Distribution of the IgG Fc receptor, FcRn, in the human fetal intestine.

The intestinal Fc receptor, FcRn, functions in the maternofetal transfer of gamma globulin (IgG) in the neonatal rodent. In humans, most of this transfer is presumed to occur in utero via the placenta. Although the fetus swallows amniotic fluid that contains immunoglobulin, it is unknown whether this transfer also occurs via the fetal intestine. A human FcRn has been identified in the syncytiotrophoblast that mediates the maternofetal transfer of antibody. It has also been identified in human fetal intestine and is postulated to function in IgG transport. We hypothesize that the human fetal intestinal FcRn may play a role in IgG transport from the amniotic fluid into the fetal circulation. The aim of this study was to characterize the distribution of the FcRn along the human fetal intestine. Lysates prepared from human fetal intestine and from a nonmalignant human fetal intestinal epithelial cell line (H4) were subjected to Western blot analysis and probed using anti-FcRn antibodies. A 42-kD band, consistent with the known molecular weight of the FcRn, was detected along the human fetal intestine and in H4 cells. Expression of the human FcRn was confirmed with immunohistochemistry. Our study demonstrates the expression of FcRn along the human fetal intestine and in a human nonmalignant fetal intestinal epithelial cell line (H4), which by location indicates that FcRn could play a role in the uptake and transport of IgG in the human fetus.