LOCALIZATION OF TARTRATE-RESISTANT ACID-PHOSPHATASE IN HUMAN PLACENTA

Tartrate-resistant acid phosphatase is an inducible marker of cell dif ferentiation and activation expressed by specialized cells of macropha ge Lineage and some activated lymphocytes. Clinically, this phosphatas e is a diagnostic marker for hairy cell leukaemia and osteoclast activ ity. The cDNA for this enzyme has been cloned from a placental express ion library, yet the cell(s) expressing the enzyme protein has not bee n determined with certainty. Our laboratories have developed a monoclo nal antibody, 9C5, suitable for immunohistochemical localization of ta rtrate-resistant acid phosphatase in paraffin sections. The purpose of this study was to use antibody 9C5 to identify cells expressing tartr ate-resistant acid phosphatase in sections of paraffin-embedded, norma l, full-term placenta and to determine if those cells expressed other macrophage markers including CD68 (PG-M1 antibody), LN5, lysozyme, alp ha(1)-antitrypsin and alpha(1)-antichymotrypsin. Histochemical localiz ation of activity in frozen sections was compared with immunohistochem ical localization in paraffin sections of the same tissue specimens. T he activity and antigenicity of this enzyme were detected in decidual cells, syncytiotrophoblast, and some macrophages distributed throughou t maternal and embryonic tissues, but not in neutrophils. Unlike other tissues previously examined, placenta contains significant numbers of the phosphate-positive cells that are not of macrophage origin.