Staphylococcal protein A (SpA) does not induce production of interferon-gamma in human mononuclear blood cells

Preparations of protein A (SpA) from Staphylococcus aureus and low-molecular-weight SpA induce production of interferon-gamma (IFN-gamma) and are potent mitogens when added to human lymphocytes. The IFN-gamma-inducing and main mitogenic activity of these preparations can be separated from SpA by gel filtration and affinity chromatography. These activities can also be partially inhibited by antiserum to staphylococcal enterotoxin A (SEA) in a specific manner. It is concluded that the IFN-gamma-inducing activity and most of the mitogenic activity of SpA preparations are not attributable to intact or low-molecular-weight fragments of SpA but depend on the presence of SEA and other non-SpA products in the preparations of SpA.