HETEROGENEITY OF FC-GAMMA RECEPTOR-BEARING CELLS IN HUMAN TERM AMNIOCHORION

Confocal microscopy has been used to study immunoreactivity to monoclonal antibodies directed against the three characterized human leucocyte Fcγ receptors in term amniochorion. FcγRI (CD64), FcγRII (CDw32) and FcγRIII (CD16) are expressed by cells of the maternal decidual layer associated with the amniochorion. These three subtypes of receptor are also expressed by cells of the fibroblast and reticular layers although not all cells of these layers express receptors which suggest that they are heterogeneous cell populations. We were not able to demonstrate FcγRII immunoreactivity in decidual layer endothelial cells. Human IgG specific immunofluorescence was detected in the extracellular matrix of the tissue and associated with the Fcγ receptor-bearing cells of mesenchymal origin and the maternal decidua, as demonstrated by dual labelling immunofluorescence studies. Two epithelial layers of cells (amniotic and trophoblast) lack Fcγ receptors that are present in placental chorionic villi, and which may be necessary for trans-epithelial transport of IgG. The cells of these layers also contain no demonstrable endogenous IgG. These data support the hypothesis that maternally derived IgG is acquired by the fetus across the vascular system of the placenta only and not via a transamniochorion route. The demonstration of Fcγ receptors on cells of extraembryonic mesodermal lineage is a novel finding that may suggest a potential immunological role within the amniochorion. © 1994.