Localization of tartrate-resistant acid phosphatase in human placenta

Tartrate-resistant acid phosphatase is an inducible marker of cell differentiation and activation expressed by specialized cells of macrophage lineage and some activated lymphocytes. Clinically, this phosphatase is a diagnostic marker for hairy cell leukaemia and osteoclast activity. The cDNA for this enzyme has been cloned from a placental expression library, yet the cell(s) expressing the enzyme protein has not been determined with certainty. Our laboratories have developed a monoclonal antibody, 9C5, suitable for immunohistochemical localization of tartrate-resistant acid phosphatase in paraffin sections. The purpose of this study was to use antibody 9C5 to identify cells expressing tartrate-resistant acid phosphatase in sections of paraffin-embedded, normal, full-term placenta and to determine if those cells expressed other macrophage markers including CD68 (PG-M1 antibody), LN5, lysozyme, alpha 1-antitrypsin and alpha 1-antichymotrypsin. Histochemical localization of activity in frozen sections was compared with immunohistochemical localization in paraffin sections of the same tissue specimens. The activity and antigenicity of this enzyme were detected in decidual cells, syncytiotrophoblast, and some macrophages distributed throughout 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.