Abstract
In order to analyse the epitope structure of carcinoembryonic antigen (CEA) which could be used for active immunotherapy, seven anti-idiotypic monoclonal antibodies (anti-Id MoAbs) were generated from a BALB/c mouse immunized with anti-CEA MoAb P 1-356, which was prepared from a synthetic peptide of domain I of CEA. These anti-Id MoAbs were divided into 4 groups by cross blocking assay. The MoAbs specifically reacted with MoAb P 1-356 and inhibited the binding of CEA and MoAb P 1-356; they did not react with other MoAbs. These results indicate that all of these anti-Id MoAbs recognized private idiotopes at the combining site of MoAb P 1-356.
Polyclonal anti-anti idiotypic antiserum (Ab 3) induced from anti-Id MoAb M 315 blocked the binding of CEA and 125I-labelled MoAb P 1-356 (Ab 1) and reacted with CEA, suggesting that it contains “Ab 1 like Ab 3”. Therefore, we prepared anti-anti-Id MoAbs using anti-Id MoAb M 315. Among 13 candidates, anti-anti-Id MoAb 11 B 2 was chosen, because it inhibited the binding of MoAb P 1-356 (Ab 1) and 125I-labelled MoAb M 315 (Ab 2). MoAb 11 B 2 (Ab 3) directly reacted with CEA and competed with MoAb P 1-356 (Ab 1) in the competition assay. Direct binding assay using purified 125I-labelled MoAb 11 B 2 revealed that it reacted not only with purified CEA from cells, but also with CEA synthetic peptide P 1. In addition, MoAb 11 B 2 (Ab 3) reacted with both CEA-producing cultured cells and colonic cancerous tissues in immunostaining. These results indicate that anti-anti-Id MoAb 11 B 2 is “Ab 1 like Ab 3”. Therefore, it is suggested that anti-Id MoAb M 315 bears an “internal image” of the MoAb P 1-356-defined epitope on CEA.
