Autoantibodies to the GM2-1 islet ganglioside and to GAD-65 at type 1 diabetes onset

The GM2-1 islet ganglioside has been sequenced, found to be a novel ganglioside structure with a sialic acid moiety in the terminal position and two residues of non-acetylated galactosamine and also shown to be a target of autoantibodies in a subset of ICA(+) relatives of type 1 diabetic patients who subsequently progressed to the overt disease. In the present study we determined whether antibodies to GM2-1 or to other pancreatic gangliosides (a) are also expressed at disease onset and (b) are correlated with other diabetes-associated autoantibodies. Pancreatic gangliosides were extracted from human pancreas and purified by thin layer chromatography (TLC). Anti-ganglioside autoantibodies were determined using an indirect immunoperoxidase technique performed directly on TLC plates in the following groups of patients: (a) newly diagnosed type 1 diabetic subjects before insulin therapy (n=45); all were tested for GAD65 autoantibodies in a fluid-phase RIA using S-35-methionine-labelled recombinant human GAD65. Of these patients, 24 were also tested for insulin autoantibodies (IAA) by a competitive fluid phase radioimmunoassay and 21 were tested for GAD67 reactivity. (b) Forty-two age-and sex-matched normal control subjects. Autoantibodies to GM2-1, but not to other pancreatic gangliosides (GM3, GD3, GD1a), were expressed in 31 of 45 new-onset type 1 diabetic subjects and in one of 42 normal controls (P<0.01), while anti-GAD65, IAA and anti-GAD67 were found in 31 of 45, 12 of 24 and three of 21 patients respectively, but not in the control group of subjects. Interestingly, occurrence of GM2-1 autoantibodies was significantly correlated (P<0.005) with positivity for GAD65 autoantibodies, but not for IAA or GAD67 autoantibodies. It is of note that both GAD and gangliosides are mainly expressed in islets and in neuronal tissues and, therefore, type 1 diabetes may be regarded as a neuroendocrine autoimmune disease. (C) 1997 Academic Press Limited.