To investigate the expression of class II histocompatibility antigens HLA-DR in the thyrocytes in autoimmune thyroid diseases, 47 thyroidectomy specimens were examined by immunofluorescence with monoclonal antibodies to the non-polymorphic region of the DR molecule. Aberrant DR expression was most marked in the Hashimoto gland, with the entire section being strongly stained. DR expression was seen in discrete groups of follicles in 20/26 thyroids from patients with Graves' disease, in 2/9 non-toxic nodular goitres, and in none of 11 specimens of "normal" thyroid. The presence of lymphoid foci, "activated" T-cells, and immune complexes on the follicular basement membrane were not regularly associated with the DR-positive thyroid acini. HLA-A,B,C expression was also increased in the diseased glands. Expression of HLA-DR thus seems to be one of the earliest manifestations of autoimmune lymphocytic thyroiditis.
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