When WT mice were infected with 1.0 LD50 of PR8 and then treated intranasally with GM-CSF, there was a significant increase in the concentration of GM-CSF in the blood of PR8-infected mice only three hours after treatment with GM-CSF at 3 and 6 days post-infection indicating that lung injury induced by influenza infection induces a porous lung that facilitates the escape of GM-CSF from alveolar space (Fig 4A). This evidence concerns the gene CSF2 and influenza.