Placental protein 21. Localization in human placenta and concentrations in the body fluids of men and nonpregnant and pregnant women.

Abstract

The immunohistochemical localization of placental protein 21 (PP21) was marked in the syncytial brush border and basal membrane during the 1st and 2nd trimesters of pregnancy and also in the chorionic epithelial brush border and basement membrane at term. A weaker stain was found in the cell membranes of amniotic epithelial and chorionic trophoblast cells. Neither heparin nor changes in temperature significantly influenced PP21 concentration. Relatively high serum PP21 concentrations were measured during the follicular and luteal phases in healthy nonpregnant women and in healthy men whose seminal plasma also showed a high PP21 concentration. Serum PP21 levels in normal pregnancy rose from a median of 29.1 ng/ml at 6-7 weeks of gestation to 82.0 ng/ml at 36-37 weeks of gestation. Although maternal urine showed low PP21 levels during pregnancy, amniotic fluid PP21 levels were higher at 7-21 weeks of gestation than at term. Cord blood sera showed almost the same PP21 concentration as maternal sera, but retroplacental blood showed much higher levels. Maternal serum PP21 levels in hydatidiform mole patients did not differ from the normal pregnancy range, although their molar vesicular fluids contained higher PP21 concentrations. These results suggest an extraplacental source for PP21.