Figure 5: Infection and replication of H7N9 viruses with different PB2 genotypes in mice.
(a) Groups of mice were infected with 25 μl inoculums containing 104, 105 or 106 PFU of reverse genetic versions of viruses, as specified. Mice were observed daily for changes in body weight for 14 days (day 0 to day 14). Animals that lost >25% of their pre-infection weight were euthanized, in accordance with our institutional animal ethics guidelines. The MLD50 values were calculated by the method described by Reed and Muench56. To test virus replication in mice, groups of nine BALB/c mice were each inoculated intranasally with 2.25 × 104 PFU (25 μl) of H7N9 recombinant virus containing PB2-526R/627K, PB2-627K, PB2-526R/701N, PB2-701N, avian-PB2, avian-PB2-526R or with a wholly reverse genetic version of avian H7N9 virus (avian RG). Results compare the mean percentage weight loss or gain for groups of mice infected with 627K or 526R/627K viruses or administered PBS (control) (b), 701N or 526R/701N viruses or PBS control (c) and avian RG, avian-PB2 or avian-PB2-526R viruses or PBS control (d); error bars represent s.d. The fractional number labels within the graphs indicate the number of surviving mice in each of the groups at the end of the experiment. Three mice from each of the groups infected with viruses carrying 627K or 526R/627K (a, right panel), 701N or 526R/701N (b, right panel) or with RG avian H7N9 virus, avian-PB2 or PB2-526R in the backbone of a human isolate (A/Zhejiang/DTID-ZJU01/2013) were killed at 72 h post infection. Lung tissues were removed and homogenated for estimation of virus replication by the plaque assay. The values displayed represent the log10 mean titres±s.d. Statistical significance was calculated by one-way analysis of variance, corrected by the Bonferroni post-test: **P<0.01 and *P<0.05. d.p.i., days post infection.
