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

Abstract

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