Measurement of the binding activity of defined IgG aggregates to macrophage Fc receptors

Abstract

Small soluble IgG aggregates of defined size were prepared from pooled human IgG by gel filtration chromatography, and examined by analytical ultracentrifugation. Three such fractions, dimer-rich, trimer-rich and 25S aggregate were used to inhibit IgG monomer binding in a study of the influence of aggregation in the binding of human IgG1 to mouse macrophage Fc receptors. Of the polymers tested, IgG in the trimeric form was found to bind with the greatest avidity, being 158 times more active than monomeric IgG, whereas IgG as a larger 25S aggregate had an increased binding activity of 80 times; the avidity of IgG as dimer was increased by a factor of 2 over monomeric IgG. The possible mechanisms involved in achieving enhanced binding are discussed.