Intermediate trophoblast: further immunocytochemical characterization.

Intermediate trophoblast has been recently described as a distinctive subpopulation of trophoblast. Previous immunocytochemical studies demonstrated that these cells react with antibodies against human placental lactogen (hPL) but fail to react with antibodies against beta-human chorionic gonadotropin (beta-hCG). To further characterize the immunocytochemical features of intermediate trophoblast and to possibly identify a more sensitive marker, we studied 88 placentas and implantation sites ranging from 4 to 40 wk gestation with a panel of antibodies that included keratin, epithelial membrane antigen (EMA), placental alkaline phosphatase (PLAP), alpha-hCG, and prolactin. Keratin was found in all intermediate trophoblast cells throughout gestation, and EMA was present in intermediate trophoblast in the second and third trimesters but was less consistently expressed than keratin. Comparison with the distribution of hPL revealed that keratin and EMA were present in intermediate trophoblast cells that were hPL-positive as well as many that were hPL-negative. alpha-hCG showed reactivity in intermediate trophoblast in the first and second trimester. PLAP and prolactin showed little or no reactivity in intermediate trophoblast. Decidual cells, which may be difficult to distinguish from intermediate trophoblast at the implantation site, failed to react with any of the antibodies tested. Cytotrophoblast and syncytiotrophoblast were positive for keratin throughout gestation, but EMA was negative in cytotrophoblast and inconsistently expressed in syncytiotrophoblast. Thus, antibodies against keratin and EMA are more sensitive than those directed against hPL in identifying intermediate trophoblast and are therefore useful in distinguishing intermediate trophoblast from decidua.