Isolation and characterization of human fetal macrophages from placenta.

Human fetal macrophages expressing class II major histocompatibility complex (MHC) antigens have been isolated from the stroma of the chorionic plate of term placentas, using enzymatic digestion procedures, and enriched by Percoll density centrifugation. These cells are adherent, phagocytic and express Fc receptors for IgG. By rosetting with bovine erythrocytes coated with IgG, they can be enriched to 77-95% purity. Placental macrophages isolated in this way stimulate the proliferation of lymphocytes from unrelated donors in mixed-cell cultures, and act as accessory cells in oxidative mitogenesis. In a family study, placental macrophages stimulated proliferation of maternal and paternal lymphocytes but there was no evidence for either priming to, or suppression by, the fetal cells when the responses of lymphocytes from the mother and her HLA identical twin were compared. The possibility that these cells can protect the fetus from infection and/or stimulate the production of maternal anti-fetal HLA-antibodies is discussed.