Immunologic and biological properties and clinical significance of placental proteins PP5 and PP12.

Among the number of newly isolated placental proteins, PP5 and PP12 share some common characteristics: Both are present in the syncytiotrophoblast of normal placenta and hydatidiform mole, but less frequently, if at all, in choriocarcinoma. The levels in heparinized plasma of both proteins are lower than those in serum, and both are heat-labile. The function of PP12 is completely unknown, whereas PP5 appears to be related to the blood coagulation and fibrinolytic systems at the placental site through its antiplasmin activity. Many exciting avenues of research have been opened to uncover the biological role of these proteins in fetal development and cancer. We are pursuing this research with the immediate goal of assessing the role of PP12 in the blood coagulation system and of studying the expression of both proteins in various forms of cancer.