Immunobiology of the human placenta. I. IgGFc receptors in trophoblastic villi.

Qualitative and quantitative studies were performed on IgGFc receptors in the trophoblastic villi of human placentae ranging in gestational age from less than 4 weeks to full term. IgGFc receptors were detected on cells of the syncytiotrophoblast (ST) using two different assay systems; EA rosette formation and direct immunofluorescence with deaggregated human IgG. The ST IgGFc receptors had high affinity for native IgG molecules (deaggregated IgG) as well as affinity for antigen-antibody complexes (EA). The receptors for deaggregated IgG were present on a majority of ST cells in first and second trimester trophoblast, but were significantly less frequent on ST cells in older placentae. Similar receptors also were detected on cells lining some fetal vessels in the trophoblastic villi. Not only were the IgGFc receptors expressed on ST cells, but in vivo bound IgG was detected in association with the ST and the two patterns of IgG binding were essentially identical. In contrast to the qualitative nature of the receptors on ST cells, cells in the stromal (central) region of the trophoblastic villi expressed IgGFc receptors that had high affinity for EA but failed to bind the deaggregated IgG except at a high concentration. The results are discussed with respect to the possible role of the IgGFc receptors in the specific transfer of IgG from maternal to fetal circulations.