Absorption of peroxidase-conjugated immunoglobulin G by human placenta: an in vitro study.

The uptake of IgG-HRP into human placental villi has been demonstrated. Initial uptake occurred via coated pits at the surface of the syncytium. It was subsequently localized in small vesicles and larger vacuoles (multivesicular bodies) within the syncytium. Reaction product was also localized in occasional cytotrophoblastic cells. The basal lamina contained some reaction product; protein was apparently capable of diffusing through the basal lamina, as evidenced by the presence of reaction product in and around fetal capillaries, and in placental macrophages (Hofbauer cells). Within the fetal capillary endothelium small vesicles were labelled, suggesting movement across this layer was vesicle-mediated and not by movement through the intercellular space.