Antibodies against the COOH-terminal region of E. coli ClpP protease in patients with primary biliary cirrhosis

A case report of primary biliary cholangitis combined with ankylosing spondylitis

RATIONALE

A chronic autoimmune liver disease known as primary biliary cholangitis (PBC) that selectively destructs small intrahepatic biliary epithelial cells and may result in biliary cirrhosis and eventually liver transplantation or death. PBC is associated with various other extrahepatic autoimmune diseases; however, the combination of PBC with ankylosing spondylitis has been rarely reported in the literature. Here, we reported a case of PBC with ankylosing spondylitis to improve our understanding of such coexistence and provide new ideas for the treatment of such patients.

PATIENT CONCERNS

A 54-year-old man was presented to the Department of Rheumatology because of an abnormal liver function test for 7 years, chest and back pain for 1 year, and low back pain for 2 months.

DIAGNOSES

Primary biliary cholangitis, ankylosing spondylitis, and old pulmonary tuberculosis.

INTERVENTIONS

The patient refused to use nonsteroidal anti-inflammatory drugs, conventional synthetic disease-modifying antirheumatic drugs, and biologic disease-modifying antirheumatic drugs; thus, he was treated with methylenediphosphonate (99Tc-MDP) and ursodeoxycholic acid (UDCA).

OUTCOMES

The patient achieved remission with UDCA and 99Tc-MDP therapy.

LESSONS

In the treatment of PBC combined with other disorders, the characteristics of different diseases should be considered. The patient reported herein was treated with 99Tc-MDP and UDCA, and his condition improved; thus, we consider 99Tc-MDP to be an effective treatment. Furthermore, in line with the current understanding of the pathogenesis of PBC and ankylosing spondylitis, we hypothesize that interleukin-17 inhibitor is an effective treatment for such patients.

Mining Autoimmune-Disorder-Linked Molecular-Mimicry Candidates in Clostridioides difficile and Prospects of Mimic-Based Vaccine Design: An In Silico Approach

Molecular mimicry, a phenomenon in which microbial or environmental antigens resemble host antigens, has been proposed as a potential trigger for autoimmune responses. In this study, we employed a bioinformatics approach to investigate the role of molecular mimicry in Clostridioides difficile-caused infections and the induction of autoimmune disorders due to this phenomenon. Comparing proteomes of host and pathogen, we identified 23 proteins that exhibited significant sequence homology and were linked to autoimmune disorders. The disorders included rheumatoid arthritis, psoriasis, Alzheimer's disease, etc., while infections included viral and bacterial infections like HIV, HCV, and tuberculosis. The structure of the homologous proteins was superposed, and RMSD was calculated to find the maximum deviation, while accounting for rigid and flexible regions. Two sequence mimics (antigenic, non-allergenic, and immunogenic) of ≥10 amino acids from these proteins were used to design a vaccine construct to explore the possibility of eliciting an immune response. Docking analysis of the top vaccine construct C2 showed favorable interactions with HLA and TLR-4 receptor, indicating potential efficacy. The B-cell and T-helper cell activity was also simulated, showing promising results for effective immunization against C. difficile infections. This study highlights the potential of C. difficile to trigger autoimmunity through molecular mimicry and vaccine design based on sequence mimics that trigger a defensive response.

Immunological abnormalities in patients with primary biliary cholangitis

Primary biliary cholangitis (PBC), an autoimmune liver disease occurring predominantly in women, is characterized by high titers of serum anti-mitochondrial antibodies (AMAs) and progressive intrahepatic cholestasis. The immune system plays a critical role in PBC pathogenesis and a variety of immune cell subsets have been shown to infiltrate the portal tract areas of patients with PBC. Amongst the participating immune cells, CD4 T cells are important cytokine-producing cells that foster an inflammatory microenvironment. Specifically, these cells orchestrate activation of other immune cells, including autoreactive effector CD8 T cells that cause biliary epithelial cell (BEC) injury and B cells that produce large quantities of AMAs. Meanwhile, other immune cells, including dendritic cells (DCs), natural killer (NK) cells, NKT cells, monocytes, and macrophages are also important in PBC pathogenesis. Activation of these cells initiates and perpetuates bile duct damage in PBC patients, leading to intrahepatic cholestasis, hepatic damage, liver fibrosis, and eventually cirrhosis or even liver failure. Taken together, the body of accumulated clinical and experimental evidence has enhanced our understanding of the immunopathogenesis of PBC and suggests that immunotherapy may be a promising treatment option. Herein, we summarize current knowledge regarding immunological abnormalities of PBC patients, with emphasis on underlying pathogenic mechanisms. The differential immune response which occurs over decades of disease activity suggests that different therapies may be needed at different stages of disease.

Liver immunology: How to reconcile tolerance with autoimmunity

There are several examples of liver tolerance: the relative ease by which liver allografts are accepted and the exploitation of the hepatic microenvironment by the malarial parasite and hepatotrophic viruses are notable examples. The vasculature of the liver supports a unique population of antigen presenting cells specialised to maintain immunological tolerance despite continuous exposure to gut-derived antigens. Liver sinusoidal endothelial cells and Kupffer cells appear to be key to the maintenance of immune tolerance, by promoting T cell anergy or deletion and the generation of regulatory cell subsets. Despite this, there are three liver diseases with likely autoimmune involvement: primary biliary cirrhosis, primary sclerosing cholangitis and autoimmune hepatitis. How can we reconcile this with the inherent tolerogenicity of the liver? Genetic studies have uncovered several associations with genes involved in the activation of the innate and adaptive immune systems. There is also evidence pointing to pathogenic and xenobiotic triggers of autoimmune liver disease. Coupled to this, impaired immunoregulatory mechanisms potentially play a permissive role, allowing the autoimmune response to proceed.

Autoantibodies in primary biliary cirrhosis: Recent progress in research on the pathogenetic and clinical significance

Primary biliary cirrhosis (PBC) is a chronic progressive cholestatic liver disease characterized by immune-mediated destruction of the small- and medium-sized intrahepatic bile ducts and the presence of antimitochondrial antibodies (AMA) in the serum. AMA are detected in over 90% of patients with PBC, whereas their prevalence in the general population is extremely low, varying from 0.16% to 1%. Previous studies have shown that the unique characteristics of biliary epithelial cells undergoing apoptosis may result in a highly direct and very specific immune response to mitochondrial autoantigens. Moreover, recent studies have demonstrated that serum from AMA-positive PBC patients is reactive with a number of xenobiotic modified E2 subunits of the pyruvate dehydrogenase complex, which is not observed in the serum of normal individuals. These findings indicate that chemicals originating from the environment may be associated with a breakdown in the tolerance to mitochondrial autoantigens. While it is currently generally accepted that AMA are the most specific serological markers of PBC, more than 60 autoantibodies have been investigated in patients with PBC, and some have previously been considered specific to other autoimmune diseases. This review covers the recent progress in research on the pathogenetic and clinical significance of important autoantibodies in PBC. Determining the pathogenic role of those autoantibodies in PBC remains a priority of basic and clinical research.

Popular and unpopular infectious agents linked to primary biliary cirrhosis

Primary biliary cirrhosis (PBC) is a progressive cholestatic liver disease characterized by the autoimmune destruction of the biliary epithelial cells of the small and medium-size bile ducts. The disease affects middle aged women and usually affects more than one member within a family. The pathognomonic serological hallmark of the disease is the presence of circulating anti-mitochondrial antibodies, and disease-specific anti-nuclear antibodies. Susceptibility genes and environmental risk factors such as infections and smoking have been reported as important for the development of the disease. Among the environmental agents, infectious triggers are the best studied. Most of the work published so far has investigated the role of infections caused by Novosphingobium aromaticivorans and Escherichia coli. This review will discuss the popular and unpopular infectious agents causatively linked to PBC. It will also examine reports investigating the epidemiological aspects of the disease and their direct or indirect implications to bacterial-induced PBC.

Predicting and preventing autoimmunity: the case of anti-mitochondrial antibodies

To be able to predict who will develop autoimmune disease would allow for early treatment which may dramatically alter the course of the disease. In some cases, it may also lead to prevention of the disease development. The prediction of disease development is based on the analysis of risk factors which have been associated with the disease in question. These factors include genetic susceptibility, as well as immunological and environmental factors. One autoimmune disease that may serve as a model for disease prediction is primary biliary cirrhosis (PBC), an autoimmune liver disease affecting the small- and medium-sized bile ducts. PBC could be an ideal model due to recent advances in elucidating its genetic associations. As well, a variety of immunological and environmental risk factors have been well established. Indeed, the presence of PBC-specific antimitochondrial antibodies and/or antinuclear antibodies has been shown to be predictor of disease development and possibly prognosis. This review will examine the current evidence which suggests that we may potentially be able to predict the development of PBC in some individuals. These concepts may also be applied to autoimmune diseases in general.

Immunopathogenesis of primary biliary cirrhosis: an old wives' tale

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

Bacteria and primary biliary cirrhosis

Infectious agents have been postulated to play a pathogenic role in the loss of immunological tolerance and the induction of primary biliary cirrhosis, an immune-mediated cholestatic liver disease characterized by progressive destruction of the small intrahepatic bile ducts and subsequent cirrhosis and liver failure. This review discusses emerging issues implicating infectious agents such as Escherichia coli, mycobacteria, chlamydia, helicobacter species, lactobacilli, Novosphingobium aromaticivorans, and betaretroviruses in the pathogenesis of primary biliary cirrhosis. We also review the immunopathological mechanisms responsible for the induction of the disease with special emphasis on the role of molecular mimicry and microbial/self immunological cross-reactivity.

Comparison of two ELISA assays for anti-Sp100 determination

Antibodies to Sp100 have been described not only in primary biliary cirrhosis (PBC), but also in other diseases. Two assays for detection of Sp100 levels by enzyme-linked immunosorbent assay (ELISA) have been compared in a cohort of patients from our area: (a) Sp100 kit produced by IMTEC, Immunodiagnostica GmbH, and (b) Quanta Lite Sp100 kit produced by INOVA Diagnostics. We analyze here the correlation between the two assays and compare their efficiency in diagnosing PBC. We also comment on the exceptions derived from reactivity with other diseases. We studied 78 sera by IIF with the typical multiple nuclear dots (MND) pattern from patients who suffered from PBC, hepatopathies different from PBC, systemic lupus erythematosus (SLE), other connective tissue diseases (CTD), skeletal diseases, lung diseases, hematological disorders, a miscellaneous group, and a healthy IIF negative control group. The tests work equally well despite their different quantification system: (a) it is based on a standard curve; and (b) it is based on a single-point antigen-specific calibration. Some discrepancies could be explained by differences in the immunodominant epitope used in the ELISA. The main finding of this study is that the presence of MND/Sp100-positive antibodies were detected not only in hepatic diseases, mainly PBC, but also in other clinical conditions, confirmed by both tests. Diagnosis of PBC must be established in the right clinical context, because other diseases recognizing the same epitope, mainly SLE, may also show high Sp100 levels. Sera from PBC patients with antimitochondrial antibodies (AMA) showed higher anti-Sp100 than the AMA-negative group.

Correlation of Chlamydia pneumoniae infection with primary biliary cirrhosis

AIM: To evaluate the association between Chlamydia pneumoniae (Cpn) infection and primary biliary cirrhosis (PBC).

METHODS: Cpn IgG and IgM were determined by enzyme-linked immunosorbent assay (ELISA) in 41 well-established PBC patients and two race-matched control groups (post-hepatitis cirrhosis, n = 70; healthy controls, n = 57).

RESULTS: The mean level and seroprevalence of Cpn IgG in PBC group and post-hepatitis cirrhosis (PHC) group were significantly higher than those in healthy controls (46.8 ± 43.4 RU/mL, 49.5 ± 45.2 RU/mL vs 28.3 ± 32.7 RU/mL; 68.3%, 71.4%, 42.1%, respectively; P < 0.05). There was a remarkably elevated seroprevalence of Cpn IgM in patients with PBC (22.0%) compared to the PHC and healthy control (HC) groups. For the PBC patients versus the HCs, the odds ratios (ORs) of the presence of Cpn IgG and IgM were 2.7 (95% CI 0.9-6.1) and 5.1 (95% CI 1.4-18.5), respectively. Though there was no correlation in the level of Cpn IgG with total IgG in sera of patients with PBC (r = -0.857, P = 0.344 > 0.05), Cpn IgM was related with the abnormally high concentrations of total IgM in PBC group.

CONCLUSION: The results of this study do not support the hypothesis that infection with Chlamydia pneumoniae may be a triggering agent or even a causative agent in PBC, but suggest that Chlamydia pneumoniae infection probably contributes to the high level of IgM present in most patients with PBC.

Epidemiology and pathogenesis of primary biliary cirrhosis

Primary biliary cirrhosis is an autoimmune disease of unknown etiology leading to progressive destruction of small intrahepatic bile ducts and eventually to liver cirrhosis and failure. It is characterized by female predominance (with most cases observed between the ages of 40 and 60) and serum autoantibodies to mitochondrial antigens as highly specific hallmarks. Epidemiologic data indicate a variable incidence and prevalence of the disease. A number of genetic factors have been indicated as playing a role in determining disease susceptibility or progression, although no definitive conclusion has been reached so far. However, as suggested by some epidemiologic observations, a number of environmental factors, including molecular mimicry by either microorganisms or xenobiotics, have also been proposed. A hypothesis gaining support is that environmental factors may trigger disease in genetically predisposed individuals. In this review, the available data regarding the epidemiology and pathogenesis of primary biliary cirrhosis will be described and discussed.

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

Infectious and environmental agents have been proposed as immunologic triggers for primary biliary cirrhosis (PBC). Recently, a ubiquitous organism that metabolizes organic compounds and estrogens, Novosphingobium aromaticivorans, has been defined. Importantly, 2 bacterial proteins have homology with the E2 component of the pyruvate dehydrogenase complex (PDC-E2). Sera from 97 patients with PBC, 46 first-degree relatives, 10 spouses, and 195 controls were studied for reactivity against N. aromaticivorans and Escherichia coli. The reactivity was defined by absorption, affinity purification, and using monoclonal antibodies to PDC-E2. Stool samples from 20 patients with PBC and 34 controls were analyzed by polymerase chain reaction (PCR) for the presence of N. aromaticivorans. Sera from 100% of anti-PDC-E2 positive (77/77), 33% of anti-BCOADC E2 positive (1/3), and 12% of antimitochondrial antibody (AMA) negative patients with PBC (2/17) reacted with titers up to 10(-6) against two known lipoylated bacterial proteins (47 and 50 kd) from N. aromaticivorans, including patients with early disease. This titer was approximately 100- to 1,000-fold higher than against E. coli and verified by absorption, use of affinity-purified sera, and monoclonal antibody reagents. Moreover, 78 of 80 AMA-positive and 5 of 17 AMA-negative patients with PBC had antibodies against 3 other N. aromaticivorans proteins. In contrast, 0 of 195 control sera reacted against N. aromaticivorans. Approximately 25% of patients and controls had N. aromaticivorans in their fecal specimens. In conclusion, based on protein homology, capacity to metabolize xenobiotics as well as modulate estrogens, its presence in feces, and specific immunologic response, we propose that N. aromaticivorans is a candidate for the induction of PBC.

The immunology of primary biliary cirrhosis: the end of the beginning?

The chronic liver disease primary biliary cirrhosis (PBC) is characterised by autoreactive B-cell and T-cell responses directed against mitochondrial antigens. In recent years these responses have been extensively characterised and the principal PBC associated autoantigen identified as pyruvate dehydrogenase complex (PDC). The identification of anti-PDC responses (present in over 95% of PDC patients) has given rise to important questions pertinent to our understanding of the pathogenesis of PBC. What specific role to anti-PDC responses play in target cell damage? How and why does immune tolerance break down to as highly conserved and ubiquitously expressed self-antigen as PDC? Why does breakdown in tolerance to an antigen present in all nucleated cells result in damage restricted to the intra-hepatic bile ducts? In attempting to answer these key questions we have, in this review, proposed a unifying hypothesis for the pathogenesis of PBC.

Investigation of a mechanism for accelerated breakdown of immune tolerance to the primary biliary cirrhosis-associated autoantigen, pyruvate dehydrogenase complex

Primary biliary cirrhosis (PBC) is an autoimmune liver disease characterized by autoreactive T- and B-cell responses to the highly conserved enzyme pyruvate dehydrogenase complex (PDC). In this study we have examined the breakdown of T-cell tolerance to self-PDC using a mouse model. Female SJL/J mice were sensitized intraperitoneally with foreign-PDC (bovine) and/or self-PDC (murine) in complete Freund's adjuvant, and serum, spleen, and liver tissue was taken 8 weeks later. Animals sensitized with foreign-PDC produced IgG antibodies that were reactive with both foreign and self-PDC, but splenic T cells from these animals only responded to stimulation with foreign PDC. Sensitization with self-PDC elicited neither antibodies nor reactive T cells. Significantly, cosensitization with mixed self-PDC and foreign-PDC resulted in a full breakdown of self-tolerance, with generation of both antibody and T-cell responses to self-PDC of the type seen exclusively in human PBC patients. Mild bile duct lesions deficient in CD8(+) T cells were seen 8 weeks after sensitization with either foreign or self-PDC. However, after sensitization with mixed self-PDC and foreign-PDC, these lesions were significantly larger and heavily infiltrated by CD8(+) T cells. Liver-infiltrating T cells derived from the self-PDC and foreign-PDC cosensitized but not from control animals showed reactivity with self-PDC, suggesting a possible role for autoreactive PDC-specific T-cell responses in the pathogenesis of the observed histologic changes. It is likely that B-cell cross-reactivity between foreign and self-PDC enhances the potential for breakdown of T-cell self-tolerance by allowing efficient presentation of self-antigens in the inoculum. This model may provide a useful system for investigating the etiology and treatment of PBC.

Antibodies against homologous microbial caseinolytic proteases P characterise primary biliary cirrhosis

BACKGROUND/AIMS

Antibodies to caseinolytic protease P(177-194) (ClpP(177-194)) of the proteolytic subunit of the Clp complex of Escherichia coli (E. coli) are uniquely present in primary biliary cirrhosis (PBC). Molecular mimicry between the regulatory subunit ClpX and the principal T-cell epitope of pyruvate dehydrogenase complex (PDC-E2) in PBC, has been proposed to account for this. Since ClpP is highly conserved among bacteria we investigated whether the micro-organisms triggering these antibodies may be other than E. coli.

METHODS/RESULTS

E. coli ClpP(177-194) is homologous with ClpP peptides of Yersinia enterocolitica (YEREN) and Haemophilus influenzae (HAEIN). Enzyme linked immunosorbent assay (ELISA) reactivity to these peptides was tested in 45 patients with PBC, 44 pathological and 32 healthy controls. Reactivity to at least one of the ClpP peptides was observed in 21 (47%) PBC patients, 5.8% pathological and 3.1% healthy controls (P<0.01 for all). Among these 21 seropositive PBC patients, 15 (71%) reacted to ECOLI ClpP(177-194), alone or in association with YEREN and/or HAEIN peptides, compared to three (14.2%) reactive with YEREN, two (9.5%) with YEREN/HAEIN and one (4.7%) with HAEIN peptide. Simultaneous reactivity to homologous sequences was due to cross-reactivity as confirmed by competition ELISAs.

CONCLUSIONS

The PBC-specificity of anti-microbial ClpP reactivity is confirmed: the questions as to primary trigger(s) and relevance to PBC pathogenesis remain open.

Molecular mimicry and autoimmune liver disease: virtuous intentions, malign consequences

The pathogenesis of autoimmune liver disease and autoimmunity associated with chronic viral hepatitis remains poorly understood. One of the major hurdles to a deeper understanding of these pathological processes is the absence of clearly defined inductive mechanisms, which, if identified and characterised, could guide clinical strategies for their prevention or allow therapeutic intervention. Molecular mimicry leading to crossreactive autoimmune responses has gained strong experimental support in the past decade. A fundamental premise of this hypothesis is the involvement of a mimicking environmental trigger. In view of the numerous viral and bacterial agents epidemiologically linked to autoimmune liver diseases, we and others have proposed molecular mimicry to be an important mechanism in these diseases. We also propose similar crossreactive mechanisms to operate in the generation of autoimmunity in viral hepatitis. This review focuses on molecular mimicry at the level of the B-cell, as few data on T-cell crossreactivity in liver disease are thus far available.