Fig. 6

The NS1 E152/E153 residues confer the in vivo pathogenicity of IAV infection. A The growth curve of recombinant IAV WT virus (PR8) and NS1 E152A/E153A virus (PR8) in MDCK cells. Values represent the mean ± SD of duplicate samples. NS stands for “not significant” (Student’s t-test). Data are representative of three experiments. B, C Mice were infected with WT virus (50 PFU; n=10) or NS1 E152A/E153A virus (50 PFU; n=10) by intranasal (i.n.) infection. The percentage of weight loss (B) and survival rates (C) of mice were monitored daily for 14 days. The weight loss difference between the two groups of mice was statistically significant (***P < 0.0001 by two-way ANOVA). Values represent the mean ± SEM. Kaplan-Meier survival curves of the two groups were statistically significant (**P<0.01 by Log-rank (Mantel-Cox) Test). D-G Mice were infected with WT virus (1000 PFU; n=3) or NS1 E152A/E153A virus (1000 PFU; n=3) by i.n. infection. Lung viral titers of infected mice were measured on day 3 postinfection by plaque assay and analyzed by the Mann-Whitney U test (D). The production of IFN-β (E), IFN-α (F), and IL-6 (G) in lung homogenates was determined by ELISA. Values represent the mean ± SEM. *P < 0.05, and NS stands for “not significant” (Student’s t-test). H-K Mice were infected with WT virus (50 PFU; n=3) or NS1 E152A/E153A virus (50 PFU; n= 4) by i.n. infection. Like panels D-G, viral titers and cytokines were measured on day 7 postinfection by plaque assay and ELISA