Contribution of Interferon-β to the Murine Macrophage Response to the Toll-like Receptor 4 Agonist, Lipopolysaccharide

Interferon-β (IFN-β) has been identified as the signature cytokine induced via the Toll-like receptor (TLR) 4, “MyD88-independent” signaling pathway in macrophages stimulated by Gram-negative bacterial lipopolysaccharide (LPS). In this study, we analyzed the responses of macrophages derived from wild-type (IFN-β+/+) mice or mice with a targeted mutation in IFN-β (IFN-β-/-) to the prototype TLR4 agonist, Escherichia coli LPS. A comparison of basal and LPS-induced gene expression (by reverse transcription-PCR, real-time PCR, and Affymetrix microarray analyses) resulted in the identification of four distinct patterns of gene expression affected by IFN-β deficiency. Analysis of a subset of each group of differentially regulated genes by computer-assisted promoter analysis revealed putative IFN-responsive elements in all genes examined. LPS-induced activation of intracellular signaling molecules, STAT1 Tyr-701, STAT1 Ser-727, and Akt, but not p38, JNK, and ERK MAPK proteins, was significantly diminished in IFN-β-/-versus IFN-β+/+ macrophages. “Priming” of IFN-β-/- macrophages with exogenous recombinant IFN-β significantly increased levels of LPS-induced gene expression for induction of monocyte chemotactic protein 5, inducible nitric-oxide synthase, IP-10, and IL-12 p40 mRNA, whereas no increase or relatively small increases were observed for IL-1β, IL-6, monocyte chemotactic protein 1, and MyD88 mRNA. Finally, IFN-β-/- mice challenged in vivo with LPS exhibited increased survival when compared with wild-type IFN-β+/+ controls, indicating that IFN-β contributes to LPS-induced lethality; however, not to the extent that one observes in mice with more complete pathway deficiencies (e.g. TLR4-/- or TRIF-/- mice). Collectively, these findings reveal unanticipated regulatory roles for IFN-β in response to LPS in vitro and in vivo.