AUTOANTIBODY AGAINST THYROID IODIDE TRANSPORTER IN THE SERA FROM PATIENTS WITH HASHIMOTOS-THYROIDITIS POSSESSES IODIDE TRANSPORT INHIBITORYACTIVITY

Recently we have newly identified an autoantibody against thyroid iodi de transporter (TIT) in the sera from patients with autoimmune thyroid disease. In order to study the function of these autoantibodies, we e stablished CHO-K1 cells stably expressing recombinant rat TIT (CHO-TIT cells), and the effect of IgGs from the patients with Hashimoto's thy roiditis on iodide uptake activity of CHO-TIT cells was investigated. We found that 4 out of 34 sera from patients with Hashimoto's thyroidi tis strongly recognized TIT by Western blot analysis. These 4 IgGs, pu rified by protein A column chromatography, caused 14 to 62% inhibition of I- accumulation in CHO-TIT cells. Next, using synthetic peptides, we determined the recognition site of the autoantibody on the TIT mole cule. The autoantibody reacted with the synthetic peptide correspondin g to the 6th extracellular loop of the TIT molecule. These results sug gest that autoantibody against TIT in the sera from patients with Hash imoto's thyroiditis binds to the 6th extracellular loop of TIT protein and inhibits I- transport into the thyrocytes. Anti-TIT autoantibody might participate in the pathogenesis of Hashimoto's thyroiditis and m odulate thyroid function of patients with the disease. (C) 1996 Academ ic Press, Inc.