- Thyroid-stimulating immunoglobins are components of the immunoglobulin G (IgG) fraction of plasma proteins and are antibodies to TSH receptors on the thyroid gland.  IgG bind to TSH receptors and, like TSH, stimulate the thyroid gland to secrete T3 and T4.  They circulate in high concentrations in patients with Grave's Disease, which is characterized by high circulating levels of thyroid hormones, and accordingly, low concentrations of TSH (caused by feedback inhibition of thyroid hormones on the anterior pituitary gland).

- Antibodies against thyroid-stimulating hormone (TSH) receptors cause Graves' disease

Reference:
1. Ganong's Review of Medical Physiology: 23rd Edition.  Kim E. Barrett et al.  McGraw-Hill Publishing. 2010.