We have prepared antisera specific for Igh-V-linked determinants (alpha Igh-V) in order to study Igh-V restriction during the development of protective, T cell-mediated anti-idiotypic immunity in autoimmune interstitial nephritis. Suppressor T cells in this network use an antigen-binding (RE-Id+) factor (TsF1) secreted by first-order suppressor cells (Ts-1) to induce an anti-idiotypic (RE-alpha Id+) soluble factor (TsF1) released by effector-phase, Ts-2 suppressor cells. Each of these soluble suppressor factors requires homology in the Igh-V region to complete its regulatory functions. Our alpha Igh-V antisera, adsorbed against network idiotypes, can interfere with the Igh-V restriction used in the induction of Ts-2 suppression by TsF1. The antisera bind both TsF1 and TsF2 in an allele-specific manner and are cytotoxic to induced Ts-2 cells, but not their precursors. These Igh-V determinants appear to behave like activation molecules. They lie outside of the ligand-binding site, do not map with the serologic binding of idiotype, and thus act as distinct associative-recognition elements in the maturation of anti-idiotypic immunity.