Detection of GAD-reactive CD4+ cells in so-called "type 1B" diabetes

Objective - Although the majority of type 1 diabetes is considered to be type 1A, some patients with type 1 diabetes have no islet-associated autoantibody in their serum. This type of type 1 diabetes has usually been diagnosed as type 1B on the basis of islet-associated autoantibody-negativity. In this study, we tried to demonstrate the existence of islet-associated antigen-specific T cells in type 1 diabetes without islet-associated autoantibody. Research Design and Methods - Peripheral blood samples were obtained from 110 Japanese diabetic patients, including 15 type 2 diabetic patients. Measurement of islet-associated antigen-specific cytokine response was performed by intracellular cytokine staining for flow cytometry. Results - The number of GAD-reactive IFN-γ-producing CD4+ cells in 50,000 CD4+ cells in diabetics with type 1B (113.6 ± 34.6, median 45), type 1A (132.4 ± 33.3, median 25), and LADA (154.4 ± 44.1, median 20) was higher than that in type 2 diabetics (03 ± 0.3, median 0) and control subjects (3.8 ± 2.4, median 0). When the normal upper limit of the number of GAD-reactive CD4+ cells was set at the mean + 3SD of values in control subjects, at least half (52.4%) of the so-called "type 1B" patients were positive for GAD-reactive IFN-γ-producing CD4+ cells, a significantly larger proportion than that in type 2 diabetics (0%; p < 0.001). Conclusions - Assessment of T cell reactivity against islet-associated antigen may contribute to the diagnosis of "autoimmune-related" type 1 diabetes.