Plasmacytoid dendritic cells (pDCs) competent to make type I interferon were rigorously defined as a Ly-6C ؉ and CD11c Lo subset of the B220 ؉ CD19 ؊ CD43 ؉ CD24 Lo bone marrow (BM) Fraction A. Otherwise similar Ly6C ؊ cells expressed the natural killer (NK) markers DX5 and NK1.1. pDCs represented a stable, discrete, and long-lived population. Stem cells and early lymphoid progenitors (ELPs), but not prolymphocytes, were effective precursors of pDCs, and their differentiation was blocked by ligation of Notch receptors. Furthermore, pDCs were present in the BM of RAG1 ؊/؊ , CD127/IL-7Ra ؊/؊ , and Pax5 ؊/؊ mice. pDCs in RAG1/GFP knock-in mice could be subdivided, and immunoglobulin D H -J H rearrangements, as well as transcripts for the B-lineagerelated genes Pax5, mb1/CD79a, ebf, and Bcl11a, were identified only in the green fluorescent protein-positive (GFP ؉ ) pDC1 subset. All pDCs expressed terminal deoxynucleotidyl transferase (TdT), the ETS transcription factor Spi-B, the nuclear factor-B transcription factor RelB, toll-like receptor 9 (TLR9), and interferon consensus sequence binding protein (ICSBP)/interferon regulatory factor 8 (IRF-8) transcripts; lacked CD16 and granulocyte colony-stimulating factor receptor (G-CSFR); and were uniformly interleukin-7 receptor ␣ (IL-7R␣ ؊ ) AA4.1 Lo , CD27 ؊ , Flk-2 Lo , c-Kit ؊ , DX-5 ؊ , and CD11b ؊ , while CD4 and CD8␣ were variable. GFP ؉ pDC1 subset was less potent than GFP ؊ pDC2s in T allostimulation and production of tumor necrosis factor ␣ (TNF␣), interferon ␣ (IFN␣), and interleukin-6 (IL-6), while only pDC2s made IFN␥ and IL-12 p70. Thus, 2 functionally specialized subsets of pDCs arise in bone marrow from progenitors that diverge from B, T, and NK lineages at an early stage. IntroductionPlasmacytoid dendritic cells (pDCs) are believed to play central roles in defense of viral infection and maintenance of T-cell tolerance. They represent a principal source of type I interferon and can produce inflammatory cytokines such as interleukin-12 (IL-12) p70, IL-6, and tumor necrosis factor ␣ (TNF␣). 1,2 Furthermore, pDCs have been implicated in the pathogenesis of lupus in humans. [3][4][5] While information is rapidly accumulating about pDCs, important questions remain about their origin, heterogeneity, and lifespan. The focus of our study was on pDCs that reside within bone marrow (BM).CD11c Ϫ CD123 Hi HLA class II Hi BDCA (blood dendritic cell antigen) ϩ pDCs were originally defined in human blood and distinguished from conventional CD11c ϩ CD123 Ϫ dendritic cells (DCs). [6][7][8][9] The murine counterparts of human pDCs express CD11c and CD45R/B220, but not CD19, 10,11 while murine DCs as a whole can be divided into CD8 Ϫ and CD8 ϩ subpopulations. 12 Although distinct from classical murine CD8 ϩ DCs, pDCs express variable levels of CD8. 1,13,14 They were formerly defined as CD11c Lo B220 ϩ Gr1 ϩ in spleen and as CD11c ϩ B220 ϩ CD11b Ϫ cells when derived from BM cultured with FMS-like tyrosine kinase 3 ligand (Flt3-L). 15 Expression of Ly6G/Gr1 on pDCs is controve...

RAG1/GFP knock-in mice were used to precisely chart the emergence and expansion of cells that give rise to the immune system. Lymphopoietic cells detectable in stromal co-cultures arose as early as E8.5, i.e. prior to establishment of the circulation within the paraaortic splanchnopleura (P-Sp). These cells were Tie2While yolk sac (YS) also contained lymphopoietic cells after E9.5, CD41+ YS cells from р25-somite embryos produced myelo-erythroid cells but no lymphocytes. Notch receptor signaling directed P-Sp cells to T lymphocytes but did not confer lymphopoietic potential on YS cells. Thus, definitive hematopoiesis arises in at least two independent sites that differ in lymphopoietic potential. Expression of RAG1, the earliest known lymphoid event, first occurred around E10.5 within the embryos. RAG1/GFP + cells appeared in the liver at E11.0 and progenitors with B and/or T lineage potential were enumerated at subsequent developmental stages.

Notch family receptors control critical events in the production and replenishment of specialized cells in the immune system. However, it is unclear whether Notch signaling regulates abrupt binary lineage choices in homogeneous progenitors or has more gradual influence over multiple aspects of the process. A recently developed coculture system with Delta 1-transduced stromal cells is being extensively used to address such fundamental questions. Different from fetal progenitors, multiple types of adult marrow cells expanded indefinitely in murine Delta-like 1-transduced OP9 cell cocultures, progressed to a DN2/DN3 thymocyte stage, and slowly produced TCR+ and NK cells. Long-term cultured cells of this kind retained some potential for T lymphopoiesis in vivo. Adult marrow progressed through double-positive and single-positive stages only when IL-7 concentrations were low and passages were infrequent. Lin−c-KitlowGFP+IL-7Rα+/− prolymphocytes were the most efficient of adult bone marrow cells in short-term cultures, but the assay does not necessarily reflect cells normally responsible for replenishing the adult thymus. Although marrow-derived progenitors with Ig DH-JH rearrangements acquired T lineage characteristics in this model, that was not the case for more B committed cells with VH-DHJH rearrangement products.

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Lymphocyte production in bone marrow (BM) requires substantial cell division, but the relationship between largely quiescent stem cells and dividing lymphoid progenitors is poorly understood. Therefore, the proliferation and cell cycle status of murine hematopoietic progenitors that have just initiated the lymphoid differentiation program represented the focus of this study. Continuous bromo-2'-deoxyuridine incorporation (BrdU) and DNA/RNA analysis by flow cytometry revealed that a surprisingly large fraction of RAG-1 + c-kit Hi early lymphoid progenitors (ELP) and RAG-1 + c-kit Lo pro-lymphocytes (Pro-L) in adult BM were in cell cycle quiescence. In contrast, their counterparts in 14 day fetal liver actively proliferated. Indeed, the growth fraction (cells in G 1 -S-G 2 -M phases) of fetal ELP was on average 80% versus only 30% for adult ELP. Following 5-fluorouracil treatment, as many as 60% of the adult ELP-enriched population was in G 1 -S-G 2 -M and 34% incorporated BrdU in 6 hours. Transcripts for Bcl-2, p21Cip1/Waf1 and p27 Kip1 cell cycle regulatory genes correlated inversely well with proliferative activity. Interestingly, adult lymphoid progenitors in rebound had the high potential for B lymphopoiesis in culture typical of their fetal counterparts. Thus, lymphocyte production is sustained during adult life by quiescent primitive progenitors that divide intermittently. Some, but not all aspects of the fetal differentiation program are reacquired following chemotherapy.

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The introduction of induced pluripotent stem (iPS) cells has been a milestone in the field of regenerative medicine and drug discovery. iPS cells can provide a continuous and individualized source of stem cells and are considered to hold great potential for economically feasible personalized stem cell therapy. Various diseases might potentially be cured by iPS cell-based therapy including Parkinson's disease, Alzheimer's disease, Huntington disease, ischemic heart disease, diabetes and so on. Moreover, iPS cells derived from patients suffering from unique incurable diseases can be developed into patient-and disease-specific cell lines. These cells can be used as an effective approach to study the mechanisms of diseases, providing useful tools for drug discovery, development and evaluation. The development of suitable methods for the culture and expansion of iPS cells and their differentiated progenies make feasible modern drug discovery techniques such as high-throughput screening. Furthermore, iPS cells can be applied in the field of toxicological and pharmacokinetics tests. This review focuses on the applications of iPS cells in the field of pharmaceutical industry.