scholarly journals Origin, Kinetics, and characteristics of pulmonary macrophages in the normal steady state.

1979 ◽  
Vol 149 (6) ◽  
pp. 1504-1518 ◽  
Author(s):  
A B van oud Alblas ◽  
R van Furth
Keyword(s):  
Bone Marrow ◽  
Steady State ◽  
Mixed Population ◽  
Cell Renewal ◽  
Pulmonary Tissue ◽  
Macrophage Population ◽  
Pulmonary Macrophage ◽  
Pulmonary Macrophages

Pulmonary macrophages of mice in the steady state were isolated by lavage with PBS containing EDTA and subsequent enzymatic digestion of tissue with pronase and DNA-ase. By this method, the total pulmonary macrophage population was obtained in two cell suspensions, one with a pure population of pulmonary alveolar macrophages (PAM) and the other with a mixed population of pulmonary alveolar and pulmonary tissue macrophages (PTM). The morphological, cytochemical, and functional characteristics of both PAM and PTM were like those of mature tissue macrophages except for the presence of C3 receptors. These receptors were almost absent on PAM and present on a larger number of cells in the mixed population of PAM and PTM. The total pulmonary macrophage population of mice in the steady state is approximately equal to 2 x 10(6), of which about 93% are PAM and about 7% are PTM. In labeling experiments with 3H-thymidine, the low in vitro labeling indices (less than 3%) for both PAM and the mixture of PAM and PTM, showed that both are essentially nondividing cells. In vivo labeling studies showed an increase in the number of labeled macrophages that can only be attributed to labeled monocytes migrating into the lungs. Additional evidence was provided by a decrease in the labeling indices of pulmonary macrophages when mice were treated with hydrocortisone acetate, which causes a severe monocytopenia, thus preventing monocyte influx into the lungs. Confirmation of the bone marrow origin was obtained in mice labeled after x-irradiation with partial bone marrow shielding: labeled pulmonary macrophages were found in the exposed lungs. In all experiments, the labeling indices were identical in the two macrophage populations isolated. These results show that the influx of monocytes is the source of cell renewal for the pulmonary macrophages. No indications for an interstitial division or maturation compartment in the lung were found. Quantitation of the efflux of labeled monocytes from the blood, and the number of labeled pulmonary macrophages, showed that in the steady state about 15% of the monocytes leaving the circulation become pulmonary macrophages and that the turnover time of pulmonary macrophages is approximately equal to 27 d.

Sex chiniaerism and germ cell distribution in a series of chimaeric mice

Development ◽  
1975 ◽  
Vol 33 (1) ◽  
pp. 205-216
Author(s):  
Anne McLaren
Keyword(s):  
Bone Marrow ◽  
Blood Cells ◽  
Chromosome Analysis ◽  
Chromosome Morphology ◽  
Mixed Population ◽  
Cell Distribution ◽  
Single Sex ◽  
Xx Males

1. Of 30 mice born from aggregation of embryos from a multiple recessive strain with F1 embryos carrying the contrasting alleles, 4 females and 20 males proved to be overtly chimaeric. 2. Three XX/XX females, five XY/XY males and eight XY/XX males were identified by chromosome analysis. Thus 50 % of the population analysed were sex chimaeras, and all of these developed as phenotypic males, though one showed evidence of hermaphroditism. 3. In seven XY/XX chimaeras that bred, the genetic component undergoing spermatogenesis coincided in every case with the component identified by chromosome morphology as XY. 4. The F1 component predominated in metaphase plates derived from cultured blood cells. Comparison with direct preparations from bone marrow suggested selection in favour of F1 cells, either through differential proliferation of stem cells in vivo or differential response to phytohaemagglutinin in vitro. 5. In XY/XX males, the percentage of XX cells detected varied from 1 % to 98 % in blood, and from 0 % to 80 % in bone marrow. 6. Of eight ‘single-sex’ chimaeras progeny-tested (three XX/XX, five XY/XY), only one showed evidence of a mixed population of germ cells. The proportion of the two types of progeny varied significantly from litter to litter, but was unrelated to the age of the male.

scholarly journals The immunosuppressant rapamycin blocks in vitro responses to hematopoietic cytokines and inhibits recovering but not steady-state hematopoiesis in vivo

Blood ◽  
1994 ◽  
Vol 84 (5) ◽  
pp. 1543-1552 ◽  
Author(s):  
VF Quesniaux ◽  
S Wehrli ◽  
C Steiner ◽  
J Joergensen ◽  
HJ Schuurman ◽  
...  
Keyword(s):  
Bone Marrow ◽  
Steady State ◽  
T Cell ◽  
T Cell Response ◽  
Colony Stimulating Factor ◽  
Gm Csf ◽  
Hematopoietic Recovery ◽  
Stimulating Factor

Abstract The immunosuppressive drug rapamycin suppresses T-cell activation by impairing the T-cell response to lymphokines such as interleukin-2 (IL- 2) and interleukin-4 (IL-4). In addition, rapamycin blocks the proliferative response of cell lines to a variety of hematopoietic growth factors, including interleukin-3 (IL-3), interleukin-6 (IL-6), granulocyte-colony stimulating factor (G-CSF), granulocyte macrophage- colony stimulating factor (GM-CSF), and kit ligand (KL), suggesting that it should be a strong inhibitor of hematopoiesis. In this report, we studied the effects of rapamycin on different hematopoietic cell populations in vitro and in vivo. In vitro, rapamycin inhibited the proliferation of primary bone marrow cells induced by IL-3, GM-CSF, KL, or a complex mixture of factors present in cell-conditioned media. Rapamycin also inhibited the multiplication of colony-forming cells in suspension cultures containing IL-3 plus interleukin-1 (IL-1) or interleukin-11 (IL-11) plus KL. In vivo, treatment for 10 to 28 days with high doses of rapamycin (50 mg/kg/d, orally) had no effect on myelopoiesis in normal mice, as measured by bone marrow cellularity, proliferative capacity, and number of colony-forming progenitors. In contrast, the same treatment strongly suppressed the hematopoietic recovery normally seen 10 days after an injection of 5-fluorouracil (5- FU; 150 mg/kg, intravenously [i.v.]). Thus, rapamycin may be detrimental in myelocompromised individuals. In addition, the results suggest that the rapamycin-sensitive cytokine-driven pathways are essential for hematopoietic recovery after myelodepression, but not for steady-state hematopoiesis.

Enhanced Erythroblast Mobilization in Nix-Deficient Mice Confers Resistance to Phenylhydrazine-Induced Anemia Despite Accelerated Erythrocyte Turnover.

Blood ◽  
2007 ◽  
Vol 110 (11) ◽  
pp. 3659-3659
Author(s):  
Abhinav Diwan ◽  
Andrew G. Koesters ◽  
Amy M. Odley ◽  
Theodosia A. Kalfa ◽  
Gerald W. Dorn
Keyword(s):  
Bone Marrow ◽  
Steady State ◽  
Half Life ◽  
Hematopoietic Cells ◽  
Dynamic Regulation ◽  
Genetic Ablation ◽  
Deficient Mice ◽  
Erythrocyte Fragility

Abstract Steady-state and dynamic regulation of erythrocyte production occurs by altering the balance of cell-survival versus apoptosis signaling in maturing erythroblasts. Previously, the pro-apoptotic factor Nix was identified as a critical death signal in normal erythropoietic homeostasis, acting in opposition to erythroblast-survival signaling by erythropoietin and Bcl-xl. However, the role of Nix in stress-erythropoiesis is not known. Here, by comparing the consequences of erythropoietin administration, acute phenylhydrazine-induced anemia, and aging in wild-type and Nix-deficient mice, we show that complete absence of Nix, or its genetic ablation specifically in hematopoietic cells, mimics the effects of erythropoietin (Epo). Both Nix ablation and Epo treatment increase early erythroblasts in spleen and bone marrow and increase the number of circulating reticulocytes, while maintaining a pool of mature erythroblasts as an “erythropoietic reserve”. As compared with WT, Nix null mice develop polycythemia more rapidly after Epo treatment, consistent with enhanced sensitivity to erythropoietin observed in vitro. After phenylhydrazine administration, anemia in Nix-deficient mice is less severe and recovers more rapidly than in WT mice, despite lower endogenous Epo levels. Anemic stress depletes mature erythroblasts in both WT and Nix null mice, but Nix null mice with basal erythroblastosis are resistant to anemic stress. These findings show that Nix null mice have greatly expanded erythroblast reserve and respond normally to Epo- and anemia-stimulated induction of erythropoiesis. However, the hematocrits of young adult Nix null mice are not elevated, and these mice paradoxically develop anemia as they age with decreased hemoglobin content (10g/dl) and hematocrit (36%; at 80±3 weeks of age) compared to WT mice (13g/dl and 46%; 82±5 weeks of age), inspite of persistent erythoblastosis observed in the bone marrow and spleen. Nix null erythrocytes, which are macrocytic and exhibit membrane abnormalities typically seen in immature cells or with accelerated erythropoiesis, demonstrate shorter life span with a half life of 5.2±0.6 days in the peripheral circulation by in vivo biotin labeling (as compared with a half life of 11.7±0.9 days in WT), and increased osmotic fragility as compared with normal erythrocytes. This suggests that production and release of large numbers of reticulocytes in Nix null mice can decrease erythrocyte survival. To rule out a non-hematopoietic consequence of Nix ablation that contributes to or causes increased erythrocyte fragility and in vivo consumption, such as primary hypersplenism, we undertook Tie2-Cre mediated conditional Nix gene ablation. Nixfl/fl + Tie2-Cre mice (hematopoietic-cell specific Nix null) develop erythroblastosis with splenomegaly, reticulocytosis, absence of polycythemia and increased erythrocyte fragility; suggesting that erythroblastosis and accelerated erythrocyte turnover are a primary consequence of Nix ablation in hematopoietic cells. Hence, dis-inhibition of erythropoietin-mediated erythroblast survival pathways by Nix ablation enhances steady-state and stress-mediated erythropoiesis.

Megakaryocytes Exchange Significant Levels of Their Alpha-Granular PF4 with Their Environment

Blood ◽  
2014 ◽  
Vol 124 (21) ◽  
pp. 1432-1432 ◽  
Author(s):  
Michele P Lambert ◽  
Ronghua Meng ◽  
Dawn Harper ◽  
Liqing Xiao ◽  
Michael S. Marks ◽  
...  
Keyword(s):  
Bone Marrow ◽  
Steady State ◽  
Whole Body ◽  
Platelet Factor ◽  
Hematopoietic Stem ◽  
Murine Bone Marrow ◽  
Background Staining ◽  
The Media

Abstract Platelet factor 4 (PF4, CXCL4) is a major chemokine in megakaryocytes (megs). It is synthesized almost exclusively by megs during their development and may have important roles in regulating both hematopoietic stem cell and megakaryocyte proliferation. We now show that megs both release significant amounts of PF4 into their environment as well as take up PF4 into alpha granules. This PF4 is then available for release by thrombin activation. We examined PF4 recycling during megakaryopoiesis based on the observation that in vitro-cultured human meg hematopoietic precursors release significant amounts of PF4 into the media beginning after approximately 7 days of culture, when definitive megs begin to emerge. Using immunohistochemistry, we find that in vivo in murine bone marrow, human PF4 (hPF4) is released by hPF4 transgenic (hPF4+) megs during the steady-state, and this release is markedly accentuated 48 hours after sub-lethal 660 cGy whole body irradiation from an X-ray source to induce bone marrow injury. By comparison, animals without endogenous PF4 expression (Pf4-/-) showed only background staining. After irradiation, the levels of PF4 staining within the hPF4+ megs decreased with a concomitant increase in background staining suggesting that the stored PF4 was released into the bone marrow milieu. The increase in the PF4 staining in the intramedullary space was not due to released PF4 from entrapped platelets as similar changes were seen in untreated hPF4+ mice and in mice made thrombocytopenic by injection of antiCD41 antibody. We then asked whether the released PF4 could be taken back up by the megs and whether internalized PF4 could reach significant levels compared to endogenously synthesized PF4. We show that murine megs can take up significant levels of hPF4 so that peak hPF4 uptake at 24 hours (19±2 ng/10e6 cells) is equivalent to the amount of mouse (m) PF4 (30±1 ng/106 cells) natively present within the megs. Blocking antibodies to either PF4 itself or to lipoprotein receptor related protein 1 (LRP1) prevented PF4 uptake (53±17 IU/10e6 cells and 32±9 IU/10e6, respectively, vs 95±9 IU/10e6 cells, p <0.01, for either vs. no treatment), consistent with our previous report that LRP1 was necessary for PF4’s negative paracrine effect on megakaryopoiesis. The PF4 that was taken up by megs localizes at least in part to alpha granules, as evidenced by co-localization with P-selectin by immunofluorescence microscopy. Quantification showed a higher degree of colocalization between endogenous mPF4 and internalized hPF4 than between other alpha-granule markers, including vWF, P-selectin and internalized fibrinogen. Moreover like endogenous mPF4, the internalized PF4 can be re-released upon thrombin-induced meg activation. Finally, we asked whether the PF4 uptake was unusual and began by studying uptake of the related chemokine, platelet basic protein (PBP, CXCL7), another protein synthesized by megs and stored in alpha-granules. Unlike PF4, PBP was not internalized by megs as judged by immunohistochemistry or ELISA, indicating that the ability to be internalized and re-released is a relatively unique property of PF4. In summary, we demonstrate that PF4 - an important regulator of megakaryopoiesis and hematopoiesis - is released by megs in the intramedullary space at steady-state and even more so when stressed. Moreover, the released PF4 can be taken up into alpha-granules and stored for potential rerelease. Whether this complex cycle of PF4 in megs is unique to PF4 or applies to other alpha-granular proteins and whether it is necessary for the PF4 effect on hematopoiesis/ megakaryopoiesis needs further investigation Disclosures Xiao: ECRI Institute: Employment.

High-Vorticity with Periodic Flow Enhances in Vitro Biogenesis of Healthy Platelets from iPSC-Derived-Megakaryocytes

Blood ◽  
2016 ◽  
Vol 128 (22) ◽  
pp. 2181-2181
Author(s):  
Yukitaka Ito ◽  
Sou Nakamura ◽  
Tomohiro Shigemori ◽  
Naoshi Sugimoto ◽  
Yoshikazu Kato ◽  
...  
Keyword(s):  
Bone Marrow ◽  
Steady State ◽  
Ex Vivo ◽  
Annexin V ◽  
Poor Quality ◽  
Flow Chamber ◽  
Physical Parameters ◽  
Platelet Production

Abstract Each transfusion requires 200-300 billion platelets in patients with thrombocytopenia. To continuously supply such a huge number of platelets by ex vivo generation, two distinct steps, megakaryopoiesis and platelet shedding, must be both considered. For the former, one approach is to increase the number of source cell, megakaryocytes. For example, the immortalized megakaryocyte cell line (imMKCL) system uses self-renewing megakaryocyte (MK) cell lines derived from induced pluripotent stem cells (iPSCs) (Nakamura et al., Cell Stem Cell, 2014). For the latter, there have been an idea of bioreactors whereby shedding of platelets from proplatelets could be promoted by flow-dependent shear force within the bone marrow in vivo (Junt et al., Science, 2007; Zhang et al., J Exp Med, 2012). Based upon this idea, we constructed a flow chamber type bioreactor recapitulating in vivo blood flow shear rate. However, this bioreactor failed to efficiently yield platelets, and moreover, the produced platelets had poor quality as indicated by high Annexin V levels (Exp Hematol, 2011 and unpublished result). Recently, we demonstrated two different kinetics of platelet biogenesis from bone marrow MKs, whereby either thrombopoietin (TPO) mostly regulates steady-state shedding of platelets from proplatelets, or interleukin-a (IL-1a) triggers inflammation-dependent rupture of MK cytoplasm contributing to a quick increase of platelet count at higher rate (Nishimura et al., J Cell Biol, 2015). However, the rupture type platelets revealed shorter half-life with relatively higher Annexin V levels. Therefore, to gain insights from platelet biogenesis in vivo, we focused on biophysical analysis of steady-state platelet biogenesis via proplatelets in bone marrow. Our observations strongly indicated that the presence of 'vorticity' defined by vortex turbulence in addition to shear-dependent 'stress' and 'strain' correlates with the efficient shedding of competent platelets. From this new finding, we developed an alternative bioreactor system, which enabled generation of 100 billion platelets from imMKCL in a 16L-scale liquid culture condition without any adherent machinery using two 10L-bioreactors. Furthermore, platelets generated via new bioreactors showed low Annexin V levels (<10-15%) and shortened bleeding time post transfusion into NOG mice and rabbits with thrombocytopenia, comparable to human blood product platelets. Regarding the platelet production using WAVE bag system (GE healthcare, UK), the system is already clinically available for cord blood cell expansion in most countries, but lacks adequate levels of vorticity and shear strain/stress. Accordingly, the produced platelets had high Annexin V levels (i.e., 50-65%) as well as diminished yield efficiency (P<0.001). In conclusion, our study has uncovered the novel biophysical aspect of platelet biogenesis. The application of the new set of physical parameters in constructing large sized bioreactors shall facilitate the industrialization of platelet production. Disclosures Eto: Megakaryon Co. Ltd.: Research Funding.

scholarly journals THE ORIGIN AND KINETICS OF MONONUCLEAR PHAGOCYTES

1968 ◽  
Vol 128 (3) ◽  
pp. 415-435 ◽  
Author(s):  
Ralph van Furth ◽  
Zanvil A. Cohn
Keyword(s):  
Bone Marrow ◽  
Steady State ◽  
Peripheral Blood ◽  
Mononuclear Cells ◽  
Calf Serum ◽  
Peritoneal Macrophages ◽  
Mononuclear Phagocytes ◽  
Sterile Inflammation

The origin and turnover of efferent populations of mouse mononuclear phagocytes has been described. Mononuclear phagocytes were defined as mononuclear cells which are able to adhere to glass and phagocytize. In vitro labeling studies with thymidine-3H showed that monocytes in the peripheral blood and peritoneal macrophages do not multiply and can be considered end cells in a normal, steady state situation. However, the mononuclear phagocytes of the bone marrow appear to be rapidly dividing cells. This conclusion was supported by in vivo labeling experiments. A peak of labeled mononuclear phagocytes of the bone marrow was found 24 hr after a pulse of thymidine-3H. This was followed, 24 hr later, by a peak of labeled monocytes in the peripheral blood. From these experiments it was concluded that the rapidly dividing mononuclear phagocytes of the bone marrow, called promonocytes, are the progenitor cells of the monocytes. Labeling studies after splenectomy and after X-irradiation excluded other organs as a major source of the monocytes. Peak labeling of both the blood monocyte and peritoneal macrophages occurred at the same time. A rapid entry of monocytes from the blood into the peritoneal cavity was observed, after a sterile inflammation was evoked by an injection of newborn calf serum. These data have led to the conclusion that monocytes give rise to peritoneal macrophages. No indications have been obtained that mononuclear phagocytes originate from lymphocytes. In the normal steady state the monocytes leave the circulation by a random process, with a half-time of 22 hr. The average blood transit time of the monocytes has been calculated to be 32 hr. The turnover rate of peritoneal macrophages was low and estimated at about 0.1% per hour. On the basis of these studies the life history of mouse mononuclear phagocytes was formulated to be: promonocytes in the bone marrow, → monocytes in the peripheral blood, → macrophages in the tissue.

scholarly journals Mouse bone marrow-derived mast cells (mBMMC) obtained in vitro from mice that are mast cell-deficient in vivo express the same panel of granule proteases as mBMMC and serosal mast cells from their normal littermates.

1994 ◽  
Vol 180 (1) ◽  
pp. 67-73 ◽  
Author(s):  
K K Eklund ◽  
N Ghildyal ◽  
K F Austen ◽  
D S Friend ◽  
V Schiller ◽  
...  
Keyword(s):  
Bone Marrow ◽  
Mast Cell ◽  
Steady State ◽  
Mast Cells ◽  
Induced Expression ◽  
Mast Cell Protease ◽  
Steady State Levels ◽  
Mouse Mast Cell

The ear, skin, and purified serosal mast cells of WBB6F1/J-(+/+) (WB-(+/+)) and WCB6F1/J-(+/+) (WC-(+/+)) mice contain high steady-state levels of the transcripts that encode mouse mast cell protease (mMCP) 2, mMCP-4, mMCP-5, mMCP-6, and mouse mast cell carboxypeptidase A (mMC-CPA). In contrast, no mast cell protease transcripts are present in abundance in the ear and skin of WBB6F1/J-W/Wv (W/Wv) and WCB6F1/J-Sl/Sld (Sl/Sld) mice which are mast cell-deficient in vivo due to defects in their c-kit and c-kit ligand genes, respectively. We now report that the immature bone marrow-derived mast cells (mBMMC) obtained in vitro with recombinant interleukin 3 (rIL-3) or WEHI-3 cell conditioned medium from WB-(+/+), WC-(+/+), W/Wv, and Sl/Sld mice all contain high steady-state levels of the mMCP-2, mMCP-4, mMCP-5, mMCP-6, and mMC-CPA transcripts. As assessed immunohistochemically, mMCP-2 protein and mMCP-5 protein are also present in the granules of mBMMC from WB-(+/+), WC-(+/+), and W/Wv mice. That Sl/Sld and W/Wv mBMMC contain high steady-state levels of five granule protease transcripts expressed by the mature serosal, ear, and skin mast cells of their normal +/+ littermates suggests that c-kit-mediated signal transduction is not essential for inducing transcription of these protease genes. Because rIL-4 inhibits the rIL-10-induced expression of mMCP-1 and mMCP-2 in BALB/cJ mBMMC, the ability of rIL-4 to influence protease mRNA levels in WC-(+/+) mBMMC and W/Wv mBMMC was investigated. Although rIL-10 induced expression of the mMCP-1 transcript in WC-(+/+) and W/Wv mBMMC, rIL-4 was not able to suppress the steady-state levels of the mMCP-1 transcript or any other protease transcript in these cultured mast cells. Thus, not only do BALB/cJ mBMMC express fewer granule proteases than mBMMC from mast cell-deficient strains and their normal littermates but the subsequent induction of late-expressed proteases in BALB/cJ mBMMC is more tightly regulated by IL-3 and IL-4.

Apoptosis in circulating PMN: increased susceptibility in L-selectin-deficient PMN

1997 ◽  
Vol 272 (6) ◽  
pp. H2852-H2858 ◽  
Author(s):  
K. T. Matsuba ◽  
S. F. Van Eeden ◽  
S. G. Bicknell ◽  
B. A. Walker ◽  
S. Hayashi ◽  
...  
Keyword(s):  
Bone Marrow ◽  
Dna Fragmentation ◽  
Peripheral Blood ◽  
Magnetic Beads ◽  
Mixed Population ◽  
Enzyme Linked Immunosorbent Assay ◽  
Morphological Criteria ◽  
Increased Susceptibility

Previous work from our laboratory has shown that polymorphonuclear leukocytes (PMN) lose L-selectin as they age in the circulation. The present study was designed to examine the relationship between PMN age and susceptibility to apoptosis in the circulation using L-selectin as a marker of PMN age in rabbits. L-selectin-deficient leukocytes were separated from a mixed population of PMN in leukocyte-rich plasma using magnetic beads. Apoptosis was measured both with both morphological criteria and by determining the level of DNA fragmentation. The L-selectin-deficient cells separated in vitro showed morphological features of apoptosis (P < 0.01) and had higher levels of DNA fragmentation (P < 0.01) than the mixed population of PMN from which they were obtained. To determine if aging had a similar effect in vivo, PMN were labeled in the bone marrow with 5'-bromo-2'-deoxyuridine (BrdU) and L-selectin levels (immunocytochemistry) and DNA fragmentation (sandwich enzyme-linked immunosorbent assay) were measured in BrdU-labeled PMN in peripheral blood. The results showed that the peak release of BrdU-labeled PMN from the bone marrow into peripheral blood was associated with high levels of L-selectin expression, and these PMN had the lowest levels of DNA fragmentation. These results confirm that the level of L-selectin expression can be used as a marker of cell age and extend this observation by showing that aging in the circulation is associated with an increased susceptibility to apoptosis.

Reciprocal expression of CD38 and CD34 by adult murine hematopoietic stem cells

Blood ◽  
2001 ◽  
Vol 97 (9) ◽  
pp. 2618-2624 ◽  
Author(s):  
Fumihito Tajima ◽  
Takao Deguchi ◽  
Joseph H. Laver ◽  
Haiqun Zeng ◽  
Makio Ogawa
Keyword(s):  
Stem Cells ◽  
Bone Marrow ◽  
Steady State ◽  
Adult Stem Cells ◽  
Human Stem Cells ◽  
Hematopoietic Stem ◽  
Reciprocal Expression

Abstract The effects of activation of adult murine stem cells on their expression of CD38 were studied using a murine transplantation model. First, the published finding that the majority of long-term engrafting cells from normal adult steady-state marrow are CD38+ was confirmed. Next, it was determined that the majority of stem cells activated in vivo by injection of 5-fluorouracil (5-FU) or mobilized by granulocyte colony-stimulating factor are CD38−. Stem cells that were activated in culture with interleukin-11 and steel factor were also CD38−. Previous studies have shown that expression of CD34 by adult stem cells is also modulated by in vivo or in vitro activation. To determine whether there is reciprocal expression of CD38 and CD34, 4 populations of post–5-FU marrow cells were analyzed. The majority of the stem cells were in the CD38−CD34+ fraction. However, secondary transplantation experiments indicated that when the bone marrow reaches steady state, the majority of the stem cells become CD38+CD34−. In addition, the minority populations of CD34+ stem cells that occur in steady-state bone marrow are CD38−. This reversible and reciprocal expression of CD38 and CD34 by murine stem cells may have implications for the phenotypes of human stem cells.

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