Endothelial Expression of Fc Gamma Receptor IIb in the Full-term Human Placenta

In the third trimester, human placental endothelial cells express Fc gamma receptor IIb (FcγRIIb). This expression is unique because FcγRIIb is generally expressed on immune cells and is typically undetectable in adult endothelial cells. Recently, we found a novel FcγRIIb-defined, IgG-containing organelle in placental endothelial cells; this organelle may be a key structure for the transcytosis of IgG across the endothelial layer. In this study, we verify the expression of FcγRIIb in endothelial placenta cells and use reverse transcriptase-polymerase chain reaction (RT-PCR) and sequencing analyses to define the expressed FCGR2B mRNA transcript variant. We also investigated the distribution of FCGR2B mRNA and protein within the vascular tree of the full-term human placenta by RT-PCR and quantitative microscopy. The mRNA sequence of FCGR2B expressed specifically in placental endothelial cells is that of transcript variant 2. FcγRIIb expression and synthesis occur throughout the placental vascular tree but do not extend into the umbilical cord. This study provides additional information on FcγRIIb expression in the human placenta.