Biliary apotopes and anti-mitochondrial antibodies activate innate immune responses in primary biliary cirrhosis

Our understanding of primary biliary cirrhosis (PBC) has been significantly enhanced by the rigorous dissection of the multilineage T and B cell response against the immunodominant mitochondrial autoantigen, the E2 component of the pyruvate dehydrogenase complex (PDC-E2). PDC-E2 is a ubiquitous protein present in mitochondria of nucleated cells. However, the damage of PBC is confined to small biliary epithelial cells (BECs). We have previously demonstrated that BECs translocate immunologically intact PDC-E2 to apoptotic bodies and create an apotope. To define the significance of this observation, we have studied the ability of biliary or control epithelial apotopes to induce cytokine secretion from mature monocyte-derived macrophages (MDMphis) from either patients with PBC or controls in the presence or absence of anti-mitochondrial antibodies (AMAs). We demonstrate that there is intense inflammatory cytokine production in the presence of the unique triad of BEC apotopes, macrophages from patients with PBC, and AMAs. The cytokine secretion is inhibited by anti-CD16 and is not due to differences in apotope uptake. Moreover, MDMphis from PBC patients cultured with BEC apoptotic bodies in the presence of AMAs markedly increase tumor necrosis factor-related apoptosis-inducing ligand expression.

CONCLUSION

These results provide a mechanism for the biliary specificity of PBC, the recurrence of disease after liver transplantation, and the success of ursodiol in treatment. They further emphasize the critical role of the innate immune system in the perpetuation of this autoimmune disease.

Definition of human autoimmunity--autoantibodies versus autoimmune disease

The critical function of the immune system is to discriminate self from non-self. Tolerance against self-antigens is a highly regulated process and, in order to maintain it, the immune system must be able to distinguish self-reactive lymphocytes as they develop. The presence of autoantibodies is the consequence of breakdown of tolerance and, although they are an important serological feature of autoimmune diseases, their presence is not exclusive of these conditions. Antibodies against self-antigens are also found in cancer, during massive tissue damage and even in healthy subjects. Natural autoantibodies provide immediate protection against infection and also prevent inflammation by facilitating the clearance of oxidized lipids, oxidized proteins, and apoptotic cells; their role in development of autoimmunity is still unclear. Detection of serum autoantibodies in clinical practice has become more available to clinicians worldwide while providing a powerful diagnostic tool. This review discusses the clinical significance of autoantibodies, their pathogenic mechanisms in autoimmune diseases and, finally, illustrates the technology available for appropriate autoantibody detection.

Apotopes and the biliary specificity of primary biliary cirrhosis

Primary biliary cirrhosis (PBC) is characterized by antimitochondrial antibodies (AMAs), directed to the E2 component of the pyruvate dehydrogenase complex (PDC-E2). Notwithstanding the presence of mitochondria in virtually all nucleated cells, the destruction in PBC is limited to small intrahepatic bile ducts. The reasons for this tissue specificity remain unknown, although biliary epithelial cells (BECs) uniquely preserve the PDC-E2 epitope following apoptosis. Notably, PBC recurs in an allogeneic transplanted liver, suggesting generic rather than host PBC-specific susceptibility of BEC. We used cultured human intrahepatic BECs (HIBECs) and other well-characterized cell lines, including, HeLa, CaCo-2 cells, and nontransformed human keratinocytes and bronchial epithelial cells, to determine the integrity and specific localization of PDC-E2 during induced apoptosis. All cell lines, both before and after apoptosis, were tested with sera from patients with PBC (n = 30), other autoimmune liver and rheumatic diseases (n = 20), and healthy individuals (n = 20) as well as with a mouse monoclonal antibody against PDC-E2 and AMA with an immunoglobulin A isotype. PDC-E2 was found to localize unmodified within apoptotic blebs of HIBECs, but not within blebs of various other cell lineages studied. The fact that AMA-containing sera reacted with PDC-E2 on apoptotic BECs without a requirement for permeabilization suggests that the autoantigen is accessible to the immune system during apoptosis.

CONCLUSION

Our data indicate that the tissue (cholangiocyte) specificity of the autoimmune injury in PBC is a consequence of the unique characteristics of HIBECs during apoptosis and can be explained by exposure to the immune system of intact immunoreactive PDC-E2 within apoptotic blebs.

Primary biliary cholangitis

Primary biliary cholangitis is an autoimmune liver disease that predominantly affects women. It is characterised by a chronic and destructive, small bile duct, granulomatous lymphocytic cholangitis, with typical seroreactivity for antimitochondrial antibodies. Patients have variable risks of progressive ductopenia, cholestasis, and biliary fibrosis. Considerations for the cause of this disease emphasise an interaction of chronic immune damage with biliary epithelial cell responses and encompass complex, poorly understood genetic risks and environmental triggers. Licensed disease-modifying treatment focuses on amelioration of cholestasis, with weight-dosed oral ursodeoxycholic acid. For patients who do not respond sufficiently, or patients with ursodeoxycholic acid intolerance, conditionally licensed add-on therapy is with the FXR (NR1H4) agonist, obeticholic acid. Off-label therapy is recognised as an alternative, notably with the pan-PPAR agonist bezafibrate; clinical trial agents are also under development. Baseline characteristics, such as young age, male sex, and advanced disease, and serum markers of liver injury, particularly bilirubin and ALP, are used to stratify risk and assess treatment responsiveness. Parallel attention to the burden of patient symptoms is paramount, including pruritus and fatigue.

Is autoimmunity a matter of sex?

Autoimmune diseases include several conditions that cumulatively are estimated to affect over 5% of the US population with a striking female predominance reported for most of them. The cause and mechanisms of this sex bias remains unknown despite multiple proposed hypotheses. Indeed, it is well established in several experimental settings that the human immune system exhibits sexual dimorphism with basic immune responses differing between females and males. Among candidate factors to explain these differences we note that particular attention has been primarily devoted to sex hormones, yet data have been inconclusive or have not been confirmed. The same seems to apply to the hypothesis of fetal microchimerism. Most recently, sex chromosome abnormalities and skewed X chromosome inactivation have been suggested as novel players, particularly in later-onset diseases. We review herein the most recent data on the mechanisms proposed for the female predominance. We also attempt to determine whether observed sex ratios are in fact the result of sex-biased awareness in case-finding studies.

Evolving Trends in Female to Male Incidence and Male Mortality of Primary Biliary Cholangitis

Primary biliary cholangitis (PBC) has been regarded as female-predominant without evidence of gender difference in survival. We aimed to compare the overall survival, incidence and prevalence of PBC in two well defined population-based studies over a recent decade, considering also sex ratios and mortality. We have taken advantage of population-wide records, during 2000-2009, in Lombardia, Northern Italy, and Denmark. We focused on the incident cases of PBC, including gender and outcome, among 9.7 million inhabitants of Lombardia and 5.5 million of Denmark. In Lombardia there were 2,970 PBC cases with a female:male ratio of 2.3:1. The age/sex-adjusted annual incidence of PBC was 16.7 per million. Point prevalence was 160 per million on January 1(st) 2009. In Denmark there were 722 cases of incident PBC, female:male ratio was 4.2:1, and the annual incidence was 11.4 per million, a point prevalence of 115 per million in 2009. Cox regression multivariate analysis identified male sex as an independent predictor of all-cause mortality in both Italian (HR 2.36) and Danish population (HR 3.04). Our data indicate for PBC a sex ratio significantly lower than previously cited, a reversal of the usual latitudinal difference in prevalence and a surprisingly higher overall mortality for male patients.

The consequences of apoptosis in autoimmunity

The clearance of apoptotic cells is a highly regulated mechanism, normally associated with anti-inflammatory response. During early stages of apoptosis the cell is promptly recognized and engulfed by professional phagocytes or tissue cells to avoid the outflow of intracellular content and limit the immunological reaction against released antigens. However, increasing evidences suggest that impairment in the uptake of apoptotic cell debris is linked to the development of autoimmunity. In fact, autoantigens have been demonstrated to be content within apoptotic bodies and apoptotic cells seems to be critical in the presentation of antigens, activation of innate immunity and regulation of macrophage cytokine secretion. We herein review the known mechanisms for regulating the uptake of the products of apoptosis in the development of autoimmunity.

Immunoglobulin M levels inversely correlate with CD40 ligand promoter methylation in patients with primary biliary cirrhosis

The cross-talk of cluster of differentiation (CD)40/CD40 ligand (CD40L) plays a key role in CD4(+) T-cell priming, B-cell terminal maturation, and immunoglobulin (Ig) class-switch recombination. Genetic defects in the CD40L lead to a disorder characterized by elevated concentrations of serum IgM and immunodeficiency. Patients with primary biliary cirrhosis (PBC) characteristically show circulating antimitochondrial antibodies (AMAs), liver-infiltrating autoreactive T lymphocytes against mitochondrial antigens, and high levels of IgM. We hypothesized that CD40L may play a key role in the pathogenesis of the elevated serum IgM and analyzed genetic and epigenetic modifications of the gene coding for CD40L in CD4(+) and CD8(+) T cells isolated from circulating mononuclear cells from PBC patients and healthy controls. We herein demonstrate significantly lower levels of DNA methylation of the CD40L promoter in CD4(+) T cells from PBC patients, as compared with controls, and this decreased methylation was inversely correlated with levels of serum IgM in PBC patients.

CONCLUSION

The findings of an absence of genetic modifications of the CD40L gene, in concert with decreased DNA methylation of the CD40L promoter in PBC patients, suggests that environmental factors, rather than genetics, must play a major role in the pathogenesis of elevated serum IgM in PBC.

The Pathogenesis of Primary Biliary Cholangitis: A Comprehensive Review

Primary biliary cholangitis (PBC) is a chronic cholestatic liver disease characterized by autoimmune destruction of small to medium size intrahepatic bile ducts. The etiology of PBC remains unknown and pathogenesis features immune-mediated biliary injury, alongside the consequences of chronic cholestasis. PBC is strongly associated with the loss of immune tolerance against mitochondrial antigens and the subsequent presence of an articulated immunologic response that involves both humoral and cellular responses. Both environmental factors and genetic variants increase PBC susceptibility. Biliary epithelial cells have often been considered a passive target of the immune attack in PBC; however, cholangiocyte dedifferentiation, senescence, stress, and deoxyribonucleic acid damage have been recognized to play an active role in the pathogenesis of PBC. This review highlights and discusses the most relevant pathogenetic mechanisms in PBC, focusing on the key factors that lead to the onset of cholestasis and immune activation.

Autophagy: highlighting a novel player in the autoimmunity scenario

Autophagy is a physiological cellular mechanism that degrades and recycles proteins and other molecules to maintain an adequate amino acid level during nutritional starvation of the cell. Autophagy is involved in cellular homeostasis and differentiation, as well as in tissue remodeling, aging, cancer, and other diseases. Under particular environmental conditions, autophagy can also be a contributor to programmed cell death, or can act as a defense mechanism for the elimination of intracellular bacteria and viruses. According to recent experimental data, autophagy may be implicated in autoimmunity by promotion of major histocompatibility complex (MHC) class II presentation of cytosolic antigens and control of T lymphocyte homeostasis, and its induction by Th1 cytokines and perhaps by specific serum autoantibodies. We review herein the role of autophagy in immune function and its possible contribution to breakdown of tolerance and development of autoimmunity.

Y chromosome loss in male patients with primary biliary cirrhosis

Sex chromosome abnormalities have been advocated to be involved in the striking female prevalence of primary biliary cirrhosis (PBC) and women with PBC manifest an increased X chromosome loss in peripheral blood mononuclear cells compared to age-matched healthy women. Our knowledge of the etiopathogenesis of autoimmunity in male patients remains, however, limited. Next to the possible role of androgens and their imbalances, the Y chromosome appears as a potential candidate for influence of the immune function in men. Herein we analyzed a population of male patients with primary biliary cirrhosis (n = 26) and healthy controls (n = 88) to define a potential association of disease and the loss of the Y chromosome. We demonstrate that Y chromosome loss indeed is higher in PBC males compared to healthy controls, and this phenomenon increases with aging. We were, thus, able to confirm the existence of an analogous mechanism in the male population to previously identified X haploinsufficiency in female patients with organ-specific autoimmune disease. We propose that this commonality might represent a relevant feature in the etiopathogenesis of autoimmune diseases that should be further investigated.

DNA methylation profiling of the X chromosome reveals an aberrant demethylation on CXCR3 promoter in primary biliary cirrhosis

BACKGROUND

Although the etiology of primary biliary cirrhosis (PBC) remains enigmatic, there are several pieces of data supporting the thesis that a strong genetic predisposition and environmental factors interact to produce a selective loss of tolerance. The striking female predominance of PBC has suggested that this sex predisposition may be secondary to epigenetic alterations on the X chromosome. In the present study, we rigorously defined the X chromosome methylation profile of CD4, CD8, and CD14 cells from 30 PBC patients and 30 controls. Genomic DNA from sorted CD4, CD8, and CD14 subpopulations was isolated, sonicated, and immunoprecipitated for analysis of methylation. All products were hybridized to a custom-tiled four-plex array containing 27,728 CpG islands annotated by UCSC and 22,532 well-characterized RefSeq promoter regions. Furthermore, bisulfite sequencing was then used for validation on a subsequent group of independent samples from PBC patients and controls. Thence, expression levels of selected X-linked genes were evaluated by quantitative real-time PCR with cDNA samples from all subjects.

RESULTS

We report herein that a total of 20, 15, and 19 distinct gene promoters reflected a significant difference in DNA methylation in CD4+ T, CD8+ T, and CD14+ cells in patients with PBC. Interestingly, there was hypermethylation of FUNDC2 in CD8+ T cells and a striking demethylation of CXCR3 in CD4+ T cells, which inversely correlated with CXCR3 expression levels in CD4+ T cells from early-stage PBC patients.

CONCLUSIONS

Our data provides a set of genes with epigenetic alteration likely to be indicators of autoimmunity and emphasizes the role of CXCR3 in the natural history of PBC.

Shotgun proteomics: identification of unique protein profiles of apoptotic bodies from biliary epithelial cells

Shotgun proteomics is a powerful analytic method to characterize complex protein mixtures in combination with multidimensional liquid chromatography-tandem mass spectrometry (LC-MS/MS). We used this platform for proteomic characterization of apoptotic bodies in an effort to define the complex protein mixtures found in primary cultures of human intrahepatic biliary epithelial cells (HiBEC), human renal proximal tubular epithelial cells, human bronchial epithelial cells, isolated intrahepatic biliary epithelial cells from explanted primary biliary cirrhosis (PBC), and control liver using a total of 24 individual samples. Further, as additional controls and for purposes of comparison, proteomic signatures were also obtained from intact cells and apoptotic bodies. The data obtained from LC-MS/MS, combined with database searches and protein assembly algorithms, allowed us to address significant differences in protein spectral counts and identify unique pathways that may be a component of the induction of the signature inflammatory cytokine response against BECs, including the Notch signaling pathway, interleukin (IL)8, IL6, CXCR2, and integrin signaling. Indeed, there are 11 proteins that localize specifically to apoptotic bodies of HiBEC and eight proteins that were specifically absent in HiBEC apoptotic bodies.

CONCLUSION

Proteomic analysis of BECs from PBC liver compared to normal liver are significantly different, suggesting that an immunological attack affects the repertoire of proteins expressed and that such cells should be thought of as living in an environment undergoing continuous selection secondary to an innate and adaptive immune response, reflecting an almost "Darwinian" bias.

Primary biliary cholangitis: a comprehensive overview

Primary biliary cholangitis (PBC) is an autoimmune liver disease characterized by biliary destruction, progressive cholestasis, and potentially liver cirrhosis. Patients develop a well-orchestrated immune reaction, both innate and adaptive, against mitochondrial antigens that specifically targets intrahepatic biliary cells. A puzzling feature of PBC is that the immune attack is predominantly organ specific, although the mitochondrial autoantigens are found in all nucleated cells. The disease results from a combination of genetic and environmental risk factors; however, the exact pathogenesis remains unclear. Serologically, PBC is characterized by presence of antimitochondrial antibodies, which are present in 90-95 % of patients and are often detectable years before clinical signs appear. Like other complex disorders, PBC is heterogeneous in its presentation, symptomatology, disease progression, and response to therapy. A significant number of patients develop end-stage liver disease and eventually require liver transplantation. Recent studies from large international cohorts have better identified prognostic factors, suggesting a change in patient management based on risk stratification. Therapeutic options are changing. In this review we discuss data on the autoimmune responses and treatment of the disease.

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 mimetopes 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.

Autoimmunity and Turner's syndrome

Turner Syndrome (TS) is a common genetic disorder, affecting female individuals, resulting from the partial or complete absence of one sex chromosome, and occurring in approximately 50 per 100,000 liveborn girls. TS is associated with reduced adult height and with gonadal dysgenesis, leading to insufficient circulating levels of female sex steroids and to infertility. Morbidity and mortality are increased in TS but average intellectual performance is within the normal range. TS is closely associated to the presence of autoantibodies and autoimmune diseases (AID), especially autoimmune thyroiditis and inflammatory bowel disease. Despite the fact that the strong association between TS and AID is well known and has been widely studied, the underlying immunopathogenic mechanism remains partially unexplained. Recent studies have displayed how TS patients do not show an excess of immunogenic risk markers. This is evocative for a higher responsibility of X-chromosome abnormalities in the development of AID, and particularly of X-genes involved in immune response. For instance, the long arm of the X chromosome hosts a MHC-locus, so the loss of that region may lead to a deficiency in immune regulation. Currently no firm guidelines for diagnosis exist. In conclusion, TS is a condition associated with a number of autoimmune manifestations. Individuals with TS need life-long medical attention. As a consequence of these findings, early diagnosis and regular screening for potential associated autoimmune conditions are essential in the medical follow-up of TS patients.

Predictors of hepatocellular carcinoma in HCV cirrhotic patients treated with direct acting antivirals

BACKGROUND

Despite the dramatic improvement in viral eradication rates that has been reached with direct antiviral agents (DAAs), the real benefit of viral eradication after DAAs on hepatocellular carcinoma (HCC) development is still controversial.

AIM

To prospectively assess the risk of HCC occurrence and early recurrence in a large cohort of DAA-treated HCV-cirrhotic patients and to identify potential predictors of HCC development.

METHODS

We analyzed data prospectively collected from 1927 consecutive HCV-infected cirrhotic patients treated with DAA from January to December 2015 in 10 tertiary liver centers in Italy and followed-up for one year after therapy. 161 patients had a previous HCC.

RESULTS

38/161 subjects developed tumor recurrence during the follow-up (recurrence rate = 24.8 per 100-year), patients with SVR had a significantly lower rate of recurrence. Lack of SVR and alpha-fetoprotein (AFP) were independent predictors of HCC recurrence. 50/1766 patients without a previous HCC history developed HCC during follow-up (incidence rate = 2.4 per 100-year). Lack of SVR was the strongest predictor of HCC development. Furthermore, patients with SVR and no stigmata of portal hypertension have a lower incidence rate of HCC (1.0 per 100-year).

CONCLUSIONS

SVR is associated with a significant decrease of recurrent or de novo HCC. Baseline AFP and signs of portal hypertension can help to stratify the risk of HCC.

Role of cholangiocytes in primary biliary cirrhosis

Primary biliary cirrhosis (PBC) is an autoimmune liver disease characterized by selective destruction of intrahepatic cholangiocytes. Mechanisms underlying the development and progression of the disease are still controversial and largely undefined. Evidence suggests that PBC results from an articulated immunologic response against an immunodominant mitochondrial autoantigen, the E2 component of the pyruvate dehydrogenase complex (PDC-E2); characteristics of the disease are also the presence of disease-specific antimitochondrial autoantibodies (AMAs) and autoreactive CD4 and CD8 T cells. Recent evidence suggests that cholangiocytes show specific immunobiological features that are responsible for the selective targeting of those cells by the immune system. The immune reaction in PBC selectively targets small sized, intrahepatic bile ducts; although a specific reason for that has not been defined yet, it has been established that the biliary epithelium displays a unique heterogeneity, for which the physiological and pathophysiological features of small and large cholangiocytes significantly differ. In this review article, the authors provide a critical overview of the current evidence on the role of cholangiocytes in the immune-mediated destruction of the biliary tree that characterizes PBC.

Hepatotoxicity of immune check point inhibitors: Approach and management

Therapeutic reversal of immune tolerance following immune checkpoint inhibitors (ICPI) administration, has proven effective in prolonging survival of patients with a variety of solid and liquid tumors, often however at the expenses of discrete toxicities known as immune-related adverse events (AEs). Such reactions result from activation of the immune system and often present with generalized symptoms including fatigue or fever and, in some patients, may cause organ-specific damage. Skin, gut, endocrine, lung and musculoskeletal are the most frequent targets of ICPI toxicity whereas, cardiovascular, hematologic, renal, neurologic and ophthalmologic AEs occur much less frequently. While the majority of AEs are mild to moderate, serious, occasionally life-threatening reactions have been reported, including severe colitis, pneumonitis, encephalitis, toxic epidermal necrolysis, myocarditis, and diabetic ketoacidosis, with a death toll of 2%. Hepatocellular carcinoma (HCC) is becoming an attractive area for immunotherapy. Owing to the fact that the association of HCC with cirrhosis may jeopardize tolerability of ICPI therapy, attention has been paid to identifying, preventing, and treating the AEs associated with ICPI, with a focus on liver safety. Though in most studies AEs resolved with interruption of treatment and short course of steroids, identification of predictive biomarkers of response might help sparing patients from potentially life-threatening toxicity in the absence of clinical benefit.

Primary biliary cirrhosis and autoimmune hepatitis: apotopes and epitopes

Autoimmune liver diseases (ALDs) represent a wide spectrum of chronic inflammatory diseases that are characterized by an immune-mediated attack against either hepatocytes (in the case of autoimmune hepatitis types 1 and 2, AIH-1, 2) or cholangiocytes (in primary biliary cirrhosis, PBC). PBC is considered a model autoimmune disease due to the homogeneity of patients, the high specificity of antimitochondrial antibodies (AMAs), and the specificity of biliary epithelial cell (BEC) destruction. It ensues from a multi-lineage loss of tolerance to the E2 component of the pyruvate dehydrogenase complex (PDC-E2). One of the major unanswered questions in the pathogenesis of PBC is the specificity of small intrahepatic bile duct attack while PDC-E2 is present in mitochondria of nucleated cells. Recent findings suggest that the apoptosis of BECs may be of considerable importance for understanding PBC, and that they are more than simply an innocent victim of an immune attack. Rather, they attract immune attack by virtue of the unique biochemical mechanisms by which they handle PDC-E2. The role of apoptotic cells in AIH is not well defined, but advances in the study of autoreactive T cells stem mostly from AIH type 2, where the main autoantigen (CYP2D6) is known, enabling the characterization of antigen-specific immune responses. This review article is intended to provide a critical overview of current evidence on tissue specificity in ALDs, as well as the characteristics of the relevant epitopes and apotopes and their biological and clinical significance.

The risk of liver cancer in autoimmune liver diseases

Hepatocellular carcinoma (HCC), the dominant primary malignancy of the liver, has almost invariably a fatal outcome that can be averted only by early diagnosis and treatment. While the close association of HCC with chronic viral hepatitis and alcohol abuse has impacted favourably on screening and treatment of this deadly tumour, at the same time it has long obscured the etiologic role of autoimmune liver diseases. Recently, a systematic analysis of 25 published cohorts disclosed a 3.1 × 1000 patients/year incidence of HCC in autoimmune hepatitis patients that tripled in those with cirrhosis. HCC is also a sequela of primary biliary cholangitis, where the incidence is more relevant in males, those with advanced liver disease and nonresponders to ursodeoxycholic acid therapy. Cholangiocarcinoma (CCA), the second ranking primary cancer of the liver, is also on the rise with its intrahepatic pattern, in part reflecting an association with chronic liver diseases of diverse aetiology. In the USA and northern Europe, perihilar CCA is a frequent complication of primary sclerosing cholangitis, a cholestatic disorder thought to be immune mediated. International Guidelines clearly recommend HCC screening with abdominal ultrasonography every 6 months in autoimmune cirrhotic patients. While surveillance of patients with autoimmune liver disorders who are at risk of HCC affects both early diagnosis and radical therapy of this tumour, this is not the case for CCA, where early diagnosis is challenged by the lack of sensitive and accurate tests for screening.

Apotopes and innate immune system: novel players in the primary biliary cirrhosis scenario

Our understanding of primary biliary cirrhosis has been rapidly growing over the past decade and the disease is now regarded as a model for other female-predominant, organ-specific autoimmune conditions. Primary biliary cirrhosis ensues from a multi-lineage loss of tolerance to the E2 component of the pyruvate dehydrogenase complex. One of the major unanswered questions in the pathogenesis of primary biliary cirrhosis is the specificity of small intrahepatic bile ducts attack while PDC-E2 is present in mitochondria of all nucleated cells. Recent findings suggest that the uniqueness of the primary target tissue, biliary epithelium, may be of considerable importance for understanding primary biliary cirrhosis and that the biliary epithelial cell is more than an innocent victim. Rather, it attracts an immune attack by virtue of the unique apoptotic mechanisms and by the way it handles PDC-E2. Moreover, recent evidence suggests that apoptotic bodies of biliary epithelial cell are able to activate the innate immune system in the presence of anti-mitochondrial antibodies. This review article is intended to provide a critical overview of the role of apoptosis in biliary epithelial cells, the activation of the innate immune system, and its biological and clinical significance in primary biliary cirrhosis.

Quantitation of the Rank-Rankl Axis in Primary Biliary Cholangitis

There is substantial data that suggests an abnormality of innate immunity in patients with primary biliary cholangitis (PBC) which includes the transcription factor nuclear factor-kB (NF-kB) and well as downstream inflammatory signaling pathways. In addition, ImmunoChip analysis has identified a novel PBC-associated locus near the receptor activator of NF-kB ligand (RANKL) gene. Based on these observations, we investigated the role of the RANKL axis in the liver of patients with PBC compared to controls. We used immunohistochemistry to quantitate liver expression of RANKL, its receptor (RANK), and importantly the decoy receptor osteoprotegerin (OPG), including a total of 122 liver samples (PBC = 37, primary sclerosing cholangitis = 20, autoimmune hepatitis = 26, chronic hepatitis B = 32 and unaffected controls = 7). In addition, we studied RANKL-RANK-OPG co-localization in CD4 and CD8 T cells, B cells, dendritic cells, macrophages, NK, NKT cells, hepatocytes, and cholangiocytes. We report herein that RANK is constitutively expressed by cholangiocytes in both unaffected and diseased liver. However, cholangiocytes from PBC express significantly higher levers of RANK than either the unaffected controls or liver diseased controls. CD4, CD8 and CD19 cells with in the portal areas around bile ducts in PBC express significantly higher levels of RANKL compared to controls. Importantly, the overall hepatic RANKL level and the ratio of hepatic RANKL/OPG correlated with disease severity in PBC. In conclusion, our data indicate a role of RANK-RANKL axis in the innate immune activation in PBC and we hypothesize that the damaged cholangiocytes, which express high levels of RANK, lead to the recruitment of RANKL positive cells and ultimately the classic portal tract infiltrates.