H7N9 NS1 S212P mutation causes a decrease of its ability to suppress RIG-I expression and STAT1 activation. A, B 293T cells transfected with plasmids expressing H7N9 NS1-WT (WT), NS1-S212P (S212P) or EV were infected with WSN (A) or PR8 delNS1 virus (B) (MOI = 1) for 12 h, followed by quantitative real-time PCR to detect RIG-I mRNA levels. In each experiment, the RIG-I level in mock-infected cells was normalized to 1. Plotted are the average levels from three independent experiments. The error bars represent the s.e.m. (C, D) 293T cells transfected with plasmids expressing H7N9 NS1-WT (WT), NS1-S212P (S212P) or EV were infected with WSN (C) or PR8 delNS1 virus (D) as described in (A, B), then cells were harvested and cell extracts were prepared for Western blotting using indicated antibodies. The results are representative of three independent experiments. *P < 0.05, **P < 0.01.