Priming at an extreme age leads to normal secondary influenza-specific CD8⁺ T cell responses.

<p>(A) For the secondary responses of the old-primed mice, naïve B6 mice were i.p. primed with 1.5×10⁷ pfu of the PR8 virus either at 6 weeks of age (young mice) or at 22 months (primed late aged mice), followed by a secondary i.n. challenge with 1×10⁴ pfu of the HK influenza strain 6 weeks later. (B) The magnitude of CD8⁺ T cell responses in the spleen at the peak (d8) of secondary phase following influenza virus infection are shown for young (6–8 weeks) and aged (22 months old) B6 mice. Immunodominant D^bNP₃₆₆⁺ and D^bPA₂₂₄⁺ influenza-specific CD8⁺ T cell responses were assessed by IFN-γ production in an <i>ex vivo</i> ICS assay. (C, D) Polyfunctionality of influenza-specific CD8⁺ T cell responses was assessed by simultaneous production of IFN-γ, TNF-α and IL-2 in the spleen and of young and aged mice. (E) The contribution of immunodominant D^bNP₃₆₆⁺CD8⁺ and D^bPA₂₂₄⁺CD8⁺ T cell responses in comparison to subdominant D^bPB1₇₀₃⁺CD8⁺ and K^bPB1-F2₆₂⁺CD8⁺ sets was calculated based on the proportions of IFN-γ⁺CD8⁺ populations depicted in (B for D^bNP₃₆₆⁺CD8⁺ and D^bPA₂₂₄⁺CD8⁺ and data not shown for D^bPB1₇₀₃⁺CD8⁺ and K^bPB1-F2₆₂⁺CD8⁺). TCR Vβ usage for the (F) D^bNP₃₆₆ and (G) D^bPA₂₂₄ CD8⁺ sets in the spleen of recall responses of mice primed late. TCR Vβ results represent individual mice of 3 per group. * = p<0.05.