Antibodies against ganglioside G(T3) in the sera of patients with type I diabetes mellitus

Clinical and experimental data support the concept that type I diabetes mellitus results from autoimmune destruction of pancreatic β cells. Although both proteins and glycolipids are targets of anti-islet cell antibodies, the Ag have not been purified or characterized. Previously, we observed that rat insulinoma (RIN) cell lines varied in their reactivity with both human antibodies and murine mAb A2B5, which binds to polysialo gangliosides. To determine the chemical basis of the varied immunoreactivity, we analyzed the glycosphingolipids of 5 RIN lines. Glycolipids bound by two mAb and by antibodies in the sera of type I diabetics were identified. The more immunoreactive RIN lines contained a much higher content of gangliosides and a higher proportion of complex gangliosides. The major gangliosides were G(M3), G(D3), and G(T3). By high performance TLC immunostaining, we demonstrated that A2B5 and R2D6, an anti-β cell murine mAb, bound most strongly to ganglioside G(T3). The binding of human sera to gangliosides was analyzed by an ELISA assay. Although both normal and diabetic sera contained antibodies to various glycolipids, binding to G(T3) was significantly elevated in 31 new-onset type I diabetics (p < 0.001). The presence of G(T3) trisialosyl epitope on human islet cells was shown by immunofluorescent staining by both R2D6 and A2B5. These findings support previous suggestions that gangliosides play an important role in the immunopathology of type I diabetes, and identify for the first time a specific ganglioside Ag that is the target for autoantibodies in a subset of diabetic patients.