CCL21 is important for neonatal SP thymocyte egress. (A) Flow cytometric analysis and quantitation of CD4/CD8 thymocyte subsets from postnatal day–10 (P10) Ccl21a^−/− (n = 15; red bars) and Ccl21a^+/− (n = 16; blue bars) littermate controls. Quantitation of immature CD69⁺CD62L⁻ and mature CD69⁻CD62L⁺ subsets of cSP4 (B) and TCRβ^hi SP8 (C) thymocytes in Ccl21a^−/− (n = 15; red bars) and Ccl21^+/− (n = 16; blue bars) littermate P10 neonatal mice. (D) Numbers and frequencies of M2a, M2b, and M2c subsets of cSP4 and SP8 thymocytes in Ccl21a^+/− (blue bars) and Ccl21a^−/− (red bars) mice. For analysis of data in panel D, multiple comparison analysis was achieved by a 2-way analysis of variance followed by Sidak’s posttest in GraphPad Prism to determine statistical differences. In all cases, error bars represent mean ± SEM. Flow cytometric data representative of 3 independent experiments. *P < .05, ***P < .001, ****P < .0001.