Journal of Clinical Endocrinology & Metabolism, Vol 77, 658-663, Copyright © 1993 by Endocrine Society
Dual mechanism of perturbation of thyrotropin-mediated activation of thyroid cells by antibodies to the thyrotropin receptor (TSHR) and TSHR- derived peptides
RK Desai, JS Dallas, MK Gupta, GS Seetharamaiah, JL Fan, K Tahara, LD Kohn and BS Prabhakar
Department of Microbiology, University of Texas Medical Branch, Galveston, 77555.
To further define the epitopes with which anti-TSH receptor (anti-TSHR)
antibodies react and mediate their biological effects, we used antibodies
against the extracellular domain of TSHR (ETSHR) protein and nine peptides
derived from the ETSHR. Peptides were chosen based on their predicted
immunogenicity as well as their uniqueness to the TSHR. Antipeptide
antibodies showed varying degrees of reactivity against ETSHR, with
antipeptide-2-(352-366) and -3A-(357-372) showing relatively stronger
reactivity with the receptor. Antibodies were tested for their ability to
stimulate thyroid cells and were found to be ineffective in causing both
cAMP release and iodide uptake. However, anti-3A and anti-ETSHR showed
blocking TSHR antibody (TSHRAb) activities of 76.9% and 79.7%,
respectively, which were significantly different (P < 0.005) compared to
that of preimmune serum. Anti-2 and - 91 (AA 32-46) also showed blocking
TSHRAb activities of 37.5% and 35.6%, respectively (P < 0.05). Antisera
were also tested for their ability to block TSH binding to thyroid
membranes in a RRA. Anti-ETSHR, but not any of the antipeptide antibodies,
displayed TSH binding inhibitory immunoglobulin activity. These findings
suggest that there might be different mechanisms that mediate blocking TSHR
antibody activity. One mechanism involves the inhibition of TSH binding to
the receptor, and the other probably involves a step subsequent to TSH
binding.