Protein A is a bacterial protein derived from Staphylococcus aureus. Protein A has a binding site for the Fc portion of mammalian IgG allowing it to bind with high affinity to human IgG1 and IgG2, as well as mouse IgG2a and IgG2b. The capacity of Protein A to bind antibodies with high affinity allows for large-scale antibody production. The protein A used for production of antibodies is most commonly bound to a stationary phase chromatography resin. Other uses of Protein A include, serving as a non species-specific reagent for binding primary antibodies or surface IgG in mammalian tissues, as well as preparing isotypically pure IgG from certain species.