GAD⁶⁵ and Insulin B Chain Peptide (9-23) are not Primary Autoantigens in the Type 1 Diabetes Syndrome of the BB Rat

Abstract

To investigate whether GAD⁶⁵ whole molecule, GAD⁶⁵ p³⁵ or insulin B chain peptide (amino acids 9-23) play an essential role in the pathogenesis of type 1 diabetes in the BioBreeding (BB) rat, we gave serial injections of GAD⁶⁵, p³⁵ or insulin B chain (9-23) to six groups of BB/Worcester rats. The individual antigens were administered either intrathymically on day 2 and intraperitoneal in MF 59-0 adjuvant 5 times during the first 5 weeks, or by intranasal instillation once neonatally and 5 days/week for the following 6 weeks. Control groups were injected with vehicle only. Age of onset of diabetes and degree of insulitis were not different between controls and antigen-treated rats. Rats that received GAD⁶⁵ intrathymically and intraperitoneal!) developed high GAD⁶⁵-antibody titers without altering diabetes development. In GAD⁶⁵-treated animals, serum antibodies recognized epitopes at 3 sites on GAD⁶⁵ in diabetic animals but only at 1 site in non-diabetic animals. GAD⁶⁵-injected animals also showed a significant reduction of IFN-γ mRNA expression in the thymus. This study provides evidence against the hypothesis that GAD⁶⁵ and insulin B chain peptide (9-23) are primary diabetogenic autoantigens in BB rats because immunizations with these antigens and GAD⁶⁵-induced immune deviation did not alter the development of diabetes.

Key Words:

• GAD⁶⁵
• GAD⁶⁵ p³⁵
• Insulin B chain peptide (9-23)
• GAD⁶⁵ antibody
• Immunization
• Tolerization
• Type 1 diabetes