Characterization of CCR9 expression on mature SP thymocytes.

Thymocytes were stained in 4-color experiments with anti-CD4 and anti-CD8 to gate in the SP thymocyte subpopulations. The gates used for CD4⁺ and CD8⁺ cells were those with numbers 5 and 8 in Figure 2, respectively. Gated cells were then analyzed for expression of CCR9 and CD69 (A) or CD62L (C). (B) CD69⁻and CD69⁺ thymocyte subsets were purified as described (“Materials and methods”), and migration in response to 300 nM CCL25 was assayed in Transwell inserts. A migration index was established as the ratio between cell number migrated in response to CCL25/cell number migrated to buffer. Results shown are representative of 4 independent experiments performed.