Differential expression of Fc gamma receptor II in the human placenta

Abstract

Human macrophages express Fc gamma receptor II (FcγRIIa, FcγRIIb, and FcγRIIc). While FcγRIIa mediates phagocytosis, FcγRIIb negatively regulates the phagocytic signaling pathway. In this study, we investigated the expression of FcγRIIa/c and FcγRIIb in the human placenta during gestation by immunohistochemistry. Human first-trimester and full-term placentas were obtained according to a protocol approved by the Nippon Medical School Hospital Ethics Committee. Anti-peptide antibodies to human FcγRIIa/c and FcγRIIb were produced. FcγRIIb was present exclusively in fetal endothelial cells labeled with anti-CD31 and not in the syncytiotrophoblast, macrophages, or other stromal cells in placental chorionic villi. Endothelial FcγRIIb expression was much higher in full-term than in first-trimester placenta. In contrast, FcγRIIa/c was expressed specifically in placental macrophages (i.e., Hofbauer cells) labeled with anti-CD14, whereas other types of cells displayed no staining in the placental chorionic villi. Hofbauer cells constitutively lack the expression of FcγRIIb during gestation. But instead of Hofbauer cells, placental endothelial cells express FcγRIIb. This expression is unique because FcγRIIb is typically undetectable in adult endothelial cells. The results may provide new clues for understanding of FcγRII function in placental immunology.