[Thyroid stimulating activity of human TSH-R peptide antibody]

We have synthesized a TSH-R peptide (N-peptide) corresponding to the unique N-terminal segment (#29-57) and immunized it into rabbits. We found that the N-peptide antibody possessed thyroid stimulating antibody (TSAb) activity but lacked TSH-binding inhibitor immunoglobulin (TBII) activity. We then produced rabbit antibodies against the peptides corresponding to the mid-region (#172-202, C-peptide), the region near the transmembrane domain (#341-370, P-peptide), and the extracellular loops (#648-662, E1-peptide; #561-580, E2-peptide; #648-662, E3-peptide). All these peptide-antibodies showed also TSAb activities. These results suggest that the domains responsible for TSAb might span the entire extracellular components of the receptor and that even the extracellular loops are the candidates for the epitope against autoantibodies from Graves' patients.