Identification of major linear epitopes on the sp100 nuclear PBC autoantigen by the gene-fragment phage-display technology

Comprehensive mapping of SARS-CoV-2 peptide epitopes for development of a highly sensitive serological test for total and neutralizing antibodies

Quantification of the anti-SARS-CoV-2 antibody response has proven to be a prominent diagnostic tool during the COVID-19 pandemic. Antibody measurements have aided in the determination of humoral protection following infection or vaccination and will likely be essential for predicting the prevalence of population level immunity over the next several years. Despite widespread use, current tests remain limited in part, because antibody capture is accomplished through the use of complete spike and nucleocapsid proteins that contain significant regions of overlap with common circulating coronaviruses. To address this limitation, a unique epitope display platform utilizing monovalent display and protease-driven capture of peptide epitopes was used to select high affinity peptides. A single round of selection using this strategy with COVID-19 positive patient plasma samples revealed surprising differences and specific patterns in the antigenicity of SARS-CoV-2 proteins, especially the spike protein. Putative epitopes were assayed for specificity with convalescent and control samples, and the individual binding kinetics of peptides were also determined. A subset of prioritized peptides was used to develop an antibody diagnostic assay that showed low cross reactivity while detecting 37% more positive antibody cases than a gold standard FDA EUA test. Finally, a subset of peptides were compared with serum neutralization activity to establish a 2 peptide assay that strongly correlates with neutralization. Together, these data demonstrate a novel phage display method that is capable of comprehensively and rapidly mapping patient viral antibody responses and selecting high affinity public epitopes for the diagnosis of humoral immunity.

The Fate of Speckled Protein 100 (Sp100) During Herpesviruses Infection

The constitutive expression of Speckled-100 (Sp100) is known to restrict the replication of many clinically important DNA viruses. This pre-existing (intrinsic) immune defense to virus infection can be further upregulated upon interferon (IFN) stimulation as a component of the innate immune response. In humans, Sp100 is encoded by a single gene locus, which can produce alternatively spliced isoforms. The widely studied Sp100A, Sp100B, Sp100C and Sp100HMG have functions associated with the transcriptional regulation of viral and cellular chromatin, either directly through their characteristic DNA-binding domains, or indirectly through post-translational modification (PTM) and associated protein interaction networks. Sp100 isoforms are resident component proteins of promyelocytic leukemia-nuclear bodies (PML-NBs), dynamic nuclear sub-structures which regulate host immune defenses against many pathogens. In the case of human herpesviruses, multiple protein antagonists are expressed to relieve viral DNA genome transcriptional silencing imposed by PML-NB and Sp100-derived proteinaceous structures, thereby stimulating viral propagation, pathogenesis, and transmission to new hosts. This review details how different Sp100 isoforms are manipulated during herpesviruses HSV1, VZV, HCMV, EBV, and KSHV infection, identifying gaps in our current knowledge, and highlighting future areas of research.

Toward precision medicine in primary biliary cholangitis

Primary biliary cholangitis is a chronic, cholestatic liver disease characterized by a heterogeneous presentation, symptomatology, disease progression and response to therapy. In contrast, clinical management and treatment of PBC is homogeneous with a 'one size fits all' approach. The evolving research landscape, with the emergence of the -omics field and the availability of large patient cohorts are creating a unique opportunity of translational epidemiology. Furthermore, several novel disease and symptom-modifying agents for PBC are currently in development. The time is therefore ripe for precision medicine in PBC. In this manuscript we describe the concept of precision medicine; review current approaches to risk-stratification in PBC, and speculate how precision medicine in PBC might develop in the near future.

A pre-eclampsia-associated Epstein-Barr virus antibody cross-reacts with placental GPR50

To characterize antibody specificities associated with pre-eclampsia (PE), bacterial displayed peptide library screening and evolution was applied to identify peptide epitopes recognized by plasma antibodies present in women with PE near the time of delivery. Pre-eclamptic women exhibited elevated IgG1 titers towards a peptide epitope KRPSCIGCK within the Epstein-Barr virus nuclear antigen 1 (EBNA-1). EBNA-1 epitope antibodies cross-reacted with a similar epitope within the extracellular N-terminus of the human G protein-coupled receptor, GPR50, expressed in human placental tissue and immortalized placental trophoblast cells. We observed increased antibody binding activity to epitopes from EBNA-1 and GPR50 among women with PE (n=42) compared to healthy-outcome pregnancies (n=43) and nulligravid samples (n=21). The EBNA-1 peptide potently blocked binding of the PE-associated antibody to the GPR50 epitope (IC50=58-81pM). These results reveal the existence of molecular mimicry between EBNA-1 and placental GPR50, supporting a mechanism for IgG1 deposition in the pre-eclamptic placenta.

Detection of anti-SP100 antibodies in primary biliary cirrhosis. Comparison of ELISA and immunofluorescence

Primary biliary cirrhosis (PBC) is, which a chronic, autoimmune liver disease. Some patients have antinuclear antibodies anti-Sp100, which are considered to be disease-specific. We compared an enzyme-linked immunosorbent assay (ELISA) and indirect immunofluorescence (IIF) for detection of anti-Sp100. The sensitivity of anti-Sp100 determined by ELISA and IIF was 44% and 34%, respectively. Specificity was 99% for ELISA and 98% for IIF, respectively. The positive and negative predictive value (PPV, NPV) for anti-Sp100 determined by ELISA were 98%, 60% and 95%, 56% for IIF respectively. IIF required substantial experience in interpreting subjective patterns, whereas ELISA was more sensitive, cheaper, less time consuming, and produced clear-cut quantitative results.

Virtual interactomics of proteins from biochemical standpoint

Virtual interactomics represents a rapidly developing scientific area on the boundary line of bioinformatics and interactomics. Protein-related virtual interactomics then comprises instrumental tools for prediction, simulation, and networking of the majority of interactions important for structural and individual reproduction, differentiation, recognition, signaling, regulation, and metabolic pathways of cells and organisms. Here, we describe the main areas of virtual protein interactomics, that is, structurally based comparative analysis and prediction of functionally important interacting sites, mimotope-assisted and combined epitope prediction, molecular (protein) docking studies, and investigation of protein interaction networks. Detailed information about some interesting methodological approaches and online accessible programs or databases is displayed in our tables. Considerable part of the text deals with the searches for common conserved or functionally convergent protein regions and subgraphs of conserved interaction networks, new outstanding trends and clinically interesting results. In agreement with the presented data and relationships, virtual interactomic tools improve our scientific knowledge, help us to formulate working hypotheses, and they frequently also mediate variously important in silico simulations.

Epitope-specific anti-nuclear antibodies are expressed in a mouse model of primary biliary cirrhosis and are cytokine-dependent

Although the hallmark of primary biliary cirrhosis (PBC) is the presence of anti-mitochondrial antibodies (AMA), a significant number of patients have anti-nuclear antibodies (ANA) directed primarily against two nuclear proteins, gp210 and sp100. In PBC, there are considerable data on the specificity of these anti-nuclear antibodies as well as suggestive evidence that antibodies to gp210 predict a poor outcome. However, a further understanding of the significance of these autoantibodies has been hampered by limitations in accessing human subjects in a preclinical or early asymptomatic stage. To overcome this limitation, we have taken advantage of transgenic mice with abrogated transforming growth factor-β signalling in T cells (dnTGF-βRII) that develop histological features of PBC as well as the same AMA specificity. We studied these mice for serum ANA, including specific autoantibodies against gp210 and sp100. We further examined sera from dnTGF-βRII mice with concurrent deletions of the genes encoding interleukin (IL)-12p35, IL-12p40, IL-23p19, IL-17, IL-6, interferon (IFN)-γ or tumour necrosis factor (TNF)-α. Sera from all the dnTGF-βRII mouse lines contained antibodies against gp210 and sp100. Of significance, mice with germline deletions of the genes encoding IL-12p40, IL-23p19, IL-17, IL-6 and TNF-α had significantly lower titres of anti-gp210 antibodies. These results provide a platform to dissect the mechanisms of gp210 and sp100 autoantibody production in dnTGF-βRII mice as well as to study the possible role of ANA in the pathophysiology of PBC.

Antinuclear antibodies as ancillary markers in primary biliary cirrhosis

Antimitochondrial antibodies are the serological hallmark of primary biliary cirrhosis (PBC). Besides antimitochondrial antibodies, the autoantibody profile of PBC includes antinuclear antibodies (ANA) which are detectable by indirect immunofluorescence in up to 50% of PBC patients. Two immunofluorescence patterns are considered 'PBC-specific': the multiple nuclear dots and rim-like/membranous patterns. The target antigens of the multiple nuclear dots pattern have been identified as Sp100 and promyelocytic leukemia protein, whereas the rim-like/membranous pattern is given by autoantibodies recognizing multiple proteins such as gp210, nucleoporin p62 and the lamin B receptor. Other ANA, especially those already known in the rheumatological setting, such as anticentromere, anti-SSA/Ro and anti-dsDNA antibodies, can be frequently found in PBC, often coexisting in the same patient. In this article, we will report on recent progress in the antigenic characterization of ANA in PBC, their detection with both traditional assays and Western blot/ELISA with molecularly defined nuclear antigens, and we will discuss their clinical significance.

PBC screen: an IgG/IgA dual isotype ELISA detecting multiple mitochondrial and nuclear autoantibodies specific for primary biliary cirrhosis

A dual isotype (IgG, IgA) enzyme-linked immunosorbent assay (ELISA) designed to provide enhanced detection of primary biliary cirrhosis (PBC)-specific autoantibodies against both major mitochondrial and nuclear antigens has been developed and recently become commercially available. The assay (PBC Screen) simultaneously detects IgG and IgA autoantibodies to the immunodominant portions of the 3 major mitochondrial (MIT3) and nuclear (gp210, and sp100) antigens. The aim of this study was to compare the performance of the PBC Screen to the combined performance obtained with individual IgG ELISAs to MIT3, gp210, and sp100 on a large group of selected patients from multiple centers. A total of 1175 patients with PBC and 1232 subjects without PBC were evaluated. Non-PBC groups included healthy controls (624) as well as individuals with autoimmune hepatitis (281), primary sclerosing cholangitis (77), viral hepatitis (91 hepatitis B and 98 hepatitis C), other liver diseases (31), and other infectious or autoimmune diseases (30). The PBC Screen at the receiver operator characteristic optimized cutoff of 27.8 units, had an overall sensitivity of 83.8%, specificity of 94.7% and area under curve of 0.9212. This was similar to the specificity of 96.1% obtained by the combined results of individual MIT3, sp100, and gp210 IgG ELISAs (kappa index at 0.898). Of the 253 PBC patients without AMA detectable by immunofluorescence, 113 (44.7%) were interpreted as positive for PBC-specific autoantibodies. In conclusion, the PBC Screen is an appropriate first-line test for the diagnosis of PBC, including for patients negative for markers assessed using conventional methods.

The use of phage display in neurobiology

Phage display has been extensively used to study protein-protein interactions, receptor- and antibody-binding sites, and immune responses, to modify protein properties, and to select antibodies against a wide range of different antigens. In the format most often used, a polypeptide is displayed on the surface of a filamentous phage by genetic fusion to one of the coat proteins, creating a chimeric coat protein, and coupling phenotype (the protein) to genotype (the gene within). As the gene encoding the chimeric coat protein is packaged within the phage, selection of the phage on the basis of the binding properties of the polypeptide displayed on the surface simultaneously results in the isolation of the gene encoding the polypeptide. This unit describes the background to the technique, and illustrates how it has been applied to a number of different problems, each of which has its neurobiological counterparts. Although this overview concentrates on the use of filamentous phage, which is the most popular platform, other systems are also described.

Nuclear envelope protein autoantigens in primary biliary cirrhosis

Antinuclear antibodies are detectable in approximately 50% of subjects with primary biliary cirrhosis (PBC). Most clinical laboratories use indirect immunofluorescence microscopy to detect antinuclear antibodies and two labeling patterns that predominate in PBC are nuclear rim and multiple nuclear dots. Antibodies giving these patterns most often recognize nuclear envelope protein gp210 and nuclear body protein sp100, respectively. Fewer subjects with PBC have autoantibodies giving nuclear rim labeling that recognize nucleoporin p62 and LBR. Gp210 is an integral protein localized to the nuclear pore membranes. Approximately 25% of subjects with PBC have detectable serum anti-gp210 antibodies. The vast majority of anti-gp210 antibodies from patients with PBC recognize a stretch of only 15 amino acids in the carboxyl-terminal tail that faces the nuclear pore complex. Enzyme-linked immunosorbent assays using either recombinant protein expressed in bacteria or chemically synthesized polypeptides have been established to reliably detect these autoantibodies. Although initial studies did not find a correlation between the presence of anti-gp210 antibodies and prognosis in PBC, recent data suggest that the presence of antinuclear envelope protein antibodies correlate with an unfavorable disease course and more rapid progression.

Comparison of two ELISA assays for anti-Sp100 determination

Antibodies to Sp100 have been described not only in primary biliary cirrhosis (PBC), but also in other diseases. Two assays for detection of Sp100 levels by enzyme-linked immunosorbent assay (ELISA) have been compared in a cohort of patients from our area: (a) Sp100 kit produced by IMTEC, Immunodiagnostica GmbH, and (b) Quanta Lite Sp100 kit produced by INOVA Diagnostics. We analyze here the correlation between the two assays and compare their efficiency in diagnosing PBC. We also comment on the exceptions derived from reactivity with other diseases. We studied 78 sera by IIF with the typical multiple nuclear dots (MND) pattern from patients who suffered from PBC, hepatopathies different from PBC, systemic lupus erythematosus (SLE), other connective tissue diseases (CTD), skeletal diseases, lung diseases, hematological disorders, a miscellaneous group, and a healthy IIF negative control group. The tests work equally well despite their different quantification system: (a) it is based on a standard curve; and (b) it is based on a single-point antigen-specific calibration. Some discrepancies could be explained by differences in the immunodominant epitope used in the ELISA. The main finding of this study is that the presence of MND/Sp100-positive antibodies were detected not only in hepatic diseases, mainly PBC, but also in other clinical conditions, confirmed by both tests. Diagnosis of PBC must be established in the right clinical context, because other diseases recognizing the same epitope, mainly SLE, may also show high Sp100 levels. Sera from PBC patients with antimitochondrial antibodies (AMA) showed higher anti-Sp100 than the AMA-negative group.

Gene cloning and fusion expression of human autoantigen Sp100 in yeasts

AIM: To clone and construct the plasmid cont-aining human autoantigene Sp100 gene, and then to identify the immunoreactivity of the purified recombinant protein.

METHODS: The Sp100 gene was amplified from human liver cDNA library, and then was cloned into PEGH vector to induce the Sp100 expression. The obtained products were identified and analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and Western blot.

RESULTS: The sequence of Sp100 autoantigene gene was confirmed to be the same as the sequence reported in GenBank. The fusion pro-teins were found at 53-, 55-, 52-, 37-, 42-, and 47-ku strip on SDS-PAGE gel. Western blot analysis showed that the fusion protein with 55, 52, 42 and 47 ku had the same immunoreactivity as human Sp100 autoantigene.

CONCLUSION: Human plasmid containing Sp100 gene is successfully cloned and expressed in yeast Y258.

Amino acids critical for binding of autoantibody to an immunodominant conformational epitope of the pyruvate dehydrogenase complex subunit E2: Identification by phage display and site-directed mutagenesis

The E2 subunit of the mitochondrial multienzyme pyruvate dehydrogenase complex (PDC-E2) is the major autoantigen in the liver disease, primary biliary cirrhosis (PBC). An epitope region which has been localized to amino acids 91-227 is believed to include the residue K173 to which is attached the lipoyl cofactor. We investigated structural features of this epitope region by screening random peptide phage-displayed libraries and identified prevalent phagotopes that contained likely contact amino acids in separate regions of the linear sequence, H132M133, and F178, V180. These were confirmed by site-directed alanine mutagenesis singly or in combination of the HM and FV residues in wild-type (wt) PDC-E2, and by immunization of rabbits with phage that expressed peptides MHLNTPP or FVLPWRI. The lipoyl lysine K173 also was mutated. Reactivities of mutants and wild-type (wt) PDC-E2, compared by ELISA using 12 PBC sera, showed decremental reactivity of mutant versus wt PDC-E2 (normalized to 100%): wt PDC-E2 (100%)>>PDC-E2(F178A,V180A) (mean+/-S.D., 59+/-17%)>PDC-E2(M133A) (50+/-13%)>PDC-E2(H132A) (36+/-13%)>PDC-E2(H132A,M133A) (28+/-8%)>PDC-E2(H132A,M133A,F178V,M180A) (18+/-13%). Notably PDC-E2(K173A) retained full reactivity (93+/-21%). Rabbits immunized with phage peptides generated antibodies reactive with entire PDC-E2. Our data convincingly validate phage library technology for defining spatially disparate contact residues for conformational epitopes. Ensuing data could be generally applicable to search for occult extrinsic agents as initiators of autoimmunity.

Characterizing monoclonal antibody epitopes by filtered gene fragment phage display

In the present paper, we describe a novel approach to map monoclonal antibody epitopes, using three new monoclonal antibodies that recognize h-TG2 (human transglutaminase 2) as an example. The target gene was fragmented and cloned upstream of an antibiotic-resistance gene, in the vector pPAO2, to select for in-frame polypeptides. After removal of the antibiotic-resistance gene by Cre/Lox recombination, an antigen fragment phage display library was created and selected against specific monoclonal antibodies. Using the h-TG2 fragment library, we were able to identify epitopes. This technique can also be broadly applied to the study of protein-protein interactions.

[Primary biliary liver cirrhosis and overlap syndrome. Diagnosis and therapy]

Primary biliary cirrhosis represents a chronic cholestatic liver disease of unknown etiology. It primarily affects females, is associated with extrahepatic immune-mediated syndromes, shows an immunogenetic association with HLA DR8, and displays serum autoantibodies, which makes an autoimmune etiology likely. The diagnosis is reached in patients with elevated alkaline phosphatase, gamma glutamyl transferase and bilirubin levels who exhibit normal bile ducts upon ultrasound examination, and in whom specific antimitochondrial autoantibodies are detectable. Half of all PBC patients additionally show specific antinuclear autoantibodies. Immunosuppressive therapy is ineffective; steroids, transplant immunosuppressants, colchicine, d-penicillamine and methotrexate are of limited clinical benefit. Ursodeoxycholic acid has few side effects and leads to a biochemical response and a delay of disease progression in most cases. When ursodeoxycholic acid therapy is ineffective an overlap syndrome with autoimmune hepatitis can be present, which can respond to steroid treatment. The only curative option is liver transplantation which should be considered when bilirubin levels exceed 100 microM/l.

Antinuclear antibodies specific for primary biliary cirrhosis

The serological hallmark of primary biliary cirrhosis (PBC) is the presence of antimitochondrial antibodies. However, antinuclear antibodies (ANA) are also detectable in approximately 50% of subjects with PBC. Most clinical laboratories use indirect immunofluorescence microscopy to detect ANA and two labeling patterns that predominate in PBC are 'punctate nuclear rim' and 'multiple nuclear dots.' Work over the past several years has shown that antibodies giving these patterns most often recognize nuclear pore membrane protein gp210 and nuclear body protein sp100, respectively. These ANA are highly specific for PBC and detected in approximately 25% of patients. Less frequently, ANA apparently unique to PBC recognize other proteins of the nuclear envelope and nuclear bodies. While antibodies against gp210, sp100 and some other nuclear proteins are very specific to PBC and may therefore be useful diagnostic markers, their connection to pathogenesis remains to be elucidated.

Selecting open reading frames from DNA

We describe a method to select DNA encoding functional open reading frames (ORFs) from noncoding DNA within the context of a specific vector. Phage display has been used as an example, but any system requiring DNA encoding protein fragments, for example, the yeast two-hybrid system, could be used. By cloning DNA fragments upstream of a fusion gene, consisting of the beta-lactamase gene flanked by lox recombination sites, which is, in turn, upstream of gene 3 from fd phage, only those clones containing DNA fragments encoding ORFs confer ampicillin resistance and survive. After selection, the beta-lactamase gene can be removed by Cre recombinase, leaving a standard phage display vector with ORFs fused to gene 3. This vector has been tested on a plasmid containing tissue transglutaminase. All surviving clones analyzed by sequencing were found to contain ORFs, of which 83% were localized to known genes, and at least 80% produced immunologically detectable polypeptides. Use of a specific anti-tTG monoclonal antibody allowed the identification of clones containing the correct epitope. This approach could be applicable to the efficient selection of random ORFs representing the coding potential of whole organisms, and their subsequent downstream use in a number of different systems.

Autoantigens in primary biliary cirrhosis

The automimmune liver disease primary biliary cirrhosis (PBC) is characterised by serum autoantibodies directed at mitochondrial and nuclear antigens (seen in most patients and a subset of patients, respectively). The antimitochondrial antibodies (AMA) characteristic of PBC are directed at members of the 2-oxoacid dehydrogenase components of multienzyme complexes; in particular, the E2 and E3 binding protein (E3BP) components of the pyruvate dehydrogenase complex (PDC). The presence of autoantibodies reactive with PDC-E2 and/or E3BP is strongly predictive of the presence of PBC. Therefore, the detection of these antibodies plays a very important role in the diagnosis of PBC. Originally demonstrated using immunofluorescence approaches, AMA can now be detected by the use of commercially available enzyme linked immunosorbent assays (ELISAs). Although the ELISA based approaches have advantages in terms of laboratory practicality, they are slightly less sensitive for the diagnosis of PBC than immunofluorescence (occasional patients with PBC show reactivity with PDC related antigens not present in the antigen preparations available for use with ELISA). Therefore, immunofluorescence should continue to be available as a complementary diagnostic test for use in occasional patients. In a subset of patients with PBC, autoantibodies are directed at increasingly well characterised nuclear antigens. Antinuclear antibody (ANA) positive patients are typically AMA negative. There are no significant differences in disease phenotype between AMA positive and AMA negative groups. At present, the clinical detection of ANA is mostly by Hep2 immunofluorescence, although ELISA kits for individual nuclear antigens are increasingly becoming available.

Analysis of the autoimmune epitopes on human testicular NASP using recombinant and synthetic peptides

The human nuclear autoantigenic sperm protein, NASP, is a testicular histone-binding protein of 787 amino acids to which most vasectomized men develop autoantibodies. In this study to define the boundaries of antigenic regions and epitope recognition pattern, recombinant deletion mutants spanning the entire protein coding sequence and a human NASP cDNA sublibrary were screened with vasectomy patients' sera. Employing panel sera from 21 vasectomy patients with anti-sperm antibodies, a heterogeneous pattern of autoantibody binding to the recombinant polypeptides was detected in ELISA and immunoblotting. The majority of sera (20/21) had antibodies to one or more of the NASP fusion proteins. Antigenic sites preferentially recognized by the individual patients' sera were located within aa 32-352 and aa 572-787. Using a patient's serum selected for its reactivity to the whole recombinant protein in Western blots, cDNA clones positive for the C-terminal domain of the molecule were identified. The number and location of linear epitopes in this region were determined by synthetic peptide mapping and inhibition studies. The epitope-containing segment was delimited to the sequence aa 619-692 and analysis of a series of 74 concurrent overlapping 9mer synthetic peptides encompassing this region revealed four linear epitopes: amino acid residues IREKIEDAK (aa 648-656), KESQRSGNV (aa 656-664), AELALKATL (aa 665-673) and GFTPGGGGS (aa 680-688). All individual patients' sera reacted with epitopes within the sequence IREellipsis.GGS (aa 648-688). The strongest reactivity was displayed by peptides corresponding to the sequence AELALKATL (aa 665-673). Thus, multiple continuous autoimmune epitopes in NASP involving sequences in the conserved C-terminal domain as well as in the less conserved testis-specific N-terminal region comprising the histone-binding sites, as predicted for an antigen-driven immune response, may be a target of autoantibodies in vasectomized men and may provide a relevant laboratory variable to describe more accurately the spectrum of autoantibody specificities associated with the clinical manifestation of vasectomy.

Autoimmune tests in primary biliary cirrhosis

Primary biliary cirrhosis (PBC) is characterized by an immune mediated, irreversible destruction of the small intrahepatic bile ducts leading to progressive liver cirrhosis and frequently to liver failure. The course of the disease is variable and an early diagnosis is desirable to identify individuals with rapidly progressing disease, to initiate adequate therapeutic measures and to evaluate the necessity of liver transplantation. Serological tests represent the single most important diagnostic feature of PBC because liver histology, biochemistry, or clinical syndrome alone are not reliable in this respect. The molecular definition of the autoantigen targets of antimitochondrial antibodies (AMA) has resulted in the development of reproducible and effective serological testing strategies. AMA directed against the ketoacid dehydrogenase complex are highly disease-specific but not directed against liver-specific target structures. Despite a high disease specificity, their usefulness for predicting the course of disease, the timing of liver transplantation, or disease recurrence after transplantation is limited. The realization that about 5% of patients with PBC do not display AMA has led to the identification of PBC-specific antinuclear autoantibodies directed against the nuclear pore complex and other targets. The overlap of PBC with autoimmune hepatitis and primary sclerosing cholangitis represents a diagnostic challenge in which autoantibody determinations play a central role and contribute to the administration of suitable treatment options.