Cleavage region TSH receptor antibodies influence thyroid cell survival in vivo.

BACKGROUND: Graves' disease (GD) is associated with TSH receptor (TSHR) antibodies of variable bioactivity. Recently we have characterized antibodies that bind to the cleavage region of the TSHR ectodomain (C-TSHR-Ab) and demonstrated their ability to induce thyroid cell apoptosis in vitro via excessive cell stress involving multiple organelles .

METHODS: To investigate the in vivo effects of C-TSHR-Ab, we first developed a murine monoclonal antibody (mAb) directed against residues 337 to 356 of the TSHR cleavage region and then injected into mice.

RESULTS: These injections caused reduced serum total T3 and T4 and increased TSH levels when compared to a control mAb injected mice. The C-TSHR-mAb induced histological evidence of ER-stress, mitochondrial stress and apoptosis in the thyroid glands. C-TSHR-mAb-mediated apoptosis was associated with cellular infiltrates consisting mostly of macrophages, dendritic cells and neutrophils while T- and B-lymphocytes were scarce. Citrullinated histone H3 (Citr-H3), a central player in the neutrophil release of nuclear chromatin known as neutrophil extracellular traps (NET) was the consequence of apoptotic thyrocytes. Examination of thyroid tissue from patients with Graves' disease also showed increased stress and some thyrocyte apoptosis compared to normal thyroid tissues.

CONCLUSIONS: The fact that the C-TSHR-mAb induced accumulation of macrophages, neutrophils and dendritic cells indicates that innate immunity plays a central role in shaping the adaptive immune response to the TSH receptor. In addition, this study provides further evidence that the hinge region of the TSHR ectodomain is intimately involved in the initiation of the immune response in autoimmune thyroid disease.