Interaction of Human Polyclonal IgE and IgG from Different Species with Protein A from Staphylococcus aureus: Demonstration of Protein‐A‐reactive Sites Located in the Fab2 Fragment of Human IgG

Abstract

The peptic fragments F(ab′)₂ and Fc″ of human polyclonal IgE were tested by the SpA-IgE radioimmunoassay for interaction with protein A from Staphylococcus aureus. The Fab″_2ɛ fragment but nut the Fc″ɛ fragment retained the ability to react with protein A. IgG preparations from different species were tested for their capacity to inhibit the reaction between ¹²⁵I-IgE and protein A. IgG preparations from man and the dog, pig, guinea-pig and rhesus monkey were all potent inhibitors whereas those from the rabbit, rat, sheep, horse, cow, goat and mouse were very poor inhibitors. The inhibition of the binding of ¹²⁵I-IgE to protein A by Fab′₂γ fragments, but not by Feγ fragments, suggests a novel type of interaction of protein A with immunoglobulins.