Induction of thyrotropin receptor (TSH-R) autoantibodies and thyroiditis in mice immunised with the recombinant TSH-R.

Two groups of 10 Balbc by Jico male mice were immunised on days 0, 15 and 35, with the extra cellular domain (ECD) of the human thyrotropin receptor (TSH-R) expressed as a fusion protein in bacteria (group 1) or with the maltose binding protein (MBP) fusion partner alone (group 2). Blood was obtained on days 0, 22, 32, 42 and 49 and samples from the individual animals pooled for each group. Serum and immunoglobulin (IgG) preparations were tested, using CHO cells expressing the human TSH-R (JP26 and JP09) for thyroid stimulating (TSAb); thyroid blocking (TBAb) and thyrotropin binding inhibiting (TBII) activities. Neither serum nor IgGs were found to contain TSAb at any time point. TBII activity was present in the serum of both groups on day 32 and in group 1 only on day 49; when the test was performed on IgGs, only the MBP-ECD day 49 preparation remained significantly positive for TBII (p < 0.005). Significant TBAb activity was present in both the serum and IgG of group 1 day 49 (p < 0.005) and to a lesser extent on 42 (p < 0.02). Following the second immunisation (day 15) both groups and had decreased circulating T4 levels (p < 0.05) when compared with day 0 in each case. Group 2 were unaffected by the third immunisation on day 35 but the MBP-ECD group again had significantly decreased T4 levels (p < 0.02) compared with MBP day 49 and (p < 0.03) when compared with MBP-ECD day 0. Histological examination of thyroids from group 1 animals revealed extensive vascularisation and an atypical lymphoblastoid infiltration which was not observed in control mice. These preliminary results indicate that care is required in interpreting data since a non-receptor antigen was shown to decrease circulating thyroxine and serum from these animals had apparent TBII like activity. However, the results obtained with the IgGs suggest that receptor autoantibodies can be induced by immunising with the human TSH-R, in addition, the immunised mice show histological evidence for the development of thyroiditis.