Equivalent recognition of free and ACT-complexed PSA in a monoclonal-polyclonal sandwich assay is conferred by binding specificity of the monoclonal antibody.
The Bayer Immuno 1 PSA Assay measures free and ACT-complexed PSA on an equimolar basis, although it uses a monoclonal antibody (MM1) for capture and polyclonal antibodies for detection. Competitive inhibition studies using antibodies directed at various epitopes on PSA and PSA-ACT demonstrated that the capture antibody, MM1, does not bind to free PSA simultaneously with antibodies against Epitope E which is exposed only in free PSA. Affinity studies showed that the affinity constants of MM1 for both free PSA and PSA-ACT are similar. One explanation for the properties of MM1 is that it precludes the binding of antibodies to Epitope E due to steric hindrance. Alternatively, the binding of MM1 causes a conformation change within the free PSA molecule, so that Epitope E is altered in a way that causes a loss of binding affinity. The unusual properties of MM1 are responsible for the equimolar response of this monoclonal-polyclonal sandwich assay for free and ACT-complexed PSA.
Business Group Diagnostics, Immunodiagnostics Business Unit, Bayer Corporation, Tarrytown, New York 10591-5097, USA.
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D000469:Alkaline Phosphatase / Q000276:immunology; D000906:Antibodies / Q000276:immunology*; D000911:Antibodies, Monoclonal / Q000276:immunology*; D000918:Antibody Specificity; D000939:Epitopes; D016650:Fluorescein-5-isothiocyanate; D006801:Humans; D007118:Immunoassay; D017430:Prostate-Specific Antigen / Q000032:analysis* / Q000276:immunology / Q000378:metabolism; D011485:Protein Binding; D000514:alpha 1-Antichymotrypsin / Q000378:metabolism*
D000906:Antibodies; D000911:Antibodies, Monoclonal; D000939:Epitopes; D000514:alpha 1-Antichymotrypsin; D000469:Alkaline Phosphatase; D017430:Prostate-Specific Antigen; D016650:Fluorescein-5-isothiocyanate