Fig. 1.

Schematic of reporter gene-based functional bioassay for TBAb. CHO cells are engineered to constitutively express the human TSHR and to express luciferase following induction of cAMP. The binding of bovine (b) TSH to the TSH receptor on the surface of the cells induces a signaling cascade that leads to an increase of intracellular cAMP and subsequently to the luciferase expression. However, the presence of blocking anti-TSHR-Ab (TBAb) in serum of patients with autoimmune thyroid diseases inhibits the bTSH stimulation of the luciferase reporter gene. The TBAb level is correlated with blocking activity which is defined as percent inhibition of luciferase expression relative to induction with bTSH alone.