in the pathogenesis of ground-glass cells, which are hepatocytes containing nonsecretable viral surface proteins within dilated vesicles and are commonly found during chronic hepatitis B. Interestingly, DNA-containing virion particles are secreted into the medium by cells transfected with the mutant DNA, in amounts that are slightly larger than those secreted from wild-type-transfected cells, apparently because the amount of large surface protein is insufficient to block virion secretion. This finding may explain how such mutants can become the predominant circulating species in the serum, especially if there are selection pressures against the wild-type virus.

Hepatitis B virus immunopathology

Approximately 5% of the world population is infected by the hepatitis B virus (HBV) which causes a necroinflammatory liver disease of variable duration and severity. Chronically infected patients with active liver disease carry a high risk of developing cirrhosis and hepatocellular carcinoma. The immune response to HBV-encoded antigens is responsible both for viral clearance and for disease pathogenesis during this infection. While the humoral antibody response to viral envelope antigens contributes to the clearance of circulating virus particles, the cellular immune response to the envelope, nucleocapsid and polymerase antigens eliminates infected cells. The class I- and class II-restricted T cell responses to the virus are vigorous, polyclonal and multispecific in acutely infected patients who successfully clear the virus, and they are relatively weak and more narrowly focussed in chronically infected patients who do not. The pathogenetic and antiviral potential of the cytotoxic T lymphocyte (CTL) response to HBV have been demonstrated by the induction of a severe necroinflammatory liver disease following the adoptive transfer of HBV surface antigen-specific CTL into HBV transgenic mice, and by the noncytolytic suppression of viral gene expression and replication in the same animals by a post-transcriptional mechanism mediated by interferon-gamma, tumor necrosis factor-alpha and interleukin-2. The dominant cause of viral persistence during HBV infection is the development of a weak antiviral immune response to the viral antigens. While neonatal tolerance probably plays an important role in viral persistence in patients infected at birth, the basis for poor responsiveness in adult onset infection is not well understood and requires further analysis. Viral evasion by epitope inactivation and T cell receptor antagonism may contribute to the worsening of viral persistence in the setting of an ineffective immune response, as can the incomplete down-regulation of viral gene expression and the infection of immunologically privileged tissues. Chronic liver cell injury and the attendant inflammatory and regenerative responses create the mutagenic and mitogenic stimuli for the development of DNA damage that can cause hepatocellular carcinoma. Elucidation of the immunological and virological basis for HBV persistence may yield immunotherapeutic and antiviral strategies to terminate chronic HBV infection and reduce the risk of its life-threatening sequellae.

Tumor necrosis factor receptors in patients with chronic hepatitis B virus infection

BACKGROUND/AIMS

Patients with chronic hepatitis B infection have elevated plasma tumor necrosis factor (TNF) alpha levels. Two TNF-alpha receptors have been identified, each responsible for distinct TNF-alpha activities. The aim of this study was to evaluate the biological function of the elevated TNF-alpha in chronic hepatitis B virus infection by examining the two TNF signaling pathways in the evolution of hepatitis B-related liver injury.

METHODS

The hepatic expression of the two TNF receptors and the corresponding serum levels of the soluble forms of both TNF receptors were determined and correlated with hepatic inflammation and virus replication in 98 chronic hepatitis B surface antigen carriers. Forty hepatitis B e antigen-positive patients were also studied prospectively, while on interferon alfa treatment, to examine the TNF receptor response during viral clearance.

RESULTS

In chronic hepatitis B virus infection, the hepatic expression and serum levels of TNF receptors, in particular 75-kilodalton TNF receptor subtype (TNF-R p75), are significantly enhanced in association with hepatic inflammation and hepatocytolysis but not with hepatitis B virus replication. During interferon alfa treatment, a significant increase of soluble TNF-R p75 always precedes the hepatitis B e antigen antibody against hepatitis B e antigen seroconversion in responders to treatment.

CONCLUSIONS

In chronic active hepatitis B infection, there is an up-regulation of the TNF receptor system, preferentially the TNF-R p75 signaling pathway, which suggests that the TNF-alpha/TNF receptor system has an important role in the pathogenesis of liver damage and viral clearance.

Hepatic expression of tumour necrosis factor-alpha in chronic hepatitis B virus infection

AIM

To determine the hepatic expression of tumour necrosis factor-alpha (TNF alpha) in patients with chronic hepatitis B virus (HBV) infection.

METHODS

Frozen liver biopsy sections from 19 patients with chronic HBV infection were studied, 12 of whom were HBeAg positive and 10 serum HBV DNA positive. Hepatic expression of TNF alpha was determined using immunohistochemistry.

RESULTS

Only infiltrating mononuclear cells showed immunoreactive staining for TNF alpha (median 2, range 0-3; n = 19) which appeared as diffuse positive staining material in the cytoplasm. Patients with active liver disease, assessed histologically and biochemically, had a higher level of expression, both in the number of TNF alpha positive cells and the proportion of TNF alpha positive infiltrating mononuclear cells. There was no correlation between the expression of TNF alpha and serological parameters of viral infection (HBeAg and HBV DNA status and HBV DNA concentrations).

CONCLUSION

Hepatic expression of TNF alpha is increased in chronic HBV infection and is related to the activity of liver disease and not to the level of HBV replication.

Expression of cytokine-dependent immune adhesion molecules by hepatocytes and bile duct cells in chronic hepatitis C

BACKGROUND/AIMS

The pathogenesis of liver cell injury in chronic hepatitis C is poorly understood. To test whether immune-mediated mechanisms might be involved in the pathogenesis of liver cell injury during infection by hepatitis C virus, the expression of cytokine-dependent immune molecules by hepatocytes and bile duct cells during chronic hepatitis C was studied.

METHODS

In 35 patients, expression of class I and II HLA antigens, intercellular adhesion molecule (ICAM) 1, and lymphocyte function antigen (LFA) 3 was studied by immunohistochemistry and scored by a semiquantitative grading system. Statistical analysis was performed using Spearman's test and t test.

RESULTS

Class I HLA antigens were induced on hepatocytes in 20 cases. In all cases, HLA-DR, ICAM-1, and/or LFA-3 were detected on hepatocytes in piecemeal necrosis and intralobular clusters. Bile duct cells expressed HLA-DR in 32 cases and ICAM-1 and LFA-3 in 14 cases. Expression levels of immune molecules on hepatocytes correlated with aminotransferase activity (P < 0.035), histological activity (P < 0.001), and score of necrosis (P < 0.01). ICAM-1 expression on hepatocytes was higher in patients with intraportal lymphoid nodules (P = 0.005). Expression levels of ICAM-1 and LFA-3 on bile ducts correlated with the severity of bile duct damage (P < 0.015).

CONCLUSIONS

These results suggest the involvement of immune-mediated mechanisms in the pathogenesis of liver cell injury in chronic hepatitis C.

Fibrosing cholestatic hepatitis in a hepatitis B surface antigen carrier after renal transplantation

A 45-year-old hepatitis B surface antigen carrier had an allograft kidney transplantation and maintenance immunosuppression with cyclosporin A and prednisolone. Six months later, she experienced a rapidly progressive hepatic failure manifested by elevation of serum bilirubin level, prolongation of prothrombin time, and mild to modest increase of serum aminotransferase levels. She died in 6 weeks. Postmortem liver histology showed canalicular and cellular cholestasis and ground-glass appearance and ballooning of most hepatocytes, but only mild inflammatory cell infiltration. Immunohistochemical staining showed massive loads of hepatitis B surface and core antigens in the hepatocytes and extensive periportal fibrosis. The whole picture was compatible with fibrosing cholestatic hepatitis described in hepatitis B virus-infected liver transplant. Sequencing of the hepatitis B virus genome amplified from the patient's serum indicated a precore mutant but few mutations in the core, pre-S, and S genes. Little inflammatory reaction was observed histologically despite HLA compatibility, a situation differing from that in liver transplant. This observation indicates that fibrosing cholestatic hepatitis may also occur in non-liver transplant setting.

Cellular expression of tumour necrosis factor-alpha and interferon-gamma in the liver biopsies of children with chronic liver disease

The liver biopsies of patients with autoimmune liver diseases have a dense portal tract mononuclear cell infiltrate. To investigate whether these cells produce tumour necrosis factor-alpha and interferon-gamma, cytokines which could be involved in the autoimmune attack through a direct cytopathic effect and/or through induction/enhancement of major histocompatibility complex antigen expression, we immunohistochemically stained cryostat liver sections from 21 children with autoimmune liver disease and from 15 children with metabolic liver disorders and histological evidence of portal tract inflammation as controls. Tumour necrosis factor-alpha and interferon-gamma producing cells were detected simultaneously within the inflammatory cell infiltrate in the liver biopsies of 18 patients with autoimmune liver disease, but only one patient with a metabolic disorder was positive for tumour necrosis factor-alpha. There was a significant correlation between frequency of tumour necrosis factor-alpha and interferon-gamma producing cells, intensity of inflammatory cell infiltrate (p < 0.03 and p < 0.05, respectively) and transaminase levels (p < 0.008 and p < 0.03, respectively). These results suggest that tumour necrosis factor-alpha and interferon-gamma play a pathogenic role in autoimmune liver cell damage.

Liver cell death: patterns and mechanisms

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T cell activation-associated hepatic injury: mediation by tumor necrosis factors and protection by interleukin 6

This study investigates the molecular mechanisms underlying the induction of and protection from T cell activation-associated hepatic injury. When BALB/c mice were given a single intravenous injection of concanavalin A (Con A) (> or = 0.3 mg/mouse), they developed acute hepatic injury as assessed by a striking increase in plasma transaminase levels within 24 h. Histopathologically, only the liver was injured while moderate infiltration of T cells and polymorphonuclear cells occurred in the portal areas and around the central veins. The induction of hepatic injury was dependent on the existence as well as the activation of T cells, as untreated BALB/c nu/nu mice or BALB/c mice pretreated with a T cell-specific immunosuppressive drug, FK506, failed to develop disease. Significant increases in the levels of various cytokines in the plasma were detected before an increase in plasma transaminase levels. Within 1 h after Con A injection, tumor necrosis factor (TNF) levels peaked, this being followed by production of two other inflammatory cytokines, interleukin 6 (IL-6) and IL-1. Passive immunization with anti-TNF but not with anti-IL-1 or anti-IL-6 antibody, conferred significant levels of protection. Moreover, administration of rIL-6 before Con A injection resulted in an IL-6 dose-dependent protection. A single administration of a given dose of rIL-6 completely inhibited the release of transaminases, whereas the same regimen induced only 40-50% inhibition of TNF production. More than 80% inhibition of TNF production required four consecutive rIL-6 injections. These results indicate that: (a) TNFs are critical cytokines for inducing T cell activation-associated (Con A-induced) hepatitis; (b) the induction of hepatitis is almost completely controlled by rIL-6; and (c) rIL-6 exerts its protective effect through multiple mechanisms including the reduction of TNF production.

Cytotoxic T lymphocytes inhibit hepatitis B virus gene expression by a noncytolytic mechanism in transgenic mice

During hepatitis B virus (HBV) infection, distinct host-virus interactions may establish the patterns of viral clearance and persistence and the extent of virus-associated pathology. It is generally thought that HBV-specific class I-restricted cytotoxic T lymphocytes (CTLs) play a critical role in this process by destroying infected hepatocytes. This cytopathic mechanism, however, could be lethal if most of the hepatocytes are infected. In the current study, we demonstrate that class I-restricted HBV-specific CTLs profoundly suppress hepatocellular HBV gene expression in HBV transgenic mice by a noncytolytic process, the strength of which greatly exceeds the cytopathic effect of the CTLs in magnitude and duration. We also show that the regulatory effect of the CTLs is initially mediated by interferon gamma and tumor necrosis factor alpha, is delayed in onset, and becomes independent of these cytokines shortly after it begins. The data indicate that the anti-viral CTL response activates a complex regulatory cascade that inhibits hepatocellular HBV gene expression without killing the cell. The extent to which this mechanism contributes to viral clearance or viral persistence during HBV infection remains to be determined.

Interleukin-2 and alpha/beta interferon down-regulate hepatitis B virus gene expression in vivo by tumor necrosis factor-dependent and -independent pathways

We have recently reported that administration of recombinant tumor necrosis factor alpha (TNF-alpha) to hepatitis B virus (HBV) transgenic mice reduces the hepatic steady-state content of HBV-specific mRNA by up to 80% in the absence of liver cell injury. In the current study, we analyzed the regulatory effects of several other inflammatory cytokines in the same transgenic model system. Hepatic HBV mRNA content was reduced by up to 90% following administration of a single noncytopathic dose (100,000 U) of interleukin 2 (IL-2). Comparable effects were produced by administration of alpha and beta interferons (IFN-alpha and IFN-beta), but only after multiple injections of at least 500,000 U per mouse. Importantly, the regulatory effect of IL-2 was completely blocked by the prior administration of antibodies to tumor necrosis factor alpha (TNF-alpha), which did not block the effect of IFN-alpha or IFN-beta. In contrast to these observations, recombinant IFN-gamma, IL-1, IL-3, IL-6, TNF-beta, transforming growth factor beta, and granulocyte-monocyte colony-stimulating factor were inactive in this system. These results suggest that selected inflammatory cytokines can down-regulate HBV gene expression in vivo by at least two pathways, one that is dependent on TNF-alpha and another that is not. These results imply that antigen-nonspecific products of the intrahepatic HBV-specific inflammatory response may contribute to viral clearance or persistence during HBV infection.

Expression of the hepatitis delta virus large and small antigens in transgenic mice

Simultaneous infection with hepatitis delta virus (HDV) and hepatitis B virus (HBV) in humans is often associated with severe viral liver disease including fulminant hepatitis. Since HBV is thought to be noncytopathic to the hepatocyte, the enhanced disease severity observed during dual infection has been attributed to either simultaneous immune responses against the two viruses or direct cytotoxic effects of HDV products on the hepatocyte or both. To examine these alternate possibilities, we produced transgenic mice that express the small and large delta antigens (HDAg) in hepatocyte nuclei at levels equal to those observed during natural HDV infection. No biological or histopathological evidence of liver disease was detectable during 18 months of observation, suggesting that neither the large nor small form of HDAg is directly cytopathic to the hepatocyte in vivo.