IL-27 regulates morbidity during influenza infection. C57BL/6 mice were infected with 100 PFU of influenza A PR/8/34 and sacrificed at days 2–14 post-infection. IL-27 mRNA gene expression in lung tissue was measured by RT-PCR, n = 3-4 (A). C57BL/6, WT and IL-27Rα−/− mice, were infected with 100 PFU of influenza A PR/8/34 for 7 days. Cellular inflammation was examined by total cells per milliliter in the bronchoalveolar lavage fluid (BAL) (B), cell differentials (C) and hematoxylin and eosin-stained lung sections that were quantified for lung inflammation (KMR and JFA) blinded to the groups (D), n = 7. *p < 0.05 IL-27Rα−/− versus WT mice. All data are reported as means ± SEM for each group by unpaired t test (B) and two-way analysis of variance with the Bonferroni’s post-test (C, D). Data are the combined results of two replicate experiments.