T helper type 17 (Th17) cells have been characterized based on production of interleukin-17 (IL-17) and association with autoimmune diseases. We studied the role of Th17 cells in aplastic anemia (AA) by isolating Th17 cells from patients blood (n ‫؍‬ 41) and bone marrow (BM) mononuclear cells (n ‫؍‬ 7). The frequency and total number of CD3 ؉ CD4 ؉ IL-17-producing T cells were increased in AA patients at presentation compared with healthy controls (P ‫؍‬ .0007 and .02, respectively) and IntroductionTh17 cells have been characterized recently in mice as a novel subset of CD4 ϩ T cells that produce interleukin-17A (IL-17A), IL-17-F, and IL-22, 1,2 and serve as immune effectors in various settings, including inflammation, infection, and autoimmunity. 3,4 Th17 cells produce a large amount of IL-17A, a cytokine that coordinates tissue inflammation by inducing the expression of proinflammatory cytokines (such as IL-6 and tumor necrosis factor [TNF]), chemokines (such as KC, MCP-1, and MIP-2), and matrix metalloproteases that mediate tissue infiltration and tissue destruction. 5 In mice, the differentiation program of Th17 cells from naive CD4 ϩ T cells requires the activation of the transcription factor, orphan nuclear receptor ROR␥t, 6 and the presence of IL-6 and transforming growth factor-␤ (TGF-␤). 7,8 In humans, Th17 differentiation is under the control of IL-1␤, 10 Several studies have reported the association of IL-17 with inflammatory disorders, such as rheumatoid arthritis, asthma, multiple sclerosis, and lupus, 11 as well as hematologic disorders, such as myelodysplastic syndrome 12,13 and acute myeloid leukemia. 14 Aplastic anemia (AA), a disease characterized by peripheral blood pancytopenia and bone marrow (BM) hypoplasia, 15 is an immunemediated disorder in most cases with active destruction of hematopoietic cells by effector T lymphocytes. 16 Recovery of autologous hematopoiesis in patients who failed to engraft after conditioning and stem cell transplantation, 17 and responsiveness of patients to immunosuppressive therapies, 18 provided powerful evidence for the pivotal role of the immune system in the disease pathophysiology. Immoderate production of interferon-␥ (IFN-␥), TNF-␣, and IL-2 from patients'T cells suggests that the hematopoietic cells are destroyed through a Th1 response, [19][20][21] as illustrated by the up-regulation of the transcription factor T-bet in patient T cells. 22 The description of nonrandom skewing of the V␤ chain families of the T-cell receptor in patient peripheral blood (PB) revealed that expanded oligoclonal or monoclonal specific V␤ subfamilies selectively induced apoptosis of hematopoietic progenitor cells. 23 Regulatory T cells (Tregs), which control and suppress autoreactive T cells, are decreased at disease presentation in almost all patients. 24 We have developed murine models for immune-mediated BM failure by the infusion of allogeneic lymph node (LN) cells into sublethally irradiated recipients for which treatment with limited number of Treg cells, 25 or anti-IFN...

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In many animals, blood cell production occurs in the bone marrow. Hematopoiesis is complex, requiring self-renewing and pluripotent stem cells, differentiated progenitor and precursor cells, and supportive stroma, adipose tissue, vascular structures, and extracellular matrix. Although imaging is a vital tool in hematology research, the 3-dimensional architecture of the bone marrow tissue in situ remains largely uncharacterized. The major hindrance to imaging the intact marrow is the surrounding bone structures are almost impossible to cut/image through. We have overcome these obstacles and describe a method whereby whole-mounts of bone marrow tissue were immunostained and imaged in 3 dimensions by confocal fluorescence and reflection microscopy. We have successfully mapped by multicolor immunofluorescence the localization pattern of as many as 4 cell features simultaneously over large tiled views and to depths of approximately 150 m. Three-dimensional images can be assessed qualitatively and quantitatively to appreciate the distribution of cell types and their interrelationships, with minimal perturbations of the tissue. We demonstrate its application to normal mouse and human marrow, to murine models of marrow failure, and to patients with aplastic anemia, myeloid, and lymphoid cell malignancies. The technique should be generally adaptable for basic laboratory investigation and for clinical diagnosis of hematologic diseases. (Blood. 2010;116(15):e41-e55)

Hematopoietic stem cells (HSCs) and HSC-independent progenitors are generated from hemogenic endothelium. Yokomizo et al. show that Hlf expression distinguishes nascent HSCs from HSC-independent progenitors. HSC specification, regulated by the Evi-1/Hlf axis, is activated only within Hlf+ nascent hematopoietic clusters.