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Testing Methods Compared for Myositis Specific Autoantibodies

By LabMedica International staff writers
Posted on 28 Jun 2016

Image: A histopathology of polymyositis showing endomysial mononuclear inflammatory infiltrate and muscle fiber necrosis (Photo courtesy of Ramesh Pappu, MD, DPH).

The performance of a line blot assay for the identification of autoantibodies in sera of patients affected by myositis has been compared with immunoprecipitation (IP) as gold standard.

Myositis refers to any condition causing inflammation in muscles and weakness, swelling, and pain are the most common myositis symptoms. Myositis causes include infection, injury, autoimmune conditions, and drug side effects and treatment of myositis varies according to the cause.

Immunologists at the University of Brescia (Italy) and their colleagues tested sera of 66 sera of patients with myositis, 23 polymyositis, eight anti-synthetase syndromes, 29 dermatomyositis and six overlap syndromes, by a commercial line blot (LB, Euroimmun, Lubeck, Germany); 57 sera were analyzed also by IP of K562 cell extract radiolabeled with 35S-methionine. Inter-rater agreement was calculated with Cohen's κ coefficient.

The scientists found that myositis-specific antibodies (MSA) could be detected in 36/57 (63%) of sera by IP and in 39/66 (59%) of sera by LB. The most frequent MSA found by LB were anti- histidyl tRNA synthetase (Jo1) and anti-Mi2 nuclear antigen found in 15% (10/66) of sera, followed by anti- nuclear matrix protein 2 (NXP2) and anti- signal recognition particle (SRP) detected in 10.6% (7/66) of sera. Anti- transcriptional intermediary factor 1 gamma (TIF1γ) and anti- Melanoma Differentiation-Associated protein 5 (MDA5) were found in six (9%) and five sera (7.6%), respectively.

The authors concluded that the use of the LB assay allowed the detection of new MSA, such as anti-MDA5, anti-MJ and anti-TIF1gamma antibodies, previously not found with routine methods. However, the high prevalence of multiple positives and the high discordant rate of anti-Jo1 antibodies could create some misinterpretation of the results from the clinical point of view. The study was published in the June 2016 issue of the Journal of Immunological Methods.

Related Links:
University of Brescia
Euroimmun