Epitope spreading and a varying but not disease-specific GAD65 antibody response in Type I diabetes. The Childhood Diabetes in Finland Study Group

Diabetologia. 2000 Feb;43(2):210-7. doi: 10.1007/s001250050031.


Aims/hypothesis: The aim of this study was to analyse the conformational and linear epitope profiles of glutamic acid decarboxylase antibody (GAD65-ab)-positive sera to find disease-specific epitope profiles and to study, whether GAD65-ab epitope recognition changes or spreads during the prediabetic period and, thus, can provide markers to differentiate early from later stages of progression to diabetes.

Methods: Sera from subjects before (n = 21), at onset (n = 44), or at increased risk of Type I (insulin-dependent) diabetes mellitus (n = 20) and from patients with stiff-man syndrome (SMS, n = 18) or polyendocrine autoimmune syndrome (PAS, n = 21) were analysed for conformational and linear GAD65 epitope recognition by an immunohistochemical blocking test based on human monoclonal GAD65-ab (MICA 1-10) and western blotting of a GAD65 epitope-cDNA-library.

Results: A redundant reactivity of many GAD65-ab positive sera to three major conformational (EP-1, EP-2, EP-3) and two dominant linear epitope clusters (amino acid 1-124 and 535-585) was observed in diabetes, polyendocrine autoimmune syndrome and stiff-man syndrome and no disease-specific epitopes or epitope-profiles were detected. Epitope recognition broadened with higher titres and with the vulnerability of patients to acquire additional autoimmune diseases apart from diabetes. Low GAD65-ab serum titres (< 1200 arbitrary units) and EP-1 recognition in the absence of EP-2 binding characterised the early immune response. Changing epitope profiles combined stable recognition of EP-1 with gain or loss of reactivity to C-terminal epitopes during follow-up.

Conclusion/interpretation: A maturing autoantibody response, which could spread from EP-1-recognition to other regions of GAD65, resulted in titre-related rather than disease-specific epitope profiles which were not sufficient to predict whether GAD65-ab positive subjects will progress to Type I diabetes, autoimmune polyendocrine syndrome or stiff-man syndrome.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adolescent
  • Adult
  • Autoimmune Diseases / blood
  • Autoimmune Diseases / immunology
  • Child
  • Child, Preschool
  • Diabetes Mellitus, Type 1 / blood
  • Diabetes Mellitus, Type 1 / immunology*
  • Epitopes / immunology
  • Female
  • Glutamate Decarboxylase / chemistry
  • Glutamate Decarboxylase / immunology*
  • Humans
  • Infant
  • Isoenzymes / chemistry
  • Isoenzymes / immunology*
  • Male
  • Middle Aged
  • Prediabetic State / blood
  • Prediabetic State / immunology*
  • Risk Factors
  • Stiff-Person Syndrome / blood
  • Stiff-Person Syndrome / immunology


  • Epitopes
  • Isoenzymes
  • Glutamate Decarboxylase
  • glutamate decarboxylase 2