Cigarette smoke exposure reduced the severity of H9N2 infection in mice.

<p>The mice were exposed to room air or cigarette smoke for 21 days and then infected with H9N2 virus. A) Body weight changes of mice infected with H9N2 virus. There were 6–7 mice per group. Data are representative of three independent experiments. ***<i>p</i><0.001 was compared between Air+H9N2 and Smoke+H9N2 and was examined by multiple regression analysis adjusted for time. B) Lung virus titers of H9N2 infected mice. There were 4–7 mice per group. C) Absolute number of lung cells on day 9 of H9N2 infection. Macrophages (CD11b⁺, F4/80⁺), neutrophils (CD11b⁺, Ly-6G⁺), NK cells (CD3⁻, NK1.1⁺), CD4⁺ T cells (CD3⁺, CD4⁺) and CD8⁺ T cells (CD3⁺, CD8a⁺). There were 4–5 mice per group. D) Histopathological analysis of pulmonary tissues collected on day 9 of H9N2 infection. Results are representative pictures (200X) of hematoxylin and eosin stained pulmonary tissues. Scale bar: 100 µm. Inflammation score and cell infiltration score were evaluated by a board-certified pathologist. There were 4 mice per group. Results represent mean ± SEM. ^###<i>p</i><0.001 was tested by ANOVA of four groups; *<i>p</i><0.05; **<i>p</i><0.01; ***<i>p</i><0.001 were determined by Tukey post hoc test (C and D).