Importance of GAD65 peptides and I-A(g7) in the development of insulitis in nonobese diabetic mice

Insulin-dependent diabetes mellitus (IDDM) develops in nonobese diabetic (N OD) mice through the destruction of the B cells in pancreatic Langerhans is lets by islet autoantigen-specific T cells. The islet autoantigen glutamic acid decarboxylase 65 (GAD65) is thought to be a major target autoantigen i n IDDM. In the present report, we established GAD65-specific T-cell clones using overlapping peptides that cover the amino acid sequences of mouse GAD 65. T-cell epitopes of GAD65 were characterized by proliferation and bindin g assays using various analogue peptides and wild-type or mutant I-A(g7) tr ansfectants. The efficacy of the peptide vaccine in IDDM was determined by administering T-cell epitope peptides to NOD mice and evaluating the histop athology of their insulitis. We obtained two types of T-cell clone, one spe cific for peptide p316-335 and another specific for p531-545 of GAD65. The p531-545 site has already been identified, but we report the p316-335 site for the first time. T-cell clones recognized those peptides in the wild-typ e I-A(g7) but not in the mutant I-A(g7) in which the serine at position 57 of the beta-chain was replaced by an aspartic acid. Both the p316-335 and p 531-545 peptides bound weakly to I-A(g7). Some peptides with amino acid sub stitutions had antagonistic activity, and administration of a large amount of wild-type peptide reduced the severity of insulitis in NOD mice. Our res ults suggest that peptide vaccine therapy may be useful in autoimmune disea ses, including IDDM.