Studies of anin VitroBinding Reaction Between Thyroid Microsomes and Long Acting Thyroid Stimulator Globulin (LATS): I. Development of Solid-State Competitive Binding Radioassay Methods for Measurement of Antimicrosomal and Antithyroglobulin Antibodies1
Using plastic tubes or plastic cups coated with a diluted homogenate of human thyroid microsomes and incubating with radioiodinated long acting thyroid stimulator globulin (LATS-IgG) of very high biologic potency for several hours in the presence of dog serum, we have demonstrated fixation of about 1 % of the label to the tube surface. Addition to the incubate of either the unlabeled LATS-IgG, the original LATS serum, or serum from a patient with Hashimoto's thyroiditis (containing antithyroglobulin and antimicrosomal antibodies) resulted in a dose-dependent inhibition of the binding reaction. Normal human serum, normal human IgG globulin or human TSH neither inhibits the binding reaction nor binds to thyroid microsomes. Evidence is presented which indicates that the binding reaction observed is due to the presence of relatively large amounts of antimicrosomal antibody. The method described permits a quantitative estimation of this antibody with a sensitivity about 10 times that of the immunofluorescent method. Using the same basic method, but substituting purified human thyroglobulin for thyroid microsomes, and radioiodinated antithyroglobulin-IgG for LATS-IgG, a sensitive quantitative binding assay for antithyroglobulin was devised. Each method is capable of detecting as little as 0.1 μg IgG of the respective antibody preparations used in the study. The method should be generally applicable to the measurement of any antibody whose specific antigen possesses adequate adhesiveness to plastic. Explanations are offered for the failure of the system to measure LATS. Evidence is presented which suggests that LATS-specific molecules do not bind to thyroid microsomes.