Preparation and characterization of anti-anti-idiotypic monoclonal antibody ("Ab1-like Ab3") in relation to carcinoembryonic antigen.

In order to analyze the epitope structure of carcinoembryonic antigen (CEA) and the idiotype network system, seven anti-idiotypic monoclonal antibodies (anti-Id MoAbs) were generated from a BALB/c mouse immunized with anti-CEA MoAb P1-356, which recognized a synthetic peptide P1 of CEA, domain I. These MoAbs were divided into four groups. The anti-Id MoAbs specifically reacted with MoAb P1-356, but not with any MoAb, and inhibited the binding of MoAb P1-356 to CEA, indicating that all of these anti-Id MoAbs recognized private idiotopes at the combining sites of MoAb P1-356. Polyclonal anti-anti-idiotypic antiserum (Ab3) generated with anti-Id MoAbs M315 (Ab2), blocked the binding of MoAb P1-356 (Ab1) to CEA and reacted with CEA(Ag) and synthetic peptide P1. The analysis of serological assays suggested that it contains "Ab1-like Ab3." Therefore, we prepared anti-anti-Id MoAbs using anti-Id MoAb M315. Among 13 candidates, anti-anti-Id MoAb 11B2 was selected, because it competed with MoAb P1-356 (Ab1) binding to CEA. A direct binding assay using MoAb11B2 showed that it reacted with purified CEA and with CEA synthetic peptide P1. In addition, MoAb 11B2 (Ab3) reacted with both CEA-producing cultured cells and colonic cancerous tissues in immunostaining. These results indicate that anti-anti-Id MoAb 11B2 is "Ab1-like Ab3." Therefore, it is suggested that anti-Id MoAb M315 bears an "internal image" of the MoAb P1-356-defined epitope on CEA.