Autoantibodies against insulin (IAA), C-peptide (CAA), and glucagon (GAA) in new-onset type 1 diabetic patients.

Autoantibodies against insulin, C-peptide, and glucagon were determined by radio-binding assay in 63 new-onset Type 1 (insulin-dependent) diabetic patients as well as in 70 controls. Plasma peptide binding was determined by means of 125I-labeled peptides and charcoal-dextran separation technique. Binding values exceeding the mean plus three standard deviations of the controls were considered as antibody-positive. Sixteen patients (25%) were positive for IAA, as 6 (10%) were positive for CAA and 2 (3%) for GAA. Of all control subjects, none were positive for either IAA or CAA, whereas 2 (2%) had GAA. The mean 125I-glucagon binding in the patients' group was, however, slightly enhanced and could be suppressed to normal values by excess unlabeled glucagon. The presence of IAA and/or CAA was significantly associated with more severe symptoms at diabetes manifestation. These results indicate that in new-onset Type 1 diabetics autoimmunity arises against all the insular peptides tested but is predominantly directed against those antigens secreted from the beta cells. Nevertheless, extremely low-binding GAA seem to be common in these patients. The determination of IAA/CAA might be useful in detecting a possible heterogeneity of Type 1 diabetes with regard to its clinical mode of manifestation.