Immune response of mice transgenic for human histocompatibility leukocyte Antigen-DR to human thyrotropin receptor-extracellular domain.
BACKGROUND
Hyperthyroidism of Graves' disease is caused by auto-antibodies to human thyrotropin receptor (hTSH-R). To elucidate important T-cell epitopes in TSH-R, we studied three models of immunity to TSH-R in mice.


METHODS
Mice transgenic for histocompatibility leukocyte antigen DR3 or DR2 were immunized with cDNA for hTSH-R-extracellular domain (hTSH-R-ECD), or hTSH-R-ECD protein, or hTSH-R peptide epitopes. Proliferative responses of immunized splenocytes to epitopes derived from the hTSH-ECD sequence, anti-TSH-R antibody responses, serum thyroxine and TSH, and thyroid histology were recorded.


RESULTS
DR3 mice responded to genomic immunization with proliferative responses to several epitopes, which increased in intensity and spread to include more epitopes, during a 6-week immunization program. DR2 transgenic mice developed weak proliferative responses. Both types of mice developed anti-TSH-R antibodies measured by enzyme-linked immunosorbent assay or TSH-binding inhibition assay in 16-60% of animals. There was evidence of weak thyroid stimulation in one group of animals. Immunization of DR3 transgenic mice to hTSH-R-ECD protein induced a striking response to an epitope with sequence ISRIYVSIDVTLQQLES (aa78-94). Immunization to peptides derived from the TSH-R-ECD sequence (including aa78-94) caused strong responses to the epitopes, and development of immune responses to several other nonoverlapping epitopes within the hTSH sequence (epitope spreading) and antibodies reacting with hTSH-R. This implies that immunization with hTSH-R epitopes produced immunity to mouse TSH-R.


CONCLUSIONS
T-cell and B-cell responses to genetic immunization differ in DR3 and DR2 transgenic mice, and there is less genetic control of antibody than of T-cell responses. During both genomic and peptide epitope immunization there was evidence of epitope spreading during the immunization. Several functionally important epitopes are evident, especially aa78-94. However, if similar progressive epitope recruitment occurs in human disease, epitope-based therapy will be difficult to achieve.
Inaba
Hidefumi
H
Division of Endocrinology, Department of Medicine, Brown University, Providence, Rhode Island, USA.
Pan
Deshun
D
Shin
Young-Ha
YH
Martin
William
W
Buchman
George
G
De Groot
Leslie J
LJ
D000595:Amino Acid Sequence; D000818:Animals; D001323:Autoantibodies / Q000235:genetics / Q000276:immunology; D001402:B-Lymphocytes / Q000276:immunology; D049109:Cell Proliferation; D004797:Enzyme-Linked Immunosorbent Assay; D018985:Epitopes, B-Lymphocyte / Q000235:genetics / Q000276:immunology; D018984:Epitopes, T-Lymphocyte / Q000235:genetics / Q000276:immunology*; D015802:HLA-DR2 Antigen / Q000235:genetics / Q000276:immunology*; D015803:HLA-DR3 Antigen / Q000235:genetics / Q000276:immunology*; D006801:Humans; D007114:Immunization; D051379:Mice; D008822:Mice, Transgenic; D008969:Molecular Sequence Data; D011989:Receptors, Thyrotropin / Q000008:administration & dosage* / Q000235:genetics / Q000276:immunology*; D013194:Staining and Labeling; D013601:T-Lymphocytes / Q000276:immunology; D013961:Thyroid Gland / Q000276:immunology
D001323:Autoantibodies; D018985:Epitopes, B-Lymphocyte; D018984:Epitopes, T-Lymphocyte; D015802:HLA-DR2 Antigen; D015803:HLA-DR3 Antigen; D011989:Receptors, Thyrotropin