IFN-α mRNA expression in local immune tissues infected with the GPE--derived viruses and with vEy-37. The IFN-α mRNA level of tonsils, spleen and mesenteric lymph nodes collected from 3 pigs per group at 120 hpi was analyzed by qPCR. The mRNA levels are shown as mean value after normalization with GAPDH mRNA content. The mean values with error bars represent the standard error. The statistical significance of the differences between the IFN-α mRNA levels 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.