Memory CD8⁺ T cells initially primed i.p. acquire the characteristics of i.n.-primed cells after a secondary i.n. challenge. Donor mice (CD45.1⁺CD90.2⁺ and CD45.2⁺CD90.2⁺) were infected either i.p. or i.n. with Sendai virus, respectively. 30 d later, splenocytes were enriched for CD8⁺ cells using negative selection columns and total memory cells (CD44^hi) were purified by cell sorting. Cells were combined such that the number of Sendai NP_324-332/K^b+ cells derived from each donor was equivalent and intravenously transferred into recipient mice (CD45.2⁺CD90.1⁺). 1 d after transfer, the recipient mice were i.n. challenged with Sendai virus and analyzed 1 mo later. (A) Relative recruitment of i.n.-primed donor CD8⁺ T cells versus i.p.-primed donor CD8⁺ T cells at day 29 after challenge. Horizontal bars represent the mean. (B) Frequency of CD69⁺ cells among CD8⁺tetramer⁺ cells in the spleen and MLN for secondary memory T cells from each donor population and host primary memory T cells. Error bars indicate SD. (C) i.p.-primed CD8⁺tetramer⁺ donor cells in the MLN after secondary i.n. challenge with Sendai virus. The numbers indicate the percentage of cells in each quadrant gated on tetramer⁺ CD8⁺ cells. Samples were pooled from five mice. The data are representative of two independent experiments.