Localization of a normal prostatic secretory product using the monoclonal antibody KR-P8

We previously reported that the monoclonal antibody KR-P8 detects a prostate organ-specific antigen that is distinct from other markers such as prostatic acid phosphatase and prostate specific antigen. In this report we demonstrate that the antigen recognized by KR-P8 is among the secretory products of both normal and malignant prostatic epithelium. Immunoperoxidase staining patterns showed that the antigen was concentrated on the luminal surfaces of the glandular epithelial cells of prostate, and also that the antigen was localized within secretory vacuoles of cells of the prostate tumor line PC3. In addition, using an immunoblotting assay the KR-P8 binding antigen was detected in the growth media of PC3 cells and also found to be present in human urine and seminal plasma. The data suggest that the antigen recognized by KR-P8 may be a useful marker for studying the secretory processes of the prostate gland.