Enzyme immunoassay for antibodies to thyroxine in human serum using synthesized antibody as a calibrator.

We prepared human IgG labeled with rabbit antibodies to thyroxine, and used it for the assay of antibodies to thyroxine in human serum as a calibrator. The assay system consisted of thyroxine labeled with beta-D-galactosidase and a microcolumn containing goat antibodies to human IgG immobilized on Sepharose 4B. Each serum sample or standard serum containing human IgG labeled with anti-thyroxine antibodies was incubated with the enzyme-labeled thyroxine, and the reaction mixture was passed through the microcolumn. The column was washed to remove the unbound label, and enzyme activity of the bound label was assayed. The minimum detectable amount of the anti-thyroxine antibodies was 0.3 ng/assay tube. The analytical recoveries of human IgG labeled with the antibodies added to human serum were from 103% to 108%. We measured anti-thyroxine antibodies in human sera from 187 patients with autoimmune thyroid diseases. The antibodies were detected in 32 serum samples, and the values in positive samples varied from 0.31 to 2.31 micrograms/ml. On the other hand, in 58 sera from patients with non-thyroid diseases, the antibodies were detected in only two samples.