Isolation and characterization of an Fc receptor from neonatal rat small intestine.

Receptors for the Fc region of IgG from neonatal rat intestinal brush borders were solubilized using 3-[(3-cholamidopropyl)dimethyl-ammonio]-1-propane sulfonate and purified by affinity chromatography. Analysis of IgG-binding material by sodium dodecyl sulfate-polyacrylamide gel electrophoresis under reducing conditions reveals two components with apparent Mr of 41 000-50 000 and 15 000. The larger component is glycosylated and may dimerize, giving a 100-110-kDa band on nonreduced gels. Both proteins are localized in the proximal small intestine, where IgG is specifically taken up during the first three weeks of neonatal life, and disappear when specific transport stops after weaning. Electron irradiation of brush borders shows that the functional unit for IgG binding has a molecular weight in situ of 110 kDa. These data suggest that a dimer of the 41-50-kDa protein together with the 15 kDa and other proteins may mediate intestinal transport of maternal IgG.