Immunoglobulin idiotype and anti-anti-idiotype utilize the same variable region genes irrespective of antigen specificity.

Idiotypic determinants characterizing certain antibody specificities have been proven valuable structural and genetic markers in studies of antibody diversity and regulation. The heritable predominant idiotype associated with the response to p-azophenylarsonate in A/J mice consists of a set of highly homologous (greater than 95%) heavy and light chain variable region amino acid sequences probably arising by somatic mutation from one or a few V region genes. We examined a peculiar set of monoclonal antibodies that have been defined as CRI by serologic analysis, but that have no affinity for the hapten Ars. These antibodies were elicited by immunization with anti-CRI rather than by the conventional immunization with antigen. The amino acid sequences of the amino terminal half of the V regions of these anti-(anti-CRI) antibodies are indistinguishable from those of conventional Ars-binding CRI antibodies. Thus, Ars-binding CRI and Ars-nonbinding anti-(anti-CRI) are derived from similar or identical VH and VL genes.