Treg lineage-restricted BACH2 expression is required for maintenance of immune homeostasis. (A and B) Representative flow cytometry showing CD44 and CD62L expression on CD8⁺ T cells (A) and frequencies of indicated CD8⁺ T cell subsets (B) within spleens of animals of the indicated genotypes treated with tamoxifen for 8 wk. (C) IFN-γ expression by gated CD8⁺ T cells from spleens of animals of the indicated genotypes treated with tamoxifen for 8 wk. (D) Foxp3 expression among CD4⁺ T cells in spleens of tamoxifen-treated nonchimeric Foxp3^{EGFP-Cre-ERT2/EGFP-Cre-ERT2} animals of the indicated Bach2 genotypes. (E) Representative flow cytometry plots (left) and replicate measurements (right) of cell surface CD62L and CD44 expression by Treg cells isolated from the spleen of control and CKO mice given tamoxifen feed for 8 wk. (F) Representative expression (left) and replicate measurements (right) of ICOS on splenic Treg cells from animals of indicated genotypes treated with tamoxifen. (G) Experimental schema of pulse-labeling experiments using animals of the indicated genotypes Bach2^fl/flRosa26^flSTOP-tdRFPFoxp3^EGFP-CreERT2 administered tamoxifen by oral gavage over 4 d at the start of the experiments. (H) Flow cytometry measurements (left) and replicate measurements (right) of the frequency of RFP⁺ (pulse-labeled) cells within the bulk Foxp3^EGFP+ Treg population in the blood of animals of the indicated genotypes at the indicated time points after the start of the pulse-labeling experiment in G. Frequencies shown are normalized to mean frequency of RFP⁺ cells of GFP⁺ Treg cells in Bach2^+/+Rosa26^flSTOP-tdRFPFoxp3^EGFP-CreERT2 animals. Unnormalized frequencies are shown in Fig. S5 C. Data are representative of two independently repeated experiments with nine (B–F) and five to seven (H) mice per group. ns, not significant; **, P < 0.01; ***, P < 0.005; ****, P < 0.001; unpaired two-tailed Student’s t test (B–F and H). Numbers in gates show percentages. Bars and error show mean and SEM.