Short communication: selective placental transport of maternal IgG to the fetus.

During pregnancy there is a dramatic reduction in the serum levels of agalactosyl IgG (G0IgG) in both normal women and those with rheumatoid arthritis. In order to determine if a similar reduction in G0IgG were apparent in fetal serum, a comparison of the galactose content of IgG from nine paired samples of umbilical vein or fetal blood and peripheral maternal serum, at gestational ages ranging from 16-41 weeks was performed. The full-term maternal IgG samples were highly galactosylated, so confirming previous observations of reduced G0IgG levels during pregnancy. In addition every paired sample of fetal IgG had a higher level of galactosylation than the corresponding maternal IgG. Therefore, during pregnancy there is both a reduced biosynthesis of the G0IgG glycoform by the mother, and a restriction of its transport across the placenta. The ratio of estimated G0IgG in fetal and maternal serum was found to be related to changes in IgG transport, and in particular the active transport of IgG1 across the placenta during gestation. Our data suggest that the placental IgG transport mechanism is either carbohydrate independent by discriminating for IgG1, or is carbohydrate dependent selecting for highly galactosylated IgG glycoforms. This study emphasizes the need for further investigations on the biological function of G0IgG in normal physiological states, in addition to disease states, such as juvenile and adult rheumatoid arthritis, where elevated G0IgG levels correlate with disease activity.