Macropahge-specific Irf3 prevents viral inflammation

Viral inflammation contributes to pathogenesis and mortality during respiratory virus infections. We recently uncovered Irf3, a critical component of innate antiviral immune responses, interacts with pro-inflammatory transcription factor NF-kB, and inhibits its activity. Irf3, using this mechanism, suppresses inflammatory gene expression in virus-infected cells and mice. In this study, we evaluated the cells responsible for Irf3-mediated suppression of viral inflammation using newly engineered conditional Irf3Δ/Δ mice. Irf3Δ/Δ mice, upon respiratory virus infection, showed increased susceptibility and mortality. Irf3 deficiency caused enhanced inflammatory gene expression, lung inflammation, immunopathology, and damage, which were accompanied by increased infiltration of pro-inflammatory macrophages. Deletion of Irf3 in macrophages (Irf3-MKO) displayed, similar to Irf3Δ/Δ mice, increased inflammatory responses, macrophage infiltration, lung damage, and lethality, indicating Irf3 in these cells suppressed lung inflammation. RNA-seq analyses revealed enhanced NF-kB-dependent gene expression along with activation of inflammatory signaling pathways in infected Irf3MKO lungs. Targeted analyses revealed activated MAPK signaling in Irf3MKO lungs. Therefore, Irf3 inhibited inflammatory signaling pathways in myeloid cellsmacrophages to prevent viral inflammation and pathogenesis. To understand the role of Irf3 in macrophages in suppressing viral inflammation, we generated C57/BL6 mice with Irf3 knock out in macrophages. This was done by crossing Irf3 fl/Δ mice with LysM-Cre mice. The two groups -Irf3 fl/Δ and Irf3 fl/Δ Cre+ were then subjected to intransal inoculation of either PBS or Sendai virus (52 strain). The lung from these animals (n=3 per group) was harvested 5 days post infection, RNA was isolated and sent for gene expression analysis studies.