Enhanced susceptibility to IAV in TLR3-mutated fibroblasts, and rescue by WT TLR3. (A) IAV replication, quantified by plaque assays, in SV40-fibroblasts from three CTLs, P3, P554S/WT, TLR3^−/−, IRF7^−/−, and STAT1^−/− patients, 1, 8, 12, 24, and 36 h after infection at a MOI of 10. Cells were untreated or subjected to pretreatment with IFN-α2b, IFN-β, or IFN-λ for 16 h before infection. The data shown are representative of three independent experiments, with biological duplicates in each experiment. (B) Production of IFN-β and IFN-λ in the absence of infection or after 24 h of infection with IAV at a MOI of 1, in SV40-fibroblasts from seven CTLs, P2, P3, a TLR3 P554S/WT HSE patient, TLR3^−/−, IRF7^−/−, and NF-κB essential modulator (NEMO)–deficient patients, as assessed by ELISA. (C) Production of IFN-β and IFN-λ in the absence of infection or after 24 h of infection with IAV at a MOI of 5 or 10, in SV40-fibroblasts from a CTL and P3, without plasmid transfection or after transfection with Luc, Flag-tagged WT TLR3, and in fibroblasts from a TLR3^−/− patient. (D) IAV replication, quantified by plaque assays, in SV40-fibroblasts from two CTLs and P3, without plasmid transfection or after transfection with Luc, Flag-tagged WT TLR3, and in fibroblasts from a TLR3^−/− patient, 1, 8, 12, 24, and 36 h after infection at a MOI of 5. Mean values ± SD from five (B) or three (C and D) independent experiments are shown. Biological duplicates were tested in each experiment. **, P < 0.01; ***, P < 0.001.