Induction of human gamma interferon by protein A fromStaphylococcus aureus

Abstract

Protein A from Staphylococcus aureus (SpA) has been observed to stimulate the production of human gamma interferon (HuIFN γ) by peripheral blood mononuclear cells (MNC). Dose-response experiments showed donor-to-donor variation in the concentration of SpA required for maximum IFN production although 50 μ g/ml consistently produced near peak IFN γ titers for each donor. Kinetic studies revealed that peak IFNγ production occurred 24 hr after SpA stimulation. Physicochemical and antigenic characterization showed that SpA-induced IFN possessed the characteristics of IFN γ in that it was inactivated by treatment at pH 2, heating at 56 C and anti-HuIFN γ serum but not by anti-HuIFN α serum. Further studies showed that maximum IFN γ production could be achieved by stimulating 5 × 10⁶ MNC/ml and IFN γ could be harvested for 3 successive days by removing IFNγ-containing supernatant fluids and adding fresh medium to stimulated MNC cultures. Preliminary cell fractionation studies suggest that the mononuclear cell that produces IFN γ after SpA stimulation is a nonadherent lymphocyte that lacks high affinity receptors for sheep erythrocytes and expresses Fc receptors for IgG. Moreover, unlike other mitogen inducers, SpA appears to be less dependent on the presence of macrophages for IFNγ production.