Figure 2. Effects hyperoxia on lung histology and bacterial clearance in Nrf2^−/− mice.

Nrf2^+/+ and Nrf2^−/− mice were exposed to room air or hyperoxia and then infected with P. aeruginosa at a dose of 10⁵ cfu for 4 h. One group of hyperoxia exposed mice were allowed to recover for 72 h (recovery) and then infected with P. aeruginosa. After 4 h post-infection, mice were killed and left lobes were fixed in formalin, while right lobes were lavaged with 1ml of PBS. (A) Histopathology of lungs of Nrf2^+/+ and Nrf2^−/− mice infected for 4 h showing signs of cellular infiltration and alveolar damage. (B) Bacterial burden in the lungs of Nrf2^+/+ and Nrf2^−/− mice exposed to room air (RA) hyperoxia (hyp) and under recovery (Rec). Graphs represent the number of cfu of bacteria remaining in the lung and in the BAL fluid, which were quantified as detailed in Methods. Each bar represents the mean value of five mice with SD. *P ≤ 0.05 vs. room air control of the same genotype; † P ≤ 0.05, Nrf2^−/− mice vs. Nrf2^+/+ mice subjected to hyperoxia. (C and D) Lung histology and bacterial clearance of hyperoxia primed Nrf2^+/+ and Nrf2^−/− mice after 72 h infection. Nrf2^+/+ and Nrf2^−/− mice were exposed to room air or hyperoxia and then infected with a dose of 10⁶ cfu P. aeruginosa. After 72 h post-inoculum, mice were sacrificed and left lobes were fixed in formalin for histological analysis while the right lobes were used for BAL collection and bacterial colony counting. Histopathology of lungs of Nrf2^+/+ and Nrf2^−/− mice infected for 72 h, showing signs of cellular infiltration and alveolar damage (panel C). Graph represents the number of cfu bacteria remaining in the lung and in BAL fluid (panel D). Bars represent the mean values with SD. *P ≤ 0.05 vs. room air control of the same genotype (n=5); † P ≤ 0.05, Nrf2^−/− mice vs. Nrf2^+/+ mice subjected to hyperoxia.