poly(I:C) and LPS induce distinct IRF3 and NF‐κB signaling during type‐I IFN and TNF responses in human macrophages

Macrophages play major roles in the onset of immune responses and inflammation by inducing a variety of cytokines such as TNF and IFN‐β. The pathogen‐associated molecular pattern, polyinosinic‐polycytidylic acid [poly(I:C)], and LPS were used to study type‐I IFN and TNF responses in human macrophages. Additionally, activation of the key signaling pathways, IFN‐regulatory factor 3 (IRF3) and NF‐κB, were studied. We found that TNF production occurred rapidly after LPS stimulation. LPS induced a strong IFN‐β mRNA response within a short time‐frame, which subsided at 8 h. The IFN‐stimulated genes (ISGs), ISG56 and IFN‐inducible protein 10, were strongly induced by LPS. These responses were associated with NF‐κB and IRF3 activation, as shown by IRF3 dimerization and by nuclear translocation assays. poly(I:C), on the other hand, induced a strong and long‐lasting (>12 h) IFN‐β mRNA and protein response, particularly when transfected, whereas only a protracted TNF response was observed when poly(I:C) was transfected. However, these responses were induced in the absence of detectable IRF3 and NF‐κB signaling. Thus, in human macrophages, poly(I:C) treatment induces a distinct cytokine response when compared with murine macrophages. Additionally, a robust IFN‐β response can be induced in the absence of detectable IRF3 activation.