Monoclonal antibodies to human alpha-foetoprotein: analysis of the behaviour of three different antibodies

Three mouse monoclonal antibodies directed to different epitopes on human alpha-foetoprotein have been produced. Two are of IgG1 subclass and the third is IgA. The polyethylene glycol-dependent immunoprecipitation system, designed for conventional antisera, had to be adapted before reproducible results could be obtained with the reagents. In this adapted system, as well as in a radioimmunoassay using solid-phase second antibody, a mixture of the 3 monoclonal antibodies exhibits cooperativity. However, the sensitivity of the radioimmunoassay with pooled monoclonals is not good as that of conventional antiserum. Low affinity monoclonal antibodies have been used for immunopurification of the antigen, whilst the high affinity one is useful for antigen quantitation in a labelled antibody-dependent system which requires absolute antibody specificity.