Enhancement of thyrocyte HLA class II expression by thyroid stimulating hormone.

HLA Class II molecules are expressed by human thyroid epithelial cells (thyrocytes) in thyroid autoimmunity, although these cells are normally Class II-. gamma-Interferon (gamma-IFN) is probably involved in this expression, as suggested by its ability to induce Class II in cultured normal thyrocytes. We have now found that thyroid stimulating hormone (TSH) enhances Class II expression induced in cultured thyrocytes by gamma-IFN, and effects similar to those of TSH were obtained with dibutyryl cyclic AMP. A proportion of thyrocytes also expressed Class II following treatment with TSH or dibutyryl cyclic AMP in the absence of gamma-IFN, but the optimal activity of these mediators then appeared to be dependent upon the occurrence of some pre-existing Class II expression. These findings give insights into how a variety of mediators may influence Class II expression in thyroid autoimmunity.