Membrane-binding antibodies in patients with Graves' disease and other autoimmune diseases

Abnormally high levels of activity (BA) of immunoglobulins (Igs) to membranes containing TSH receptors were observed in patients with Graves' disease. The assay to detect such BA used guinea pig fat as the membrane source. [125I]Protein A was used to develop the binding antibodies (in serum or IgG). The assay was able to detect specific BA in microgram quantities or less of IgG in about 50% of the sera of patients with Graves' disease. The presence or amount of serum BA did not correlate consistently with either the presence in serum of TSH binding inhibitory Ig or the clinical estimate of thyrotoxicity in Graves' disease. High levels of BA were frequently found in sera of patients with other autoimmune diseases, such as Hashimoto's thyroiditis, rheumatoid arthritis, mixed connective tissue disease, and systemic lupus erythematosus. However, BA found in the latter disorders frequently was positive not only when using fat cell membranes but also when using liver kidney, or skeletal muscle membranes. The assay may detect a heterogeneous population of Igs binding specifically to membranes and may reflect a general state of autoimmunity.