Human decidual stromal cells express alpha-smooth muscle actin and show ultrastructural similarities with myofibroblasts

Previous reports in human and mouse material demonstrated that decidual str omal cells expressed antigens associated with haematopoietic cells, exerted immune functions, and originated from bone marrow. These findings suggeste d that these cells belonged to the haematopoietic lineage. We purified and expanded in culture precursors of human decidual stromal cells, and found i n electron microscopic images that the ultrastructure of these cells was si milar to that of myofibroblasts, which are of mesenchymal origin. The relat ionship between these two types of cell was confirmed by the detection (by flow cytometry) in the decidual precursors of alpha-smooth muscle actin, a contractile microfilament expressed solely by smooth muscle cells, myofibro blasts and related cells. This filament was also detected in decidual strom al cells decidualized in vitro by the effect of progesterone. We also found vimentin in decidual precursors and decidualized cells. This intermediate filament has been previously reported to be expressed by all decidual strom al cells and also by myofibroblasts. Desmin, another intermediate filament expressed by myofibroblasts, was not detected in the decidual precursors; h owever, this filament was observed in decidualized cells. The expression of alpha-smooth muscle actin by decidual stromal cells was also found by immu nostaining in cryostat sections of early decidua. Our results suggest that decidual stromal cells are related to myofibroblasts.