Fig. 5.

Effect of granulocyte/macrophage colony-stimulating factor (GM-CSF) overexpression during influenza A virus (IAV) infection on lung epithelial permeability was examined using FITC-dextran. Airway GM-CSF-overexpressing transgenic (DTGM) or littermate control (LM) mice were infected with IAV, and doxycycline was administered in drinking water starting at 3 days postinfection. At 10 days postinfection, mice were tracheotomized, received FITC-dextran via the tracheostomy needle, and were ventilated for 15 min. Serum FITC-dextran levels were measured by spectrophotometry in uninfected LM (△) and DTGM (▲) mice and at 10 days postinfection in LM (○) and DTGM (●) mice. GM-CSF overexpression in the absence of IAV infection significantly increased lung permeability (*P < 0.05). While IAV infection increased lung permeability compared with uninfected LM mice (**P < 0.01), in IAV-infected animals (○ and ●), GM-CSF overexpression did not affect serum levels of FITC-dextran.