Session Type: Abstract Submissions (ACR)
Anti-transcriptional intermediary factor 1 (TIF-1) and anti-Mi-2 antibodies (Abs) are myositis-specific autoantibodies (MSA) selectively detected in dernatomyositis (DM) patients. Anti-TIF-1 Ab is frequently found in juvenile DM and cancer-associated adult DM. Anti-Mi-2 Ab is predominantly detected in patients with classic DM with favorable prognosis. TIF-1 and Mi-2 proteins share similar molecular structures and amino acid sequences, suggesting a potential crossreactivity. In this study, we have established enzyme-linked immunosorbent assays (ELISAs) for anti-Mi-2 and anti-TIF-1γ Abs, and have assessed their utility and crossreactivity.
Serum samples were obtained from 242 patients with idiopathic inflammatory myopathy (IIM) who were followed up at 8 medical centers across Japan. IIM patients included 104 with classic DM, 68 with clinically amyopathic DM (CADM) and 70 with polymyositis. Serum samples from 190 patients with other connective tissue diseases (CTDs) including 45 with rheumatoid arthritis, 67 with systemic lupus erythematosus, 43 with systemic sclerosis, 20 with mixed connective tissue disease, 8 with Sjögren’s syndrome, and 7 with others, and 123 healthy individuals were also assessed.
Full-length TIF-1γ and Mi-2β proteins were produced by a baculovirus expression system. Purified proteins were respectively coated on ELISA plates, on which serum antibody levels were examined. To assess the crossreactivity, partial-length Mi-2β proteins with or without mutations were produced and processed similarly, before subjected to ELISA.
Cutoff levels for anti-TIF-1γ and anti-Mi-2 ELISAs were calculated using Receiver Operating Characteristic analysis based on the results from the gold standard IP assay of 242 IIM samples. When compared with IP assay, anti-TIF-1γ ELISA showed 100% sensitivity and 100% specificity, while anti-Mi-2 ELISA showed 100% sensitivity and 99.6% specificity.
Anti-TIF-1γ Ab was positive in 30 (28.8%) with classic DM and 4 (5.9%) with CADM, whereas 14 (13.5%) with classic DM, but none with CADM, were positive for anti-Mi-2 Ab. Anti-TIF-1γ and anti-Mi-2 Abs were both positive in 2 (1.1%) with CTDs other than IIM, respectively. Of 30 anti-TIF-1γ positive DM patients, 23 (67.6%) and 5 (14.7%) had malignancy and interstitial lung disease (ILD), respectively. By contrast, 3 (21.4%) had malignancy in 14 anti-Mi-2 positive DM patients, but none had ILD. Both Abs were negative in normal subjects.
Although no samples positive for anti-Mi-2 Ab exceeded the cutoff level of anti-TIF-1γ Ab, they showed substantially higher levels than those negative for anti-TIF-1γ Ab. ELISA analyses after absorption with various truncated Mi-2 proteins with and without inserted mutations identified that anti-Mi-2 Ab weakly crossreacted with the 896-903 amino acid sequence (ggdllcce) within a Plant Homeo domain of TIF-1γ protein, due to the sequence homology with Mi-2β protein (458-465, ggellccd).
The current study demonstrates the utility of newly established ELISAs for anti-TIF-1γ and anti-Mi-2 Abs, which can serve as easier detection systems for routine testing. Developing these ELISAs needs attention to crossreactivity of anti-Mi-2 Ab with TIF1 antigen.
Medical & Biological Laboratories Co., Ltd,
Medical & Biological Laboratories Co., Ltd.,
employee of Medical & Biological Laboratories Co., Ltd.,
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ACR Meeting Abstracts - https://acrabstracts.org/abstract/enzyme-linked-immunosorbent-assays-for-detection-of-anti-transcriptional-intermediary-factor-1-gamma-and-anti-mi-2-autoantibodies-in-dermatomyositis-utility-and-crossreactivity/