Effect of antithyroid autoantibodies on pancreatic islet-cell function

Insulin-dependent diabetes mellitus is frequently associated with organ-specific autoimmune diseases and/or high titers of organ-specific autoantibodies. The effects of thyroid autoantibodies on islet-cell function were examined in the present study. Islet cell surface antibody (ICSAb) was detected in sera from 6 of 40 patients with autoimmune thyroid disease (AITD) who were positive for thyroid microsomal autoantibodies (TMA). Furthermore, all of the ICSAb-positive patients had high TMA titers. In vitro study using isolated rat pancreatic islets revealed that TMA positive sera significantly suppressed glucose-induced insulin release. Only one of 19 (5%) AITD patients showed complement-dependent antibody-mediated cytotoxicity and only one of 6 AITD patients (17%) was positive for antibody-dependent cellular cytotoxicity. These results suggest that TMA has an effect on an antigen of the islet cell membrane in which insulin releasing mechanism might be involved.