The IgG and Transferrin Receptors of the Human Syncytiotrophoblast Microvillus Plasma Membrane*

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Abstract
Fcγ receptor activity has been demonstrated using a radioisotopic assay on human syncytiotrophoblast microvillus plasma membrane (StMPM) vesicle preparations isolated from normal full‐term placentas. Prior chaotropic extraction to remove extrinsic membrane protein from StMPM preparations was shown to increase radiolabeled IgG uptake by up to 30%. Polyacrylamide disc gel electrophoresis (PAGE) has been used to indicate that the StMPM receptor for transferrin solubilizes in 1% sodium deoxycholate and retains its binding activity for transferrin. Quantitative data for both Fcγ and transferrin receptors obtained following study of isolated StMPM preparations are summarized. Current concepts for the potential role of trophoblast Fey and transferrin receptors in the mechanisms of transplacental passage of IgG and iron, respectively, from mother to fetus are illustrated and discussed.