Crossreactivity and inheritance of idiotypes restricted to human anti-tetanus toxoid antibodies.

The presence of cross-reactive idiotypes on human IgG antibodies of tetanus toxoid (TT) antigen was assessed by examining the capacity of two anti-idiotypic (ID) antisera raised against IgG (Fab')2 anti-TT (idiotype) from two subjects to bind radiolabeled "idiotype" and to inhibit the binding of radiolabeled TT to IgG from unrelated subjects and from family members of the idiotype donors. Idiotypic crossreactivity with unrelated individuals was infrequent and weak but was frequent and stronger among siblings. The strongest idiotypic crossreactivity was seen between identical twins in studies using four anti-ID raised against the anti-TT idiotypes of two sets of twins. The results of the present study suggest that idiotypic determinants restricted to human anti-TT antibodies are, at least in part, encoded by inherited genes, which are infrequently shared among unrelated individuals.