IgA contamination of IgG prepared on a protein A column.

When protein A is used for the isolation of IgG from pooled human serum further purification steps may be necessary since the IgG is contaminated with approximately 30% of the IgA originally present in the starting material. No preference for binding of an IgA subclass to protein A was found. In addition part of the IgG3 subclass binds to protein A.