Characterization of epitope structure for 53 monoclonal antibodies against prostate-specific antigen.

Prostate-specific antigen (PSA) is the most widely used marker of prostate cancer. Assays for PSA are based on anti-PSA antibodies, and the characterization and selection of these antibodies is important for determining their optimum performance. In our study, we characterized the reactivity of 53 antibodies, submitted to the ISOBM TD-3 PSA Workshop, using free PSA, PSA complexed to alpha1-antichymotrypsin (ACT) and purified ACT. Immunoblotting was performed after native agarose gel or reducing sodium dodecyl polyacrylamide gel electrophoresis. Immunoblotting after agarose gel electrophoresis revealed 10 antibodies that recognized only the free form of PSA, and 43 antibodies that detected both free PSA and PSA-ACT. Immunoblotting of reducing sodium dodecyl-polyacrylamide gels showed the linear or conformation-dependent nature of the epitopes. Two antibodies specific for free PSA and 18 antibodies that recognized both free PSA and PSA-ACT complex recognized linear epitopes. Moreover, 7 antibodies also detected fragmented forms of PSA.