NS1 mutation affects the expression of IFN-β, and RSV N and NS1 mRNAs. A549 cells were infected with either NS1F, NS1F-ELCmut, ΔNSI, or mock infected, and total RNA was extracted 24h p.i. The levels of mRNA encoding (a) IFN-β or (b) RSV N were measured by RT-qPCR. (c) The ratio of IFN-β to RSV N mRNA was calculated. (d) The expression of NS1 mRNA was also measured by RT-qPCR. The level of expression of each mRNA was calculated using the 2 -ΔΔCt formula in relation to mock-infected samples, and was normalised to β-actin. The ratio of IFN-β/N mRNA was significantly higher in cells infected with NS1F-ELCmut and ΔNS1F compared to NS1F (* P < 0.01, ** P = 0.038).