Radioimmunoassay for Human Antithyroglobulin Antibodies. II. Determination of Antigen-Binding Capacity

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Abstract
The radioimmunoassay using a double antibody technique has been developed to measure the total binding capacity (ABC) of serum antibodies for thyroglobulin (Tg). Serum is incubated with 125I-radiolabeled thyroglobulin and then precipitated by sheep antihuman gamma globulin. The thyroglobulin binding capacity of serum antithyroglobulin antibody is measured on a saturation curve as the maximum mg bound per ml in the presence of increasing amounts of Tg. With this method it is possible to accurately and precisely measure ABC for Tg from 0.002 to several mg/ml serum. In a group of 88 adolescents with goiter and thyroditis and in a group of 25 adults with chronic thyroiditis or primary myxedema, the ABC showed only partial correlation with other tests such as tanned red cell haemagglutination (TRC). In the diagnosis of thyroiditis the ABC technique, compared with TRC, was found to be not only more sensitive (80% positive, compared with 55% with TRC) but also more specific (with ABC 1 out of 59 of the normal adolescents was positive, whereas 17% gave a positive TRC). Studies carried out with rabbit anti-human IgM failed to detect IgM antibodies in almost all the cases. Determination of total thyroglobulin binding capacity of serum antibodies for Tg provides a quantitative and specific method to evaluate antibodies in both clinical and experimental work.

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