Autoimmune and non-autoimmune thyroid diseases have different patterns of cellular HLA class II expression.

Abstract

Surface HLA-DR antigen is usually only expressed by antigen-presenting cells (APC). In autoimmune thyroid disease, follicle cells function as APC, thus expressing HLA-DR. However, non-autoimmune thyroid diseases may also express surface class II antigens. To evaluate the presence and pattern of HLA class II expression in autoimmune and non-autoimmune thyroid disorders. Retrospective: histopathological and immunohistochemical analysis. Referral center, university hospital. Ten histologically normal thyroids, 11 Graves' disease, 7 Hashimoto's thyroiditis, 10 atoxic multinodular goiter and 3 toxic adenomas were analyzed by immunohistochemistry, using a monoclonal antibody anti-HLA-DR. The presence of these antigens in thyroid follicular cells and their relation to inflammatory infiltrate was evaluated. The pattern of HLA-DR expression in thyroid follicular cells was analyzed: membrane, cytoplasmic or both. Although HLA-DR antigens were sparsely present in one of the 8 normal thyroids, in 6 of the 9 atoxic multinodular goiter and in 2 of the 3 toxic adenomas a net positivity could be seen in large areas. In all 5 Hashimoto's thyroiditis and in 7 of the 10 Graves' disease cases. This expression occurred in follicle cells either in contact with inflammatory cells or not. In non-autoimmune thyroid disease, HLA-DR positivity was essentially cytoplasmic, whereas in Graves' disease and Hashimoto thyroiditis it was mainly in cell membranes. It is suggested that the HLA class II expression on the surface of follicle cells could be related to auto-antigen presentation to the immune system by these cells, leading to inflammation.