Antibodies cross-reacting with thyroglobulin and thyroid peroxidase are induced by immunization of rabbits with an immunogenic thyroglobulin 20mer peptide.

Thyroglobulin (Tg) and thyroid peroxidase (TPO) are two major autoantigens in autoimmune thyroid diseases (AITD). Cross-reactive anti-Tg/TPO antibodies have been identified in patients with AITD and in mice immunized with Tg or TPO. In the present study, we investigated the production of anti-Tg/TPO antibodies in rabbits immunized with human Tg and with a highly immunogenic Tg peptide (namely TgP41, sequence 2651-2670 of human Tg), by noncompetitive and competitive ELISA. TgP41 was found previously to induce intramolecular epitope spreading. We found that Tg-immunized rabbits developed a serological immune response to TPO due to cross-reactivity with Tg, since serum TPO reactivity was inhibited by soluble Tg and affinity-purified anti-Tg antibodies cross-reacted with TPO. Moreover, TgP41-immunized rabbits responded to Tg and TPO. This serological response was attributed to anti-Tg/TPO antibodies, based on the observation that serum TPO reactivity was again inhibited by soluble Tg, and affinity-purified anti-Tg antibodies, induced by TgP41-immunization, cross-reacted with TPO. Purified anti-TgP41 antibodies did not react with TPO, suggesting that a putative common antigenic determinant is not included in the peptide sequence. We propose that intermolecular spreading of reactivity to TPO observed after administration of the Tg-peptide is a result of intramolecular epitope spreading to determinant(s) responsible for Tg/TPO cross-reactivity.