Testing for myositis specific autoantibodies: Comparison between line blot and immunoprecipitation assays in 57 myositis sera.

Abstract

OBJECTIVE:

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

METHODS:

66 sera of patients with myositis (23 polymyositis, 8 anti-synthetase syndromes, 29 dermatomyositis and 6 overlap syndromes) were tested by commercial LB (Euroimmun, Lubeck, Germany); 57 sera were analyzed also by IP of K562 cell extract radiolabeled with (35)S-methionine. Inter-rater agreement was calculated with Cohen's k coefficient.

RESULTS:

Myositis-specific antibodies (MSA) were detected in 36/57 sera (63%) by IP and in 39/66 sera (59%) by LB. The most frequent MSA found by LB were anti-Jo1 and anti-Mi2 found in 15% (10/66) of sera, followed by anti-NXP2 and anti-SRP detected in 106% (7/66) of sera. Anti-TIF1gamma and anti-MDA5 were found in 6 (9%) and 5 sera (7.6%), respectively. A good agreement between methods was found only for anti-TIF1γ, anti-MDA5 and anti-NXP-2 antibodies, while a moderate agreement was estimated for anti-Mi2 and anti-EJ. By contrast, a high discordance rate for the detection of anti-Jo1 antibodies was evident (k: 0.3). Multiple positivity for MSA were found in 11/66 (17%) by LB and 0/57 by IP (p: 0001). Comparing the clinical features of these 11 sera, we found total discrepancies between assays in 3 sera (27.3%), a relative discrepancy due to the occurrence of one discordant autoantibody (not confirmed by IP) in 5 cases (45.5%) and a total discrepancy between LB and IP results, but with a relative concordance with clinical features were found in other 3 sera (27.3%). The semiquantitative results do not support the interpretation of the data.

CONCLUSIONS:

The use of 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 positivities and the high discondant rate of anti-Jo1 antibodies could create some misinterpretation of the results from the clinical point of view. These data should be confirmed by enlarging the number of myositis cases.

• Authors: Ilaria Cavazzana, Micaela Fredi, Angela Ceribelli, Cristina Mordenti, Fabio Ferrari, Nice Carabellese, Angela Tincani, Minoru Satoh, Franco Franceschini
• Journal: Journal of immunological methods (J Immunol Methods) Vol. 433 Pg. 1-5 (06 2016) ISSN: 1872-7905 [Electronic] Netherlands
• PMID: 26906088 (Publication Type: Comparative Study, Journal Article)
• Copyright: Copyright © 2016 Elsevier B.V. All rights reserved.

Chemical References

• Antibodies, Antinuclear
• DNA-Binding Proteins
• Jo-1 antibody
• TRIM33 protein, human
• Transcription Factors
• Adenosine Triphosphatases
• IFIH1 protein, human
• MORC3 protein, human
• Interferon-Induced Helicase, IFIH1

Topics

• Adenosine Triphosphatases (immunology)
• Adult
• Antibodies, Antinuclear (blood)
• DNA-Binding Proteins (immunology)
• Female
• Humans
• Immunoassay (methods)
• Immunoprecipitation
• Interferon-Induced Helicase, IFIH1 (immunology)
• K562 Cells
• Male
• Middle Aged
• Myositis (blood, diagnosis)
• Retrospective Studies
• Sensitivity and Specificity
• Transcription Factors (immunology)