On the mechanisms of thyrocyte proliferation and death in autoimmune thyroid diseases

: Lymphocytes isolated from diffuse toxic goiter (Graves' disease, GD) stimulate the proliferation of "normal" thyrocytes (isolated from euthyroid goiter) in primary culture, and give them the properties of GD-thyrocytes (loss of sensitivity to the growth-promoting factors of FCS and lesser capacity of binding antibodies from GD patients' serum). The complement-free sera of GD patients (but not the sera of patients with Hashimoto's thyroiditis, HT) induce the death of "normal" thyrocytes more rarely than full-complement sera do. Both types of serum cytotoxicity are manifested on GD-thyrocytes much more rarely than on "normal" cells. The Fas-receptor on GD-thyrocytes in situ is expressed less than on "normal" and especially on HT-cells. The level of soluble Fas-ligand in the serum of some complement-free patients was found to be increased. These sera induce apoptosis in "normal" thyrocytes, but not in GD-cells nor in human skin fibroblasts. In the authors' opinion, the proliferation of GD-thyrocytes in situ is stimulated by intrathyroid lymphocytes, which directly stimulate this process and induce the loss of receptors which mediate the cytotoxic effects of serum factors.