Dissecting linear and conformational epitopes on the native thyrotropin receptor.

Area of Science:

• Immunology
• Endocrinology
• Molecular Biology

Background:

• Graves' disease is an autoimmune disorder where antibodies target the thyroid-stimulating hormone receptor (TSHR).
• These autoantibodies can stimulate or block TSHR function, leading to hyperthyroidism.
• Understanding the specific epitopes targeted by these antibodies is crucial for diagnosis and treatment.

Purpose of the Study:

• To investigate the epitopes on the native TSHR recognized by autoantibodies from a Graves' disease model.
• To differentiate the binding characteristics of thyroid-stimulating versus blocking TSHR autoantibodies.

Main Methods:

• Utilized polyclonal antisera and monoclonal antibodies (mAbs) from immunized Armenian hamsters.
• Employed cell-binding competition assays with fluorescently labeled mAbs to map conformational epitopes.
• Analyzed TSHR-mAbs from both hamster and mouse models, including stimulating and blocking types.

Main Results:

• Identified two distinct conformational epitopes (A and B) and one linear epitope (C) on the TSHR.
• Epitope A was recognized by both stimulating and blocking mAbs, while epitope B was only recognized by blocking mAbs.
• Stimulating TSHR-mAbs exclusively bound to epitope A, and blocking antibodies recognized both A and B.

Conclusions:

• The natively conformed TSHR presents a limited set of epitopes to autoantibodies.
• The binding site for TSHR-stimulating antibodies is highly conserved.
• High-affinity TSHR-blocking antibodies recognize conformational epitopes, one of which overlaps with the stimulating epitope, precluding distinction based solely on epitope recognition.