IMMUNOGLOBULIN-G THAT INTERFERES WITH THYROID-STIMULATING ANTIBODY MEASUREMENTS CAN BE ELIMINATED SPECIFICALLY BY INCUBATION WITH SYNTHETICPEPTIDES CORRESPONDING TO PARTIAL SEQUENCES OF THE HUMAN THYROTROPIN RECEPTOR

Two IgG preparations out of more than 100 tested, distinct from the ty pical Graves' disease IgG, were shown specifically to enhance the cAMP production of FRTL-5 cells by the addition of a synthetic peptide, P- 218, corresponding to the partial amino acid sequence from No. 354 to 367 of the h thyroid-stimulating hormone (TSH) receptor. IgG obtained from a patient with Graves' disease revealed a serial alteration of th e enhancement; negative in July, 1989, potent in January, 1991, and we ak in September 1991. During this time there was no remarkable change in the patient's serum protein components or TSH receptor antibody act ivities. A peptide with a completely reverse sequence of P-218 showed little effect, and P-218 in combination with bTSH or forskolin did not affect cAMP production by these ligands, and did not alter the inhibi tory activity of thyroid-stimulation-blocking antibody. High concentra tions of P-218 resulted in reduction of such enhancing effects of cAMP by thyroid-stimulating antibody. P-218 affinity chromatography showed almost complete absorption and recovery of thyroid-stimulating antibo dy and P-218 reactivity. In the 15 synthesized peptides with proximal sequences of P-218 (from 338 to 378), regions thought to be involved w ith the enhancement were defined as follows: 354-367 (P-218) is a crit ical unit; 354-357 and 364-367 are considered to be the essential site s; several amino acid extensions on both N- and C-terminal sides of P- 218 show additional enhancement. In conclusion, evidence was shown to indicate the presence of IgG that interferes with thyroid-stimulating antibody measurements.