Immunohistochemical localization of serine-protease inhibitors in the human placenta

Proteases and their inhibitors play a pivotal role in developmental and differentiative processes. In the present report we investigated the immunohistochemical localization of alpha 1-antitrypsin, alpha 1-antichymotrypsin and inter-alpha-trypsin inhibitor in first trimester as well as in term human placentas. For this purpose polyclonal antibodies against these serine-protease inhibitors were used. All inhibitors were expressed in the villous syncytiotrophoblast of first and last trimester placentas. Placental fibrinoid was positively stained for alpha 1-antitrypsin and inter-alpha-trypsin inhibitor throughout gestation. alpha 1-Antitrypsin and alpha 1-antichymotrypsin showed a strong immunostaining in the Hofbauer cells (first trimester and full term placentas). Extravillous cytotrophoblast was negative for the three protease inhibitors throughout gestation. The presence of the three inhibitors in the syncytiotrophoblast suggests a role in coagulative, invasive and immunomodulatory processes. Fibrinoid, staining for alpha 1-antitrypsin and inter-alpha-trypsin inhibitor, could also have an important immunoprotective function. The presence of protease inhibitors in the Hofbauer cells suggests an involvement of these cells in villous remodelling and differentiative processes.