Immunohistochemical localization of new placental proteins (PP20, PP25, PP26) in normal pregnancy and gestational trophoblastic disease

Summary Placental Proteins 20, 25, and 26 (PP20, PP25, PP26) were isolated from a soluble fraction of term placenta and characterized by Bohn (1985, 1991). To clarify the localization of these proteins, normal placenta, ectopic pregnancy, endometrium, and trophoblastic disease were studied by indirect immunohistochemical method. Each protein was localized in cytoplasm of syncytiotrophoblast (ST) of early and term placenta. Positive staining for PP25 and PP26 was recognized in the extravillus trophoblast (ET) of basal plate and membrane. Proliferative and secretory phase endometria were not stained for these proteins. However, PP25 and PP26 were localized on decidualized endometrium from ectopic pregnant patients and PP26 showed positive staining on decidua. Although PP20, 25, and 26 were localized on ST of placenta, there was a possibility of extra placental production. PP26 was localized in syncytio and intermediate trophoblastic cells of gestational trophoblastic disease. PP26 is proposed to be a useful new histochemical marker of trophoblastic disease.