PA-X reduces activation of a MAVS-dependent pathway. Wild-type and Mavs−/− mice were infected with 50,000 pfu of PR8 WT, PR8 FS or mock infected via the intranasal route. Mice were weighed every 24 h and sacrificed 48 h.p.i. (A) Weight loss in mice infected with PR8 WT and PR8 FS. Data are represented as mean weight loss ± s.e.m and are from 3 (mock) and 9–10 (infected) mice per group, pooled from two independent experiments. (B) Levels of Ifnb1 and Ifna4 mRNA in the lung were measured by qRT-PCR. Data are represented as expression relative to the housekeeping gene Gapdh ± s.e.m. and are from 11–16 (mock) and 18–24 (infected) mice per group and are pooled from five independent experiments. (C) Expression of the IAV M RNA was measured by qRT-PCR. Data are from 7 (mock) and 13–14 (infected) mice per group ± s.e.m and are pooled from three independent experiments. (D) Viral loads in the right lungs of infected mice were determined using a TCID50 assay. Data are from 14 (mock; none detected) and 18–19 (infected) mice per group ± s.e.m and are pooled from four independent experiments. (E) Expression of Ifi44 mRNA in the lungs was quantified by qRT-PCR. Data are from 9–16 (mock) and 23–24 (infected) mice per group ± s.e.m and are pooled from five independent experiments. ***P ≤ 0.001, ****P ≤ 0.0001, ns not significant; unpaired Student’s t-test (A) and two-way ANOVA (B–E).