The human fallopian tube contains placental protein 5.

Placental protein 5 (PP5), a glycoprotein with properties of a serine protease inhibitor, was found in human Fallopian tubes removed during proliferative (n = 6) and secretory (n = 6) phases of the menstrual cycle. The content of PP5 did not differ in fimbrial, ampullar and isthmic parts of the tube. In gel filtration, PP5-immunoreactivity from Fallopian tube extracts eluted as one major peak corresponding to a mol. wt of 36 kd. In radioimmunoassay, the dose--response curves of purified placental PP5 and Fallopian tubal extracts were parallel. In immunofluorescence staining, utilizing polyclonal and monoclonal antibodies, PP5 was localized to the epithelium of the Fallopian tube, but weaker staining was observed also in the stroma. As a potential serine protease inhibitor, PP5 might play a part in the implantation of the fertilized ovum.