Comparative catabolic rates of anti-hapten IgG antibodies of different affinities

Abstract

Rabbit IgG anti-fluorescyl antibodies were purified from immune antisera by immunoadsorption into subpopulations on the basis of affinities for the homologous ligand. Low and high affinity populations from individual rabbits were radioiodinated in dual-isotope studies. Antibodies, in approximately equal concentrations, were passively administered simultaneously (intravenously) to the same rabbit from which the antibodies were derived (i.e. autologous). Rate of decay studies showed that high affinity antibodies were catabolized 2–3 times faster than low affinity antibody molecules. Pepsin digestion experiments inferred that the F c fragment was responsible for different catabolic rates. It is proposed that differences in the carbohydrate content of F c fragments of IgG molecules with differing affinities for the fluorescyl ligand, are important in determining catabolic rates. This proposal is consistent with previous studies which showed that low and high affinity antibody molecules differ qualitatively and quantitatively in their carbohydrate content (Mitchell et all., 1976).