Objective
Thyrotropin receptor antibody (TRAb) is a causative antibody of Graves’ disease. Epstein-Barr virus (EBV) persists in human B cells and occasionally reactivates. During EBV reactivation, the host B cells differentiate to be plasma cells and produce IgM-dominant antibodies. We have previously observed that TRAb-IgM disruptes thyroid follicular epithelial cells and does not transduce thyroid hormone-producing signals. However, it is still unclear how it works on receptor-binding of TSH. We aimed to investigate this.
Methods
TRAb-IgM were separated from sera or EBV-reactivated culture media of peripheral blood mononuclear cells from Graves’ disease patients. TSH binding-inhibitory activity of TRAb-IgM was assessed by a commercial radio-receptor assay kit.
Results & Discussion
All TRAb-IgM samples showed gamma-ray counts that were almost twice that of the 0 standard. This meant that two molecules of ¹²⁵I-TSH bound to one TRAb-IgM binding complex because TRAb-IgM kept a TSH receptor for the separation procedure. This result indicated that TRAb-IgM bound to almost all TSH receptors coated in the test tubes, and did not inhibit TSH binding to TSH receptors. Although thyroid-stimulating TRAb is IgG type, TRAb-IgM may has particular role on Graves’ disease.
Conclusions
TRAb-IgM did not inhibit TSH binding to the TSH receptor. TRAb-IgM does not function as an antagonist.