The rapid isolation of ribonuclease-free immunoglobulin G by protein A-sepharose affinity chromatography.

A rapid method is described for the simultaneous removal of contaminant ribonuclease activity and isolation of immunoglobulin G from fractionated or whole serum using insolubilized protein A. Protein A, isolated from the Cowan I strain of Staphylococcus aureus, was covalently attached to Sepharose CL-4B resin and used as a specific affinity absorbent for immunoglobulin G. Affinity column-purified immunoglobulin G preparations were examined for the presence of contaminating serum proteins, retention of antibody activity, and retention of antigenic properties. Following chromatography on protein A-Sepharose, immunoglobulin G preparations were devoid of contaminating serum proteins, in particular ribonuclease activity, that are not normally removed using conventional techniques of salt precipitation in combination with ion-exchange chromatography. There was no significant alteration of either antibody activity or antigenic properties of protein A-Sepharose purified immunoglobulin G.