Interactions between mouse immunoglobulins and staphylococcal protein A.

When mouse serum or ascites is applied on protein A-Sepharose columns and washed with enough phosphate-buffered saline, a second protein peak is often eluted with the same buffer after the first major peak of unbound proteins. This second peak is almost pure Ig G1. More IgG1 plus IgG2a, IgG2b and IgG3 are thereafter eluted with acid saline. 90% of the IgG1 whichhad been eluted with neutral buffer could be re-eluted at the same retarded position with the same buffer. When a gradient from 0 to 3 M sodium thiocyanate was started after the major peak of unbound proteins, all IgG1 was eluted before IgG2 and IgG3. These results suggest that IgG1 has a much lower affinity for protein A than IgG2 or IgG3 and that normal mouse serum IgG1 can be purified by such a simple procedure.