Binding properties of protein A and protein G for human IgE

We studied the binding of protein A and protein G to human monoclonal and polyclonal IgE. An ELISA was used to measure human IgE. Protein A-Sepharose did not bind to monoclonal IgE, but bound to 12-14% of serum polyclonal IgE and to -3% of the polyclonal IgE purified from the serum. No difference in binding to protein A was found between IgE from an allergic patient and that from a non-allergic subject. Protein G bound to neither polyclonal IgE nor monoclonal IgE. Thus, protein G is better than protein A with respect to separation of IgE from IgG.