CCL20 regulates accumulation of CD4 T cells in secondary lymphoid organs. (A) Thymectomized irradiated B6 recipients were reconstituted with a 50:50 mixture of T-cell–depleted bone marrow from CCR6⁺ (OM⁺Ly5.1⁺, ○) and CCR6^–/– (OM^–Ly5.1^–, •) donors. (B) Euthymic irradiated B6 recipients were reconstituted with a 50:50 mixture of T-cell–depleted bone marrow from non–OM-transgenic CCR6⁺ (Ly5.1⁺, ○) and CCR6^–/– (Ly5.1^–, •) donors. Panels A and B show the proportion (mean ± SD from 2 experiments involving a total of 6 mice per group) of CCR6⁺ and CCR6^– cells in the recipients' bone marrow and lymphoid organs. Symbols of statistical significance (§, ¥, *) shown at the top of panels refer to the proportion of CCR6⁺ versus CCR6^– cells at various stages of differentiation. Also indicated (joined arrows) is the significant increase in the proportion of CCR6⁺ CD4 T cells present in the secondary (spleen) relative to the “primary” T-lymphoid organ (B6 thymus and LckOM LN). (C) Non–OM-transgenic CCR6^–/– (▪) and CCR6⁺ (□) mice were given BrdU-supplemented water for 10 days. The proportion of BrdU-labeled T cells among CD62L^lo and CD62L^hi CD4 spleen T cells is depicted. (D) Numbers of CD4 CD62L^lo T cells in non–OM-transgenic CCR6^–/– (▪) and CCR6⁺ (□) mice; gated on LN CD4 T cells. Data in panels C and D represent the mean ± SD from one experiment with 4 mice per group. §P < .05; ¥P < .01; *P < .001.