Overrepresentation of CCR4-deficient post-positive selection thymocytes in mixed bone marrow chimeras requires antigen presentation by hematopoietic cells and does not reflect cell-intrinsic changes in proliferation or apoptosis. (A) The percentage of thymocytes in cell cycle (S/G2/M) was calculated by flow cytometric analysis of DNA content in the indicated CD45.2⁺ cell subsets from mixed bone marrow chimeric recipients analyzed in Fig. 3. Means + SEM compiled from three independent experiments with a total of nine mice per group. (B–D) Ccr4^+/+ and Ccr4^−/− thymocytes were incubated in the presence or absence of 1 µM CCL22 or CCL17, as indicated. The percentage of viable cells relative to the total number of viable cells input for each subset was quantified after 24 h. Mean + SEM from three independent experiments with three technical replicates per experiment. (E) Experimental schematic for the generation of MHCII^−/− competitive mixed bone marrow chimeras. Thymic chimerism was analyzed by flow cytometry 6 wk after transplantation. (F) The ratio of CD45.2/CD45.1 cellularity was calculated and normalized for each thymocyte subset as in Fig. 3. Data are compiled from two experiments with a total of six mice per group. No significant differences were observed based on unpaired Student’s t tests in all panels.