Id-anti-Id interaction constitutes an immune network that is involved in the regulation of the immune response. We prepared several anti-Id mAb to anti-CEA mAb MA 208 which was found to recognize the peptide of CEA. These anti-Id mAb were then used for idiotope mapping and for developing anti-anti-Id antibodies to analyze the Id network system relating to CEA. Anti-anti-Id mAb M 7-625 antisera (Ab 3) reacted with purified CEA in binding assay and in Western blot analysis, and competed with Ab1 binding to CEA. It is indicated that Ab2 mimicks the structure of the epitope in CEA which was recognized with Ab1. These serologic findings suggest that anti-Id mAb M 7-625 carries the internal image of the Ag. According to the amino acid sequences of CDR 1, 2, and 3 of the mAb M 7-625 variable region, there exists a homology of amino acid sequences between CDR 2 in the H chain (5 amino acids of 10) and CDR 3 in the L chain (3 amino acids of 9) of mAb M 7-625 and domain III of CEA (545-554). Internal image bearing anti-Id antibodies may be useful for the induction of a host's immune response against tunors.
