Enhanced influenza A viral resistance in cultured fibroblasts isolated from transgenic pigs. (A) Ear fibroblasts isolated from Mx1 transgenic pigs and age-matched controls were infected with influenza A virus PR8 or NIBRG-14. After 24 hours, cells were fixed and stained for NP expression (red: NP, blue: nuclei; 4 × magnification). (B) Quantification of NP-positive cells. Values represent the mean ± s.d., n = 3. *P < 0.01 compared with the non-transgenic group.