原发性胆汁性肝硬化最新综述（来自柳叶刀）

Seminar 1600 www.thelancet.com Vol 377 May 7, 2011 Primary biliary cirrhosis Carlo Selmi, Christopher L Bowlus, M Eric Gershwin, Ross L Coppel Primary biliary cirrhosis is a chronic liver disease characterised by intrahepatic bile-duct destruction, cholestasis, and, in some cases, cirrhosis. Evidence supporting the autoimmune nature of this disorder includes the appearance of highly specifi c antimitochondrial antibodies (AMAs) and autoreactive T cells. Concordance rates in monozygotic twins, familial prevalence, and genetic associations underscore the importance of genetic factors, whereas fi ndings of epidemiological studies and murine models suggest a possible role for exogenous chemicals and infectious agents through molecular mimicry. The incidence of primary biliary cirrhosis has increased over recent decades, possibly attributable to augmented testing of liver biochemistry rather than a rise in disease incidence. AMAs remain the hallmark of diagnosis in most cases and allow detection of asymptomatic patients. Symptomatic individuals usually present with either pruritus or fatigue and, more rarely, with either jaundice or complications of cirrhosis. The prognosis of primary biliary cirrhosis has improved because of early diagnosis and use of ursodeoxycholic acid, the only established medical treatment for this disorder. Although not a cure, treatment can slow disease progression and delay the need for liver transplantation. However, some patients do not respond adequately to ursodeoxycholic acid and might need alternative therapeutic approaches. Introduction Primary biliary cirrhosis is an autoimmune liver disease characterised by the presence in serum of highly specifi c antimito chondrial antibodies (AMAs) and progressive destruction of intrahepatic bile ducts, resulting in chronic cholestasis, portal infl ammation, and fi brosis that can lead to cirrhosis and, ultimately, liver failure. The disease predominantly aff ects women, who are diagnosed typically in their fi fth and sixth decade, although younger patients have been described, including children, albeit rarely.1 Loss of bile ducts leads to intrahepatic retention of detergent bile acids, resulting in liver damage through interaction with cell membranes and organelles. Disruption of enterohepatic bile acid circulation is probably the cause of other pathophysiological changes, which contribute to extra hepatic manifestations of this disease. In 1761, the Italian pathologist Giovanni Battista Morgagni described biliary cirrhosis, and the earliest report of non-obstructive biliary cirrhosis was made by Addison and Gull in 1851.2 The term primary biliary cirrhosis was coined more than 50 years later.3 Presence of AMAs in serum samples of patients with primary biliary cirrhosis was recognised in 1965 by Walker and colleagues,4 and in 1987, antigens to these antibodies were cloned and identifi ed as subunits of the pyruvate dehydrogenase complex, located on the inner mito chondrial membrane.5,6 Clinical features and natural history of primary biliary cirrhosis vary greatly between aff ected individuals, ranging from either asymptomatic and stable or only slowly progressive to symptomatic and rapidly progressive. The typical clinical presentation has changed over the past few decades because the natural history has been modifi ed by early recognition of more indolent cases and use of ursodeoxycholic acid. Epidemiology Data about incidence and prevalence of primary biliary cirrhosis have generally been obtained passively and might not indicate true rates in the general population; regional diff erences could vary on the basis of medical awareness and expertise. Indeed, a population-based approach to case detection has little feasibility for primary biliary cirrhosis because of its rarity. As a result, reported prevalence ranges between 19 and 402 cases per million.7,8 By contrast, fi ndings of serological studies with indirect immuno- fl uorescence in large groups of unselected serum samples show that prevalence of AMAs in the general population can be as high as 0·5%, with lower frequencies when blood donors are investigated.9 Diff erences in estimates of incidence and prevalence of primary biliary cirrhosis are probably secondary to variable diagnostic criteria, case- fi nding methods, doctors’ awareness, and quality levels of health-care systems. On the basis of data from case-fi nding studies, however, a latitudinal geoepidemiological pattern of occurrence of primary biliary cirrhosis has been proposed,10 with the disease being most frequent in northern Europe and North America. Indeed, the highest prevalence and incidence rates have been reported in Scandinavia, Great Britain, and the northern midwest region of the USA. Exceptions to this pattern are the high rates noted in the Spanish area of Sabadell.11 Some researchers suggest that incidence of primary biliary cirrhosis is also growing. Indeed, rates rose from 5·8 to Lancet 2011; 377: 1600–09 Published Online April 28, 2011 DOI:10.1016/S0140- 6736(10)61965-4 Department of Translational Medicine, IRCCS-Istituto Clinico Humanitas, University of Milan, Milan, Italy (Prof C Selmi MD); Divisions of Gastroenterology and Hepatology (C L Bowlus MD) and Rheumatology, Allergy, and Clinical Immunology (Prof M E Gershwin MD), University of California at Davis, Davis, CA, USA; and Department of Microbiology, Monash University, Clayton, Vic, Australia (Prof R L Coppel PhD) Correspondence to: Prof Ross L Coppel, Monash University, Clayton, VIC 3800, Australia ross.coppel@monash.edu Search strategy and selection criteria We searched Medline with the terms “primary biliary cirrhosis” and “autoimmune cholangitis” for original research published in peer-reviewed journals between 1970 and 2010. We focused on publications from the past 5 years, but we did not exclude commonly cited and highly regarded older publications. We also searched the reference lists of reports identifi ed by this search strategy and selected articles we judged relevant. Reviews obtained by the same Medline search were included when they provided a comprehensive overview of issues beyond the scope of this Seminar. Abstracts presented at international scientifi c meetings were cited when the content seemed of seminal importance. We only included clinical trials published after peer-review, randomised controlled trials, or both, in which survival, biochemical response, symptom improvement, or changes in histology were reported. Seminar www.thelancet.com Vol 377 May 7, 2011 1601 20·5 cases per million population of Sheffi eld, UK, per year between 1980 and 1999,12,13 and from 11 to 32 cases per million population per year in Newcastle-upon-Tyne, UK, between 1976 and 1994.14,15 This increase was paralleled by prevalence reaching more than 200 cases per million in the middle to late 1990s. Whether these changes are due to rising disease incidence or are secondary to augmented detection of mild asymptomatic cases or slowly progressing disease remains to be established. However, age at diagnosis of mid-to-late 50s has remained consistent across diff erent periods of study. Most autoimmune diseases are predominant in female patients, and in primary biliary cirrhosis, this prepon- derance is especially striking—the ratio of aff ected females to males is as high as 10:1.16 The observation that, in the general population, detection of AMAs in serum is not skewed to females16 suggests either that the diagnosis of primary biliary cirrhosis might be suspected more frequently in women than men or that progression from loss of tolerance to the autoantigen to clinical liver disease is more common in female patients. Risk factors associated with an uncommon disease such as primary biliary cirrhosis are diffi cult to ascertain because of obstacles in undertaking studies of suffi cient size; however, some associations have been found frequently enough to suggest validity of associations. Cumulatively, risk of development of primary biliary cirrhosis is raised with a positive family history of the disease, a history of urinary or vaginal infections,17 comorbidity with other autoimmune diseases, past or present smoking, and previous pregnancies. Frequent use of nail polish or hair dye has a weak association with disease risk.18,19 Cause and pathogenesis Three important observations must be taken into account for us to understand the pathogenic basis of primary biliary cirrhosis (fi gure 1). First, appearance of AMAs before liver disease suggests that loss of tolerance to the mitochondrial autoantigen is an early event and could be independent of the development of liver disease. Second, although the autoantigen is present ubiquitously in all nucleated cells, the immune response is restricted to epithelial cells of intrahepatic bile ducts and, to a lesser degree, to cells of salivary and lacrimal glands. Finally, recurrence of primary biliary cirrhosis after liver transplantation supports the idea that the bile duct epithelial cell is a generic target and is not unique to the patient with primary biliary cirrhosis.20 Similar to other complex diseases, the combination of a susceptible genetic background and exposure to environmental triggers is needed to initiate and promote the disorder. Observations that 1–6% of individuals with primary biliary cirrhosis have at least one family member manifesting disease,18 and a 63% concordance rate in monozygotic twins (vs null concordance in dizygotic sets),21 show the substantial genetic eff ect on disease susceptibility, one of the strongest for any autoimmune disorder. Many candidate genes have been investigated for a role in susceptibility to primary biliary cirrhosis, disease progression, or both in case-control cross- sectional studies. Findings of a genome-wide association study undertaken in a northern American set of patients and controls22 indicated a signifi cant association between primary biliary cirrhosis and polymorphisms of HLA-DQB1, IL12A, IL12RB2, and to a minor extent, STAT4, and these associations have been confi rmed in an independent cohort of Italian patients and controls with a combined analysis.23 Several environmental factors—mainly infectious and chemical—are also thought to contribute to the onset of primary biliary cirrhosis, largely through molecular mimicry or modifi cation of autoantigens. Geographic clustering of cases near toxic waste sites in New York City24 and space-time clustering in northeast England25 provide epidemiological evidence for a role of chemicals, infectious agents, or both. Additional data that lend support to a role for infections in disease development include the signifi cantly higher prevalence than usual of recurrent urinary-tract infections in patients with primary biliary cirrhosis17,18 and experimental fi ndings of sequence similarity between the E2 enzyme of the pyruvate dehydrogenase complex recognised by autoantibodies and bacterial proteins.26 Several bacterial strains— including the non-pathogenic gram-negative bacterium Novosphingobium aromaticivorans—have the highest known homology to the immunodominant autoepitope of the E2 enzyme.18,27 Several other infectious agents have been proposed, including Escherichia coli, Helicobacter spp,28 organisms of the genus Mycoplasma,29 and a human β retrovirus,30 although support for the retrovirus has not been substantiated.31 Other environmental factors proposed to trigger disease onset are foreign chemicals (ie, xenobiotics) that can either alter or form a complex with a defi ned self or non-self protein, causing a change in the protein’s molecular structure that induces an immune response. Lipoic acid is attached to only a few proteins, yet it is a vital component of the E2 epitope.32 The structure of the E2 enzyme exposes lipoic acid at the exterior of the protein complex, making this compound accessible to chemical modifi cation.33 The role of xenobiotics in Figure 1: Factors possibly entailed in onset and perpetuation of bile-duct injury in primary biliary cirrhosis PDC-E2=E2 component of the pyruvate dehydrogenase complex. AMAs=antimitochondrial antibodies. Host susceptibility eg, female sex, risk alleles in MHC, IL12A, and IL12RB2 loci, innate immunity (IgM hyper-responsiveness) eg, bacterial mimics (eg, Novosphingobium aromaticvorans), xenobiotic chemicals eg, defective regulatory T cells, production of AMAs, autoreactive CD4/CD8 T cells to PDC-E2 eg, immune response, entailing bile duct apoptotic blebs and AMAs, primary biliary cirrhosis macrophages Environmental exposures Loss of immune tolerance to PDC-E2 Bile duct damage Seminar 1602 www.thelancet.com Vol 377 May 7, 2011 primary biliary cirrhosis is supported by serum reactivity against specifi c organic compounds with structures similar to lipoic acid;34 furthermore, two of these compounds (6-bromohexanoate and 2-octynoic acid) can induce AMAs and liver lesions similar to those of primary biliary cirrhosis in guinea pigs35 and mouse models.36,37 Primary biliary cirrhosis has been regarded as an autoimmune disease from the time of the fi rst seminal reports38 because of the predominance of female patients, frequent autoimmune comorbidities, and, most importantly, by loss of immune tolerance to self-mitochondrial proteins.39 Panel 1 summarises Witebsky’s criteria both for and against the autoimmune basis of primary biliary cirrhosis.40 Although most evidence argues that primary biliary cirrhosis is a disease of autoimmunity directed against antimito- chondrial antigens on biliary epithelial cells, proof of a direct pathogenic role for serum autoantibodies is scarce: seronegative patients manifest similar disease features to those of their AMA-positive counterparts;48 changes in AMA titres do not correlate with severity of primary biliary cirrhosis, disease stage, or both; and immuno suppressive treatment has been fairly ineff ective in patients with primary biliary cirrhosis. AMAs in serum are highly sensitive and specifi c for primary biliary cirrhosis: they are detected in nearly 95% of patients, with specifi city close to 100% when tested with recombinant antigens.41 Indirect immuno- fl uorescence remains the test used for screening, but it can be associated with a substantial number of false- positive results.49 Follow-up data from AMA-positive individuals without signs of liver disease suggest that autoantibodies arise several years before onset of primary biliary cirrhosis and have a high predictive value.50 Epitopes recognised by AMAs include lipoylated domains (via the Asx-Lys-Ala motif) within subunits of the 2-oxoacid dehydrogenase family of enzymes of the mitochondrial respiratory chain,6 in particular, E2 subunit and E3 binding-protein components of the pyruvate dehydro genase complex and E2 components of the 2-oxoglutarate dehydrogenase and branched-chain 2-oxo acid dehydro genase complexes (table).51,52 In addition to AMAs, autoreactive CD8+ and CD4+ T cells to the E2 component of the pyruvate dehydrogenase complex have been identifi ed both in peripheral blood and within the liver of patients with primary biliary cirrhosis, and the immunodominant epitope of these T cells maps in close proximity to the epitope recognised by AMAs in serum. Autoreactive CD4+ cell clones specifi c for the E2 enzyme have been isolated in intrahepatic and peripheral lymphocytes, not only in AMA-positive individuals but also in patients without antibodies, thus corroborating the notion that primary biliary cirrhosis either positive or negative for AMAs is one nosological entity.43 CD4+ CD25high regulatory T cells act to prevent autoreactivity, as shown in several autoimmune diseases, including autoimmune hepatitis.65 Patients with primary biliary cirrhosis are characterised by substantially lower frequencies of CD4+ CD25high regulatory T cells as proportions of total T-cell receptor-αβ+/CD4+ cells, and this factor could be important in the breakdown of tolerance.45 Moreover, raised amounts of polyclonal IgM and hyper-responsiveness to CpG (cytosine-phosphate- guanine dinucleotide motif),66 and enhanced natural killer cell67,68 and monocyte responses,69 which are all features found in primary biliary cirrhosis, also lend support to a role for innate immunity. Panel 1: Features of primary biliary cirrhosis for and against autoimmune pathogenesis In support of autoimmunity • Specifi c serum autoantibodies41,42 • Autoreactive T cells43 • Adaptive transfer of cholangitis using CD8+ T cells (in murine models)44 • Functional T regulatory defects45 • Female predominance16 • Autoimmune comorbidity46,47 • MHC association22 Against autoimmunity • Absence of disease after autoantibody transfer (in mice) • Absence of correlation between titre of antimitochondrial antibodies and disease severity48 • Failure to respond to immunosuppressive agents (based on limited data)46,47 Features shown according to Witebsky’s criteria, as modifi ed by Rosa and Bona.40 Indirect immunofl uorescence ELISA Immunoblotting AMAs General53,54 70–90% .. .. PDC-E254 .. 79·6% 81·7% OGDC-E254 .. NA 27·4% BCOADC-E255 .. 56·7% 59·1% pMIT342,54 .. 94% 92% ANAs Rim-like pattern56,57 10–52% .. .. Gp21056,58 .. 16–32% 10–42% Nup6259,60 .. NA 22–32% Multiple nuclear dots61 13–25% .. .. Sp10062 .. 21–39% NA PML .. NA NA Centromere General63 9–20% .. .. CENP A, B, C64 .. 26% 21% AMAs=antimitochondrial antibodies. E2=E2 component. PDC=pyruvate dehydrogenase complex. OGDC=2-oxo-glutarate dehydrogenase. BCOADC=branched-chain 2-oxo acid dehydrogenase. ANAs=antinuclear antibodies. Gp210=glycoprotein 210. Nup62=nucleoporin 62. PML=promyelocytic leukaemia. CENP=centromere protein. NA=data not available. For ELISA and immunoblotting, only data obtained with recombinant antigens are shown, and references are for the largest studies. Table: Sensitivity of serum autoantibodies in primary biliary cirrhosis Seminar www.thelancet.com Vol 377 May 7, 2011 1603 Once tolerance to AMAs is lost, additional mechanisms entailed in the immune response to a ubiquitous autoantigen begin to be unravelled. These lead to specifi c injury of biliary epithelial cells and seem to be linked to unique processes of apoptosis.70–73 Unlike other cell types, the E2 component of the pyruvate dehydrogenase complex remains intact in bile-duct cells after apoptosis, thus probably retaining its immunogenicity.74 Furthermore, this enzyme is found within apoptotic blebs and is accessible to AMAs75 and local antigen-presenting cells. Moreover, fi ndings of in-vitro experiments have shown an intense and specifi c immune response when macrophages of patients with primary biliary cirrhosis are combined with apoptotic blebs of biliary epithelial cells and AMAs.76 However, recurrence of primary biliary cirrhosis after liver transplantation suggests that this occurrence is not an intrinsic defect of bile-duct cells of aff ected individuals but is a feature of biliary epithelia in general, not seen in other epithelial cells. Clinical features The clinical features and natural history of primary biliary cirrhosis vary greatly between patients, ranging from asymptomatic and slowly progressive to symptomatic and rapidly evolving. The frequency of asymptomatic disease seems to be increasing, probably because of raised awareness of the disease together with broad use of routine testing of liver biochemistry. Many asymptomatic patients will, however, develop symptomatic liver disease within 5 years of diagnosis, although a third could remain symptom-free for many years.77 Although non-specifi c, fatigue is the most common symptom of prima