The endothelium but not the syncytiotrophoblast of human placenta expresses caveolae.

The human placenta is a complex specialized structure that mediates the interchange of molecules, ions, and gases between maternal and foetal circulation. We have investigated the distribution and expression of caveolae/caveolin in the placenta. Using immunochemical, immunocytochemical, and ultrastructural methods, we show that the placenta expresses caveolin-1 and caveolin-2, which are marker proteins for caveolae. These proteins and caveolae were expressed at high levels in endothelium of placental capillaries and in endothelial and smooth muscle cells of larger vessels. In addition, fibroblasts in areas of the placenta with high connective tissue content also expressed caveolin. However, we were unable to detect these proteins or caveolae-like structures in the syncytiotrophoblast layer or in cytotrophoblasts. These results have important implications for further understanding placental biology and for the role of caveolae in cell regulation in this organ.

Production and characterisation of antibodies against isolated placental retroviral-like particles.

The mammalian genomic DNA is known to contain a variety o f endogenous proviruses but their expression is usually restricted to reproductive tissues such as the placenta and a variety of human tumour cells. More definitive characterization of retroviral gene products has been hampered by unavailability of specific biological reagents. In this study, polyclonal and a total of six monoclonal antibodies (mAbs) were raised against endogenous (intact) retroviral particles isolated from human placental villous tissue. These antibodies were characterized using immunohistochemical and biochemical methods. Five polyclonal antibodies and one mAb (RV1-17) showed strong specific immunohistochemical and immunogold staining with submembraneous structures within placental syncytiotropblast. The reactivity of these antibodies was consistent with the pattern of apical syncytiotrophoblastic budding of retroviral particles previously reported in ultrastructural analyses.