Fig. 1

RPMECs were susceptible to H9N2 infection. a Expression of vascular endothelial growth factor receptor 2 (VEGFr2) in the RPMECs. The RPMECs were seeded on the bottom of a glass dish and fixed with methanol-acetone. After being rinsed with PBS, the cells were incubated with a polyclonal rabbit antibody against rat VEGFr2 and a FITC-labeled goat anti-rabbit secondary antibody (green). The cell nuclei were counterstained with DAPI (blue). The left picture was a negative control that was incubated with the secondary antibody. b The expression of the AIV-specific SA2-3Gal receptor on RPMECs. The cells were incubated without lectin (negative control, left picture) or with MAA II and then stained with FITC-conjugated avidin D (green) and DAPI (blue). c Viral titers in the supernatants at 24 h post infection with the H9N2 virus with different MOIs. d Viral titers at 0, 12, 24, 36 and 48 h post infection at an MOI of 1