The immunobiology of primary sclerosing cholangitis

Primary sclerosing cholangitis (PSC) is a chronic cholestatic liver disease histologically characterized by the presence of intrahepatic and/or extrahepatic biliary duct concentric, obliterative fibrosis, eventually leading to cirrhosis. Approximately 75% of patients with PSC have inflammatory bowel disease. The male predominance of PSC, the lack of a defined, pathogenic autoantigen, and the potential role of the innate immune system suggest that it may be due to dysregulation of immunity rather than a classic autoimmune disease. However, PSC is associated with several classic autoimmune diseases, and the strongest genetic link to PSC identified to date is with the human leukocyte antigen DRB01*03 haplotype. The precise immunopathogenesis of PSC is largely unknown but likely involves activation of the innate immune system by bacterial components delivered to the liver via the portal vein. Induction of adhesion molecules and chemokines leads to the recruitment of intestinal lymphocytes. Bile duct injury results from the sustained inflammation and production of inflammatory cytokines. Biliary strictures may cause further damage as a result of bile stasis and recurrent secondary bacterial cholangitis. Currently, there is no effective therapy for PSC and developing a rational therapeutic strategy demands a better understanding of the disease.     

The role of complement activation in autoimmune liver disease

IntroductionThe complement system, an essential part of the innate immune system, is involved in various autoimmune diseases. Activation of the complement system by autoantibodies results in immune activation and tissue damage. At the moment little is known about the role of the complement system in autoimmune liver disease, including primary biliary cholangitis (PBC), primary sclerosing cholangitis (PSC) and autoimmune hepatitis (AIH). Since inhibition of the complement system is currently being tested in several autoimmune diseases as a therapeutic option, its role in autoimmune liver disease requires further clarification.MethodsA review of the literature was performed on studies investigating complement activation in PBC, PSC and AIH. Since data on AIH were lacking immunohistochemical staining for IgG, C1q, C3d, C4d and C5b9 was performed on liver tissue of nine AIH patients, two healthy controls and one positive control (acute liver failure caused by paracetamol intoxication).ResultsImmunohistochemical analysis in AIH revealed increased production of C3 and C4 by hepatocytes. Despite a strong staining for IgG in the immune infiltrate in AIH, C3d, C4d and C5b9 deposition was only present in one AIH patient and the deposition was restricted to the interface between portal tracts and liver parenchyma. No deposition was found in all other AIH patients or healthy controls.Literature review showed raised plasma C3 and C4 levels in AIH, PBC and PSC patients compared to healthy controls. For PBC and PSC no complement depositions at the bile ducts were reported.Conclusion and discussionAlthough complement is involved in various autoimmune diseases, the role of complement in autoimmune liver disease seems limited. Therefore it is unlikely that complement inhibition will become a novel treatment option for these diseases.     

Atypical p-ANCA in PSC and AIH: A Hint Toward a “leaky gut”?

Primary sclerosing cholangitis (PSC) and autoimmune hepatitis (AIH) are enigmatic chronic inflammatory diseases of the liver, which are frequently associated with chronic inflammatory bowel diseases. Both types of liver disease share various distinct autoantibodies such as atypical perinuclear antineutrophil cytoplasmic antibodies (p-ANCA), and thus are considered autoimmune disorders with atypical features. The discovery that atypical p-ANCA recognize both tubulin beta isoform 5 in human neutrophils and the bacterial cell division protein FtsZ has renewed the discussion on the potential role of microorganisms in the pathogenesis of both diseases. In this paper, we review the evidence for microbial infection in PSC and AIH and discuss new concepts how cross-recognition between microbial antigens in the gut and host components by the immune system along with stimulation of pattern recognition receptors might give rise to chronic hepatic inflammatory disorders with features of autoimmunity.     

Role of NKT cells in autoimmune liver disease

The three main broad categories of autoimmune liver disease are autoimmune hepatitis (AIH), primary biliary cirrhosis (PBC), and primary sclerosing cholangitis (PSC). The etiologies of these diseases are still incompletely understood, but seem to involve a combination of immune, genetic and environmental factors. Although each of these diseases has relatively distinct clinical, serologic and histological profiles, all of them share common pathways of immune-mediated liver injury. The development of autoimmune liver diseases is thought to be due to an imbalance of proinflammatory and anti-inflammatory immune responses within the liver, with proinflammatory immune responses being upregulated and anti-inflammatory ones downregulated. The available evidence, suggest that during autoimmune responses within the liver, “self” antigens are presented by antigen presenting cells (APCs) which then activate, directly and/or indirectly, NKT cells and other innate immune cells within the liver. Importantly, the hepatic innate immune system plays an increasingly recognized role in the development and propagation of autoimmune liver injury. NKT cells predominantly reside in the liver sinusoids, and through their ability to rapidly produce a wide variety of cytokines (e.g. Th1, TH2, Th17 cytokine patterns), are a critical checkpoint that bridges innate and adaptive immune responses. Specifically, activated NKT cells are capable of transactivating other innate and adaptive immune cells within the liver to amplify and regulate subsequent immune responses within the liver. It has been hypothesized that NKT cells in the setting of autoimmune liver disease can play diverse roles, including driving both anti-inflammatory and proinflammatory responses, as well as regulating the hepatic recruitment of other types of immunoregulatory cells, including regulatory T cells.     

The Immunophysiology and Apoptosis of Biliary Epithelial Cells: Primary Biliary Cirrhosis and Primary Sclerosing Cholangitis

Biliary epithelial cells (BECs) provide the first line of defense against lumenal microbes in the biliary system. BECs express a variety of pathogen recognition receptors and can activate several intracellular signaling cascades to initiate antimicrobial defenses, including production of several anti-microbial peptides, cytokines, chemokines, and adhesion molecules. BECs also secrete immunoglobulin A and interact with other cells through expression and release of adhesion molecules and immune mediators. Recently, several reports suggest a correlation between apoptosis and autoimmunity through ineffective clearance of self-antigens. Primary biliary cirrhosis (PBC) is a slowly progressive, autoimmune cholestatic liver disease characterized by highly specific antimitochondrial antibodies (AMAs) and the specific immune-mediated destruction of BECs. We have demonstrated that the AMA self-antigen, namely the E2 subunit of the pyruvate dehydrogenase complex, is detectable in its antigenically reactive form within apoptotic blebs from human intrahepatic biliary epithelial cells and activates innate immune responses. Primary sclerosing cholangitis (PSC) is a chronic cholestatic liver disease characterized by inflammation and the presence of concentric fibrosis of intrahepatic and/or extrahepatic bile ducts, eventually leading to cirrhosis. However, apoptosis does not appear to play a central role in PSC. Despite both diseases involving immune-mediated injury to bile ducts, apoptosis occurs more commonly overall in PBC where it likely plays a unique role.     

Immunopathogenesis of primary sclerosing cholangitis

Primary sclerosing cholangitis (PSC) is a chronic cholestatic liver disease of unknown etiology; however, lymphocytic portal tract infiltration is suggestive of an immune-mediated basis for PSC. Associations with inflammatory bowel disease— especially ulcerative colitis—and with other auto-immune diseases, together with genetic associations, further suggest that PSC may be an immune-mediated disease. The immunogenetics of PSC have been the subject of active research, and several human leukocyte antigen (HLA)- and non-HLA-associated genes have been implicated in the development of the disease. Lymphocytes derived from the inflamed gut may enter the liver via the enterohepatic circulation to cause hepatic disease. PSC may be triggered in genetically susceptible individuals by infections or toxins entering the portal circulation through a permeable colon and, therefore, evoking an abnormal immune response.     

In situ mass spectrometry of autoimmune liver diseases

Primary biliary cirrhosis (PBC), primary sclerosing cholangitis (PSC) and autoimmune hepatitis (AIH) are the major forms of autoimmune liver diseases each characterized by the destruction of a specific liver cell type and the presence of differing auto-antibodies. We took a proteomic approach utilizing in situ matrix-assisted laser desorption/ionization mass spectrometry (MALDI MS) to obtain profiles directly from liver samples of patients with PBC, PSC, AIH and controls. The ability to precisely localize the region for acquisition of MALDI MS allowed us to obtain profiles from bile ducts, inflammatory infiltrates and hepatocytes from each biopsy sample. Analysis tools developed to identify peaks and compare peaks across diseases and cell types were used to develop models to classify the samples. Using an initial set of testing samples from PBC patients and controls, we identified unique peaks present in bile ducts, inflammatory infiltrates and hepatocytes that could classify samples in a validation cohort with 88-91% accuracy. Interestingly, profiles of PSC and AIH did not differ significantly from PBC. Identification of proteins in these peaks may represent novel autoantigens or effector molecules. These findings illustrate the potential of a proteomic approach to autoimmune diseases with in situ MALDI MS.     

Primary sclerosing cholangitis

Primary sclerosing cholangitis (PSC) is a fibrosing disease of the intra- and extra-hepatic bile ducts, and is closely associated with inflammatory bowel disease. It is immune mediated, rather than being a classical autoimmune disease. A range of immune abnormalities have been demonstrated in PSC, in particular the findings of a range of autoantibodies, a portal tract infiltrate of functional T cells, a restricted T-cell receptor repertoire, and aberrant expression of HLA molecules on biliary epithelial cells. The immunogenetics of PSC is currently under study and to date 4 key HLA haplotypes associated with PSC have been developed. The trigger factor for the initiation of the immune response may be the ingress of bacteria or other toxic metabolites into the portal circulation through a diseased and permeable bowel wall.     

Distinct clinicopathological entity 'autoimmune pancreatitis-associated sclerosing cholangitis'

Autoimmune pancreatitis (AIP) is a recently proposed disease entity, in which an elevated serum IgG4 is characteristic. This disease is sometimes associated with other inflammatory diseases: Sjögren's disease, or sclerosing cholangitis. The aim of the present paper was to examine the difference in pathophysiology between AIP‐associated sclerosing cholangitis (AIP‐SC) and primary sclerosing cholangitis (PSC). The clinicopathological findings and the immunohistochemical expressions of IgG subclasses (IgG1, IgG2, IgG3, and IgG4) were evaluated for the two aforementioned diseases (six patients with each disease). Radiologically, the extrahepatic bile duct was involved in AIP‐SC, whereas both extrahepatic and intrahepatic bile ducts were involved in PSC. Clinically, bile duct lesions in the former responded well to steroid therapy. Histologically, various degrees of mononuclear cell infiltration and fibrosis around bile ducts and portal tracts were found in all patients. Immunohistochemically, the IgG4‐positive plasma cell/mononuclear cell ratio was significantly higher in AIP‐SC than in PSC (P < 0.05). The IgG4‐positive plasma cell/mononuclear cell ratio is a useful index to help distinguish AIP‐SC from PSC. A mechanism similar to that involved in AIP may be involved in AIP‐SC. The latter is a distinct clinicopathological entity that should be distinguished from PSC because it responds well to steroid therapy.     

Role of liver biopsy in autoimmune liver disease

This article will review histological aspects of three chronic liver diseases – autoimmune hepatitis (AIH), primary biliary cirrhosis (PBC) and primary sclerosing cholangitis (PSC) – in which autoimmune mechanisms are thought to be involved. The changing role of liver biopsy in the diagnosis and management of patients with autoimmune liver disease will also be discussed. In the case of autoimmune hepatitis, histological assessments remain important in establishing a diagnosis, identifying prognostic features and monitoring therapeutic responses. By contrast, for many patients with PBC and PSC a diagnosis can now be made on the basis of biochemical, serological and/or radiological findings alone and histological confirmation may not be required. Liver biopsy can still be used to assess disease severity in such cases and remains important in establishing a diagnosis in patients with atypical features (e.g. AMA-negative PBC or the small-duct variant of PSC). Liver biopsy is also increasingly used in the assessment of patients suspected to have “overlap syndromes” involving AIH and PBC or PSC.     

Anti-Saccharomyces cerevisiae antibodies (ASCA) and autoimmune liver diseases

Antibodies to the baker's yeast Saccharomyces cerevisiae (ASCA), recently proposed as a serological marker of Crohn's disease, have also been detected in other autoimmune disorders. The aim of this study was to determine prevalence and clinical significance of ASCA in autoimmune liver disease. The presence of IgG and IgA ASCA was evaluated using a commercially available immunoassay in 215 patients with autoimmune liver disease (primary biliary cirrhosis, PBC, 123 cases; autoimmune hepatitis, AIH, 67 cases; primary sclerosing cholangitis, PSC, 25 cases), 48 with inflammatory bowel disease and 19 healthy blood donors. Anti neutrophil cytoplasmic antibodies with the perinuclear pattern (p-ANCA) were assessed by indirect immunofluorescence in PSC patients. The main clinical and biochemical parameters between ASCA-positive and negative patients were analysed and compared. ASCA are predominant in Crohn's disease (70%); among liver patients, PSC and AMA-negative PBC show the highest ASCA prevalence (53% and 44%). In PBC ASCA correlate with higher levels of circulating IgA (P < 0.05). In PSC the detection of either ASCA or p-ANCA is neither associated with any clinical or biochemical feature, nor with an underlying inflammatory bowel disease. ASCA can not be considered an additional serological marker of autoimmune liver disease, but the possibility of detecting such a reactivity in autoimmune liver disorders should be considered; their correlation with elevated IgA in PBC suggests that ASCA may be an indirect sign of enhanced mucosal immunity; in PSC patients neither ASCA nor p-ANCA predict the occurrence of a concomitant inflammatory bowel disease.     

The Hepatitic/Cholestatic "Overlap" Syndrome: An Italian Experience

Background: Patients with hepatitic and cholestatic autoimmune liver disease ("overlap syndrome") represent a diagnostic and therapeutic challenge. Aim: To evaluate the prevalence of the "hepatitic/cholestatic overlap" in a large series of consecutive patients with cholestatic autoimmune liver disease. Methods: We re-evaluated the diagnosis of 235 patients with autoimmune liver disease, including 70 with type 1 autoimmune hepatitis (AIH), 142 with primary biliary cirrhosis (PBC), and 23 with primary sclerosing cholangitis (PSC), using the revised International Autoimmune Hepatitis Group (IAIHG) scoring system. Anti-mitochondrial, anti-nuclear, anti-smooth muscle, anti-liver kidney microsomal type 1, anti-liver cytosol type 1, perinuclear anti-neutrophil nuclear and anti-soluble liver antigen antibodies were evaluated in each patient. Results: Ten patients (3 with a previous diagnosis of PBC and 7 of PSC) scored as "probable" or "definite" AIH. These patients did not have a specific autoantibody profile. Conclusions: Among patients with PBC, the occurrence of a PBC/AIH overlapping syndrome is rare (2.1%), whereas among patients with PSC an overlap between PSC and AIH is frequent (30.4%). Whether patients with the hepatitic/cholestatic overlap syndrome would benefit from a combination therapy with immunosuppression and ursodeoxycholic acid remains to be established.     

Medical Treatment of Primary Sclerosing Cholangitis: A Role for Novel Bile Acids and other (post-)Transcriptional Modulators?

Primary sclerosing cholangitis (PSC) is a rare chronic cholestatic disease of the liver and bile ducts that is associated with inflammatory bowel disease, generally leads to end-stage liver disease, and is complicated by malignancies of the biliary tree and the large intestine. The pathogenesis of PSC remains enigmatic, making the development of targeted therapeutic strategies difficult. Immunosuppressive and antifibrotic therapeutic agents were ineffective or accompanied by major side effects. Ursodeoxycholic acid (UDCA) has consistently been shown to improve serum liver tests and might lower the risk of colon carcinoma and cholangiocarcinoma by yet unknown mechanisms. Whether “high dose” UDCA improves the long-term prognosis in PSC as suggested by small pilot trials remains to be demonstrated. The present overview discusses potential therapeutic options aside of targeted immunological therapies and UDCA. The C23 bile acid norUDCA has been shown to markedly improve biochemical and histological features in a mouse model of sclerosing cholangitis without any toxic effects. Studies in humans are eagerly being awaited. Nuclear receptors like the farnesoid-X receptor (FXR), pregnane-X receptor (PXR), vitamin D receptor (VDR), and peroxisome-proliferator-activator receptors (PPARs) have been shown to induce expression of diverse carriers and biotransformation enzymes of the intestinal and hepatic detoxification machinery and/or to modulate fibrogenesis. Pros and cons of respective receptor agonists for the future treatment of PSC are discussed in detail. In our view, the novel bile acid norUDCA and agonists of PPARs, VDR, and PXR appear particularly attractive for further studies in PSC.     

Stromal cell-derived factor-1 from biliary epithelial cells recruits CXCR4-positive cells: implications for inflammatory liver diseases

Although stromal cell-derived factor-1 (SDF-1) plays an important role in hematopoiesis in the fetal liver, the role after birth remains to be clarified. We investigated the role of SDF-1 and its receptor, CXCR4, in 75 patients; this included controls and patients with viral hepatitis, liver cirrhosis, primary biliary cirrhosis, primary sclerosing cholangitis, and autoimmune hepatitis. Interestingly, SDF-1 appeared up-regulated in biliary epithelial cells (BEC) of inflammatory liver disease. Furthermore, in inflammatory liver diseases, SDF-1 was expressed by BEC of interlobular and septal bile ducts and by proliferated bile ductules. The message expression of SDF-1 in BEC was confirmed at a single-cell level by RT-PCR and laser capture microdissection. The plasma levels of SDF-1 were significantly higher in patients with liver diseases than in normal controls. Flow cytometric analysis of the surface expression of CXCR4 showed that most liver-infiltrating lymphocytes express CXCR4 and the intensity was up-regulated more significantly in liver-infiltrating lymphocytes than in peripheral blood lymphocytes. These results suggest that increased SDF-1 production by BEC may play an important role in the recruitment of CXCR4-positive inflammatory cells into the diseased livers. These data are significant because modulation of the SDF-1/CXCR4 interaction has therapeutic implications for inflammatory liver diseases.     

Geoepidemiology of autoimmune liver diseases

Autoimmune liver diseases are characterized by immune mediated injury of bile ducts or hepatocytes, thus including cholangiopathies such as primary biliary cirrhosis, primary sclerosing cholangitis, and immunoglobulin G4-associated cholangitis, and autoimmune hepatitis. Although the liver was one of the earliest recognized sites of autoimmune aggression, the aetiology of autoimmune liver diseases remains largely obscure and their clinical management still difficult. Since an ever increasing applicability of immunology to a wide variety of chronic diseases, basic and clinical knowledge on autoimmune liver diseases grow rapidly in the last few years. This review will mainly focus on the available geoepidemiology data of these disorders, but it will deal also on their main clinical characteristics, as well as mechanisms of etiopathogenesis, for each of the above diseases, together with their overlap forms. In particular, we will discuss the major underlying immunomolecular mechanisms of development, the genetic influences, the growing number of immuno-serological diagnostic markers, and the increasingly effective therapeutic possibilities.     

Bile duct epithelia as target cells in primary biliary cirrhosis and primary sclerosing cholangitis

 Primary biliary cirrhosis (PBC) and primary sclerosing cholangitis (PSC) are chronic autoimmune-mediated diseases of the biliary tree, resulting in a loss of bile ducts. There are morphological features that clearly distinguish them from each other: in PBC, there is overt destruction of the bile ducts with disruption of the basement membrane; in PSC there is abundant periductular fibrosis with shrinkage and subsequent loss of the bile ducts. In order to see if the disparate histopathology is paralleled by different immunohistology we looked at a panel of epitopes on bile duct epithelia especially to see if biliary epithelial cells may present as targets for cell mediated immune respone. In PBC bile duct epithelial cells mostly expressed CD58 (lymphocyte function-associated antigen 3), CD80 (B7 BB1), and CD95 (Fas). In PSC, however, these epitopes were only expressed in a few examples to a lower degree. The respective effector T lymphocytes were positive for CD2 and CD28. Subtyping of the lymphocytes in the liver tissue further showed a predominance of CD4 positive T cells over CD8 cells up to 2-to-1 in both diseases. Determination of lymphocytes by cytokines to Th1 or Th2 subtype showed a majority of Th1 lymphocytes in PBC and PSC. We conclude that in PBC bile duct epithelial cells may display features of target cells of a T cell-mediated immune reaction with the Th1 cells predominating. In PSC other mechanisms of bile duct loss may play a role, since in this disease the majority of cells lack essential epitopes that constitute targets of cell mediated immunity. Received: 19 November 1996 / Accepted: 26 February 1997     

Follicular cholangitis and pancreatitis - clinicopathological features and differential diagnosis of an under-recognized entity

Zen Y, Ishikawa A, Ogiso S, Heaton N & Portmann B
(2012) Histopathology  60, 261–269
Follicular cholangitis and pancreatitis – clinicopathological features and differential diagnosis of an under‐recognized entity Aims: Biliary and pancreatic ductal systems can be involved in several lymphoplasmacytic inflammatory conditions, including primary sclerosing cholangitis, immunoglobulin G (IgG) 4‐related cholangitis and autoimmune pancreatitis. Here in we describe an unusual pancreatocholangitis whose features suggest a distinct disease entity. Methods and results: The study group consists of five adult patients, three with predominantly hilar bile duct stricture and two with a bulky pancreatic head. Four patients were treated surgically for suspected malignancy and one patient underwent liver transplantation with a clinical diagnosis of primary sclerosing cholangitis. Histological examination revealed extensive lymphoplasmacytic inflammation centred on large biliary or pancreatic ducts. Many lymphoid follicles with germinal centres were noted around the affected ducts. Whipple specimens from two patients with a pancreatic head mass showed similar follicular inflammation histologically around bile ducts. In contrast to autoimmune pancreatitis, diffuse infiltration of IgG4⁺ plasma cells, granulocytic epithelial lesions and obliterative phlebitis were not identified. The postoperative course was uneventful, without evidence of recurrence (follow‐up period 17–65 months). Conclusions: This study suggests that a disease entity which can be named follicular cholangitis and pancreatitis exists and may be under‐recognized. The disease mainly affects the hilar bile ducts and pancreatic head in adults.     

Innate lymphocytes: pathogenesis and therapeutic targets of liver diseases and cancer

The liver is a lymphoid organ with unique immunological properties, particularly, its predominant innate immune system. The balance between immune tolerance and immune activity is critical to liver physiological functions and is responsible for the sensitivity of this organ to numerous diseases, including hepatotropic virus infection, alcoholic liver disease, nonalcoholic fatty liver disease, autoimmune liver disease, and liver cancer, which are major health problems globally. In the past decade, with the discovery of liver-resident natural killer cells, the importance of innate lymphocytes with tissue residency has gradually become the focus of research. In this review, we address the current knowledge regarding hepatic innate lymphocytes with unique characteristics, including NK cells, ILC1/2/3s, NKT cells, γδ T cells, and MAIT cells, and their potential roles in liver homeostasis maintenance and the progression of liver diseases and cancer. A better understanding of the immunopathogenesis of hepatic innate lymphocytes will be helpful for proposing effective treatments for liver diseases and cancer.     

A review of the physiological and immunological functions of biliary epithelial cells: targets for primary biliary cirrhosis, primary sclerosing cholangitis and drug-induced ductopenias

Our understanding of biliary epithelial cells (BEC) in physiobiology and immunology has steadily expanded. BEC transports IgA as well as IgM into bile, synthesizes and secretes various chemokines, cytokines, and expresses adhesion molecules involved in cell interaction and signal transduction. These then suggest a myriad of potential roles for BEC in defense from invading microorganisms as well as the pathogenesis of diverse immunologically driven diseases such as primary biliary cirrhosis (PBC), graft-versus-host disease, and primary sclerosing cholangitis (PSC). Despite the progress, there still remain many areas of BEC biology that require further investigation. Most importantly, it remains to be clarified that the extent to which the immunologic activities observed in BEC represent a BEC response to tissue injury or whether BEC themselves are the active participants in the pathogenesis of various cholestatic immunological diseases, including PBC and PSC.