(a) Expression of genes encoding MSC components (right margin) in bronchial epithelial cells (two replicates; one per column) at various times after infection with PR8 (above columns), showing genes upregulated (yellow) or downregulated (blue) over 1.5-fold relative to their expression before infection (key). (b) Luciferase activity of 293T cells transfected with the control TK-Renilla plasmid and a firefly luciferase reporter plasmid containing the IFNB promoter, plus empty vector (EV) or vector encoding various MSC components (horizontal axis), together with plasmid encoding the amino-terminal domain of RIG-I (N-RIG-I); results are presented relative to those of the renilla luciferase control. Below, immunoblot analysis of Strep-tagged MSC proteins and FLAG-tagged N-RIG-I in total lysates of the cells above. (c,d) Viral replication in RAW264.7 cells transfected with EPRS-specific siRNA (siEPRS) or control (non-targeting) siRNA (siCtrl) (key) and infected with PR8-GFP (multiplicity of infection (MOI) = 1) (top row) or VSV-GFP (MOI = 0.5) (bottom row), assessed by fluorescence microscopy (c) and fluorescence absorbance and plaque assay (d) at 24 h after infection. PFU, plaque-forming units. (e,f) Concentration of IFN-β (e) or IL-6 (f) in supernatants of RAW264.7 cells transfected with siRNA as in c,d (key) and infected with PR8-GFP, VSV-GFP or HSV-GFP (MOI = 1) or treated with poly(I:C) (80 µg) (above plots). (g) Immunoblot analysis of phosphorylated (p-) and total (inactive) IRF3 and STAT1, and of EPRS and actin (loading control), in PR8-GFP-infected RAW264.7 cells expressing EPRS-specific (shEPRS) or non-targeting control (shCtrl) short hairpin RNA. (h–j) Fluorescence microscopy (h), fluorescence absorbance and plaque assay (i), and secretion of IFN-β or IL-6 (j) of RAW264.7 cells transfected with empty vector (Ctrl) or vector encoding EPRS and infected with PR8-GFP. Scale bars (c,h), 100 µm. *P < 0.05, **P < 0.01 and ***P < 0.001 (Student’s t-test). Data are representative of one experiment (a) or three experiments with similar results (b–j), with at least three (b–f,h–j) or two (g) independent biological replicates (mean and s.d. of triplicates in b,d,e,f,i,j).