Human leukocyte antigen in primary biliary cirrhosis: an old story now reviving

How could our genetics impact COVID-19 vaccine response?

INTRODUCTION

The COVID-19 pandemic, caused by the SARS-CoV-2 virus, has posed unprecedented global health challenges since its emergence in December 2019. The rapid availability of vaccines has been estimated to save millions of lives, but there is variation in how individuals respond to vaccines, influencing their effectiveness at an individual, and population level.

AREAS COVERED

This review focuses on human genetic factors influencing the immune response and effectiveness of vaccines, highlighting the importance of associations across the HLA locus. Genome-Wide Association Studies (GWAS) and other genetic association analyses have identified statistically significant associations between specific HLA alleles including HLA-DRB1*13, DBQ1*06, and A*03 impacting antibody responses and the risk of breakthrough infections post-vaccination. Relationships between these associations and potential mechanisms and links with risks of natural infection or disease are explored, and this review concludes by emphasizing how understanding the mechanisms of these genetic determinants may inform the development of tailored vaccination strategies.

EXPERT OPINION

Although complex, we believe these findings from the SARS-CoV2 pandemic offer a unique opportunity to understand the relationships between HLA and infection and vaccine response, with a goal of optimizing individual protection against COVID-19 in the ongoing pandemic, and possibly influencing wider vaccine development in the future.

Sequence of events leading to primary biliary cholangitis

Primary biliary cholangitis (PBC) is a chronic cholestatic liver disease that is observed more frequently in middle-aged women. This disorder is considered an autoimmune disease, since liver injury is sustained by the presence of self-directed antimitochondrial antibodies targeting the bile duct cells. The prognosis may vary depending on an early diagnosis and response to therapy. However, nearly a third of patients can progress to liver cirrhosis, thus requiring a liver transplant. Traditional immunosuppressive therapies, commonly employed for other autoimmune diseases, have limited effects on PBC. In fact, dramatic functional changes that occur in the biliary epithelium in the course of inflammation play a major role in perpetuating the injury. In this minireview, after a background on the disease and possible predisposing factors, the sequential cooperation of cellular/molecular events leading to end-stage PBC is discussed in detail. The rise and maintenance of the autoimmune process, as well as the response of the biliary epithelia during inflammatory injury, are key factors in the progression of the disease. The so-called "ductular reaction (DR)", intended as a reactive expansion of cells with biliary phenotype, is a process frequently observed in PBC and partially understood. However, recent findings suggest a strict relationship between this pathological picture and the progression to liver fibrosis, cell senescence, and loss of biliary ducts. All these issues (onset of chronic inflammation, changes in secretive and proliferative biliary functions, DR, and its relationship with other pathological events) are discussed in this manuscript in an attempt to provide a snapshot, for clinicians and researchers, of the most relevant and sequential contributors to the progression of this human cholestatic disease. We believe that interpreting this disorder as a multistep process may help identify possible therapeutic targets to prevent evolution to severe disease.

X Chromosome Contribution to the Genetic Architecture of Primary Biliary Cholangitis

BACKGROUND & AIMS

Genome-wide association studies in primary biliary cholangitis (PBC) have failed to find X chromosome (chrX) variants associated with the disease. Here, we specifically explore the chrX contribution to PBC, a sexually dimorphic complex autoimmune disease.

METHODS

We performed a chrX-wide association study, including genotype data from 5 genome-wide association studies (from Italy, United Kingdom, Canada, China, and Japan; 5244 case patients and 11,875 control individuals).

RESULTS

Single-marker association analyses found approximately 100 loci displaying P < 5 × 10-4, with the most significant being a signal within the OTUD5 gene (rs3027490; P = 4.80 × 10-6; odds ratio [OR], 1.39; 95% confidence interval [CI], 1.028-1.88; Japanese cohort). Although the transethnic meta-analysis evidenced only a suggestive signal (rs2239452, mapping within the PIM2 gene; OR, 1.17; 95% CI, 1.09-1.26; P = 9.93 × 10-8), the population-specific meta-analysis showed a genome-wide significant locus in East Asian individuals pointing to the same region (rs7059064, mapping within the GRIPAP1 gene; P = 6.2 × 10-9; OR, 1.33; 95% CI, 1.21-1.46). Indeed, rs7059064 tags a unique linkage disequilibrium block including 7 genes: TIMM17B, PQBP1, PIM2, SLC35A2, OTUD5, KCND1, and GRIPAP1, as well as a superenhancer (GH0XJ048933 within OTUD5) targeting all these genes. GH0XJ048933 is also predicted to target FOXP3, the main T-regulatory cell lineage specification factor. Consistently, OTUD5 and FOXP3 RNA levels were up-regulated in PBC case patients (1.75- and 1.64-fold, respectively).

CONCLUSIONS

This work represents the first comprehensive study, to our knowledge, of the chrX contribution to the genetics of an autoimmune liver disease and shows a novel PBC-related genome-wide significant locus.

Fibrotic Events in the Progression of Cholestatic Liver Disease

Cholestatic liver diseases including primary biliary cholangitis (PBC) and primary sclerosing cholangitis (PSC) are associated with active hepatic fibrogenesis, which can ultimately lead to the development of cirrhosis. However, the exact relationship between the development of liver fibrosis and the progression of cholestatic liver disease remains elusive. Periductular fibroblasts located around the bile ducts seem biologically different from hepatic stellate cells (HSCs). The fibrotic events in these clinical conditions appear to be related to complex crosstalk between immune/inflammatory mechanisms, cytokine signalling, and perturbed homeostasis between cholangiocytes and mesenchymal cells. Several animal models including bile duct ligation (BDL) and the Mdr2-knockout mice have improved our understanding of mechanisms underlying chronic cholestasis. In the present review, we aim to elucidate the mechanisms of fibrosis in order to help to identify potential diagnostic and therapeutic targets.

Environmental risk factors and comorbidities of primary biliary cholangitis in Korea: a case-control study

BACKGROUND/AIMS

The risk factors for the development of primary biliary cholangitis (PBC) is unclear. This study aimed to investigate the risk factors associated with PBC in Korea through a questionnaire survey.

METHODS

Consecutively enrolled 103 PBC patients from six referral hospitals and 100 age- and sex-matched community controls participated in this study. A standardized questionnaire survey including demographics, lifestyle, individual and familial medical history and reproductive history was prospectively collected and analyzed.

RESULTS

The PBC patients had a mean age of 58.3 years and a female proportion of 86.4%. The age- and sex-matched controls had a similar educational level and economic status to the PBC patients. Among the lifestyle factors, the multivariable analysis showed smoking including both first-hand and second-hand (odds ratio [OR], 2.03; 95% confidence interval [CI], 1.06 to 3.93), history of autoimmune diseases (OR, 2.46; 95% CI, 1.06 to 6.35), and family history of PBC (OR, 17.76; 95% CI, 1.77 to 2,418.74) were significantly associated with PBC, whereas alcohol intake was negatively associated with PBC. Among reproductive factors, the number of induced abortions was significantly associated with PBC, while the number of full-term deliveries was negatively associated with PBC.

CONCLUSION

A family history of PBC, accompanying autoimmune diseases, and smoking were significantly associated with PBC. More induced abortions and less full-term deliveries were associated with PBC in women. In contrast, mild to moderate alcohol intake was negatively associated with PBC. Further studies are warranted to validate the results of this study and to search for clues about the pathogenesis of PBC.

Single Topic Conference on Autoimmune Liver Disease from the Canadian Association for the Study of the Liver

Autoimmune liver disease (AILD) spans a spectrum of chronic disorders affecting the liver parenchyma and biliary system. Three main categories of AILD are autoimmune hepatitis (AIH), primary biliary cirrhosis (PBC), and primary sclerosing cholangitis (PSC). This review condenses the presentation and discussions of the Single Topic Conference (STC) on AILD that was held in Ottawa, Ontario, in November 2019. We cover generalities regarding disease presentation and clinical diagnosis; mechanistic themes; treatment paradigms; clinical trials, including approaches and challenges to new therapies; and looking beyond traditional disease boundaries. Although these diseases are considered autoimmune, the etiology and role of environmental triggers are poorly understood. AILDs are progressive and chronic conditions that affect survival and quality of life. Advances have been made in PBC treatment because second-line treatments are now available (obeticholic acid, bezafibrate); however, a significant proportion still present suboptimal response. AIH treatment has remained unchanged for several decades, and data suggest that fewer than 50% of patients achieve a complete response and as many as 80% develop treatment-related side effects. B-cell depletion therapy to treat AIH is in an early stage of development and has shown promising results. An effective treatment for PSC is urgently needed. Liver transplant remains the best option for patients who develop decompensated cirrhosis or hepatocellular carcinoma within specific criteria, but recurrent AILD might occur. Continued efforts are warranted to develop networks for AILD aimed at assessing geo-epidemiological, clinical, and biochemical differences to capture the new treatment era in Canada.

Primary Biliary Cholangitis and Bile Acid Farnesoid X Receptor Agonists

Primary biliary cholangitis (PBC) is a chronic autoimmune liver disease characterized by the progressive destruction of the intrahepatic bile ducts. Currently, the first line drug for PBC is ursodeoxycholic acid (UDCA) characterized by anti-apoptotic, anti-inflammatory and protective actions on cholangiocytes. Despite its recognized therapeutic action, 30–40% of PBC patients only partially benefit from UDCA therapy. This has led to the identification of the role of the farnesoid x receptor (FXR) in cholestatic liver diseases and, consequently, to the development of obeticholic acid (OCA), a steroid FXR agonist that has been recently approved for the treatment of PBC. OCA though is not effective in all patients and can cause itch, which eventually induces treatment drop out. Therefore, the search for new therapeutic strategies for PBC has begun. This review, in addition to summarizing the current treatments for PBC, provides overview of the chemical characteristics of new steroid FXR agonist candidates that could represent a future perspective for the treatment of PBC.

Primary biliary cholangitis: pathogenesis and therapeutic opportunities

Primary biliary cholangitis is a chronic, seropositive and female-predominant inflammatory and cholestatic liver disease, which has a variable rate of progression towards biliary cirrhosis. Substantial progress has been made in patient risk stratification with the goal of personalized care, including early adoption of next-generation therapy with licensed use of obeticholic acid or off-label fibrate derivatives for those with insufficient benefit from ursodeoxycholic acid, the current first-line drug. The disease biology spans genetic risk, epigenetic changes, dysregulated mucosal immunity and altered biliary epithelial cell function, all of which interact and arise in the context of ill-defined environmental triggers. A current focus of research on nuclear receptor pathway modulation that specifically and potently improves biliary excretion, reduces inflammation and attenuates fibrosis is redefining therapy. Patients are benefiting from pharmacological agonists of farnesoid X receptor and peroxisome proliferator-activated receptors. Immunotherapy remains a challenge, with a lack of target definition, pleiotropic immune pathways and an interplay between hepatic immune responses and cholestasis, wherein bile acid-induced inflammation and fibrosis are dominant clinically. The management of patient symptoms, particularly pruritus, is a notable goal reflected in the development of rational therapy with apical sodium-dependent bile acid transporter inhibitors.

Fine mapping of the MHC region identifies major independent variants associated with Han Chinese primary biliary cholangitis

The genetic association of primary biliary cholangitis with major histocompatibility complex (MHC) has been widely confirmed among different ethnicities. To map specific MHC region variants associated with PBC in a Han Chinese cohort, we imputed HLA antigens and amino acids (AA) in 1126 PBC cases and 1770 healthy control subjects using a Han-MHC reference database. We demonstrate that HLA-DRB1 and/or HLA-DQB1 contributed the strongest signals, and that HLA-DPB1 was a separate independent locus. Regression analyses with classical HLA alleles indicate that HLA-DQB1*03:01 or HLA-DQβ1-Pro55, HLA-DPB1*17:01 or HLA-DPβ1-Asp84 and HLA-DRB1*08:03 could largely explain MHC association with PBC. Forward stepwise regression analyses with HLA amino acid variants localize the major signals to HLA-DRβ1-Ala74, HLA-DQβ1-Pro55 and HLA-DPβ1-Asp84. Electrostatic potential calculations implicated AA variations at HLA-DQβ1 position 55 and HLA-DPβ1 position 84 as critical to peptide binding properties. Furthermore, although several critical Han Chinese AA variants differed from those shown in European populations, the predicted effects on antigen binding are likely to be very similar or identical and underlie the major component of MHC association with PBC.

HLA-DQA1 & DQB1 variants associated with hepatitis B virus-related chronic hepatitis, cirrhosis & hepatocellular carcinoma

Background & objectives:

Clinical outcome after hepatitis B virus (HBV) exposure varies extremely from spontaneous clearance to chronic hepatitis B and often progresses to liver cirrhosis (LC) and hepatocellular carcinoma (HCC). Host genetic factor plays an important role in the regulation of immune response. This study was aimed to investigate whether HLA class II DQA1 and DQB1 gene polymorphism were associated with chronic hepatitis B infection and in the development of HBV-related LC and HCC.

Methods:

DQA1 and DQB1 allele polymorphism were studied in 187 patients with HBV-related liver diseases (which included 73 chronic hepatitis B, 84 LC and 30 HCC patients) and 109 controls who had spontaneously recovered from HBV infection using polymerase chain reaction amplification with sequence-specific primers.

Results:

Our data suggested that DQA1*0101/2/4 [odds ratio (OR)=2.78; P^c=0.003], DQA1*0103 (OR=2.64; P^c=0.0007) and DQB1*0302/3 (OR=2.15; P^c=0.01) were associated with the protection from chronic HBV infection, whereas DQB1*0402 (OR=0.25; P^c=0.001) showed susceptible effect on chronic HBV infection. DQB1*0601 (OR=3.73; P^c=0.006) conferred protective effect from developing LC; similarly, DQB1*0302/3 (OR=5.53; P^c=0.05) and DQB1*0402 (OR=0.00; P^c=0.001) conferred protective effect from developing HCC. However, DQA1*0601 and DQB1*0503 showed susceptible effect on chronic HBV infection; these associations were no longer significant after Bonferroni correction.

Interpretation & conclusions:

Our results revealed HLA-DQA1*0101/2/4 - DQA1*0103 - DQB1*0302/3 and DQB1*0601 as protective and DQB1*0402 as risk alleles. The study suggests that various subtypes of HLA-DQA1 and DQB1 are associated with both HBV clearance and development of chronic HBV infections.

The impact of human leukocyte antigen donor and recipient serotyping and matching on liver transplant graft failure in primary sclerosing cholangitis, autoimmune hepatitis, and primary biliary cholangitis

Human leukocyte antigen (HLA) serotyping is not considered to have significant impact on liver graft survival and does not factor into U.S. organ allocation. Immune-related liver diseases such as primary sclerosing cholangitis (PSC), autoimmune hepatitis (AIH), and primary biliary cholangitis (PBC) have been speculated to represent a disease subgroup that may have significantly different graft outcomes depending on HLA donor/recipient characterization. The aim of this study was to investigate whether HLA serotyping/matching influenced post-transplant graft failure for immune-related liver diseases using the United Network for Organ Sharing database. From 1994 to 2015, 5665 patients underwent first-time liver-only transplants for PSC, AIH, and PBC with complete graft survival and donor/recipient HLA data. Graft failure was noted in 38.6% (2188/5665), and all groups had comparable 5-year graft survival (75.1%-78.8%, P = 0.069). The overall degree of, and loci-specific mismatch level, did not influence outcomes. Multivariable Cox proportional hazards regression noted increased graft failure risk for recipient HLA-B7, HLA-B57, HLA-B75, HLA-DR13 and donor HLA-B55, HLA-B58, and HLA-DR8 for PSC patients, protective effects for recipient HLA-DR1 and HLA-DR3 for AIH patients, and increased risk for HLA-DR7 for AIH patients. These findings warrant further investigation to evaluate the impact of HLA serotyping on post-transplant outcomes.

NI-0801, an anti-chemokine (C-X-C motif) ligand 10 antibody, in patients with primary biliary cholangitis and an incomplete response to ursodeoxycholic acid

NI-0801 is a fully human monoclonal antibody against chemokine (C-X-C motif) ligand 10 (CXCL10), which is involved in the recruitment of inflammatory T cells into the liver. The safety and efficacy of NI-0801 was assessed in patients with primary biliary cholangitis. In this open-label phase 2a study, patients with primary biliary cholangitis with an inadequate response to ursodeoxycholic acid received six consecutive intravenous administrations of NI-0801 (10 mg/kg) every 2 weeks. Patients were followed up for 3 months after the last infusion. Liver function tests, safety assessments, as well as pharmacokinetic and pharmacodynamic parameters were evaluated at different time points throughout the dosing period and the safety follow-up period. Twenty-nine patients were enrolled in the study and were treated with NI-0801. The most frequently reported adverse events included headaches (52%), pruritus (34%), fatigue (24%), and diarrhea (21%). No study drug-related serious adverse events were reported. NI-0801 administration did not lead to a significant reduction in any of the liver function tests assessed at the end of the treatment period (i.e., 2 weeks after final NI-0801 administration) compared to baseline. Conclusion: Despite clear pharmacologic responses in the blood, no therapeutic benefit of multiple administrations of NI-0801 could be demonstrated. The high production rate of CXCL10 makes it difficult to achieve drug levels that lead to sustained neutralization of the chemokine, thus limiting its targetability. (Hepatology Communications 2018;2:492-503).

Principal contribution of HLA-DQ alleles, DQB1*06:04 and DQB1*03:01, to disease resistance against primary biliary cholangitis in a Japanese population

Identification of the primary allele(s) in HLA class II associated diseases remains challenging because of a tight linkage between alleles of HLA-DR and -DQ loci. In the present study, we determined the genotypes of seven HLA loci (HLA-A, -B, -DRB1, -DQA1, -DQB1, -DPA1 and -DPB1) for 1200 Japanese patients with primary biliary cholangitis and 1196 controls. Observation of recombination derivatives facilitated an evaluation of the effects of individual HLA alleles consisting of disease-prone/disease-resistant HLA haplotypes. Consequently, a primary contribution of DQB1*06:04 (odds ratio: 0.19, p = 1.91 × 10⁻²²), DQB1*03:01 (odds ratio: 0.50, p = 6.76 × 10⁻¹⁰), DRB1*08:03 (odds ratio: 1.75, p = 1.01 × 10⁻⁷) and DQB1*04:01 (odds ratio: 1.50, p = 9.20 × 10⁻⁶) was suggested. Epistasis of the protective DQB1*06:04 to risk conferred by DRB1*08:03 was demonstrated by subpopulation analysis, implicating the presence of an active immunological mechanism that alleviates pathogenic autoimmune reactions. Further, the contribution of the aforementioned HLA alleles as well as an HLA-DP allele, DPB1*02:01 to the association signals of 304 loci among 4103 SNPs in the HLA region at the genome-wide level of significance (p values less than 5 × 10⁻⁸) was demonstrated by the stepwise exclusion of the individuals possessing these HLA alleles from the comparison.

The epigenetics of PBC: The link between genetic susceptibility and environment

Primary biliary cholangitis (PBC) previously known as primary biliary cirrhosis is an autoimmune disease-associated with progressive cholestasis, the presence of autoreactive T cell and characteristic serological autoantibodies. Genetic and genome-wide association studies (GWAS) have recently shed light on the genetic background of PBC. Besides that some causal nucleotide changes and mechanisms remain largely unknown as suggested for example, by the observation that monozygotic twins have an identical DNA sequence even if presents some phenotypic differences that may be consequences of different exposures to environmental stressors. For this reason, it is believed that epigenetic mechanisms may be involved in PBC pathogenesis, as already demonstrated in many autoimmune diseases and can eventually provide an understanding that has been missed from genetics alone. This review will focus on the most commonly studied epigenetic modifications already demonstrated in PBC; special attention will be paid also to other epigenetic mechanisms so far not demonstrated in PBC patients, but that could increase our understanding in PBC pathogenesis.

Relationship between HLA-DRB1 allele polymorphisms and familial aggregations of hepatocellular carcinoma

OBJECTIVE

We explored the relationship between HLA-DRB1 allele polymorphisms and familial aggregation of hepatocellular carcinoma (fhcc).

METHODS

Polymerase chain reaction sequence-specific primers were used to determine HLA-DRB1 genotypes for 130 members of families with 2 or more liver cancer patients and for 130 members of families without any diagnosed cancers. The genotype profiles were then compared to explore the relationship between HLA-DRB1 gene polymorphism and fhcc.

RESULT

Of 11 selected alleles, the frequencies of DRB1*11 and DRB1*12 were significantly lower in the fhcc group than in no-cancer group (p < 0.05; odds ratio: 0.286; 95% confidence interval: 0.091 to 0.901; and odds ratio: 0.493; 95% confidence interval: 0.292 to 0.893). Differences in the frequencies of the other 9 alleles were not statistically significant in the two groups (p > 0.05).

CONCLUSIONS

Our research suggests that if genetic factors play a role in fhcc, the deficiency in the DRB1*11 and DRB1*12 alleles might be the risk factor at work in Guangxi Zhuang Autonomous Region, P.R.C.

A Common Variant in CLDN14 is Associated with Primary Biliary Cirrhosis and Bone Mineral Density

Primary biliary cirrhosis (PBC), a chronic autoimmune liver disease, has been associated with increased incidence of osteoporosis. Intriguingly, two PBC susceptibility loci identified through genome-wide association studies are also involved in bone mineral density (BMD). These observations led us to investigate the genetic variants shared between PBC and BMD. We evaluated 72 genome-wide significant BMD SNPs for association with PBC using two European GWAS data sets (n = 8392), with replication of significant findings in a Chinese cohort (685 cases, 1152 controls). Our analysis identified a novel variant in the intron of the CLDN14 gene (rs170183, Pfdr = 0.015) after multiple testing correction. The three associated variants were followed-up in the Chinese cohort; one SNP rs170183 demonstrated consistent evidence of association in diverse ethnic populations (Pcombined = 2.43 × 10(-5)). Notably, expression quantitative trait loci (eQTL) data revealed that rs170183 was correlated with a decline in CLDN14 expression in both lymphoblastoid cell lines and T cells (Padj = 0.003 and 0.016, respectively). In conclusion, our study identified a novel PBC susceptibility variant that has been shown to be strongly associated with BMD, highlighting the potential of pleiotropy to improve gene discovery.

The Immunogenetics of Autoimmune Cholestasis

The immune-mediated hepatobiliary diseases, primary biliary cirrhosis and primary sclerosing cholangitis are relatively rare, albeit and account for a significant amount of liver transplant activity and liver-related mortality globally. Precise disease mechanisms are yet to be described although a contributory role of genetic predisposition is firmly established. In addition to links with the major histocompatibility complex, a number of associations outside this region harbor additional loci which underscore the fundamental role of breaks in immune tolerance and mucosal immunogenicity in the pathogenesis of autoimmune biliary disease. We provide an overview of these key discoveries before discussing putative avenues of therapeutic exploitation based on existing findings.

Exploring the Role of Killer Cell Immunoglobulin-Like Receptors and Their HLA Class I Ligands in Autoimmune Hepatitis

Background

Natural killer cells are involved in the complex mechanisms underlying autoimmune diseases but few studies have investigated their role in autoimmune hepatitis. Killer immunoglobulin-like receptors are key regulators of natural killer cell-mediated immune responses.

Methods and Findings

KIR gene frequencies, KIR haplotypes, KIR ligands and combinations of KIRs and their HLA Class I ligands were investigated in 114 patients diagnosed with type 1 autoimmune hepatitis and compared with a group of 221 healthy controls. HLA Class I and Class II antigen frequencies were compared to those of 551 healthy unrelated families representative of the Sardinian population. In our cohort, type 1 autoimmune hepatitis was strongly associated with the HLA-B18, Cw5, DR3 haplotype. The KIR2DS1 activating KIR gene and the high affinity HLA-C2 ligands were significantly higher in patients compared to controls. Patients also had a reduced frequency of HLA-Bw4 ligands for KIR3DL1 and HLA-C1 ligands for KIR2DL3. Age at onset was significantly associated with the KIR2DS1 activating gene but not with HLA-C1 or HLA-C2 ligand groups.

Conclusions

The activating KIR gene KIR2DS1 resulted to have an important predictive potential for early onset of type 1 autoimmune hepatitis. Additionally, the low frequency of the KIR-ligand combinations KIR3DL1/HLA-Bw4 and KIR2DL3/HLA-C1 coupled to the high frequency of the HLA-C2 high affinity ligands for KIR2DS1 could contribute to unwanted NK cell autoreactivity in AIH-1.

Genome-Wide Association Studies in Primary Biliary Cirrhosis

Genome-wide association studies (GWASs) have been a significant technological advance in our ability to evaluate the genetic architecture of complex diseases such as primary biliary cirrhosis (PBC). To date, six large-scale studies have been performed that have identified 27 risk loci in addition to human leukocyte antigen (HLA) associated with PBC. The identified risk variants emphasize important disease concepts; namely, that disturbances in immunoregulatory pathways are important in the pathogenesis of PBC and that such perturbations are shared among a diverse number of autoimmune diseases-suggesting the risk architecture may confer a generalized propensity to autoimmunity not necessarily specific to PBC. Furthermore, the impact of non-HLA risk variants, particularly in genes involved with interleukin-12 signaling, and ethnic variation in conferring susceptibility to PBC have been highlighted. Although GWASs have been a critical stepping stone in understanding common genetic variation contributing to PBC, limitations pertaining to power, sample availability, and strong linkage disequilibrium across genes have left us with an incomplete understanding of the genetic underpinnings of disease pathogenesis. Future efforts to gain insight into this missing heritability, the genetic variation that contributes to important disease outcomes, and the functional consequences of associated variants will be critical if practical clinical translation is to be realized.

The genetics of human autoimmune disease: A perspective on progress in the field and future directions

Progress in defining the genetics of autoimmune disease has been dramatically enhanced by large scale genetic studies. Genome-wide approaches, examining hundreds or for some diseases thousands of cases and controls, have been implemented using high throughput genotyping and appropriate algorithms to provide a wealth of data over the last decade. These studies have identified hundreds of non-HLA loci as well as further defining HLA variations that predispose to different autoimmune diseases. These studies to identify genetic risk loci are also complemented by progress in gene expression studies including definition of expression quantitative trait loci (eQTL), various alterations in chromatin structure including histone marks, DNase I sensitivity, repressed chromatin regions as well as transcript factor binding sites. Integration of this information can partially explain why particular variations can alter proclivity to autoimmune phenotypes. Despite our incomplete knowledge base with only partial definition of hereditary factors and possible functional connections, this progress has and will continue to facilitate a better understanding of critical pathways and critical changes in immunoregulation. Advances in defining and understanding functional variants potentially can lead to both novel therapeutics and personalized medicine in which therapeutic approaches are chosen based on particular molecular phenotypes and genomic alterations.

Primary biliary cirrhosis: Clinical and laboratory criteria for its diagnosis

Primary biliary cirrhosis (PBC) is a chronic progressive cholestatic granulomatous, and destructive inflammatory lesion of small intralobular and septal bile ducts, which is likely to be caused by an autoimmune mechanism with a the presence of serum antimitochondrial antibodies and a potential tendency to progress to cirrhosis. Despite the fact that the etiology of this disease has been unknown so far, there has been a considerable body of scientific evidence that can reveal the clinical and laboratory signs of PBC and the individual components of its pathogenesis and elaborate diagnostic criteria for the disease and its symptomatic therapy. Deficiencies in autoimmune tolerance are critical factors for the initiation and perpetuation of the disease. The purpose of this review is to summarize the data available in the literature and the author’s findings on clinical and laboratory criteria for the diagnosis of PBC. This review describes the major clinical manifestations of the disease and the mechanisms of its development. It presents the immunological, biochemical, and morphological signs of PBC and their significance for its diagnosis. A great deal of novel scientific evidence for the problem of PBC has been accumulated. However, the inadequate efficiency of therapy for the disease lends impetus to the quest for its etiological factors and to further investigations of its pathogenetic mechanisms and, on this basis, to searches for new methods for its early diagnosis.

The cumulative effects of known susceptibility variants to predict primary biliary cirrhosis risk

Multiple genetic variants influence the risk for development of primary biliary cirrhosis (PBC). To explore the cumulative effects of known susceptibility loci on risk, we utilized a weighted genetic risk score (wGRS) to evaluate whether genetic information can predict susceptibility. The wGRS was created using 26 known susceptibility loci and investigated in 1840 UK PBC and 5164 controls. Our data indicate that the wGRS was significantly different between PBC and controls (P=1.61E-142). Moreover, we assessed predictive performance of wGRS on disease status by calculating the area under the receiver operator characteristic curve. The area under curve for the purely genetic model was 0.72 and for gender plus genetic model was 0.82, with confidence limits substantially above random predictions. The risk of PBC using logistic regression was estimated after dividing individuals into quartiles. Individuals in the highest disclosed risk group demonstrated a substantially increased risk for PBC compared with the lowest risk group (odds ratio: 9.3, P=1.91E-084). Finally, we validated our findings in an analysis of an Italian PBC cohort. Our data suggested that the wGRS, utilizing genetic variants, was significantly associated with increased risk for PBC with consistent discriminant ability. Our study is a first step toward risk prediction for PBC.

Fatigue and pruritus at onset identify a more aggressive subset of primary biliary cirrhosis

BACKGROUND & AIMS

In recent years, primary biliary cirrhosis is mostly diagnosed in patients who are asymptomatic; however, a proportion of cases still present with typical complaints such as fatigue and/or pruritus. We compared biochemical, histological and immunological features of patients with or without fatigue and/or pruritus at onset to see whether the different clinical presentation may eventually impact on disease progression.

METHODS

We analysed the Bologna cohort of 216 patients with primary biliary cirrhosis referred to our Centre between 1997 and 2007, according to symptomatic (fatigue and/or pruritus) or asymptomatic presentation. Clinical, biochemical, histological and immunological feature at diagnosis, response to ursodeoxycholic acid and progression of the disorder were compared after a mean follow-up of 81 ± 75 months.

RESULTS

At diagnosis, symptomatic patients were significantly more often women (98.6% vs. 87.2%, P = 0.004), younger (mean age 49 ± 12 vs. 55 ± 12 years, P = 0.003) and with more pronounced biochemical activity, as indicated by higher alkaline phosphatase (mean 2.93 ± 2 vs. 2.12, P = 0.002) and aminotransferase (mean 1.92 ± 1 vs. 1.47 ± 1.27, P = 0.014) levels, whereas histological stage and autoantibody profile were similar. Symptomatic patients were less likely to respond to ursodeoxycholic acid therapy (63% vs. 81%, P = 0.006) and developed more often cirrhosis and its complications (31% vs. 13%, P = 0.004).

CONCLUSIONS

Fatigue and/or pruritus at onset identify a subset of patients with primary biliary cirrhosis who preferentially are women, younger, with a particularly active disease, less responsive to ursodeoxycholic acid treatment, and more inclined to evolve to cirrhosis and its complications.

Genetics of autoimmune liver disease: a brief summary for clinicians

Autoimmune liver diseases are rare chronic immune-mediated liver injuries in which the consequences of hepatic and biliary inflammation are cirrhosis and end-stage liver disease. Epidemiological surveys of individuals, families and populations strongly support a model of disease for which environmental and genetic influences are highly relevant to why any individual develops disease. The overlapping clinical presentations of primary biliary cirrhosis, primary sclerosing cholangitis and autoimmune hepatitis further highlight the likelihood for shared pathways to disease. Of late, the application of high-throughput genetic technology, paralleled by large patient cohort development, has led to new insights into the nature of the host genetic risk. This risk is now robustly demonstrable for the HLA locus as well as in various non-HLA loci and is summarized in this brief review article.

Molecular mechanisms of liver injury: apoptosis or necrosis

Hepatic apoptosis is thought of as a prevalent mechanism in most forms of liver injury. However, the role of hepatic apoptosis is often intermixed with the cellular necrosis. It remains unknown how apoptosis is relevant to the progression of the liver injury. This review summarizes the characteristics of both hepatic apoptosis and necrosis in pathogenesis of liver diseases. Apoptosis and necrosis represent alternative outcomes of different etiology during liver injury. Apoptosis is a main mode of cell death in chronic viral hepatitis, but is intermingled with necrosis in cholestatic livers. Necrosis is the principal type of liver cell killing in acetaminophen-induced hepatotoxicity. Anti-apoptosis as a strategy is beneficial to liver repair response. Therapeutic options of liver disease depend on the understanding toward pathogenic mechanisms of different etiology.

HLA-DR polymorphism and primary biliary cirrhosis: evidence from a meta-analysis

BACKGROUND AND AIMS

We undertook this study to review and quantitatively analyze the association between human leukocyte antigen (HLA) DR polymorphisms and susceptibility of primary biliary cirrhosis (PBC).

METHODS

All relevant publications on the association between HLA-DR polymorphisms and PBC were searched through June 2013. Odds ratios (OR) and confidence intervals (CI) for the comparisons between case and control group were calculated. Statistical analysis was performed using Stata 11.0 software.

RESULTS

Nineteen articles (or 20 studies including the substudies) were identified. For DR*7 allele, the ORs (95% CIs) were 1.530 (1.310, 1.788), 1.757 (1.285, 2.403) and 1.495 (1.211, 1.845) in overall, Asian and European populations, respectively. For DR*8 alleles, the ORs (95% CIs) were 3.158 (1.822, 5.475), 2.803 (2.420, 3.247) and 3.056 (2.573, 3.629) in Asian, American and European subgroups, respectively. The subgroup analysis for DR*11 and DR*13 showed a significant association in Asian and European population. For DR*12 and *15 alleles, the overall ORs (95% CIs) were 0.551 (0.404, 0.753) and 0.721 (0.607, 0.857). However, in subgroup analysis for DR*12 allele, the association was only found in Asian population. In addition, statistical significance exists in American and European populations in the subgroup analysis for DR*15 allele.

CONCLUSION

Our meta-analysis suggested that HLA-DR *7 and *8 allele polymorphisms contributed to the susceptibility of PBC, whereas DR*11, *12, *13 and *15 allele polymorphisms are protective factors in certain population.

Implications of genome-wide association studies in novel therapeutics in primary biliary cirrhosis

Genome-wide association studies (GWAS) have revolutionized the search for genetic influences on complex disorders, such as primary biliary cirrhosis (PBC). Recent GWAS have identified many disease-associated genetic variants. These, overall, highlighted the remarkable contribution of key immunological pathways in PBC that may be involved in the initial mechanisms of loss of tolerance and the subsequent inflammatory response and chronic bile duct damage. Results from GWAS have the potential to be translated in biological knowledge and, hopefully, clinical application. There are a number of immune pathways highlighted in GWAS that may have therapeutic implications in PBC and in other autoimmune diseases, such as the anti-interleukin-12/interleukin-23, nuclear factor-kb, tumor necrosis factor, phosphatidylinositol signaling and hedgehog signaling pathways. Further areas in which GWAS findings are leading to clinical applications either in PBC or in other autoimmune conditions, include disease classification, risk prediction and drug development. In this review we outline the possible next steps that may help accelerate progress from genetic studies to the biological knowledge that would guide the development of predictive, preventive, or therapeutic measures in PBC.

Tracing environmental markers of autoimmunity: introducing the infectome

We recently introduced the concept of the infectome as a means of studying all infectious factors which contribute to the development of autoimmune disease. It forms the infectious part of the exposome, which collates all environmental factors contributing to the development of disease and studies the sum total of burden which leads to the loss of adaptive mechanisms in the body. These studies complement genome-wide association studies, which establish the genetic predisposition to disease. The infectome is a component which spans the whole life and may begin at the earliest stages right up to the time when the first symptoms manifest, and may thus contribute to the understanding of the pathogenesis of autoimmunity at the prodromal/asymptomatic stages. We provide practical examples and research tools as to how we can investigate disease-specific infectomes, using laboratory approaches employed from projects studying the “immunome” and “microbiome”. It is envisioned that an understanding of the infectome and the environmental factors that affect it will allow for earlier patient-specific intervention by clinicians, through the possible treatment of infectious agents as well as other compounding factors, and hence slowing or preventing disease development.

The association of HLA-DRB1 alleles and drug use with HIV infection in a Chinese Han Cohort

Objective

To investigate the relationship between the polymorphism of human leukocyte antigen (HLA)-DRB1 and the susceptibility and repellency of drug use combined with HIV infection in Chinese.

Methods

A total of 213 unrelated healthy people, 41 HIV-infected drug users, 24 HIV-uninfected drug users, and 64 HIV-infected non-drug users were recruited. Their HLA-DRB1 allele frequencies were analyzed by PCR-SSP and allele distribution was analyzed.

Results

Compared with healthy controls, in drug users, the frequencies of HLA-DRB1 *0401-041, *1001 were significantly higher; in HIV-infected patients, the frequencies of HLA-DRB1 *0101-0103, *0401-0411, *1001 were significantly higher, while the frequencies of DRB1 *1501-1502, *1101-1105, *1301-1302, DRB4, DRB5 were significantly lower; in HIV-infected drug users, the frequencies of HLA-DRB1 *0101-0103, *0401-0411, *0801-0806, *1001, *1401/1404/1405 were significantly higher, while the frequencies of DRB1 *1301/1302, 1501-1502, DRB5 were significantly lower.

Conclusion

There is close relationship between the polymorphism of HLA-DRB1 alleles and drug use with HIV infection, which plays an important role in elucidating the pathogenesis and providing the basis for therapeutics and prophylaxis of patients with drug use and HIV infection.

Liver immunology

The liver is the largest organ in the body and is generally regarded by nonimmunologists as having little or no lymphoid function. However, such is far from accurate. This review highlights the importance of the liver as a lymphoid organ. Firstly, we discuss experimental data surrounding the role of liver as a lymphoid organ. The liver facilitates tolerance rather than immunoreactivity, which protects the host from antigenic overload of dietary components and drugs derived from the gut and it is instrumental to fetal immune tolerance. Loss of liver tolerance leads to autoaggressive phenomena, which if not controlled by regulatory lymphoid populations, may lead to the induction of autoimmune liver diseases. Liver-related lymphoid subpopulations also act as critical antigen-presenting cells. The study of the immunological properties of liver and delineation of the microenvironment of the intrahepatic milieu in normal and diseased livers provides a platform to understand the hierarchy of a series of detrimental events that lead to immune-mediated destruction of the liver and the rejection of liver allografts. The majority of emphasis within this review will be on the normal mononuclear cell composition of the liver. However, within this context, we will discuss selected, but not all, immune-mediated liver disease and attempt to place these data in the context of human autoimmunity.

Association of human leukocyte antigen class II with susceptibility to primary biliary cirrhosis: a systematic review and meta-analysis

Purpose

Several previous studies suggested that HLA-ClassII may be associated with susceptibility to primary biliary cirrhosis (PBC), but data from individual studies remain controversial. Therefore, a systematic review and meta-analysis is needed to comprehensively evaluate the association between HLA-ClassII and PBC risk.

Methods

All published reports of an association between HLA class II and PBC risk were searched in PubMed, EMBASE (updated to 22 May 2012). ORs with 95% confidence intervals (CIs) were extracted from each included study and the meta-analysis was performed using the fixed- or random-effects model.

Results

A total of 3,732 PBC patients and 11,031 controls from 34 studies were included in the meta-analysis. An assessment of study quality revealed that the majority of studies included (18 studies) were of high quality. The serological group DR8 was found to be a risk factor for PBC (OR = 2.82, 95%CI: 1.84–4.30). At the allelic level, HLA-DR*08 and HLA-DR*0801 were identified as risk factors for PBC (OR = 2.30, 95%CI: 1.76-3.00; OR = 3.23, 95%CI: 2.22–4.70, respectively), whereas HLA-DR*11 and HLA-DR*13 were potent protective factors (OR = 0.31, 95%CI: 0.27-0.38; OR = 0.62, 95%CI: 0.48-0.81, respectively). HLA-DQB1 and HLA-DQB1*0402 conferred a predisposition to PBC development (OR = 3.47, 95%CI: 2.35–5.13), whereas HLA-DQB1*0604 was protective against PBC (OR = 0.3, 95%CI: 0.18–0.58). No HLA-DPB1 allele was observed to be associated with PBC susceptibility (P > 0.05).

Conclusions

The present study revealed that HLA-ClassII components are closely associated with the development of PBC.

Vitamin D in autoimmune liver disease

The development of autoimmune disease is based on the interaction of genetic susceptibility and environmental causes. Environmental factors include infectious and non-infectious agents, with some of these factors being implicated in several autoimmune diseases. Vitamin D is now believed to play a role in the development (or prevention) of several autoimmune diseases, based on its immunomodulatory properties. As well, the increasing incidence of autoimmune disease as one moves away from the equator, may be due to the lack of sunlight, which is crucial for the maintenance of normal vitamin D levels. A deficiency in vitamin D levels or vitamin D receptors is commonly indicated in autoimmune diseases, with multiple sclerosis (MS) being one of the best-studied and well-known examples. However, the role of vitamin D in other autoimmune diseases is not well defined, including autoimmune liver diseases such as primary biliary cirrhosis, autoimmune hepatitis, and primary sclerosing cholangitis. This review will examine the role of vitamin D as an immunomodulator, followed by a comparison of vitamin D in MS versus autoimmune liver disease. From this comparison, it will become clear that vitamin D likely plays a role in the development of autoimmune liver disease, but this area requires further investigation.

Liver auto-immunology: the paradox of autoimmunity in a tolerogenic organ

The study of the liver as a lymphoid organ is a growing field fueled by our better knowledge of the different component of the immune system and how they orchestrate an immune-related response. The liver have highly specialized mechanisms of immune tolerance, mainly because is continuously exposed to microbial and environmental antigens, and dietary components from the gut. Accordingly, the liver contains specialized lymphoid subpopulations acting as antigen-presenting cells. Growing evidences show that the liver is also associated with obesity-associated diseases because of its immune-related capacity to sense metabolic stress induced by nutritional surplus. Finally, the liver produces a pletora of neo-antigens being the primary metabolic organ of the body. Common immune mechanisms play a key pathogenetic role in most of acute and chronic liver diseases and in the rejection of liver allografts. Any perturbations of liver-related immune functions have important clinical implications. This issue of the Journal of Autoimmunity is focused on the more recent advances in our knowledge related to the loss of liver tolerance, a paradox for a tolerogenic organ, that leads to overactivation of the innate and adaptive immune response and the development of autoimmune liver diseases, such as autoimmune hepatitis, primary biliary cirrhosis, and primary sclerosing cholangitis. The invited expert review articles capture the underlying immunomolecular mechanisms of the development and progression of autoimmune liver diseases, the novel field of the immune-related "liver-gut" axis influences to the development of liver autoimmunity, the predominant role of genetic factors, and the increasingly effective immuno-therapeutic possibilities.

The genetics of complex cholestatic disorders

Cholestatic liver diseases are caused by a range of hepatobiliary insults and involve complex interactions among environmental and genetic factors. Little is known about the pathogenic mechanisms of specific cholestatic diseases, which has limited our ability to manage patients with these disorders. However, recent genome-wide studies have provided insight into the pathogenesis of gallstones, primary biliary cirrhosis, and primary sclerosing cholangitis. A lithogenic variant in the gene that encodes the hepatobiliary transporter ABCG8 has been identified as a risk factor for gallstone disease; this variant has been associated with altered cholesterol excretion and metabolism. Other variants of genes encoding transporters that affect the composition of bile have been associated with cholestasis, namely ABCB11, which encodes the bile salt export pump, and ABCB4, which encodes hepatocanalicular phosphatidylcholine floppase. In contrast, studies have associated primary biliary cirrhosis and primary sclerosing cholangitis with genes encoding major histocompatibility complex proteins and identified loci associated with microbial sensing and immune regulatory pathways outside this region, such as genes encoding IL12, STAT4, IRF5, IL2 and its receptor (IL2R), CD28, and CD80. These discoveries have raised interest in the development of reagents that target these gene products. We review recent findings from genetic studies of patients with cholestatic liver disease. Future characterization of genetic variants in animal models, stratification of risk alleles by clinical course, and identification of interacting environmental factors will increase our understanding of these complex cholestatic diseases.

Differential binding of pyruvate dehydrogenase complex-E2 epitopes by DRB1*08:01 and DRB1*11:01 Is predicted by their structural motifs and correlates with disease risk

DRB1*08:01 (DR0801) and DRB1*11:01 (DR1101) are highly homologous alleles that have opposing effects on susceptibility to primary biliary cirrhosis (PBC). DR0801 confers risk and shares a key feature with other HLA class II alleles that predispose to autoimmunity: a nonaspartic acid at beta57. DR1101 is associated with protection from PBC, and its sequence includes an aspartic acid at beta57. To elucidate a mechanism for the opposing effects of these HLA alleles on PBC susceptibility, we compared the features of epitopes presented by DR0801 and DR1101. First, we identified DR0801- and DR1101-restricted epitopes within multiple viral Ags, observing both shared and distinct epitopes. Because DR0801 is not well characterized, we deduced its motif by measuring binding affinities for a library of peptides, confirming its key features through structural modeling. DR0801 was distinct from DR1101 in its ability to accommodate charged residues within all but one of its binding pockets. In particular, DR0801 strongly preferred acidic residues in pocket 9. These findings were used to identify potentially antigenic sequences within PDC-E2 (an important hepatic autoantigen) that contain a DR0801 motif. Four peptides bound to DR0801 with reasonable affinity, but only one of these bound to DR1101. Three peptides, PDC-E2145-159, PDC-E2(249-263), and PDC-E2(629-643), elicited high-affinity T cell responses in DR0801 subjects, implicating these as likely autoreactive specificities. Therefore, the unique molecular features of DR0801 may lead to the selection of a distinct T cell repertoire that contributes to breakdown of self-tolerance in primary biliary cirrhosis, whereas those of DR1101 promote tolerance.

The role of vitamin d in primary biliary cirrhosis: possible genetic and cell signaling mechanisms

Primary biliary cirrhosis (PBC) is an immune-mediated chronic inflammatory disease of the liver of unknown etiology. Vitamin D deficiency is highly prevalent in patients with PBC, and many studies have demonstrated the significant effect of calcitriol on liver cell physiology. Vitamin D has antiproliferative and antifibrotic effects on liver fibrosis. Genetic studies have provided an opportunity to determine which proteins link vitamin D to PBC pathology (e.g., the major histocompatibility complex class II molecules, the vitamin D receptor, toll-like receptors, apolipoprotein E, Nramp1, and cytotoxic T lymphocyte antigen-4). Vitamin D also exerts its effect on PBC through cell signaling mechanisms, that is, matrix metalloproteinases, prostaglandins, reactive oxygen species, and the transforming growth factor betas. In conclusion, vitamin D may have a beneficial role in the treatment of PBC. The best form of vitamin D for use in the PBC is calcitriol because it is the active form of vitamin D3 metabolite, and its receptors are present in the sinusoidal endothelial cells, Kupffer cells, and stellate cells of normal livers, as well as in the biliary cell line.

Infectome: a platform to trace infectious triggers of autoimmunity

The "exposome" is a term recently used to describe all environmental factors, both exogenous and endogenous, which we are exposed to in a lifetime. It represents an important tool in the study of autoimmunity, complementing classical immunological research tools and cutting-edge genome wide association studies (GWAS). Recently, environmental wide association studies (EWAS) investigated the effect of environment in the development of diseases. Environmental triggers are largely subdivided into infectious and non-infectious agents. In this review, we introduce the concept of the "infectome", which is the part of the exposome referring to the collection of an individual's exposures to infectious agents. The infectome directly relates to geoepidemiological, serological and molecular evidence of the co-occurrence of several infectious agents associated with autoimmune diseases that may provide hints for the triggering factors responsible for the pathogenesis of autoimmunity. We discuss the implications that the investigation of the infectome may have for the understanding of microbial/host interactions in autoimmune diseases with long, pre-clinical phases. It may also contribute to the concept of the human body as a superorganism where the microbiome is part of the whole organism, as can be seen with mitochondria which existed as microbes prior to becoming organelles in eukaryotic cells of multicellular organisms over time. A similar argument can now be made in regard to normal intestinal flora, living in symbiosis within the host. We also provide practical examples as to how we can characterise and measure the totality of a disease-specific infectome, based on the experimental approaches employed from the "immunome" and "microbiome" projects.

Effect of the polymorphisms of tumor necrosis factor-α gene on the susceptibility to primary biliary cirrhosis: a meta-analysis

BACKGROUND

Previous studies have shown the genetic association of tumor necrosis factor (TNF)-α polymorphisms and susceptibility to primary biliary cirrhosis (PBC), but the results of individual studies have remained contradictory. Therefore, a meta-analysis was carried out to evaluate comprehensively the association of TNF-α polymorphisms and susceptibility to PBC.

METHODS

The relevant published articles were searched in PubMed, EMBASE, and Cochrane library. Data were extracted using standardized forms and odds ratios (ORs) with 95% confidence intervals (CIs) were calculated for each study. Pooled data were estimated by fixed-effects and random-effects models when appropriate. We analyzed the association between the 'A' allele at position -308(rs1800629) and -238(rs361525) and the risk of PBC.

RESULTS

We examined eight publications, showing that all eight studies discussed the TNF-α -308(rs1800629) polymorphism; four studies were relevant with -238(rs361525). No significant associations were found between the 'A' allele frequency of rs1800629 and rs361525 and the risk of PBC in the overall population (OR=0.89, 95% CI 0.71-1.11, P=0.91; OR=0.98, 95% CI 0.66-1.47, P=0.93) and in Whites (OR=0.94, 95% CI 0.74-1.19, P=0.58; OR=1.01, 95% CI 0.64-1.59, P=0.97). Besides, it was also found that the genotype (AA+AG vs. GG, GG+AG vs. AA) was not linked to susceptibility to PBC.

CONCLUSION

The meta-analysis indicated that none of these two polymorphisms (-308G/A and -238G/A) showed any significant association with the risk of PBC.

Rheumatoid arthritis and primary biliary cirrhosis: cause, consequence, or coincidence?

Primary biliary cirrhosis (PBC) is a progressive cholestatic liver disease characterized serologically by cholestasis and the presence of high-titre antimitochondrial antibodies and histologically by chronic nonsuppurative cholangitis and granulomata. PBC patients often have concomitant autoimmune diseases, including arthropathies. This raises the question as to whether there are shared features in the pathogenesis of those diseases with the pathogenesis of PBC. Epidemiological and large case studies have indicated that although the incidence of rheumatoid arthritis (RA) is not significantly raised in PBC patients, there appears to be a higher rate of RA in PBC patients and their relatives. Genetic studies have demonstrated that several genes implicated in PBC have also been implicated in RA. Epigenetic studies provided a wealth of data regarding RA, but the findings on epigenetic changes in PBC are very limited. As well, certain infectious agents identified in the pathogenesis of PBC may also play a role in the pathogenesis of RA. These data suggest that although RA is not significantly present in PBC, some individuals with certain genetic traits and environmental exposures may develop both conditions. This concept may also apply to other concomitant diseases found in PBC patients.

Recent advances in understanding the pathogenesis of primary biliary cirrhosis

Primary biliary cirrhosis (PBC) is a chronic progressive cholestatic autoimmune liver disease characterized by the destruction of small intrahepatic bile ducts and the presence of highly specific serum antimitochondrial antibodies (AMAs). The human leukocyte antigen (HLA) gene has been proved to have strongest association with PBC susceptibility, and non-HLA genes, including IL12A, IL12RB2, STAT4, IRF5-TNPO3, ORMDL3/IKZF3, MMEL1, SPIB, CTLA-4, FCRL3 and A2BP1, are also closely associated with PBC susceptibility. Four AMAs including anti-M2, anti-M4, anti-M8 and anti-M9, and antinuclear antibodies (ANAs), such as antinuclear dot antibodies (SP100, PML, NDP52, SP140), antinuclear pore antibodies (gp210, p62), antinuclear envelope antibodies (Lamin and Lamin B receptor), and anti-centromere antibodies, may also be involved in the pathogenesis of PBC. The imbalance between Th17 cells and regulatory T lymphocytes (Treg) may also play an important role in the pathogenesis of PBC. In addition, senescence, autophagy, apoptosis of biliary epithelial cells (BECs), and environmental factors, such as Epstein-Barr virus (EBV) infection and smoking, may also contribute to the pathogenesis of PBC. Understanding of the mechanisms responsible for the pathogenesis of PBC has important implications for the treatment of PBC.

Role for mycobacterial infection in pathogenesis of primary biliary cirrhosis?

Primary biliary cirrhosis (PBC) is a progressive cholestatic liver disease characterized by the immune-mediated destruction of biliary epithelial cells in small intrahepatic bile ducts. The disease is characterized by circulating antimitochondrial antibodies (AMAs) as well as disease-specific antinuclear antibodies, cholestatic liver function tests, and characteristic histological features, including granulomas. A variety of organisms are involved in granuloma formation, of which mycobacteria are the most commonly associated. This has led to the hypothesis that mycobacteria may be involved in the pathogenesis of PBC, along with other infectious agents. Additionally, AMAs are found in a subgroup of patients with mycobacterial infections, such as leprosy and pulmonary tuberculosis. Antibodies against species-specific mycobacterial proteins have been reported in patients with PBC, but it is not clear whether these antibodies are specific for the disease. In addition, data in support of the involvement of the role of molecular mimicry between mycobacterial and human mitochondrial antigens as triggers of cross-reactive immune responses leading to the loss of immunological tolerance, and the induction of pathological features have been published. Thus, antibodies against mycobacterial heat shock protein appear to cross-recognize AMA-specific autoantigens, but it is not clear whether these autoantibodies are mycobacterium-species-specific, and whether they are pathogenic or incidental. The view that mycobacteria are infectious triggers of PBC is intriguing, but the data provided so far are not conclusive.

Review article: overlap syndromes and autoimmune liver disease

BACKGROUND

Autoimmune hepatitis (AIH), primary biliary cirrhosis (PBC) and primary sclerosing cholangitis (PSC) all nestle within the family of autoimmune liver diseases, whereby the result of immune-mediated liver injury gives rise to varied clinical presentations. Some patients demonstrate a phenotype whereby there is evidence of either PBC or PSC together with overlapping features of AIH. Due to an absence of well-validated diagnostic criteria and a lack of large therapeutic trials, treatment of overlap conditions is empiric and extrapolated from data derived from the primary autoimmune liver diseases.

AIMS

To review overlaps in the context of autoimmune liver diseases.

METHODS

General and specific review of published articles using PubMed, Medline and Ovid search engines, alongside pre-existing clinical management protocols, guidelines, and the authors' own knowledge of the published literature.

RESULTS

The challenges in diagnosis, clinical presentation, determining natural history and outcome of overlaps are presented, as well as present-day management suggestions, some based on evidence, others on consensus and opinion.

CONCLUSIONS

Overlapping autoimmune features, be they clinical, serological, histological or radiological are not infrequent, but appropriate diagnosis remains hindered by a lack of standardised diagnostic criteria. Optimum care for those with suspected overlap should thus focus on attention to detail over the fundamental aspects of timely secure diagnosis of the dominant disease entity. Clinicians should counsel patients carefully with regard to the risks and benefits of treatment, bearing in mind the paucity of randomised and controlled outcome data for medical interventions.

Immunochip analyses identify a novel risk locus for primary biliary cirrhosis at 13q14, multiple independent associations at four established risk loci and epistasis between 1p31 and 7q32 risk variants

To further characterize the genetic basis of primary biliary cirrhosis (PBC), we genotyped 2426 PBC patients and 5731 unaffected controls from three independent cohorts using a single nucleotide polymorphism (SNP) array (Immunochip) enriched for autoimmune disease risk loci. Meta-analysis of the genotype data sets identified a novel disease-associated locus near the TNFSF11 gene at 13q14, provided evidence for association at six additional immune-related loci not previously implicated in PBC and confirmed associations at 19 of 22 established risk loci. Results of conditional analyses also provided evidence for multiple independent association signals at four risk loci, with haplotype analyses suggesting independent SNP effects at the 2q32 and 16p13 loci, but complex haplotype driven effects at the 3q25 and 6p21 loci. By imputing classical HLA alleles from this data set, four class II alleles independently contributing to the association signal from this region were identified. Imputation of genotypes at the non-HLA loci also provided additional associations, but none with stronger effects than the genotyped variants. An epistatic interaction between the IL12RB2 risk locus at 1p31and the IRF5 risk locus at 7q32 was also identified and suggests a complementary effect of these loci in predisposing to disease. These data expand the repertoire of genes with potential roles in PBC pathogenesis that need to be explored by follow-up biological studies.

Autoimmune hepatitis type 2 associated with an unexpected and transient presence of primary biliary cirrhosis-specific antimitochondrial antibodies: a case study and review of the literature

Background

Unlike other autoimmune liver diseases, primary biliary cirrhosis (PBC) has never been reported in early childhood, while type 2 autoimmune hepatitis (AIH) is eminently a paediatric disease.

Case presentation

We describe a case of type 2 AIH with serological positivity for PBC-specific anti-mitochondrial antibodies (AMA) in a 3-year old girl. We found this observation intriguing as AMA and indeed an overlap with PBC are virtually absent in Type 2 AIH, a pediatric form of AIH which is distinct precisely because it is characterized by pathognomonic anti-liver kidney microsomal type 1 (LKM-1) showing a remarkable antigen-specificity directed against cytochrome P4502D6. We also review the literature in relation to AMA positivity in paediatric age and adolescence. In our case, the presence of AIH-2-specific anti-LKM-1 and PBC-specific AMA was confirmed by indirect immunofluorescence (IIF), and immunoblotting and ELISA based on recombinant mitochondrial antigens. The clinical, laboratory and histological features of the child are given in detail. Interestingly the mother was AMA positive without other features of PBC. The child was successfully treated with immunosuppression and five years after the original diagnosis is on a low dose of prednisolone and azathioprine, with no signs of relapse. Anti-LKM-1 antibodies are still present in low titres. AMA were detectable for the first 4 years after the diagnosis and disappeared later.

Conclusion

This is the first case report in the literature of AIH type 2 with an unexpected PBC-specific AMA positivity in a young child. Response to immunosuppressive treatment was satisfactory and similar to that described in AIH. A review of published reports on AMA positivity in paediatric age shows that the antibody may arise in the context of immunodeficiency and is variably associated with liver damage.