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Comprehensive line blots for myositis diagnostics


Autoantibodies are important biomarkers in the diagnosis of myositis and are useful for differentiating different subforms of the disease. Broad multiparameter testing is recommended to maximise the serological detection rate. EUROLINE Autoimmune Inflammatory Myopathies Profiles from EUROIMMUN provide parallel monospecific detection of up to 20 myositis-relevant autoantibodies and include new and exclusive target antigens.


diopathic inflammatory myopathies (IIM) are a group of systemic autoimmune rheumatic diseases, which are characterised by chronic inflammation of skeletal muscle. They can affect both children and adults. The hallmark symptoms of IIM are muscle inflammation, proximal muscle weakness, arthritis, cutaneous rashes, calcinosis, ulceration, malignancy and interstitial lung disease (ILD). Based on clinical and immunopathological criteria, the disease is divided into the subforms polymyositis (PM), dermatomyositis (DM), anti-synthetase syndrome (ASS), sporadic inclusion body myositis (sIBM), necrotising myositis (NM) and overlap myositis (OM). Some subforms can be associated with malignancy, for example cancer-associated DM (caDM). Diagnosis of myopathies is challenging due to the rarity of the diseases, their similar clinical presentation to other rheumatic diseases, and the possibility of overlap syndromes. In particular, the rare form sIBM has a high misdiagnosis rate and a mean delay to diagnosis of five to eight years. Accurate diagnosis and differentiation of IIM subforms is, however, essential due to varying therapy possibilities.


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Autoantibody markers Autoantibodies are key biomarkers for differentiation of IIM subforms and they form the basis of serological diagnostics. The antibodies are directed against nuclear and cytoplasmic target antigens and are divided into myositis-specific autoantibodies (MSA), which are found primarily in patients with IIM, and myositis-associated autoantibodies (MAA), which are not specific for IIM but are nevertheless important markers.


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Autoantibodies in myositis are detected using the indirect immunofluorescence test (IIFT) with human epithelial cells plus primate liver and monospecific tests for characterisation of antibody specificities. Monospecific assays such as line blot are particularly important for determination of cytoplasmic antibodies, which are not always clearly detectable by IIFT. Since many of the autoantibodies in IIM are rare and typically occur in isolation, multiparameter testing encompassing an extensive range of MSA and MAA is crucial to gain maximum diagnostic information. Immunoblots enable parallel monospecific detection of many different autoantibodies and are thus valid and useful to identify subgroups of IIM with specific clinical features.


Multiparameter immunoblots EUROLINE Autoimmune Inflammatory Myopathies Profiles from EUROIMMUN are the most comprehensive commercially available line blots for myositis diagnostics, encompassing up to 20 target antigens in one test. The antigen portfolio encompasses the MSA target antigens Zo, Ks, Ha, cN-1A, OJ, EJ, PL-12, Pl-7, SRP, Jo-1, SAE1, NXP2, MDA5, TIF1, Mi-2, Mi-2, as well as the MAA target antigens Ku, PM-Scl75, PM-Scl100 and Ro-52. The exclusive antigen cN-1A enables detection of anti-cN-1A autoantibodies – the only known serological biomarker for sIBM. The antigens Ha, Ks and Zo are new additions to the portfolio and expand the tRNA synthetase antigen spectrum for ASS diagnostics. Each antigen or groups of antigens is printed onto a separate membrane chip to provide optimal efficiency of detection. Various profiles are available offering different combinations of myositis-relevant antigens, for example 20, 17, 16, 11, or 7 antigens per test strip


MSA against Associated diseases cN-1A


sIBM


EJ Ha


HMGCR Jo-1 KS


MDA5 Mi-2 Mi-2 NXP2 OJ


PL-12 PL-7 SAE1 SRP


TIF1 Zo


ASS, ILD ASS NM


ASS ASS


DM, ILD


DM, caDM DM, caDM


DM, ILD, caDM ASS, ILD ASS, ILD ASS, ILD


DM, ILD, caDM ASS, NM DM, caDM ASS


MAA against Associated diseases Ku


OM


PM-Scl75 PM-Scl100 Ro-52


OM, DM OM, DM ILD


Myositis-relevant autoantibodies and associated diseases.


catering to different laboratories’ requirements. Further EUROLINE profiles are also available for autoantibody diagnostics in other rheumatic diseases, for example detection of anti-nuclear antibodies, anti-cytoplasmic antibodies, or antibodies that occur in systemic sclerosis. All EUROLINE assays can be fully automated using the EUROBlotOne device with EUROLineScan software, providing increased standardisation and efficiency. ●


www.euroimmun.com 15


Mende M. et al. Mediterr J Rheumatol 30(3):155-161 (2019)


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