HIGHLY SPECIFIC MONOCLONAL-ANTIBODY DEMONSTRATES THAT PREGNANCY-SPECIFIC GLYCOPROTEIN (PSG) IS LIMITED TO SYNCYTIOTROPHOBLAST IN HUMAN EARLY AND TERM PLACENTA

Pregnancy specific glycoproteins (PSG) in humans constitute a family o f 11 closely related glycoproteins (PSG1-8, PSG11-13) of unknown funct ion(s), which are produced in large amounts by the placenta. As a step toward understanding the biology of PSG, specific monoclonal antibodi es (mAbs) against PSG were developed and used to investigate the ultra structural localization of PSG in the early and term placenta and in f irst trimester decidua. One mAb, BAP-3, was found to react with all si x individually expressed PSGs representing five alternatively spliced forms, but not with any of the seven expressed members of the carcinoe mbryonic antigen (CEA) subfamily. The BAP-3 epitope is located in the PSG B2 domain. Using the BAP-3 mAb, PSGs were found to be expressed ex clusively by the syncytiotrophoblast of first trimester and term villi . The intensity of the staining was much higher in early than in term placenta. All three main cellular compartments involved in the biosynt hesis pathway of secreted proteins, i.e. rough endoplasmic reticulum, the Golgi complex and secretory vesicles, were stained for PSG. A seco nd PSG-reactive mAb, BAP-1, also stained the apical plasma membrane of some glandular epithelial cells in first trimester decidua in additio n to syncytiotrophoblast. This staining was most likely due to cross-r eactivity with biliary glycoprotein (BGP). (C) 1997 W. B. Saunders Com pany Ltd.