An assay for antibodies to thyroid plasma membrane using the isotope-labeled protein A

An assay for detection of serum IgG binding to thyroid membrane using 125I-Protein A was examined. The test serum is incubated with purified thyroid membranes, and the IgG bound to the membrane is detected by its interaction with 125I-Protein A. Most of the bound IgG is not bound to the TSH receptor, because TSH does not induce any appreciable decrease in the binding of the IgG to thyroid membranes. Increased serum IgG binding to thyroid membrane is found in most patients with Graves' disease and Hashimoto's thyroiditis, but not in patients with thyroid cancer or simple goiter. Many sera with positive binding activity showed positive microsomal antibody. Serum IgG binding to thyroid membrane in Graves' disease correlates neither with LATS activity nor thyroglobulin antibody. This finding suggests that TSH receptor is not involved in the reaction. The assay method is useful for measuring the binding immunoglobulin for thyroid membrane that is frequently increased in autoimmune thyroid disease, and the present data provide further support to the concept that thyroid autoimmune disorders are associated with antibodies to thyroid cell surface components.