HLA-DR alpha chain expression in human thyroid cells

Using a cDNA probe encoding the human major histocompatibility Class II antigen HLA-DR alpha chain, we have detected a single DR alpha chain-specific transcript in total cellular RNA prepared from human thyroid tissue. The hybridizable RNA in thyroid samples was indistinguishable in size from the DR mRNA in the Raji human B lymphoblastoid cell line. Of the thyroid glands examined, samples from patients with autoimmune thyroid disease consistently demonstrated the highest DR alpha chain transcript levels, with a mean +/- SEM OF 62 +/- 13% of levels found in DR-positive Raji cells. Cytoplasmic dot blot analyses of 5-day thyroid cell cultures depleted of lymphocytes and monocytes indicated that normal thyrocytes contain readily-detectable levels of DR alpha chain-mRNA. These transcript levels varied from individual to individual, with a mean of 16 +/- 9% relative to Raji cell control values and were shown to correlate after lectin or gamma interferon stimulation with enhanced numbers of immunoreactive DR antigen-positive cells. Such findings demonstrate expression of HLA Class II antigen genes in normal unstimulated human thyroid cells and suggest that quantitative variation in thyroid Class II antigen (DR) gene expression may be a major factor in thyroid immunoregulation.