Immunization with
thyrotropin receptor (TSHR)-adenovirus is an effective approach for inducing
thyroid stimulating antibodies and Graves'
hyperthyroidism in BALB/c mice. In contrast, mice of the same strain vaccinated with TSHR-
DNA have low or absent TSHR
antibodies and their T cells recognize restricted
epitopes on the TSHR. In the present study, we tested the hypothesis that immunization with TSHR-adenovirus induces a wider, or different, spectrum of TSHR
T cell epitopes in BALB/c mice. Because TSHR antibody levels rose progressively from one to three TSHR-adenovirus
injections, we compared T cell responses from mice immunized once or three times. Mice in the latter group were subdivided into animals that developed
hyperthyroidism and those that remained euthyroid. Unexpectedly, splenocytes from mice immunized once, as well as splenocytes from
hyperthyroid and euthyroid mice (three
injections), all produced
interferon-gamma in response to the same three synthetic
peptides (
amino acid residues 52-71, 67-86 and 157-176). These
peptides were also the major
epitopes recognized by TSHR-
DNA plasmid vaccinated mice. We observed lesser responses to a wide range of additional
peptides in mice injected three times with TSHR-adenovirus, but the pattern was more consistent with increased background 'noise' than with spreading from primary
epitopes to dominant secondary
epitopes. In conclusion, these data suggest that factors other than particular TSHR
T cell epitopes (such as adenovirus-induced expression of conformationally intact TSHR
protein), contribute to the generation of
thyroid stimulating antibodies with consequent
hyperthyroidism in TSHR-adenovirus immunized mice.