GAD65-specific antoantibodies enhance the presentation of an immunodominant T-cell epitope from GAD65

GAD65 autoantibodies (GAD65Ab) are highly prevalent in type 1 diabetes, but their functional role in the pathogenesis of the disease and their relatio nship to T-cell reactivity to GAD65 is still unclear. We tested the hypothe sis that GAD65Ab modulate presentation of GAD65 to T-cells, T-cell hybridom a T33.1, which recognizes the GAD65 274-286 epitope in the context of HLA-D RB1*0401, was incubated with antigen-presenting cells exposed to recombinan t human GAD65 alone or complexed with GAD65Ab(+) or GAD65Ab(-) sera. Stimul ation of the T33.1 hybridoma was greatly enhanced by multiple GAD65Ab(+) se ra. The enhancement effect was most prominent with sera from patients with high GAD65 autoantibody levels. Sera from GAD65Ab(-) subjects had no effect . The correlation between T-cell stimulation and GAD65Ab levels was not abs olute, suggesting that other variables such as autoantibody recognition of different regions of GAD65 and variable effects on processing of the 274-28 6 epitope may contribute. Uptake of antibody-complexed GAD65 was Fc recepto r (FcR)-mediated because the enhancement of presentation was inhibited by m onoclonal antibodies against FcR. Our results support the hypothesis that G AD65Ab modulate presentation of GAD65 to T-cells. Increased antigen uptake and heterogeneity in the autoantibody specificity may provide a mechanism f or antibody-facilitated T-cell response influencing the progression of type 1 diabetes.