Chemotactic activity of SDF-1 and CKβ-11/MIP-3β/ELC for TN thymocyte subsets, CD25⁻CD44⁺(A), CD25⁺CD44⁺ (B), CD25⁺CD44⁻ (C), and CD25⁻CD44⁻ (D) subsets. Isolated TN thymocytes were added to the upper chambers, and the 2 chemokines were added to the lower chambers as indicated in the figure. Data are expressed as the mean percentage of migration (±differences of duplicated experiments) for each subset. *Significant differences (P < .05) from background migration.