GAD65-reactive T cells in a non-diabetic stiff-man syndrome patient

GAD65 (glutamic acid decarboxylase) is an important autoantigen in both typ e 1 (insulin-dependent) diabetes mellitus (IDDM) and the neurological autoi mmune disease stiff-man syndrome SMS), and is expressed in pancreatic islet s as well as the nervous system. Still, only 30% of SMS patients also have type 1 diabetes. To study regulation of T cell responsiveness to GAD65, we investigated a non-diabetic SMS patient with HLA-DR3/7 (predisposing to typ e 1 diabetes) and high levels of type 1 diabetes-associated autoantibodies against GAD65 and islet cells, and compared the results with those of her d iabetic son and two other SMS patients. T cell responses to GAD65 were repe atedly absent in primary stimulation, whereas IA-2, islet antigen and tetan us toroid induced significant T cell proliferation. However, after in vitro restimulation, GAD65 reactive T cell lines and clones were obtained that w ere HLA-DR3 restricted, and cross-reactive with a homogenate of purified hu man pancreatic islets. These T cells produced the immunoregulatory cytokine IL-10 in combination with IFN-gamma and IL-4 (Th0). The dominant T cell ep itope was mapped to the central region of GAD65. Although no primary respon se to whole GAD65 was detectable, the naturally processed GAD65 peptide epi tope was recognized vigorously in the primary stimulation assay. The lack o f detectable primary T cell responses to GAD65, together with the GAD65-spe cific cytokine production of restimulated T cells, suggest that GAD65-speci fic cellular autoimmunity in this patient is suppressed and may;be related to the absence of diabetes despite humoral autoreactivity and genetic predi sposition. (C) 1999 Academic Press.