The neuronal toxic factor in serum of type 1 diabetic patients is a complement-fixing autoantibody

Type 1 diabetes is an autoimmune disease resulting in destruction of pancreatic beta cells. Many of the pancreatic beta cell autoantigens are also neuronal cell components. Using adrenergic neuroblastoma cells, we have previously demonstrated that humoral mechanisms may contribute to the development of diabetic neuropathy in Type 1 patients. We hypothesize that the toxic factor in Type 1 diabetic serum is an immunoglobulin. When neuroblastoma cells were exposed to immunoglobulins precipitated from serum of Type 1 diabetes patients with neuropathy, cell growth was significantly inhibited by day 5 (3.8 +/- 2.4 x 10(5) cells) compared to cells cultured with immunoglobulins from control (8.2 +/- 2.3 x 10(5) cells) or Type 2 diabetic serum (7.0 +/- 3.0 x 10(5) cells). The inhibitory effect (3.2 +/- 0.9 x 10(5) cells) could be removed from Type 1 diabetic serum by affinity precipitation with protein A-agarose (8.0 +/- 0.8 x 10(5) cells). Mild heat denaturing of the serum reversed the inhibitory effect (3.8 +/- 0.9 vs 1.4 +/- 1.4 x 10(5) cells), indicating a requirement for complement. Immunofluorescent labelling with anti-IgG secondary antibody of cells exposed to Type 1 diabetic serum indicated recognition of a membrane-bound antigen. The studies in this report support the hypothesis that autoimmune neuronal destruction may contribute to the development of diabetic autonomic neuropathy in patients with Type 1 diabetes.