Molecular mimicry in primary biliary cirrhosis. Evidence for biliary epithelial expression of a molecule cross-reactive with pyruvate dehydrogenase complex-E2

Autoimmune Markers in Primary Biliary Cholangitis

Primary biliary cholangitis (PBC) is a chronic cholestatic liver disease. The most common antibody associated with PBC is the anti-mitochondrial antibody (AMA), present in 90% to 95% of patients. For patients who are AMA-negative, novel biomarkers, such as antinuclear antibody-specific antibodies Sp100 and gp210 and anti-kelch-like-12 and anti-hexokinase-1 antibodies, may further aid in the diagnosis of PBC. Several laboratory methods, including immunofluorescence, enzyme-linked immunosorbent assay, immunoblotting, and bead-based assays, exist to evaluate for the presence of antibodies. This article describes various methods used to evaluate antibodies as well as describe the antibodies present in PBC.

Linking Human Betaretrovirus with Autoimmunity and Liver Disease in Patients with Primary Biliary Cholangitis

Primary biliary cholangitis (PBC) is an autoimmune liver disease characterized by the production of diagnostic antimitochondrial antibodies (AMA) reactive to the pyruvate dehydrogenase complex. A human betaretrovirus (HBRV) resembling mouse mammary tumor virus has been characterized in patients with PBC. However, linking the viral infection with the disease is not a straight-forward process because PBC is a complex multifactorial disease influenced by genetic, hormonal, autoimmune, environmental, and other factors. Currently, PBC is assumed to have an autoimmune etiology, but the evidence is lacking to support this conjecture. In this review, we describe different approaches connecting HBRV with PBC. Initially, we used co-cultivation of HBRV with biliary epithelial cells to trigger the PBC-specific phenotype with cell surface expression of cryptic mitochondrial autoantigens linked with antimitochondrial antibody expression. Subsequently, we have derived layers of proof to support the role of betaretrovirus infection in mouse models of autoimmune biliary disease with spontaneous AMA production and in patients with PBC. Using Hill’s criteria, we provide an overview of how betaretrovirus infection may trigger autoimmunity and propagate biliary disease. Ultimately, the demonstration that disease can be cured with antiviral therapy may sway the argument toward an infectious disease etiology in an analogous fashion that was used to link H. pylori with peptic ulcer disease.

Antigen-Specific Immunotherapy for Treatment of Autoimmune Liver Diseases

The liver is a critical organ in controlling immune tolerance. In particular, it is now clear that targeting antigens for presentation by antigen presenting cells in the liver can induce immune tolerance to either autoantigens from the liver itself or tissues outside of the liver. Here we review immune mechanisms active within the liver that contribute both to the control of infectious diseases and tolerance to self-antigens. Despite its extraordinary capacity for tolerance induction, the liver remains a target organ for autoimmune diseases. In this review, we compare and contrast known autoimmune diseases of the liver. Currently patients tend to receive strong immunosuppressive treatments and, in many cases, these treatments are associated with deleterious side effects, including a significantly higher risk of infection and associated health complications. We propose that, in future, antigen-specific immunotherapies are adopted for treatment of liver autoimmune diseases in order to avoid such adverse effects. We describe various therapeutic approaches that either are in or close to the clinic, highlight their mechanism of action and assess their suitability for treatment of autoimmune liver diseases.

[Autoimmune hepatitis: Immunological diagnosis]

Autoimmune hepatopathies (AIHT) including autoimmune hepatitis (AIH), primary biliary cirrhosis (PBC), primary sclerosing cholangitis (PSC) and autoimmune cholangitis (AIC), represent an impressive entities in clinical practice. Their pathogenesis is not perfectly elucidated. Several factors are involved in the initiation of hepatic autoimmune and inflammatory phenomena such as genetic predisposition, molecular mimicry and/or abnormalities of T-regulatory lymphocytes. AIHT have a wide spectrum of presentation, ranging from asymptomatic forms to severe acute liver failure. The diagnosis of AIHT is based on the presence of hyperglobulinemia, cytolysis, cholestasis, typical even specific circulating auto-antibodies, distinctive of AIH or PBC, and histological abnormalities as well as necrosis and inflammation. Anti-F actin, anti-LKM1, anti-LC1 antibodies permit to distinguish between AIH type 1 and AIH type 2. Anti-SLA/LP antibodies are rather associated to more severe hepatitis, and particularly useful for the diagnosis of seronegative AIH for other the antibodies. Due to the relevant diagnostic value of anti-M2, anti-Sp100, and anti-gp210 antibodies, the diagnosis of PBC is more affordable than that of PSC and AIC. Based on clinical data, the immunological diagnosis of AIHT takes advantage of the various specialized laboratory techniques including immunofluorescence, immunodot or blot, and the Elisa systems, provided of a closer collaboration between the biologist and the physician.

Chronic Autoimmune Epithelitis in Sjögren's Syndrome and Primary Biliary Cholangitis: A Comprehensive Review

Within the spectrum of autoimmune diseases, Sjögren's syndrome and primary biliary cholangitis are exemplary and can be coined as chronic epithelitis based on their frequent coexistence in clinical practice and the highly specific immune-mediated injury of the small bile ducts and the exocrine glands. The pathogenic mechanisms underlying the diseases are similar, with apoptosis being the key element leading to organ-specific immune-mediated injury directed against the small bile ducts and salivary gland epithelia, respectively along with similar epidemiological features, such as female predominance and the age of onset in the fifth decade of life. Indeed, novel insights into the pathogenesis of the diseases have been obtained in recent years, including a better definition of the role of B and T cells, particularly Th17 cells, and the mechanisms of autoantibody-mediated tissue injury, with anti-mitochondrial antibodies and SS-A/SS-B being identified as specific for primary biliary cholangitis and Sjögren's syndrome, respectively. These findings have opened the possibility to new targeted therapies, but most clinical needs remain unmet, particularly from a therapeutic standpoint where options diverge, with bile acids being the predominant treatment strategy in primary biliary cholangitis and immunomodulators being used to treat Sjögren's syndrome. Here we provide a comprehensive review of the most recent findings on the pathogenesis, clinical manifestations and therapeutic options for Sjögren's syndrome and primary biliary cholangitis, respectively, while stressing the common traits between these conditions. Our cumulative hypothesis is that similarities outnumber differences and that this may prove advantageous towards a better management of patients.

Deletion of Galectin-3 Enhances Xenobiotic Induced Murine Primary Biliary Cholangitis by Facilitating Apoptosis of BECs and Release of Autoantigens

Galectin-3 (Gal-3) is a carbohydrate binding lectin, with multiple roles in inflammatory diseases and autoimmunity including its antiapoptotic effect on epithelial cells. In particular, increased expression of Gal-3 in epithelial cells is protective from apoptosis. Based on the thesis that apoptosis of biliary epithelial cells (BECs) is critical to the pathogenesis of Primary Biliary Cholangitis (PBC), we have analyzed the role of Gal-3 in the murine model of autoimmune cholangitis. We took advantage of Gal-3 knockout mice and immunized them with a mimotope of the major mitochondrial autoantigen of PBC, 2-octynoic acid (2-OA) coupled to BSA (2OA-BSA) and evaluated the natural history of subsequent disease, compared to control wild-type mice, by measuring levels of antibodies to PDC-E2, immunohistology of liver, and expression of Gal-3. We report herein that deletion of Gal-3 significantly exacerbates autoimmune cholangitis in these mice. This is manifested by increased periportal infiltrations, bile duct damage, granulomas and fibrosis. Interestingly, the BECs of Gal-3 knockout mice had a higher response to apoptotic stimuli and there were more pro-inflammatory lymphocytes and dendritic cells (DCs) in the livers of Gal-3 knockout mice. In conclusion, Gal-3 plays a protective role in the pathways that lead to the inflammatory destruction of biliary epithelial cells.

The coexistence of Sjögren's syndrome and primary biliary cirrhosis: a comprehensive review

Organ-specific and systemic autoimmune diseases share numerous features and often coexist in the same patient. Autoimmune cholangitis/primary biliary cirrhosis and Sjogren syndrome represent paradigmatic examples of the common grounds of different autoimmunity phenotypes based on similarities in clinical manifestations and immunopathogenesis. In fact, primary biliary cirrhosis and Sjogren's syndrome have both been coined as an autoimmune epithelitis in which apoptosis may be in both cases the key element to explain the organ-specific immune-mediated injury against the biliary and exocrine gland epithelia, respectively. Further, growing evidence supports in both diseases the view that B cells, T cytotoxic cells, and T helper cells are involved in chronic inflammation, likely via the altered expression of pro-inflammatory cytokines. The presence of estrogen receptors on the biliary and exocrine gland epithelia has been advocated as a key to the female predominance encountered in primary biliary cirrhosis and Sjogren's syndrome. Sadly, despite available data, therapeutic approaches remain largely unsatisfactory and recent studies with mechanistic approaches (as in the case of B cell depletion with rituximab) have been of partial benefit only. Future studies should focus on new molecular tools (single-cell transcriptomics, microRNA, epigenetics) to provide unique insights into common mechanisms.

The intestinal microbiota and microenvironment in liver

The intestinal microbiome plays a significant role in the development of autoimmune diseases, in particular, inflammatory bowel diseases. But the interplay between the intestinal tract and the liver may explain the increased association with autoimmune liver diseases and inflammatory bowel diseases. The gut-liver axis involves multiple inflammatory cell types and cytokines, chemokines and other molecules which lead to the destruction of normal liver architecture. Triggers for the initiation of these events are unclear, but appear to include multiple environmental factors, including pathogenic or even commensal microbial agents. The variation in the gut microbiome has been cited as a major factor in the pathogenesis of autoimmune liver disease and even other autoimmune diseases. The unique positioning of the liver at the juncture of the peripheral circulation and the portal circulation augments the interaction between naïve T cells and other hepatic cells and leads to the disruption in the development of tolerance to commensal bacteria and other environmental agents. Finally, the innate immune system and in particular toll-like receptors play a significant role in the pathogenesis of autoimmune liver disease.

Presence of disease specific autoantibodies against liver sinusoidal cells in primary biliary cirrhosis

AIM: To investigate the presence of autoantibodies directed against liver sinusoidal cells in primary biliary cirrhosis (PBC).

METHODS: Liver biopsies from 21 PBC patients were studied and compared with 12 liver biopsies from disease controls [3 patients with hepatitis B (HBV) virus, 3 patients with hepatitis C virus (HCV), 3 patients with non-alcoholic steatohepatitis and 3 patients with acute alcoholic hepatitis (AAH)]. As healthy controls, we used tissue specimens adjacent to metastatic liver adenocarcinoma. Normal serum was taken from staff members of the unit. The determination of the cell type targeted by autoantibodies present in the patients sera was performed by indirect immunofluorescence (IIF) analysis using paraffin-embedded liver sections as a substrate. Sera from homologous or heterologous PBC patients or sera from the disease control group were used as primary antibodies. The presence of autoantibodies was identified using confocal microscopy.

RESULTS: In total, 18/21 (85.7%) PBC patients exhibited positive staining in the sinusoidal cells, 10/21 (47.6%) in lymphocytes, 8/21 (38%) in cholangiocytes and 7/21 (33.3%) in hepatocytes, when homologous serum and fluorescein isothiocyanate-conjugated immunoglobulin type G (IgG) secondary antibody were used. PBC sections incubated with heterologous PBC serum showed reduced staining (20% for sinusoidal cells, 20% for lymphocytes, 20% for cholangiocytes and 13.3% for hepatocytes). When IgM immunoglobulin, instead of IgG, was used as secondary antibody, positive staining was observed in 75% of lymphocytes, 62.5% of cholangiocytes, 37.5% of hepatocytes and 50% of the sinusoidal cells with a much stronger staining intensity. No staining was observed when either normal or PBC sera were used as a primary antibody on liver sections from the disease control group. When PBC sera were incubated with healthy control sections, weak positive staining of cholangiocytes was observed in 3/21 (14.3%) PBC serum samples. Steatohepatitis serum on PBC sections gave a positive staining of some hepatocytes and lymphocytes but no staining on viral hepatitis sections. Incubation with HBV sera stained some hepatocytes, cholangiocytes and intra-sinusoidal or portal lymphocytes of PBC, HBV and AAH patients but not HCV patients.

CONCLUSION: In this study, for the first time in diseased liver tissue, we have demonstrated that a large proportion of PBC patients have disease specific autoantibodies against liver sinusoidal cells.

Apotopes and innate immune system: novel players in the primary biliary cirrhosis scenario

Our understanding of primary biliary cirrhosis has been rapidly growing over the past decade and the disease is now regarded as a model for other female-predominant, organ-specific autoimmune conditions. Primary biliary cirrhosis ensues from a multi-lineage loss of tolerance to the E2 component of the pyruvate dehydrogenase complex. One of the major unanswered questions in the pathogenesis of primary biliary cirrhosis is the specificity of small intrahepatic bile ducts attack while PDC-E2 is present in mitochondria of all nucleated cells. Recent findings suggest that the uniqueness of the primary target tissue, biliary epithelium, may be of considerable importance for understanding primary biliary cirrhosis and that the biliary epithelial cell is more than an innocent victim. Rather, it attracts an immune attack by virtue of the unique apoptotic mechanisms and by the way it handles PDC-E2. Moreover, recent evidence suggests that apoptotic bodies of biliary epithelial cell are able to activate the innate immune system in the presence of anti-mitochondrial antibodies. This review article is intended to provide a critical overview of the role of apoptosis in biliary epithelial cells, the activation of the innate immune system, and its biological and clinical significance in primary biliary cirrhosis.

The immunobiology and pathophysiology of primary biliary cirrhosis

Primary biliary cirrhosis (PBC) is an autoimmune disease characterized by clinical homogeneity among patients, an overwhelming female predominance, production of a multilineage immune response to mitochondrial autoantigens, inflammation of small bile ducts, and in some patients the development of fibrosis and cirrhosis. The targets in this disease are small bile ducts, and the prototypic serologic response includes antimitochondrial antibodies (AMAs). Several key observations have greatly advanced our understanding of PBC. First, the multilineage immune response, including AMAs, is directed at the E2 component of the 2-oxo-dehydrogenase pathway, particularly PDC-E2. Second, such autoantibodies may be identified years before the clinical diagnosis of disease. Third, the autoreactive T cell precursor frequency for both CD4 and CD8 cells is significantly higher in liver and regional lymph node than in blood, so the multilineage antimitochondrial response may be required for the development of this disease. Fourth, the apotope of biliary cells contains intact PDC-E2; this apotope, in a setting that includes granulocyte macrophage colony-stimulating factor-stimulated macrophages and AMAs, produces an intense proinflammatory response. Fifth, several mouse models of PBC highlight the importance of loss of tolerance to PDC-E2 as well as a critical role for the interleukin (IL)-12 signaling pathway. Finally, genome-wide association studies suggest an important role for the IL-12 pathway in disease susceptibility. Taken together, these findings have resulted in a better understanding of the mechanism for selective biliary cell destruction and have also suggested unique pathways for therapeutic intervention.

Increased expression of mitochondrial proteins associated with autophagy in biliary epithelial lesions in primary biliary cirrhosis

BACKGROUND/AIMS

We have reported the involvement of deregulated autophagy and subsequent cellular senescence in biliary epithelial lesions in primary biliary cirrhosis (PBC). Given that mitochondria are a major target of autophagy, we hypothesized that deregulated autophagy of mitochondria may be involved in autoimmune pathogenesis in PBC.

METHODS

We examined immunohistochemically the expression of pyruvate dehydrogenase complex-E2 component (PDC-E2) and cytochrome c oxidase, subunit I (CCO), in livers taken from patients with PBC (n = 42) and control livers (n = 76). The colocalization of mitochondrial antigens with an autophagy marker microtubule-associated protein-light chain 3β (LC3), a deregulated autophagy marker p62/sequestosome-1 (p62) and a lysosomal marker LAMP-1 was examined by double immunofluorescence. We examined the colocalization of mitochondrial antigens with LC3, p62 and LAMP-1 and the cell-surface expression of PDC-E2 in cultured biliary epithelial cells (BECs) treated with various stresses.

RESULTS

Intense granular expression of PDC-E2 and CCO was seen in the damaged small bile ducts (SBDs) in PBC and the expression was significantly more frequent in PBC than in control livers (P < 0.01). The granular expression of mitochondrial antigens was colocalized with LC3 in damaged SBDs in PBC. The accumulation of LC3-expressing punctae colocalized with PDC-E2 and CCO was significantly more increased in cultured BECs treated with various stresses. The cell-surface expression of PDC-E2 was induced by various stresses in BECs.

CONCLUSION

Deregulated autophagy may contribute to the abnormal expression of mitochondrial antigens and may be involved in the autoimmune pathogenesis of bile duct lesions in PBC.

Autoimmune hepatitis type 2 associated with an unexpected and transient presence of primary biliary cirrhosis-specific antimitochondrial antibodies: a case study and review of the literature

Background

Unlike other autoimmune liver diseases, primary biliary cirrhosis (PBC) has never been reported in early childhood, while type 2 autoimmune hepatitis (AIH) is eminently a paediatric disease.

Case presentation

We describe a case of type 2 AIH with serological positivity for PBC-specific anti-mitochondrial antibodies (AMA) in a 3-year old girl. We found this observation intriguing as AMA and indeed an overlap with PBC are virtually absent in Type 2 AIH, a pediatric form of AIH which is distinct precisely because it is characterized by pathognomonic anti-liver kidney microsomal type 1 (LKM-1) showing a remarkable antigen-specificity directed against cytochrome P4502D6. We also review the literature in relation to AMA positivity in paediatric age and adolescence. In our case, the presence of AIH-2-specific anti-LKM-1 and PBC-specific AMA was confirmed by indirect immunofluorescence (IIF), and immunoblotting and ELISA based on recombinant mitochondrial antigens. The clinical, laboratory and histological features of the child are given in detail. Interestingly the mother was AMA positive without other features of PBC. The child was successfully treated with immunosuppression and five years after the original diagnosis is on a low dose of prednisolone and azathioprine, with no signs of relapse. Anti-LKM-1 antibodies are still present in low titres. AMA were detectable for the first 4 years after the diagnosis and disappeared later.

Conclusion

This is the first case report in the literature of AIH type 2 with an unexpected PBC-specific AMA positivity in a young child. Response to immunosuppressive treatment was satisfactory and similar to that described in AIH. A review of published reports on AMA positivity in paediatric age shows that the antibody may arise in the context of immunodeficiency and is variably associated with liver damage.

Immunopathogenesis of primary biliary cirrhosis: an old wives' tale

Primary biliary cirrhosis (PBC) is a cholestatic liver disease characterised by the autoimmune destruction of the small intrahepatic bile ducts. The disease has an unpredictable clinical course, but may progress to fibrosis and cirrhosis. Although medical treatment with urseodeoxycholic acid is largely successful, some patients may progress to liver failure requiring liver transplantation. PBC is characterised by the presence of disease specific anti-mitochondrial (AMA) antibodies, which are pathognomonic for PBC development. The disease demonstrates an overwhelming female preponderance and virtually all women with PBC present in middle age. The reasons for this are unknown; however several environmental and immunological factors may be involved. As the immune systems ages, it become less self tolerant, and mounts a weaker response to pathogens, possibly leading to cross reactivity or molecular mimicry. Some individuals display immunological changes which encourage the development of autoimmune disease. Risk factors implicated in PBC include recurrent urinary tract infection in females, as well as an increased prevalence of reproductive complications. These risk factors may work in concert with and possibly even accelerate, immune system ageing, contributing to PBC development. This review will examine the changes that occur in the immune system with ageing, paying particular attention to those changes which contribute to the development of autoimmune disease with increasing age. The review also discusses risk factors which may account for the increased female predominance of PBC, such as recurrent UTI and oestrogens.

Disease-specific autoantibodies in primary biliary cirrhosis

Anti-mitochondrial autoantibodies (AMA) are specific markers of primary biliary liver cirrhosis (PBC), a cholestatic autoimmune disease which is characterised by a progressive destruction of the biliary epithelial cells followed by fibrosis, cirrhosis and liver failure. The prevalence of AMA in PBC is more than 90% and they can precede long before the clinical symptoms. AMA are conventionally detected by indirect immunofluorescence (IIF) using rodent liver, kidney, and stomach sections as substrates. Additionally, different PBC-specific anti-nuclear autoantibodies (ANA) can be observed in 30% of patients presenting with multiple nuclear dot or nuclear membrane staining patterns, which preferentially are identified using HEp-2 cells as substrate. The identification of the major PBC-specific mitochondrial and nuclear targets has allowed the generation of monospecific antigenic targets which are increasingly used in solid-phase assays for routine detection of AMA and ANA in mono- or multiparametric screen test systems. In the present paper, we give an overview of the diagnostic significance of autoantibodies in PBC, discuss the competencies of different techniques used for their determination and propose an effective diagnostic strategy.

Risk factors and prediction of long-term outcome in primary biliary cirrhosis

The natural history of the disease varies greatly among individual patients with primary biliary cirrhosis (PBC). Some patients live long without any symptoms while other patients present jaundice and develop hepatic failure in early phases of the disease. Previous studies showed that the natural course of PBC is altered by the use of ursodeoxy cholic acid (UDCA). In this review we discuss variation in the natural course of the disease and it's alteration by UDCA, and risk factors that predict disease progression. Based on clinical observations, there are three types of clinical evolution in PBC: 1) minimal to slow progression over several years; 2) rapid progression to jaundice and hepatic failure, and 3) progression to portal hypertension without developing deep jaundice. Notably, based on our analyses accelerated progression to jaundice and liver failure are reflected by a sustained serologic presence of anti-gp210 antibodies whereas patients with portal hypertension in the absence of jaundice have anti-centromere autoantibodies. These observations highlight the clinical importance of antinuclear antibody analysis in patients with PBC.

Primary biliary cirrhosis and autoimmune hepatitis: apotopes and epitopes

Autoimmune liver diseases (ALDs) represent a wide spectrum of chronic inflammatory diseases that are characterized by an immune-mediated attack against either hepatocytes (in the case of autoimmune hepatitis types 1 and 2, AIH-1, 2) or cholangiocytes (in primary biliary cirrhosis, PBC). PBC is considered a model autoimmune disease due to the homogeneity of patients, the high specificity of antimitochondrial antibodies (AMAs), and the specificity of biliary epithelial cell (BEC) destruction. It ensues from a multi-lineage loss of tolerance to the E2 component of the pyruvate dehydrogenase complex (PDC-E2). One of the major unanswered questions in the pathogenesis of PBC is the specificity of small intrahepatic bile duct attack while PDC-E2 is present in mitochondria of nucleated cells. Recent findings suggest that the apoptosis of BECs may be of considerable importance for understanding PBC, and that they are more than simply an innocent victim of an immune attack. Rather, they attract immune attack by virtue of the unique biochemical mechanisms by which they handle PDC-E2. The role of apoptotic cells in AIH is not well defined, but advances in the study of autoreactive T cells stem mostly from AIH type 2, where the main autoantigen (CYP2D6) is known, enabling the characterization of antigen-specific immune responses. This review article is intended to provide a critical overview of current evidence on tissue specificity in ALDs, as well as the characteristics of the relevant epitopes and apotopes and their biological and clinical significance.

The autoimmunity of primary biliary cirrhosis and the clonal selection theory

Primary biliary cirrhosis (PBC) is a chronic cholestatic liver disease in which an immune-mediated injury targets the small intrahepatic bile ducts. PBC is further characterized by highly specific serum antimitochondrial autoantibodies (AMA) and autoreactive T cells, a striking female predominance, a strong genetic susceptibility, and a plethora of candidate environmental factors to trigger the disease onset. For these reasons PBC appears ideal to represent the developments of the clonal selection theory over the past decades. First, a sufficiently potent autoimmunogenic stimulus in PBC would require the coexistence of numerous pre-existing conditions (mostly genetic, as recently illustrated by genome-wide association studies and animal models) to perpetuate the destruction of the biliary epithelium by the immune system via the persistence of forbidden clones. Second, the proposed modifications of mitochondrial autoantigens caused by infectious agents and/or xenobiotics well illustrate the possibility that peculiar changes in the antigen structure and flexibility may contribute to tolerance breakdown. Third, the unique apoptotic features demonstrated for cholangiocytes are the ideal setting for the development of mitochondrial autoantigen presentation to the immune system through macrophages and AMA thus turning the non traditional mitochondrial antigen into a traditional one. This article will review the current knowledge on PBC etiology and pathogenesis in light of the clonal selection theory developments.

Demographic, lifestyle, medical and familial factors associated with primary biliary cirrhosis

BACKGROUND & AIMS

Primary biliary cirrhosis (PBC) is believed to result from the interaction of genetic and environmental factors. The controlled studies aiming to assess risk factors for PBC are still limited. Our aim was to identify risk factors and co-morbidities associated with PBC in a large monocentric cohort.

METHODS

We enrolled 222 patients with PBC and 509 controls matched for age, gender, and residential location. Standardized questionnaire data, including more than 200 questions regarding demographic and anthropometric features, lifestyle, individual and familial medical history, and reproductive history, were prospectively collected and examined. Risk factors with odds ratio (OR) and confidence intervals (CI) were determined using conditional logistic regression analyses.

RESULTS

Family history of PBC (OR 6.8, 95% CI 2.8-16.4) or autoimmune thyroid disease (AITD) (OR 7.1, 95% CI 3.5-14.5) in first-degree relatives, and individual history of active or passive smoking (OR 3.1, 95% CI 2.0-5.0), recurrent urinary tract infections (UTI) (OR 2.7; 95% CI 2.0-3.7), AITD (OR 7.7, 95% CI 4.8-12.3), Sjögren syndrome (OR 11.9, 95% CI 5.4-26.3), Raynaud syndrome (OR 7.2, 95% CI 4.3-12.1), pruritus during pregnancy (OR 3.9, 95% CI 2.8-5.3), or abortion (OR 2.0, 95% CI 1.6-2.5) were significantly associated with increased risk of PBC, while use of oral contraceptives (OR 0.6; 95% CI 0.5-0.8) was associated with decreased risk.

CONCLUSION

This study confirms some of the previously reported risk factors for PBC, namely family history of disease and individual history of smoking, UTI, and autoimmune conditions, and further identifies the use of oral contraceptives as a putative protective factor.

Primary biliary cirrhosis: a 2010 update

Primary biliary cirrhosis (PBC) is a chronic inflammatory autoimmune disease that mainly targets the cholangiocytes of the interlobular bile ducts in the liver. The condition primarily affects middle-aged women. Without treatment, PBC generally progresses to cirrhosis and eventually liver failure over a period of 10-20 years. PBC is a rare disease with prevalence of less than 1/2000. PBC is thought to result from a combination of multiple genetic factors and superimposed environmental triggers. The contribution of the genetic predisposition is evidenced by the familial clustering. Several risk factors, including exposure to infectious agents and chemical xenobiotics, have been suggested. Ursodeoxycholic acid (UDCA) is currently the only FDA-approved medical treatment for PBC. When administered at doses of 13-15 mg/kg/day, a majority of patients with PBC have a normal life expectancy without additional therapeutic measures. One out of three patients does not adequately respond to UDCA therapy and may need additional medical therapy and/or liver transplantation. This review summarises current knowledge on the epidemiology, ethiopathogenesis, clinical, and therapeutic aspects of PBC.

Loss of tolerance in C57BL/6 mice to the autoantigen E2 subunit of pyruvate dehydrogenase by a xenobiotic with ensuing biliary ductular disease

There have been important advances in defining effector mechanisms for several human autoimmune diseases. However, for most human autoimmune diseases, the induction stage is less well defined and there are very few clues on etiology. Our laboratory has focused on defining the molecular basis of autoantibody recognition and epitope modification in primary biliary cirrhosis (PBC). Our work has demonstrated that antibodies to mitochondria, the hallmark of disease, are directed against a very conserved site of pyruvate dehydrogenase, the E2 subunit of pyruvate dehydrogenase (PDC-E2). We have also demonstrated that several chemical xenobiotics, chosen based on quantitative structural activity relationship analysis and rigorous epitope analysis, when coupled to the lysine residue that normally binds the lipoic acid cofactor of PDC-E2, reacts as well or better to PBC sera than native autoantigen. In the present studies, we immunized C57BL/6 mice with one such xenobiotic, 2-octynoic acid, coupled to bovine serum albumin and we followed the mice for 24 weeks. Animals were studied for appearance of histologic lesions as well as appearance of antibodies to PDC-E2, serum levels of tumor necrosis factor-alpha and interferon-gamma, and splenic and liver lymphoid phenotyping by flow cytometry. Mice immunized with 2-octynoic acid manifest autoimmune cholangitis, typical mitochondrial autoantibodies, increased liver lymphoid cell numbers, an increase in CD8(+) liver infiltrating cells, particularly CD8(+) T cells that coexpress CD44, and finally an elevation of serum tumor necrosis factor-alpha and interferon-gamma.

CONCLUSION

these data provide a persuasive argument in favor of an environmental origin for human PBC.

Anti-mitochondrial antibody-negative primary biliary cirrhosis

The recent development in the authors' laboratory of a sensitive bead assay able to detect AMA in 20% of otherwise AMA-negative sera seems to support the hypothesis that many AMA-negative cases of primary biliary cirrhosis (PCB) are secondary to limits in the methods used and do not represent an independent clinical entity. Clinical data demonstrate that patients without detectable serum AMA do not differ in their natural history from their seropositive counterparts. Anti-nuclear antibodies have been associated repeatedly with more severe disease and are helpful tools in the management of patients who have PBC, particularly those lacking AMA.

The causes of primary biliary cirrhosis: Convenient and inconvenient truths

The most difficult issue in autoimmunity remains etiology. Although data exist on effector mechanisms in many autoimmune diseases, the underlying cause or causes are still generically ascribed to genetics and environmental influences. Primary biliary cirrhosis (PBC) is considered a model autoimmune disease because of its signature antimitochondrial autoantibody (AMA), the homogeneity of clinical characteristics, and the specificity of biliary epithelial cell (BEC) pathology. Twenty years ago, we reported the cloning and identification of the E2 component of pyruvate dehydrogenase (PDC-E2) as the immunodominant autoantigen of PBC, allowing for vigorous dissection of T and B lymphocyte responses against PDC-E2 and development of several valid experimental models. There has also been considerable study of the biology of BECs, which has included the unique properties of apoptosis in which there is exposure of PDC-E2 to the effector processes of the immune system. In this review, we present these data in the context of our proposal that the proximal cause of PBC is autoimmunity directed against well-identified mitochondrially located autoantigens in individuals with inherited deficits of immune tolerance. We present these data under the umbrella of convenient truths that support this thesis as well as some inconvenient truths that are not readily accommodated by current theory.

CONCLUSION

We emphasize that the potential initiator of PBC includes inter alia particular environmental xenobiotics; pathogenesis is aided and abetted by genetic weaknesses in mechanisms of immune regulation; and subsequent multilineage immunopathology impacts upon uniquely susceptible BECs to culminate clinically in the chronic autoimmune cholangiolitis of PBC.

Antimitochondrial antibodies of immunoglobulin G3 subclass are associated with a more severe disease course in primary biliary cirrhosis

BACKGROUND/AIMS

Primary biliary cirrhosis (PBC) is characterised by the presence of immunoglobulin (Ig) G antimitochondrial antibodies (AMA), which are routinely detected by indirect immunofluorescence (IFL) using composite rodent tissue substrate. The IgG subclass distribution and clinical significance of IFL-detected AMA in patients with PBC have not been previously studied in detail.

METHODS

We have examined IgG subclass-specific AMA detected by IFL on rodent liver, kidney and stomach tissue substrate using affinity-purified IgG subclass monospecific antisera as revealing reagents in 95 AMA-positive PBC patients from Greece.

RESULTS

AMA of any of the IgG1, IgG2 or IgG3 subclasses were present in 89/95 (93.7%) patients. Among those 89, 55 (61.8%) had IgG1, 2, 3 AMA positivity; eight (9%) had IgG1, 2; seven (7.9%) had IgG2, 3; eight (9%) had IgG1, 3; nine (10.1%) had IgG1 subclass and two (2.2%) single IgG3 AMA reactivity. IgG4 AMA was absent. IgG3 titres were higher than IgG2 and IgG1 (P<0.001) and IgG1 higher than IgG2 (P<0.001). IgG3 AMA-positive patients had a histologically more advanced disease (P<0.01) and were more frequently cirrhotic compared with those who were negative (P<0.01). There was a positive correlation between AMA IgG3 titre and Mayo risk score (r=0.55, P=0.009, Spearman's correlation).

CONCLUSIONS

Our findings suggest that AMA are not restricted to a specific IgG subclass. AMA of the IgG3 subclass are associated with a more severe disease course, possibly reflecting the peculiar ability of this isotype to engage mediators of damage.

T cell targeting and phagocytosis of apoptotic biliary epithelial cells in primary biliary cirrhosis

Primary biliary cirrhosis (PBC) is characterized by loss of tolerance against ubiquitously expressed mitochondrial autoantigens followed by biliary and salivary gland epithelial cell (BEC and SGEC) destruction by autoreactive T cells. It is unclear why BECs and SGECs are targeted. Previous work demonstrated that the reduced form of the major PBC autoantigen predominated in apoptotic BECs and SGECs as opposed to an oxidized form in other apoptotic cells. This led to the hypothesis that presentation of novel self-peptides from phagocytosed apoptotic BECs might contribute to BEC targeting by autoreactive T cells. The effect of autoantigen redox status on self-peptide formation was examined along with the phagocytic ability of BECs. Oxidation of PBC autoantigens first was shown to be due to protein S-glutathionylation of lipoyllysine residues. Absence of protein S-glutathionylation generated novel self-peptides and affected T cell recognition of a lipoyllysine containing peptide. Liver biopsy staining revealed BEC phagocytosis of apoptotic BECs (3.74+/-2.90% of BEC) was present in PBC (7 of 7 cases) but not in normal livers (0 of 3). BECs have the ability to present novel mitochondrial self-peptides derived from phagocytosed apoptotic BECs. Apoptotic cell phagocytosis by non-professional phagocytes may influence the tissue specificity of autoimmune diseases.

Anti-gp210 and anti-centromere antibodies are different risk factors for the progression of primary biliary cirrhosis

The predictive role of antinuclear antibodies (ANAs) remains elusive in the long-term outcome of primary biliary cirrhosis (PBC). The progression of PBC was evaluated in association with ANAs using stepwise Cox proportional hazard regression and an unconditional stepwise logistic regression model based on the data of 276 biopsy-proven, definite PBC patients who have been registered to the National Hospital Organization Study Group for Liver Disease in Japan (NHOSLJ). When death of hepatic failure/liver transplantation (LT) was defined as an end-point, positive anti-gp210 antibodies (Hazard ratio (HR) = 6.742, 95% confidence interval (CI): 2.408, 18.877), the late stage (Scheuer's stage 3, 4) (HR = 4.285, 95% CI:1.682,10.913) and male sex (HR = 3.266, 95% CI: 1.321,8.075) were significant risk factors at the time of initial liver biopsy. When clinical progression to death of hepatic failure/LT (i.e., hepatic failure type progression) or to the development of esophageal varices or hepatocellular carcinoma without developing jaundice (Total bilirubin < 1.5 mg/dL) (i.e., portal hypertension type progression) was defined as an end-point in the early stage (Scheuer's stage 1, 2) PBC patients, positive anti-gp210 antibodies was a significant risk factor for hepatic failure type progression [odds ratio (OR) = 33.777, 95% CI: 5.930, 636.745], whereas positive anti-centromere antibodies was a significant risk factor for portal hypertension type progression (OR = 4.202, 95% CI: 1.307, 14.763). Histologically, positive anti-gp210 antibodies was most significantly associated with more severe interface hepatitis and lobular inflammation, whereas positive anticentromere antibodies was most significantly associated with more severe ductular reaction.

CONCLUSION

These results indicate 2 different progression types in PBC, hepatic failure type and portal hypertension type progression, which may be represented by positive-anti-gp210 and positive-anticentromere antibodies, respectively.

[Seropositivity for Chlamydia pneumoniae in patients with primary biliary cirrhosis]

INTRODUCTION

Primary biliary cirrhosis (PBC) is a chronic cholestatic liver disease characterized by inflammatory injury and bile duct destruction. Recent studies suggest that Chlamydia pneumoniae could be associated with the development of PBC. The aim of this study was to determine the seroprevalence of C. pneumoniae in a cohort of patients with PBC.

PATIENTS AND METHODS

The presence of IgG antibodies against C. pneumoniae was investigated in 46 patients with PBC and in 105 subjects without cirrhosis.

RESULTS

Twenty-one patients (46%) with PBC had antibodies against C. pneumoniae compared with 74 subjects (71%) in the control group (OR = 0.6; 95% CI, 0.3-1.2; p = NS). Subanalysis of the PBC group showed that patients with C. pneumoniae antibodies had a higher frequency of advanced Child-Pugh stages (24% A, 52% B and 24% C vs 64% A, 32% B and 4% C; p = 0.01), a higher score on the Mayo Clinic Prognostic Index (7.8 +/- 2.1 vs 5.6 +/- 1.2; p = 0.004), a higher frequency of ascites (29% vs 4%; OR = 9.6; 95% CI, 1-87; p = 0.02), higher total bilirubin levels (4.5 +/- 2.5 mg/dl vs 2.4 +/- 4.3 mg/dl, p = 0.001) and lower serum albumin levels (2.6 +/- 0.9 g/dl vs 3.3 +/- 0.6 g/dl, p = 0.02).

CONCLUSION

No association was found between C. pneumoniae infection and PBC in this study. An association was found between the severity of PBC and C. pneumoniae, which may suggest a deleterious effect of C. pneumoniae infection or a predisposition in advanced stages of PBC to acquire infection with this microorganism.

New insights to the immunopathology and autoimmune responses in primary biliary cirrhosis

Primary biliary cirrhosis (PBC) is an autoimmune liver disease with profound changes in different compartments of the immune system, including those involved in innate, and adaptive immunity. New data from epidemiological studies of PBC have reinforced the thesis that the cause for this relatively uncommon disease is likely to be a combination of both environmental factors and a susceptible genetic predisposition. Recent findings of abnormalities of the innate immune system in PBC suggest that they may serve as links between the environmental factors and the early events in PBC development. Viral and bacterial infections as well as xenobiotics are some of the potential environmental factors that have been implicated in this complex process. Identification of the etiological factors for PBC will point to new preventive or therapeutic treatments.

Transgenic mice aberrantly expressing pyruvate dehydrogenase complex E2 component on biliary epithelial cells do not show primary biliary cirrhosis

Primary biliary cirrhosis (PBC) is an autoimmune disorder that specifically destroys biliary epithelial cells (BECs). In patients with PBC, the immunodominant pyruvate dehydrogenase complex E2 component (PDC-E2), identified as an antigen for disease-specific anti-mitochondrial antibody, is expressed aberrantly in the BEC cytoplasm. The present study focused on the pathophysiological role of aberrant PDC-E2 in the development of PBC. The BEC-specific cytokeratin-19 promoter and PDC-E2 gene were cloned from a mouse cDNA library. The constructed transgene was microinjected into fertilized eggs of mice, and the offspring were identified by Southern blotting and reverse transcriptase-polymerase chain reaction. The protein expression was confirmed by immunoprecipitation, immunoblotting and immunohistochemical staining. Five founder lines were identified as carrying the PDC-E2 gene, and one of these lines expressed PDC-E2 mRNA. The protein expression of exogenous PDC-E2 was detected in the liver. The transgenic mouse line showed diffuse expression of PDC-E2 in the BEC cytoplasm. Biochemical, serological and histological features of PBC were not detected. We established transgenic mice that constitutively express PDC-E2. The results indicated that aberrant PDC-E2 expression in the cytoplasm of BECs is not sufficient for the initiation of autoimmunity. Additional factors may be required to establish a model of PBC.

Characterization of biliary intra-epithelial lymphocytes at different anatomical levels of intrahepatic bile ducts under normal and pathological conditions: numbers of CD4+CD28- intra-epithelial lymphocytes are increased in primary biliary cirrhosis

Distribution of intra-epithelial lymphocytes along intrahepatic biliary tree (bIEL), and their density and phenotype were examined in normal and diseased livers, particularly in primary biliary cirrhosis (PBC). Immunohistochemically, bIEL were examined in 28 normal livers, 13 cases of chronic viral hepatitis (CVH), 13 cases of PBC, five cases of primary sclerosing cholangitis (PSC), seven cases of extrahepatic biliary obstruction (EBO), and 16 hepatolithiatic livers. In normal livers, bIEL were relatively dense at large and septal bile ducts compared to interlobular ducts. Most of them were positive for CD3 and CD8, while a few were positive for CD4, CD20 and CD57. In CVH, PSC and EBO, neither distribution, phenotype nor density of bIEL differed from normal liver. In hepatolithiasis, numbers of CD8(+)bIEL were increased in stone-containing ducts. In PBC, numbers of CD4(+)CD28(-)bIEL, which are reportedly responsible for target tissue destruction in autoimmune diseases, were markedly increased in damaged interlobular ducts. In conclusion, CD3(+)CD8(+)bIEL may be involved in immune homeostasis of intrahepatic bile ducts in normal livers and in CVH, PSC and EBO. Altered distribution and phenotypes of bIEL in PBC and hepatolithiasis may reflect their participation in biliary lesions. Increased CD4(+)CD28(-)bIEL in damaged bile ducts of PBC may be related to immune-mediated biliary damage.

Low specificity of anti-tissue transglutaminase antibodies in patients with primary biliary cirrhosis

The association between celiac disease (CD) and primary biliary cirrhosis (PBC) is well documented in medical literature; however, a high frequency of false positive results of the anti-transglutaminase (anti-tTG) test has been reported in patients with PBC. To verify if the positive results for anti-tTG autoantibody are false positives due to cross reactivity with mitochondrial antigens, we studied 105 adult patients affected with PBC, positive for anti-mitochondrial M2 antibodies. Anti-tTG IgA antibodies were studied by using six different immunoenzymatic assays that employ the tTG antigen obtained from different sources (human recombinant, placenta, red blood cells, and guinea pig liver). On the whole, 28 out of 105 PBC subjects tested positive for anti-tTG IgA antibodies, but only two were eventually found to be affected by CD; the other 26 were shown to be false positive. The specificity of the various antigenic substrates ranged from 88.5% of the human erythrocytes tTG to 97.1% of the human recombinant tTG. The results of this study showed that a true association between PBC and CD was present in only 2% of the patients and that, in most cases, the false positive results were attributable to the type of substrate utilized in the assay.

Increased expression of nuclear envelope gp210 antigen in small bile ducts in primary biliary cirrhosis

The sustained antibody response to nuclear envelope gp210 antigen indicates a group of primary biliary cirrhosis (PBC) patients at high risk for the progression to end-stage hepatic failure. To address this issue, we immunohistochemically studied the expression of gp210 antigen in needle liver biopsy specimens from PBC patients using a monoclonal antibody specific for gp210 antigen. The specimens from autoimmune hepatitis (AIH), chronic viral hepatitis B (CHB) and C (CHC) patients served as disease controls. The expression of gp210 antigen was apparently increased on the nuclear envelope of biliary epithelial cells (BECs) of small bile ducts in almost all specimens from PBC. In contrast, the expression of gp210 antigen was negative in BECs of small bile ducts in normal liver, while relatively weak anti-gp210 immunostaining was observed in AIH, CHC and CHB. In addition, the degree of gp210 expression in BECs of small bile ducts was positively correlated to that of portal inflammation, interface hepatitis and lobular inflammation in PBC. These results indicate that the increased expression of gp210 in small bile ducts, which is probably associated with damage to BECs by inflammation, is possibly involved in autoimmune response to gp210 leading to the progression to end-stage hepatic failure in PBC.

Primary biliary cirrhosis: an infectious disease caused by Chlamydia pneumoniae?

BACKGROUND/AIMS

The etiology and pathogenesis of primary biliary cirrhosis (PBC) remain elusive. Both an infectious etiology and molecular mimicry have been implicated. The aim is to study the prevalence of Chlamydial antigens and RNA in the liver tissue of patients with PBC.

METHODS

We compared the prevalence of Chlamydial antigen and RNA in 25 explants with PBC who underwent orthotopic liver transplantation with 105 explanted livers from other chronic liver disease. We also studied 14 liver biopsies from patients with early stages of PBC. Donor livers were also studied.

RESULTS

In all 39 patients with PBC, Chlamydia pneumoniae antigens were present but not Chlamydia trachomatis, and only 9/105 (8.5%) of patients in the other categories were positive (P<0.01) for C. pneumoniae. Eight explanted PBC livers were tested for C. pneumoniae 16S RNA by in situ hybridization and were positive.

CONCLUSIONS

The presence of C. pneumoniae antigen and RNA in liver tissue of patients with PBC suggests that C. pneumoniae antigen may trigger an immune response based on molecular mimicry.

Primary biliary cirrhosis and autoimmune cholangiopathy

AMA are detected in the serum of 92% to 95% of patients with PBC using indirect immunofluorescent methods. AIC is the term used to describe the 5% to 8% of AMA-negative PBC patients who uniformly have ANA and SMA. Recent applications of more sensitive and specific tests to detect serum AMA have shown that most, if not all, patients with AIC actually do have AMA. Emerging evidence that AMA and mitochondrial autoantigens play important roles in the immunopathogenesis of NSDC also suggests that AIC and PBC are likely to be a single disease, exhibiting variation in the types of autoantibodies and in both the concentrations and immunoglobulin isotypes of AMA.

Primary biliary cirrhosis: the future

The answers to these questions are key to understanding the pathogenesis of PBC. Although the study of PBC is significantly retarded by the lack of an adequate animal model, the molecular technology to address these issues is advancing rapidly. In addition, the ability to isolate and culture human biliary epithelial cells greatly facilitates in vitro studies. With the advent of these tools, investigators are well poised to address the important issues of PBC in the future.

Pathogenesis of primary biliary cirrhosis

Primary biliary cirrhosis is an enigmatic autoimmune disease that predominantly affects women. The serologic signatures of PBC are high titer antimitochondrial antibodies that are directed at the inner lipoyl domains of the 2-oxo-dehydrogenase enzymes, particularly PDC-E2. Of note, is that the antibody response and the CD4 and CD8 response, are all directed at a similar epitope, the inner lipoyl domain. This unique immunologic response suggests that modification of the inner lipoyl domain is associated with the immunogenetic basis of disease.

Primary biliary cirrhosis

Primary biliary cirrhosis is a chronic cholestatic liver disease of adults. This disorder is characterised histologically by chronic non-suppurative destruction of interlobular bile ducts leading to advanced fibrosis, cirrhosis, and liver failure. The precise aetiopathogenesis of primary biliary cirrhosis remains unknown, although dysregulation of the immune system and genetic susceptibility both seem to be important. Affected patients are typically middle-aged women with abnormal serum concentrations of alkaline phosphatase. Presence of antimitochondrial antibody in serum is almost diagnostic of the disorder. Identification of primary biliary cirrhosis is important, because effective treatment with ursodeoxycholic acid has been shown to halt disease progression and improve survival without need for liver transplantation. However, therapeutic options for disease-related complications-including fatigue and metabolic bone disease-remain unavailable. Mathematical models have been developed that accurately predict the natural history of primary biliary cirrhosis in individuals. Despite advances in understanding of the disease, it remains one of the major indications for liver transplantation worldwide.

Molecular mimicry of mitochondrial and nuclear autoantigens in primary biliary cirrhosis

BACKGROUND & AIMS

The mechanism for development of primary biliary cirrhosis (PBC) remains enigmatic, but molecular mimicry has been implicated because of well-known cross-reactivity of human mitochondrial autoantigens and equivalent bacterial antigens. Virtually all patients with PBC have antimitochondrial autoantibodies (AMA), but, interestingly, approximately 50% also manifest antinuclear antibodies (ANA).

METHODS

To determine whether generation of ANA are due to molecular mimicry of mitochondrial peptides, we established 6 T-cell clones selected by a peptide corresponding to the E2 subunit of mitochondrial pyruvate dehydrogenase complex and analyzed for reactivity to mimicry peptides derived from mitochondrial and nuclear autoantigens, including control sequences.

RESULTS

For mitochondrial autoantigens, 1 peptide from the E2 subunit of the pyruvate dehydrogenase complex, 1 peptide from the E2 subunit of the oxo-glutarate dehydrogenase complex, 1 peptide from the E2 subunit of the branched-chain 2-oxoacid dehydrogenase complex, and 1 peptide from the E3-binding protein cross-reacted with these T-cell clones. For the nuclear autoantigens, 5 peptides from gp210 and 1 from Sp100 cross-reacted with these clones. Furthermore, 1 of 3 T-cell clones selected by recombinant gp210 protein reacted with a mimicry peptide corresponding to amino acids 188-201 of gp210, indicating that this part of the protein is a naturally processed immunodominant T-cell epitope.

CONCLUSIONS

These results demonstrate molecular mimicry between mitochondrial and nuclear autoantigens in PBC and that a mimicry peptide may become an immunodominant T-cell epitope. These data have significance not only for PBC but also for the production of ANA in other disease processes.

T cell immunity and primary biliary cirrhosis

T lymphocytes play a pivotal role in the autoimmune response in primary biliary cirrhosis (PBC). Recent studies have shown that there is overlapping in the PDC-E2-specific T and B cell epitopes. In addition, helper T and cytotoxic T cell epitopes all contain a shared peptide sequence. In addition, recognition of exogenous antigens including bacterial antigens by autoantigen-specific T cell and the mechanism of molecular mimicry provide a clue to clarifying the pathogenesis of PBC. Furthermore, the findings that autoantigen-immune complexes cross present and also that the presentation of autoantigen is of a higher relative efficiency, define a unique role of autoantibodies in the pathogenesis of the autoimmune disease. The mechanism of immune-mediated bile duct damage in PBC, including the possible role of T cell-mediated cytotoxicity and molecular mimicry is discussed.

Characterization of recombinant monoclonal IgA anti-PDC-E2 autoantibodies derived from patients with PBC

Primary biliary cirrhosis (PBC) is an autoimmune liver disease characterized by the presence of autoantibodies to mitochondria (AMA). Recent evidence suggests that PBC develops after a locally driven response in the mucosa, where immunoglobulin A (IgA) is the dominant antibody isotype. In this study, we produced recombinant pyruvate dehydrogenase complex (PDC-E2)-specific dimeric human IgA monoclonal antibodies (mAbs) in a baculovirus expression system. By using 2 anti-PDC-E2 IgG mAbs derived from patients with PBC, we constructed 2 recombinant baculoviruses, each containing heavy chains with the Calpha constant region. These were simultaneously co-infected into Sf9 insect cells with recombinant baculovirus containing the J chain. A sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) immunoblotting profile of the IgA using a 6% nonreducing gel verified the dimeric nature of the autoantibodies. Both recombinants retained their original specificity for PDC-E2. In addition, the antibody showed a mitochondrial staining pattern in HEp2 cells and apically stained the biliary epithelial cells (BECs) in the liver of a patient with PBC but not a normal patient. Transcytosis experiments performed using human polymeric immunoglobulin receptor (pIgR) expressing Madine-Darby canine kidney (MDCK) cells showed that one of the recombinants showed a high degree of colocalization with PDC-E2. In conclusion, these data provide further support of the hypothesis that PDC-E2-specific IgA may enter biliary epithelial cells of PBC patients via the pIgR and complex with PDC-E2, thereby potentially contributing to the pathology of BECs. Moreover, this recombinant PDC-E2-specific mAb provides a tool for further determination of the role of anti-PDC-E2 IgA in the pathogenesis of PBC.

Primary biliary cirrhosis and idiopathic retroperitoneal fibrosis: a rare association

Primary biliary cirrhosis has rarely been reported to be associated with idiopathic retroperitoneal fibrosis. We describe the case of a 57-year-old man who was confirmed to have both conditions, reflecting the likely autoimmune aetiopathogenesis common to both disorders.

Primary biliary cirrhosis: seeking the silent partner of autoimmunity

Primary biliary cirrhosis is a disorder characterised by an intense inflammatory response in the septal and interlobular bile ducts and is considered to be an autoimmune disease. Evidence to suggest that chronic viral infection could be a crucial element in the development of biliary epithelial cell damage and activation of the associated autoimmune response is reviewed

Hepatoimmunology: a perspective

Premises for the subspecialty of hepatoimmunology include the recognition that the liver is a lymphoid organ with unique immunological properties. These properties ensure efficient innate defence against intestinal microbes and toxins, confer a particular capacity for induction of tolerance, and provide for apoptotic disposal of redundant lymphocytes. Pathological responses within the liver are elicited when: (i) hepatotropic viruses (hepatitis virus B and C) escape immune elimination and reside in hepatocytes; (ii) the liver becomes the site of autoimmune responses directed against either hepatocytes (autoimmune hepatitis) or biliary ductules (primary biliary cirrhosis); or (iii) the liver in the course of disposal of drugs generates neoantigens that provoke adverse allergic responses. Recent advances in the understanding of the immunopathogenesis of these entities are reviewed.

Identification of HLA-A2-restricted CD8(+) cytotoxic T cell responses in primary biliary cirrhosis: T cell activation is augmented by immune complexes cross-presented by dendritic cells

Primary biliary cirrhosis (PBC) is characterized by an intense biliary inflammatory CD4(+) and CD8(+) T cell response. Very limited information on autoantigen-specific cytotoxic T lymphocyte (CTL) responses is available compared with autoreactive CD4(+) T cell responses. Using peripheral blood mononuclear cells (PBMCs) from PBC, we identified an HLA-A2-restricted CTL epitope of the E2 component of pyruvate dehydrogenase (PDC-E2), the immunodominant mitochondrial autoantigen. This peptide, amino acids 159-167 of PDC-E2, induces specific MHC class I-restricted CD8(+) CTL lines from 10/12 HLA-A2(+) PBC patients, but not controls, after in vitro stimulation with antigen-pulsed dendritic cells (DCs). PDC-E2-specific CTLs could also be generated by pulsing DCs with full-length recombinant PDC-E2 protein. Furthermore, using soluble PDC-E2 complexed with either PDC-E2-specific human monoclonal antibody or affinity-purified autoantibodies against PDC-E2, the generation of PDC-E2-specific CTLs, occurred at 100-fold and 10-fold less concentration, respectively, compared with soluble antigen alone. Collectively, these data demonstrate that autoantibody, helper, and CTL epitopes all contain a shared peptide sequence. The finding that autoantigen-immune complexes can not only cross-present but also that presentation of the autoantigen is of a higher relative efficiency, for the first time defines a unique role for autoantibodies in the pathogenesis of an autoimmune disease.