GAD-reactive CD4+ Th1 cells induce diabetes in NOD/SCID mice

Although glutamic acid decarboxylase (GAD) has been implicated in IDDM, there is no direct evidence showing GAD-reactive T cells are diabetogenic in vivo, To address this issue, 3-wk-old NOD mice received two injections of purified rat brain GAD; one mouse rapidly developed diabetes 3 wk later. Splenocytes from this mouse showed a proliferative response to purified GAD, and were used to generate a CD4+ T cell line, designated 5A, that expresses TCRs encoding V beta 2 and V beta 12, 5A T cells exhibit a MHC restricted proliferative response to purified GAD, as well as GAD65 peptide 524-543, After antigen-specific stimulation, 5A T cells secrete IFN gamma and TNF alpha/beta, but not IL-4, They are also cytotoxic against NOD-derived hybridoma cells (expressing I-A(g7)) that were transfected with rat GAD65, but not nontransfected hybridoma cells. Adoptive transfer of 5A cells into NOD/SCID mice produced insulitis in all mice, Diabetes occurred in 83% of the mice, We conclude that GAD injection in young NOD mice may, in some cases, provoke diabetes due to the activation of diabetogenic T cells reactive to GAD65 peptides, Our data provide direct evidence that GAD65 autoimmunity may be a critical event in the pathogenesis of IDDM.