In order to establish a new assay to detect shedding tumor associated antigens, anti-idiotypic monoclonal antibodies were prepared against monoclonal antibody 149.53 which reacted with human high moleculor weight-melanoma associated antigen. Serological characterization of anti-idiotypic monoclonal antibodies suggested that these monoclonal antibodies recognized private and distinct idiotopes of monoclonal antibody 149.53. Idiotype mapping of monoclonal antibody 149.53 showed that there might be at least three idiotopes on it ; one idiotope at a combining site, one at a noncombining site and another at an intermediate site. A new assay to detect shedding antigens is based on the inhibition of idiotype-anti-idiotype interaction. Anti-idiotypic monoclonal antibody against near combining site showed high % inhibition of idiotype-anti-idiotype interaction, while anti-idiotypic monoclonal antibody against non-combining site did not. The results of this assay were correlated significantly with those of double deter-minant immuno assay. The assay requires only one epitope of a given antigen, while double determinant immuno assay requires two distinct epitopes that are spatially far from each other on the same antigenic molecule, And therefore it may be useful for detection of shedding antigen.
