Fig. 2

Effects of the PB1-S216G mutation on virus replication and virulence in mice. a Growth curves for the PR8, PR8^PB1(S216G), PR8^PB1(I563R), PR8/TW126^PB1(G216S), and PR8/TW126^PB1 viruses in MDCK cells at 12–42 h post-infection. b Virus titers in lung tissue homogenates from 18 female BALB/c mice infected PR8, PR8^PB1(S216G), PR8/TW126^PB1(G216S), and PR8/TW126^PB1 viruses at 72 h post-infection were determined by plaque assay. Error bars, standard error of the mean of three independent experiments; NS, not significant (p > 0.05) by Student’s t-test for (a-b). c Groups of 18 female BALB/c mice at 6 weeks of age were challenged by infections of PR8, PR8/TW126^PB1, PR8/TW126^PB1(G216S), PR8^PB1(S216G), or PR8^PB1(I563R). Survival rates of the infected mice were recorded daily for 14 days. Log-rank (Mantel–Cox) test was used to confirm the statistically significant differences in survival rate. *#p = 0.032; *p = 0.0258; **p = 0.0048; and ****p < 0.0001