Immunoreactivity of multiple molecular forms of human thyroglobulin

Human thyroglobulin (Tg) was purified from thyroids of normal individuals and of patients with Graves' disease using gel filtration (Sephacryl S-400) and ion-exchange (DEAE) column chromatography. We isolated five protein peaks of Tg from the DEAE column, using a step gradient, characterized them for protein and iodine content, and assessed their immunological properties by reactivity to polyclonal and monoclonal antibodies (mAbs). Normal and Graves' Tgs differed in the relative protein content of these five protein peaks from the DEAE column. In the case of normal Tg, the majority of Tg was eluted in peak 2 but in the Graves' Tg, most of the protein was eluted in peak 1 of this column. The immunoreactivity of these five protein peaks of Tg was studied using 11 mouse mAbs prepared against human Tg, sera from patients with autoimmune thyroiditis and polyclonal antibody from a rabbit immunized with human Tg. All of five protein peaks of Tg reacted equally with rabbit antibody. The sera of five thyroiditis patients showed greater binding to peak 1 of Graves' Tg than peak 1 of normal Tg. Similarly, most mAbs showed greater binding to peak 1 of Graves' Tg than the peak 1 of normal Tg. Of particular interest was one mAb (42C3) which reacted only with Tgs containing iodine. The immunoreactivity of this mAb paralleled the iodine content of Tg. This mAb might be useful for evaluating the role of iodine in the antigenicity of human Tg.