Dynamics of Thyroid-Stimulating and -Blocking Antibodies to the Thyrotropin Receptor in a Murine Model of Graves’ Disease

Graves' disease is characterized by the presence of autoantibodies to the TSH receptor (TSHR). There are multiple antibodies to the TSHR, with thyroid-stimulating antibodies (TSAbs) and TSH-stimulating blocking antibodies (TSBAbs), which in patients can fluctuate over time, resulting in changes in disease activity. Recently, animal models of Graves' disease have been developed, but it is not known whether the induced TSAbs and TSBAbs change spontaneously with time to influence disease. We used fibroblasts expressing major histocompatability complex (MHC) class II and human TSHR murine model to study anti-TSHR antibody patterns in serial bleeds of 23 animals. Anti-TSHR antibody responses were first detectable after 7-8 wk of first immunization. Moreover, the pattern of the TSAbs or TSBAbs was selected early in the response. The majority of the animals showed anti-TSHR antibodies that were either TSAb or TSBAb responses and were maintained throughout the course of 17-24 wk of the experiment. Remarkably, a proportion of mice (13%) displayed presence of antibodies with both TSAbs and TSBAbs, which appeared to cycle over time and thus mimic the fluctuations described in some hyperthyroid patients. Analyses of the linear epitopes to TSHR by peptide scanning showed that there was no early restricted epitope response. Thus, despite using an inbred strain, the initial response appears to target different regions of the receptor in different animals. Our data show that anti-TSHR antibody epitopes in the model display heterogeneity in TSHR epitopes, which vary in individual animals as well as in their regulation.