Antigen capturing in the skin and antigen trafficking into regional lymph nodes (LN) initiate immune responses. In this study, employing melanin granule (MG) as an easily traceable antigen in two mouse strains that carried steel factor or hepatocyte growth factor transgenes and had melanocytosis in the epidermis or in the dermis respectively, we investigated the mechanism of antigen trafficking from the skin. MG captured in the epidermis or dermis accumulated in the regional LN, but not other tissues. Only in alymphoplastic mice did MG-laden cells pass through the lymphatics and reached many tissues. Since inflammatory regions were not observed in the skin of either type of transgenic mouse, our developmental system enables us to investigate constitutive capturing and trafficking of insoluble antigens in the steady state. Both dendritic cells and macrophages were laden with MG in the regional LN. To determine which cells traffic antigens to the LN, we prepared double mutants that carried the transgenes and lacked transforming growth factor (TGF)-beta1, since mice lacking TGF-beta1 are reported to be deficient of Langerhans cells. Few MG were observed in the regional LN of these double-mutant mice. We also showed that signaling via macrophage colony stimulating factor receptor or Flt3/Flk2 is not essential for development of the cells for this antigen trafficking. These results indicate that antigens in the epidermis and dermis in the steady state are trafficked into regional LN only by TGF-beta1-dependent cells, which may be a dendritic cell lineage.

Osteoclasts are derived from hematopoietic precursor cells belonging to the monocyte/macrophage lineage. Osteoclast development has been reported to be regulated by several molecules such as macrophage colony-stimulating factor (M-CSF), receptor activator of nuclear factor (NF)-B ligand (RANKL), and a decoy receptor of RANKL, osteoprotegerin (OPG). Recently, it was demonstrated that the Notch signaling pathway regulates myeloid differentiation and antagonizes cell fate determination, however, the effect of Notch signaling on the osteoclast lineage has not been reported. In this study, we examined the effect of signaling via Notch receptors on the differentiation into osteoclasts by using cells from the bone marrow, spleen, and peritoneal cavity, and a cloned macrophagelike cell line IntroductionThe control of cell fate by Notch signaling was first described for Drosophila melanogaster neural/epidermal precursors as a mechanism involving lateral inhibition. 1,2 At present, 4 Notch receptors, Notch-1, -2, -3, and -4, and their ligands, Delta-1, -3, and -4, and Jagged-1 and -2 have been identified in mammals. [3][4][5][6][7][8][9][10][11] Notch ligands bind to Notch receptors through their extracellular domain, trigger proteolytic processing, and release the Notch intracellular domain (NIC) from the cell membrane. Cleaved NIC interacts with the DNA-binding transcription factor CBF1/RBP-J, and the complex is translocated into the nucleus. 12,13 This complex binds to the Hairy enhancer of split (Hes1) promoter and stimulates the transcription of the Hes1 gene. 14,15 Overexpressed NIC acts as a constitutively active form of Notch receptor. 16 Recently, several studies have reported the roles of Notch signaling in hematopoietic cell development. 17-20 NIC transgenic mice have defective B-cell development. 21 Notch signaling influences the decision of differentiation into ␣␤ versus ␥␦T cells, 22 as well as that of differentiation into CD4 versus CD8 T cells. 23 Delta-1 blocks differentiation into the B-cell lineage, while it promotes the emergence of T/natural killer (NK) cell precursors. 24 In myeloid cell lineages, an immobilized form of the extracellular domain of Delta-1 induces monocytes to undergo apoptosis when treated with macrophage colony-stimulating factor (M-CSF) 25 and inhibits the differentiation of monocytes into mature macrophages when treated with granulocyte/macrophage (GM)-CSF, but permits their differentiation into dendritic cells in the presence of GM-CSF and interleukin-4 (IL-4). 26 Osteoclasts are also included in the myeloid lineage and are derived from hematopoietic precursor cells shared with the macrophage and dendritic cell lineages. 27,28 Osteoclast differentiation is a multistep process that eventually leads to expression of tartrateresistant acid phosphatase (TRAP), multinucleation, and boneresorbing activity. [29][30][31][32][33] Osteoclastogenesis is dependent on stromal cells that support hematopoiesis, [34][35][36] and it has been demonstrated that the critical molecules produced by s...

The ability to self-renew is essential for all kinds of stem cells regardless of tissue type. One of the best candidate genes involved in conferring self-renewal capacity is Bmi-1, which has been proven to be essential for the maintenance of both normal adult hematopoietic and leukemia stem cells, as well as adult neural stem cells. To investigate the possible role of Bmi-1 in other cell types that also self-renew, we generated Bmi-1-green fluorescent protein (