Fig. 3.
The PB2-D253N mutation of H9N2/Y280 virus causes more weight loss but not virus replication in mice. Female BALB/c mice were infected intranasally with 1 × 105 PFU of H9N2/Y280 or the D253N mutant in PB2. A The weights of the infected mice were expressed as the percentage change compared with the weight at day 0. Results from each time point are expressed as means ± standard deviations of eight mice. B The nasal wash and C lungs were harvested for viral titration at 3 and 6 days postinoculation. Lungs were homogenized in 1 mL PBS, and 200 μL PBS was used as a nasal wash. The results from each group are represented by the average titers of three mice. The viral titers were determined by calculating the TCID50 in MDCK cells. Results from each time point were expressed as means ± standard deviations. *P < 0.05.