title: On the occurrence of the diabetes-associated antigen GAD 65 in human sera.
abstract: BACKGROUND
  Glutamic acid decarboxylase (GAD 65) is involved as an antigen in diabetes mellitus type 1 and is generally considered to be located intracellularly in pancreas β-cells. In this study we demonstrate its appearance in 64 human sera samples representing a cross-section of a blood bank.
  
  
  METHODS
  The proof of GAD 65 in sera was done using an enzyme-linked immunosorbent assay (ELISA) setup where it was detected by interaction with corresponding antibodies labeled with an enzyme. The enzyme catalyzes a substrate reaction, resulting in a change of color, that is used for the quantitative evaluation of the antigen-antibody interaction.
  
  
  RESULTS
  The measurements showed that GAD 65 exists in various amounts in the sera of blood donors, with an average concentration of 58.00 ng/ml. The correlation analysis of samples stored at -80° C and at room temperature demonstrates the stability of GAD 65 at room temperature. The correlation coefficient between the GAD 65 concentrations of samples stored at room temperature and of the same samples after 1 week shows that the molecule remains stable.
  
  
  CONCLUSIONS
  Our results encourage us to propose antigen GAD 65, due to its frequency in human sera in different concentrations and its stability, as a biomarker for the early diagnosis of type 1 diabetes and related inflammations.
authors.affiliation: Medical University of Graz, Graz, Austria. gernot.tilz@meduni-graz.at
authors.forename: G P
authors.initials: GP
authors.lastname: Tilz
authors.forename: M
authors.initials: M
authors.lastname: Wiltgen
authors.forename: M
authors.initials: M
authors.lastname: Borkenstein
mesh_terms: D001324:Autoantigens / Q000097:blood*; D015415:Biomarkers / Q000097:blood* / Q000737:chemistry; D003922:Diabetes Mellitus, Type 1 / Q000175:diagnosis* / Q000276:immunology; D005968:Glutamate Decarboxylase / Q000097:blood* / Q000737:chemistry; D006801:Humans; D050417:Insulin-Secreting Cells / Q000276:immunology / Q000378:metabolism* / Q000473:pathology; D055550:Protein Stability; D013696:Temperature
chemical_list: D001324:Autoantigens; D015415:Biomarkers; D005968:Glutamate Decarboxylase; C401141:glutamate decarboxylase 2