Myofibroblast as a major cellular constituent of villous stroma in human placenta.

The human placenta requires contractile structures to generate energy for blood propulsion. Smooth muscle cells are not present in significant numbers in the human placenta while fibroblasts lack effective contractile properties. This study provides the following evidence that the stromal cells of the placental villi, cotyledonary septa and perivascular connective tissue are myofibroblasts. (I) Stromal cells are strongly positive for dipeptidylpeptidase IV (EC 3.4.14.5) which occurs exclusively in myofibroblasts as far as connective tissue cells are concerned. (2) The isoenzyme pattern of the placental dipeptidylpeptidase IV is identical to that of myofibroblasts in palmar fibromatosis on isoelectric focusing. (3) Antibodies raised against isolated placental dipeptidylpeptidase IV cross-react with dipeptidylpeptidase IV from myofibroblasts of palmar fibromatosis as shown by immunohistochemistry. (4) On electron microscopic examination, stromal cells present all the ultrastructural features of myofibroblasts. It is concluded that, except for the vascular component and a negligible number of Hofbauer cells, myofibroblasts make up nearly all the cellular constituents of human placental villous stroma.