Monospecific Polyclonal Anti‐Anti‐Idiotypic Antibodies to the Carboxyterminal Undecapeptide of the SV40 Large Tumour Antigen

The murine monoclonal antibody PAb1605 defines an epitope, peptide Lys(698)‐Thr(708) (KT), on the carboxyterminus of the tumour(T)antigen of SV40‐transformed cells. In vivo and in vitro experiments had shown that this sequence represents an epitope for both humoral and cellular immune responses. When injected into rabbits PAb1605 induces anti‐idiotypic antibodies (Ab‐2). Ab‐2β (internal image type) was purified by adsorption chromatography and characterized by the ability of KT to compete with the binding of ab‐2 with ab‐1. Murine anti‐anti‐idiotypic antibodies (ab‐3) were obtained by immunization of mice with ab‐2β. Both ab‐1 and ab‐3 JgG showed affinities to immunoprecipitated SV40 T antigen by immunoblot analysis and to nuclear SV40 T antigen by the immunofluorescence assay. The binding of ab‐3 to SV40 T antigen was completely inhibited by competition with KT. We conclude that the polyclonal ab‐3 is of the ab‐3 subtype and specific for only one epitope which is represented by KT and defined by ab‐1. The results demonstrate that the specificity for a defined peptide epitope of an antibody was conserved even after two consecutive steps of anti‐idiotypic‐antibody formation in two host species. Since this postulate of network theory could be verified for a sequence of a tumour‐associated antigen which represents a B‐ and T cell epitope, this model is of great interest for further tumour immunological studies.