Immunocytochemical localization of heparan sulfate proteoglycan in human decidual cell secretory bodies and placental fibrinoid

A distinct ultrastructural feature of human decidual cells is the presence of membrane-bound secretory bodies, 0.3-0.5 micron in diameter, located within club-shaped processes at the cell periphery. These secretory bodies contain 30-60 nm electron-dense granules. Using specific antibody and the protein A-gold technique, we examined the localization of heparan sulfate proteoglycan in human decidual cells. Morphometric analysis of gold particles in cellular compartments was performed with a Zeiss Videoplan computer system. Immuno-gold staining was present in the decidual cell cytoplasm and the extracellular space, especially in the zone of the external lamina. Gold particles, indicating the locale of heparan sulfate proteoglycan, were concentrated over the electron-dense granular material within decidual secretory bodies contained in club-shaped processes at the cell periphery. Immunolabeling of placental fibrinoid was also observed. This report provides the first identification of a specific molecular constituent of decidual secretory bodies and indicates a role for these structures in secretion of the peri-decidual cell extracellular matrix.