Fcγ‐receptor activity in the developing human placenta

Abstract

The expression of Fey receptors (FcγR) and annexin II in 20 placentae (range 8–27 weeks' gestation) and in 3 full‐term placentae was studied using monoclonal antibodies (mAbs) and soluble immune complexes. Functionally active FcyR was detected on the trophoblast, endothelial cells, and stromal cells (Hofbauer cells) from the 8th week of gestation. FcγRI (mAb 32.2) and FcγRIII (mAb 3G8) were detected only on Hofbauer cells, whereas FcγRII (IV3 and C1KM5) were detected both on Hofbauer cells and endothelial cells. FcγRIII (anti‐Leu‐lib) and the IgG‐binding molecule annexin II (mAb B1D6) were expressed by Hofbauer cells, endothelial cells, and the trophoblast. There was some variation in staining among the different specimens, but the number of positive cells as well as the staining intensity increased from the first to the second trimester. In first trimester placenta, staining was localized both to the syncytio‐ and cytotrophoblast, with the strongest intensity in the cytotrophoblast and at the boundary between the two cell layers. In second and third trimester placenta, staining was localized to the syncytiotrophoblast. The localization and distribution of FcγR on the trophoblast during ontogeny is of interest with regard to its presumed role in the transport of IgG from mother to fetus.

Estrogen Targets Genes Involved in Protein Processing, Calcium Homeostasis, and Wnt Signaling in the Mouse Uterus Independent of Estrogen Receptor-α and -β

“…Since estrogen is an absolute requirement for implantation in mice, it is possible that one of the actions of estrogen in implantation is to induce CalM via a non-ER pathway. CalP is localized in the syncytiotrophoblast cells in the developing human placenta and possesses Fc gamma receptor activity, suggesting its role in immunomodulation (60). Uterine CalP expression by estrogen may have a role in local immunomodulation.…”

Human placental Fcγ‐binding proteins in the maternofetal transfer of IgG

“…FcRII is expressed on Hofbauer cells and on endothelial cells in a punctuate pattern (194,179,300,198,348,43). mRNA of one isoform of FcRII, hFcRIIc, has been detected on iso- (194,333,179,300,198,255,348,40,41,310).…”

“…FcRIII is expressed on Hofbauer cells (194,179,300,348,43), and on syncytiotrophoblasts (194,333,179,348,43,41). In first trimester placenta, FcRIII was present in both cytoand syncytiotrophoblasts, and in term placenta at the apical aspect of syncytiotrophoblasts (348,43,41,310). In term syncytiotrophoblast, it appears that the transmembraneous FcRIIIa isotype and not the GPI-linked receptor is expressed, although the latter has been demonstrated in first term trophoblast (348).…”

“…FcRIIIa mediates phagocytosis through the y and subunits (154), but there are no reports on expression of these FcRIII subunits on syncytiotrophoblasts. Interestingly, antibody-enhancement of HIV-1 infection in cultured human term cytotrophoblast cells has been partly inhibited using mAb to FcRIII (335) Some studies also report on the presence of FcRIII on chorionic endothelial cells not corroborated by others (194,348,310). However, these studies employed the anti-Leullb, and there is some uncertainty on the identity of the placental antigen for this mAb (348).…”

Expression of placental alkaline phosphatase does not correlate with IgG binding, internalization and transcytosis

“…However, in the third trimester, the number of cytotrophoblasts is greatly reduced and the feto-maternal barrier then consists of the syncytiotrophoblast and the fetal capillary endothelium [5]. Although Fc receptors have been localized in syncytiotrophoblast as well as in fetal endothelial cells [4,[6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25]], the precise mechanism by which IgG crosses the term placenta is not fully understood.…”