IMMUNIZATION WITH THE LARGER ISOFORM OF MOUSE GLUTAMIC-ACID DECARBOXYLASE (GAD(67)) PREVENTS AUTOIMMUNE DIABETES IN NOD MICE

The 65-kDa isoform of glutamic acid decarboxylase (GAD(65)) has been implicated in autoimmune diabetes in NOD mice, but the role of the 67-kDa GAD isoform (GAD(67)) is less clear. We found that immunization of 4-week-old NOD mice with purified recombinant mouse GAD(67) prevented or significantly delayed the onset of diabetes. To further explore this phenomenon, we characterized anti-GAD(67) immune responses in naive and GAD-immunized NOD mice. Anti-GAD(67) antibodies titers were relatively low in naive mice at all ages, but a single immunization with GAD(67) at 4 weeks induced high titers of anti-GAD antibodies by 6 weeks of age. in both 4-weekold and diabetic NOD mice, there were significant endogenous T-cell proliferative responses against purified recombinant mouse GAD(67). These T-cell proliferative responses were blocked by anti-I-A(NOD) and anti-CD4 antibodies. To characterize the anti-GAD T-cell responses in the NOD mice, we established T-cell Lines and T-cell clones which recognized GAD(65), and we used recombinant subfragments of GAD to localize the predominant T-cell epitopes in GAD(67). T-cells from naive NOD mice proliferated in response to all GAD subfragments, whereas T-cells horn diabetic mice responded primarily to the COOH-terminal 83 amino acids of GAD(67). These results suggest that GAD(67) is an autoantigen in IDDM and immunization of prediabetic NOD mice with GAD(67) can prevent the onset of diabetes.