Stimulation of natural interferon-alpha beta-producing cells by Staphylococcus aureus

Human peripheral blood mononuclear cells (PBMCs) produced high levels of antiviral activity, as determined by bioassay, when stimulated by Staphylococcus aureus Cowan I (SAG) and E. coli. Specific immunoassays demonstrated the presence of both TFN-alpha and gamma and, for SAG, also low levels of IFN-beta. The frequencies of SAC-induced IFN-alpha-producing cells (TPCs) were up to 1-2 per 10(3) PBMCs, These IPCs expressed the HLA-DR and CD4 antigens but not CD3, CD14, or CD19, thus resembling the natural IFN-alpha-producing cells (NIPC), The SAC was more efficient as IFN inducer when heat killed than when streptomycin inhibited, The SAC was inhibitory to virally induced IFN-alpha responses, in particular when streptomycin inhibited, Both pronase treatment and mechanical disruption of SAC cells abolished their capacity to induce IFN-alpha production, Staphylococcal strains lacking or expressing low levels of protein A (SpA) showed a decreased ability to induce IFN-alpha production, However, purified SpA did not itself induce IFN-alpha. Possibly, SpA together with other bacterial surface proteins is important for the capacity of SAC to induce IFN-alpha production in NIPC.