Detection of a regulatory idiotype on a spontaneous neonatal self-reactive hybridoma antibody

To investigate the physiologic relevance of an idiotype-driven regulation of the immune system, we began a search for spontaneous self-reactive hybridomas in neonatal BALB/c mice. We sought hybridoma antibodies reactive with thyroglobulin (Tg) and expressing Id62, a recurrent idiotype with regulatory properties borne on induced adult autoantibodies to Tg. We describe herein such a neonatal Tg binding/Id62-positive monoclonal antibody (mAb) B10H2, and compare it with prototype mAb 62, an adult Tg-binding/Id62-positive mAb. Both mAb react with the same Tg epitope, as demonstrated by their abilities to totally inhibit the binding of the other to Tg. Moreover, as assessed by a double-reciprocal plot of their binding to Tg, their relative affinities for Tg are comparable. Likewise, mAb B10H2 appears idiotypically similar to mAb 62 because it totally inhibits the binding of mAb 62 to homologous anti-idiotype. Finally, as previously shown for mAb 62, mAb B10H2 expresses Id62 independently on both heavy (H) and light (L) chains, as evidenced by the immunoblot binding of a specific anti-Id62 probe to separated H and L chains. By molecular genetic analysis both antibodies appear to have made use of a member of the same VH 7183 gene family. Altogether, these findings suggest that neonatal mAb B10H2 and adult mAb 62 are very similar if not identical, and regulatory idiotype Id62 may be germline encoded. Furthermore this observation supports, in general, the concept of an idiotype-driven regulation for autoimmune responses.