i.p.-primed memory CD8⁺ T cells display defective recruitment to the lung airways. C57BL/6 mice were infected either i.p. (10⁴ 50% egg infectious dose [EID₅₀]) or i.n. (250 EID₅₀) with Sendai virus. (A) The virus titers in the lung at days 7 and 11 after infection determined by plaque assay. The dashed line indicates the lower limit of detection. (B) Cells were isolated from the spleen, lung tissues (cells located in the airways are not included), and lung airways at the indicated time points and stained with anti-CD8 and Sendai nucleoprotein (NP)_324-332/K^b tetramer (n = 3–10 at each time point). Shown are the actual numbers of CD8⁺tetramer⁺ cells in each tissue. (C) C57BL/6 mice were infected either i.p. or i.n. with Sendai virus. Cells were isolated from the spleen at the indicated time points and stained with anti-CD8, the indicated marker-specific mAb, and Sendai NP_324-332/K^b tetramer (n = 3–10 at each time point). The percentage of tetramer⁺CD8⁺ cells expressing each marker is indicated. Error bars indicate SD.