Differential binding properties of protein A and protein G for dog immunoglobulins.

We studied the binding of dog immunoglobulins G, A, M and E to protein A and protein G. Passive cutaneous anaphylaxis (PCA) testing was used for the measurement of dog IgE and enzyme-linked immunosorbent assays (ELISA) were used for the measurements of dog IgG, IgA and IgM. Protein A from lyophilized cells of Staphylococcus aureus bound 97% of IgE, 98% of IgG, 81% of IgA, and 97% of IgM. Protein A-Sepharose CL-4B bound 87% of IgE, 100% of IgG and IgA, and 98% of IgM. In a stepwise elution with varying pH, a small amount of IgE was eluted at pH 5 and pH 6 and all the remaining Igs were eluted at pH 3 from the protein A column. In contrast to protein A, dog IgE was not bound to Protein G-Sepharose, while 100% of IgG, 95% of IgA, and 44% of IgM were bound to Protein G-Sepharose.