title: Testing for myositis specific autoantibodies: Comparison between line blot and immunoprecipitation assays in 57 myositis sera.
abstract: 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.
  
  
  
  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.
  
  
  
  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.
  
  
  
  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.affiliation: Rheumatology and Clinical Immunology Unit, Rheumatology Chair, Spedali Civili, Università degli Studi di Brescia, Brescia, Italy.
authors.forename: Ilaria
authors.initials: I
authors.lastname: Cavazzana
authors.affiliation: Rheumatology and Clinical Immunology Unit, Rheumatology Chair, Spedali Civili, Università degli Studi di Brescia, Brescia, Italy.
authors.forename: Micaela
authors.initials: M
authors.lastname: Fredi
authors.affiliation: Humanitas Research Hospital BIOMETRA Department, Rozzano, Italy.
authors.forename: Angela
authors.initials: A
authors.lastname: Ceribelli
authors.affiliation: Rheumatology and Clinical Immunology Unit, Rheumatology Chair, Spedali Civili, Università degli Studi di Brescia, Brescia, Italy.
authors.forename: Cristina
authors.initials: C
authors.lastname: Mordenti
authors.affiliation: Rheumatology and Clinical Immunology Unit, Rheumatology Chair, Spedali Civili, Università degli Studi di Brescia, Brescia, Italy.
authors.forename: Fabio
authors.initials: F
authors.lastname: Ferrari
authors.affiliation: Rheumatology and Clinical Immunology Unit, Rheumatology Chair, Spedali Civili, Università degli Studi di Brescia, Brescia, Italy.
authors.forename: Nice
authors.initials: N
authors.lastname: Carabellese
authors.affiliation: Rheumatology and Clinical Immunology Unit, Rheumatology Chair, Spedali Civili, Università degli Studi di Brescia, Brescia, Italy.
authors.forename: Angela
authors.initials: A
authors.lastname: Tincani
authors.affiliation: School of Health Sciences University of Occupational and Environmental Health, Kitakyushu, Japan.
authors.forename: Minoru
authors.initials: M
authors.lastname: Satoh
authors.affiliation: Rheumatology and Clinical Immunology Unit, Rheumatology Chair, Spedali Civili, Università degli Studi di Brescia, Brescia, Italy.
authors.forename: Franco
authors.initials: F
authors.lastname: Franceschini
mesh_terms: D000251:Adenosine Triphosphatases / Q000276:immunology; D000328:Adult; D000974:Antibodies, Antinuclear / Q000097:blood*; D004268:DNA-Binding Proteins / Q000276:immunology; D005260:Female; D006801:Humans; D007118:Immunoassay / Q000379:methods*; D047468:Immunoprecipitation; D000072640:Interferon-Induced Helicase, IFIH1 / Q000276:immunology; D020014:K562 Cells; D008297:Male; D008875:Middle Aged; D009220:Myositis / Q000097:blood* / Q000175:diagnosis; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D014157:Transcription Factors / Q000276:immunology
chemical_list: D000974:Antibodies, Antinuclear; D004268:DNA-Binding Proteins; C046750:Jo-1 antibody; C511956:TRIM33 protein, human; D014157:Transcription Factors; D000251:Adenosine Triphosphatases; C452815:IFIH1 protein, human; C551732:MORC3 protein, human; D000072640:Interferon-Induced Helicase, IFIH1
keywords: Anti-Jo1; Anti-synthetase syndrome; Autoantibodies; Immunoprecipitation; Line blot; Myositis