Demonstration of P29, an oestrogen receptor-associated tumor marker, in human term placenta

A Mr29,000 serine phosphoprotein (P29) related to oestradiol receptor was studied in human term placenta with the use of a specific monoclonal antibody (D5). D5 was used with two different methods, immunohistochemistry and immunoradiometry. For immunohistochemistry, an indirect immunoperoxidase method was chosen to detect P29 in methacarn-fixed, wax-embedded sections. P29 was mostly confined to the syncytiotrophoblast surrounding placental villi, staining being positive in both cytoplasm and nuclei. The stroma of villi was negative. Content of P29 was uniformly high in crude placental cytosol, as measured by immunoradiometry assays. Specificity of D5 against P29 in placenta was tested by an immunoblotting technique. This showed a single band corresponding to a molecular weight of 29 kDa. The biological meaning of the finding is unknown at present.