Primary biliary cirrhosis and mitochondrial autoantigens--insights from molecular biology

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.

Decreased serum levels of immunoglobulin A, immunoglobulin M and immunoglobulin G in a patient with primary biliary cirrhosis: A case report

Primary biliary cirrhosis (PBC) is a cholestatic liver disease with an elevated serum immunoglobulin (Ig)M level. Patients with PBC may develop extrahepatic manifestations, including hypogammaglobulinemia. However, hypogammaglobulinemia seldom occurs, and the associated changes of lymphocytes remain unknown. Furthermore, the impact of Ig on the progression of PBC is still unclear. Here, we describe a case of hypogammaglobulinemia developed in a female patient with PBC. The patient was diagnosed with PBC at the age of 46 years and treated with ursodeoxycholic acid and bezafibrate. At the age of 50 years, the patient developed bronchitis, and laboratory test results indicated a marked decrease in serum levels of IgA, IgM and IgG. Then, the patient was diagnosed as having idiopathic hypogammaglobulinemia and treated with Ig replacement therapy; however, respiratory infections recurred frequently, leading to the patient's death at the age of 53 years. An autopsy revealed hyperplastic bone marrow with CD3, CD20 and IgG positive lymphocytes. However, no CD79a, CD138, IgA and IgM positive lymphocytes were observed. Moreover, the severity of PBC progressed even after the onset of hypogammaglobulinemia. In addition, CD3 positive cells were seen around chronic non-suppurative destructive cholangitis in the autopsy specimen of the liver. Thus, the present case demonstrated changes of lymphocytes in hypogammaglobulinemia developed in patients with PBC. Furthermore, the clinical course of the present case of PBC may indicate that the Ig-mediated mechanisms may be non-essential for the progression of PBC.

Murine models of autoimmune cholangitis

PURPOSE OF REVIEW

Primary biliary cirrhosis (PBC) is a human autoimmune liver disease whose molecular pathogenesis is poorly understood because of the difficulty in accessing human tissue and the absence of appropriate animal models. Recently, several unique murine models of human PBC have been discovered. These models have great potential for illustrating the cause and the cellular events that lead to biliary-specific damage. The purpose of this review is to summarize recent progress in these models.

RECENT FINDINGS

The murine models of autoimmune cholangitis include the transforming growth factor beta receptor II (TGF-betaRII) dominant-negative (dnTGF-betaRII), IL-2 receptor alpha deleted (IL-2Ralpha-/-), scurfy, nonobese diabetic (NOD) c3c4, and Ae2 gene-disrupted (Ae2a,b-/-) mice. Recently, we have also established a successful murine model following the immunization with a chemical mimicry of the lipoyl-lysine residue of the E2 component of PDC-E2.

SUMMARY

These emerging murine models have greatly enabled researchers to address the pathogenesis of human PBC and to elucidate pathogenic factors. These models will ultimately lead to new therapeutic options for human PBC.

Serum inflammatory cytokines, complement components, and soluble interleukin 2 receptor in primary biliary cirrhosis

Primary biliary cirrhosis (PBC) is a chronic cholestatic autoimmune liver disease characterized by selective destruction of the intrahepatic bile ducts and highly specific serum anti-mitochondrial autoantibodies (AMA). Several studies have attempted to determine the cytokine pattern characterizing PBC, yet no definitive data have been gathered. The present study was designed to evaluate pro-inflammatory cytokines (IL-1beta, IL-6, TNFalpha), soluble IL-2 receptor (sIL-2R, e.g. soluble CD25), and complement components (C1q, C3, factor B, properdin) levels in sera from 84 patients with PBC and 41 controls. PBC was characterized by significantly higher levels of all pro-inflammatory cytokines when compared to controls; these included IL-1beta (433.3 +/- 13.2 vs. 316.6 +/- 14.7 pg/ml, P < 0.001), IL-6 (701 +/- 17.4 vs. 158 +/- 22.5 pg/ml, P < 0.001), TNFalpha (3.38 +/- 0.6 pg/ml vs. undetectable, P = 0.001), and sIL-2R (1527.1 +/- 106 vs. 566.4 +/- 28.7 U/ml, P < 0.001). Similarly, all complement components were also significantly higher in PBC compared to control sera. In conclusion, PBC sera manifest higher levels of sIL-2R and complement components and this may reflect a perpetuated immune activation. As expected, we also report that all major pro-inflammatory cytokine levels are enhanced in PBC. Further longitudinal analyses could demonstrate a correlation between these markers and disease stage or inflammatory activity, to predict histological staging, disease activity, and response to treatment.

A tribute to an outstanding immunologist - Ian Reay Mackay

The 11th Australasian Autoimmunity Workshop was held in Melbourne, Australia from July 6-8, 2007 organized by the Monash University Autoimmunity Network. The workshops, founded by the late Kevin Lafferty, are a chance for Australasians interested in research into autoimmune disease to present and discuss their work. This workshop also was a chance to acknowledge Ian Mackay, a pioneer clinician-scientist who has made major contributions to our understanding of autoimmune diseases. Friends, colleagues and former students attended the Workshop and acknowledged Ian's expertise and mentorship. This edition of the Journal of Autoimmunity pays tribute to Ian Mackay. It features articles from attendees at the workshop, and contributions from some of Ian's past students and past and current collaborators.

Primary biliary cirrhosis: what we know and what we want to know about human PBC and spontaneous PBC mouse models

Human autoimmune cholangiopathy comprises several intractable liver diseases that ultimately lead to hepatic failure. Primary biliary cirrhosis (PBC), allograft rejection, graft versus host diseases, and, possibly, primary sclerosing cholangitis are representative of immune-mediated cholangiopathies. Among them, PBC is the best-investigated human autoimmune cholangiopathy. The immunological approach to PBC has provided much critical information regarding its pathogenesis. The breakdown of self-tolerance in both B cells and T cells toward E2 components of the pyruvate dehydrogenase complex is evident. However, a number of questions regarding its etiology are unclear, in particular, the mechanisms involved in the selectivity of cholangiocyte destruction. In this brief review, we discuss what we know and we do not know regarding the pathogenesis of PBC.

AMA production in primary biliary cirrhosis is promoted by the TLR9 ligand CpG and suppressed by potassium channel blockers

We previously reported that peripheral blood mononuclear cells (PBMCs) from patients with primary biliary cirrhosis (PBC) produce significantly higher levels of polyclonal IgM than controls after exposure to CpG. Furthermore, the prevalence and unusually high levels of antimitochondrial antibodies (AMAs) in patients with PBC suggest a profound loss ofB cell tolerance. We have addressed the issue of whether CpG will promote the production ofAMAs and whether new experimental agents that inhibit the lymphocyte potassium channels Kv1.3 and KCa3.1 can suppress CpG-mediated B cell activation and AMA production. PBMCs were stimulated with and without CpG and were subsequently analyzed for phenotype, including expression of TLR9, CD86, and KCa3.1 concurrent with measurements of AMA and responses to a control antigen, tetanus toxoid, in supernatants. Additionally, K+ channel expression on B cells from PBC patients and controls was studied using whole-cell patch-clamp technology. In patients with PBC, CpG induces secretion of AMAs in PBMCs andalso up-regulates B cell expression of TLR9, CD86, and KCa3.1. Additionally, K+ channel blockers suppress secretion of AMA without a reduction of CpG-B-enhanced IgM production. Furthermore, there is diminished up-regulation of TLR9 and CD86 without affecting proliferation of B cells, B cell apoptosis, or viability.

CONCLUSION

These data suggest that the hyperresponsiveness of B cells in PBC accelerates B cell-mediated autoimmunity.

Role of auto-antibodies for the diagnosis of chronic cholestatic liver diseases

Auto-antibodies are an integral part of the diagnostic armentarium in chronic cholestatic liver disorders, such as primary sclerosing cholangitis (PSC), primary biliary cirrhosis (PBC),auto-immune cholangitis, or overlap syndromes among these disorders. However, care should be taken not to overestimate the diagnostic specificity. Auto-antibodies to mitochondrial antigens(AMAs) with reactivity to the E2 subunit of the pyruvate dehydrogenase complex represent the hallmark antibody for the diagnosis of PBC, whereas antinuclear antibodies (ANAs)with low disease specificity are found in up to 50% of these sera. Antibodies that recognize nuclear envelope proteins exert a similarly high diagnostic specificity as AMA in PBC but occur at a rather low prevalence. The role of auto-antibodies is less well-studied for patients with PSC, but there is growing evidence that only antineutrophil cytoplasmic antibodies(ANCAs) are of relevant diagnostic significance. In contrast, auto-antibodies-particularlyAMAs-do not contribute to the diagnosis of auto-immune cholangitis, whereas ANCAs,ANAs, smooth muscle antibodies, and AMAs are of varying significance in PBC-auto-immune hepatitis (AIH) or PSC-AIH overlap syndromes. It has been widely accepted that the course of the auto-antibody serum end point titers are not suited for the clinical management of patients with chronic cholestatic liver disorders. Additionally, auto-antibodies in these disorders usually do not contribute to the immunopathogenesis of the disease.

A retrospective study on clinical features and prognostic factors of biopsy-proven primary biliary cirrhosis in Chinese patients

OBJECTIVES

Though extensive research has been performed on primary biliary cirrhosis (PBC) in Caucasian patients, little is known about the disease in the Asian population.

PATIENTS AND METHODS

This was a retrospective study of Chinese patients with biopsy-proven PBC. Electronic records of results from all liver biopsies (n = 1,021) performed between January 1996 and April 2004, together with records of patients labeled as "biliary cirrhosis," were retrieved. Patients with biopsy-proven PBC were identified, and their medical notes were reviewed. The demographic, clinical, biochemical, and histological parameters of these patients were analyzed for mortality predictors.

RESULTS

Thirty-nine patients with biopsy-proven PBC and a median follow-up of 44 (range: 5-114) months were identified. Twelve patients (30.8%) were asymptomatic at diagnosis. The patients were approximately equally divided into one-thirds at stages I, II, and III of the histological disease. Hepatic decompensation or hepatocellular carcinoma developed in 14 (35.9%) patients during the follow-up period. The overall 5-yr survival probability was 81.4%. Hypoalbuminemia was found to be the only independent predictor of mortality on multivariate analysis (hazard ratio = 0.50 per 1 g/L increase, 95% CI 0.30-0.84, p= 0.008). Using the median serum albumin level as the cutoff, the 5-yr survival probability was significantly higher for patients with serum albumin levels >35 g/L than for those with serum albumin levels < or =35 g/L (100% vs 69%, p= 0.007). No significant difference was found when baseline serum albumin was compared with the Mayo Risk Score and the model for end-stage liver disease (MELD) score for prediction of patient survival (p= 0.68) and death (p= 0.12) at 5 yr.

CONCLUSIONS

In this longitudinal cohort study of biopsy-proven PBC with up to 9 yr of follow-up, we found that Chinese patients with PBC had significant morbidity and mortality. Hypoalbuminemia at presentation was an independent and strong predictor of mortality.

Clinical and pathological characteristics of the autoimmune hepatitis and primary biliary cirrhosis overlap syndrome

BACKGROUND AND AIMS

The defining of the autoimmune hepatitis (AIH) and primary biliary cirrhosis (PBC) overlap syndrome as a separate clinicopathological entity has been controversial and temporally and geographically subjective.

METHODS

From 1979 until 2000, 227 patients diagnosed with AIH, PBC or the overlap thereof were treated. Cases with genuine AIH/PBC overlap syndrome were sorted out using close clinical follow up and serial liver biopsies.

RESULTS

Of the 227 patients, 19 (8.4%) were diagnosed with the AIH/PBC overlap syndrome. They all cleared a score >10 for the diagnosis of AIH, and tested positive for antimitochondrial antibodies during their courses. Long-term follow up with frequent histological examinations, however, established the diagnosis of AIH/PBC overlap syndrome in only two (0.8%) patients. The most powerful factor distinguishing AIH from PBC was acidophilic bodies in lobules that were detected significantly more frequently in patients with AIH than PBC or spurious overlap syndrome (39/46 [85%]vs 3/85 [4%], P < 0.001). It was more reliable than bile-duct lesions for the distinction of PBC from AIH.

CONCLUSIONS

Although AIH/PBC overlap syndrome does exist, it is infrequent and needs to be diagnosed carefully using close clinical and histological follow up to enable timely and effective treatment.

Antimitochondrial antibody profiles: are they valid prognostic indicators in primary biliary cirrhosis?

OBJECTIVE

Retrospective studies have reported that subtypes of antimitochondrial antibodies (AMAs) discriminate between a benign and a progressive course in patients with primary biliary cirrhosis (PBC). Four AMA profiles (A-D) were defined: profiles A and B associated with a benign course and C and D with a progressive course. We aimed to confirm whether AMA profiles predict prognosis in a large sample of North American patients with PBC.

METHODS

Stored pretreatment sera from patients with PBC from two centers were tested for AMA profiles using standard techniques. Proportions of patients in each profile group reaching the endpoints of liver transplantation or death from liver disease were compared. Kaplan-Meier curves were constructed comparing AMA profiles.

RESULTS

All 472 patients studied had AMA positive, biopsy-confirmed PBC. Mean age at diagnosis was 53 yr, 90% were female, mean follow-up was 7.6 yr (range = 0.5-23), and 51% received ursodeoxycholic acid for >6 months. Profile A was not detected; 16.7% had profile B; 51.1%, profile C; and 32.2%, profile D. Duration of follow-up was comparable among the different profile groups. The proportions of patients reaching endpoints of death from liver disease or transplantation did not differ among the AMA profiles. No difference in the Kaplan-Meier curves between the different profile groups was observed (p > 0.05).

CONCLUSION

AMA profiles do not predict prognosis in patients with PBC.

Immunopathogenesis of cholestatic autoimmune liver diseases

Primary biliary cirrhosis and primary sclerosing cholangitis are well recognized chronic cholestatic liver diseases that are considered to have an autoimmune basis. Recent progress in the study of autoimmune liver diseases has improved the recognition and characterization of these conditions. An important component of this progress has been the identification of liver disease-associated autoantibodies and their respective target antigens, and the development of specific assays for these autoantibodies. In addition, some nonhumoral immunological findings imply an involvement of specific immunopathogenic mechanisms in the development of these conditions. Furthermore, immunogenetic factors associated with increased susceptibility to some of these diseases have been identified. This article reviews the most relevant information relating to the postulated autoimmune pathogenesis of these diseases, with special emphasis on their associated humoral and cellular immunological abnormalities and immunopathogenetic factors. Some of the remaining important unresolved issues relating to the pathogenesis of these diseases, that need to be addressed in further research, are highlighted.

Autoimmune tests in primary biliary cirrhosis

Primary biliary cirrhosis (PBC) is characterized by an immune mediated, irreversible destruction of the small intrahepatic bile ducts leading to progressive liver cirrhosis and frequently to liver failure. The course of the disease is variable and an early diagnosis is desirable to identify individuals with rapidly progressing disease, to initiate adequate therapeutic measures and to evaluate the necessity of liver transplantation. Serological tests represent the single most important diagnostic feature of PBC because liver histology, biochemistry, or clinical syndrome alone are not reliable in this respect. The molecular definition of the autoantigen targets of antimitochondrial antibodies (AMA) has resulted in the development of reproducible and effective serological testing strategies. AMA directed against the ketoacid dehydrogenase complex are highly disease-specific but not directed against liver-specific target structures. Despite a high disease specificity, their usefulness for predicting the course of disease, the timing of liver transplantation, or disease recurrence after transplantation is limited. The realization that about 5% of patients with PBC do not display AMA has led to the identification of PBC-specific antinuclear autoantibodies directed against the nuclear pore complex and other targets. The overlap of PBC with autoimmune hepatitis and primary sclerosing cholangitis represents a diagnostic challenge in which autoantibody determinations play a central role and contribute to the administration of suitable treatment options.

Suppression of hepatic lesions in a murine graft-versus-host reaction by antibodies against adhesion molecules

BACKGROUND/AIMS

The injection of parental CD4+ T cells into major histocompatibility complex (MHC) class II disparate F1 hybrid mice induced an autoimmune graft-versus-host reaction (GVHR) which is analogous to autoimmune liver diseases. The interaction of adhesion molecules such as vascular cell adhesion molecule-1 (VCAM-1) and very late antigen-4 (VLA-4) has been known to be profoundly involved in the trafficking of lymphocytes into the inflammatory tissues. The aim of this study was to clarify the role of VLA4 or VCAM-1 in the development of GVHR-induced hepatic lesions in our model.

METHODS

B6 T spleen cells were injected into (B6.C-H-2bm12xB6) F1 mice intravenously. Anti-VLA-4 mAbs and/or anti-VCAM-1 mAbs were injected intraperitoneally at a dose of 2.5 mg/kg of each mAbs per body weight of mouse. We examined the changes in GVHR-induced hepatic lesions, serum levels of antimitochondrial antibodies (AMA) and cytokine mRNA expressions of liver-infiltrating lymphocytes using H.E. and immunohistochemical staining, enzyme-linked immunosorbent assay (ELISA), and reverse transcription-polymerase chain reaction (RT-PCR), respectively.

RESULTS

Hepatic lesions of anti-VLA-4 mAbs-treated mice were inhibited compared with those of GVHR mice. However, the administration of mAbs did not interfere with the induction of splenomegaly, the invasion of CD4+, CD8+, B220+, or Mac-1+ cells around bile ducts, nor the production of AMA. Liver-infiltrating CD4+ T cells obtained from these treated mice did not alter the expression of T helper (Th)1 and Th2 cytokine mRNA.

CONCLUSION

The results suggest that treatment with antibodies against these adhesion molecules could inhibit the infiltration of lymphocytes without affecting the Th1/Th2 balance. The blockade of VLA-4-mediated cell infiltration into the liver in this model may have a possible novel therapeutic role of VLA-4 mAbs.

Familial primary biliary cirrhosis in Hiroshima

Primary biliary cirrhosis (PBC) is an autoimmune liver disease characterized by the presence of anti-mitochondrial antibodies and chronic inflammatory destruction of septal and intrahepatic bile ducts. Although there are no obvious associations of PBC with MHC class I or class II genes, there appears to be a significant increased risk of developing disease within families. Clearly, a combination of genetic and environmental factors play a role in disease pathogenesis, although the relative contributions of each are unclear. In this study, we have taken advantage of the well-defined health-care system in Hiroshima prefecture, where PBC is a reportable disease. In the period 1988-1997, 156 new patients with PBC in a total population of 2,873,000 were diagnosed. These patients included 18 subjects that were derived from eight different families in which more than one family member had a history of PBC; this reflects a frequency of 5.1% and further shows that the prevalence of PBC is greatly increased in family members. Of interest, the median age of onset of PBC in second generation patients was much younger (33.4+/-10.8 years) compared to median disease onset in general patients with PBC in Hiroshima (55.6+/-12 years). In fact, it was striking that the onset of disease in family members often occurred within a few years of each other. We also noted that sera of affected members had similar AMA reactive profiles against recombinant PDC-E2, BCKD-E2 and OGDC-E2; the major autoantigens of PBC. Similar HLA types were found within affected members of a pedigree but the data is limited because of absence of similar typing of unaffected members. The increased family history of PBC, and the earlier onset of disease in second generation members, suggests that environmental agents are an important risk factor for the development of disease. We suggest that genomic analysis in familial PBC will be important to identify the mechanisms of genetic susceptibility.

In situ nucleic acid detection of PDC-E2, BCOADC-E2, OGDC-E2, PDC-E1alpha, BCOADC-E1alpha, OGDC-E1, and the E3 binding protein (protein X) in primary biliary cirrhosis

The characteristic serological feature of primary biliary cirrhosis (PBC) is the presence of antimitochondrial antibodies (AMAs), and the major proteins recognized by AMAs are subunits of the 2-oxo acid dehydrogenase complexes (2-OADC), including the E2 components of the pyruvate dehydrogenase complex (PDC), the 2-oxo-glutarate dehydrogenase complex (OGDC), the branched-chain 2-oxoacid dehydrogenase complex (BCOADC), the E3 binding protein (E3BP or protein X) and the E1a component of mammalian PDC. Previous work has postulated that either E3BP, or a molecule cross-reactive with the PDC-E2 molecule, is uniquely expressed on the surface of biliary epithelial cells in PBC. To address this issue, we performed in situ hybridization for all of the major 2-OADC components at the mRNA level, including PDC-E2, BCOADC-E2, OGDC-E2, PDC-E1a, BCOADC-E1a, OGDC-E1, and E3BP using 13 PBC and 9 control livers using 7 mitochondrial antisense probes. In both PBC and controls, the expression of all 2-OADC component mRNA studied herein were found in hepatocytes and infiltrating mononuclear cells, without significant differences. Interestingly, however, despite published data on immunohistochemical staining, interlobular bile ducts including the injured bile ducts in PBC were generally negative or only faintly positive, with the exception of 1 bile duct in 1 of 13 cases of PBC and 1 of 9 control liver specimens. Moreover, confocal microscopic examination and image analysis revealed that the mRNA signal intensity of each of the 2-OADC components in the bile ducts of PBC was relatively lower in comparison with control liver diseases. These data suggest that continuous enhanced synthesis of the 2-OADC components is not likely to be occurring in the biliary epithelial cells in PBC, and that an increase of PDC-E2 or E3BP immunoreactivity in PBC is caused by exogenous imported or cross-reactive molecules.

Characterization of the overlap syndrome of primary biliary cirrhosis (PBC) and autoimmune hepatitis: evidence for it being a hepatitic form of PBC in genetically susceptible individuals

Some patients with autoimmune liver disease present with a clinical and/or histological picture showing characteristic findings of both autoimmune hepatitis (AIH) and primary biliary cirrhosis (PBC). Various names, mostly overlap syndrome, have been used to describe these cases, which have thus far not been more closely characterized. The aim of this study was the comparison of 20 patients with overlapping features to representative patients considered suffering from typical AIH or typical PBC (20 patients in each group). We found these patients to indeed show a very mixed picture of both conditions biochemically, serologically, and histologically. However, closer analysis suggested that all of these patients were primarily suffering from PBC as all of them had at least either bile duct destruction on histology or anti-M2 positive antimitochondrial antibodies (AMA). We suggest that these PBC patients because of their genetic susceptibility, evidenced by the AIH-characteristic histocompatibility leukocyte antigen (HLA) type B8, DR3, or DR4, developed a more hepatitic picture. Response to immunosuppressive therapy was excellent. We propose that the name "overlap syndrome" be abandoned for "PBC, hepatitic form." These observations not only have pathophysiological implications, but also suggest that therapy of PBC should be guided by the degree of biochemical and histological hepatic involvement.

Identification of major linear epitopes on the sp100 nuclear PBC autoantigen by the gene-fragment phage-display technology

Approximately 20-30% of sera from patients suffering from primary biliary cirrhosis contain autoantibodies against a nuclear protein termed sp100. By indirect cytoimmunofluorescence it was shown that the sp100 autoantigen is distributed in up to 20 dot-like structures per nucleus co-localizing with the so-called nuclear bodies. In western blots these sera react with a protein with an apparent molecular mass of 100kDa. By screening expression libraries with affinity-purified anti-sp100 antibodies we isolated a full-length sp100 cDNA whose sequence exactly matched the previously published sp100 sequence and encodes a protein of 481 amino acids with a deduced molecular mass of 53 kDa. In an attempt to determine immunoreactive regions on the sp100 antigen with the recently developed gene-fragment phage-display technology we were able to identify a stretch of sixteen amino acids (IKKEKPFSNSKVECQA) at position 296-311 as a major antigenic region (antigenic region 1) on the sp100-autoantigen. A second antigenic region (antigenic region 2) of twenty amino acids in length could be identified between amino acids 332-351 (EGSTDVDEPLEVFISAPRSE). By using immobilized synthetic peptides and various sp100-positive PBC patient sera the corresponding epitopes could be shown to be centered around epitope cores of six amino acids (SNSKVE, antigenic region 1) and nine amino acids (EPLEVFISA, antigenic region 2) respectively.

Characterization of antimitochondrial antibodies in health adults

The detection of antimitochondrial antibodies (AMAs) is an important criterion for the diagnosis of primary biliary cirrhosis (PBC). During the last decade, the mitochondrial autoantigens have been cloned, sequenced, and identified as members of the 2-oxo-acid dehydrogenase pathway, including the E2 subunits of pyruvate dehydrogenase (PDC-E2), branched-chain 2-oxo-acid dehydrogenase (BCOADC-E2), and 2-oxo-glutarate dehydrogenase (OGDC-E2). We have developed a rapid and sensitive diagnostic test for use in PBC based on a triple hybrid recombinant molecule (r-MIT3) that contains the autoepitopes of PDC-E2, BCOADC-E2, and OGDC-E2. To help understand the frequency and antigen specificity of AMAs in an asymptomatic population and to identify patients with early disease, we investigated the prevalence of AMA, by enzyme-linked immunosorbent assay (ELISA), in a cohort of 1,530 people from northern Italy. Positive sera were further analyzed for immunoglobulin (Ig) isotypes, subclasses, and epitopes of AMA by a combination of ELISA and immunoblotting. In this cohort of 1,530 people, 9 (0.5%) reacted to r-MIT3 by ELISA. Of the 9 reactive sera, 2 recognized PDC-E2, 2 of 9 recognized BCOADC-E2, 1 of 9 recognized OGDC-E2, 2 of 9 recognized both PDC-E2 and BCOADC-E2, and 1 of 9 recognized PDC-E2 and OGDC-E2. AMA reactivity was primarily IgM and IgA. Epitope mapping revealed an AMA pattern of reactivity to PDC-E2 that differed from that found in patients with histologically proven PBC in most of the sera. However, 1 sera of a 72-year-old female with a normal alkaline phosphatase had an AMA profile identical to typical PBC. After a variable follow-up period (8-14 months), sera from 8 of 9 of these people were re-obtained for AMA and relative epitope mapping. Interestingly, the reactivity had a wider AMA pattern than before.

Primary biliary cirrhosis. Is (and how much of) the pathology preventible?

Primary biliary cirrhosis (PBC) is a chronic, progressive cholestatic liver disease, which is invariably fatal. Circumstantial and indirect evidence suggests that autoimmune mechanisms have a role in the pathogenesis of PBC. Antimitochondrial antibodies (AMA) are highly sensitive and specific markers that can predict the development of the disease in a healthy individual. Long-term administration of ursodeoxycholic acid (UDCA), a naturally occurring bile acid, safely slows the progression of PBC, delays the need for liver transplantation, and postpones death. An effort should be made to identify the patients with PBC in the asymptomatic stage by the presence of AMA and to conduct a clinical trial in order to assess the benefit of long-term administration of UDCA on the prevention of the overt disease in these individuals.

Neurofibromin colocalizes with mitochondria in cultured cells

Mutations in neurofibromatosis type 1 target the gene coding for neurofibromin. While neurofibromin is able to accelerate the rate of GTP hydrolysis by cellular Ras proteins, its biological function is not well understood. To gain information regarding its function, the intracellular localization of neurofibromin was analyzed in cultured cell lines using polyclonal antisera raised against four neurofibromin-specific peptides, three from the carboxyl terminus and one from the amino terminus. In methanol-fixed cells distinct rod-like structures distributed throughout the cytoplasm were recognized by the antisera. Similar structures were seen with each antiserum, including affinity-purified antibodies, and in each of the cultured cell lines tested. Similar structures were seen in paraformaldehyde-fixed cells. Double staining experiments showed that these structures colocalize with mitochondria, but not with actin, beta-tubulin, or endoplasmic reticulum. When actin or tubulin structures within the cell were disrupted by separate antimitotic drugs, these stained structures retained their shape. Neurofibromin association with mitochondria was confirmed biochemically when highly purified mitochondrial fractions from bovine heart tissue were shown in Western analysis to contain neurofibromin. This association might be helpful in predicting identification of some of the cellular proteins with which neurofibromin interacts.

Molecular biological xxxmethods in diagnosis and treatment of liver diseases

Molecular biology is making a tremendous impact on the diagnosis and treatment of liver diseases. Methods such as the polymerase chain reaction are changing the way physicians diagnose and monitor patients with viral hepatitis. Assays based on recombinant protein antigens allow for detection of specific autoantibodies in diseases such as primary biliary cirrhosis. The diagnosis of inherited metabolic diseases, such as hemochromatosis and Wilson disease, is being revolutionized by discovery of the defective genes involved and the development of methods to rapidly sequence DNA and identify mutations. Treatments and preventive measures are now possible with use of drugs and vaccines produced by recombinant DNA technology. Gene therapy and nucleic acid-based therapeutics are also realistic future treatment options for individuals with liver diseases.

Identification of an autoantibody against alpha-enolase in primary biliary cirrhosis

BACKGROUND

Primary biliary cirrhosis is a chronic cholestatic liver disease in which autoreactive T cells may play an important role in the destruction of intrahepatic bile ducts. However, target antigens remain unknown. Alpha-enolase-derived peptide binds to human leukocyte antigen (HLA)-DR8, which is implicated in the development of primary biliary cirrhosis in Japanese patients. Partial homology between alpha-enolase and the inner lipoyl domain of E2 component of pyruvate dehydrogenase (PDH-E2) is also observed.

METHODS

Using alpha, beta and gamma enolase isozymes obtained from humans and/or rabbits, we examined serum samples of 56 patients with primary biliary cirrhosis, 19 autoimmune hepatitis, 38 acute and chronic viral hepatitis and 36 healthy subjects by immunoblotting.

RESULTS

Anti-alpha-enolase antibody was present in a significantly higher percentage of patients with primary biliary cirrhosis (16 of 56, 28.6%) and autoimmune hepatitis (6 of 19, 31.6%) than in normal subjects (p<0.005, p<0.01, respectively). Antibodies against beta and gamma-enolases were not detected in any serum sample. Although there was no significant correlation between the presence of anti-alpha-enolase antibody and clinical features of primary biliary cirrhosis, the mortality rate associated with hepatic failure in patients with positive autoantibody was significantly higher than that of antibody-negative PBC patients (6 of 16, 37.5% vs 5 of 40, 12.5%, p<0.05).

CONCLUSIONS

Since alpha-enolase is expressed on the cell surface, our data suggest that the immunological reaction to alpha-enolase might be involved in biliary epithelial destruction and be relevant to the disease progression.

Diagnosis and therapy of cholestatic liver disease

The majority of cholestatic liver diseases can be diagnosed with a carefully performed history taking, physical examination, and appropriate imaging studies. In a minority of cases, however, liver biopsy may be necessary to establish the diagnosis. In addition to the treatment of the specific liver disease, therapy should address the management of complications unique to cholestasis and progressive liver failure.

Hepatic portal infiltrates in mice immunized with syngeneic lymphoid cells: connotations for models of autoimmune liver disease

The aim of this study was to investigate liver histology in mice after immunization with the conserved self molecule dihydrolipoamide dehydrogenase, E3, a subunit of the mitochondrial 2-OADC enzyme family identified as the M2 autoantigen in the liver disease, primary biliary cirrhosis. Mice were immunized by a novel procedure. The autoantigen E3 was introduced by pinocytosis into hypertonically treated syngeneic lymphoid cells to facilitate intracellular antigen processing and presentation and the generation of a cytolytic T cell response. Liver sections were examined and scored for evidence of an inflammatory response by two independent procedures: standard microscopy with visual scoring, and automated scanning with computerized scoring. There was a close correlation between read-outs of liver histology by standard microscopy and automated scanning, using the index of mononuclear cellular infiltrations in hepatic portal tracts. Such infiltrates were prominent in the immunized mice, but, unexpectedly, the degree of infiltration was similar in mice injected with autoantigen (E3)-loaded syngeneic cells, or syngeneic cells treated only with hypertonic medium. The equivalent changes in the liver with the experimental and control protocol is indicative of the reactivity of the liver to any provocative immune stimulus, and is cautionary for protocols designed for the induction of autoimmune liver disease in experimental animals.

Antibodies to colonic epithelial cells from the serum and colonic mucosal washings in ulcerative colitis

It has been suggested that antibodies to a colonocyte protein of 40 kD (an intestinal isoform of tropomyosin) are specifically found in the serum and mucosa of patients with ulcerative colitis, which has important pathogenic implications. This study isolated and purified tropomyosin from the colonic mucosa, but no specific binding to this protein has been detected in serum samples or immunoglobulins isolated from mucosal washings of 20 ulcerative colitis (UC) patients by enzyme linked immunosorbent assay (ELISA) compared with 21 controls or 17 Crohn's disease (CD) patients. Samples from a further 12 patients with UC and primary sclerosing cholangitis (it is proposed that cross reactivity against the intestinal tropomyosin isoform accounts for the extraintestinal disease) also did not show binding to tropomyosin, whereas monoclonal antitropomyosin antisera bound both ELISAs and western blots. This study also examined the proteins in the normal colonic biopsy specimens on western blots that are bound by both serum samples and mucosal immunoglobulin preparations from these patients groups; there was no specific IgG or IgA binding to patients with UC or UC/primary sclerosing cholangitis, whereas binding to mitochondrial proteins of 70,000 and 45,000 was seen in samples from 12 primary biliary cirrhosis positive controls. This work does not support the hypothesis that autoimmune activity against the intestinal isoform or tropomyosin is important in the pathogenesis of ulcerative colitis.

Mitochondrial antigens, molecular mimicry and autoimmune disease

The immune system is normally tolerant to mitochondrial self-antigens, but responsive against bacteria. Low-titre anti-mitochondrial antibodies (AMA) might be involved in this discrimination. Tolerance is broken in diseases characterised by high titre AMA. Some of these AMA, against cardiolipin, cross-react with DNA. The best studied AMA are those characterising primary biliary cirrhosis (PBC). These are directed against E2 subunits of the oxo-acid dehydrogenase complexes, and also against subunits E1 alpha, E1 beta and X of the pyruvate dehydrogenase complex. AMA of PBC patients also react with bacterial E2s. Reactivities are primarily peptide-specific but with cross-reactivity between mitochondrial and microbial antigens and between E2s of respective complexes. Immunodominant epitopes, for anti E2 AMA, include the conserved sequence flanking the site of lipoyl attachment. It is proposed that the initial stimulus for antibody production is chronic urinary tract infection. AMA themselves are not pathogenic, but CD4+ T-cells would be primed, recognising the lipoyl domain epitope in association with class II HLA. Inappropriate expression of class II antigens on bile duct epithelia, (as found in PBC), might lead to presentation of a particular fragment of HLA-DR alpha, known to be a major MHC presented self-peptide in the mouse. That sequence strongly mimics the lipoyl domain and might be recognised by primed T-cells, initiating the autoimmune cascade. In the mouse, a peptide of ND1 of Complex I is presented in association with class I MHC. Cells exhibiting somatic mutation of such a peptide might thus be subject to attack by CD8+ T-cells. If such peptides were presented by class II HLA, autoimmune diseases might arise, related to mimicry between such peptides and microbial sequences and/or self-antigens. These considerations might apply in Leber's disease and in age-related pathology.

Enzyme-linked immunosorbent assays for the determination of IgG, IgA, and IgM autoantibodies to pyruvate dehydrogenase in primary biliary cirrhosis

Autoantibodies to the recently described mitochondrial autoantigen, pyruvate dehydrogenase, have been shown to be specific for primary biliary cirrhosis. In the present study we describe enzyme-linked immunosorbent assays to detect antibodies of IgG, IgA, and IgM classes reactive with pyruvate dehydrogenase. These assays showed high sensitivity (95%) and specificity (100%) for primary biliary cirrhosis when evaluated in 28 patients with primary biliary cirrhosis, 59 disease controls, and 214 healthy persons. Quantitation of these autoantibodies by calculating the areas under the sera titration curves of 10 primary biliary cirrhosis patients indicated that an increase in IgA antibodies to pyruvate dehydrogenase is related to more rapid disease progression.

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

Sera from patients with primary biliary cirrhosis (PBC) react with enzymes of the 2-oxo dehydrogenase pathways, particularly PDC-E2. These enzymes are present in all nucleated cells, yet autoimmune damage is confined to biliary epithelial cells. Using a panel of eight mouse monoclonal antibodies and a human combinatorial antibody specific for PDC-E2, we examined by indirect immunofluorescence and confocal microscopy sections of liver from patients with PBC, progressive sclerosing cholangitis, and hepatocarcinoma. The monoclonal antibodies gave typical mitochondrial immunofluorescence on biliary epithelium and on hepatocytes from patients with either PBC, progressive sclerosing cholangitis, or hepatocarcinoma. However, one of eight mouse monoclonal antibodies (C355.1) and the human combinatorial antibody reacted with great intensity and specificity with the luminal region of biliary epithelial cells from patients with PBC. Simultaneous examination of these sections with an antiisotype reagent for human IgA revealed high IgA staining in the luminal region of biliary epithelial cells in patients with PBC. IgG and IgA antibodies to PDC-E2 were detected in the bile of patients with PBC but not normal controls. We believe that this data may be interpreted as indicating that a molecule cross-reactive with PDC-E2 is expressed at high levels in the luminal region of biliary epithelial cells in PBC.

Chromosome localization and RFLP analysis of PDC-E2: the major autoantigen of primary biliary cirrhosis

Patients with primary biliary cirrhosis are well known for the presence of titer antibodies against dihydrolipoamide acetyltransferase, the E2 subunit of the pyruvate dehydrogenase complex. We have taken advantage of a cDNA probe for dihydrolipoamide acetyltransferase to explore the possibility of polymorphism of the E2 subunit by probing genomic DNA from 38 patients with primary biliary cirrhosis and 26 healthy controls. To detect restriction fragment length polymorphism, DNA was digested with ten specific restriction enzymes that often detect polymorphism, including Bam HI, Bgl II, Eco RI, Hind III, Hinf I, Msp I, Pst I, Pvu II, Rsa I and Taq I. A Taq I polymorphism was found in 19 of 38 patients with PBC and 6 of 26 normal controls. In addition, using fluorescence in situ hybridization, the gene for dihydrolipoamide acetyltransferase was mapped on human chromosome 11 band q23.1. Interestingly, this region of the long arm of chromosome 11 is often associated with cytogenetic abnormalities, including translocations.

Autoantibodies to the nuclear Sp100 protein in primary biliary cirrhosis and associated diseases: epitope specificity and immunoglobulin class distribution

Sp100, a protein with a dot-like intranuclear localization in immunofluorescence microscopy, is a major target for patient autoantibodies in primary biliary cirrhosis (PBC) and occasionally in rheumatic disorders. The human Sp100 cDNA has recently been cloned, and the deduced amino acid sequence was found to contain sequence similarities with an MHC class I domain and several transacting regulatory proteins, including HIV-1 nef proteins. In this study, recombinant Sp100 fusion proteins were used to differentiate the immunoglobulin isotypes and to map the epitopes involved in the anti-Sp100 autoimmune response. PBC patients developed IgG as well as IgM and/or IgA class anti-Sp100 autoantibodies whereas most patients with rheumatic diseases developed IgG class autoantibodies only. For epitope mapping, truncated versions of the Sp100 protein were probed for immunoreactivity in ELISA and immunoblotting. With 55 sera, 17 different reaction patterns were obtained, and at least three non-overlapping major autoantigenic domains were recognized by the majority of sera. One domain, which contains the sequence similarity with HIV nef proteins, was recognized by all anti-Sp100 sera and harbours multiple, in part discontinuous, epitopes. These data demonstrate a heterogeneous and patient-specific anti-Sp100 autoimmune response which is antigen-driven and, at least in terms of isotype composition, different in PBC and non-PBC patients.

Antimitochondrial (pyruvate dehydrogenase) autoantibodies in autoimmune rheumatic diseases

Anti-pyruvate dehydrogenase (PDH) antibodies were determined in 1451 sera of patients with primary biliary cirrhosis (PBC) and several autoimmune rheumatic conditions by ELISA and immunoblotting. They were detected in sera of 93% of the patients with PBC (179 of 192 patients) in 60 of 277 (22%) patients with Sjogren's syndrome (SjS), 34 of 437 (8%) patients with scleroderma, 33 of 191 patients with SLE (17%), and 5 of 55 (10%) patients with rheumatoid arthritis (RA) but in none of the patients with polymyositis or the antiphospholipid syndrome. The ELISA studies were confirmed by immunoblots showing binding of autoimmune rheumatic sera to the same epitope (74 kd) of mitochondria that the PBC sera reacted with. The identical binding characteristics were also confirmed by protein competition assays with purified PDH. In 4 of 53 patients with SjS who were positive for anti-PDH, high titers as in PBC were detected. The anti-PDH antibodies in Sjogren's patients were associated with deranged liver function tests and extraglandular features but did not correlate with any other non-organ-specific antibody. Follow-up studies confirmed the association of the emergence of anti-PDH antibodies with defects in liver function tests. The antibodies were more prevalent in SLE and RA when they were associated with Sjogren's syndrome (30 and 18.8%, respectively). Among patients with different forms of scleroderma, anti-PDH antibodies were noted in subjects with systemic sclerosis, morphea, and Raynaud's phenomenon.(ABSTRACT TRUNCATED AT 250 WORDS)

A patient with primary biliary cirrhosis and multiple sclerosis

A 48-year-old woman with primary biliary cirrhosis (PBC) and multiple sclerosis (MS) is reported. She presented with a visual deficit in 1975. In the course of a diagnostic evaluation, she was found to have PBC. In 1986, the diagnosis of MS was made. The patient's liver function deteriorated and liver transplantation was performed in May 1988. This is the third known case of this association.

Primary biliary cirrhosis: new therapeutic directions

The immunologic mechanisms responsible for the development of primary biliary cirrhosis (PBC) remain poorly defined, although recent investigations have provided new clues as to the role of cellular membrane proteins such as the mitochondrial autoantigens and intercellular adhesion molecules. Additionally, new therapeutic agents have become available that markedly enhance the prospect for medical management of both hepatic and extrahepatic manifestations of PBC. Definitive therapy with ursodeoxycholic acid and/or methotrexate, and symptomatic relief of pruritus with rifampicin or metronidazole may become standard in the years ahead. The results of their use to date in the treatment of PBC are detailed in this review. Successful therapy of hepatic osteodystrophy associated with PBC has yet to be achieved, although early data suggest a role for ursodeoxycholic acid, estrogen, calcium, and vitamin D in the management of this debilitating problem. Orthotopic liver transplantation continues to be successful for the management of advanced disease (greater than 70% 5-year survival) and will remain an essential therapeutic tool until definitive medical therapy for PBC becomes available.

A biliary protein identified by immunoblotting stimulates proliferation of peripheral blood T lymphocytes in primary biliary cirrhosis

The source of activation of T lymphocytes in primary biliary cirrhosis (PBC) is undefined. Hence, T-cell-mediated reactivity against a biliary tract antigenic protein from human bile was studied. The bile protein was fractionated by 30-50% saturated ammonium sulphate and gel-chromatography, and analysed by SDS-PAGE and Western immunoblotting using rabbit antisera to the bile protein. The antisera reacted specifically with human bile duct epithelium. Western blotting of bile proteins showed two major bands, the B1 and B2 antigens. B1 stained for sialoglycoprotein but not lipid, but B2 was negative for both. Cell-mediated reactivity was tested by proliferation of peripheral lymphocytes against B1. Taking the upper limit of the normal range for stimulation indices (S.I.) as less than 1.89 (= mean + 2 SD), a mitogenic response was detected in 14 of 16 patients with PBC (S.I.: 11.7 to 2.3), and in 4 of 15 patients with chronic active hepatitis, but in none of 12 patients with drug-induced intrahepatic cholestasis or obstructive jaundice. The B2 protein was non-stimulatory. Lymphocyte proliferation to B1 in PBC was confined to T cell fractions of peripheral blood leucocytes. There was no cross-antigenicity between B1 and the M2 antigens, according to Western blotting using the rabbit antisera and PBC sera with anti-M2 reactivity. Thus, the B1 biliary protein is a possible source of T cell activation in PBC and hence could be an immunological co-factor in the pathogenesis of this disease.

Specific reactivity of recombinant human PDC-E1 alpha in primary biliary cirrhosis

The mitochondrial autoantigens recognized by autoantibodies in patients with primary biliary cirrhosis have been identified as components of related multi-enzyme complexes, including acyltransferases of the pyruvate dehydrogenase complex (PDC), the branched-chain alpha-keto acid dehydrogenase complex (BCODH), the alpha-ketoglutarate dehydrogenase complex (OGDC), protein X and pyruvate dehydrogenase (PDC) E1 alpha and E1 beta. The major autoantigens, PDC-E2, BCODH-E2 and OGDC-E2, share some sequence homology; the epitopes on these antigens appear to be close to, or identical with, the lipoic acid binding site. Furthermore, all three antigens share some structural homology. In contrast, antibodies to PDC-E1 alpha are present in lower titers, and have been more difficult to detect. PDC-E1 alpha also differs from the three major autoantigens in that it lacks any covalently bound lipoic acid. PDC-E1 alpha cannot be purified in large quantities and becomes unstable in the absence of PDC-E1 beta. To address these problems, we have subcloned recombinant human PDC-E1 alpha to pGEX, pGEX is a vector which produces a recombinant polypeptide fused to glutathione S-transferase. The resultant E1 alpha fusion protein is stable and has a low background in immunoassays. Using the recombinant protein, we have developed an ELISA that allows rapid and reproducible quantification of antibodies to human PDC-E1 alpha. Finally, we demonstrate that a major epitope on PDC-E1 alpha is within a 300 amino acid region that contains the enzyme functional sites, namely the phosphorylation site and the TPP binding site.

High serum levels of CD8 antigen in primary biliary cirrhosis: a possible cause of suppressor cell dysfunction?

Reduced suppressor cell number and function have been described in a number of autoimmune diseases and this may contribute to pathogenesis. Suppressor cell function depends upon the interaction of the CD8 antigen expressed on suppressor cells with other limbs of the immune system. Recently, soluble membrane antigens including CD8 have been identified in serum and it is possible that the loss of such antigens from viable cells could result in functional deficit. In order to examine whether the decreased suppressor cell function reported in autoimmune type of chronic liver disease is associated with soluble serum CD8 levels, sera from 23 patients with primary biliary cirrhosis (PBC), 12 with autoimmune chronic active hepatitis (AI-CAH) and 21 healthy controls were tested using a commercially available enzyme immunoassay. The proportion of cells expressing the CD8 antigen and the intensity of its display were also determined using an immunofluorescent technique and an ELISA, respectively, for 12 PBC and 10 healthy controls. The soluble serum CD8 levels were significantly higher in PBC (mean U/ml +/- s.d., 777 +/- 331), and AI-CAH (575 +/- 291) than controls (322 +/- 115) (P less than 0.001 and P = 0.004, respectively). While the intensity of CD8 antigen expression on suppressor/cytotoxic populations was not significantly different in PBC (347 +/- 125 per 10(4) cells) compared with controls (441 +/- 206), the mean proportion of CD8 positive cells was significantly less in PBC (14.1 +/- 6.8%) than controls (20 +/- 4.7%) (P less than 0.05). These data suggest that the apparent reduction in suppressor cell number found for patients with PBC and AI-CAH may be a consequence of the shedding or secretion of CD8 antigen from cell membrane of CD8 positive lymphocyte. It is also possible that the loss of this antigen is responsible for the reduced suppressor cell function seen in these conditions.

New monoclonal antibodies reacting with bile ducts: further insights into the pathogenesis of bile ductular proliferation in biliary diseases

We have produced a range of monoclonal antibodies which stain human intrahepatic bile ducts of different sizes. Amongst 26 monoclonal antibodies produced, five clones reacted specifically with bile ducts of different sizes, of which three have been maintained in culture and their viability following freezing and thawing confirmed. Staining patterns varied between normal adult liver tissue, normal fetal liver tissue and a variety of hepatobiliary diseases. The antibodies provide further evidence of the immunological heterogeneity of the human intrahepatic biliary tree and support the hypothesis that proliferating bile ductules are derived from periseptal hepatocytes. The preparation of the antibodies, their staining reactions in normal adult, normal fetal and a variety of liver diseases are described.

Anti-pyruvate dehydrogenase autoantibodies in primary biliary cirrhosis

Antimitochondrial antibodies (AMA) may be detected in 95% of patients with primary biliary cirrhosis (PBC). The target autoantigens for the AMA were recently identified as four closely related metabolic enzymes located in the mitochondria. We have purified the pyruvate dehydrogenase (PDH) enzyme from bovine heart, showing that all PBC sera reacted with a 74-kd band. PDH was utilized to establish an ELISA assay for detecting the relevant antibodies. One hundred twelve of 120 sera from patients with PBC (95%) reacted with the PDH but none of the 201 control sera, including normal subjects and a panel of sera from other patients with liver diseases, showed similar reactivity. In 77% of the PBC sera the anti-PDH antibody isotype was identified as a combination of IgG and IgM, while in 18% only IgM was detected. In 5% of the sera the isotype was confined to IgG. PBC sera specifically inhibited the PDH enzyme activity. The enzyme inhibition correlated with the anti-PDH antibody titers. Thus, PDH seems to be one of the major target epitopes for AMA observed in sera of patients with PBC.

PBC 95k, a 95-kilodalton nuclear autoantigen in primary biliary cirrhosis

We have identified a novel antinuclear antibody (ANA) in the sera of patients with primary biliary cirrhosis (PBC). Sera from 22 of 50 PBC patients stained the nuclei of HEp-2 cells in a pattern of 5-20 discrete dots, on indirect immunofluorescence. Typically, the titers were higher than 1:1,280. This staining pattern was seen in only 4 of 1,240 ANA-positive samples from patients with other connective tissue diseases, and in none of the ANA-positive sera from 49 patients with other liver diseases. Sera which stained the nuclear dots bound a 95-kd polypeptide in immunoblots of HeLa nuclei and in immunoprecipitates of 35S-methionine-labeled HeLa extracts. Affinity-purified antibodies from the 95-kd protein reproduced the nuclear dot immunofluorescence staining pattern, demonstrating that this polypeptide is located in the nuclear dots. ANA of this type, therefore, occur in 44% of patients with PBC, and they appear to be specific for PBC. These antibodies bind a 95-kd protein that is discrete and is scattered throughout the nucleus.

Primary biliary cirrhosis: paradigm or paradox for autoimmunity

Primary biliary cirrhosis has been classified as a model autoimmune disease based on striking defects in immune regulation and the presence of autoantibodies to mitochondria. Until recently the significance and definition of mitochondrial autoreactivity was unknown. Since 1987, there has been a vast improvement in the understanding and definition of the biochemical and molecular target autoantigens. The cloning of complementary DNAs for mitochondrial antigens has led to the identification of three enzymes of the 2-oxo-acid dehydrogenase family as the targets of the autoantibodies to mitochondria in patients with primary biliary cirrhosis. The major reactive autoantigen is the E2 subunit of pyruvate dehydrogenase. Immunodominant sites on pyruvate dehydrogenase E2 (autoepitopes) have been mapped and have been shown to be the site of attachment of the functionally important lipoic acid prosthetic group. The autoepitope for the other enzymes probably occupies an equivalent site on the enzyme. The availability and definition of these mitochondrial autoepitopes have allowed specific questions to be addressed relating to the processing and targeting of these autoantigens as well as further studies on mechanisms of immunopathology. Similarly, the availability of well-defined autoantigens could contribute to the development of valid animal models in addition to the already described reproduction of the biliary ductular lesions by transfer of peripheral blood lymphocytes from patients with primary biliary cirrhosis into severe combined immunodeficient mice. Such models will facilitate specific study of the role of major histocompatibility complex expression and the characterization of T-cell reactivity. Thus, primary biliary cirrhosis is a key example of significant progress in autoimmunity being made by use of recombinant DNA technology.

Plasma membrane association of primary biliary cirrhosis mitochondrial marker antigen M2

Antibody reactivity against the 'mitochondrial M2 antigen' was determined in sera from 10 patients with primary biliary cirrhosis (PBC), using Western blotting after SDS-PAGE separation of rat liver mitochondria (RLM) and plasma membrane proteins. The molecular weights of the major M2 antigens in rat liver mitochondria were 67 and 50 kD. Two of the 10 PBC patients did not react to any of these major antigens, eight reacted to the 67-kD and four of those also to the 50-kD antigen. The 67- and 50-kD antigens were present in both plasma membrane and RLM and had affinity to concanavalin A. Antibody reactivity against the 67-kD antigen could be detected in both IgG and IgA as well as in the IgM class. The reactive IgG subclasses to both types of antigen preparations were mainly of the G1 and G3 isotypes. This reactivity was always stronger with antigens from the plasma membrane preparations. Sera from two patients with high antibody titres against mitochondria also reacted with IgG2 against the 50-kD antigen from plasma membrane, but not to the corresponding antigen in mitochondria. Reactivity of antibodies in PBC sera to the periphery of viable hepatocytes and radioactive surface labelling of the 50-kD component are both consistent with a plasma membrane localization of M2. Serum from healthy controls and several patients with different diseases did not contain antibodies reactive against any of the antigens described. We suggest that antigens, partly identical to the mitochondrial M2, are located in the plasma membrane compartment. The PBC pathogenetical consequences of these findings are discussed.

Antimitochondrial autoantibodies of primary biliary cirrhosis as a novel probe in the study of 2-oxo acid dehydrogenases in patients with mitochondrial myopathies

Autoantibodies present in the autoimmune disease primary biliary cirrhosis react by immunoblotting with four human skeletal muscle mitochondrial antigens of 70 kDa, 52 kDa, 50 kDa and 45 kDa, identified as the lipoate acetyl transferases (E2) of the pyruvate dehydrogenase, component X of E2 pyruvate dehydrogenase, E2 of 2-oxo glutarate dehydrogenase and E2 of branched-chain 2-oxo acid dehydrogenase complexes respectively. These autoantibodies have been employed as a novel probe to study whether there is a defect in the synthesis of the 2-oxo acid dehydrogenase complexes in patients with mitochondrial respiratory chain disorders. The reactive antigens are present normally in four patients with oculomyopathy in whom partial deletions of the mtDNA have been detected, and in two patients with MERRF and MELAS encephalomyopathy. Thus, unlike in the yeast Saccharomyces cerevisiae, there appear to be no regulatory interactions which coordinate the assembly of the mitochondrial respiratory chain with the development of the pyruvate dehydrogenase complex, which plays an important role in regulating the flow of metabolic intermediates to oxidative energy metabolism.

Antibody binding and inhibition of pyruvate dehydrogenase (PDH) in sera from patients with primary biliary cirrhosis

Autoantibodies reactive against mitochondria which are present in sera from patients with primary biliary cirrhosis (PBC) have been shown to bind to the lipoamide acetyltransferase moiety (E2) of the pyruvate dehydrogenase enzyme complex (PDH). This newly described antigen has been shown to be identical to M2, a 70-kD antigen of the inner mitochondrial membrane. Sera from 10 patients with PBC, 11 patients with chronic active hepatitis (CAH), 20 healthy controls and patients with thyroiditis and systemic lupus erythematosus (SLE) were tested by ELISA for the presence of antibodies (IgG and IgM classes and IgG subclasses) reactive against PDH. The effect of serum and separated IgG and IgM on the PDH enzyme activity was measured spectrophotometrically. Nine out of 10 PBC sera were positive by immunofluorescence for mitochondria (M2 pattern). These nine sera reacted strongly with both IgG and IgM to PDH in the ELISA and also inhibited the enzyme activity by 80% (s.d. 25%). This was significantly different compared with the controls (4 +/- 6%; P less than 0.001). Enzyme inhibition was mainly caused by IgG. Of all control sera (from healthy and patient individuals) only one patient with CAH reacted significantly in the tests. This CAH patient had a high antibody titre against mitochondria as measured by immunofluorescence.