Serum autoantibodies reacting with the hepatic asialoglycoprotein receptor protein (hepatic lectin) in acute and chronic liver disorders

The Origin of Capsid-Derived Immune Complexes and Their Impact on HBV-Induced Liver Diseases

Over 240 million people worldwide are chronically infected with Hepatitis B Virus (HBV), a hepatotropic DNA virus with an evolutionary root of over 400 million years. Persistent HBV infection exhibits distinct and diverse phases of disease, from minimal liver pathology to fulminant Hepatitis, that vary in duration and severity among individuals. Although huge progress has been made in HBV research which has yielded an effective prophylactic vaccine and potent antiviral therapy, our understanding of its virology and immunobiology is still far from complete. For example, the recent re-discovery of serum HBV RNA in chronic Hepatitis B (CHB) patients has led to the proposal of noncanonical viral particles such as RNA virion and capsid-derived immune complex (Capsid-Antibody-Complexes, CACs) that contradict long-established basic theory. Furthermore, the existence of capsid-derived immune complex may hint at novel mechanism of HBV-induced liver disease. Here, we summarize the past and recent literature on HBV-induced immune complex. We propose that the release of capsid-derived particles by HBV has its deep evolutionary origin, and the associated complement activation serves as an indispensable trigger for intrahepatic damage and a catalyst for further cell-mediated immunopathology.

Mesenchymal stem cells-based therapy in liver diseases

Multiple immune cells and their products in the liver together form a complex and unique immune microenvironment, and preclinical models have demonstrated the importance of imbalances in the hepatic immune microenvironment in liver inflammatory diseases and immunocompromised liver diseases. Various immunotherapies have been attempted to modulate the hepatic immune microenvironment for the purpose of treating liver diseases. Mesenchymal stem cells (MSCs) have a comprehensive and plastic immunomodulatory capacity. On the one hand, they have been tried for the treatment of inflammatory liver diseases because of their excellent immunosuppressive capacity; On the other hand, MSCs have immune-enhancing properties in immunocompromised settings and can be modified into cellular carriers for targeted transport of immune enhancers by genetic modification, physical and chemical loading, and thus they are also used in the treatment of immunocompromised liver diseases such as chronic viral infections and hepatocellular carcinoma. In this review, we discuss the immunological basis and recent strategies of MSCs for the treatment of the aforementioned liver diseases. Specifically, we update the immune microenvironment of the liver and summarize the distinct mechanisms of immune microenvironment imbalance in inflammatory diseases and immunocompromised liver diseases, and how MSCs can fully exploit their immunotherapeutic role in liver diseases with both immune imbalance patterns.

Diverse Virus and Host-Dependent Mechanisms Influence the Systemic and Intrahepatic Immune Responses in the Woodchuck Model of Hepatitis B

Woodchuck infected with woodchuck hepatitis virus (WHV) represents the pathogenically nearest model of hepatitis B and associated hepatocellular carcinoma (HCC). This naturally occurring animal model also is highly valuable for development and preclinical evaluation of new anti-HBV agents and immunotherapies against chronic hepatitis (CH) B and HCC. Studies in this system uncovered a number of molecular and immunological processes which contribute or likely contribute to the immunopathogenesis of liver disease and modulation of the systemic and intrahepatic innate and adaptive immune responses during hepadnaviral infection. Among them, inhibition of presentation of the class I major histocompatibility complex on chronically infected hepatocytes and a role of WHV envelope proteins in this process, as well as augmented hepatocyte cytotoxicity mediated by constitutively expressed components of CD95 (Fas) ligand- and perforin-dependent pathways, capable of eliminating cells brought to contact with hepatocyte surface, including activated T lymphocytes, were uncovered. Other findings pointed to a role of autoimmune response against hepatocyte asialoglycoprotein receptor in augmenting severity of liver damage in hepadnaviral CH. It was also documented that WHV in the first few hours activates intrahepatic innate immunity that transiently decreases hepatic virus load. However, this activation is not translated in a timely manner to induction of virus-specific T cell response which appears to be hindered by defective activation of antigen presenting cells and presentation of viral epitopes to T cells. The early WHV infection also induces generalized polyclonal activation of T cells that precedes emergence of virus-specific T lymphocyte reactivity. The combination of these mechanisms hinder recognition of virus allowing its dissemination in the initial, asymptomatic stages of infection before adaptive cellular response became apparent. This review will highlight a range of diverse mechanisms uncovered in the woodchuck model which affect effectiveness of the anti-viral systemic and intrahepatic immune responses, and modify liver disease outcomes. Further exploration of these and other mechanisms, either already discovered or yet unknown, and their interactions should bring more comprehensive understanding of HBV pathogenesis and help to identify novel targets for therapeutic and preventive interventions. The woodchuck model is uniquely positioned to further contribute to these advances.

Autoimmune hepatitis

Autoimmune hepatitis (AIH) is a severe liver disease that affects children and adults worldwide. The diagnosis of AIH relies on increased serum transaminase and immunoglobulin G levels, presence of autoantibodies and interface hepatitis on liver histology. AIH arises in genetically predisposed individuals when a trigger, such as exposure to a virus, leads to a T cell-mediated autoimmune response directed against liver autoantigens; this immune response is permitted by inadequate regulatory immune control leading to a loss of tolerance. AIH responds favourably to immunosuppressive treatment, which should be started as soon as the diagnosis is made. Standard regimens include fairly high initial doses of corticosteroids (prednisone or prednisolone), which are tapered gradually as azathioprine is introduced. For those patients who do not respond to standard treatment, second-line drugs should be considered, including mycophenolate mofetil, calcineurin inhibitors, mechanistic target of rapamycin (mTOR) inhibitors and biologic agents, which should be administered only in specialized hepatology centres. Liver transplantation is a life-saving option for those who progress to end-stage liver disease, although AIH can recur or develop de novo after transplantation. In-depth investigation of immune pathways and analysis of changes to the intestinal microbiota should advance our knowledge of the pathogenesis of AIH and lead to novel, tailored and better tolerated therapies.

Autoantibodies in Autoimmune Hepatitis: Can Epitopes Tell Us about the Etiology of the Disease?

Autoimmune hepatitis (AIH), primary biliary cholangitis (PBC), and primary sclerosing cholangitis (PSC) are serious autoimmune liver diseases that are characterized by a progressive destruction of the liver parenchyma and/or the hepatic bile ducts and the development of chronic fibrosis. Left untreated autoimmune liver diseases are often life-threatening, and patients require a liver transplantation to survive. Thus, an early and reliable diagnosis is paramount for the initiation of a proper therapy with immunosuppressive and/or anticholelithic drugs. Besides the analysis of liver biopsies and serum markers indicating liver damage, the screening for specific autoantibodies is an indispensable tool for the diagnosis of autoimmune liver diseases. Such liver autoantigen-specific antibodies might be involved in the disease pathogenesis, and their epitope specificity may give some insight into the etiology of the disease. Here, we will mainly focus on the generation and specificity of autoantibodies in AIH patients. In addition, we will review data from animal models that aim toward a better understanding of the origins and pathogenicity of such autoantibodies.

Cutting edge issues in autoimmune hepatitis

Autoimmune hepatitis (AIH) is a severe liver disease affecting all age groups worldwide. Novel basic and clinical aspects of AIH, addressed at a Monothematic Conference in London in September 2015, are highlighted in this review. The diagnosis of AIH relies upon detection of characteristic autoantibodies, hypergammaglobulinemia, and interface hepatitis on liver histology. The International Autoimmune Hepatitis Group (IAIHG) has devised diagnostic scoring systems to help in comparative studies and clinical practice. AIH arises in a genetically predisposed host, when yet unknown triggers - such an encounter with a pathogen - lead to a T cell-mediated immune response targeting liver autoantigens. This immune response is inadequately controlled because regulatory mechanisms are impaired. The mainstay of treatment for AIH is immunosuppression, which should be instituted as soon as the diagnosis is made. Standard treatment regimens include relatively high doses of predniso(lo)ne, which are tapered gradually as azathioprine is introduced. Recent guidelines have described newer treatment regimens and have tightened the goal of therapy to complete normalization of biochemical, serological and histological parameters. Mycophenolate mofetil, calcineurin inhibitors, mTOR inhibitors and biological agents are potential salvage therapies, but should be reserved for selected non-responsive patients and administered only in experienced centers. Liver transplantation is a life-saving option for those patients who progress to end-stage liver disease. Further dissection of cellular and molecular pathways involved in AIH pathogenesis is likely to lead to the discovery of novel, tailored and better tolerated therapies.

Diagnosis and Management of Autoimmune Hepatitis: Current Status and Future Directions

Autoimmune hepatitis is characterized by autoantibodies, hypergammaglobulinemia, and interface hepatitis on histological examination. The features lack diagnostic specificity, and other diseases that may resemble autoimmune hepatitis must be excluded. The clinical presentation may be acute, acute severe (fulminant), or asymptomatic; conventional autoantibodies may be absent; centrilobular necrosis and bile duct changes may be present; and the disease may occur after liver transplantation or with features that suggest overlapping disorders. The diagnostic criteria have been codified, and diagnostic scoring systems can support clinical judgment. Nonstandard autoantibodies, including antibodies to actin, α-actinin, soluble liver antigen, perinuclear antineutrophil antigen, asialoglycoprotein receptor, and liver cytosol type 1, are tools that can support the diagnosis, especially in patients with atypical features. Prednisone or prednisolone in combination with azathioprine is the preferred treatment, and strategies using these medications in various doses can ameliorate treatment failure, incomplete response, drug intolerance, and relapse after drug withdrawal. Budesonide, mycophenolate mofetil, and calcineurin inhibitors can be considered in selected patients as frontline or salvage therapies. Molecular (recombinant proteins and monoclonal antibodies), cellular (adoptive transfer and antigenic manipulation), and pharmacological (antioxidants, antifibrotics, and antiapoptotic agents) interventions constitute future directions in management. The evolving knowledge of the pathogenic pathways and the advances in technology promise new management algorithms.

Noninvasive markers in the assessment and management of autoimmune liver diseases

Historically, liver biopsy has been used to determine the etiology of liver disease, the degree of inflammation, the stage of liver fibrosis, and the response to treatments. In the last decade, the advent of noninvasive tests has improved the diagnosis and management of autoimmune liver diseases. For example, serum markers can identify hepatic inflammation, whereas ultrasound and MRI can diagnose liver fibrosis. Physicians now have a much larger repertoire of diagnostic tests to assess the liver parenchyma compared with liver biopsy alone. In some rare cases, noninvasive tests may provide an alternative to liver biopsy. In general, however, these noninvasive tests complement liver biopsy and provide quick, accurate, and reliable adjunctive data.

Anti-phosphoenolpyruvate carboxykinase 2 antibody in patients with autoimmune hepatitis

AIM

To identify a novel autoantibody specific to autoimmune hepatitis (AIH) and to evaluate its clinical significance.

METHODS

Non-nuclear component protein extracted from normal human liver cell CyrohNHpes cultures that reacted with sera from AIH patients on a western blot was identified as an antigenic protein and subjected to N-terminal amino acid analysis to identify phosphoenolpyruvate carboxykinase 2 (PCK2). Enzyme-linked immunoassay (ELISA) for anti-PCK2 antibody was conducted on sera samples from patients with AIH (n = 42), primary biliary cirrhosis (PBC; n = 48), non-alcoholic steatohepatitis (NASH, n = 41), chronic hepatitis C (CHC, n = 20), drug-induced liver injury (DILI, n = 10), systemic lupus erythematosus (SLE, n = 16) and on sera samples from healthy volunteers (n = 30). Clinical findings were compared for AIH patients testing positive and negative for anti-PCK2 antibody.

RESULTS

ELISA findings showed that mean anti-PCK2 antibody titer in sera from AIH patients was significantly higher than in PBC, NASH, CHC, DILI and SLE patients, as well as in healthy volunteers. Anti-PCK2 antibody was present in 50.0% (21/42) of AIH, 14.6% (7/48) of PBC, 4.9% (2/41) of NASH, and 10.0% (2/20) of CHC patients, 0% (0/10) of DILI, 12.5% (2/16) of SLE and in 3.3% (1/30) of healthy volunteers. The sensitivity, specificity and accuracy of using the detection of anti-PCK2 antibody in diagnosing AIH were 50.0%, 91.5% and 83.1%, respectively. None of the AIH patients positive for anti-PCK2 antibody showed characteristic clinical features.

CONCLUSION

Although further investigations into the clinical usefulness are necessary, anti-PCK2 may have potential as a diagnostic marker for AIH.

The role of autoantibodies in autoimmune hepatitis type 2

Antibodies play an important role in autoimmune liver diseases, such as autoimmune hepatitis (AIH). On the one hand, they are essential diagnostic markers to identify not only the presentation of AIH, but also the AIH subtype characterized by the presence of particular antibodies to target autoantigens in the liver. On the other hand, such autoantibodies might be directly involved in the etiology and/or pathogenesis of AIH. This review will reflect on the evidence of how specific autoantibodies influence AIH and will further provide insight into the necessities for generating therapeutic antibodies to treat AIH in the future.

Asialoglycoprotein receptor (ASGPR): a peculiar target of liver-specific autoimmunity

Asialoglycoprotein receptor (ASGPR) autoantibodies have been considered specific markers of autoimmune hepatitis (AIH). The exact mechanisms responsible for the development of these autoantibodies and leading to autoimmunity to this peculiar liver receptor remain elusive. Furthermore, loss of T cell tolerance to ASGPR has been demonstrated in patients with AIH, but it is poorly understood whether such liver-specific T cell responses bear a pathogenic potential and/or participate in the precipitation of AIH. Newly developed enzyme-linked immunosorbent assays have led to the investigation of the sensitivity and specificity of anti-ASGPR antibodies for AIH. The present review provides an overview of the diagnostic and clinical relevance of anti-ASGPR antibodies. A thorough investigation of the autoreactivity against ASGPR may assist efforts to understand liver autoimmunity in susceptible individuals.

Cutting edge issues in autoimmune hepatitis

Autoimmune hepatitis is an inflammatory liver disease affecting mainly females and characterised histologically by interface hepatitis, biochemically by elevated transaminase levels and serologically by circulating autoantibodies and increased levels of immunoglobulin G. Autoimmune hepatitis responds to immunosuppressive treatment, which should be instituted as soon as diagnosis is made. Seropositivity for smooth muscle and/or antinuclear antibody defines type 1 autoimmune hepatitis, while positivity for liver kidney microsomal type 1 antibody defines type 2 autoimmune hepatitis. The aetiology of autoimmune hepatitis is unknown, though both genetic and environmental factors are involved in its expression. The major mechanism of liver damage involves immune reactions against host liver antigens that are not adequately controlled by defective regulatory T cells. Current research aiming at potentiating regulatory T cell function in vitro to reconstitute tolerance in vivo has given promising results.

Asialoglycoprotein receptor (ASGPR) as target autoantigen in liver autoimmunity: lost and found

Asialoglycoprotein receptor (ASGPR) has attracted the attention of liver immunologists for many years. This liver-specific lectin was found to be a major B and T cell autoantigenic target in patients with autoimmune liver diseases, and in particular in autoimmune hepatitis (AIH). This review discusses the biological significance of ASGPR and its relevance to the pathogenesis of autoimmune and virus-triggered liver diseases. We also discuss emerging data on the diagnostic and clinical relevance of anti-ASGPR antibodies in light of recent reports based on commercially available anti-ASGPR enzyme-linked immunosorbent assays. Finally, we critically revisit the data reporting on disease-specific cellular immune responses against ASGPR and their relevance in relation to the pathogenesis of AIH.

Autoantibody-negative autoimmune hepatitis

Autoimmune hepatitis has a variable clinical phenotype, and the absence of conventional autoantibodies does not preclude its diagnosis or need for treatment. The goals of this review are to describe the frequency and nature of autoantibody-negative autoimmune hepatitis, indicate its outcome after corticosteroid treatment, and increase awareness of the diagnosis in patients with unexplained acute and chronic hepatitis. The frequency of presumed autoantibody-negative autoimmune hepatitis in patients with acute and acute severe presentations is ≤7%, and its frequency in patients with chronic presentations is 1-34%. Patients with acute presentations can have normal serum γ-globulin levels, centrilobular zone 3 necrosis, and low pre-treatment international diagnostic scores. Liver tissue examination is essential for the diagnosis, and hepatic steatosis can be a co-morbid feature. The comprehensive international scoring system can support but never override the clinical diagnosis pre-treatment, and non-standard serological markers should be sought if the clinical diagnosis is uncertain or the diagnostic score is low. A 3-month treatment trial with corticosteroids should be considered in all patients, regardless of the serological findings, and improvements have occurred in 67-87% of cases. Autoantibody-negative autoimmune hepatitis may be associated with an autoantibody outside the conventional battery; it may have a signature autoantibody that is still undiscovered, or its characteristic autoantibodies may have been suppressed or have a delayed expression. The pathogenic mechanisms are presumed to be identical to those of classical disease. Autoantibody-negative autoimmune hepatitis is an infrequent but treatable disease that must be considered in unexplained acute and chronic hepatitis.

Pathogenesis of autoimmune hepatitis

The mechanisms underlying the pathogenesis of autoimmune hepatitis are not fully understood, though there is growing evidence that genetic predisposition, molecular mimicry and/or impairment of regulatory T-cells are involved in the initiation and perpetuation of the autoimmune liver attack. The histological picture of interface hepatitis, characterized by a dense portal mononuclear cell infiltrate, was the first to suggest an autoaggressive cellular immune attack in the pathogenesis of this condition. Liver damage is likely to be orchestrated by CD4(pos) T-cells recognizing an autoantigenic liver peptide. For autoimmunity to arise, the peptide must be presented by antigen-presenting cells to naïve CD4(pos) T-helper (Th0) cells. Once activated, Th0-cells can differentiate into Th1-, Th2-, or Th17-cells, initiating a cascade of immune reactions that are determined by the cytokines they produce. Autoantigen recognition and the above effector mechanisms are opposed by regulatory T-cells, a cell subset numerically and functionally impaired in autoimmune hepatitis.

Autoimmune hepatitis

Autoimmune hepatitis (AIH) is an inflammatory liver disease that mainly affects females. It is characterized histologically by interface hepatitis, biochemically by increased aspartate and alanine aminotransferase levels, and serologically by the presence of autoantibodies and increased levels of immunoglobulin G. AIH affects both adults and children, and is particularly aggressive in the latter group. It is a relatively rare but devastating disease, which progresses rapidly unless immunosuppressive treatment is started promptly. With appropriate treatment 80% of patients achieve remission and long-term survival. Those patients who progress to end-stage liver disease because they are unresponsive or nonadherent to treatment, and those with fulminant liver failure (encephalopathy grade II-IV) at diagnosis, require liver transplantation. Seropositivity for smooth muscle and/or antinuclear antibodies defines type 1 AIH, while positivity for liver kidney microsomal type 1 antibodies defines type 2 AIH. The primary cause of AIH is unknown; however, considerable knowledge about the mechanisms of liver damage involved has been gathered over the past 30 years, which is likely to provide the basis for specific modes of treatment and a possible cure.

A new splice variant of the major subunit of human asialoglycoprotein receptor encodes a secreted form in hepatocytes

BACKGROUND

The human asialoglycoprotein receptor (ASGPR) is composed of two polypeptides, designated H1 and H2. While variants of H2 have been known for decades, the existence of H1 variants has never been reported.

PRINCIPAL FINDINGS

We identified two splice variants of ASGPR H1 transcripts, designated H1a and H1b, in human liver tissues and hepatoma cells. Molecular cloning of ASGPR H1 variants revealed that they differ by a 117 nucleotide segment corresponding to exon 2 in the ASGPR genomic sequence. Thus, ASGPR variant H1b transcript encodes a protein lacking the transmembrane domain. Using an H1b-specific antibody, H1b protein and a functional soluble ASGPR (sASGPR) composed of H1b and H2 in human sera and in hepatoma cell culture supernatant were identified. The expression of ASGPR H1a and H1b in Hela cells demonstrated the different cellular loctions of H1a and H1b proteins at cellular membranes and in intracellular compartments, respectively. In vitro binding assays using fluorescence-labeled sASGPR or the substract ASOR revealed that the presence of sASGPR reduced the binding of ASOR to cells. However, ASOR itself was able to enhance the binding of sASGPR to cells expressing membrane-bound ASGPR. Further, H1b expression is reduced in liver tissues from patients with viral hepatitis.

CONCLUSIONS

We conclude that two naturally occurring ASGPR H1 splice variants are produced in human hepatocytes. A hetero-oligomeric complex sASGPR consists of the secreted form of H1 and H2 and may bind to free substrates in circulation and carry them to liver tissue for uptake by ASGPR-expressing hepatocytes.

Primary biliary cirrhosis: What do autoantibodies tell us?

Primary biliary cirrhosis (PBC) is a chronic, progressive, cholestatic, organ-specific autoimmune disease of unknown etiology. It predominantly affects middle-aged women, and is characterized by autoimmune-mediated destruction of small- and medium-size intrahepatic bile ducts, portal inflammation and progressive scarring, which without proper treatment can ultimately lead to fibrosis and hepatic failure. Serum autoantibodies are crucial tools for differential diagnosis of PBC. While it is currently accepted that antimitochondrial antibodies are the most important serological markers of PBC, during the last five decades more than sixty autoantibodies have been explored in these patients, some of which had previously been thought to be specific for other autoimmune diseases.

Autoantibodies as prognostic markers in autoimmune liver disease

Certain autoantibodies in autoimmune liver disease have prognostic implications that are under-utilized and under-developed. The goals of this review are to indicate progress in characterizing the autoantibodies with prognostic connotations and to indicate the feasibility and importance of discovering other markers. Prime source and review articles in English were selected by a Medline search through 2010. Antibodies to soluble liver antigen, actin, liver cytosol type 1, asialoglycoprotein receptor, chromatin, cyclic citrullinated peptide, and uridine glucuronosyltransferases have been associated with the occurrence, severity, and progression of autoimmune hepatitis, and antibodies to Sp100, gp210, and centromere have had similar implications in primary biliary cirrhosis. Antibodies to soluble liver antigen have shown the most promise in autoimmune hepatitis as they have been associated with severe histological changes, long durations of treatment, relapse after drug withdrawal, and high frequency of liver failure. Antibodies to the nuclear rim pore protein, gp210, have shown the most promise in primary biliary cirrhosis as they have been associated with severe interface hepatitis, lobular inflammation, and progression to liver failure. The major limitations of the autoantibodies have been their lack of standardized assays, low negative predictabilities, and fluctuating levels. Performance parameters will improve as critical pathogenic pathways, comprehensive testing batteries, and standardized assays through international exchange workshops are developed. Progress has been made in identifying the serological markers of prognosis in autoimmune liver disease, and they promise to reflect critical disease mechanisms and enhance patient management.

Aetiopathogenesis of autoimmune hepatitis

Interface hepatitis, histological hallmark of autoimmune hepatitis (AIH), is a dense portal mononuclear cell infiltrate invading the parenchyma, consisting of CD4 and CD8 T-lymphocytes, monocytes/macrophages and plasma cells. What triggers AIH is unknown, but there is evidence that failure of immune homeostasis plays a permissive role allowing liver autoantigen-specific cells to attack hepatocytes. Damage is likely to be orchestrated by CD4 T-lymphocytes recognizing an autoantigenic liver peptide. For autoimmunity to arise, the peptide, embraced by an HLA class II molecule, must be presented to naïve CD4 T-helper (T(H)0) cells by professional antigen-presenting cells. Once activated, T(H)0 cells can differentiate into T(H)1 cells, which are pivotal to macrophage activation, enhance HLA class I expression, rendering liver cells vulnerable to CD8 T-cell attack, and induce HLA class II expression on hepatocytes; or into T(H)2 cells producing IL-4, IL-10 and IL-13, cytokines favouring autoantibody production by B-lymphocytes. Autoantigen recognition is tightly controlled by regulatory mechanisms, such as those exerted by CD4+CD25+ regulatory T-cells (T-regs). Numerical and functional T-reg impairment characterizes AIH, particularly during active disease. Advances in the study of autoreactive T-cells stem mostly from AIH type 2, where the main autoantigen, CYP2D6, is known enabling characterization of antigen-specific immune responses. Monocyte involvement in the autoimmune liver attack has been recently reported.

Autoantibodies to asialoglycoprotein receptor (ASGPR) measured by a novel ELISA--revival of a disease-activity marker in autoimmune hepatitis

BACKGROUND

The liver-specific ASGPR is an autoantigen in autoimmune hepatitis (AIH) patients. Anti-ASGPR antibody correlates with disease activity, however, only in-house assays have been reported so far.

METHODS

Rabbit ASGPR was purified by affinity chromatography on galactose-Sepharose and used for standardised detection of anti-ASGPR by ELISA. Anti-ASGPR IgG was measured in sera from 45 patients with AIH, PBC (n=43), alcoholic liver disease (n=13), HBV infection (n=35), HCV infection (n=53), and 118 blood donors. Anti-ASGPR was correlated with biochemical parameters of disease activity in 22 AIH patients with consecutive samples.

RESULTS

Twenty-one of 30 untreated (70%) and five of 15 treated AIH patients (30%) showed elevated anti-ASGPR at first presentation. Only one blood donor demonstrated anti-ASGPR. ALD and PBC patients were all negative. ROC curve analysis of AIH and disease-control patients revealed a sensitivity of 77.8% and a specificity of 99.4%. Three (8.6%) of 35 HBV and 7 (13.2%) of 53 HCV patients demonstrated elevated anti-ASGPR. In AIH patients, anti-ASPGR correlated with liver-transaminases levels. In 22 follow-up patients, elevation of anti-ASPGR preceded liver-transaminases increase.

CONCLUSIONS

The novel anti-ASGPR ELISA is a readily available and specific diagnostic tool for anti-ASGPR detection in AIH. Quantification of anti-ASGPR is helpful in monitoring disease activity.

Autoimmune hepatitis

Autoimmune hepatitis (AIH) is an inflammatory liver disease affecting mainly females and characterised histologically by interface hepatitis, biochemically by elevated transaminase levels and serologically by the presence of autoantibodies and increased levels of immunoglobulin G. AIH responds to immunosuppressive treatment, which should be instituted as soon as diagnosis is made. Seropositivity for smooth muscle and/or anti-nuclear antibody defines type 1 AIH, while positivity for liver kidney microsomal type 1 antibody defines type 2 AIH. The aetiology of AIH is unknown, though both genetic and environmental factors are involved in its expression. Immune reactions against host liver antigens are believed to be the major mechanism of liver damage.

Aetiopathogenesis of autoimmune hepatitis

The histological hallmark of autoimmune hepatitis (AIH) is a dense portal mononuclear cell infiltrate that invades the surrounding parenchyma and comprises T and B lymphocytes, macrophages, and plasma cells. An unknown but powerful stimulus must be promoting the formation of this massive inflammatory cellular reaction that is likely to initiate and perpetuate liver damage. An autoimmune attack can follow different pathways to inflict damage on hepatocytes. Liver damage is likely to be orchestrated by CD4⁺ T lymphocytes recognizing an autoantigenic liver peptide. To trigger an autoimmune response, the peptide must be embraced by an HLA class II molecule and presented to naïve CD4⁺ T helper (Th0) cells by professional antigen presenting cells, with the co-stimulation of ligand-ligand fostering interaction between the two cells. Th0 cells become activated, differentiate into functional phenotypes according to the cytokines prevailing in the microenvironment and the nature of the antigen, and initiate a cascade of immune reactions determined by the cytokines produced by the activated T cells. Th1 cells, arising in the presence of the macrophage-derived interleukin (IL) -12, secrete mainly IL-2 and interferon-gamma (IFN-γ), which activate macrophages, enhance expression of HLA classI(increasing liver cell vulnerability to a CD8⁺ T cell cytotoxic attack), and induce expression of HLA class II molecules on hepatocytes. Th2 cells, which differentiate from Th0 if the microenvironment is rich in IL-4, produce mainly IL-4, IL-10, and IL-13 which favour autoantibody production by B lymphocytes. Physiologically, Th1 and Th2 antagonize each other. Th17 cells, a recently described population, arise in the presence of transforming growth factor beta (TGF-β) and IL-6 and appear to have an important effector role in inflammation and autoimmunity. The process of autoantigen recognition is strictly controlled by regulatory mechanisms, such as those exerted by CD4⁺CD25⁺ regulatory T cells, which derive from Th0 in the presence of TGF-β, but in the absence of IL-6. If regulatory mechanisms fail, the autoimmune attack is perpetuated. Over the past three decades different aspects of the above pathogenic scenario have been investigated. In particular, a defect in immunoregulation affecting CD4⁺CD25⁺ regulatory T cells (T-regs) has been demonstrated in AIH, particularly at diagnosis or during relapse. Advances in the study of autoreactive T cells have occurred mostly in AIH type 2, since the knowledge that CYP2D6 is the main autoantigen has enabled the characterization of both CD4 and CD8 T cells targeting this cytochrome. CD4 T cells from patients with type 2 AIH positive for the predisposing HLA allele DRB1*0701 recognize seven regions of CYP2D6, five of which are also recognized by CD8 T cells. High numbers of IFN-γ producing CD4 T cells and CD8 T cells are associated with biochemical evidence of liver damage, suggesting a combined cellular immune attack.

Autoantibody profiling of Chinese patients with autoimmune hepatitis using immunoproteomic analysis

In the present study, immunoproteomic analysis was utilized to systemically characterize global autoantibody profiles in autoimmune hepatitis (AIH). Sera from 21 patients with AIH and 15 healthy controls were analyzed for the antibody reactivity against the protein antigens of HepG2, a human hepatoma cell line. The lysates of HepG2 cells were separated by two-dimensional electrophoresis and then immunoblotted with each serum sample. Matrix-assisted laser desorption/ionization mass spectrometry or/and nanoelectrospray ionization MS/MS were then used to identify antigens, among which a bifunctional enzyme in mitochondrial, fumarate hydratase (FH), was further analyzed by ELISA using recombinant FH as a coating antigen. A total of 18 immunoreactive spots were identified as 13 proteins, 8 of which have not been reported in AIH. Immune reactivity to FH was detected in 66.67% of patients with AIH, 19.35% of patients with primary biliary cirrhosis (PBC), 12.31% of patients with chronic hepatitis B (CHB), 6.35% of patients with chronic hepatitis C (CHC), 11.32% of patients with systemic lupus erythematosus (SLE), and 3.57% of normal individuals. The differences of prevalence between AIH patients and healthy controls as well as other diseases were of statistical significance (P<0.001). These data demonstrate the serological heterogeneity in AIH and suggest the diversity of the mechanisms underlying AIH. FH, recognized mainly in AIH rather than in viral hepatitis and other autoimmune diseases, may have utility in improved diagnosis of AIH.

[Antireceptor and antichannel autoantibodies]

This review of literature concerns the different autoantibodies directed against membrane receptors and ion channels. The target antigens, the associated pathologies, the pathogenesis and the methods of detection of these autoantibodies will be addressed. Some of these autoantibodies are thought to be closely related to the auto-immune disease whereas for some others their pathogenesis role is still unclear. Overall, the roles of antibodies are different between diseases, but the presence of such autoantibodies support the basis of intervening immunotherapy, antibody titers predicted the activity of the diseases and some of them are very specific and become the useful markers for the diagnosis. Some autoantibodies are detected routinely as the antiacetylcholine receptor, voltage-gated potassium and calcium channels autoantibodies whereas most of them are detected very rarely and only by specialized laboratories. This review will be divided in three parts with the following classification: the first group of autoantibodies directed against membrane receptors included receptors with an enzymatic activity (mostly tyrosine kinase) with one transmembrane domain, receptors associated to G protein with seven transmembrane domains, ion channels and receptors associated to the membrane by the glycosylphosphatidylinositol and the second group of intracellular receptor autoantibodies directed to the estrogens, androgens, lamin and kinesin receptors.

Autoimmune hepatitis and primary sclerosing cholangitis

Autoimmune liver disease in children presents predominantly as autoimmune hepatitis (AIH) and primary sclerosing cholangitis (PSC). These diagnoses must be considered in patients who have acute and chronic hepatitis, particularly when an extrahepatic autoimmune disorder is present. In AIH, the timely and sustained control of liver inflammation is critical to improve the short- and long-term outcomes. No effective treatment for PSC has been identified to date, but supportive care, careful attention to complications and associated nonhepatic diseases, and liver transplantation significantly improve the long-term outcome.

Anti-cyclic citrullinated peptide antibodies in type 1 autoimmune hepatitis

BACKGROUND

Besides the autoantibodies included in the diagnostic criteria of type 1 autoimmune hepatitis, many other autoantibodies have been described in this condition. Recently, antibodies against cyclic citrullinated peptide have been validated as specific diagnostic and prognostic markers of rheumatoid arthritis.

AIM

To assess whether these antibodies are part of the autoantibody repertoire of type 1 autoimmune hepatitis and correlate with rheumatological manifestations.

METHODS

Antibodies against cyclic citrullinated peptide were tested by a commercially available enzyme-linked immunosorbent assay.

RESULTS

The antibodies were found in 12 of 133 (9%) type 1 autoimmune hepatitis, two of 49 (4%) with primary biliary cirrhosis, one of 80 (1%) with hepatitis C virus-related chronic liver disease and 53 of 89 (60%) with rheumatoid arthritis serum samples. High titres were found only in rheumatoid arthritis and type 1 autoimmune hepatitis. No clinical (in particular rheumatological manifestations), biochemical or immunoserological differences were detectable between antibodies against cyclic citrullinated peptide positive and negative type 1 autoimmune hepatitis sera, with the exception of rheumatoid factor, always negative in the positive ones.

CONCLUSIONS

Antibodies against cyclic citrullinated peptide can be detected in a subgroup of patients with type 1 autoimmune hepatitis. They might be part of the wide range of autoantibody production characteristic of this condition and/or, less probably, be predictive of future rheumatoid arthritis development.

Detection of circulating autoantibodies directed against the asialoglycoprotein receptor using recombinant receptor subunit H1

BACKGROUND/AIMS

The asialoglycoprotein-receptor (ASGPR) is a major liver-specific target autoantigen in autoimmune hepatitis. ASGPR heteromers of two subunits H1 and H2 provide clearance of circulating asialoglycoproteins by receptor-mediated endocytosis. The aim of this study was to establish whether a recombinantly expressed subunit H1 presenting conformational epitopes is capable of detecting autoantibodies against ASGPR in patients with inflammatory liver disease.

METHODS

The major subunit H1 was expressed in human-embryo-kidney 293-cells and prepared by ligand-affinity-chromatography similar to the complete receptor from normal liver. Reactivities of anti-ASGPR positive sera from 219 patients with both recombinant H1 and natural receptor were compared using enzyme-immunoassay (EIA).

RESULTS

194 of 219 sera (88.6%) showed absorbance values on 293-H1 within a range of +/-15% compared to the natural receptor. 145 of 149 sera (97.3%) positive on ASGPR were also positive on recombinant H1. Titers of 61/62 sera (98.4%) revealed no deviation of more than one dilution step. ASGPR reactivity could be inhibited in 29 sera with up to 50 ng/microl of 293-H1.

CONCLUSIONS

These results indicate that the antigenic sites of the human ASGPR are mainly located on the mammalian-expressed subunit H1. Therefore, 293-H1 is a powerful tool for the detection of autoantibodies against ASGPR.

Mechanisms of autoimmune hepatitis

Autoimmune hepatitis (AIH) is a progressive inflammatory liver disease with a female preponderance, responsive to immunosuppressive treatment. Two types of AIH are described: type 1 AIH is characterized by positivity for smooth muscle and/or antinuclear antibody, while type 2 AIH is positive for liver kidney microsomal type 1 antibody. The putative mechanisms leading to the development of this condition include genetic predisposition to autoimmunity through possession of specific human leukocyte antigen alleles, immune reactions to liver cell antigens, possibly triggered by a mechanism of molecular mimicry, where immune responses to external pathogens, e.g. viruses, become directed toward structurally similar self-components, and an impairment in immune regulation. AIH has been described to arise de novo after liver transplantation. The mechanisms leading to post-transplant autoimmunity remain to be defined.

Asialoglycoprotein receptor facilitates hemolysis in patients with alcoholic liver cirrhosis

Hemolysis in patients with advanced alcoholic liver disease is a common clinical problem and indicates an unfavorable prognosis. In many cases, the etiology of the hemolysis remains unknown. We observed three patients with alcoholic liver disease, suffering from severe hemolytic anemia, requiring multiple blood transfusions. Steroid therapy was ineffective and two of the patients died. All patients had a soluble variant of the human asialoglycoprotein receptor (s-ASGP-R) in their serum, as well as high titers of autoantibodies against this receptor (anti-ASGP-R). Consecutively, examination of 60 patients with alcoholic liver disease revealed a high incidence for s-ASGP-R (36%) and anti-ASGP-R (27%) in patients with alcoholic liver cirrhosis (ALC) compared to patients with cirrhosis due to viral hepatitis. The potential etiology of hemolysis was studied in vitro on erythrocytes from patients with ALC and from healthy donors. Isolated ASGP-R but not anti-ASGP-R bound to the surface of erythrocytes preferentially of blood group A1 and caused dose-dependent agglutination and hemolysis, while this phenomenon was much lower using erythrocytes of the blood group B and almost absent with blood group O-erythrocytes. Furthermore, agglutination and hemolysis only occurred in erythrocytes from ALC-patients or after the pre-treatment of cells with neuraminidase. ASGP-R induced agglutination and hemolysis was blocked by the competitive ASGP-R inhibitor asialofetuin. In conclusion, our results indicate a new, non-immunological mechanism for hemolysis in patients with alcoholic liver disease, mediated through agglutination by a soluble variant of the human asialoglycoprotein receptor and mechanical shear stress.

Autoantibodies in the diagnosis and management of liver disease

Autoantibodies are nonpathogenic manifestations of immune reactivity, and they may occur in acute and chronic liver diseases. Autoantibodies may be consequences rather than causes of the liver injury, and they should be regarded as diagnostic clues rather than etiologic markers. Conventional autoantibodies used in the categorization of autoimmune liver disease are antinuclear antibodies, smooth muscle antibodies, antibodies to liver/kidney microsome type 1, antimitochondrial antibodies, and atypical perinuclear anti-neutrophil cytoplasmic antibodies. Ancillary autoantibodies that enhance diagnostic specificity, have prognostic connotation, or direct treatment are antibodies to endomysium, tissue transglutaminase, histones, doubled-stranded DNA, and actin. Autoantibodies that have an emerging diagnostic and prognostic significance are antibodies to soluble liver antigen/liver pancreas, asialoglycoprotein receptor, liver cytosol type 1, and nuclear pore complex antigens. Autoantibodies of uncertain clinical value that remain under investigation are antibodies to chromatin, lactoferrin, and Saccharomyces cervisiae. Continued recognition and characterization of autoantibodies should improve diagnostic precision, provide prognostic indices, and elucidate target autoantigens. These advances may in turn clarify pathogenic mechanisms, facilitate the development of animal models, and generate novel site-specific therapies.

Modulation of the outcome and severity of hepadnaviral hepatitis in woodchucks by antibodies to hepatic asialoglycoprotein receptor

Viral hepatitis is frequently accompanied by humoral autoimmune responses toward both organ-nonspecific and liver-specific antigens, but contribution of these reactivities to liver injury remains unrecognized. Infection with woodchuck hepatitis virus (WHV) has been identified as a potent inducer of autoantibodies against asialoglycoprotein receptor (anti-ASGPR), a molecule essentially unique to hepatocytes that mediates clearance of desialylated serum proteins. In this study, we applied the WHV-woodchuck model of hepatitis B to examine the effect of experimentally elicited anti-ASGPR on the progression and the severity of WHV hepatitis in initially healthy animals immunized with the receptor and then infected with WHV and in woodchucks with ongoing chronic WHV hepatitis. The results implied that the induction of anti-ASGPR prior to WHV infection tends to modulate acute viral hepatitis toward chronic outcome and, in animals with established chronic WHV infection, exacerbates histologic severity of liver lesions. The findings also suggest that the liver compromised by chronic hepadnavirus infection might be prone to anti-ASGPR-directed complement-mediated hepatocellular injury and that this is associated with formation of the ASGPR-anti-ASGPR immune complexes on hepatocyte surface. In conclusion, the host's immune response mounted against a hepatocyte-specific autoantigen may modulate both the outcome and the severity of liver injury in viral hepatitis.

Autoimmune hepatitis

Autoimmune hepatitis is the archetype of liver autoimmune disease. It is divided into two types, according to the autoantibody profile. It should be suspected and diagnosed early since treatment is highly effective in preventing liver failure and transplant. The possible pathogenic scenario is described in the present review.

Role of the asialoglycoprotein receptor in binding and entry of hepatitis C virus structural proteins in cultured human hepatocytes

We used a baculovirus-based system to prepare structural proteins of hepatitis C virus (HCV) genotype 1a. Binding of this preparation to cultured human hepatic cells was both dose dependent and saturable. This binding was decreased by calcium depletion and was partially prevented by ligands of the asialoglycoprotein receptor (ASGP-R), thyroglobulin, asialothyroglobulin, and antibody against a peptide in the carbohydrate recognition domain of ASGP-R but not preimmune antibody. Uptake by hepatocytes was observed with both radiolabeled and dye-labeled HCV structural proteins. With hepatocytes expressing the hH1 subunit of the ASGP-R fused to green fluorescent protein, we could show by confocal microscopy that dye stain cointernalized with the fusion protein in an area surrounding the nucleus. Internalization was more efficient with a preparation containing p7 than with one that did not. The two preparations bound to transfected 3T3-L1 cells expressing either both (hH1 and hH2) subunits of the ASGP-R (3T3-22Z cells) or both hH1 and a functionally defective variant of hH2 (3T3-24X cells) but not to parental cells. Additionally, uptake of dye-labeled preparation containing p7 was observed with 3T3-22Z cells but not with 3T3-L1 or 3T3-24X cells or with the preparation lacking p7, suggesting that p7 regulates the internalization properties of HCV structural proteins. Our observations suggest that HCV structural proteins bind to and cointernalize with the ASGP-R in cultured human hepatocytes.

Pathogenesis of autoimmune hepatitis

Autoimmune hepatitis is initiated by CD4 T cells that recognize self-antigen. The effector cells differentiate into functional phenotypes according to cytokines in the microenvironment and the nature of the triggering antigen. Hepatocytes can express class II molecules and present antigenic peptides through a bystander mechanism. NKT cells reside in the normal liver but may be involved in liver cell damage possibly through the expression of Fas ligand. Autoantibodies may also participate in the process by complexing with antigen on the hepatocyte membrane surface and by interacting with mononuclear cells with Fc receptors. Molecular mimicry generates cross-reactivities that predispose the immune system to cross-react with self-antigens. Multiple exposures to pathogens with antigenic similarities may prime a cross-reactive subset of T cells in the genetically predisposed host. Autoimmunity against one self-antigen may then spread through molecular mimicry to other homologous self-antigens and may lead to overt autoimmune disease. Anatomically distant tissues may also become involved as autoreactive T cells that had been activated in one organ expand and infiltrate other organs that express similar epitopes.

Autoimmune hepatitis: diagnostic criteria, subclassifications, and clinical features

The diagnosis of AIH depends on the finding of several suggestive features together with careful exclusion of liver diseases of other etiologies. Wherever possible, the diagnosis should be confirmed histologically by an experienced hepatopathologist. Seronegativity for the conventional autoantibodies at presentation does not exclude a diagnosis of AIH. It is important to test for anti-LKM1 antibodies to avoid missing a diagnosis of type 2 AIH, with potentially serious consequences. Although the syndrome is associated with characteristic biochemical abnormalities, and biochemical parameters are commonly used for monitoring response to therapy, it should be borne in mind that neither these nor autoantibody titers are completely reliable indices of disease activity. Although the various systems that have been promulgated for classification of the disease may identify different groups of patients on pathogenetic or clinical criteria and are useful for research purposes, none is yet sufficiently exclusive in terms of defining prognosis or planning treatment strategies to be applicable to the individual patient seen in the clinic. Clinical management should therefore continue to be individually tailored.

Autoimmune hepatitis

Autoimmune hepatitis (AIH) is a rare disease, characterized by female predominance, hypergammaglobulinemia, autoantibodies, association with HLA DR3 and HLA DR4 and a good response to immunosuppression. Different subtypes of AIH may be distinguished, based on differences in the autoantibody patterns. AIH type 1 is characterized by anti-nuclear (ANA) and/or anti-smooth muscular (SMA) autoantibodies. AIH type 2 is characterized by liver/kidney microsomal autoantibodies (LKM). AIH type 3 may be distinguished by autoantibodies to soluble liver proteins (SLA) or the liver pancreas antigen (LP). AIH-2 affects predominantly pediatric patients and is characterized by a more severe clinical course, a higher frequency of relapse under immunosuppressive treatment and a more frequent progression to cirrhosis. In contrast, AIH types 1 and 3 show a higher age of onset and a better long-term response to immunosuppressive treatment. At present, the treatment of choice is prednisone alone or a combination with prednisone and azathioprine. Both treatment protocols show high survival rates. However, a rate of 13% of treatment failures and the failure to induce permanent remission in most patients underlines the urgent need to develop additional treatment regimens. A yet unknown genetic predisposition is believed to act as the underlying etiological factor in AIH. This genetic predisposition includes a few known risk factors such as the presence of HLA DR3 or HLA DR4, deletions of C4A alleles and female gender. Furthermore, it has to be postulated that defects in immunoregulatory genes exist. A model for such defects may be the autoimmune polyglandular syndrome type 1 (APS1), which results from the defects in a single gene, the autoimmune regulator type 1 (AIRE-1). Patients with APS1 suffer from mucocutaneous candidiasis and a number of organ-specific autoimmune diseases. Characteristic is a high variability in the number and character of the disease components in APS1, indicating that other genetic and environmental factors may strongly modulate the outcome of disease. Environmental factors may comprise chemical influences, such as nutritional compounds and drugs, or virus infections. Several drugs or chemicals were shown to induce hepatitis with autoimmune involvement, e.g. tienilic acid, dihydralazine and halothane. Adduct formation of an activated metabolite is believed to act as a trigger and to induce a specific immune response. Similarly, viruses were repeatedly shown to trigger autoimmune hepatitis. In virus infections, sequence similarities between viral and self-proteins may trigger autoimmune processes and the simultaneous presence of inflammatory cytokines during virus infection may further increase the risk of developing self-perpetuating autoimmune reactions which overshoot.

Enzyme Immunoassay for Autoantibodies to Human Liver-Type Arginase and Its Clinical Application

Background: Arginase is an enzyme of the urea cycle, and one of the two isoenzymes is the liver-type enzyme. We examined serum autoantibodies to this liver-type enzyme in patients with hepatitis.

Methods: Antibodies to recombinant human liver-type arginase were measured by ELISA in 95 patients and 55 healthy controls.

Results: The mean absorbance values in the ELISA assays of patients with definite autoimmune hepatitis (n = 11; P &lt;0.0001), probable autoimmune hepatitis (n = 31; P &lt;0.0001), and hepatitis C (HCV; n = 20; P &lt;0.01) were significantly different from those of healthy controls, but the values in patients with hepatitis B (HBV; n = 23) and other autoimmune diseases (n = 10) were not significantly different from those of healthy controls. When the cutoff was fixed at the upper 95th percentile of the absorbance value in healthy controls, positive reactions were found in 18.2%, 32.3%, 20.0%, 13.0%, and 10.0% of patients with definite autoimmune hepatitis, probable autoimmune hepatitis, HCV hepatitis, HBV hepatitis, and other autoimmune diseases, respectively. All of these positive reactions were abolished by inhibition of serum with recombinant antigen. The specificity and sensitivity of this ELISA were 96% and 29%, respectively. The intraassay and interassay coefficients of variation were 2.3–7.5% and 9.8–11%, respectively. There was no relationship between these antibodies and anti-nuclear, anti-smooth muscle, or anti-cytochrome P450IID6 antibodies.

Conclusions: The ELISA for anti-liver-type arginase autoantibody improved the detectability of autoimmune hepatitis when compared with established assays for liver-specific autoantibodies.

Pathogenesis of autoimmune hepatitis

Autoimmune hepatitis (AIH) is an idiopathic disorder affecting the hepatic parenchyma. There are no morphological features that are pathognomonic of the condition but the characteristic histological picture is that of an interface hepatitis without other changes that are more typical of other liver diseases. It is associated with hypergammaglobulinaemia, high titres of a wide range of circulating auto-antibodies, often a family history of other disorders that are thought to have an autoimmune basis, and a striking response to immunosuppressive therapy. The pathogenetic mechanisms are not yet fully understood but there is now considerable circumstantial evidence suggesting that: (a) there is an underlying genetic predisposition to the disease; (b) this may relate to several defects in immunological control of autoreactivity, with consequent loss of self-tolerance to liver auto-antigens; (c) it is likely that an initiating factor, such as a hepatotropic viral infection or an idiosyncratic reaction to a drug or other hepatotoxin, is required to induce the disease in susceptible individuals; and, (d) the final effector mechanism of tissue damage probably involves auto-antibodies reacting with liver-specific antigens expressed on hepatocyte surfaces, rather than direct T-cell cytotoxicity against hepatocytes.

Study of antigenic sites on the asialoglycoprotein receptor recognized by autoantibodies

The aim of this study was to identify the epitopes recognized by antibodies to the asialoglycoprotein receptor, a specific hepatocyte protein, from sera of patients with autoimmune hepatitis. An ELISA test was used to detect anti-asialoglycoprotein receptor antibodies in the sera of patients with autoimmune hepatitis. Positive sera were tested against the same antigen by slot blot, by Western blot and by immunoprecipitation of the untreated protein and following treatment with beta-mercaptoethanol (beta-ME) and endoglycosidase F. The mature, unglycosylated and partially glycosylated forms of the asialoglycoprotein receptor synthesized by HepG2 cells were tested against positive patients' sera, as well as the in vitro translated unglycosylated form of the H1 subunit of the receptor. Sera from patients with autoimmune hepatitis recognized equally the native form, as well as the beta-ME-modified form, but less well the deglycosylated form of the human mature receptor. No reactivity was found when these sera were tested against the denatured human protein. In addition, neither the unglycosylated H1 subunit nor any of the HepG2-synthesized asialoglycoprotein receptor forms bound to the antibodies. Altogether, these results show that anti-asialoglycoprotein receptor antibodies in the sera of patients with autoimmune hepatitis are directed against conformational structures of the mature hetero-oligomeric form of the human liver protein and that at least some epitopes were located on the extracellular domain of the antigen.

Complement-mediated cytotoxicity and inhibition of ligand binding to hepatocytes by woodchuck hepatitis virus-induced autoantibodies to asialoglycoprotein receptor

Hepadnavirus invasion in woodchucks has been identified as a potent inducer of autoantibodies against asialoglycoprotein receptor (anti-ASGPR), a molecule essentially unique to hepatocytes that mediate clearance of desialylated serum proteins. We evaluated the possible pathogenetic importance of anti-ASGPR triggered by woodchuck hepatitis virus (WHV), using anti-ASGPR-reactive serum immunoglobulins (Igs) from five animals with different stages of WHV hepatitis or self-limited WHV infection and isolated woodchuck hepatocytes or HepG2 cells as targets. The results revealed that WHV-induced anti-ASGPR can specifically inhibit asialoglycoprotein recognition by both homologous and heterologous liver cells, as tested in an asialofetuin (ASFN)-binding radioassay. However, the extent of the interference significantly varied (from 85% inhibition to none) for anti-ASGPR with similar titer from different animals, indicating a high degree of heterogeneity in the ASGPR epitope specificity and in the potential biological effects of these autoantibodies. The WHV-triggered anti-ASGPR also induced complement-mediated hepatocytolysis in a microculture tetrazolium (MTT) assay, which ranged from 8.9% +/- 0.3% to 33.6% +/- 3.6% (mean +/- SD) for different animals and target cell numbers. This cytopathic effect was strictly ASGPR-specific, complement-dependent, and was not related to the anti-ASGPR ability to inhibit ligand-hepatocyte binding. Our findings indicate that among pathways by which anti-ASGPR autoimmunity could cause liver damage, hepadnavirus-induced anti-ASGPR might impair hepatocytes by both disrupting clearance of desialylated proteins and activation of the complement-mediated cytolysis. These cytopathic effects might contribute to the pathogenesis, aggravate severity, and prolong recovery from liver injury in viral hepatitis.

A novel antibody directed against a three-dimensional configuration of a 95-kDa protein in patients with autoimmune hepatic diseases

Sera from patients with primary biliary cirrhosis recognize various cellular components, such as mitochondria, centromere, nuclear envelope, and multiple nuclear dot antigens. There also appears to be a novel antibody reacting with a particular protein in these sera. The presence of this antibody was investigated by double immunodiffusion using rat liver cytoplasmic antigens, by immunoprecipitation of [35S]-methionine labelled HeLa cell extracts, and by immunoblot using disrupted HeLa cell extracts. Test sera were obtained from 491 patients with various liver diseases. Nine of the 491 sera were found to react with a 95-kDa protein as determined by immunoprecipitation of [35S]-methionine labelled HeLa cell extracts and by double immunodiffusion using a rat liver microsomal preparation. However, these same nine sera showed no reaction in the immunoblot assay. On the basis of its molecular mass and its presence in the cytoplasmic fraction, this antigen was named p95 C. This anti-p95 C antibody was detected in six of 50 (12%) sera from patients with primary biliary cirrhosis, and in three of 31 (9.7%) sera from patients with autoimmune hepatitis, but not in any of the remaining 410 sera obtained from patients with other hepatic diseases. It is concluded that anti-p95 C antibody reacts primarily with the native form of the 95-kDa protein, and represents another possible analyte for diagnosing autoimmune liver diseases.

Specific liver autoreactivity in schistosomiasis mansoni

To investigate the possible involvement of autoimmune mechanisms in the development of hepatosplenic schistosomiasis (HSS), 234 patients with chronic Schistosoma mansoni infections were screened for a wide range of non-organ-specific autoantibodies as well as for antibodies reacting with the GOR peptide and with a liver-specific autoantigen, the hepatic asialoglycoprotein receptor (ASGP-R). Thirty-five (15.0%) were seropositive for antinuclear, smooth muscle or gastric parietal cell antibodies at low titres (< or = 1:80), and 15/176 (8.5%) had anti-GOR, all of whom had concomitant hepatitis C viral (HCV) infections. Anti-ASGP-R was found in 64 (27.4%) of the 234 patients at titres similar to those found in 18 untreated auto-immune hepatitis patients studied concurrently. Anti-ASGP-R seropositivity occurred significantly (P < 0.005) more frequently in patients with HSS (62/190, 32.6%) than in those with hepatointestinal schistosomiasis (2/44, 4.5%), but did not correlate with severity of liver disease or with the presence of the non-organ-specific autoantibodies. Anti-ASGP-R was found significantly (P < < 0.0005) less frequently in HSS patients who had had a splenectomy for portal hypertension (5/86, 5.8%) than in those who had not had a splenectomy (57/104, 54.8%). The findings suggest that liver-specific autoreactivity may play a role in the development of HSS.

Autoimmune hepatitis. Definition--classification--histopathology--immunopathogenesis

Autoimmune hepatitis (AIH) is a distinct form of acute and chronic inflammatory liver disease in which immune reactions against host antigens are found to be the major pathological mechanism. If left untreated it carries an unfavourable prognosis, and the diagnosis should be made as soon as possible. The diagnostic approach has been greatly facilitated by the establishment of a panel of marker autoantibodies, which do not define distinct therapeutic groups of AIH, but do allow a subgrouping based on differences in patient populations, some clinical features and prognosis. The characterization of organ-specific components of the liver cell surface as targets of cellular and humoral autoimmune reactions give new insights into the pathogenesis of the disease, even though the primary event triggering the disease remains to be defined. The most important disease-promoting factor seems to be a genetically determined background for autoimmunity. Without this different environmental factors, including viruses, toxins, cytokines and drugs, are only able to induce transient autoimmune phenomena and not autoimmune disease. The histopathology of AIH is in keeping with the present pathogenetic concept. Although there is no pathognomonic feature distinguishing this type of hepatitis from virus-induced forms, some distinct morphological lesions are regarded as characteristic. Clinical research on AIH has benefited greatly from observations of experimental AIH in mice. Recognition of the critical role of autoreactive T-lymphocytes in the pathogenesis and the observation of spontaneous recovery from AIH in the animal model associated with antigen-specific and antigen-non-specific T-cell suppression have made basic contributions to our improved understanding of the natural course of AIH in humans.

Composition, antigenic properties and hepatocyte surface expression of the woodchuck asialoglycoprotein receptor

We have purified woodchuck hepatic asialoglycoprotein receptor (ASGPR) by ligand affinity chromatography and have identified it as a heterooligomeric complex comprised of two subunits with molecular masses of 40 and 47 kD, designated as woodchuck hepatic lectin 1 and 2 (WHL1 and WHL2), respectively. With the help of antisera generated against the soluble, bioactive woodchuck and rabbit ASGPRs and anti-subunit monospecific antibodies, distinct antigenic specificity of each of the ASGPR polypeptide subunits and interspecies immunologic cross-reactivity of the receptor polypeptides displaying comparable molecular masses were documented. In contrast to the purified woodchuck receptor, WHL2 antigenic reactivity was not identifiable in woodchuck hepatocyte plasma membranes unless the intact membranes were exposed to an asialylated ligand or a soluble membrane fraction was incubated with anti-receptor antibody. These findings imply that both WHL1 and WHL2 are expressed on the hepatocyte surface and contribute to ligand binding, since antibody specific to either subunit blocks ligand attachment. Our results also indicate that ligand binding modifies antigenic properties of the membrane expressed ASGPR.