[HTML][HTML] Noncanonical placental Fc receptors: What is their role in modulating transplacental transfer of maternal IgG?

DR Martinez, GG Fouda, X Peng, ME Ackerman… - PLoS …, 2018 - journals.plos.org
PLoS pathogens, 2018journals.plos.org
The transplacental transfer of maternal Immunoglobulin G (IgG) to the fetus is critical for
protection against infectious diseases in the first year of life [1]. Maternal protective IgG is
transferred from the maternal to the fetal circulatory system via the placenta, and this process
begins in the first trimester of pregnancy [2]. By 37–40 weeks of gestation, maternal
passively acquired IgG concentrations in newborns can exceed maternal IgG serum levels
in normal pregnancies [3–7]. Yet, the molecular mechanisms of transplacental transfer of …
The transplacental transfer of maternal Immunoglobulin G (IgG) to the fetus is critical for protection against infectious diseases in the first year of life [1]. Maternal protective IgG is transferred from the maternal to the fetal circulatory system via the placenta, and this process begins in the first trimester of pregnancy [2]. By 37–40 weeks of gestation, maternal passively acquired IgG concentrations in newborns can exceed maternal IgG serum levels in normal pregnancies [3–7]. Yet, the molecular mechanisms of transplacental transfer of maternal IgG remain poorly understood. In order to reach the fetal circulatory system, maternal IgG must traverse three distinct placental anatomical barriers:(1) the syncytiotrophoblast cell barrier,(2) the villous stroma containing placental fibroblasts and Hofbauer cells, and (3) fetal endothelial cells. It is well established that IgG crosses the syncytiotrophoblast by binding to the canonical IgG shuttle receptor: Fragment crystallizable (Fc) receptor neonatal (FcRn)[2, 8]. However, how maternal IgG traverses the subsequent placental barriers is not completely understood, as they do not express FcRn, yet recent RNAseq analyses have shown that Fcγ receptors, including FcγRIIIa, FcγRIIa, FcγRIIb, and FcγRI, are expressed in term placentas [9]. However, it should be cautioned that it is not yet known if these noncanonical placental FcRs play a role, if at all, in the transplacental transfer of maternal IgG. A deeper understanding of the molecular mechanism (s) of IgG binding to placentally expressed Fc receptors could be important (1) for the design of novel maternal IgG-based therapeutics and vaccines with optimal transplacental transfer efficiency, with the ultimate goal of increasing infant protection against congenital and neonatal infectious diseases, and (2) to optimize the Fc region of immunomodulatory IgG monoclonal antibody therapeutics for blunted transplacental transfer to potentially reduce the transplacental transport of maternal self-reactive IgG in women with autoimmune disorders.
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