Figure 3: TLR2 deficiency abolishes S. aureus-mediated prevention of influenza-mediated lung injury.

(a) Three days after S. aureus priming, WT mice, Tlr2^−/− mice and Tlr4^−/− mice were infected with 0.5 HA of PR8 and analysed for survival. (b) Hematoxylin and eosin staining and inflammation scores of the lungs from control Tlr2^−/− and Tlr4^−/− mice and S. aureus-primed Tlr2^−/− and Tlr4^−/− mice at day 4 after infecting with 0.1 HA of PR8. Scale bars represent 200 μm. (c) BCA protein assay of total protein in BALF from control Tlr2^−/− mice and S. aureus-primed Tlr2^−/− mice at days 5 and 7 after infecting with 0.1 HA of PR8. (d) ELISA of cytokines in BALF from control Tlr2^−/− mice and S. aureus-primed Tlr2^−/− mice at day 7 after infecting with 0.1 HA of PR8. (e) Three days after priming WT mice with a single dose of Pam3csk4 (a TLR2 agonist), multiple Pam3csk4 doses (twice a day for 3 days), or 1 × 10⁷ CFU of S. aureus, mice were then infected with 0.5 HA of PR8 and analysed for survival. (f) Three days after priming with 1 × 10⁷ CFU of either live S. aureus or heat-killed S. aureus, WT mice were infected with 0.5 HA of PR8 and analysed for survival. Two-tailed Student’s t-tests; NS, not significant; ***P<0.001. Data are expressed as mean±s.e.m. Data represent three independent experiments with at least five mice per group in (a–d), or represent two independent experiments with at least five mice per group in (e,f).