Induction and immunochemical properties of a novel anti-antibody.

This paper describes results which characterize an induced antibody in normal outbred rabbits which we have, for convenience, called parareactant (PR). PR resulting from autoimmunization of rabbits with either keyhole limpet hemocyanin-anti-tetanus toxoid F(ab')2 or with tetanus toxoid-anti-tetanus toxoid F(ab')2 complexes was studied. PR activity was directed solely to autologous, homologous or heterologous F(ab')2 fragments regardless of their specificity. PR failed to react with intact antibodies or with antigen-antibody complexes consisting of homologous antibody bound to specific antigen. Radioimmunoassay and ELISA inhibition assays showed that reactivity between PR and autologous anti-tetanus toxoid F(ab')2 or homologous anti-bovine serum albumin F(ab')2 fragments was specifically inhibited with antigen. Anti-allotypic antibodies specific for a2 and b6 markers strongly inhibited binding of 125I-anti-micrococcal carbohydrate F(ab')2 (a2, b6) with PR (a3, b4, b5). PR specificity thus appears to be directed against non-idiotypic determinants present in Fv regions. Affinity immunoblotting was used to analyze clonality of PR in the sera collected from individual rabbits during the course of an active immune response. PR-positive sera displayed clonally restricted spectrotype patterns. PR molecules were predominantly IgG with isoelectric points of 5.9-6.8. These results strongly suggest that these PR molecules are coded by a small number of V region genes.