Fig. 3.

Mice primed i.p. 8 weeks previously with 10⁸ eID₅₀ of the PR-RG and mutant viruses were challenged i.n. with 10^6.3 eID₅₀ of the homologous HK variants. At various time points after infection, the splenic CD8⁺ T cell response was measured by staining with the D^bNP₃₆₆ (A and D), D^bPA₂₂₄ (B and E), and K^bPB1₇₀₃ (C and F) tetramers. The results are expressed as the percentage of cells staining (A–C) and the numbers of epitope-specific cells (D–F) that were calculated from the percentage values and the total cell counts (data not shown). The results are expressed as mean ± SD, and significant differences from the HK-RG are shown as * (P < 0.05) and † (P < 0.01). X denotes 100% death.