Stimulation of Natural Interferon-α/β-Producing Cells byStaphylococcus aureus

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Abstract
Human peripheral blood mononuclear cells (PBMCs) produced high levels of antiviral activity, as determined by bioassay, when stimulated by Staphylococcus aureus Cowan I (SAC) and E. coli. Specific immunoassays demonstrated the presence of both IFN-α and γ and, for SAC, also low levels of IFN-β. The frequencies of SAC-induced IFN-α-producing cells (IPCs) were up to 1–2 per 103 PBMCs. These IPCs expressed the HLA-DR and CD4 antigens but not CD3, CD14, or CD19, thus resembling the natural IFN-α-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-α responses, in particular when streptomycin inhibited. Both pronase treatment and mechanical disruption of SAC cells abolished their capacity to induce IFN-α production. Staphylococcal strains lacking or expressing low levels of protein A (SpA) showed a decreased ability to induce IFN-α production. However, purified SpA did not itself induce IFN-α. Possibly, SpA together with other bacterial surface proteins is important for the capacity of SAC to induce IFN-α production in NIPC.

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