Human combinatorial autoantibodies and mouse monoclonal antibodies to PDC-E2 produce abnormal apical staining of salivary glands in patients with coexistent primary biliary cirrhosis and Sjögren's syndrome

Systemic Complications of Primary Biliary Cholangitis

Chronic cholestasis is the hallmark clinical feature of primary biliary cholangitis. In addition to progressive liver damage, chronic cholestasis can lead to serious complications, many of which occur outside the liver. Bile acids are ligands for nuclear hormone receptors, and alterations in their concentration disrupt normal functioning of numerous different cell types. This article discusses the clinical presentation, pathophysiology, and management of pruritus (itching), fatigue, osteoporosis, hyperlipidemia, fat-soluble vitamin deficiencies, malignancies, cardiac dysfunction, bacterial cholangitis, cholemic (bile cast) nephropathy, and Sicca syndrome.

Cutaneous and Mucosal Manifestations of Sjögren's Syndrome

Sjögren's syndrome is currently considered an "autoimmune epithelitis," as exocrine glands, especially salivary and lacrimal, are progressively destructed by an immune-mediated process associated with specific serum autoantibodies and local lymphocyte infiltrate. Xerostomia remains a key complain in patients with Sjögren's syndrome but should be evaluated also for other causes such as xerogenic medications, followed by radiation and chemotherapy for head and neck cancers, hormone disorders, infections, or other connective tissue diseases. Further, xerophtalmia (also known as dry eye) frequently associated with keratoconjunctivitis sicca cumulatively affects approximately 10-30% of the general population with increasing incidence with age and is more frequently secondary to non-autoimmune diseases. On the other hand, numerous patients with Sjögren's syndrome manifest signs of systemic dryness involving the nose, the trachea, the vagina, and the skin, suggesting that other glands are also affected beyond the exocrine epithelia. Skin involvement in Sjögren's syndrome is relatively common, and various manifestations may be present, in particular xeroderma, eyelid dermatitis, annular erythema, and cutaneous vasculitis. Additional skin non-vasculitic manifestations include livedo reticularis which may occur in the absence of vasculitis, and localized nodular cutaneous amyloidosis possibly representing lymphoproliferative diseases related to Sjögren's syndrome. The treatment of skin and mucosal manifestations in Sjögren's syndrome is similar regardless of the cause, starting from patient education to avoid alcohol and tobacco smoking and to pursue dental hygiene. In conclusion, a strict collaboration between the dermatologist and the rheumatologist is essential in the adequate management of Sjögren's syndrome skin and mucosal manifestations.

Chronic Autoimmune Epithelitis in Sjögren's Syndrome and Primary Biliary Cholangitis: A Comprehensive Review

Within the spectrum of autoimmune diseases, Sjögren's syndrome and primary biliary cholangitis are exemplary and can be coined as chronic epithelitis based on their frequent coexistence in clinical practice and the highly specific immune-mediated injury of the small bile ducts and the exocrine glands. The pathogenic mechanisms underlying the diseases are similar, with apoptosis being the key element leading to organ-specific immune-mediated injury directed against the small bile ducts and salivary gland epithelia, respectively along with similar epidemiological features, such as female predominance and the age of onset in the fifth decade of life. Indeed, novel insights into the pathogenesis of the diseases have been obtained in recent years, including a better definition of the role of B and T cells, particularly Th17 cells, and the mechanisms of autoantibody-mediated tissue injury, with anti-mitochondrial antibodies and SS-A/SS-B being identified as specific for primary biliary cholangitis and Sjögren's syndrome, respectively. These findings have opened the possibility to new targeted therapies, but most clinical needs remain unmet, particularly from a therapeutic standpoint where options diverge, with bile acids being the predominant treatment strategy in primary biliary cholangitis and immunomodulators being used to treat Sjögren's syndrome. Here we provide a comprehensive review of the most recent findings on the pathogenesis, clinical manifestations and therapeutic options for Sjögren's syndrome and primary biliary cholangitis, respectively, while stressing the common traits between these conditions. Our cumulative hypothesis is that similarities outnumber differences and that this may prove advantageous towards a better management of patients.

The management of autoimmunity in patients with cholestatic liver diseases

Cholestatic liver diseases are rare diseases that often lead to cirrhosis and its consequent complications. In addition to liver-related morbidity, patients with cholestatic liver diseases often suffer from autoimmune diseases that affect several organs and tissues. The robust and efficient data collection and collaboration between hepatologists and rheumatologists have led to significant advancements in understanding the relationship between the cholestatic liver diseases and associated autoimmune diseases. In this paper, we discuss the cholestatic liver diseases (primary biliary cirrhosis, primary sclerosing cholangitis and immunoglobulin G4 associated cholangitis) and associated autoimmune diseases.

The coexistence of Sjögren's syndrome and primary biliary cirrhosis: a comprehensive review

Organ-specific and systemic autoimmune diseases share numerous features and often coexist in the same patient. Autoimmune cholangitis/primary biliary cirrhosis and Sjogren syndrome represent paradigmatic examples of the common grounds of different autoimmunity phenotypes based on similarities in clinical manifestations and immunopathogenesis. In fact, primary biliary cirrhosis and Sjogren's syndrome have both been coined as an autoimmune epithelitis in which apoptosis may be in both cases the key element to explain the organ-specific immune-mediated injury against the biliary and exocrine gland epithelia, respectively. Further, growing evidence supports in both diseases the view that B cells, T cytotoxic cells, and T helper cells are involved in chronic inflammation, likely via the altered expression of pro-inflammatory cytokines. The presence of estrogen receptors on the biliary and exocrine gland epithelia has been advocated as a key to the female predominance encountered in primary biliary cirrhosis and Sjogren's syndrome. Sadly, despite available data, therapeutic approaches remain largely unsatisfactory and recent studies with mechanistic approaches (as in the case of B cell depletion with rituximab) have been of partial benefit only. Future studies should focus on new molecular tools (single-cell transcriptomics, microRNA, epigenetics) to provide unique insights into common mechanisms.

The immunogenetics of primary biliary cirrhosis: A comprehensive review

Primary biliary cirrhosis (PBC), a classic autoimmune liver disease, is characterised by a progressive T cell predominant lymphocytic cholangitis, and a serologic pattern of reactivity in the form of specific anti-mitochondrial antibodies (AMA). CD4+ T cells are particularly implicated by PBC's cytokine signature, the presence of CD4+ T cells specific to mitochondrial auto-antigens, the expression of MHC II on injured biliary epithelial cells, and PBC's coincidence with other similar T cell mediated autoimmune conditions. CD4+ T cells are also central to current animal models of PBC, and their transfer typically also transfers disease. The importance of genetic risk to developing PBC is evidenced by a much higher concordance rate in monozygotic than dizygotic twins, increased AMA rates in asymptomatic relatives, and disproportionate rates of disease in siblings of PBC patients, PBC family members and certain genetically defined populations. Recently, high-throughput genetic studies have greatly expanded our understanding of the gene variants underpinning risk for PBC development, so linking genetics and immunology. Here we summarize genetic association data that has emerged from large scale genome-wide association studies and discuss the evidence for the potential functional significance of the individual genes and pathways identified; we particularly highlight associations in the IL-12-STAT4-Th1 pathway. HLA associations and epigenetic effects are specifically considered and individual variants are linked to clinical phenotypes where data exist. We also consider why there is a gap between calculated genetic risk and clinical data: so-called missing heritability, and how immunogenetic observations are being translated to novel therapies. Ultimately whilst genetic risk factors will only account for a proportion of disease risk, ongoing efforts to refine associations and understand biologic links to disease pathways are hoped to drive more rational therapy for patients.

Role of novel retroviruses in chronic liver disease: assessing the link of human betaretrovirus with primary biliary cirrhosis

A human betaretrovirus resembling mouse mammary tumor virus has been characterized in patients with primary biliary cirrhosis. The agent triggers a disease-specific phenotype in vitro with aberrant cell-surface expression of mitochondrial antigens. The presentation of a usually sequestered self-protein is thought to lead to the loss of tolerance and the production of anti-mitochondrial antibodies associated with the disease. Similar observations have been made in mouse models, where mouse mammary tumor virus infection has been linked with the development of cholangitis and production of anti-mitochondrial antibodies. The use of combination antiretroviral therapy has been shown to impact on histological and biochemical disease in mouse models of autoimmune biliary disease and in clinical trials of patients with primary biliary cirrhosis. However, the HIV protease inhibitors are not well tolerated in patients with primary biliary cirrhosis, and more efficacious regimens will be required to clearly link reduction of viral load with improvement of cholangitis.

Presence of disease specific autoantibodies against liver sinusoidal cells in primary biliary cirrhosis

AIM: To investigate the presence of autoantibodies directed against liver sinusoidal cells in primary biliary cirrhosis (PBC).

METHODS: Liver biopsies from 21 PBC patients were studied and compared with 12 liver biopsies from disease controls [3 patients with hepatitis B (HBV) virus, 3 patients with hepatitis C virus (HCV), 3 patients with non-alcoholic steatohepatitis and 3 patients with acute alcoholic hepatitis (AAH)]. As healthy controls, we used tissue specimens adjacent to metastatic liver adenocarcinoma. Normal serum was taken from staff members of the unit. The determination of the cell type targeted by autoantibodies present in the patients sera was performed by indirect immunofluorescence (IIF) analysis using paraffin-embedded liver sections as a substrate. Sera from homologous or heterologous PBC patients or sera from the disease control group were used as primary antibodies. The presence of autoantibodies was identified using confocal microscopy.

RESULTS: In total, 18/21 (85.7%) PBC patients exhibited positive staining in the sinusoidal cells, 10/21 (47.6%) in lymphocytes, 8/21 (38%) in cholangiocytes and 7/21 (33.3%) in hepatocytes, when homologous serum and fluorescein isothiocyanate-conjugated immunoglobulin type G (IgG) secondary antibody were used. PBC sections incubated with heterologous PBC serum showed reduced staining (20% for sinusoidal cells, 20% for lymphocytes, 20% for cholangiocytes and 13.3% for hepatocytes). When IgM immunoglobulin, instead of IgG, was used as secondary antibody, positive staining was observed in 75% of lymphocytes, 62.5% of cholangiocytes, 37.5% of hepatocytes and 50% of the sinusoidal cells with a much stronger staining intensity. No staining was observed when either normal or PBC sera were used as a primary antibody on liver sections from the disease control group. When PBC sera were incubated with healthy control sections, weak positive staining of cholangiocytes was observed in 3/21 (14.3%) PBC serum samples. Steatohepatitis serum on PBC sections gave a positive staining of some hepatocytes and lymphocytes but no staining on viral hepatitis sections. Incubation with HBV sera stained some hepatocytes, cholangiocytes and intra-sinusoidal or portal lymphocytes of PBC, HBV and AAH patients but not HCV patients.

CONCLUSION: In this study, for the first time in diseased liver tissue, we have demonstrated that a large proportion of PBC patients have disease specific autoantibodies against liver sinusoidal cells.

Gastrointestinal and hepatic manifestations of Sjogren syndrome

Sjogren syndrome (SS) is an autoimmune disease that affects exocrine glands and therefore may affect the gastrointestinal system, from the mouth, esophagus, and bowel to the liver and pancreas. Oral involvement in SS is mainly characterized by dryness, with a wide spectrum of symptoms, from mild-to-severe xerostomia with dysgeusia and tooth decay. The dysphagia, although common, does not correlate with the reduced salivary flow rate or the dysmotility that may be present. Dyspepsia, found in up to 23% of patients, may be associated with gastritis, reduced acid production, and antiparietal cell antibodies, but rarely pernicious anemia. Pancreatic involvement, although rare, includes pancreatitis and pancreatic insufficiency. The most common causes of liver disease are primary biliary cirrhosis, autoimmune hepatitis, nonalcoholic fatty liver disease, and hepatitis C virus (HCV). Although abnormal liver tests are found in up to 49% of patients, they are usually mild. Although sicca syndrome, abnormal histology of the salivary glands, and abnormal sialograms are common in primary biliary cirrhosis, the antibodies to Ro/SSA or La/SSB antigens are infrequent. Xerostomia, sialadenitis, abnormal salivary flow rates, and abnormal Schirmer test in HCV vary widely among the studies, although the antibodies to Ro/SSA or La/SSB are only 1%. Several studies show that HCV is in saliva, although how this may impact sicca syndrome or SS in HCV is unclear. SS as a disease of exocrine glands affects many parts of the gastrointestinal system.

Abnormal intestinal permeability in primary biliary cirrhosis

Antimitochondrial antibodies (AMAs) found in patients with primary biliary cirrhosis (PBC) cross-react with bacterial proteins and hence molecular mimicry has been proposed as a mechanism for AMA development. Alterations in gastrointestinal permeability would provide a potential route for increased exposure of gut flora to the immune system. In this study we aimed to compare the measured gastrointestinal permeability in patients with PBC to that in patients with liver disease (hepatitis C) and healthy control populations. Subjects drank a mixture of sucrose, lactulose, and mannitol dissolved in water. Eight-hour urinary excretion of the sugars was measured to assess intestinal permeability. Antiendomysial antibody testing was performed to exclude subclinical celiac disease. Eighty-six patients with PBC were evaluated and compared to 69 hepatitis C patients and 155 healthy controls. The mean urinary excretion of sucrose in the PBC patients (133.89 +/- 72.56 mg) was significantly higher than that in hepatitis C patients (101.07+/-63.35) or healthy controls (89.46+/-41.76) (P=0.0001), suggesting abnormal gastric or proximal small intestinal permeability. Sucrose excretion was not increased among patients with hepatitis C compared to healthy controls. The ratio of lactulose:mannitol excretion, reflecting small bowel permeability, was also elevated in the PBC group (0.017+/-0.012) compared to healthy controls (0.012+/-0.007) (P=0.0001) but was equal to that found among patients with hepatitis C (0.016+/-0.011) (P=NS). We conclude that the permeability of both the stomach and the small bowel is increased in patients with PBC, however, it is unclear if it is a cause, consequence, or manifestation of the disease.

Transgenic mice aberrantly expressing pyruvate dehydrogenase complex E2 component on biliary epithelial cells do not show primary biliary cirrhosis

Primary biliary cirrhosis (PBC) is an autoimmune disorder that specifically destroys biliary epithelial cells (BECs). In patients with PBC, the immunodominant pyruvate dehydrogenase complex E2 component (PDC-E2), identified as an antigen for disease-specific anti-mitochondrial antibody, is expressed aberrantly in the BEC cytoplasm. The present study focused on the pathophysiological role of aberrant PDC-E2 in the development of PBC. The BEC-specific cytokeratin-19 promoter and PDC-E2 gene were cloned from a mouse cDNA library. The constructed transgene was microinjected into fertilized eggs of mice, and the offspring were identified by Southern blotting and reverse transcriptase-polymerase chain reaction. The protein expression was confirmed by immunoprecipitation, immunoblotting and immunohistochemical staining. Five founder lines were identified as carrying the PDC-E2 gene, and one of these lines expressed PDC-E2 mRNA. The protein expression of exogenous PDC-E2 was detected in the liver. The transgenic mouse line showed diffuse expression of PDC-E2 in the BEC cytoplasm. Biochemical, serological and histological features of PBC were not detected. We established transgenic mice that constitutively express PDC-E2. The results indicated that aberrant PDC-E2 expression in the cytoplasm of BECs is not sufficient for the initiation of autoimmunity. Additional factors may be required to establish a model of PBC.

Patterns of autoimmunity in primary biliary cirrhosis patients and their families: a population-based cohort study

BACKGROUND

Primary biliary cirrhosis (PBC) is a chronic liver disease with autoimmune features but uncertain aetiology. Increased risk of PBC among relatives of patients may reflect common environmental factors, or inherited immunogenetic susceptibility. Associations between PBC and other autoimmune diseases have been reported, but their true extent and pattern is unknown.

AIM

To examine the prevalence and association patterns of autoimmune disease in a representative group of PBC patients.

DESIGN

Clinical cohort study.

METHODS

We clinically assessed members of a geographically-based PBC patient cohort (n = 160) for the presence of additional autoimmune disease, using established specific diagnostic criteria.

RESULTS

Some 53% of patients had at least one additional autoimmune condition, and 63% had serum autoantibodies other than AMA or ANA. AMA+ patients had a significantly lower prevalence of additional autoimmunity than AMA- patients (49% vs. 79%; p < 0.01). The greatest relative increase in disease prevalence was for scleroderma (8% of patients). Autoimmune disease was present in 14% of first-degree relatives.

DISCUSSION

PBC patients and their families have a wide susceptibility to autoimmunity. This observation supports an autoimmune aetiology and suggests that the genetic basis of PBC is likely to be expressed, at least in part, through factors controlling immune tolerance in general.

Do autoantibodies predict autoimmune liver disease in primary Sjögren's syndrome? Data of 180 patients upon a 5 year follow-up

OBJECTIVE

To evaluate the clinical value of autoantibodies as serological markers to predict autoimmune liver diseases in primary Sjögren's syndrome (SS).

MATERIALS AND METHODS

180 patients who met the European diagnostic criteria for SS but without a history of liver disease were studied upon a 5 year follow-up. Sera taken at enrolment were evaluated by immunofluorescence analysis (IF-AMA) on rat liver, stomach and kidney sections, enzyme-linked immunosorbent assay using rat mitochondrial, microsomal and soluble liver antigens and Western blot (WB) analysis using rat mitochondrial antigens.

RESULTS

At presentation, 152 (84%) sera had autoantibodies. Antinuclear antibodies (ANA) were expressed in 58% of patients and displayed three distinct patterns (speckled, homogenous and anticentromere). Smooth muscle autoantibodies (SMAs) and parietal cell autoantibodies were found in 39 and 4.5% of patients, respectively. Three patients presented antimitochondrial antibodies by IF-AMA, and two of them developed symptomatic primary biliary cirrhosis (PBC). Two patients without IF-AMA and without evidence of cholestasis had PBC-specific AMA (anti-PDC-E2 and anti-BCKADC-E2). However, these two patients and the third IF-AMA-positive woman remained free from symptoms and biochemical signs of PBC. Autoimmune hepatitis (AIH) (n = 2), 'overlap syndrome' of AIH and chronic hepatitis C (n = 1) and autoimmune cholangiopathy (AIC) (n = 1) were diagnosed in four patients.

CONCLUSIONS

Patients with IF-AMA usually develop symptomatic PBC upon a 5 year follow-up. Our findings support the idea that patients without IF-AMA, who express PBC-specific AMA, are in early, asymptomatic stage of the disease. High-titre SMA and IF-AMA are the most specific indicators for AIH and PBC.

Immunohistochemical differences in the portal tract and acinar infiltrates between primary biliary cirrhosis and autoimmune cholangitis

BACKGROUND

Antimitochondrial antibody-negative primary biliary cirrhosis, or autoimmune cholangitis, may be indistinguishable clinically and histologically from antimitochondrial antibody-positive primary biliary cirrhosis.

AIMS

We aimed to compare the phenotypic markers of the portal and acinar infiltrates in autoimmune cholangitis and antimitochondrial antibody-positive primary biliary cirrhosis.

PATIENTS AND METHODS

Formalin-fixed, paraffin-embedded liver sections were identified from 32 patients with a clinical and histological diagnosis of primary biliary cirrhosis. Thirteen were antimitochondrial antibody-negative (autoimmune cholangitis group) and 19 were antimitochondrial antibody-positive. The groups were well matched for age, histological stage, liver biochemistry and drug treatment. Immunohistochemical staining was performed using monoclonal antibodies against CD3 (pan T cell), CD8 (cytotoxic), CD45RO (memory), CD45RA (naive), CD68 (macrophages) and against the secreted form of eosinophilic cationic protein (EG2).

RESULTS

In autoimmune cholangitis, both portal and acinar CD3 cell counts were significantly higher than in antimitochondrial antibody-positive primary biliary cirrhosis (median portal count 421 vs 257 cells/graticule, P< 0.03; median acinar count 18 vs 9 cells/graticule, P< 0.02). There were no differences between the groups in portal or lobular CD8, CD45RO, CD45RA, CD68 or EG2. Of the total group (antimitochondrial antibody positives and negatives), there were significantly more CD45RA cells in early (stage 1) compared with cirrhotic (stage 4) disease (median 19.3 vs 14 cells/graticule, P< 0.03). EG2 staining was found in eight of the 32 sections overall, but not in the patients with stage 1 disease (P< 0.04).

CONCLUSION

CD3 counts are higher in autoimmune cholangitis than in antimitochondrial antibody-positive primary biliary cirrhosis in both portal and acinar areas. However, there are no significant differences in memory/naïve T-cell subsets between both conditions and, in both, loss of naive T lymphocytes and secretion of eosinophilic cationic protein occur with disease progression. This implies that the effector pathways of bile duct destruction are similar in autoimmune cholangitis and primary biliary cirrhosis.

Antimitochondrial autoantibodies in saliva and sera from patients with primary biliary cirrhosis

BACKGROUND AND AIMS

Primary biliary cirrhosis (PBC) is a cholestatic autoimmune liver disease characterized by antimitochondrial autoantibodies (AMA) in serum, for which the reactants are E2 subunits of the three 2-oxoacid dehydrogenase (2-OAD) enzymes, particularly pyruvate dehydrogenase complex (PDC-E2). Some 70% of patients with PBC have a coexisting autoimmune disease including Sjögren's syndrome. We aimed to ascertain the frequency and isotype of AMA in saliva in PBC.

METHODS

Serum and saliva from 12 patients with PBC were tested for AMA by immunoblotting on bovine heart mitochondria, and by an automated microassay based on inhibition of the enzymatic activity of PDC.

RESULTS

Autoantibodies of the immunoglobulin (Ig)G, IgM, and IgA immunoglobulin isotypes against the E2 subunits of 2-OAD enzymes were demonstrable in PBC in serum (12 of 12 cases) and saliva (nine of 12 cases). Salivary autoantibodies, like serum autoantibodies, were predominantly reactive with PDC and of the IgG isotype. Results for serum and saliva corresponded closely with regard to reactivity with individual enzymes of the 2-OAD enzyme family, and to the autoantibody isotype that was predominantly expressed, and also in the capacity to inhibit the enzymatic activity of PDC.

CONCLUSIONS

The presence of AMA in saliva to 2-OAD enzymes indicates that salivary glands could participate in the pathogenetic process of PBC. The detection of salivary AMA by a semi-automated enzyme inhibition assay offers possibilities for rapid population screening for detection of preclinical PBC among at-risk individuals, middle-aged to older women.

Spontaneous occurrence of chronic non-suppurative destructive cholangitis and antimitochondrial autoantibodies in MRL/lpr mice: possible animal model for primary biliary cirrhosis

MRL/MP mice bearing the lymphoproliferative gene lpr (known as MRL/MP-lpr/lpr or MRL/Ipr mice) are known to spontaneously develop severe autoimmune diseases such as glomerulonephritis, arteritis and arthritis at an early stage of their life. They have also been reported to develop severe sialadenitis, suggesting that this mouse could be a model for Sjögren's syndrome. Primary biliary cirrhosis, an autoimmune disease characterized by chronic non-suppurative destructive cholangitis and the occurrence of antimitochondrial antibodies, is frequently associated with Sjögren's syndrome. In this study, we examined whether cholangitis and/or antimitochondrial antibodies occur in this mouse model, using more than 100 young and old MRL/Ipr mice. We frequently found portal inflammation associated with cholangitis of small intrahepatic bile ducts, especially in older mice. There was also infiltration of inflammatory cells (monocytes) as well as CD4-positive T cells. Epithelioid granuloma and bile-duct loss were also occasionally found. These histological features resemble primary biliary cirrhosis. In addition, antimitochondrial antibodies were shown by immunocytochemistry to be present in the sera of MRL/Ipr mice. There is currently no established animal model for primary biliary cirrhosis. Therefore, further studies on MRL/Ipr mice, with respect to pathogenesis of primary biliary cirrhosis, are warranted.

Primary biliary cirrhosis with features of autoimmune hepatitis

The diagnosis of primary biliary cirrhosis (PBC) is made via a composite of clinical, laboratory, serologic, and histologic assessments, but within each parameter there exists a wide spectrum, so that the features of PBC are not always uniform. PBC is just one of several liver diseases thought to have an autoimmune basis. Therefore, it is not surprising, given the complexity of the immune response, that some patients thought to have PBC may have features of autoimmune hepatitis (AIH). Whether such patients have PBC with features of AIH, or antimitochondrial antibody-negative PBC, or another disease altogether, remains unclear.

Secretory autoantibodies in primary biliary cirrhosis (PBC)

It is unclear how breakdown in immune tolerance to the ubiquitous self-antigen pyruvate dehydrogenase complex (PDC), seen in the autoimmune liver disease PBC, gives rise to tissue damage with such a limited distribution (restricted to the liver and salivary and lachrymal glands). One property shared by these tissues is the ability to export secretory IgA by the process of transcytosis. The aim of this study was to address whether active transcytosis of anti-PDC IgA occurs across epithelial surfaces in PBC, a finding that might implicate mucosal specific immune mechanisms in the pathogenesis of this disease. Parotid saliva was collected from PBC patients (n = 44), normal controls (n = 28) and PBC patients post-liver transplantation (n = 11). IgA and secretory component-positive antibodies specific for human PDC were quantified by ELISA and immunoblotting. PBC patients (but not control subjects) had anti-PDC IgA in their saliva. The strong correlation seen between titres detected using anti-IgA and anti-secretory component antibodies suggests that this is predominantly secretory IgA reaching the saliva by the active process of epithelial transcytosis. Titres of anti-PDC IgA remain high in PBC patients saliva post-liver transplant. Findings from studies of IgA in viral infection models raise the possibility that anti-PDC IgA could, whilst undergoing transcytosis, bind to newly translated PDC components in the cytoplasm of the epithelial cells transporting them out of the cell and inducing metabolic damage. This model would, if correct, help to explain the mechanism and tropism of tissue damage in PBC and the aberrant pattern of expression of PDC on the apical surface of biliary and salivary epithelial cells reported in this disease.

Mucosal immunity and primary biliary cirrhosis: presence of antimitochondrial antibodies in urine

We have shown that IgA-class antimitochondrial autoantibodies (AMA) can be detected in the bile and saliva of patients with PBC, suggesting that AMA are secreted into the luminal fluid across bile ducts and salivary glands. These data prompted us to determine whether AMA of the IgA isotype may be transported across other epithelial mucosa. Therefore, we tested for the presence of AMA in the urine specimens of 83 patients with PBC and 58 non-PBC controls including healthy individuals and patients with other liver diseases. Patients enrolled in this study had no history of renal disease, and we confirmed there was less than 50 microgram/mL of protein in each of the urine specimens. Interestingly, we found that AMA were present in the urine of 71/83 (86%) of all patients with PBC and in 71/78 (91%) of patients with PBC that were serum AMA positive. In contrast, AMA were not detected in any of the 58 control urine specimens. Of particular interest, AMA of the IgA isotype was present in 57/83 (69%) of patients with PBC, and in 52 of these 57, we found secretory-type IgA. In a nested random subgroup of urine samples, the prevalence of the IgA2 AMA was 6/18 (33%), significantly lower than in matched serum samples, 13/16 (81%, P =.007). These data show that AMA of the IgA isotype is secreted into urine from the uroepithelium of patients with PBC, and support the thesis that PBC originated from either a mucosal challenge or a loss of mucosal tolerance.

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.

Evidence for a locally driven mucosal response and the presence of mitochondrial antigens in saliva in primary biliary cirrhosis

Primary biliary cirrhosis (PBC) is often considered to be a dry gland disease caused by frequent involvement of salivary and lacrimal glands. Although high titers of antimitochondrial autoantibodies (AMA) have long been recognized in PBC, little is known about the presence of mitochondrial autoantigens in mucosal compartments such as saliva. We investigated saliva and sera in PBC patients and controls for the presence of AMA and mitochondrial antigens. In PBC saliva, AMA were detected in 45 of 49 (92%), with specificity directed against pyruvate dehydrogenase complex (PDC-E2) alone in 22 of 49 (45%), against PDC-E2 and branched-chain 2-oxo-acid dehydrogenase complex E2 (BCOADC-E2) in 4 of 49 (8%), to PDC-E2 and 2-oxoglutarate dehydrogenase complex E2 (OGDC-E2) in 9 of 49 (18%), and to the 3 antigens together in 10 of 49 (20%). Isotyping of the saliva AMA showed that 80% of the patients had immunoglobulin A (IgA) against PDC-E2, 18% had IgM-specific PDC-E2, and 35% had IgG specific PDC-E2. Similar to serum and bile anti-PDC-E2 IgA antibodies, the saliva autoantibodies localized their reactivity to the inner lipoyl domain of PDC-E2. Furthermore, saliva from patients with PBC but not controls inhibited pyruvate dehydrogenase enzyme activity in vitro. In addition, and of particular interest, we detected a molecule with a molecular weight corresponding to PDC-E2 (74 kd) in PBC but not control saliva. These findings make several important points: first, there appears to be localized mucosal immunity in the secretory system of PBC; second, AMA are readily detected in PBC saliva; and third, PDC-E2 may be present in the saliva of PBC.

[Primary biliary cirrhosis and systemic scleroderma (Reynolds syndrome): apropos of 8 new cases. The contribution of accessory salivary gland biopsy]

PURPOSE

We report eight new cases of the association primary biliary cirrhosis--systemic sclerosis (Reynolds' syndrome) and study the contribution of labial salivary gland biopsy to the disease diagnosis.

METHODS

We retrospectively collected clinical and biological data as well as results of labial salivary gland biopsies in eight patients with Reynolds' syndrome.

RESULTS

The eight patients were female. Systemic sclerosis corresponded to a CREST syndrome in three patients, while in two other patients two features of the CREST syndrome were observed. Anticentromere antibodies were detected in these five cases. The last three patients had systemic sclerosis with bilateral pulmonary fibrosis in two cases. All patients presented with Sjögren's syndrome. Labial salivary gland biopsies performed in six patients showed in five cases an inflammatory infiltrate and focal sialadenitis typically associated with Sjögren's syndrome. In four cases, organic microangiopathy and fibrosis were suggestive of systemic sclerosis, and in four other cases, the presence of a pericanalicular infiltrate of lymphocytes and necrosis of the excretory ducts epithelial cells suggested the existence of primary biliary cirrhosis. In three patients, all histological lesions were found in the same labial salivary gland biopsy.

CONCLUSION

Coexistence of histological lesions on the same labial salivary gland suggestive of primary biliary cirrhosis, systemic sclerosis and Sjögren's syndrome has never been described previously. The diagnostic value of labial salivary gland biopsy has to be assessed in this context.

aly/aly mice: a unique model of biliary disease

An autosomal recessive murine mutation, coined "aly/aly" or "alymphoplasia," was recently reported. Homozygotes for aly are defective in both humoral and cell-mediated immune function and have diffuse lymphoid cell infiltration of various tissues, particularly around the conduit ducts of the pancreas and salivary glands. In pilot studies in our laboratories, aly/aly mice were found to have peculiar biliary tract lesions, which were analyzed histologically and immunohistochemically in the present study. The livers of aly/aly mice older than 8 weeks consistently showed a variable lymphoid cell infiltration with lymph follicle formation in portal tracts; intrahepatic biliary epithelial cells showed various types of damage including pseudopyloric gland metaplasia and proliferative changes. In addition, the extrahepatic bile duct and intrahepatic large bile duct were found to contain an acidophilic substance in their epithelial cytoplasm. In the lumen and occasionally in the cytoplasm of these bile ducts, acidophilic crystals were also seen. Ultrastructurally, the intracytoplasmic acidophilic substances consisted of membrane-bound intracytoplasmic inclusions with homogeneous electron density, likely derived from rough endoplasmic reticulum (ER). Immunohistochemically, the cytoplasmic acidophilic substances were simultaneously positive for cystatin C, gastrin, serotonin, and somatostatin. In contrast, the acidophilic crystals did not react with any of these antibodies. These findings suggest that the intracytoplasmic acidophilic substances may contain a precursor of the peptide hormones, possibly because of defective secretion or intracellular transport. We believe that the aly/aly mouse is a useful model for the analysis of biliary metabolic events, and for studies of the interaction of the immune system and biliary destruction.

Primary biliary cirrhosis an epithelitis: evidence of abnormal salivary gland immunohistochemistry

Primary biliary cirrhosis (PBC) is an autoimmune liver disease of unknown etiology. Nearly 93% of patients with PBC exhibit evidence of focal sialoadenitis. In an earlier study, we reported evidence of aberrant expression of PDC-E2, or a mimeotope, in the salivary glands of patients with PBC that had Sjogren's syndrome. At the time of the previous study, data was not yet available regarding patients with PBC without sicca complaints. Therefore, to investigate the extent of salivary gland involvement in PBC, we collected lip biopsy sections from 9 PBC patients diagnosed as PBC by liver biopsy, without clinical or histologic features of Sjogren's syndrome and 9 PBC patients with established Sjogren's syndrome. Using immunohistochemical staining with both a murine monoclonal antibody. C355.1, and a human combinatorial antibody, SP4, we examined the ducts of these salivary glands for the presence of the characteristic aberrant staining pattern found in patients with PBC. We report that 6/9 PBC patients fulfilling established Sjogren's syndrome criteria and 6/9 PBC patients lacking features of Sjogren's syndrome showed intense staining of the ductal epithelial cells of the salivary gland. These data suggest that the PBC-specific antigen recognized by C355.1 and SP4 in bile duct epithelial cells is expressed aberrantly in the salivary gland in 66% of patients with PBC, independent of Sjogren's syndrome. This finding suggests a common disease process in these two tissues. Further, expression of this molecule may be an early marker of salivary gland involvement in patients with PBC.

Random phage mimotopes recognized by monoclonal antibodies against the pyruvate dehydrogenase complex-E2 (PDC-E2)

Dihydrolipoamide acetyltransferase, the E2 component of the pyruvate dehydrogenase complex (PDC-E2), is the autoantigen most commonly recognized by autoantibodies in primary biliary cirrhosis (PBC). We identified a peptide mimotope(s) of PDC-E2 by screening a phage-epitope library expressing random dodecapeptides in the pIII coat protein of fd phage using C355.1, a murine monoclonal antibody (mAb) that recognizes a conformation-dependent epitope in the inner lipoyl domain of PDC-E2 and uniquely stains the apical region of bile duct epithelium (BDE) only in patients with PBC. Eight different sequences were identified in 36 phage clones. WMSYPDRTLRTS was present in 29 clones; WESYPFRVGTSL, APKTYVSVSGMV, LTYVSLQGRQGH, LDYVPLKHRHRH, AALWGVKVRHVS, KVLNRIMAGVRH and GNVALVSSRVNA were singly represented. Three common amino acid motifs (W-SYP, TYVS, and VRH) were shared among all peptide sequences. Competitive inhibition of the immunohistochemical staining of PBC BDE was performed by incubating the peptides WMSYPDRTLRTS, WESYPDRTLRTS, APKTYVSVSGMV, and AALWGVKVRHVS with either C355.1 or a second PDC-E2-specific mAb, C150.1. Both mAbs were originally generated to PDC-E2 but map to distinct regions of PDC-E2. Two of the peptides, although selected by reaction with C355.1, strongly inhibited the staining of BDE by C150.1, whereas the peptide APKTYVSVSGMV consistently inhibited the staining of C355.1 on biliary duct epithelium more strongly than the typical mitochondrial staining of hepatocytes. Rabbit sera raised against the peptide WMSYPDRTLRTS stained BDE of livers and isolated bile duct epithelial cells of PBC patients more intensively than controls. The rabbit sera stained all size ducts in normals, but only small/medium-sized ductules in PBC livers. These studies provide evidence that the antigen present in BDE is a molecular mimic of PDC-E2, and not PDC-E2 itself.

Abnormal expression of the E2 component of the pyruvate dehydrogenase complex on the luminal surface of biliary epithelium occurs before major histocompatibility complex class II and BB1/B7 expression

Primary biliary cirrhosis (PBC) is a chronic autoimmune liver disease characterized histologically by nonsuppurative destructive cholangitis. Sera from patients with PBC react with a series of intramitochondrial enzymes with the immunodominant response directed against the E2 component of the pyruvate dehydrogenase complex (PDC-E2). Recently, using tissue sections of late-stage PBC, we showed that there is increased expression in biliary epithelial cells of patients with PDC-E2 or a molecule cross-reactive with PDC-E2. Previous work has shown that biliary epithelial cells of patients with PBC express an increased amount of class II. To address the sequence of events in the evolution of PBC, we have focused our attention in this study on early biliary epithelial lesions. In particular, we have studied the liver of 22 female patients with PBC that was diagnosed as either stage I or stage II using both a mouse monoclonal antibody that has reactivity similar to human autoantibodies as well as a human Fab combinatorial prepared from the lymph node of a PBC patient. Tissues were simultaneously stained using antibodies to PDC-E2, class II, and BB1/B7. As a positive control, tissues from late-stage PBC were studied concurrently. By determining the order of expression among the three molecules, PDC-E2, class II, and BB1/B7, we report that the expression of PDC-E2 or a PDC-E2-like molecule on biliary duct epithelium of patients with PBC precedes the expression of BB1/B7 and major histocompatibility complex (MHC) class II molecules. The alteration of an autoantigen in biliary duct epithelium may be the earliest lesion in PBC.