Studies on the immunoregulation of thyroid autoantibody production in vitro

The spontaneous production (without mitogen or antigen) of antithyroglobulin and antimicrosomal antibodies by peripheral (PBL) and thyroid-derived lymphocytes from patients with Hashimoto's thyroiditis (HT) has been studied with particular emphasis on the regulation of this phenomenon. Based on studies of DNA and protein synthesis, kinetic studies and B/T reconstitution experiments, in most HT patients, spontaneous production by PBL is accounted for by secretion of preformed antithyroglobulin (termed Type 1 patients), whereas active production is observed in a small minority (termed Type 2). In none of 24 HT patients could active antimicrosomal antibody production by PBL be detected. Conversely, thyroid-derived lymphocytes produced both autoantibodies by an active process. Pokeweed mitogen (PWM) stimulation enhanced antibody production by PBL in the Type 1 group but not in Type 2 or thyroid-derived lymphocytes. T lymphocytes were required for antibody synthesis in both thyroid antigen-driven and peripheral PWM-driven cultures. By separating T lymphocytes into T4+ (helper) and T8+ (suppressor) subsets with monoclonal antibodies, T-cell modulation of autoantibody production in both systems was studied. In a PWM-induced system, both thyroid and peripheral T-cell subsets were capable of modulating peripheral antibody production. In the thyroid lymphocyte antigen-specific system, further addition of thyroid derived T8+ cells alone caused partial suppression of antibody production but not with peripheral T8+ cells. Of interest was the partial decrease of antibody production by the thyroid lymphocytes by added peripheral T4+ cells. The fact that the production of thyroid autoantibodies by thyroid-derived mononuclear cells (which included T suppressor, T helper and B lymphocytes) could be reduced by the addition of more suppressor T lymphocytes suggests that an antigen-specific defect in the T4+/T8+ thyroid cell balance may account for the in vivo production of these antibodies in patients with Hashimoto's thyroiditis.