Patients with primary biliary cirrhosis react against a ubiquitous xenobiotic-metabolizing bacterium

Primary biliary cirrhosis following Lactobacillus vaccination for recurrent vaginitis

BACKGROUND/AIMS

Antimitochondrial antibodies directed against the E2 subunit of the pyruvate dehydrogenase complex, PDC-E2, and other mitochondrial 2-oxoacid dehydrogenases (AMA-M2) are the hallmark for diagnosis of primary biliary cirrhosis (PBC). AMA-M2 formation as an early step in the pathogenesis of PBC has recently been assumed to be triggered by bacterial mimics of the E2 subunit and certain reactant xenobiotics. We report a case of symptomatic PBC diagnosed after sequential immunization with a lactobacillus vaccine for recurrent vaginitis over years.

METHODS

Serum AMA-M2 specificity of the patient was evaluated by indirect immunofluorescence, immunoblotting and ELISA. Serum antibody responses against pyruvate dehydrogenase complex-E2 subunit (PDC-E2(212-226)), the major PBC-specific mitochondrial autoepitope, and microbial mimics revealed cross-reactivity with beta-galactosidase of Lactobacillus delbrueckii (LACDE BGAL(266-280)) which shows a high local homology with that of Lactobacillus species administered via the vaccine. The relative affinity of antibody reactivity to LACDE BGAL(266-280) was significantly higher than that against human PDC-E2(212-226).

CONCLUSIONS

We conclude that lactobacillus vaccination therapy may be another culprit for the development of PBC in genetically susceptible women.

The unfinished business of primary biliary cirrhosis

In nearly every multifactorial human disease, there are three periods that characterize our understanding and definition. First, there is a period in which there is rapid accumulation of descriptive data. Second, there is a longer and slower period as information is obtained that redefines and expands basic and clinical knowledge that lacks the final and important area of understanding aetiology and therapeutic intervention. Third, which is much less common for most diseases, is the vigorous definition of pathobiology and treatment. These phases are well illustrated by our current understanding of primary biliary cirrhosis (PBC). The term PBC was first used nearly 60 years ago and for the first 40 or so years, the primary research efforts were directed at clinical definitions and pathology. Subsequently, with the advent of molecular biology, there began a rigorous dissection of the immune response and, in particular, a better understanding of anti-mitochondrial antibodies. These efforts have greatly helped in our understanding of not only the effector mechanisms of disease, but also the uniqueness of the primary target tissue, biliary epithelium. However, this research has still not led to successful translation for specific therapy.

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.

Liver autoimmunity triggered by microbial activation of natural killer T cells

Humans with primary biliary cirrhosis (PBC), a disease characterized by the destruction of small bile ducts, exhibit signature autoantibodies against mitochondrial Pyruvate Dehydrogenase Complex E2 (PDC-E2) that crossreact onto the homologous enzyme of Novosphingobium aromaticivorans, an ubiquitous alphaproteobacterium. Here, we show that infection of mice with N. aromaticivorans induced signature antibodies against microbial PDC-E2 and its mitochondrial counterpart but also triggered chronic T cell-mediated autoimmunity against small bile ducts. Disease induction required NKT cells, which specifically respond to N. aromaticivorans cell wall α-glycuronosylceramides presented by CD1d molecules. Combined with the natural liver tropism of NKT cells, the accumulation of N. aromaticivorans in the liver likely explains the liver specificity of destructive responses. Once established, liver disease could be adoptively transferred by T cells independently of NKT cells and microbes, illustrating the importance of early microbial activation of NKT cells in the initiation of autonomous, organ-specific autoimmunity.

Etiopathogenesis of primary biliary cirrhosis

Primary biliary cirrhosis (PBC) is an autoimmune disease of the liver characterized by progressive bile duct destruction eventually leading to cirrhosis and liver failure. The serological hallmark of the disease is the presence of circulating antimitochondrial antibodies (AMA). These reflect the presence of autoreactive T and B cells to the culprit antigens, the E2 subunits of mitochondrial 2-oxo-acid dehydrogenase enzymes, chiefly pyruvate dehydrogenase (PDC-E2). The disease results from a combination of genetic and environmental risk factors. Genetic predisposition is indicated by the higher familial incidence of the disease particularly among siblings and the high concordance rate among monozygotic twins. Environmental triggering events appear crucial to disrupt a pre-existing unstable immune tolerance of genetic origin allowing, after a long latency, the emergence of clinical disease. Initiating mimotopes of the vulnerable epitope of the PDC-E2 autoantigen can be derived from microbes that utilize the PDC enzyme or, alternatively, environmental xenobiotics/chemical compounds that modify the structure of native proteins to make them immunogenic. A further alternative as a source of antigen is PDC-E2 derived from apoptotic cells. In the effector phase the biliary ductular cell, by reason of its proclivity to express the antigen PDC-E2 in the course of apoptosis, undergoes a multilineage immune attack comprised of CD4⁺ and CD8⁺ T cells and antibody. In this article, we critically review the available evidence on etiopathogenesis of PBC and present interpretations of complex data, new developments and theories, and nominate directions for future research.

Autoimmune liver serology: Current diagnostic and clinical challenges

Liver-related autoantibodies are crucial for the correct diagnosis and classification of autoimmune liver diseases (AiLD), namely autoimmune hepatitis types 1 and 2 (AIH-1 and 2), primary biliary cirrhosis (PBC), and the sclerosing cholangitis variants in adults and children. AIH-1 is specified by anti-nuclear antibody (ANA) and smooth muscle antibody (SMA). AIH-2 is specified by antibody to liver kidney microsomal antigen type-1 (anti-LKM1) and anti-liver cytosol type 1 (anti-LC1). SMA, ANA and anti-LKM antibodies can be present in de-novo AIH following liver transplantation. PBC is specified by antimitochondrial antibodies (AMA) reacting with enzymes of the 2-oxo-acid dehydrogenase complexes (chiefly pyruvate dehydrogenase complex E2 subunit) and disease-specific ANA mainly reacting with nuclear pore gp210 and nuclear body sp100. Sclerosing cholangitis presents as at least two variants, first the classical primary sclerosing cholangitis (PSC) mostly affecting adult men wherein the only (and non-specific) reactivity is an atypical perinuclear antineutrophil cytoplasmic antibody (p-ANCA), also termed perinuclear anti-neutrophil nuclear antibodies (p-ANNA) and second the childhood disease called autoimmune sclerosing cholangitis (ASC) with serological features resembling those of type 1 AIH. Liver diagnostic serology is a fast-expanding area of investigation as new purified and recombinant autoantigens, and automated technologies such as ELISAs and bead assays, become available to complement (or even compete with) traditional immunofluorescence procedures. We survey for the first time global trends in quality assurance impacting as it does on (1) manufacturers/purveyors of kits and reagents, (2) diagnostic service laboratories that fulfill clinicians’ requirements, and (3) the end-user, the physician providing patient care, who must properly interpret test results in the overall clinical context.

Liver transplantation in primary biliary cirrhosis

The proportion of patients who undergo liver transplantation for primary biliary cirrhosis (PBC) is steadily declining. This decline is partly from the increasing number of patients undergoing transplantation for other indications, but also perhaps because of the effect of ursodeoxycholic acid (UDCA) on the natural history of this condition. Nevertheless, patients who have PBC still constitute approximately 11% of all patients undergoing transplantation for cirrhosis. The prognosis after transplantation is excellent, with an approximately 80% 5-year survival reported by most large centres. Liver transplantation also significantly improves quality of life in survivors. The disease may recur after surgery in up to one third of patients, but recurrence has not been shown to have a significant effect on patients' survival in the medium term.

Other potential medical therapies: the use of antiviral agents to investigate and treat primary ciliary cirrhosis

A human betaretrovirus has been characterized in patients with primary biliary cirrhosis (PBC) and the related mouse mammary tumor virus linked with autoimmune biliary disease in the NOD.c3c4 mouse model. Translational studies have been performed in patients who have PBC to investigate the role of viral infection in disease. Patients treated with Combivir experienced significant improvements in hepatic biochemistry, clinical symptoms, and histology with evidence of reversal of ductopenia. Preliminary studies suggest that the NOD.c3c4 mouse model of PBC provides a good model to test safer and more potent drug regimens for future use in trials for patients who have PBC.

A possible role of histone-like DNA-binding protein of Streptococcus intermedius in the pathogenesis of bile duct damage in primary biliary cirrhosis

Bacterial infection has become a focus of attention in the pathogenesis of primary biliary cirrhosis (PBC). It was reported that anti-histone autoantibody was detected in PBC, suggesting that bacterial histone-like DNA-binding protein (HLP) may be involved in the pathogenesis of PBC. To identify bacterial species in PBC to confirm this possibility, serum reactivity to bacterial cells was studied by ELISA. The IgM class Streptococcus intermedius titers were significantly higher in PBC than chronic hepatitis due to hepatitis C virus (CH-C) and healthy subjects. Among the streptococci, S. intermedius was selected for further study. The antigenic peptide of S. intermedius of HLP was synthesized to examine the serum reactivity to Si-HLP. IgM class anti-Si-HLP peptide titers were significantly higher in PBC. Immunoreactivity to anti-Si-HLP was detected in the cytoplasm of biliary epithelial cells and inflammatory cells in the portal area in PBC patients' livers. Streptococci, especially S. intermedius, might play a key role in the pathogenesis of PBC, possibly involving HLP.

Hepatic NKT cells: friend or foe?

The innate immune system represents a critical first line of host response to infectious, injurious and inflammatory insults. NKT cells (natural killer T-cells) are an important, but relatively poorly understood, component of the innate immune response. Moreover, NKT cells are enriched within the liver, suggesting that within the hepatic compartment NKT cells probably fulfil important roles in the modulation of the immune response to infection or injury. NKT cells are characterized by their rapid activation and secretion of large amounts of numerous types of cytokines, including those within the Th1-type, Th2-type and Th17-type groups, which in turn can interact with a multitude of other cell types within the liver. In addition, NKT cells are capable of participating in a wide array of effector functions with regards to other cell types via NKT cell-surface-molecule expression [e.g. FASL (FAS ligand) and CD40L (CD40 ligand)] and the release of mediators (e.g. perforin and granzyme) contained in cellular granules, which in turn can activate or destroy other cells (i.e. immune or parenchymal cells) within the liver. Given the huge scope of potential actions that can be mediated by NKT cells, it has become increasingly apparent that NKT cells may fulfil both beneficial (e.g. clearance of virally infected cells) and harmful (e.g. induction of autoimmunity) roles in the setting of liver disease. This review will outline the possible roles which may be played by NKT cells in the setting of specific liver diseases or conditions, and will discuss the NKT cell in the context of its role as either a ‘friend’ or a ‘foe’ with respect to the outcome of these liver disorders.

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.

Natural killer T cells exacerbate liver injury in a transforming growth factor beta receptor II dominant-negative mouse model of primary biliary cirrhosis

Primary biliary cirrhosis (PBC) is an organ-specific autoimmune liver disease characterized by the presence of antimitochondrial antibodies and the destruction of small intrahepatic bile ducts with portal inflammation. In previous studies, we reported that both CD1d expression and the frequency of CD1d-restricted natural killer T (NKT) cells were increased in the livers of patients with PBC. To define a specific role of CD1d-restricted NKT cells in the pathogenesis of PBC, particularly early events, we investigated the function of hepatic CD1d-restricted NKT cells in our transforming growth factor beta (TGF-beta) receptor II dominant-negative (dnTGFbetaRII) mouse model of PBC. We generated CD1d(-/-) and CD1d(+/-) dnTGFbetaRII mice and performed a comparative study of liver immunopathology. We report herein that these dnTGFbetaRII mice demonstrate a massive increase of hyperactive CD1d-restricted NKT cells within the hepatic tissues. CD1d(-/-)dnTGFbetaRII mice, which lack CD1d-restricted CD1d-restricted NKT cells, exhibit significantly decreased hepatic lymphoid cell infiltrates and milder cholangitis compared with CD1d(+/-)dnTGFbetaRII mice. Interestingly, there was a significant increase in the production of interferon-gamma in hepatic CD1d-restricted NKT cells activated by alpha-galactosylceramide in young but not older dnTGFbetaRII mice, suggesting an age-dependent role of CD1d-restricted NKT cells.

CONCLUSION

These data demonstrate that CD1d-restricted NKT cells in dnTGFbetaRII mice are a critical factor in liver injury.

Primary biliary cirrhosis

Primary biliary cirrhosis (PBC) is a chronic and slowly progressive cholestatic liver disease of autoimmune etiology characterized by injury of the intrahepatic bile ducts that may eventually lead to liver failure. Affected individuals are usually in their fifth to seventh decades of life at time of diagnosis, and 90% are women. Annual incidence is estimated between 0.7 and 49 cases per million-population and prevalence between 6.7 and 940 cases per million-population (depending on age and sex). The majority of patients are asymptomatic at diagnosis, however, some patients present with symptoms of fatigue and/or pruritus. Patients may even present with ascites, hepatic encephalopathy and/or esophageal variceal hemorrhage. PBC is associated with other autoimmune diseases such as Sjogren's syndrome, scleroderma, Raynaud's phenomenon and CREST syndrome and is regarded as an organ specific autoimmune disease. Genetic susceptibility as a predisposing factor for PBC has been suggested. Environmental factors may have potential causative role (infection, chemicals, smoking). Diagnosis is based on a combination of clinical features, abnormal liver biochemical pattern in a cholestatic picture persisting for more than six months and presence of detectable antimitochondrial antibodies (AMA) in serum. All AMA negative patients with cholestatic liver disease should be carefully evaluated with cholangiography and liver biopsy. Ursodeoxycholic acid (UDCA) is the only currently known medication that can slow the disease progression. Patients, particularly those who start UDCA treatment at early-stage disease and who respond in terms of improvement of the liver biochemistry, have a good prognosis. Liver transplantation is usually an option for patients with liver failure and the outcome is 70% survival at 7 years. Recently, animal models have been discovered that may provide a new insight into the pathogenesis of this disease and facilitate appreciation for novel treatment in PBC.

Prevalence and incidence of primary biliary cirrhosis are increasing in Finland

OBJECTIVE

To examine the epidemiology of primary biliary cirrhosis (PBC) in Finland and to evaluate whether the possible increase in prevalence was attributable to the increasing incidence, better survival, or both.

MATERIAL AND METHODS

The Hospital Discharge Register, pathology registers, and death certificates for the years 1988 99 were scrutinized, and the patients identified were followed-up for survival until 31 October 2004. The study area covered four university hospital districts: a total of 25 hospitals. The diagnosis of PBC was regarded as definite (or probable) if three (or two) of the following criteria were fulfilled: positive antimitochondrial antibodies, constantly elevated alkaline phosphatase, and compatible liver histology.

RESULTS

In the total population of the study areas, the age-standardized prevalence of PBC increased during the study period from 103 (95% CI: 97-110) to 180 (172-189) per million inhabitants. Incidence increased from 12 (10-14) to 17 (15-20) per million inhabitants per year. The annual average increase in prevalence was 5.1% (4.2-5.9%, p <0.0001) and in incidence 3.5% (0.9%-6.0%, p =0.008). In gender-specific analyses among women, the prevalence of PBC increased from 161 (151-171) to 292 (277-207) per million during the study period and the incidence from 20 (16-24) to 27 (23-32) per million per year. The death rate was 4% per year and half the deaths were from liver-related causes. Survival after diagnosis during the study period lengthened.

CONCLUSIONS

The prevalence of PBC increased in Finland during 1988-99, owing to both the increased incidence and the prolonged survival.

Autoimmune liver disease 2007

Autoimmune liver disease (ALD) includes a spectrum of diseases which comprises both cholestatic and hepatitic forms: autoimmune hepatitis (AIH), primary biliary cirrhosis (PBC), primary sclerosing cholangitis (PSC) and the so called "overlap" syndromes where hepatitic and cholestatic damage coexists. All these diseases are characterized by an extremely high heterogeneity of presentation, varying from asymptomatic, acute (as in a subset of AIH) or chronic (with aspecific symptoms such as fatigue and myalgia in AIH or fatigue and pruritus in PBC and PSC). The detection and characterization of non organ specific autoantibodies plays a major role in the diagnostic approach of autoimmune liver disease; anti nuclear reactivities (ANA) and anti smooth muscle antibodies (SMA) mark type 1 AIH, liver kidney microsomal antibody type 1 (LKM1) and liver cytosol type 1 (LC1) are the serological markers of type 2 AIH; antimitochondrial antibodies (AMA) are associated with PBC, while no specific marker is found in PSC, since anticytoplasmic neutrophil antibodies with perinuclear pattern (atypical p-ANCA or p-ANNA) are also detected in a substantial proportion of type 1 AIH cases. Treatment options rely on immunosoppressive therapy (steroids and azathioprine) in AIH and on ursodeoxycholic acid in cholestatic conditions; in all these diseases liver transplantation remains the only therapeutical approach for the end stage of liver disease.

Environmental factors in primary biliary cirrhosis

Primary biliary cirrhosis (PBC) is a chronic cholestatic liver disease more commonly found in women (with most cases being diagnosed in the fourth to fifth decades of life) that share peculiar features. Among these, serum antimitochondrial autoantibodies (AMA), serum hyper-immunoglobulin M, and progressive destruction of intrahepatic bile ducts are the most common clinical findings. The pathogenesis of the selective destruction of small-duct biliary epithelial cells is still unknown, although an autoimmune mechanism appears likely due to the detection of autoreactive T and B cells. Genetic background is critical in determining susceptibility to the disease, despite the limited associations with alleles within the major histocompatibility complex. However, among other observations, incomplete concordance of the disease in monozygotic twins and epidemiology strongly support a role for environmental factors in PBC onset. Molecular mimicry by either infectious agents or chemicals has been proposed to induce breakdown of immune tolerance in genetically predisposed individuals. This hypothesis is further supported by clinical (risk factors) and experimental evidence obtained also in animal models.

Genetic background of primary biliary cirrhosis

The clustering of patients in a representative family as well as relatively high concordance rate in monozygotic twins strongly indicate that genetic factors play a crucial role in modulating primary biliary cirrhosis (PBC) by conferring susceptibility to, or providing protection from, the disease. Therefore, much like other autoimmune diseases, intensive investigations have attempted to elucidate which genes are incriminated in the etiology of PBC. So far, a number of genes, including major histocompatibility complex (MHC) class I and II, cytokines and cell surface molecules, have been examined to seek the possibility of whether single nucleotide polymorphisms (SNP) of the gene might be associated with susceptibility to PBC. Nevertheless, it appears that methodologicaldifficulties, mainly the limitation of the number of individuals tested in each study, hamper the detection of a convincing and reproducible link between genetic polymorphisms and the etiology of PBC. Also, the difference in genetic background among several ethnic groups may play a role in concealing the association. In this review, I will highlight the genetic association in PBC, and review the association of genetic polymorphisms with the etiology of PBC, which have been reported in various ethnicities.

Increased prevalence of antimitochondrial antibodies in first-degree relatives of patients with primary biliary cirrhosis

Primary biliary cirrhosis (PBC) is a chronic cholestatic liver disorder that can progress to cirrhosis, shortening life expectancy. PBC patients are often asymptomatic, present with biochemical cholestasis, and test positive (>or=90%) for antimitochondrial antibodies (AMAs) in serum. Although AMA positivity without biochemical cholestasis may indicate increased risk of future PBC development, the contribution of these antibodies to pathogenesis remains enigmatic. Environmental risks and genetic determinants are likely implicated in PBC etiology. Given the familial aggregation of PBC, we hypothesized that AMAs also aggregate among relatives of PBC probands. We investigated the prevalence of AMAs in first-degree relatives (FDRs) of PBC probands to examine whether AMAs aggregate in such pedigrees. Using a PBC family registry, we prospectively screened for AMAs in the serum of 306 FDRs in 145 pedigrees, 350 PBC probands, and 196 controls who were age-matched, sex-matched, race-matched, and residence-matched to probands. The prevalence of AMA in FDRs and controls was 13.1% and 1%, respectively. Greater prevalence of AMA was found in female FDRs of PBC probands [sisters (20.7%), mothers (15.1%), and daughters (9.8%)] than in male FDRs [brothers (7.8%), fathers (3.7%), and sons (0%)].

CONCLUSIONS

AMAs aggregate among FDRs of PBC probands. Our data have clinical implications for FDRs of PBC probands because AMA positivity may suggest susceptibility to PBC. Thus, the identification and follow-up of these relatives may lead to earlier disease diagnosis and treatment. Furthermore, if AMA development is heritable, this trait will provide a basis to dissect the genetic predisposition to PBC.

Reverse transcriptase activity in patients with primary biliary cirrhosis and other autoimmune liver disorders

BACKGROUND

Patients with biliary disease make retroviral antibodies and the Human Betaretrovirus has been characterized in patients with primary biliary cirrhosis.

AIM

To screen patients with autoimmune liver disease for evidence of retroviral infection.

METHODS

Real-time reverse transcriptase polymerase chain reaction was used to detect Human Betaretrovirus, and a reverse transcriptase assay to measure reverse transcriptase activity in plasma.

RESULTS

Using reverse transcriptase polymerase chain reaction, 24% of primary biliary cirrhosis samples were positive for Human Betaretrovirus when compared to 13% with autoimmune hepatitis, 5% of other liver diseases and 3% of the non-liver disease control subjects. Reverse transcriptase activity was found in 73% of patients with autoimmune hepatitis, 42% with primary biliary cirrhosis, 22% of liver patients without viral or autoimmune disease and 7% of subjects without liver disease. In patients with autoimmune liver disease, detection of reverse transcriptase activity was related to higher ALT levels, whereas others stabilized on immunosuppressive therapy either preliver or postliver transplantation were less likely to be reverse transcriptase-positive.

CONCLUSIONS

Most patients with autoimmune hepatitis have detectable reverse transcriptase activity. Investigations will be required to assess whether this represents the expression of endogenous retroviruses and retrotransposable elements in inflamed tissue, or signifies the presence of exogenous retroviral infection.

Synthesis and evaluation of stimulatory properties of Sphingomonadaceae glycolipids

Glycosphingolipids (GSLs) from the Sphingomonadaceae family of bacteria have been reported to be potent stimulators of natural killer T cells. These glycolipids include mono-, tri- and tetraglycosylceramides. Here we have prepared the GSL-1 to GSL-4 series of glycolipids and tested their abilities to stimulate natural killer T cells. Among these glycolipids, only GSL-1 (1) is a potent stimulator. Using a series of synthetic diglycosylceramides, we show that oligoglycosylceramides from Sphingomonadaceae are not effectively truncated to GSL-1 in lysosomes in antigen-presenting cells, possibly because the higher-order GSLs are poor substrates for lysosomal acyltransfer enzymes.

The biology of NKT cells

Recognized more than a decade ago, NKT cells differentiate from mainstream thymic precursors through instructive signals emanating during TCR engagement by CD1d-expressing cortical thymocytes. Their semi-invariant alphabeta TCRs recognize isoglobotrihexosylceramide, a mammalian glycosphingolipid, as well as microbial alpha-glycuronylceramides found in the cell wall of Gram-negative, lipopolysaccharide-negative bacteria. This dual recognition of self and microbial ligands underlies innate-like antimicrobial functions mediated by CD40L induction and massive Th1 and Th2 cytokine and chemokine release. Through reciprocal activation of NKT cells and dendritic cells, synthetic NKT ligands constitute promising new vaccine adjuvants. NKT cells also regulate a range of immunopathological conditions, but the mechanisms and the ligands involved remain unknown. NKT cell biology has emerged as a new field of research at the frontier between innate and adaptive immunity, providing a powerful model to study fundamental aspects of the cell and structural biology of glycolipid trafficking, processing, and recognition.

Systemic Multifocal Epithelial Inflammations Associated with PBC-like Bile Duct Damage in Chronic Colitis Harboring TCR / xAIM / Mice: Does Lipoteichoic Acid Affect the Pathogenesis of Epithelial Inflammation Followed by Fibrosis?

Autoimmune disorder and associated multifocal organ inflammations such as dry gland syndrome are occasionally observed; however, their etiologies are not clearly understood. We previously reported that chronic colitis-harboring TCR alpha(-/-) x AIM(-/-) mice show primary biliary cirrhosis (PBC)-like bile duct damage in the liver. Gram-positive bacterial infection is one of the candidates for the pathogenesis of PBC. We also reported that the bacterial cell wall component lipoteichoic acid (LTA) was detected at the sites of inflammation around damaged bile ducts in PBC patients. On the basis of these facts, we hypothesized that LTA might affect the pathogenesis of bile duct damage in the livers of TCR alpha(-/-) x AIM(-/-) mice. LTA was detected not only in the portal area with inflammation in the liver but also throughout the gastrointestinal tract, from the stomach to the colon, and especially in the epithelium at sites of inflammation. In addition, LTA was detected around both pancreatic ducts with inflammation and at the distal renal tubules with inflammation in TCR alpha(-/-) x AIM(-/-) mice. Furthermore, in the liver, pancreas, kidney, and colon, fibrous stroma were detected at the sites of LTA-positive inflammation foci. Bacterial LTA might affect the pathogenesis of epithelial inflammation followed by fibrosis in systemic multifocal epithelial inflammations in chronic colitis-harboring TCR alpha(-/-) x AIM(-/-) mice with PBC-like bile duct damage.

Animal models for autoimmune hepatitis

The liver is the target of adverse immune reactions in three putative autoimmune diseases: autoimmune hepatitis (AIH), primary biliary cirrhosis (PBC) and primary sclerosing cholangitis (PSC). These three diseases can be distinguished by clinical, histological, and immunological features. However, especially on the level of specific antibody formation an overlap can occur, which sometimes complicates diagnosis. In this review, we will concentrate on autoimmune hepatitis and the current state of animal models for this severe disease. AIH is characterized by the presence of interface hepatitis and portal plasma cell infiltration, hypergammaglobulinemia, and autoantibodies. The hallmark of type 2 AIH is the generation of autoantibodies of the LKM-1 type. The major target of these antibodies is the cytochrome P450 isoform 2D6 (CYP2D6). In the past several attempts have been made to develop a reliable animal model that reflects the persistent hepatic destruction that occurs in human AIH. However, most models were only successful in causing a transient form of hepatic damage and often used rather complex ways of disease induction.

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.

Concept on the pathogenesis and treatment of primary biliary cirrhosis

Primary biliary cirrhosis (PBC) is an organ-specific autoimmune disease that predominantly affects women and is characterized by chronic, progressive destruction of small intrahepatic bile ducts with portal inflammation and ultimately fibrosis, leading to liver failure in the absence of treatment. Little is known about the etiology of PBC. PBC is characterized by anti-mitochondrial antibodies and destruction of intra-hepatic bile ducts. The serologic hallmark of PBC is the presence of auto-antibodies to mitochondria, especially to the E2 component of the pyruvate dehydrogenase complex (PDC). Current theories on the pathogenesis of PBC favor the hypothesis that the disease develops as a result of an inappropriate immune response following stimulation by an environmental or infectious agent. Some reports suggest that xenobiotics and viral infections may induce PBC. The pathogenetic mechanism is believed to be caused by a defect in immunologic tolerance, resulting in the activation and expansion of self-antigen specific T and B lymphocyte clones and the production of circulating autoantibodies in addition to a myriad of cytokines and other inflammatory mediators. This leads to ductulopenia and persistent cholestasis, by developing end-stage hepatic-cell failure. In this review are given our own and literary data about mechanisms of development of intrahepatic cholestasis and possible ways of its correction.

Differential epitope mapping of antibodies to PDC-E2 in patients with hematologic malignancies after allogeneic hematopoietic stem cell transplantation and primary biliary cirrhosis

A unique characteristic of the autoimmune liver disease primary biliary cirrhosis (PBC) is the presence of high-titer and extremely specific autoantibodies to the E2 component of the pyruvate dehydrogenase complex (PDC-E2). Autoantibodies to PDC-E2 antigen have only been detected in patients with disease or in those who subsequently develop PBC. One exception has been a subgroup of patients with multiple myeloma (MM) who underwent allogeneic hematopoietic stem cell transplantation (HSCT) and received donor lymphocyte infusions (DLIs) after transplantation. These patients developed high-titer antibodies to a variety of myeloma-associated antigens, including PDC-E2, coincident with rejection of myeloma cells in vivo. To examine the specificity of autoantibodies to PDC in these patients, we screened sera from patients with MM, chronic leukemias, monoclonal gammopathy of unknown significance (MGUS), PBC, and healthy donors. Three of 11 patients with MM (27%) and 2 of 6 patients with chronic leukemias (33%) developed anti-PDC-E2 antibodies in association with DLI response; 2 of 12 (17%) patients in the MGUS pretreatment control population also had detectable anti-PDC responses. Interestingly, the epitope specificity of these PDC-E2 autoantibodies was distinctive, suggesting that the mechanisms leading to loss of tolerance in the transplantation patients are distinct from PBC.

Invariant natural killer T cells in the response to bacteria: the advent of specific antigens

Invariant natural killer T (iNKT) cells are a unique subset of T lymphocytes that have been implicated in diverse immune reactions, ranging from self-tolerance and development of autoimmunity to responses to pathogens and tumors. Although some degree of autoreactivity of iNKT cells has been shown, it remained controversial whether the T-cell antigen receptor expressed by these cells could recognize microbial antigens, hampering the investigation of their physiological role during tolerance and immunity. Several recent publications have now defined natural antigens for the majority of iNKT cells in some Proteobacteria and in Borrelia burgdorferi, demonstrating specificity of these cells for microbes in addition to self-reactivity. The characterization of natural antigens from bacteria, and the iNKT cell response to bacteria containing them, are decisive steps toward the clarification of the natural role of iNKT cells in host defense against pathogens, and will likely spur numerous findings in the near future.

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.

Identification of 2-nonynoic acid, a cosmetic component, as a potential trigger of primary biliary cirrhosis

Antimitochondrial antibodies (AMA) are unique among autoimmune serologic reactants because of their extremely high association with the index disease primary biliary cirrhosis (PBC). This autoantibody response is specifically directed only to the lipoyl domain of the mitochondrial 2-oxo-acid dehydrogenase complexes, which prompted us to search for environmental mimotopes in the form of xenobiotics and led to our identification of 2-octynoic acid as a high-affinity reactant for AMA. To focus on the chemical characteristics requisite for binding of AMA to the xenobiotic-modified self-peptide, quantitative structure-activity relationship (QSAR) studies were performed using a panel of alkynoic compounds, including examination of the length of the carbon chain and the location of the triple bond in the identified mimotope. Analyses of octynamides that varied in the position of the triple bond demonstrated that only the 2-octynamide reacted strongly with PBC sera. Furthermore, among 2-alkynamides with varying carbon chain length, 2-octyn-, 2-nonyn- (particularly) and 2-decynamide exhibited the highest reactivity. Thus, an optimal chemical structure of the xenobiotically modified epitope recognized by AMA-positive PBC sera is provided by 2-nonynoic acid. The methyl ester of this compound is ranked 2,324th out of 12,945 compounds to which there is occupational exposure, with an 80% female prevalence due to its use in cosmetic products. Our findings illustrate an unusual polyreactivity of anti-PDC-E2 and support the idea of epitope mimicry in the genesis of this autoantibody and perhaps of PBC itself.

Primary biliary cirrhosis: solving the enigma

Primary biliary cirrhosis (PBC) is a chronic cholestatic liver disease, most commonly affecting female patients between 40 and 60 years of age. Patient sera present autoantibodies against mitochondrial antigens (AMA) and elevated serum IgM. Histologic studies demonstrate progressive destruction of small- and medium-sized intrahepatic bile ducts and, ultimately, liver cirrhosis. The precise mechanisms leading to selective destruction of such biliary epithelial cells are still unknown, although a number of immunomediated pathways have been proposed. Genetic background is critical in determining susceptibility to the disease, although no clear association with haplotypes of the major histocompatibility complex has been identified. Molecular mimicry by either infectious agents or xenobiotics has been proposed as a means of breaking tolerance in genetically predisposed individuals, thus leading to the onset of PBC. In this review, available data and current theories regarding the immunomediated pathogenesis of PBC will be described.

Glycolipids for natural killer T cells

Natural killer T cells (NKT cells) play a central role in regulating immune responses influencing conditions ranging from autoimmune to infectious diseases. NKT cell responses are induced by recognition of glycolipid antigens presented by CD1d, an antigen presentation protein. In the last 10 years great strides have been made in understanding the types of glycolipids recognized by NKT cells. These advances have included determination of the lipid and carbohydrate recognition requirements for stimulation and identification of "natural" antigens for these cells.

Genetics of hepatobiliary diseases

With the recent publication of the first human map of genetic variation (ie, Human Haplotype Map), genomic-based discoveries will likely affect not only the research bench but also the bedside. These advances will improve the understanding of the genetics of hepatobiliary diseases, resulting in better prevention measures and diagnosis as well as more effective therapies. Currently, alcoholic liver disease, nonalcoholic fatty liver disease, and symptomatic gallbladder stones affect a sizable portion of the population. On the other hand, chronic cholestatic liver diseases, hepatocellular carcinoma, and polycystic liver disease, although rare, shorten life expectancy and diminish the quality of life of patients. In the genomic era, we have the opportunity to start dissecting the susceptibility genetic variants of liver diseases. We are now in a position to begin elucidating the complex genotype/phenotype relationships of liver diseases with the anticipation to understand disease pathogenesis better. These efforts will require the application of genomic-based approaches in large well-organized translational studies in the diseases of interest.

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.

The enigma of primary biliary cirrhosis

Primary biliary cirrhosis (PBC) is a chronic cholestatic disease characterized by a striking predominance in female patients (with most cases diagnosed between ages 40 and 60 yr) as well as serum auto-antibodies to mitochondrial antigens, elevated serum immunoglobulin M,progressive destruction of intrahepatic bile ducts, and, ultimately, liver cirrhosis and failure(1). The precise mechanisms leading to selective destruction of biliary epithelial cells lining intrahepatic bile ducts are still unknown, although numerous immunomediated pathways have been proposed. Genetic background appears to be important in determining susceptibility to the disease (2), but no clear association with alleles in the major histocompatibility complex has been identified. Molecular mimicry either by infections (3) or xenobiotics (4) has been proposed to be capable of breaking tolerance in genetically predisposed individuals, thus leading to onset of PBC. This article describes and discusses the available data regarding the immunomediated pathogenesis of PBC (with particular attention to auto-antibodies and autoreactive T-cells) and presents the recent evidence indicating a role for either xenobiotic chemicals or novel infectious agents in the induction of the disease.

Primary biliary cirrhosis: when and why does the disease develop?

Primary biliary cirrhosis is a chronic cholestatic liver disease with an autoimmune pathogenesis, that generally develops in adult life, often in perimenopausal age. The clinical features are heterogeneous, ranging from an asymptomatic presentation to end-stage liver disease. Primary biliary cirrhosis is unknown in children and its natural history has yet to be elucidated. Following a Canadian report of primary biliary cirrhosis in two girls (16 and 15 years old), we describe a clinical case developing at 17 years of age. A temporal association between Borrelia Burgdorferi infection and diagnosis of primary biliary cirrhosis was observed.

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Interferon gamma accelerates NF-kappaB activation of biliary epithelial cells induced by Toll-like receptor and ligand interaction

BACKGROUND

The Toll-like receptor (TLR) family recognises pathogen associated molecular patterns (PAMPs) and plays a pivotal role in the innate immune response. Biliary epithelial cells (BECs) lining the intrahepatic bile ducts are potentially exposed to bacterial components in bile, and murine BECs possess TLRs that recognise PAMPs, resulting in nuclear factor kappaB (NF-kappaB) activation.

AIMS

To examine the presence of TLRs in human BECs and the influence of cytokines and PAMPs on TLR expression and NF-kappaB activation.

METHODS

The expression of TLR2-5, MD-2, MyD88, and IRAK1 was examined in human liver tissue and cultured BECs by immunohistochemistry or reverse transcription polymerase chain reaction. The influence of PAMPs (peptidoglycan and lipopolysaccharide) in cultured cells preincubated with interferon gamma (IFNgamma) was evaluated by NF-kappaB activation.

RESULTS

TLR2-5, MyD88, and IRAK-1 proteins were detectable in BECs of the intrahepatic biliary tree in human liver tissue. TLR2-5, MD-2, MyD88, and IRAK-1 mRNA was demonstrated in human cultured BECs. The expression of these TLRs was upregulated by IFNgamma, and TLR2 was upregulated by tumour necrosis factor alpha. Interleukins 4 and 6 failed to induce TLR upregulation. Interestingly, preincubation with IFNgamma synergistically increased the upregulation of NF-kappaB induced by PAMPs in cultured BECs.

CONCLUSION

These results suggest that the TLR family is present in human biliary cells and participates in the innate immunity of the intrahepatic biliary tree. Disordered regulation of TLRs after intracellular signalling by cytokines and PAMPs may be involved in immune mediated biliary diseases.

Increased prevalence of primary biliary cirrhosis near Superfund toxic waste sites

Primary biliary cirrhosis (PBC) and primary sclerosing cholangitis (PSC) are uncommon liver diseases of unknown etiology. Reported clustering of PBC cases may be due to environmental factors. Individuals with PBC have a high prevalence of thyroid disease and thyroid disease is reportedly more prevalent near Superfund toxic waste sites (SFS). The objective of this study was to examine the prevalence and potential clustering of individuals with PBC and PSC near SFS. De-identified clinical and demographic data were used to determine the observed prevalence for each New York City zip code (n = 174) and borough (n = 5) of patients with PBC (PBC-OLT) or PSC (PSC-OLT) who were listed for liver transplantation. The expected prevalence was calculated using Organ Procurement and Transfer Network (OPTN) and U.S. Census data. Both PBC-OLT patients and patients not listed for liver transplantation (PBC-MSSM) were included in the cluster analysis. Prevalence ratios of PBC-OLT and PSC-OLT cases were compared for each zip code and for each borough with regard to the proximity or density of SFS, respectively. SaTScan software was used to identify clusters of PBC-OLT cases and PBC-MSSM cases. Prevalence ratio of PBC-OLT, not PSC-OLT, was significantly higher in zip codes containing or adjacent to SFS (1.225 vs. 0.670, respectively, P = .025). The borough of Staten Island had the highest prevalence ratio of PBC-OLT cases and density of SFS. Significant clusters of both PBC-OLT and PBC-MSSM were identified surrounding SFS. In conclusion, toxin exposure may be a risk factor influencing the clustering of PBC cases.

Genes and (auto)immunity in primary biliary cirrhosis

Primary biliary cirrhosis (PBC) is a chronic autoimmune cholestatic liver disease most commonly encountered in postmenopausal women; it is characterized by high-titer serum autoantibodies to mitochondrial antigens, elevated serum IgM, progressive destruction of intrahepatic bile ducts, and ultimately liver cirrhosis and failure. The cytopathic mechanisms leading to the selective destruction of intrahepatic cholangiocytes are still largely unknown. The current theory on the pathogenesis of PBC indicated that environmental factors might trigger autoimmunity in genetically susceptible individuals. In fact, genetic predisposition is critical to disease onset and progression, yet peculiar among autoimmune diseases, as indicated by the lack of a strong association with major histocompatibility complex haplotypes. Further, the recently reported concordance rate among monozygotic twins strengthens the importance of genetic factors, while also indicating that additional factors, possibly infectious agents or xenobiotics, intervene to trigger the disease. In this review, the available data regarding the genetic factors associated with PBC susceptibility and progression, as well as the available evidence regarding the immunomediated pathogenesis of PBC, will be critically illustrated and discussed.

Differential gene expression profiles in stage I primary biliary cirrhosis

OBJECTIVES

Primary biliary cirrhosis (PBC) is a progressive disease. However, little is understood about the molecular mechanisms underlying its features.

METHODS

We analyzed gene expression profiles of liver biopsy samples from 16 patients with PBC, seven with autoimmune hepatitis, eight with chronic hepatitis C, and eight normal control livers. In addition to whole liver samples, we selectively analyzed chronic nonsuppurative destructive cholangitis (CNSDC) lesions by laser capture microdissection.

RESULTS

Hierarchical clustering analysis using only early-stage liver disease demonstrated 85 genes were upregulated in stage I PBC specifically. Surprisingly, the expression of these genes was not maintained in advanced-stage PBC, while other gene clusters were upregulated. Expression analysis of CNSDC lesions in stage I PBC showed the presence of active inflammatory changes, characterized by the significant elevation of interferon-gamma and the development and maturation of lymphocytes. Expression of these genes was diminished in lymphoid cells aggregation in stage III PBC, and genes reflecting hepatocyte damage were upregulated with disease progression.

CONCLUSION

Gene expression patterns in stage I PBC are different from others. There are distinct changes in molecular pathology from early- to late-stage PBC, which might be a clue to reveal the etiology and progression of PBC.

[The significance of anti-nuclear envelope (gp210) antibody in primary biliary cirrhosis]

Primary biliary cirrhosis (PBC) is considered to be an autoimmune disease selectively targeted for interlobular bile ducts. While anti-mitochondrial antibodies are specifically detected in more than 90% of PBC patients, anti-nuclear envelope-gp210 antibodies are also specifically detected in 20-30% of PBC patients. In this review, we present 1, T cells specific for mitochondrial major epitope, PDC-E2 163-176, cross-react with peptides derived from nuclear envelope-gp210 protein, 2, PBC patients who have sustained high antibody titers to gp210 are at high risk for the progression to end-stage hepatic failure. These evidences may be very important for the epitope spreading of autoantigens from PDC-E2 to nuclear antigens and for the identification of target antigens on biliary epithelial cells which are recognized by cytotoxic T cells in PBC.

Primary biliary cirrhosis is characterized by IgG3 antibodies cross-reactive with the major mitochondrial autoepitope and its Lactobacillus mimic

The serological hallmark of primary biliary cirrhosis (PBC) is the presence of pyruvate dehydrogenase complex E2 subunit (PDC-E2) antimitochondrial antibodies (AMAs). Anti-PDC-E2 antibodies cross-react specifically with mycobacterial hsp65, and we have demonstrated that the motif SxGDL[ILV]AE shared by PDC-E2(212-226) and hsp's is a cross-reactive target. Having found that this same motif is present only in beta-galactosidase of Lactobacillus delbrueckii (BGAL LACDE), we hypothesized that this homology would also lead to cross-reactivity. The mimics were tested via ELISA for reactivity and competitive cross-reactivity using sera from 100 AMA-positive and 23 AMA-negative PBC patients and 190 controls. An Escherichia coli (ECOLI) PDC-E2 mimic that has been pathogenetically linked to PBC but lacks this motif has been also tested. Anti-BGAL(266-280) LACDE antibodies were restricted to AMA-positive patients (54 of 95, 57%) and belonged to immunoglobulin (Ig) G3. Of the 190 controls, 22 (12%; P < .001) had anti-BGAL(266-280) antibodies, mainly of the IgG4 subclass. ECOLI PDC-E2 reactivity was virtually absent. BGAL(266-280)/PDC-E2(212-226) reactivity of the IgG3 isotype was found in 52 (52%) AMA-positive PBC patients but in only 1 of the controls (P < .001). LACDE BGAL(266-280)/PDC-E2(212-226) reactivity was due to cross-reactivity as confirmed via competition ELISA. Antibody affinity for BGAL(266-280) was greater than for PDC-E2 mimics. Preincubation of a multireactive serum with BGAL(266-280) reduced the inhibition of enzymatic activity by 40%, while marginal effect (12%) or no effect (2%) was observed in human or ECOLI PDC-E2 mimics. In conclusion, IgG3 antibodies to BGAL LACDE cross-react with the major mitochondrial autoepitope and are characteristic of PBC.

Chemical xenobiotics and mitochondrial autoantigens in primary biliary cirrhosis: identification of antibodies against a common environmental, cosmetic, and food additive, 2-octynoic acid

Emerging evidence has suggested environmental factors as causative agents in the pathogenesis of primary biliary cirrhosis (PBC). We have hypothesized that in PBC the lipoyl domain of the immunodominant E2 component of pyruvate dehydrogenase (PDC-E2) is replaced by a chemical xenobiotic mimic, which is sufficient to break self-tolerance. To address this hypothesis, based upon our quantitative structure-activity relationship data, a total of 107 potential xenobiotic mimics were coupled to the lysine residue of the immunodominant 15 amino acid peptide of the PDC-E2 inner lipoyl domain and spotted on microarray slides. Sera from patients with PBC (n = 47), primary sclerosing cholangitis (n = 15), and healthy volunteers (n = 20) were assayed for Ig reactivity. PBC sera were subsequently absorbed with native lipoylated PDC-E2 peptide or a xenobiotically modified PDC-E2 peptide, and the remaining reactivity analyzed. Of the 107 xenobiotics, 33 had a significantly higher IgG reactivity against PBC sera compared with control sera. In addition, 9 of those 33 compounds were more reactive than the native lipoylated peptide. Following absorption, 8 of the 9 compounds demonstrated cross-reactivity with lipoic acid. One compound, 2-octynoic acid, was unique in both its quantitative structure-activity relationship analysis and reactivity. PBC patient sera demonstrated high Ig reactivity against 2-octynoic acid-PDC-E2 peptide. Not only does 2-octynoic acid have the potential to modify PDC-E2 in vivo but importantly it was/is widely used in the environment including perfumes, lipstick, and many common food flavorings.