Site of initial priming is essential for antigen-dependent recruitment of memory CD8⁺ T cells to the airways under steady-state conditions. (A and B) Donor mice (CD45.1⁺CD90.2⁺ and CD45.2⁺CD90.2⁺) were infected either i.p. or i.n. with Sendai virus, respectively, and splenocytes were harvested and combined as described in Fig. 2. Recipient mice were infected with either Sendai virus (A) or influenza x31 virus (B) 30 d before donor cell transfer. 7 d after transfer, cells were isolated from the BAL, lung parenchyma, pleural cavity, MLN, and spleen and Sendai-specific donor CD8⁺ T cells were detected by flow cytometry. The data are shown as the relative recruitment to the indicated tissue comparing i.n.-primed donor cells versus i.p.-primed donor cells, and each symbol represents an individual mouse. (C) C57BL/6 mice were infected i.n. with influenza x31 1 d before i.p. infection with Sendai virus. After 30 d, mice were administered CpG i.n., and the relative recruitment of i.n.- and i.p.-primed cells to the indicated tissues was determined by staining with influenza- and Sendai-specific tetramers, respectively. (D) Donor memory T cells from i.n.- and i.p.-primed mice were prepared as described in A and B and injected into naive recipient mice. 1 d later, the recipient mice were challenged with Sendai virus and the relative recruitment of effector T cells from the donor populations was assessed at day 11 after infection. The data are representative of two independent experiments. Horizontal bars represent the mean.