Inhibition of antiviral response by P. aeruginosa depends on quorum sensing and the secreted protease AprA. (A) Protease activity of P. aeruginosa CF isolates and corresponding LasR deficient strains was assessed using a skim milk agar assay. (B) BEAS2B cells were pretreated with conditioned medium of P. aeruginosa from (A) or control medium and subsequently infected with RSV. Induction of MX1 and OAS1 mRNA were analyzed by qRT-PCR after 14 h. (C) Protease activity of P. aeruginosa strain PA14 and corresponding protease deficient strains was assessed using skim milk agar. (D) BEAS2B cells were pretreated with conditioned medium of P. aeruginosa from (C) or control medium and subsequently infected with RSV. Induction of MX1 and OAS1 mRNA were analyzed by qRT-PCR after 14 h. All experiments n = 4–5, ANOVA and Bonferroni post-test was used for statistical analysis. (D) Statistical analysis was done in comparison to the control (ctr) or to treatment with PA14 (indicated by prefix #). Significant differences were considered at *p < 0.05, **p < 0.01, and ***p < 0.001 as compared to the control condition. n.s., not significant.