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Demonstration of thyroactive smaller components released from TSAb-IgG by protease digestion
Thyroid : Official Journal of the American Thyroid Association
|December 1, 1995
Summary
Thyroid stimulating antibody (TSAb) activity is found in smaller fragments, not just antigen-binding regions. These thyroactive smaller components (TSC) may be released from the TSAb-IgG by protease hydrolysis.
Area of Science:
- Endocrinology
- Immunology
- Molecular Biology
Background:
- Thyroid stimulating antibodies (TSAb) are key pathogenic factors in Graves' disease.
- Understanding the molecular components of TSAb responsible for thyroid stimulating (TS) and TSH binding inhibition (TBI) activity is crucial.
Purpose of the Study:
- To investigate the distribution of TS and TBI activities within fragments of TSAb-IgG after protease digestion.
- To identify the specific molecular components responsible for the biological activity of TSAb.
Main Methods:
- TSAb-IgG was subjected to papain and pepsin hydrolysis.
- Fragments were separated using protein A-Sepharose and Sephadex G-100 chromatography.
- TS and TBI activities were measured using cAMP production and TSH receptor assays.
- Antigen-binding activities (anti-Tg, anti-TPO) were also assessed.
Main Results:
- TS and TBI activities were detected in both Fab/F(ab')2 fragments and smaller thyroactive smaller components (TSC, 20-30 kDa) after hydrolysis.
- TSC fragments lacked antigen-binding activity (anti-Tg, anti-TPO).
- Biological activity was also found in Fc fragments containing trace amounts of Fab.
Conclusions:
- The biological activity of TSAb is not solely confined to the antigen-binding Fab or F(ab')2 regions.
- Protease digestion releases thyroactive smaller components (TSC) from TSAb-IgG, which retain TS and TBI activities.
- These findings suggest a complex structure of TSAb-IgG and potential mechanisms for fragment generation in vivo.