Cytochemistry and biochemistry of acid phosphatases VI: Immunoelectron microscopic studies on human prostatic and leukocytic acid phosphatases

Using different antisera against secretory and lysosomal prostatic acid phosphatases, the localization of the respective antigens was studied in the human prostate at the ultrastructural level. Secretory acid phosphatase was confined exclusively to the secretory vacuoles of the glandular cells. Discharge of the secretory material occurs in a merocrine type of secretion. The identical antigen could be localized in the primary and secondary granules of neutrophil and eosinophil granulocytes separated from human peripheral blood. The antiserum used was also cross‐reactive with the canine prostate, where a very distinct immunoreaction was observed with the secretory granules of the glandular cells. The antibodies directed against lysosomal acid phosphatases prepared from prostatic homogenates consistently gave a positive immunoreaction with dense bodies, lipofuscin, and secretory granules. The respective antigens were present also in neutrophil and eosinophil granulocytes. These findings do not identify the existence of a prostate‐specific acid phosphatase, which does not exist. The secretory form of the isoenzymes, however, is clearly distinct from the lysosomal form, both of which are present in granulocytes. Therefore the origin of acid phosphatases elevated in peripheral blood in cases of metastatic prostatic cancer could be either the carcinomatous cells or leukocytes destroyed during the process of metastasis.