Anti-signal recognition particle autoantibody ELISA validation and clinical associations

The aim of this study was to develop and validate a quantitative anti-signal recognition particle (SRP) autoantibody serum ELISA in patients with myositis and longitudinal association with myositis disease activity. We developed a serum ELISA using recombinant purified full-length human SRP coated o...

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Published in:Rheumatology (Oxford, England) England), 2015-07, Vol.54 (7), p.1194-1199
Main Authors: Aggarwal, Rohit, Oddis, Chester V, Goudeau, Danielle, Fertig, Noreen, Metes, Ilinca, Stephens, Chad, Qi, Zengbiao, Koontz, Diane, Levesque, Marc C
Format: Article
Language:English
Subjects:
Adult
Autoantibodies - blood
Biomarkers - blood
Case-Control Studies
Clinical Science
Enzyme-Linked Immunosorbent Assay - methods
Female
Humans
Male
Middle Aged
Muscle, Skeletal - enzymology
Myositis - blood
Myositis - diagnosis
Myositis - immunology
Predictive Value of Tests
Reproducibility of Results
Sensitivity and Specificity
Severity of Illness Index
Signal Recognition Particle - immunology
Time Factors
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Summary:The aim of this study was to develop and validate a quantitative anti-signal recognition particle (SRP) autoantibody serum ELISA in patients with myositis and longitudinal association with myositis disease activity. We developed a serum ELISA using recombinant purified full-length human SRP coated on ELISA plates and a secondary antibody that bound human IgG to detect anti-SRP binding. Protein immunoprecipitation was used as the gold standard for the presence of anti-SRP. Serum samples from three groups were analysed: SRP(+) myositis subjects by immunoprecipitation, SRP(-) myositis subjects by immunoprecipitation and non-myositis controls. The ELISA's sensitivity, specificity, positive predictive value and negative predictive value were evaluated. Percentage agreement and test-retest reliability were assessed. Serial samples from seven SRP immunoprecipitation-positive subjects were also tested, along with serum muscle enzymes and manual muscle testing. Using immunoprecipitation, we identified 26 SRP(+) myositis patients and 77 SRP(-) controls (including 38 patients with necrotizing myopathy). Non-myositis control patients included SLE (n = 4) and SSc (n = 7) patients. Anti-SRP positivity by ELISA showed strong agreement (97.1%) with immunoprecipitation (κ = 0.94). The sensitivity, specificity, positive predictive value, and negative predictive value of the anti-SRP ELISA were 88, 100, 100 and 96, respectively. The area under the curve was 0.94, and test-retest reliability was strong (r = 0.91, P < 0.001). Serial samples showed that anti-SRP levels paralleled changes in muscle enzymes and manual muscle testing. We developed a quantitative ELISA for detecting serum anti-SRP autoantibodies and validated the assay in myositis. Longitudinal assessment of SRP levels by ELISA may be a useful biomarker for disease activity.
ISSN:1462-0324
1462-0332
DOI:10.1093/rheumatology/keu436