The number of D^b/NP_366–74 CD8 T cells is increased in protected animals.

<p>B6 mice were immunized i.m. in both hind-legs with PBS or a total of 10 µg of NP protein delivered with 100 µg alum with or without 10 µg of MPL. At least 70 days later these animals were infected with PR8 influenza A i.n. and the numbers of IA^b/NP_311–25 CD4+ T cells (A and B) or D^b/NP_366–74 CD8+ (C and D) were examined in the medistinal lymph node (A and C) or in one lung lobe (B and D) 5 days after infection. Cells were gated as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0061775#pone-0061775-g001" target="_blank">Figure 1</a>. Each point represents a mouse and the line shows the mean of the group. The X axis is set at the level of detection. The relative amounts of NP specific IgG1 (E) and IgG2c (F) antibody in the serum of these animals were examined prior to and 5 days after infection, error bars show SEM. No NP specific antibodies could be detected at these time points in mice that had been infected but not immunized. Data are combined from two separate experiments with 4–5 mice per group. n.s.: not significant.