Polyclonal antibodies specific for liganded active site (metatype) of a high affinity anti-hapten monoclonal antibody

Syngeneic polyclonal antibodies were elicited to an affinity labeled high affinity (2-3 X 10(10) M-1) anti-fluorescein murine IgG2a monoclonal antibody. Hyperimmune ascites fluid was tested for reactivity with homologous liganded, affinity labeled and non-liganded Fab fragments derived from the high affinity antibody. Binding results demonstrated antibody specificity for the liganded or affinity labeled site, but no reactivity with either the non-liganded form or the fluorescyl ligand. Kinetic analysis showed that the rate of dissociation of the fluorescein ligand was slowed down significantly upon binding of the anti-affinity labeled reagent to the liganded antibody. Antibodies specific for the affinity labeled prototype were not reactive with the liganded form of an IgM monoclonal anti-fluorescyl antibody of the same affinity but idiotypically unrelated. Results of the immunological studies suggested that the antibody active site stabilized by bound ligand differed from the idiotype of the antibody. The term "metatype" was proposed for the immunological definition of the liganded active site to distinguish it from idiotype (non-liganded). The general nature of metatopes is discussed in terms of conformational or sequential epitopes.