Clinical significance of positive immunoblotting but negative immunofluorescence for antimitochondrial antibodies in patients with liver diseases other than primary biliary cirrhosis

Detection of anti-mitochondrial 2-oxoacid dehydrogenase complex subunit's antibodies for the diagnosis of primary biliary cholangitis

Anti-mitochondrial antibodies (AMA), directed against the E2 subunits of the 2-oxo acid dehydrogenase complexes, are markers of Primary Biliary Cholangitis (PBC), a chronic autoimmune liver disease. However, the clinical significance of subunits-specific AMA type PDC-E2 -E2 subunit of the pyruvate dehydrogenase complex-, BCOADC-E2 -E2 subunit of the branched-chain 2-oxo acid dehydrogenase complex-, OGDC-E2 -E2 subunit of the 2-oxo-glutarate dehydrogenase complex- and nPDC -native pyruvate dehydrogenase complex (M2-AMA) . Is not well known, and not all AMA specificities are associated with PBC. The aim of the study was to show the usefulness of the number and combination of subunits-specific AMA positive for the diagnosis of PBC. We detected AMA by indirect immunofluorescence (IIF-AMA) and M2-AMA by dot-blot. We studied the relationship of AMA with some clinical and laboratory variables in 307 patients (37% PBC) with positive dot-blot for M2-AMA. In PBC patients, we detected different E2 subunits of the 2-oxo acid dehydrogenase complexes antibodies (M2-AMA): 82.9% were specific for nPDC, 64.5% for PDC-E2, 44.4% for BCOADC-E2, and 9.6% for OGDC-E2. IIF and dot-blot tests achieved a Area Under the Receiver Operating Characteristic Curve (ROC AUC) of 0.674 (1: 320 cut-off titer, Sensibility (Se) 64.7%, Specificity (Sp) 63.4%) and 0.663 (three specificities M2-AMA, Se 43%, Sp 81.2%), respectively. The detection of different E2 subunits of the 2-oxo acid dehydrogenase complexes antibodies (M2-AMA) by dot-blot showed different ROC AUC: anti-PDC-E2 showed an AUC of 0.610, a Se of 43.7%, and a Sp of 76.4%. Finally, the combined detection of nPDC/BCOADC-E2/PDC-E2 reached an AUC of 0.6095, a Se of 59.6%, and a Sp of 70.2%.The identification of two M2-AMA specificities through dot-blot increased PBC odds ratio (OR) by 2.05 (p:0.031), as compared to the identification of one specificity. Moreover, the identification of three and four specificities increased OR by 4.63 (p:0.000) and by 21.53 (p:0.006), respectively. nPDC/OGDC-E2/PDC-E2 and nPDC/OGDC-E2/BCOADC-E2/PDC-E2 combinations increased PBC OR by 10.04 (p:0.034), as compared to any other combination. 1:320 and 1:640 IIF-AMA increased PBC OR by 4.93 (p:0.009) and 7.67 (p:0.001), respectively, as compared to IIF-AMA titers equal to or less than 1:160. M2-AMA dot-blot was less sensitive but more specific than IIF-AMA, with similar predictive capacity for PBC. Increased numbers of M2-AMA specificities clearly increased the risk of PBC. Some combinations were strongly related to PBC (nPDC/BCOADC-E2/PDC-E2), but others were not (one single M2-AMA, and nPDC plus PDC-E2). M2-AMA dot-blot was less sensitive but more specific than IIF-AMA, with similar predictive capacity for PBC. Increased numbers of M2-AMA specificities clearly increased the risk of PBC, being some combinations, such as nPDC/BCOADC-E2/PDC-E2, more related to PBC than others. Finally, the determination of the number of M2-AMA specificities was more useful than the particular subunit target for PBC diagnosis. In conclusion, the study of the number of M2-AMA specificities by dot-blot should definitely be considered for PBC diagnosis.

Clinical relevance of combined anti-mitochondrial M2 detection assays for primary biliary cirrhosis

BACKGROUND

Antimitochondrial antibody (AMA) is a specific serologic marker in primary biliary cirrhosis (PBC). The aim of this study was to evaluate the clinical relevance of combined AMA assays.

METHODS

Sera were obtained from 79 patients with PBC and 108 patients with other liver disease. They were tested by indirect immunofluorescence (IIF) using rat kidney/stomach tissue and HEp2 cells as substrate, 4 AMA-M2 assays, anti-sp100, and anti-gp210 assays.

RESULTS

Using IIF-AMA with cut-off titer of 1:40, the sensitivity and specificity for PBC were 88.6% and 87.0%, respectively. A cut-off titer of 1:80 improved the specificity to 93.5%. The 4 commercial assay kits using AMA-M2 autoantibodies showed sensitivity of 55.7-79.7% and specificity of 91.7-95.4% with moderate to good agreement. AMA-M2 assays using both native and recombinant E2 antigens had higher sensitivity. ANAs on HEp2 cells, anti-sp100, and anti-gp210 were detected in 67.1%, 13.9-15.2%, and 22.8-27.8% of PBC patients, respectively. Additional AMA-M2 specific assays in IIF-AMA negative and low titer positive (1:40) sera increased the sensitivity and specificity to 88.6% and 90.7%, respectively.

CONCLUSIONS

Serological diagnosis for PBC using IIF with high titer cut-off and additional AMA-M2 specific tests by ELISA or LIA in IIF-negative sera should be used.

Enzyme inhibition assay for pyruvate dehydrogenase complex: Clinical utility for the diagnosis of primary biliary cirrhosis

Primary biliary cirrhosis (PBC) is usually diagnosed by the presence of characteristic histopathological features of the liver and/or antimitochondrial antibodies (AMA) in the serum traditionally detected by immunofluorescence. Recently, new and more accurate serological assays for the detection of AMA, such as enzyme-linked immunosorbent assay (ELISA), immunoblotting, and enzyme inhibition assay, have been developed. Of these, the enzyme inhibition assay for the detection of anti- pyruvate dehydrogenase complex (PDC) antibodies offers certain advantages such as objectivity, rapidity, simplicity, and low cost. Since this assay has almost 100% specificity, it may have particular applicability in screening the at-risk segment of the population in developing countries. Moreover, this assay could be also used for monitoring the disease course in PBC. Almost all sera of PBC-suspected patients can be confirmed for PBC or non-PBC by the combination results of immunoblotting and enzyme inhibition assay without histopathological examination. For the development of a “complete” or "gold standard" diagnostic assay for PBC, similar assays of the enzyme inhibition for anti-2-oxoglutarate dehydrogenase complex (OGDC) and anti-branched chain oxo-acid dehydrogenase complex (BCOADC) antibodies will be needed in future.

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.

Evaluation of newly developed ELISA using "MESACUP-2 test mitochondrial M2" kit for the diagnosis of primary biliary cirrhosis

OBJECTIVES

An enzyme-linked immunosorbent assay (ELISA) using MESACUP-2 Test Mitochondria M2 kit (new-M2 ELISA) has recently become commercially available. The aim of this study was to evaluate the clinical utility of this newly developed ELISA for the diagnosis of primary biliary cirrhosis (PBC).

DESIGN AND METHODS

We tested the immunoreactivity of sera from 82 Japanese PBC patients to the 2-oxo-acid dehydrogenase complex (2-OADC) enzymes by indirect immunofluorescence, enzyme inhibition assay using commercially available TRACE Enzymatic Mitochondrial Antibody (M2) Assay (EMA) kit, commercial ELISAs using MESACUP Mitochondria M2 kit (old-M2 ELISA) and new-M2 ELISA, and immunoblotting on bovine heart mitochondria.

RESULTS

Each test gave the following positive results; antimitochondrial antibodies (AMA) by immunofluorescence in 71 (87%) out of the 82 sera, enzymatic inhibitory antibody to pyruvate dehydrogenase complex (PDC) by EMA in 61 (74%), immunoglobulin (Ig) G class anti-PDC antibody by old-M2 ELISA in 55 (67%), IgG/M/A class anti-E2 subunit of PDC (PDC-E2)/anti-E2 subunit of branched chain oxo-acid dehydrogenase complex (BCOADC-E2)/anti-E2 subunit of 2-oxoglutarate dehydrogenase complex (OGDC-E2) antibodies by new-M2 ELISA in 73 (89%), and IgG, IgM, or IgA class antibodies against at least one of the 2-OADC enzymes by immunoblotting in 82 (100%). Fifty-three of the 82 sera (65%) were all positive by these five assays. Of the 18 sera that were positive by new-M2 ELISA but negative by old-M2 ELISA, 12 were theoretically interpretable. Of the 11 sera that were negative for AMA by immunofluorescence but positive for at least one of anti-2-OADC enzymes by immunoblotting, four (36%) were positive by new-M2 ELISA, whereas only two and one sera were positive by EMA and old-M2 ELISA, respectively.

CONCLUSIONS

Our results indicated that the sensitivity of the newly developed new-M2 ELISA was higher than that of EMA and old-M2 ELISA, and comparable with that of immunofluorescence. However, it is still unclear whether the new-M2 ELISA could replace the conventional immunofluorescence testing for routine assay requests because six (7%) sera showed discrepant results between these two assays.

A possible mouse model for spontaneous cholangitis: serological and histological characteristics of MRL/lpr mice

AIMS

MRL/Mp-lpr/lpr (MRL/lpr) mice spontaneously develop lymphadenopathy, hypergammaglobulinaemia, serum auto-antibodies, and a generalised auto-immune disease including glomerulonephritis and arthritis, and have been used as a model for the study of systemic lupus erythematosus. Recently, MRL/lpr mice were also reported as a potentially suitable animal model of primary biliary cirrhosis (PBC). The aim of this study was to determine the suitability of MRL/Mp-lpr/lpr (MRL/lpr) mice as an experimental auto-immune-mediated cholangitis model for PBC.

METHODS

We investigated the serum hepatobiliary enzymes, histopathological findings, and the target antigen of antimitochondrial antibodies (AMA) in MRL/lpr mice.

RESULTS

Serum levels of total bilirubin and hepatobiliary enzymes including alanine aminotransferase (ALT), leucine aminopeptidase (LAP), and gamma-glutamyl transpeptidase (G-GTP) in older-aged (over 20 weeks old) MRL/lpr or MRL/Mp-+/+ (MRL/+) mice were not significantly higher than those in younger (8-12 weeks old) MRL/lpr, MRL/+, or older-aged control mice (C3H/HeJ and BALB/C mice). Histopathologically, 24 of 47 (51%) older-aged MRL/lpr mice showed evidence of cholangitis, compared with two of 20 (10%) younger MRL/lpr mice. Especially, epithelioid granuloma and/or bile duct loss were seen in 11 out of 47 (23%) older-aged MRL/lpr mice, whereas such findings were seen in only one of 20 (5%) younger MRL/lpr mice. None of the MRL/+, C3H/HeJ, and BALB/C mice developed cholangitis. The target antigens of AMA were not pyruvate dehydrogenase complex but 2-oxoglutarate dehydrogenase complex and/or branched-chain oxo-acid dehydrogenase complex as confirmed by immunoblotting. There was no significant correlation between the presence of AMA and severity of histological lesions in older-aged MRL/lpr mice, and there were no significant differences in these biochemical data, the proportion of mice with portal inflammation, cholangitis and AMA between male and female MRL/lpr mice.

CONCLUSION

Although several clinical features were incompatible with PBC, the serological and histopathological features of MRL/lpr mice indicate that these mice can be used as an experimental immune-mediated cholangitis model for PBC.