poly(I:C) and LPS induce distinct IRF3 and NF-kappaB 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-beta. 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-kappaB, were studied. We found that TNF production occurred rapidly after LPS stimulation. LPS induced a strong IFN-beta 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-kappaB 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-beta 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-kappaB signaling. Thus, in human macrophages, poly(I:C) treatment induces a distinct cytokine response when compared with murine macrophages. Additionally, a robust IFN-beta response can be induced in the absence of detectable IRF3 activation.