CCR9 is maintained on a subset of OT-1 cells following activation in MLNs. (a) CCR9 expression on CFSE+ CD8αβ+ OT-1 (Ly5.2+) lymphocytes. OT-1 cells were labeled with CFSE and injected into C57BL/6J-Ly5.1 mice. MLNs and PLNs were removed 2 days after intraperitoneal administration with OVA plus LPS, and the expression of CCR9 on CFSE+ OT-1 cells was determined by flow cytometry. Results are from one representative experiment of four performed with pooled cells from three to five mice. (b) Combined results of CCR9 expression on OT-1 cells from MLNs (filled symbols) and PLNs (open symbols) 2 days after stimulation with OVA plus LPS. Each symbol represents the mean ± SEM of three to four experiments with cells pooled from three to five mice per experiment. The data from cells that had undergone no divisions and one division are from two experiments, since there were too few cells for analysis in the remaining two experiments. *P < 0.02, **P < 0.002. (c) CCR9 expression on OT-1 (Ly5.2+, CD8αβ+) cells 3 days after stimulation with OVA plus LPS. Results are from the same experiment as in a and are representative of three performed.