STAGE-SPECIFIC DISTRIBUTION OF P-GLYCOPROTEIN IN FIRST-TRIMESTER AND FULL-TERM HUMAN PLACENTA

The distribution of P-glycoprotein in human placenta has been examined by immunohistochemistry using a battery of monoclonal antibodies (MRK -16, C219 and JSB-1). P-glycoprotein was located on the syncytiotropho blast microvillus border in first-trimester placentas and some of the placental macrophages (Hofbauer cells) showed weak cytoplasmic stainin g. In term placentas, however, staining was not observed in the tropho blast but most of the Hofbauer cells displayed strong cytoplasmic stai ning. In situ hybridization with specific gene probes suggested that b oth human multidrug resistance genes were expressed in the placenta, a lthough only the multidrug resistance-1 gene product would have been d etected by the MRK and JSB-1 antibodies. These results point to distin ct functions for P-glycoprotein during the different stages of placent al development and indicate that its expression may be under developme ntal control.