Characterization of a dominant anti-Ia idiotype using the Ia mutant mouse strain B6.C-H-2bm12

Initial studies of antibody recognition of Ia molecules using the IA mutant mouse strain bm12 suggested that two anti-Ia monoclonal antibodies (mAbs), 25−9−17 and 34−5−3, share several features: (1) indistinguishable serologic specificity including a lack of reactivity with Iabm12, (2) binding of the same spatial epitope (cluster), and (3) definition of a cross-reactive idiotype (CRI) as defined by xenogeneic antisera. In the present study we characterize a rabbit anti-idiotype (anti-Id) to 25−9−17 by affinity chromatography, and demonstrate that it detects at least two distinct idiotopes, one shared by 25−9−17 and 34−5−3 designated CRI (25−9−17) and one unique for 25−9−17 molecules. Experiments were also undertaken to determine whether CRI (25−9−17) represents a measurable component of allogeneic humoral responses to Iab antigens. By both absorption analyses of a polyspecific antiserum and production of antigenically-restricted antisera using bm12 mice, CRI (25−9−17) was found to represent a significant proportion of the antibodies to lab. By several criteria it was shown that the CRI (25−9−17)+ molecules were among the antibodies defining the serologic lesion of bm12 mice. In preparation for future studies to alter in vivo T-cell responses involving recognition of la (e.g. graft vs host disease and allogeneic transplant rejection), various immunization protocols and mouse strains were tested for induction of Id (25−9−17) following in vivo administration of various anti-idiotypic reagents. Rabbit anti-Id (25−9−17) successfully induced CRI (25−9−17) positive molecules in all strains tested regardless of IA or Ig genotype. Moreover, some of these treated mice produced antibodies to an la determinant missing on bm12 cells, suggesting that they recognize the same serologic determinant as mAb 25−9−17.