Induction of IFN-β and the Innate Antiviral Response in Myeloid Cells Occurs through an IPS-1-Dependent Signal That Does Not Require IRF-3 and IRF-7

Abstract

Interferon regulatory factors (IRF)-3 and IRF-7 are master transcriptional factors that regulate type I IFN gene (IFN-α/β) induction and innate immune defenses after virus infection. Prior studies in mice with single deletions of the IRF-3 or IRF-7 genes showed increased vulnerability to West Nile virus (WNV) infection. Whereas mice and cells lacking IRF-7 showed reduced IFN-α levels after WNV infection, those lacking IRF-3 or IRF-7 had relatively normal IFN-b production. Here, we generated IRF-3−/−× IRF-7−/− double knockout (DKO) mice, analyzed WNV pathogenesis, IFN responses, and signaling of innate defenses. Compared to wild type mice, the DKO mice exhibited a blunted but not abrogated systemic IFN response and sustained uncontrolled WNV replication leading to rapid mortality. Ex vivo analysis showed complete ablation of the IFN-α response in DKO fibroblasts, macrophages, dendritic cells, and cortical neurons and a substantial decrease of the IFN-β response in DKO fibroblasts and cortical neurons. In contrast, the IFN-β response was minimally diminished in DKO macrophages and dendritic cells. However, pharmacological inhibition of NF-κB and ATF-2/c-Jun, the two other known components of the IFN-β enhanceosome, strongly reduced IFN-β gene transcription in the DKO dendritic cells. Finally, a genetic deficiency of IPS-1, an adaptor involved in RIG-I- and MDA5-mediated antiviral signaling, completely abolished the IFN-β response after WNV infection. Overall, our experiments suggest that, unlike fibroblasts and cortical neurons, IFN-β gene regulation after WNV infection in myeloid cells is IPS-1-dependent but does not require full occupancy of the IFN-β enhanceosome by canonical constituent transcriptional factors.

Differential Replication of Pathogenic and Nonpathogenic Strains of West Nile Virus within Astrocytes

“…The host innate antiviral response plays a pivotal role in controlling WNV replication in many cell types (14,(42)(43)(44)(45)(46). This response consists of a direct IFN regulatory factor 3 (IRF-3)-dependent and an indirect IFN-dependent mechanism, which function to constrain viral replication within the infected cell and prevent viral spread to neighboring cells, respectively.…”

Use of IRF-3 and/or IRF-7 Knockout Mice To Study Viral Pathogenesis: Lessons from a Murine Retrovirus-Induced AIDS Model

“…he type I interferon (IFN) antiviral response (IFN-␣ and IFN-␤) plays a major role in host innate immunity to RNA and DNA virus infections (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12). This antiviral type I IFN response is tightly regulated, in part, by interferon regulatory factors (IRFs) via upstream signaling induction by various pattern recognition receptors (PRRs).…”

“…The inconsistent degrees of B6 genetic background in IRF-3 Ϫ/Ϫ , IRF-7 Ϫ/Ϫ , and DKO mice provide a cautionary note that results seen with these mice, in our studies and in those of others, may not be indicative solely of the knockout of the IRF gene(s) itself. The DKO mice have been bred at least three times independently from the single knockout mice, according to previous reports (3,10,13,15,35), and were previously reported to be of 91% B6 background, versus 97% for the IRF-7 Ϫ/Ϫ mice, via analysis of microsatellite markers (15). These levels of contamination are similar to the B6 background levels observed here by SNP analyses: Ͼ98% in IRF-7 Ϫ/Ϫ , 75% to 85% in IRF-3 Ϫ/Ϫ , and 80% to 90% in DKO mice.…”

West Nile virus NS2A protein facilitates virus-induced apoptosis independently of interferon response

“…: WT (n55) vs A30P (n55) (P50.0302), WT (n55) vs A30G (n55) (P50.0034), A30A' (n519) vs A30G (n55) (P50.0195), A30L (n55) vs A30P (n55) (P50.0013), A30L (n55) vs A30G (n55) (P50.0005), and A30L (n55) vs A30E (n55) (P50.0066). (d) Eight weeks old IRF3 "/" 7 "/" mice (Daffis et al, 2009) were inoculated intraperitoneally with 100 or 1000 p.f.u. of WT KUNV or mutant viruses A30A', A30L, A30P and A30G.…”