Three pregnancy proteins (PP12, PP14, and PAPP-A): their biological and clinical relevance

The three pregnancy proteins, PP12, PP14, and PAPP-A, reviewed here are all produced by the endometrium under the influence of progesterone. Their production is low during the secretory phase and increases dramatically after decidualization and pregnancy. PP12 and PP14 are synthesized by the epithelial cells and PAPP-A is synthesized by the stromal cells. Reflecting perhaps the relative abundance of stromal cells, PAPP-A concentrations increase progressively to term, whereas the levels of PP12 and PP14 level off and even decline after the 20th week of gestation. These proteins are also found in nonpregnant subjects in extrauterine sites: follicles, follicular fluid, luteal cells, and fallopian tubes, and in males, in seminal vesicles and seminal fluid. PP12 has been found in several forms of cancer, although not with sufficient frequency to make it a useful tumor marker. The biologic function of these proteins is still subject to speculation, but they do reflect the biosynthetic capacity of decidualized endometrium, and especially PP14 may find clinical application in the management of infertility patients.