Ia+ T cells in new onset Graves' disease.

The Ia (immune-associated, DR) antigen is a cell surface glycoprotein which is absent on normal circulating T lymphocytes but present on activated T lymphocytes. We studied the expression of this antigen on circulating T lymphocytes from patients with untreated hyperthyroid Graves' disease. All patients (n = 33) with recent onset hyperthyroid Graves' disease studied had an increased percentage and number of circulating Ia+ T cells. Patients with non-Graves's hyperthyroidism or Graves' disease patients more than 1 yr after thyroid ablation had normal values for Ia+ T cells. Other cell surface activation antigens, recognized by monoclonal antibodies 4F2 and 5E9, were not present on circulating T cells in patients with Graves' disease. The 100% positivity for increased numbers of Ia antigen-bearing T cells in hyperthyroid Graves' disease contrasts with our finding of 70% positivity in another HLA-DR-associated disease, recent onset type I diabetes mellitus. The pathogenic significance of these cells is not known, but they seem to represent selective activation of the immune system in patients with untreated hyperthyroid Graves' disease.