Analysis of two major anti-M2 antibodies (anti-PDC-E2/anti-BCOADC-E2) in primary biliary cirrhosis: relationship to titers of immunofluorescent anti-mitochondrial antibody

Magnetic resonance imaging findings of the lower limb muscles in anti-mitochondrial M2 antibody-positive myositis

Anti-mitochondrial M2 antibody (AMA-M2)-positive myositis is an idiopathic inflammatory myopathy (IIM). Of all patients with myositis, 2.5-19.5% have AMA-M2 antibodies. However, the detailed distribution of muscles affected in AMA-positive myositis is unknown. Therefore, we examined lower muscle magnetic resonance imaging (MRI) findings of patients with AMA-positive myositis. Among the 63 patients with IIM at our institute, 5 (7.9%) were positive for AMA-M2 antibodies. However, one was also positive for anti-Jo1 antibodies; therefore, four patients were finally participated in this study. All patients had high-intensity MRI signals in the proximal muscles, including the gluteus maximus and iliopsoas muscles, and in the thigh muscles, including the vastus lateralis, vastus medialis, adductor magnus, and semimembranosus muscles. Lower leg muscles were relatively spared. Fascial edema was observed in all patients and was also present in the lower leg muscles. Subcutaneous edema was observed, particularly in the proximal portion of the lower limbs. In AMA-positive myositis, proximal muscles, including the gluteus maximus, vastus lateralis, adductor magnus, and the semimembranosus, were markedly affected, while the lower leg muscles were relatively preserved. Additionally, fascial edema was evident even in lower leg muscles. Therefore, muscle MRI can be a useful diagnostic aid for AMA-positive myositis.

[Anti-mitochondrial M2 antibody-positive myositis preceded by heart failure and cardiac conduction disturbance. A case report]

A 69-year-old man visited our hospital complaining of fatigue in the lower extremities while walking. The patient had a two-year history of congestive heart failure and received a permanent artificial pacemaker implantation for sick sinus syndrome. Physical examination revealed proximal muscle weakness and exaggerated lumbar lordosis. Serum creatine kinase level was 1,455 U/l. The atrophies of the paraspinal muscles at thoracic to lumbar spine levels, rectus abdominis and soleus muscles were detected on computed tomography. Muscle biopsy showed mild to moderate variability in muscle fiber size with regenerating and necrotic muscle fibers. Mononuclear cell infiltration was not found. HLA-ABC expression was minimum. After anti-mitochondrial M2 antibody was detected, administration of oral prednisolone resulted in improvements in muscle strength and serum creatine kinase level. Based on the clinical course, examination and clinical findings, the patient was diagnosed as anti-mitochondrial M2 antibody positive myositis. Anti-mitochondrial M2 positive myositis is not only difficult to diagnose by muscle biopsy, but can also be preceded or complicated by fatal cardiac complications.

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.

Anti-mitochondrial M2 antibody-positive autoimmune hepatitis

Anti-mitochondrial M2 antibody (AMA-M2) is specific to primary biliary cirrhosis (PBC), but can also be found in certain patients with autoimmune hepatitis (AIH). Effective methods of differentiating between PBC and AIH are required, as their clinical course and management are different. Titers of AMA-M2 were analyzed before and after follow-up in patients with PBC or AIH. Patients who underwent liver biopsy and were diagnosed with either AIH (10 patients) or PBC (3 patients) were enrolled in the study. The AMA-M2 antibody titers of these patients were analyzed upon hospital admission. AMA-M2 reacted with the pyruvate dehydrogenase complex-E2, branched-chain 2-oxo acid dehydrogenase complex and 2-oxoglutaric acid dehydrogenase complex in the assay utilized for this study. The cut-off value for AMA-M2 was 5. Six AIH patients were AMA-M2(-) and 4 were AMA-M2(+). The titer for the AIH patients who were AMA-M2(+) was 24.8±14.8, compared with 324±174 in the patients with PBC (P=0.0138). Three AMA-M2(+) AIH patients were followed-up after liver biopsy. The AMA-M2 levels had decreased in all 3 patients, becoming undetectable in 2 of them. In conclusion, certain patients with AIH in this study were found to be AMA-M2(+), but the titers were significantly lower than those in the patients with PBC. At follow-up, the AIH patients exhibited decreased AMA-M2 titers.

Autoimmune features in metabolic liver disease: a single-center experience and review of the literature

Non-alcoholic steatohepatitis (NASH) is the progressive phenotype of non-alcoholic fatty liver disease associated with the metabolic syndrome. The existence of autoimmune features in NASH has been reported, but its significance remains unclear. We herein report the autoantibody profile of 54 patients with histologically proven NASH and further determined the development of autoimmunity in three different murine NASH models (monosodium glutamate, CDAA (choline-deficient L-amino acid-defined), and TSOD (Tsumura Suzuki, Obese Diabetes)) at 48 weeks of age. Forty-eight percent (26/54) of NASH cases were positive for antinuclear (ANA) or antimitochondrial antibody and manifested histological signs of overlap with autoimmune hepatitis and primary biliary cirrhosis, respectively. These patients were significantly older (60 ± 10 versus 50 ± 16 years), more frequently women (81 % versus 43 %), and with more severe portal inflammatory infiltrate compared with patients without autoimmunity. In one third of mice, regardless of the model, we observed a marked lymphoid infiltrate with non-suppurative cholangitis, and several cases were ANA-positive, but none AMA-positive. Our data suggest that autoimmunity may share some pathogenetic traits with the chronic inflammation of NASH, possibly related to advanced age.

Detection of M2 antimitochondrial antibodies by dot blot assay is more specific than by enzyme linked immunosorbent assay

AIMS

The objective of our study was, in one hand, to determine the sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) of ELISA and dot blot assay to investigate IgG M2 antimitochondrial antibodies (M2 AMA) and, on the other hand, to compare these results with those of indirect immunofluorescence technique (IIF).

METHODS

Sera from patients suffering from primary biliary cirrhosis (PBC) (n=55), systemic lupus erythematosus (n=21), celiac disease (n=30) and blood donors (n=75) were analyzed. M2 AMA were detected by ELISA and dot blot using pyruvate dehydrogenase purified from porcine heart and by IIF on cryostat sections of rat liver-kidney-stomach.

RESULTS

IIF was more sensitive (98%) than ELISA (93%) and dot blot (91%). The specificity of AMA for PBC using IIF, ELISA and dot blot reached 100%, 92% and 100%, respectively. The PPV of IIF, ELISA and dot blot was 100%, 93% and 100%, respectively. The NPV was 98% for IIF, 92% for ELISA and 91% for dot blot.

CONCLUSION

Dot blot, using purified pyruvate dehydrogenase, had a higher specificity than ELISA and may be useful in confirming the specificity of AMA in cases of doubt with IIF.

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.