Phenotypic characterization of macrophages in human term placenta

Immunohistological techniques have been used to study heterogeneity, frequency and distribution of macrophages and T lymphocytes in chorionic villous mesenchyme, stroma of the amniochorion and decidua of 36 human term placentas obtained at spontaneous normal delivery and by caesarean section, using a panel of monoclonal antibodies (mAb) specific for macrophage phenotypes appearing in acute early (mAb 27E10), late (mAb 25F9) and down-regulatory (mAb RM3/1) stages of inflammation. Significant numbers of macrophages were identified. It could be shown that RM3/1+ macrophage phenotypes which in vitro are strongly dexamethasone-inducible and in vivo appear in down-regulatory stages of inflammatory processes are the major cell population in human term placenta. Macrophages characterized by monoclonal antibodies 27E10 and 25F9, as well as CD4+ and CD8+ cells, were distributed sparsely or were completely absent. The finding of anti-inflammatory macrophage phenotypes to be the predominant mononuclear cell population in human term placenta provides support for a mechanism whereby placenta functions as an active immunosuppressive biological barrier between mother and fetus.