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Diabetic sera react with the glutamic acid decarboxylase molecule in a dimeric-oligomeric form
M J Rowley1, Q Y Chen, K L Teoh
1Department of Biochemistry and Molecular Biology and Medicine, Monash University, Clayton, Victoria, Australia.
Clinical and Experimental Immunology
|November 1, 1996
Summary
Patients with insulin-dependent diabetes mellitus (IDDM) have antibodies that target dimeric forms of Glutamic Acid Decarboxylase (GAD), not the monomeric form. This finding impacts understanding of self-tolerance and autoimmunity in IDDM.
Area of Science:
- Immunology
- Endocrinology
- Molecular Biology
Background:
- Glutamic acid decarboxylase (GAD) is a key autoantigen in insulin-dependent diabetes mellitus (IDDM).
- GAD was initially identified as a 64-65 kD protein in pancreatic islets.
Purpose of the Study:
- To investigate the antigenicity of different Glutamic Acid Decarboxylase (GAD) preparations in patients with IDDM.
- To determine the specific form of GAD recognized by autoantibodies in IDDM.
Main Methods:
- Studied radiolabelled GAD preparations (affinity purified and recombinantly expressed).
- Utilized immunoprecipitation, SDS-PAGE, and autoradiography under reducing and non-reducing conditions.
- Employed antibody-depletion experiments to analyze GAD reactivity.
Main Results:
- Immunoprecipitated GAD migrated as a higher molecular weight (110-130 kD) under non-reducing conditions, indicating dimeric forms.
- Monomeric GAD (64-65 kD) was non-reactive with potent IDDM sera after depletion of the dimeric form.
- IDDM patient sera specifically reacted with dimeric or oligomeric forms of GAD.
Conclusions:
- Autoantibodies in IDDM primarily target dimeric (or oligomeric) forms of Glutamic Acid Decarboxylase (GAD).
- This specificity for GAD dimers has significant implications for understanding self-tolerance and autoimmunity in IDDM pathogenesis.