Saline extracts of human nonpregnant endometrium were found to contain placental protein 14 (PP14). The tissue PP14 content was highest in the late secretory phase (median, 7.7 mg/g protein; n = 14), whereas proliferative endometrium (n = 8) was either PP14 negative or showed a low PP14 content (median, 0.15 mg/g protein). By immunoperoxidase staining, PP14 was localized in the glandular epithelial cells of endometrium. In tissue culture, secretory endometrium released more PP14 than proliferative endometrium, and cycloheximide markedly decreased this release. Synthesis of PP14 by secretory endometrium was demonstrated by incorporation of [35S]methionine into immunoprecipitable PP14. These results show that PP14 is synthesized and secreted by the nonpregnant endometrium.

Summary. Placental protein 14 (PP14) levels were measured in serum samples from non‐pregnant and pregnant women. amniotic fluid, cord blood, and extracts of placenta, decidua and fetal membranes. The levels were low (15–40 μg/l) in serum of non‐pregnant women. In four pregnancies following in‐vitro fertilization, the serum PP14 levels started to rise 2–12 days after embryo replacement. In normal pregnancy, the highest serum PP14 concentrations (up to 2200 μg/l) were detected between 6 and 12 weeks. After 16 weeks the level decreased and plateaued at 24 weeks to around 200 μg/l. In amniotic fluid, the highest PP14 levels (232 mg/l) were found between 12 and 20 weeks, being considerably higher than those in maternal serum throughout pregnancy. In cord blood, the levels were low (15–22 μg/l) or undetectable. In early pregnancy decidua. the PP14 content was higher (41–160 mg/g total protein) than in late pregnancy decidua (60–2700 μg/g total protein). In amnion and chorion laeve, the PP14 concentration varied from 50 to 750 and 50 to 1000 μg/g protein, respectively. Early pregnancy placenta contained 0‐25‐15 mg/g and late pregnancy placenta 3–430 μg/g protein of PP14. These results show that the levels of PP14 in pregnancy serum have a similar profile to hCG, but in contrast to other placental proteins, the amniotic fluid PP14 levels are remarkably high. This may be explained by suggesting that decidua is a source of PP14.

Placental protein 14 (PP14), also known as progestagen-dependent endometrial protein and pregnancyassociated endometrial a2-globulin, is synthesized by the human secretory endometrium and decidua. We have isolated from a human decidual cDNA library clones corresponding to PP14 and deduced its entire amino acid sequence. PP14 contains 180 amino acids, 18 of which correspond to a putative signal peptide. The predicted molecular weight of the pre-PP14 is 20,555 and that of the mature protein is 18,787. PP14 is encoded by a 1-kilobase-pair mRNA that is expressed in human secretory endometrium and decidua but not in postmenopausal endometrium, placenta, liver, kidney, and adrenals. The 162-residue-long sequence of PP14 is highly homologous to .8-lactoglobulins, with a 53.4% identity with the amino acid sequence of horse fi-lactoglobulin I. The four cysteinyl residues (positions 66, 106, 119, and 160) responsible for intramolecular disulfide bridges in .-lactoglobulins are all conserved in PP14.