title: Anti-SAE antibodies in autoimmune myositis: identification by unlabelled protein immunoprecipitation in an Italian patient cohort.
abstract: BACKGROUND
  Myositis specific autoantibodies (MSAs) are useful in the diagnosis of idiopathic inflammatory myopathies and in the definition of disease subsets. The aim of this study was to set up an unlabelled protein immunoprecipitation technique for MSA identification in the sera of myositis patients, in order to identify and investigate new antibody reactivity, undetectable by currently used methods.
  
  
  METHODS
  Sera of 183 patients with connective tissue diseases (75 adult dermatomyositis, 12 juvenile dermatomyositis, 43 polymyositis, 53 other connective tissue diseases) and 30 healthy controls were screened by an in-house procedure of unlabelled protein immunoprecipitation. In the same sera MSAs and myositis associated antibodies were determined by immunoblotting and immunoprecipitation for RNA.
  
  
  RESULTS
  The analytical specificity of unlabelled protein immunoprecipitation was demonstrated by testing reference sera with known antibody reactivity. Sera from five patients, affected with dermatomyositis (5/75=7%), immunoprecipitated two proteins of 40 and 90 kDa apparent molecular weights respectively, consistent with the subunits of the small ubiquitin like modifier activating enzyme heterodimer (SAE1/SAE2). The identity of putative SAE immunoprecipitated proteins was confirmed by immunoblotting on immunoprecipitates using commercial monospecific antibodies to SAE1 and SAE2. Major clinical features were compared between anti-SAE positive and negative patients. Interestingly, anti-SAE positive patients had mainly skin and muscle manifestations while dysphagia, interstitial lung disease, arthritis and constitutional symptoms were absent.
  
  
  CONCLUSIONS
  Unlabelled protein immunoprecipitation is a specific analytical approach, appropriate for the identification of the recently described anti-SAE autoantibody. We confirmed the role of anti-SAE antibody as marker of dermatomyositis.
authors.affiliation: Division of Rheumatology, Department of Medicine, University of Padova, Via Giustiniani 2, 35128 Padova, Italy. elenatarricone@gmail.com
authors.forename: Elena
authors.initials: E
authors.lastname: Tarricone
authors.forename: Anna
authors.initials: A
authors.lastname: Ghirardello
authors.forename: Mariaelisa
authors.initials: M
authors.lastname: Rampudda
authors.forename: Nicola
authors.initials: N
authors.lastname: Bassi
authors.forename: Leonardo
authors.initials: L
authors.lastname: Punzi
authors.forename: Andrea
authors.initials: A
authors.lastname: Doria
mesh_terms: D000293:Adolescent; D000328:Adult; D000604:Amino Acyl-tRNA Synthetases; D001323:Autoantibodies / Q000097:blood / Q000276:immunology*; D001327:Autoimmune Diseases / Q000097:blood / Q000175:diagnosis / Q000276:immunology*; D015415:Biomarkers / Q000097:blood; D002648:Child; D015331:Cohort Studies; D003882:Dermatomyositis / Q000097:blood / Q000175:diagnosis / Q000276:immunology; D003937:Diagnosis, Differential; D006801:Humans; D015151:Immunoblotting; D047468:Immunoprecipitation / Q000379:methods; D007558:Italy; D019169:Jurkat Cells; D008875:Middle Aged; D009220:Myositis / Q000097:blood / Q000175:diagnosis / Q000276:immunology*; D017285:Polymyositis / Q000097:blood / Q000175:diagnosis / Q000276:immunology; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D044764:Ubiquitin-Activating Enzymes / Q000276:immunology*
chemical_list: D001323:Autoantibodies; D015415:Biomarkers; C470301:UBA2 protein, human; D000604:Amino Acyl-tRNA Synthetases; C470299:SAE1 protein, human; D044764:Ubiquitin-Activating Enzymes