Bach1 regulates steady state development of macrophages and DCs through its intrinsic function in the BM compartment. White blood cells (WBCs) harvested from splenocytes of age-matched adult animals were subjected to FACS analyses to quantify the percentage population of (A) T lymphocytes (CD3ϵ⁺), (B) non–plasma B cells (CD19⁺), (C) natural killer cells (NK1.1⁺, CD49b⁺), (D) erythrocytes (Ter-119⁺), (E) monocyte/macrophages (F4/80⁺ CD11b⁺ CD11c⁻ MHC II⁺), and (F) DCs (CD11c⁺ MHC II⁺). (G-H) Bach1 regulates the development of DC-precursors and monocytes. WT and Bach1^−/− BM cells were subjected to flow cytometric analyses to quantify the percentage of DC-precursors (G) and monocytes (H). LIN contains a cocktail of Ter-119, CD11b, B220, GR-1, and CD3ϵ. (I) Equal numbers of splenocytes from naive WT or Bach1^−/− mice were cocultured with purified OTII CD4⁺ T cells in the absence or presence of OVA for 72 hours. The amount of secreted IL-2 was quantified by ELISA. WT versus Bach1^−/− OVA-treated samples: P < .05. (J) Macrophages and (K) DCs (right panel) in the BM of lethally irradiated C57bl/6 recipients reconstituted with BMCs from WT or Bach1^−/− donors. (L) Bach1 influences the development of BM cells into DCs in vitro. Equal numbers of WT and Bach1^−/− BMCs were cultured with 20 ng/mL GM-CSF. Total number of DCs (CD11c⁺ MHC II⁺) generated at day 7 was calculated by cell counting and flow cytometric analyses. All data represent experiments containing ≥ 3 animals per genotype. The graphs are plotted with SEM.