a) BALB/c mice were infected with RSV i.n. or left uninfected and then challenged with IAV expressing either the CD4 epitope F51–67 (IAV-F51) or the CD8 epitope M282–90 (IAV-M282) one month later. Mice were treated daily with FTY-720 i.p. for 7 days beginning 3 days prior to recombinant IAV challenge. Four days after IAV challenge, lungs were harvested, and plaque assays were performed. Viral titers of b) IAV-PR8, c) IAV-F51 and d) IAV-M282 in the lung are shown. The dotted line denotes the limit of detection (LOD) of the assay. Data are presented as mean ± SEM from two independent experiments that have been combined (n=5 mice per experiment). Statistical analysis was performed with Student’s t test, * p<0.05, ** p<0.01, *** p<0.001.