Expression, immunogenicity and clinical significance analysis of thyroid‑stimulating hormone receptor fusion proteins

Thyroid function is regulated in a substantial manner by thyroid‑stimulating hormone receptor (TSHR), and aberrant alterations in thyroid function are triggered by the interaction of TSHR with its antibodies, thyroid‑stimulating hormone receptor antibodies (TRAb). The expression, immunogenicity and clinical significance of fusion proteins comprising different structural domains of TSHR were investigated. Fusion proteins containing several human TSHR (hTSHR) structural domains were created. In vitro experiments utilized these fusion proteins as antigens to specifically bind and analyze patient sera using an ELISA. To investigate the immunogenicity and clinical significance of various structural domains of TSHR, in vivo experiments included immunizing BALB/c mice with various fusion proteins of hTSHR, measuring serum autoantibodies, assessing thyroid function, performing histological examination and using flow cytometry to identify changes in T cell subsets. Three distinct hTSHR fusion protein fragments (hTSHR289, hTSHR290 and hTSHR410) were synthesized. The hTSHR290 fusion protein demonstrated the highest binding reaction with TRAb⁺ sera from patients with hypothyroidism, and the hTSHR289 fusion protein demonstrated considerable specific binding reactivity with stimulating antibodies, as observed in sera from patients with hyperthyroidism. Pathological alterations associated with hyperthyroidism were observed in mice in the hTSHR289 fusion protein group, while pathological changes associated with hypothyroidism were observed in mice in the hTSHR290 fusion protein group. Immunized BALB/c mice exhibited increased levels of CD4⁺ T cell subsets, and decreased levels of CD8⁺CD122⁺ and CD4⁺CD25⁺ T cell subsets. Fusion proteins of different structural domains of TSHR exhibited varying immunogenicity. The hTSHR289 fusion protein and hTSHR290 fusion protein prepared in the present study could serve as a basis for the development of ELISA kits for the detection of thyroid‑stimulating immunoglobulins and TSHR‑blocking antibodies. Fusion proteins of different structural domains of TSHR induced clinical symptoms of hyperthyroidism and hypothyroidism in mice. The present study provides a scientific basis for future studies on the etiology and mechanisms of autoimmune thyroid diseases, as well as the invention of novel methods for TRAb detection.