Existence and immunological significance of circulating Ia+T cells in autoimmune thyroid diseases

We investigated the percentage of circulating HLA-DR antigen positive (Ia antigen positive: Ia+) T cells and the additive proliferation by non-specific mitogens and thyroid-specific antigens by means of a cytotoxicity test in autoimmune thyroid diseases. Furthermore, we studied the stimulative function of circulating Ia+T cells in autologous mixed lymphocyte reactions. %Ia+T cells were significantly increased in patients with autoimmune thyroid diseases compared with those in normal controls. They were additionally increased by the stimulation of TSH-receptor or thyroid-microsome in patients with Graves' disease, and by the stimulation of thyroglobulin and thyroid-microsome in patients with Hashimoto's thyroiditis. As to the cellular immune function, circulating Ia+T cells stimulated Ia-T cells in autologous MLR in patients with autoimmune thyroid diseases. These data suggest that some of the T cells are already activated in vivo, that the activation of T cells may be by thyroid-specific antigens, and that these activated (Ia+) T cells may be able sequentially to induce the activation of inactivated (Ia-) T cells in autoimmune thyroid diseases.