A monoclonal antibody-based characterization of autoantibodies against glutamic acid decarboxylase in adults with latent autoimmune diabetes.
Autoantibodies to glutamic acid decarboxylase (GAD) are an important marker of the autoimmune-mediated beta-cell destruction in insulin-dependent (Type I) diabetes. However, these autoantibodies are also found in patients with Stiff-man syndrome (SMS) without onset of diabetes and some diabetic patients who initially present as non-insulin dependent (Type II) diabetes later becoming insulin-dependent, called as latent autoimmune diabetes in adults (LADA). To study the immune response to GAD in these LADA patients a competitive radiobinding assay based on murine monoclonal antibodies recognizing three different GAD regions was performed. The monoclonal antibodies against GAD recognize two different linear epitopes localized at the N- (amino acids 4-17) and C-terminus (amino acids 572-585) and one conformation-dependent epitope region (amino acids 221-442 IDDM-E1) known to be immunodominant for diabetes-associated autoantibodies. All LADA sera (20/20) reduced substantially the 125I-GAD binding of the monoclonal antibodies reactive with the conformation-dependent epitope region IDDM-E1 and only 20% of these sera additionally diminished the 125I-GAD65 binding by those monoclonals reactive with the both linear epitopes. The SMS sera completely abolished the GAD binding of all three monoclonals, reflecting a broader repertoire including an immune response against the IDDM-E1, a conformation-dependent GAD65 epitope region, also revealed if the SMS sera are diluted to equivalent antibody concentrations. In summary, our results show that diabetes-associated GAD autoantibodies even in adult patients with a late autoimmune process preferentially recognize a conformation-dependent middle GAD65 region. An immune response to all three GAD epitope regions is seldom in these LADA patients and only detectable in association with high antibody titres.
Institute of Pathophysiology, University Greifswald, Karlsburg, Germany.
B
B
Ziegler
M
M
Strebelow
I
I
Rjasanowski
M
M
Schlosser
M
M
Ziegler
D000328:Adult; D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology*; D001323:Autoantibodies / Q000276:immunology*; D001327:Autoimmune Diseases / Q000276:immunology; D015153:Blotting, Western; D003922:Diabetes Mellitus, Type 1 / Q000276:immunology*; D003924:Diabetes Mellitus, Type 2 / Q000276:immunology; D000939:Epitopes / Q000276:immunology; D005260:Female; D005968:Glutamate Decarboxylase / Q000276:immunology*; D006801:Humans; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D008875:Middle Aged; D011233:Precipitin Tests; D016750:Stiff-Person Syndrome / Q000276:immunology
D000911:Antibodies, Monoclonal; D001323:Autoantibodies; D000939:Epitopes; D005968:Glutamate Decarboxylase