IgG1 Is the Dominant Subclass of Antibody against Glutamic Acid Decarboxylase among Type 1 Diabetes in Japanese.

Autoantibody against glutamic acid decarboxylase (GADA) is a highly sensitive predictor of insulin-dependency in adult diabetic patients as well as young individuals. A considerable number of diabetics who do not reach the insulin-dependent stage have this antibody. Recently, type 1 diabetes has been thought to be caused by T helper 1 (Thl)-type autoimmunity based on studies in non-obese diabetic mice, but it is still difficult to investigate antigen-specific T-cell function in human type 1 diabetes. We therefore assessed an IgG subclass assay for GADA, which should reflect T-helper function against GAD. Sera from 14 type 1 diabetic patients positive for GADA by radioligand binding assay were tested for the IgG subclass of GADA. The assay was based on an enzyme-linked immunosorbent assay, which showed a good correlation with radioligand binding assay. The sera of all but one of the 14 type 1 diabetic patients (93%) were positive for the IgG1 subclass of GADA. The IgG2 and IgG3 subclasses of GADA were also detected in one diabetic patient each who were also positive for IgG1. The IgG4 subclass was not detected in any of the sera we tested. We concluded that IgG1 is the dominant subclass of GADA in Japanese type 1 diabetic patients.