Are antibodies to carbonic anhydrase II specific for anti-mitochondrial antibody-negative primary biliary cirrhosis?

Meta-Analysis of Antinuclear Antibodies in the Diagnosis of Antimitochondrial Antibody-Negative Primary Biliary Cholangitis

Objective

The diagnostic value of antinuclear antibodies (ANAs) including anti-gp210 and anti-sp100 for primary biliary cholangitis/cirrhosis (PBC) has been widely reported. However, their diagnostic performances for antimitochondrial antibody- (AMA-) negative PBC were less well elucidated. Therefore, the aim of the current meta-analysis was to evaluate the diagnostic accuracy of ANAs in patients with AMA-negative PBC.

Materials and Methods

Literature on the diagnostic value of biomarkers for AMA-negative PBC was systematically searched in PubMed, MEDLINE, EMBASE, and the Cochrane Library. The qualities of the retrieved studies were assessed by the Quality Assessment of Diagnostic Accuracy Studies-version 2 (QUADAS-2) scale. Pooled sensitivity and specificity of the biomarkers were calculated with random-effects models. The areas under the summary receiver operating characteristic (AUSROC) curves were used to evaluate the overall diagnostic performance of ANAs.

Results

A total of 11 studies (400 AMA-negative PBC patients and 6217 controls) were finally included in the meta-analysis. ANAs had an overall sensitivity of 27% (95% CI: 20%, 35%) and specificity of 98% (95% CI: 97%, 99%). The pooled sensitivities for anti-gp210 and anti-sp100 were 23% (95% CI: 13%, 37%) and 25% (95% CI: 13%, 43%), respectively, and their specificities were 99% (95% CI: 97%, 100%) and 97% (95% CI: 93%, 98%), respectively.

Conclusions

ANAs exhibited high specificity but low sensitivity and therefore could be used as reliable biomarkers to reduce the necessity of liver histology.

Antimitochondrial Antibody-Negative Primary Biliary Cholangitis: Is It Really the Same Disease?

Antimitochondrial antibody (AMA)-negative primary biliary cholangitis (PBC) is a term reserved for patients with clinical and histopathological findings consistent with PBC but without positive AMA. There does not seem to be a natural progression from AMA negativity to positivity. Antinuclear and antismooth muscle antibodies are frequently found in the absence of histologic autoimmune hepatitis features. The disease course may be more severe than AMA-positive. Response to standard therapy for PBC and autoimmune hepatitis varies. Nevertheless, there is insufficient evidence to suggest AMA-negative PBC is different enough to warrant classification as a separate disease from AMA-positive PBC.

The diagnostic accuracy of biomarkers for diagnosis of primary biliary cholangitis (PBC) in anti-mitochondrial antibody (AMA)-negative PBC patients: a review of literature

Primary biliary cholangitis (PBC), also known as primary biliary cirrhosis, is an autoimmune disease of the liver characterized by anti-mitochondrial antibodies (AMA) in 90%-95% of patients. The aim of this study was to evaluate the diagnostic value of several serum biomarkers in patients with PBC but negative for AMA. Some antinuclear antibodies (ANA) pattern, detected by indirect immunofluorescence (IIF), such as multiple nuclear dot (MND) and rim-like patterns are well-known to be specific for PBC. The corresponding nuclear antigens are the components of the nuclear pore complex (Gp210 for rim-like pattern) and Sp100, PML proteins (for MND pattern) detectable by immunoblotting and ELISA methods. More recently, new biomarkers have been evaluated in order to improve the diagnostic sensitivity, such as kelch-like 12 (KLHL12) and hexokinase-1. Considering these different serum biomarkers, studies evaluating their diagnostic role in AMA-negative PBC patients compared to AMA-positive ones and controls were included in this review. Pooled sensitivity and specificity were 37% and 85%, respectively. The overall PPV and NPV mean values were 45% and 83%. Even if all biomarkers are very specific for PBC, the overall sensitivity was poor and therefore is necessary to identify a marker with a greater sensitivity for PBC in AMA-negative patients.

Primary biliary cirrhosis: What do autoantibodies tell us?

Primary biliary cirrhosis (PBC) is a chronic, progressive, cholestatic, organ-specific autoimmune disease of unknown etiology. It predominantly affects middle-aged women, and is characterized by autoimmune-mediated destruction of small- and medium-size intrahepatic bile ducts, portal inflammation and progressive scarring, which without proper treatment can ultimately lead to fibrosis and hepatic failure. Serum autoantibodies are crucial tools for differential diagnosis of PBC. While it is currently accepted that antimitochondrial antibodies are the most important serological markers of PBC, during the last five decades more than sixty autoantibodies have been explored in these patients, some of which had previously been thought to be specific for other autoimmune diseases.

Multidimensional degradomics identifies systemic autoantigens and intracellular matrix proteins as novel gelatinase B/MMP-9 substrates

The action radius of matrix metalloproteinases or MMPs is not restricted to massive extracellular matrix (ECM) degradation, it extends to the proteolysis of numerous secreted and membrane-bound proteins. Although many instances exist in which cells disintegrate, often in conjunction with induction of MMPs, the intracellular MMP substrate repertoire or degradome remains relatively unexplored. We started an unbiased exploration of the proteolytic modification of intracellular proteins by MMPs, using gelatinase B/MMP-9 as a model enzyme. To this end, multidimensional degradomics technology was developed by the integration of broadly available biotechniques. In this way, 100-200 MMP-9 candidate substrates were isolated, of which 69 were identified. Integration of these results with the known biological functions of the substrates revealed many novel MMP-9 substrates from the intracellular matrix (ICM), such as actin, tubulin, gelsolin, moesin, ezrin, Arp2/3 complex subunits, filamin B and stathmin. About 2/3 of the identified candidates were autoantigens described in multiple autoimmune conditions and in cancer (e.g. annexin I, nucleolin, citrate synthase, HMGB1, alpha-enolase, histidyl-tRNA synthetase, HSP27, HSC70, HSP90, snRNP D3). These findings led to the insight that MMPs and other proteases may have novel (immuno)regulatory properties by the clearance of toxic and immunogenic burdens of abundant ICM proteins released after extensive necrosis. In line with the extracellular processing of organ-specific autoantigens, proteolysis might also assist in the generation of immunodominant 'neo-epitopes' from systemic autoantigens. The study of proteolysis of ICM molecules, autoantigens, alarmins and other crucial intracellular molecules may result in the discovery of novel roles for proteolytic modification.

Potential for differential diagnosis of autoimmune pancreatitis and pancreatic cancer using carbonic anhydrase II antibody

OBJECTIVES

Pancreatic ductal epithelia contain an abundance of carbonic anhydrase (CA), and the presence of antibodies to this enzyme has been described in autoimmune disorders. We previously found a small amount of an immunoglobulin G-like material in purchased CAII reagents, which led to pseudopositive reactions.

METHODS

We determined the optimum measurement conditions for detecting anti-CAII antibody using an enzyme-linked immunosorbent assay and sera from 140 patients with pancreatic diseases.

RESULTS

Compared with the prevalence of anti-CAII antibody in healthy subjects, a significantly higher seroprevalence of the antibody was detected in patients with autoimmune pancreatitis (AIP) (88.9%, P < 0.02), Sjögren syndrome (67.6%, P < 0.01), and alcoholic chronic pancreatitis (45.8%, P < 0.01). No positive results were obtained among patients with pancreatic cancer. Moreover, the antibody value obtained in the pancreatic cancer patients was actually lower than that obtained in healthy subjects.

CONCLUSIONS

The anti-CAII antibody is probably not a specific marker of AIP because it was present at a higher frequency in the sera of patients with other pancreatic diseases. Nevertheless, the anti-CAII antibody may be a useful tool for the differential diagnosis of AIP and pancreatic cancer.

Autoimmune liver disease: overlap and outliers

The three main categories of autoimmune liver disease are autoimmune hepatitis (AIH), primary biliary cirrhosis (PBC), and primary sclerosing cholangitis (PSC); all are well-defined entities with diagnosis based upon a constellation of clinical, serologic, and liver pathology findings. Although these diseases are considered autoimmune in nature, the etiology and possible environmental triggers of each remain obscure. The characteristic morphologic patterns of injury are a chronic hepatitis pattern of injury with prominent plasma cells in AIH, destruction of small intrahepatic bile ducts and canals of Hering in PBC, and periductal fibrosis and inflammation involving larger bile ducts with variable small duct damage in PSC. Serological findings include the presence of antimitochondrial antibodies in PBC, antinuclear, anti-smooth muscle, and anti-LKM antibodies in AIH, and pANCA in PSC. Although most cases of autoimmune liver disease fit readily into one of these three categories, overlap syndromes (primarily of AIH with PBC or PSC) may comprise up to 10% of cases, and variant syndromes such as antimitochondrial antibody-negative PBC also occur. Sequential syndromes with transition from one form of autoimmune liver disease to another are rare.

Detection of autoantibody against carbonic anhydrase II in various liver diseases by enzyme-linked immunosorbent assay using appropriate conditions

BACKGROUND

Immunoglobulin G autoantibody against carbonic anhydrase (CA) II has been detected in the sera of patients with a variety of autoimmune diseases. Antibody against CAII has also been described as a serological marker for distinguishing between cases of autoimmune cholangitis (AIC) and those of primary biliary cirrhosis (PBC). However, the optimal antibody measurement conditions (enzyme-linked immunosorbent assay: ELISA) have not yet been established. Moreover, we also found that a small amount of an IgG-like material exists in purchased CAII reagents, which causes pseudopositive reactions.

METHODS

The sera of 96 patients with liver disease were examined for the presence of anti-CAII antibody using antigen (CAII) not containing the IgG-like material as the most suitable measurement conditions. Compared with the anti-CAII antibody prevalence of 3.8% found in normal subjects, a significantly higher seroprevalence of the antibody was detected in patients with PBC (31.0%, P<0.02), autoimmune hepatitis (AIH) (50.0%, P<0.01) and chronic viral hepatitis (27.5%, P<0.01). But, in cases of PBC, no significant correlation was noted between the level of anti-CAII antibody and the presence of anti-mitochondrial antibodies (AMA).

CONCLUSIONS

While CAII may be a target antigen in autoimmune diseases, the anti-CAII antibody is not likely to be a specific marker of AIC. The optimum measurement conditions for the ELISA for anti-CAII antibody would provide us with valuable information to elucidate the underlying immunological abnormalities in liver diseases.

'True' antimitochondrial antibody-negative primary biliary cirrhosis, low sensitivity of the routine assays, or both?

Anti-mitochondrial antibody (AMA) is considered the serological hallmark of primary biliary cirrhosis (PBC), but may be missing in a proportion of these patients. We assessed sensitivity and specificity of the currently available techniques for AMA detection in a large series of PBC patients and controls, and analysed their clinical and immunological features according to the AMA status. By indirect immunofluorescence on rat tissue sections and HEp-2 cells, Western immunoblot with bovine submitochondrial particles, and two ELISAs with AMA-specific recombinant proteins, we evaluated the presence of AMA in 127 PBC patients, 166 patients with type 1 autoimmune hepatitis and 100 with non alcoholic fatty liver disease. In PBC patients Western immunoblot detects AMA significantly more often than indirect immunofluorescence on HEp-2 cells (85%versus 72%, P = 0.02) or rodent tissue sections (71%, P = 0.01); both ELISAs are only slightly less sensitive than Western immunoblot (81% and 78%). Ten patients with non alcoholic fatty liver disease were AMA-positive by indirect immunofluorescence, but none recognized AMA-specific epitopes in Western immunoblot or in ELISAs. Twelve patients with type 1 autoimmune hepatitis were AMA-positive by indirect immunofluorescence, but only 6 (3.6%) reacted by Western immunoblot and ELISAs. Western immunoblot or ELISA should be regarded as first-line assay for the detection of AMA. Up to 15% of PBC patients are consistently AMA-negative, yet they share the same clinical, biochemical and histological features of AMA-positive PBC. Detection of AMA in type 1 autoimmune hepatitis might identify a subset of patients at risk of developing a hepatitic/cholestatic syndrome.

Primary biliary cirrhosis and autoimmune cholangiopathy

AMA are detected in the serum of 92% to 95% of patients with PBC using indirect immunofluorescent methods. AIC is the term used to describe the 5% to 8% of AMA-negative PBC patients who uniformly have ANA and SMA. Recent applications of more sensitive and specific tests to detect serum AMA have shown that most, if not all, patients with AIC actually do have AMA. Emerging evidence that AMA and mitochondrial autoantigens play important roles in the immunopathogenesis of NSDC also suggests that AIC and PBC are likely to be a single disease, exhibiting variation in the types of autoantibodies and in both the concentrations and immunoglobulin isotypes of AMA.

Antimitochondrial and other autoantibodies

Primary biliary cirrhosis (PBC) is characterized by the presence of high-titer disease specific autoantibodies directed against mitochondrial antigens (AMA) of the inner mitochondrial membrane, that are members of the 2-oxo acid complex. Among numerous other autoantibodies found in PBC the focus of ongoing studies is on the PBC-specific anti-nuclear antibodies, that are of diagnostic and clinical relevance since they can be used as a 'positive tool' in the diagnosis of AMA-negative PBC while at the same time identifying a subgroup of patients with more advanced liver disease.

The immunology of primary biliary cirrhosis: the end of the beginning?

The chronic liver disease primary biliary cirrhosis (PBC) is characterised by autoreactive B-cell and T-cell responses directed against mitochondrial antigens. In recent years these responses have been extensively characterised and the principal PBC associated autoantigen identified as pyruvate dehydrogenase complex (PDC). The identification of anti-PDC responses (present in over 95% of PDC patients) has given rise to important questions pertinent to our understanding of the pathogenesis of PBC. What specific role to anti-PDC responses play in target cell damage? How and why does immune tolerance break down to as highly conserved and ubiquitously expressed self-antigen as PDC? Why does breakdown in tolerance to an antigen present in all nucleated cells result in damage restricted to the intra-hepatic bile ducts? In attempting to answer these key questions we have, in this review, proposed a unifying hypothesis for the pathogenesis of PBC.

Primary biliary cirrhosis and other ductopenic diseases

Several distinct conditions are characterized by a reduction in the number of small and medium-sized intrahepatic bile ducts. These diseases are associated with progressive cholestasis, which in turn leads to biliary fibrosis and ultimately cirrhosis. The best-characterized ductopenic condition in adulthood is primary biliary cirrhosis (PBC) for which there is now strong evidence of an autoimmune cause. The antigenic targets are epitopes on proteins of the 2-oxoacid dehydrogenase complex within mitochondria. Some of these proteins appear to be aberrantly expressed at the surface of cholangiocytes in PBC. The basis for the breakdown in tolerance remains uncertain, although there is recent evidence to indicate that apoptosis may play a key role at early stages in the pathogenesis of the disease. Related conditions include autoimmune overlap syndromes and AMA-negative PBC (autoimmune cholangitis). Primary sclerosing cholangitis is clinically and histologically distinct, although there is evidence that it also may have an immune-mediated cause. Ductopenia may also arise on the basis of drug-induced injury; the best example of this is progressive cholestasis complicating chlorpromazine therapy.

Autoantibody studies of female patients with reproductive failure

The aim of this study was to investigate the prevalence and character of autoimmune derangements in women with reproductive failure. A total of 108 females (age range 17-43, mean 27.5 years), including 16 with primary menstrual cycle disturbances and polycystic ovaries (PCO), 20 with polycystic ovary syndrome (PCOS), 38 with endometriosis (E), and 34 with chronic anovulation, luteal phase insufficiency, subfertility or unexplained infertility (INF) were investigated. A control group of 392 women was formed from an unselected population sample (age range 17-43, mean 31.0 years). All sera were tested by indirect immunofluorescence method to assess common autoantibodies: nuclear (ANA), smooth muscle (SMA), parietal cell (PCA), thyroid microsomal (TMA), reticulin (ARA), mitochondrial (AMA) and liver/kidney microsomal autoantibodies (LKMA). Enzyme-linked immunosorbent assay was used to detect antibodies against beta2-glycoprotein I (anti-beta 2GPI) and carbonic anhydrase (anti-CA). Our results showed that 40.7% of patients' sera and 14.8% of control sera contained one or more common autoantibodies, ANA and SMA were most frequently detected (difference between two groups P<0.005). Anti-beta 2GPI were found in eight cases (7.4%), including two patients with INF but without other autoantibodies. Anti-CA were revealed in nine cases (8.3%) including patients' PCOS, E and INF. A comparison of patients' clinical data with antibody assay results did not reveal any significant associations. Our results indicate a high prevalence of autoimmune reactions in women with reproductive failure due to the most common causes PCO, PCOS and E as well as in unexplained infertility. This might reflect the propensity to develop autoimmune reactions in such patients, including pathogenic autoimmune reactions to specific target antigens.