Dynamics of immunoglobulins at the feto-maternal interface.

Transplacental transport of maternal immunoglobulin G (IgG) to the developing fetus is extremely important in the protection of the newborn from infection. Although the exact mechanisms of the selective and active transfer of IgG across the placental barrier are not fully understood, receptors for the Fc part of IgG (FcgammaRs) in the placenta are believed to play a key role. Several known Fc receptors, FcgammaRI, FcgammaRII, FcgammaRIII and FcRn (neonatal FcR), demonstrate heterogeneous expression patterns in placenta. Immunohistochemical analysis shows the expression of FcgammaRI on Hofbauer cells in stromal tissue, FcbetaRII on Hofbauer cells and fetal blood endothelium, FcgammaRIII on Hofbauer cells and trophoblasts, and FcRn on syncytiotrophoblasts and endothelial cells. Recent studies provide evidence for important associations among these receptors and transcytosis of IgG, as well as scavenger mechanisms for clearing immune complexes in the placenta during pregnancy.