Induced latent allotypes within rabbit anti-cross-reactive idiotype reagents. Direct immunoelectron microscopic evidence.

Immunization of rabbits with anti-VHa allotype antibody leads to the production of an "anti-cross-reactive idiotype (IdX)" reagent which appears to recognize a highly conserved IdX on anti-allotype antibodies. In many rabbits, a large percentage of this "anti-IdX" reagent does not express the nominal VHa framework allotype of the rabbit from which it was derived and is otherwise serologically indistinguishable from the original antigen, i.e. a1 or a2 allotype. To determine whether these anti-IdX molecules were in fact anti-IdX (or internal images) or were induced immunoglobulins bearing latent VHa allotypes, immunoelectron microscopic analysis of the molecules in complex with Fab anti-allotype antibody was conducted. The results show that the complexes do not resemble idiotype-anti-idiotype interactions but are essentially indistinguishable from allotype-anti-allotype complexes. We conclude that a major component of the "anti-idiotype" response of these anti-VHa-immunized rabbits is the production of Ig molecules bearing latent VHa allotypes.