Immunopathogenesis of primary biliary cirrhosis: an old wives' tale

Primary biliary cholangitis: primary autoimmune disease or primary secretory defect

INTRODUCTION

Primary biliary cholangitis (PBC) is a chronic cholestatic liver disease characterized by the immune-mediated destruction of small and medium intrahepatic bile ducts, involving predominantly females. PBC has long been described as an autoimmune liver disease, also because it is very often associated with many autoimmune conditions. More recently, another pathogenic mechanism exploring the damage of cholangiocytes has been hypothesized, i.e. a defect in the biliary umbrella which is physiologically responsible for the exchange of the ions Cl- and HCO3- and maintains the integrity of glycocalyx. To provide a state-of-the-art analysis of this topic, a systematic review of literature in PubMed, Scopus, and Science Direct was conducted (inclusive dates: 1986-2023).

AREA COVERED

Although the etiology remains unknown, pathogenesis consists of a complex immune-mediated process resulting from a genetic susceptibility. PBC can be triggered by an immune-mediated response to an autoantigen, which leads to a progressive destruction of bile ducts and eventually to a progressive fibrosis with cirrhosis. The defect in the 'bicarbonate umbrella' acts as a protection against the toxic hydrophobic bile acids, leading to a toxic composition of bile.

EXPERT OPINION

This review offers a summary of the current knowledge about the pathogenesis of PBC, indicating that this is probably based on the mutual relationship between the immune insult and the unbalanced secretory mechanisms.

Primary Biliary Cholangitis in Males: Pathogenesis, Clinical Presentation, and Prognosis

Primary biliary cholangitis (PBC) is an immune-mediated chronic liver disease characterized by progressive cholestasis, bile duct destruction, biliary fibrosis, and cirrhosis. Patients who respond to ursodeoxycholic acid have an expected survival similar to the general population. Although PBC primarily affects females, the prevalence in males is higher than was previously believed, with contemporary studies suggesting a female-to-male ratio of 4-6:1. A diagnosis of PBC is often delayed among males because of the myth that PBC is rare in males.

The Role of Invariant NKT in Autoimmune Liver Disease: Can Vitamin D Act as an Immunomodulator?

Natural killer T (NKT) cells are a distinct lineage of T cells which express both the T cell receptor (TCR) and natural killer (NK) cell markers. Invariant NKT (iNKT) cells bear an invariant TCR and recognize a small variety of glycolipid antigens presented by CD1d (nonclassical MHC-I). CD1d-restricted iNKT cells are regulators of immune responses and produce cytokines that may be proinflammatory (such as interferon-gamma (IFN-γ)) or anti-inflammatory (such as IL-4). iNKT cells also appear to play a role in B cell regulation and antibody production. Alpha-galactosylceramide (α-GalCer), a derivative of the marine sponge, is a potent stimulator of iNKT cells and has been proposed as a therapeutic iNKT cell activator. Invariant NKT cells have been implicated in the development and perpetuation of several autoimmune diseases such as multiple sclerosis and systemic lupus erythematosus (SLE). Animal models of SLE have shown abnormalities in iNKT cells numbers and function, and an inverse correlation between the frequency of NKT cells and IgG levels has also been observed. The role of iNKT cells in autoimmune liver disease (AiLD) has not been extensively studied. This review discusses the current data with regard to iNKT cells function in AiLD, in addition to providing an overview of iNKT cells function in other autoimmune conditions and animal models. We also discuss data regarding the immunomodulatory effects of vitamin D on iNKT cells, which may serve as a potential therapeutic target, given that deficiencies in vitamin D have been reported in various autoimmune disorders.

Increased Incidence of Post-transplant Lymphoproliferative Disorder in Autoimmune Liver Disease: An Irish National Experience

BACKGROUND

Post-Transplant Lymphoproliferative Disorder (PTLD) is a well-recognized complication post solid organs transplant. PTLD represents a broad spectrum of abnormalities ranging from an infectious mononucleosis like illness to malignant lymphoma.

METHODS

A retrospective study was performed by collecting data of orthotopic liver transplant (OLT) patients in the National Liver Unit in Ireland from December 1993 to December 2014. Data was analyzed to identify PTLD patients and determine their demographic details, the indication for liver transplant, presenting symptoms, immunosuppression regimens, Epstein"Barr virus (EBV) status and PTLD outcome.

RESULTS

From a total of 756 liver transplants recipients, 20 patients (2.6%) were diagnosed with PTLD. The median time from OLT to PTLD diagnosis was 83 months. The main primary indication for OLT of the PTLD cohort was Autoimmune Liver Disease (AiLD) (n = 13, 65%, mainly primary sclerosing cholangitis (PSC) n = 8, 40%). The combined group of auto-immune hepatitis, PSC and primary biliary cholangitis had a significantly higher incidence of PTLD compared to other etiologies (P < 0.01). In AiLD PTLD subgroup, 61.5% were positive for EBV. Five patients (38.5%) had extra-nodal disease and 3 patients had CNS disease. 61% of PTLD AiLD patients (n = 8) achieved complete response following their treatment.

CONCLUSION

PTLD has high mortality however early diagnosis and complete remission are achievable. Our study suggests that the incidence of PTLD is increased in AiLD and notably PSC patients.

Glucocorticoids Cause Gender-Dependent Reversal of Hepatic Fibrosis in the MDR2-Knockout Mouse Model

Hepatic cholestasis is associated with a significant suppression of the hypothalamus-pituitary-adrenal axis (HPA). In the present study, we tested the hypothesis that activation of the HPA axis by corticosterone treatment can reverse liver inflammation and fibrosis in a multidrug resistance protein 2 knockout (MDR2KO) transgenic mouse model of hepatic cholestasis. Friend Virus B NIH-Jackson (FVBN) control and MDR2KO male and female mice were treated with vehicle or corticosterone for two weeks, then serum and liver analyses of hepatic cholestasis markers were performed. Indicators of inflammation, such as increased numbers of macrophages, were determined. MDR2KO mice had lower corticotropin releasing hormone and corticosterone levels than FVBN controls in the serum. There was a large accumulation of CD68 and F4/80 macrophages in MDR2KO mice livers, which indicated greater inflammation compared to FVBNs, an effect reversed by corticosterone treatment. Intrahepatic biliary duct mass, collagen deposition and alpha smooth muscle actin (αSMA) were found to be much higher in livers of MDR2KO mice than in controls; corticosterone treatment significantly decreased these fibrosis markers. When looking at the gender-specific response to corticosterone treatment, male MDR2KO mice tended to have a more pronounced reversal of liver fibrosis than females treated with corticosterone.

Chronic expression of interferon-gamma leads to murine autoimmune cholangitis with a female predominance

In most autoimmune diseases the serologic hallmarks of disease precede clinical pathology by years. Therefore, the use of animal models in defining early disease events becomes critical. We took advantage of a "designer" mouse with dysregulation of interferon gamma (IFNγ) characterized by prolonged and chronic expression of IFNγ through deletion of the IFNγ 3'-untranslated region adenylate uridylate-rich element (ARE). The ARE-Del(-/-) mice develop primary biliary cholangitis (PBC) with a female predominance that mimics human PBC that is characterized by up-regulation of total bile acids, spontaneous production of anti-mitochondrial antibodies, and portal duct inflammation. Transfer of CD4 T cells from ARE-Del(-/-) to B6/Rag1(-/-) mice induced moderate portal inflammation and parenchymal inflammation, and RNA sequencing of liver gene expression revealed that up-regulated genes potentially define early stages of cholangitis. Interestingly, up-regulated genes specifically overlap with the gene expression signature of biliary epithelial cells in PBC, implying that IFNγ may play a pathogenic role in biliary epithelial cells in the initiation stage of PBC. Moreover, differentially expressed genes in female mice have stronger type 1 and type 2 IFN signaling and lymphocyte-mediated immune responses and thus may drive the female bias of the disease.

CONCLUSION

Changes in IFNγ expression are critical for the pathogenesis of PBC. (Hepatology 2016;64:1189-1201).

Changing trends of hospitalisation of liver cirrhosis in Beijing, China

Objective

To examine if the hospitalisation trends of liver cirrhosis are changing with the changes of risk factors of the disease in China.

Design

Secondary analysis of hospitalisation records in the 31 top-ranking hospitals in Beijing.

Results

Between 2006 and 2010, hospitalisation from viral hepatitis cirrhosis (VHC) decreased by 10% (95% CI=5–14%, p<0.001), but non-viral hepatitis cirrhosis (NVHC) and alcoholic cirrhosis (AC) increased by 35% (26–46%, p<0.001) and 33% (19%– 47%, p<0.001), respectively. The age patterns of hospitalisation varied with different types of liver cirrhosis. The hospitalisation risks for patients with VHC and AC were significantly high in the age groups 40–49 and 50–59 years, but risks for those with NHVC were high in all age groups of 40 years or above. Overall male-to-female hospitalisation ratios for VHC, NVHC and AC were 2.71, 1.14 and 59.9, respectively. The sex ratio became smaller with time from 2006 to 2010 in hospitalised patients with VHC, but it substantially increased in those with NVHC during the same period.

Conclusions

Hospitalisation rates for liver cirrhosis in Beijing are changing with time. The changes of viral hepatitis infection and alcohol consumption in the general population may cause these changes.

Primary biliary cirrhosis is a generalized autoimmune epithelitis

Primary biliary cirrhosis (PBC) is a chronic progressive autoimmune cholestatic liver disease characterized by highly specific antimitochondrial antibodies (AMAs) and the specific immune-mediated injury of small intrahepatic bile ducts. Unique apoptotic feature of biliary epithelial cells (BECs) may contribute to apotope presentation to the immune system, causing unique tissue damage in PBC. Perpetuation of inflammation may result in senescence of BECs, contributing to irreversible loss of bile duct. In addition to the classic liver manifestations, focal inflammation and tissue damage are also seen in salivary glands and urinary tract in a significant proportion of PBC patients. These findings provide potent support to the idea that molecular mimicry may be involved in the breakdown of autoimmune tolerance and mucosal immunity may lead to a systematic epithelitis in PBC patients. Thus, PBC is considered a generalized epithelitis in clinical practice.

Diagnostic and clinical significance of anti-centromere antibodies in primary biliary cirrhosis

Primary biliary cirrhosis (PBC) is an autoimmune disease of the liver characterised by biochemical evidence of cholestasis, elevated alkaline phosphatase levels and the presence of the highly disease specific anti-mitochondrial autoantibodies. Extra-hepatic autoimmune manifestations are common, including rheumatic disorders, such as systemic sclerosis (SSc). Notably, PBC is the most frequent autoimmune liver disease in SSc patients. Based on skin lesion extension, two major SSc disease subgroups are recognised: limited cutaneous SSc (lSSc) and diffuse cutaneous SSc. Anti-centromere antibody (ACA) positivity is highly characteristic of SSc, with up to 90% prevalence in lSSc patients. ACA has also been found in up to 30% of PBC patients and 80% of patients with a PBC/SSc overlap syndrome. The diagnostic and clinical significance of ACA positivity in patients with PBC without SSc has recently been under investigation, with several studies highlighting links to severe bile duct injury and portal hypertension. This review discusses the diagnostic and clinical relevance of ACA in patients with PBC, with or without SSc.

p38 MAPK Signaling in Pemphigus: Implications for Skin Autoimmunity

p38 mitogen activated protein kinase (p38 MAPK) signaling plays a major role in the modulation of immune-mediated inflammatory responses and therefore has been linked with several autoimmune diseases. The extent of the involvement of p38 MAPK in the pathogenesis of autoimmune blistering diseases has started to emerge, but whether it pays a critical role is a matter of debate. The activity of p38 MAPK has been studied in great detail during the loss of keratinocyte cell-cell adhesions and the development of pemphigus vulgaris (PV) and pemphigus foliaceus (PF). These diseases are characterised by autoantibodies targeting desmogleins (Dsg). Whether autoantibody-antigen interactions can trigger signaling pathways (such as p38 MAPK) that are tightly linked to the secretion of inflammatory mediators which may perpetuate inflammation and tissue damage in pemphigus remains unclear. Yet, the ability of p38 MAPK inhibitors to block activation of the proapoptotic proteinase caspase-3 suggests that the induction of apoptosis may be a consequence of p38 MAPK activation during acantholysis in PV. This review discusses the current evidence for the role of p38 MAPK in the pathogenesis of pemphigus. We will also present data relating to the targeting of these cascades as a means of therapeutic intervention.

Crohn's disease-specific pancreatic autoantibodies are specifically present in ruminants with paratuberculosis: implications for the pathogenesis of the human disease

Mycobacterium avium subspecies paratuberculosis (MAP) induces paratuberculosis (ptb) in ruminants and has clinical and histological features resebling Crohn's disease (CD). Pancreatic autoantibodies (PAB) targeting glycoprotein 2 (GP2) are specifically found in CD, but it is currently unknown whether these autoantibodies can be found in ruminants with ptb. IgG anti-MAP and anti-GP2 antibodies were tested by ELISA in 286 ruminants (212 sheep and 74 cattle). PAB testing was performed by indirect immunofluorescence (IIF) using anti-sheep or anti-cattle specific antisera. PCR analysis confirmed the presence of MAP in anti-MAP positive samples. Anti-GP2 antibodies were more prevalent in anti-MAP antibody positive (26.9%) than in anti-MAP negative ruminants (8.7%, p < 0.001). Anti-GP2 antibodies were found in 16/70 (22.9%) anti-MAP positive sheep compared to 10/142 (7%, p = 0.001) anti-MAP antibody negative and in anti-MAP positive cattle than in negative counterparts (5/8 versus 8/66, p = 0.003). Absorbance values for anti-GP2 antibodies were higher in cattle than in sheep (mean 21 AU/mL ± 25.4SD versus 12.2 AU/mL ± 23 SD, p < 0.001). There was no correlation between anti-GP2 and anti-MAP antibody concentrations. Anti-GP2 antibodies persisted up to 1/1000 and showed the characteristic IIF pancreatic pattern seen by anti-GP2 antibody positive CD samples. This is the first study to demonstrate the presence of CD-specific GP2-reactive pancreatic autoantibodies in MAP-infected ruminants. Our data suggest that CD and ptb are characterised by an antigen-driven loss of immunological tolerance to GP2, implying commonalities in the immunopathogenesis of the human and ruminant inflammatory bowel disorder.

Primary biliary cirrhosis does not increase the risk of UTIs following diagnosis compared to other chronic liver diseases?

BACKGROUND

Urinary Tract Infections (UTIs) occur more frequently in patients with Primary Biliary Cirrhosis (PBC). Previous studies have compared UTI occurrence in PBC and general population controls, however, it remains unclear if UTI is a feature of all chronic liver diseases (CLD)s, or is specific to PBC, or if this is a cause or consequence of PBC.

AIMS

We aimed to determine if UTIs are more common after a diagnosis of PBC compared to general population and CLD controls.

METHODS

A cohort study was conducted using the General Practice Research Database. We selected all cases of PBC plus 10 age- and sex-matched general population controls, and an unmatched group with other CLDs. We formed a Cox-proportional hazard model of time to first UTI following diagnosis.

RESULTS

Two hundred and forty-eight (24.6%) of PBC cases had a UTI event compared with 2127 (21.1%) of matched and 2131 (11.7%) of the unmatched CLD controls. Comparing PBC with matched controls showed an approximately 30% increased risk of UTI [hazard ratio (HR) 1.33 confidence interval (CI) 1.17-1.52]. Adjusting for diabetes, smoking and previous UTI reduced this (HR 1.25 CI 1.09-1.42). The Hazard Ratio comparing PBC with unmatched CLD controls was 2.00 (CI 1.76-2.28), but this became non-significant when adjusting for age, sex, diabetes, smoking and previous UTI 0.98 (0.86-1.12).

CONCLUSIONS

There is increased risk of UTI in PBC patients compared to general population controls, but not compared to CLD controls suggesting that this association is not specific to PBC after diagnosis.

Potential Roles for Infectious Agents in the Pathophysiology of Primary Biliary Cirrhosis: What's New?

Primary biliary cirrhosis (PBC) is a progressive cholestatic liver disease serologically characterized by the presence of high-titer antimitochondrial antibodies and, histologically by chronic nonsuppurative cholangitis and granulomata. The aetiology of the disease remains elusive, although genetic, epigenetic, environmental, and infectious factors have been considered important for the induction of the disease in genetically prone individuals. The disease shows a striking female predominance and becomes clinically overt at the fourth to sixth decade. These characteristics have prompted investigators to consider infections that predominate in women at these ages as the likely candidates for triggering the disease. Recurrent urinary tract infections due to Escherichia coli were the first infections to be considered pathogenetically relevant. Over the years, several other microorganisms have been linked to the pathogenesis of PBC owing to epidemiological, immunological, microbiological, or experimental findings in animal models. Recent studies have provided data supporting the pathogenic role of Novosphingobium aromaticivorans and betaretroviruses. Several reports have linked other organisms to the induction of the disease and/or the maintenance of the auto-aggressive responses that are perpetuated over the course of the disease. This review highlights the findings of the most recent studies investigating the link between infections and PBC. We also discuss the close interplay of the infectious agents with other environmental and genetic factors, which may explain the multifaceted nature of this puzzling disease.

The X-factor in primary biliary cirrhosis: monosomy X and xenobiotics

Primary biliary cirrhosis (PBC) is a chronic, cholestatic, autoimmune liver disease characterised by the destruction of small- and medium-sized bile ducts. The serological hallmark of PBC includes antimitochondrial antibodies (AMA). The disease has a striking female predominance, and primarily affects women of middle-age. First-degree relatives, and in particular female relatives, are known to have an increased risk of developing the disease. Several studies have attempted to explain the female predominance of PBC, and autoimmune diseases in general. Two components that are of interest in PBC include monosomy X and xenobiotics. Monosomy X has been noted to be prevalent in the peripheral blood mononuclear cells of PBC patients. Xenobiotics, which are exogenous chemicals not normally found within the body, have been implicated in the modification of, and loss of, tolerance to AMA. Several cosmetics are known to contain these xenobiotics, which is of interest given the information provided in regards to known risk factors for PBC development. This review will focus on X monosomy and xenobiotics, which appear to constitute the X-factor of PBC.

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.

Autoantibodies in autoimmune pancreatitis

Autoimmune pancreatitis (AIP) was first used to describe cases of pancreatitis with narrowing of the pancreatic duct, enlargement of the pancreas, hyper-γ-globulinaemia, and antinuclear antibody (ANA) positivity serologically. The main differential diagnosis, is pancreatic cancer, which can be ruled out through radiological, serological, and histological investigations. The targets of ANA in patients with autoimmune pancreatitis do not appear to be similar to those found in other rheumatological diseases, as dsDNA, SS-A, and SS-B are not frequently recognized by AIP-related ANA. Other disease-specific autoantibodies, such as, antimitochondrial, antineutrophil cytoplasmic antibodies or diabetes-specific autoantibodies are virtually absent. Further studies have focused on the identification of pancreas-specific autoantigens and reported significant reactivity to lactoferrin, carbonic anhydrase, pancreas secretory trypsin inhibitor, amylase-alpha, heat-shock protein, and plasminogen-binding protein. This paper discusses the findings of these investigations and their relevance to the diagnosis, management, and pathogenesis of autoimmune pancreatitis.

Sex differences associated with primary biliary cirrhosis

Primary biliary cirrhosis (PBC) is a cholestatic liver disease of autoimmune origin, characterised by the destruction of small intrahepatic bile ducts. The disease has an unpredictable clinical course but may progress to fibrosis and cirrhosis. The diagnostic hallmark of PBC is the presence of disease-specific antimitochondrial antibodies (AMA), which are pathognomonic for the development of PBC. The disease overwhelmingly affects females, with some cases of male PBC being reported. The reasons underlying the low incidence of males with PBC are largely unknown. Epidemiological studies estimate that approximately 7–11% of PBC patients are males. There does not appear to be any histological, serological, or biochemical differences between male and female PBC, although the symptomatology may differ, with males being at higher risk of life-threatening complications such as gastrointestinal bleeding and hepatoma. Studies on X chromosome and sex hormones are of interest when studying the low preponderance of PBC in males; however, these studies are far from conclusive. This paper will critically analyze the literature surrounding PBC in males.

Epstein-barr virus as a trigger of autoimmune liver diseases

The pathogenesis of autoimmune diseases includes a combination of genetic factors and environmental exposures including infectious agents. Infectious triggers are commonly indicated as being involved in the induction of autoimmune disease, with Epstein-Barr virus (EBV) being implicated in several autoimmune disorders. EBV is appealing in the pathogenesis of autoimmune disease, due to its high prevalence worldwide, its persistency throughout life in the host's B lymphocytes, and its ability to alter the host's immune response and to inhibit apoptosis. However, the evidence in support of EBV in the pathogenesis varies among diseases. Autoimmune liver diseases (AiLDs), including autoimmune hepatitis (AIH), primary biliary cirrhosis (PBC), and primary sclerosing cholangitis (PSC), have a potential causative link with EBV. The data surrounding EBV and AiLD are scarce. The lack of evidence surrounding EBV in AiLD may also be reflective of the rarity of these conditions. EBV infection has also been linked to other autoimmune conditions, which are often found to be concomitant with AiLD. This paper will critically examine the literature surrounding the link between EBV infection and AiLD development. The current evidence is far from being conclusive of the theory of a link between EBV and AiLD.

Tuberculosis Is Not a Risk Factor for Primary Biliary Cirrhosis: A Review of the Literature

Primary biliary cirrhosis (PBC) is a progressive cholestatic liver disease characterised serologically by cholestasis and the presence of high-titre antimitochondrial antibodies, and histologically by chronic nonsuppurative cholangitis and granulomata. As PBC is a granulomatous disease andMycobacterium tuberculosisis the most frequent cause of granulomata, a causal relation between tuberculosis and PBC has been suggested. Attempts to find serological evidence of PBC-specific autoantibodies such as AMA have been made and, conversely, granulomatous livers from patients with PBC have been investigated for molecular evidence ofMycobacterium tuberculosis. This paper discusses in detail the reported data in support or against an association betweenMycobacterium tuberculosisinfection and PBC. We discuss the immunological and microbiological data exploring the association of PBC with exposure toMycobacterium tuberculosis. We also discuss the findings of large epidemiologic studies investigating the association of PBC with preexistent or concomitant disorders and the relevance of these findings with tuberculosis. Genome-wide association studies in patients with tuberculosis as well as in patients with PBC provide conclusive hints regarding the assumed association between exposure to this mycobacterium and the induction of PBC. Analysis of these data suggest thatMycobacterium tuberculosisis an unlikely infectious trigger of PBC.