Abstract
Twenty three male Wistar rats were divided into five groups and were immunized with five overlapping synthetic peptides (Group I (n=5), peptide 12-30; Group II (n=5), 24-44; Group III (n=4), 308-328; Group IV (n=5), 324-344; and Group V (n=4), 339-364) of human thyrotropin receptor (TSHR), which had been conjugated with rabbit serum albumin. Sera obtained 34 days after the first immunization were investigated for their ability to displace 125I-TSH binding to thyrotropin receptor (thyrotropin binding inhibitor immunoglobulins (TBII)). In addition, biological activity, namely thyroid stimulating (TSAb) or blocking (TSBAb) activities in them were tested with cultured porcine thyroid cells. TBII activities in Group I, II, III, IV, and V rats were 12.6±4.1% (range 9.2-17.2%), 16.3±4.0% (range 11.7-22.0%), 16.7±4.9% (range 13.2-20.1%), 14.5±5.7% (range 8.1-19.0%), and 13.8±6.3% (range 8.1-14.3%), respectively, which were not significantly different from control rat sera (12.3±6.7%, range 1.2-20.1%). TSAb activities in Group I, II, III, IV, and V rats were 608±675% (range 275-1813%), 234±26% (range 209-265%), 313±175% (range 187-568%), 190±63% (range 145-301%), and 134±24% (range 107-158%), respectively. TSAb activities in Group I, II, III, and IV rats were significantly higher than those from control rat sera (P<0.01) while those of Group V were not significantly different from control rat sera. None of the rats in each group exhibited TSBAb activity. Measurement of serum T3 and T4 in each group of rats has shown a significant positive correlation between serum T3 and TSAb activity (r=0.55, P<0.05). These results are consistent with the hypothesis that the major binding site of immunoglobulins with TSAb activity is located in residues 12-30. Localization of TSBAb binding site(s) was not clear from our present investigation.
