Insulin autoantibodies (IAAs) are regarded as a serological marker of on-going autoimmunity and developement of insulin dependent diabetes mellitus (IDDM) in Caucasians. Since there have been no reports on IAAs in Japan, we studied IAAs in relatives of Japanese patients with IDDM and correlated the results with HLA, islet cell surface antibodies (ICSA) and beta cell function.
Twenty non-diabetic relatives of patients with IDDM were studied. IAAs were measured by the polyethyleneglycol (PEG) precipitation method with 125I-human insulin and expressed as insulin binding capacity. HLA was detected by a microcytotoxicity test and ICSA were examined by the indirect immunofluorescence method using Ballb/c mouse islet cells. Beta cell function was studied by a 75g oral glucose tolerance test (0-GTT). Four of 20 sera from relatives showed high 125I-human insulin binding, well above the mean+3 SD of those from helthy controls. No sera from healthy controls showed such high 125I-insulin binding. IAA-positive sera were obtained from 2 siblings and 2 children. There was no relation between IAAs and HLA, ICSA and beta cell function tested by 75g O-GTT. These results suggest that IAAs may be a serological marker of Japanese individuals at high risk to develop IDDM.
