A cell spreading factor, abundant in human placenta, contains fibronectin and fibrinogen

A salt extract from human normal-term placental extracellular matrix contains material that rapidly adsorbs to glass or tissue-culture plastic and promotes the spreading of fibroblastic and epithelioid cell lines. The cellular response to placental spreading factor (PSF) is characterized and compared with the response to fibronectin. The active component is shown to contain antigenic determinants that cross-react with antibodies to fibronectin and fibrinogen. The activity is not retained on gelatin-Sepharose but another component of the extract (approximately 185 000 molecular weight) is retained. Partial purification is reported, and the possible involvement of PSF in trophoblastic invasion of the uterine wall is discussed.