IntroductionAbnormal development of APCs can result in immunodeficiency and autoimmune disease. APCs, which include macrophages, B cells, and dendritic cells (DCs), and are critical for mediating adaptive immunity to foreign antigens as well as inducing tolerance to self-antigens. At steady state, macrophages are generated from monocytes, and classic DCs are derived from their precursor (pre-cDCs) and common DC progenitors (CDPs). [1][2][3][4][5][6] These cells are all generated from upstream macrophage-DC precursor (MDP) cells, 7-9 which are themselves derived from less lineage-restricted common myeloid progenitors (CMPs). 1 The entire populations of hematopoietic cells originate from pluripotent HSCs in the BM (see Figure 7A). Despite recent advances, the cellular factors that regulate the progression of HSCs to the development of APCs remain largely uncharacterized.Cap 'n' collar (CNC) proteins are evolutionarily conserved factors that are known to be essential for the resolution of oxidative stress. 10 In Caenorhabditis elegans, the CNC protein SKN-1 regulates longevity. 11,12 In mammals, there are 6 members within the CNC family (p45, Nrf1, Nrf2, Nrf3, Bach1, and Bach2) that heterodimerize with small Maf proteins (MafK, MafG, and MafF) to direct either gene induction or repression. 13 For instance, although the co-occupancy of p45 and MafK at genome elements activates transcription, binding of a Bach1 and MafK heterodimer to these elements results in gene repression. 14 Many different CNC and Maf heterodimers are formed, 15 causing the biology of CNC and Maf members to be complex. Although Nrf1 Ϫ/Ϫ mice are anemic and have embryonic or postnatal lethality, 16 ablation of p45 in mice leads to defective platelet production. 17 Although deletion of Bach2 in mice caused impaired antibody class switching, 18 disruption of Nrf2 resulted in a neurodegenerative disorder and autoimmune disease. [19][20][21] Deciphering the physiologic role of some of the CNC/Maf proteins has also proven to be challenging because of the potential functional redundancy among them. 22,23 The CNC/Maf network has been associated with a myriad of human disorders, including those of the skin, respiratory system, and hematopoietic system. 10,15,24 Thus, drug therapy involving the CNC pathway is actively being studied in humans for cancer chemoprevention, inflammatory diseases, and autoimmune diseases (for review, see Sykiotis and Bohmann 10 ). For example, the fumaric acid ester dimethylfumarate, which exerts neuroprotection by inducing Nrf2 expression, is currently in a phase 3 clinical trial as an orally active effective treatment of human multiple sclerosis with limited side effects. 25,26 Thus, deciphering the functions of the individual CNC subunits will not only be crucial to unraveling the overlapping and unique functions of these proteins but also provide insights to the potential of targeting CNC proteins for therapy against relevant diseases. In particular, the CNC member Bach1 is up-regulated in fetal Down syndrome (DS) brain. ...