FIG 9.

swH1N2 NA and PA genes affect early MIP-2 expression. MIP-2 expression in the BAL fluid was measured by ELISA at 24 hpi (A). Mice were intranasally infected with 5 × 10⁵ PFU of reverse genetics-derived viruses where the swH1N2 HA, NA, PA, and HNP were introduced into the huH1N1 virus along with the parental viruses. BAL fluid was collected at 24 hpi. Lung viral load was measured by TCID₅₀ on BALB/c mice infected with reverse genetics-derived viruses or the parental swH1N2 and huH1N1 viruses. Viral titers were determined at 12 and 24 h postinfection (B). All data are representative of three individual experiments. Asterisks (*) denote significance related to the pH1N1 parental virus while number signs (#) represent P values significant compared to the swH1N2 parental virus. Results were considered significant with P values of ≤0.05 (*/#), ≤0.01 (**/##), and ≤0.001 (***/###).