HLA-DR antigen expression on intrathyroidal lymphocytes and thyrocytes in Hashimoto's thyroiditis and Graves'...

In frozen sections of thyroid glands with Hashimoto's thyroiditis (HT) and Graves' disease (GD), infiltrating lymphocytes were tested for their expression of HLA-DR antigens as a marker of in situ activation. In a combination of indirect immunoperoxidase and direct immunofluorescence staining, most of the immunoglobulin D positive mature B cells were found to be DR positive (DR+) in both diseases. In HT, sizable portions of both helper/inducer T (Leu3+) and suppressor/cytotoxic T (Leu2+) cells were DR+ in interfollicular regions as well as in lymphocyte clusters and lymphoid follicles. In GD, the proportion of DR+ cells in the interfollicular Leu2+ population was significantly lower than that of HT. DR+ thyrocytes were seen in all 14 cases of HT and in 14 out of 16 cases of GD, especially in the vicinity of lymphocyte aggregates. The extent of their DR expression was not correlated with the percentage of DR+ cells in either T subset. These results indicate that a significant portion of infiltrating T cells are activated in autoimmune thyroid diseases, and there may be bidirectional interaction between DR+ thyrocytes and DR+ T cells. The difference in frequency of Leu2+ DR+ cells may account for the difference between the immunopathological features of HT and GD.