Epitopic difference among rat thyroglobulins

Epitopes on thyroglobulin (Tg) were examined using mouse monoclonal antibodies (mAbs). Two out of 6 mAbs indicated a remarkable difference in binding to three rat Tgs. Namely, they bound to one Tg as well as immunized Tg but could not bind to another at all. They could hardly bind to the third Tg. Another mAb was similar, to some extent, in binding to three rat Tgs as described above, although three other mAbs bound almost equally to three rat Tgs. Since competitive binding inhibition by Tgs supported the result of the binding study, the epitopic difference on rat Tgs was confirmed. Furthermore, competitive binding inhibition by unlabeled mAbs revealed that six mAbs recognized different epitopes individually. Therefore, there were at least two unique epitopes located on one rat Tg but not located on another. The relation between unique epitopes and thyroiditis in the rats used in the present study is also discussed.