Idiotype manipulation for autoimmune diseases: where are we going?

Receptor revision and systemic lupus

Studies over the past 10 years have shown that B cells can undergo secondary heavy- or light-chain immunoglobulin (Ig) rearrangements at various stages of their normal development, a process termed receptor editing. In the bone marrow, this mechanism is important to maintain tolerance because it can extinguish a self-reactive specificity without having to physically eliminate a potentially autoreactive B cell. In the periphery, secondary rearrangements may also play a role in the diversification and maturation of an immune response, although conclusive evidence for this process is still required. Individuals with systemic autoimmune diseases, such as lupus, show evidence of intricate abnormalities in receptor editing. On the one hand, decreased editing may not eliminate the self-reactive specificities that emerge during B-cell development in the bone marrow. Conversely, excessive secondary rearrangements, especially in the periphery where tolerance mechanisms are less effective, can result in the production of autoantibodies by edited B cells. It will be important to assess whether the complex editing defects observed during lupus are a primary susceptibility factor to this disease or if they are secondary to other abnormalities of lymphocyte development in these autoimmune patients.

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

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.