FIG 1 .

The pandemic 2009 H1N1 and H1N1 viruses from the 1930s are resistant to TRIM22 restriction. (A) Control and human TRIM22-transduced MDCK cells were infected with H1N1 strains at an MOI of 0.001. Viral titers were measured in supernatants harvested 24, 48, and 72 hpi by plaque assay, indicated as plaque-forming units (PFU). As a positive control for TRIM22 restriction activity, A/New Caledonia/20/99 (sH1N1) and two additional seasonal H1N1 strains, A/USSR/90/77 and A/Paris/1149/2008, were used to infect TRIM22-overexpressing MDCK cells. Viral titers are expressed as the means ± standard errors of the means (SEM) from three experiments performed in duplicate. P values were determined using two-way ANOVA (*, P < 0.05; ***, P < 0.001). (B) Total cell extracts from control and TRIM22-overexpressing MDCK cells infected with different H1N1 strains were analyzed by Western blotting, and viral NP expression levels were evaluated. TRIM22 expression was also examined, and β-actin was used as a normalizer. These results are representative of one out of three independent experiments.