Growth kinetics and IFN-α/β production after infection of swine cells with the GPE--derived viruses. Swine SK-L cells were inoculated at an MOI of 0.1 TCID50 per cell with the indicated viruses and incubated at 37 °C in the presence of 5% CO2. The supernatants were collected at 0, 16, 24, 48, 72, 96, 120, 144 and 168 hpi. Virus titers were determined in duplicate in SK-L cells and expressed as TCID50/mL, and IFN-α/β bioactivity was measured in duplicate using the SK6-MxLuc reporter cells. These data were compared with vGPE- and vGPE-/N136D (A), and with vGPE-/T830A; V2475A; A2563V and vGPE-/N136D; T830A; V2475A; A2563V (B). Each curve and bar presents the mean from three independent infections, with error bars showing the standard errors. The significance of the differences between was calculated using the Student’s t test. * indicates p < 0.05 between vGPE- and vGPE-/N136D. # indicates p < 0.05 between vGPE-/T830A; V2475A; A2563V and vGPE-/N136D; T830A; V2475A; A2563V.