Thyroglobulin monoclonal antibody cross-reacting with thyroperoxidase induces in syngeneic mice anti-idiotypic monoclonal antibodies with dual autoantigen binding properties. The intertope hypothesis

Abstract

Autoimmune thyroid diseases are characterized by antibodies (Ab) directed to thyroglobulin (Tg) and thyroperoxidase (TPO). Some of them, TGPO Ab, are Tg Ab with an interspecies idiotype (Id) reacting with TPO. Taking advantage of a carefully studied TGPO monoclonal antibody (mAb), we examined the basis of the hypothesis that TPO Ab would ultimately derive from TGPO Ab through idiotypic induction. We repeatedly immunized naive, syngeneic mice with the TGPO mAb and we derived three novel mAb directed to both Tg and TPO. The most reactive of them, mAb 4F8, was further purified, radiolabeled and its binding properties studied by radioimmunoassay. mAb 4F8 bound to Tg, TPO, the immunogen Ab1 and even to itself, being thus considered as a self-binding Ab2. Competitive binding inhibition experiments demonstrated that Tg, TPO, Ab1 and Ab2 cross-reacted for Ab2 binding to Tg, TPO and Ab1. Fine specificity mapping using panels of specific mAb revealed that Ab1 and Ab2 were similar because they were directed against the same immunodominant regions on Tg and TPO. We propose that unique Id of TGPO Ab resemble dominant epitopes of Tg as well as paratopes of Ab directed against dominant TPO epitopes. This category of Id that we called intertopes may induce TPO-monospecific Ab from TGPO Ab by idiotypically driven somatic mutations.

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

“…Subsequently, Ruf et al . [17,18] concluded that anti‐Tg/TPO autoantibodies react with the two antigens via different sites of antibody variable region. Binding with Tg is realized via the paratope (antigen‐binding site), while TPO is bound via an idiotypic structure, away from the paratope, which is present in some of the human anti‐Tg autoantibodies as well as in murine monoclonal antibodies with the same epitope specificity.…”

Thyroglobulin-Thyroperoxidase Autoantibodies Are Polyreactive, Not Bispecific: Analysis Using Human Monoclonal Autoantibodies

“…Experimental approaches involving the generation of monoclonal antibodies from immunized mice provide support for the TgPOAb hypothesis (11,12). However, isolation of bispecific human monoclonal Ab, rather than monoclonals from immunized mice, would definitively establish the existence of TgPOAb in human disease.…”