IMMUNOGLOBULIN-G BINDING-SITES ON THE HUMAN FETAL INTESTINE - A POSSIBLE MECHANISM FOR THE PASSIVE TRANSFER OF IMMUNITY FROM MOTHER TO INFANT

In humans, the prenatal transfer of IgG from mother to foetus is facil itated by a receptor for IgG on the placenta. However, amniotic fluid contains IgG of maternal origin, and transfer of swallowed IgG into th e circulation from the foetal intestine represents another potential p athway of passive immunization. In this study we assayed for a foetal intestinal IgG receptor to support the hypothesis of this alternate pa thway of antibody transfer. Microvillous membrane (MVM) from small bow el of aborted foetuses (18 weeks gestation) were probed with [I-125]Ig G to detect specific IgG binding sites. Binding was pH dependent and w as maximal at pH 6. Competitive inhibition of the binding of [I-125]Ig G was noted with the addition of increasing amounts of unlabelled IgG. Scatchard analysis showed one binding site with a dissociation consta nt of 1.58 x 10(-7), similar to that of the IgG receptor described on the suckling rat intestine. The binding of labelled IgG to the human M VM receptor was Fc mediated. These observations provide evidence for a n Fc receptor on the human foetal intestine.