AUTOANTIBODIES TO THE GM2-1 ISLET GANGLIOSIDE AND TO GAD-65 AT TYPE-1DIABETES ONSET

The GM2-1 islet ganglioside has been sequenced, found to be a novel ga nglioside 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 oth er pancreatic gangliosides (a) are also expressed at disease onset and (b) are correlated with other diabetes-associated autoantibodies. Pan creatic gangliosides were extracted from human pancreas and purified b y thin layer chromatography (TLC). Anti-ganglioside autoantibodies wer e determined using an indirect immunoperoxidase technique performed di rectly on TLC plates in the following groups of patients: (a) newly di agnosed type 1 diabetic subjects before insulin therapy (n=45); all we re tested for GAD65 autoantibodies in a fluid-phase RIA using S-35-met hionine-labelled recombinant human GAD65. Of these patients, 24 were a lso tested for insulin autoantibodies (IAA) by a competitive fluid pha se radioimmunoassay and 21 were tested for GAD67 reactivity. (b) Forty -two age-and sex-matched normal control subjects. Autoantibodies to GM 2-1, but not to other pancreatic gangliosides (GM3, GD3, GD1a), were e xpressed 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, bu t not in the control group of subjects. Interestingly, occurrence of G M2-1 autoantibodies was significantly correlated (P<0.005) with positi vity 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 Pr ess Limited.