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 diabeto genic in vivo, To address this issue, 3-wk-old NOD mice received two i njections of purified rat brain GAD; one mouse rapidly developed diabe tes 3 wk later. Splenocytes from this mouse showed a proliferative res ponse to purified GAD, and were used to generate a CD4+ T cell line, d esignated 5A, that expresses TCRs encoding V beta 2 and V beta 12, 5A T cells exhibit a MHC restricted proliferative response to purified GA D, as well as GAD65 peptide 524-543, After antigen-specific stimulatio n, 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 hy bridoma cells. Adoptive transfer of 5A cells into NOD/SCID mice produc ed insulitis in all mice, Diabetes occurred in 83% of the mice, We con clude that GAD injection in young NOD mice may, in some cases, provoke diabetes due to the activation of diabetogenic T cells reactive to GA D65 peptides, Our data provide direct evidence that GAD65 autoimmunity may be a critical event in the pathogenesis of IDDM.