Identification of the Peptides That Inhibit the Function of Human Monoclonal Thyroid-Stimulating Antibodies from Phage-Displayed Peptide Library1

Autoantibodies against TSH receptor (TSHR) are known to be involved in the occurrence of Graves' disease. It is obvious that mapping of epitopes of the autoantibodies found in the patients with Graves' disease is an important step in elucidating possible mechanism of generation of the autoantibodies against TSHR as well as in developing effective diagnostic and therapeutic approaches for Graves' disease. In this report we have identified the peptide sequences that bind to two human monoclonal thyroid-stimulating antibodies (mTSAbs; B6B7 and 101-2) from a disulfide-constrained phage-displayed peptide library. The peptides selected by three rounds of biopanning showed half-maximal inhibitory activities for cAMP synthesis induced by mTSAbs at about 0.1 micromol/L. SPWTLGA and TQWNMQH selected for B6B7 and 101-2, respectively, show specificity for their respective antibodies. This means that different clones of mTSAbs may have different epitopes for TSHR. The IgG of the patient from whom B6B7 was derived binds with specificity to the respective immobilized peptide in an enzyme-linked immunosorbant assay format, and its cAMP generation was also inhibited by selected peptide. It may be possible that the epitopes of TSAbs identified from the phage-displayed peptide library could be used for the classification of different clones of TSAbs present in patients with Graves' disease and for development of drugs to treat Graves' disease.