Immunohistochemical localization of hCG alpha, hCG beta CTP, hPL and SP1 on villous and extravillous trophoblasts in normal human pregnancy

Trophoblasts are divided into villous trophoblasts and extravillous trophoblasts, depending on whether they constitute a villous structure, and cell columns intervene between them. We conducted an immunohistochemical localization of human chorionic gonadotropin (hCG) alpha, hCG beta C-terminal peptide (CTP), human placental lactogen (hPL) and pregnancy-specific beta 1-glycoprotein (SP1) on the trophoblasts of normal human pregnancy, using forty-one hysterectomized pregnant uteri (6-22 weeks). In villous trophoblasts, the capacity to synthesize hCG alpha, hCG beta CTP, hPL and SP1 seemed to develop according to the morphological change from mononuclear cells to multinuclear cells. In contrast, the synthetic capacity of these proteins seemed not to correspond with the morphological change in extravillous trophoblasts: The location of hCG alpha, hCG beta CTP and SP1 was restricted to the mononuclear trophoblasts in the superficial decidua, while hPL was present extensively in extravillous trophoblasts, including multinuclear trophoblasts in the deciduomuscular junction. Therefore, it may be reasonably said that extravillous trophoblasts have many biological features distinct from villous trophoblasts and differentiate in an independent manner. Mononuclear trophoblasts in the cell column were negative for these proteins, which, together with morphological observations, strongly suggest the germinative nature of these cells.