Studies on the immunoglobulin-G Fc-fragment receptor from neonatal rat small intestine

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Abstract
A method for preparing this small-intestinal brush-border membrane of neonatal rats was described in which enzymic methods were used to remove associated polysaccharide and cell nuclei. 125I-labeled Ig(immunoglobulin)G and 125I-labeled IgG Fc fragment had high specific binding and low non-specific binding to brush borders prepared in this way. F(ab)''2 fragment did not bind, indicating the existence of a specific receptor for the Fc fragment of IgG. The receptor system was saturable, and the affinity (KA) for the binding of rat IgG was determined by equilibrium and kinetic methods. Binding of heterologous IgG species (human and bovine) was compared and demonstrated close similarity between human IgG and rat IgG in their receptor affinities. Kinetic results were presented that are consistent with previously proposed models of ligand-induced receptor aggregation.