Regulation of CCR9 expression on antigen-specific CD8αβ⁺ lymphocytes following activation in vivo. (a) OT-1 (Ly5.2⁺) cells were injected into C57BL/6J-Ly5.1 mice, and their expression of CCR9 was determined by flow cytometry 3 days after intraperitoneal OVA administration. Numbers represent the percentage of OT-1 cells that are CCR9+ with background staining removed. Results are from one representative experiment of nine (MLN), seven (PLN), and two (spleen) experiments performed. (b) OT-1 cells from the MLNs of OVA-treated mice respond to CCL25. MLN and PLN lymphocytes were isolated 3 days after intraperitoneal administration of OVA, and the ability of OT-1 cells and endogenous CD8αβ+ lymphocytes to migrate to CCL25 (250 nM) was determined. Results are the mean ± SEM of four experiments with three mice per experiment. *P < 0.005.