Sirt1 modulates fibrin production in the lung after PM_2.5 exposure. Sirt1^+/+ and Sirt1^−/− littermates were exposed to PBS or PM_2.5 (100 μg) by intranasal instillation. Twenty-four hours later, lungs were collected. (A) Fibrin immunofluorescent staining of lung cryosections of PM_2.5 24 hour treated lung tissues. Images are representative of 6 independent experiments. (B) Lung fibrin generation was examined by immunoblotting. Blots and normalized bar graphs show fibrin production in the lung. Data are presented as mean + SEM (n = 6 mice/group; *P < .05).