Iodination of human thyroglobulin alters its antigenic characteristics

Human thyroglobulin (Tg), a major autoantigen in autoimmune thyroiditis, is a 660 kDa iodoprotein in which the degree of iodination may have a major impact on its immunological properties. We previously identified a mouse monoclonal antibody (mAb), 42C3, raised against Tg that recognized Tg differently depending on the levels of iodination. It ranged from no reactivity with Tg with no detectable iodine to strong reactivity with high levels of iodination. In this study, Tg with no detectable iodine was isolated from a thyroid gland of a patient with non-toxic goiter (NTG). This NTG-Tg was iodinated in vitro with Pierce iodobeads and determined to have 150 atoms of iodine/molecule of Tg. The immunoreactivity of this Tg was evaluated by western immunoblotting before and after iodination. MAb 42C3 failed to react with the non-iodinated NTG-Tg but did react after iodination. This mAb did not react with other iodinated proteins such as iodinated bovine serum albumin. This is the first demonstration that increased iodination of Tg changes the antigenicity of Tg as measured by antibody binding.