Fig. 5.

Markedly increased recall responses following homologous 2° challenge with the HK-NPM6I and HK-NPM6T escape viruses. (A) Naïve B6 mice were primed intraperitoneally (i.p.) with wt PR8 or mutant PR8-NPM6X viruses and challenged intranasally (i.n.) 6 wk later with 1 × 10⁴ pfu of either the corresponding wt HK or mutant HK-NPM6X virus. (B and C) The magnitude of the CD8⁺ T-cell response measured on day 8 after secondary infection was determined by an IFN-γ intracellular cytokine staining assay in (B) spleen and (C) BAL. Experiments were repeated at least twice. Data represent mean ± SD (n = 5); *P ≤ 0.01.