Macrophage populations in the human placenta and amniochorion

Fetal and maternal macrophage populations in human utero-placental tissues at different stages of gestation have been studied using immunohistological and histochemical techniques. A large population of macrophages has been identified within maternal decidualized endometrium in both term and first trimester tissues, although lymphoid cells also constitute a major component of the bone marrow derived cells in the decidua of early pregnancy. In contrast, fetal macrophages have been shown to contribute nearly all of the substantial bone marrow derived cell population within placental chorionic villous mesenchyme and within the mesenchyme of the term amniochorion. Apart from a small population of stellate intensely HLA-DR positive cells in term placental villous stroma, these extra-embryonic fetal macrophages could be shown consistently to express both the leu-M3 tissue macrophage antigen and lysosomal enzyme activities. It is suggested that the major HLA-DR positive cell population of fetal amniochorion comprises 'classical' macrophages rather than dendritic type cells. These various macrophage populations may perform vital phagocytic and degradative functions within utero-placental tissues and amniochorion.