Anti‐anti‐IgE idiotypic antibodies mimic IgE in their binding to the Fc_ϵ receptor

The binding site of some anti‐idiotypic antibodies (anti‐Id) can appear as a structural image of the antigen and as such may mimic its biologic activity. We raised anti‐anti‐IgE antibodies in an attempt to obtain anti‐Id capable of interacting with the Fc_ϵ receptor (Fc_ϵR). Guinea pigs were immunized with purified murine monoclonal antibodies (mAb) that had been found to react with epitopes closely related to the site on the IgE molecule which is recognized by the Fc_ϵR. After only two injections, we could detect in the immune sera anti‐Id that inhibited the binding of IgE to the anti‐IgE mAb used as immunogens. However, only after 10 immunizations over a period of about 6 months could we detect antibodies that competed efficiently with the binding of IgE to rat basophilic leukemia (RBL) cells. The “IgE‐like” anti‐Id could be affinity purified from immunosorbents made of the anti‐IgE mAb. F(ab′)₂ and Fab′ fragments were as effective inhibitors of IgE binding as the intact anti‐anti‐Id antibodies. Some of the anti‐Id caused RBL degranulation and all of them, like IgE, inhibited the binding of specific anti‐Fc_ϵR mAb to RBL cells. In summary, by hyperimmunization with anti‐IgE mAb we could obtain anti‐Id whose antigen‐binding site is recognized by the mast cell receptor specific to the Fc portion of IgE.