In situ immune complexes, lymphocyte subpopulations, and HLA-DR-positive epithelial cells in Hashimoto thyroiditis

Surgical specimens from thyroid glands from seven patients with Hashimoto thyroiditis and two patients with non-autoimmune colloid goiter were analyzed by immunohistologic techniques (direct and indirect immunofluorescence and immunoperoxidase tests) using polyclonal antisera against total immunoglobulin, Ig classes (IgM, IgD, IgG, and IgA), and complement component C3 and monoclonal antibodies specific for B cells, T cell subpopulation, macrophages, natural killer cells, granulocytes, and HLA-DR antigen. Complement-fixing immune complexes (IgG+, C3+) were noted predominantly in areas with only slight destruction and only moderate lymphoid infiltration of thyroid follicles. In areas with intense lymphoid infiltration of thyroid follicles, where many well-developed germinal centers and significant perivascular lymphoid infiltration were seen, immune complexes were scarce. In these latter areas T helper cells (OKT4+, Leu3a+), were more abundant than T cytotoxic/suppressor cells (OKT8+), macrophages (OKM1+), and plasma cells (IgG+); only a few B lymphocytes (smIgM+, smIgD+), granulocytes (ViMD5+), and natural killer cells (VEP13+, Leu7+) were noted in the interstitium between thyroid follicles, intruding between thyroid follicular epithelial cells and merging into the thyroid follicular lumen. Many activated T cells (OKT10+, HLA-DR+) were present in these areas of advanced destruction. HLA-DR antigen expression was seen on macrophages, tissue reticulum cells, vascular endothelial cells, lymphoid cells, and, most interestingly, on thyroid epithelial cells. Normal thyroid epithelial cells did not express HLA-DR. Only a few epithelial cells in the vicinity of lymphoid infiltrations were HLA-DR+ in early stages of Hashimoto thyroiditis, and the number of HLA-DR+ epithelial cells was significantly increased in advanced stages of the disease. In our present report the potential role of HLA-DR+ thyroid epithelial cells for the in situ stimulation of the immune system within the thyroid gland of patients with Hashimoto thyroiditis is discussed, and it is hypothesized that HLA-DR+ thyroid epithelial cells may be an important factor for the progression and self-perpetuation of the disease, which is probably initiated by humoral components of the immune system but further propagated by cellular immunopathologic mechanisms.