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Niels Borregaard - One of the best experts on this subject based on the ideXlab platform.

  • mirna 130a regulates c ebp e expression during granulopoiesis
    Blood, 2014
    Co-Authors: Maria Torp Larsen, Niels Borregaard, Mattias Hager, Andreas Glenthoj, Fazila Asmar, Stine N Clemmensen, Helena Morajensen, Jack Cowland
    Abstract:

    CCAAT/enhancer binding protein-e (C/EBP-e) is considered a master transcription factor regulating terminal neutrophil maturation. It is essential for expression of secondary granule proteins, but it also regulates proliferation, cell cycle, and maturation during granulopoiesis. Cebpe(-/-) mice have incomplete granulocytic differentiation and increased sensitivity toward bacterial infections. The amount of C/EBP-e messenger RNA (mRNA) increases with maturation from myeloblasts with peak level in myelocytes (MC)/Metamyelocytes (MM), when the cells stop proliferating followed by a decline in more mature cells. In contrast, C/EBP-e protein is virtually detectable only in the MC/MM population, indicating that expression in more immature cells could be inhibited by microRNAs (miRNAs). We found that miRNA-130a (miR-130a) regulates C/EBP-e protein expression in both murine and human granulocytic precursors. Overexpression of miR-130a in a murine cell line downregulated C/EBP-e protein and lactoferrin (Ltf), cathelicidin antimicrobial protein (Camp), and lipocalin-2 (Lcn2) mRNA expression giving rise to cells with a more immature phenotype, as seen in the Cebpe(-/-) mouse. Introduction of a C/EBP-e mRNA without target site for miR-130a restored both C/EBP-e production, expression of Camp and Lcn2, and resulted in the cells having a more mature phenotype. We conclude that miR-130a is important for the regulation of the timed expression of C/EBP-e during granulopoiesis.

  • microrna profiling in human neutrophils during bone marrow granulopoiesis and in vivo exudation
    PLOS ONE, 2013
    Co-Authors: Jack Cowland, Niels Borregaard, Corinna Cavan Pedersen, Kim Theilgaardmonch, Christoffer Hother, Mattias Hager, Maria Torp Larsen
    Abstract:

    The purpose of this study was to describe the microRNA (miRNA) expression profiles of neutrophils and their precursors from the initiation of granulopoiesis in the bone marrow to extravasation and accumulation in skin windows. We analyzed three different cell populations from human bone marrow, polymorphonuclear neutrophil (PMNs) from peripheral blood, and extravasated PMNs from skin windows using the Affymetrix 2.0 platform. Our data reveal 135 miRNAs differentially regulated during bone marrow granulopoiesis. The majority is differentially regulated between the myeloblast/promyelocyte (MB/PM) and myelocyte/Metamyelocyte (MC/MM) stages of development. These 135 miRNAs were divided into six clusters according to the pattern of their expression. Several miRNAs demonstrate a pronounced increase or reduction at the transition between MB/PM and MC/MM, which is associated with cell cycle arrest and the initiation of terminal differentiation. Seven miRNAs are differentially up-regulated between peripheral blood PMNs and extravasated PMNs and only one of these (miR-132) is also differentially regulated during granulopoiesis. The study indicates that several different miRNAs participate in the regulation of normal granulopoiesis and that miRNAs might also regulate activities of extravasated neutrophils. The data present the miRNA profiles during the development and activation of the neutrophil granulocyte in healthy humans and thus serves as a reference for further research of normal and malignant granulocytic development.

  • MicroRNA Profiling in Human Neutrophils during Bone Marrow Granulopoiesis
    2013
    Co-Authors: In Vivo Exudation, Niels Borregaard, Christoffer Hother, Maria Torp Larsen, Corinna C. Pedersen, Jack B. Cowl
    Abstract:

    The purpose of this study was to describe the microRNA (miRNA) expression profiles of neutrophils and their precursors from the initiation of granulopoiesis in the bone marrow to extravasation and accumulation in skin windows. We analyzed three different cell populations from human bone marrow, polymorphonuclear neutrophil (PMNs) from peripheral blood, and extravasated PMNs from skin windows using the Affymetrix 2.0 platform. Our data reveal 135 miRNAs differentially regulated during bone marrow granulopoiesis. The majority is differentially regulated between the myeloblast/ promyelocyte (MB/PM) and myelocyte/Metamyelocyte (MC/MM) stages of development. These 135 miRNAs were divided into six clusters according to the pattern of their expression. Several miRNAs demonstrate a pronounced increase or reduction at the transition between MB/PM and MC/MM, which is associated with cell cycle arrest and the initiation of terminal differentiation. Seven miRNAs are differentially up-regulated between peripheral blood PMNs and extravasated PMNs and only one of these (miR-132) is also differentially regulated during granulopoiesis. The study indicates that several different miRNAs participate in the regulation of normal granulopoiesis and that miRNAs might also regulate activities of extravasated neutrophils. The data present the miRNA profiles during the development and activation of the neutrophil granulocyte in healthy humans and thus serves as a reference for further research of normal and malignant granulocyti

  • ficolin 1 is present in a highly mobilizable subset of human neutrophil granules and associates with the cell surface after stimulation with fmlp
    Journal of Leukocyte Biology, 2009
    Co-Authors: Sara Rørvig, Jack Cowland, Christian Honoré, Larsinge Larsson, Sophie Ohlsson, Corinna Cavan Pedersen, Lars C Jacobsen, Niels Borregaard
    Abstract:

    Ficolins are soluble molecules that bind carbohydrate present on the surface of microorganisms and function as recognition molecules in the lectin complement pathway. Three ficolins have been identified in humans: ficolin-1, ficolin-2, and ficolin-3. Ficolin-1 is synthesized in monocytes and type II alveolar epithelial cells. Ficolin-1 has been shown to be present in secretory granules of human neutrophils, but it is not known which subset of the neutrophils' secretory granules harbors ficolin-1. To determine the exact subcellular localization of ficolin-1 in neutrophils, recombinant ficolin-1 was expressed in Chinese hamster ovary cells and used for generation of polyclonal antibodies. This allowed detection of ficolin-1 in subcellular fractions of human neutrophils by ELISA, by Western blotting, and by immunohistochemistry. Real-time PCR examination of normal human bone marrow showed FCN1 gene expression largely in myelocytes, Metamyelocytes, and band cells with a profile quite similar to that of gelatinase. In accordance with this, biosynthesis studies of neutrophils precursor cells showed that ficolin-1 was primarily synthesized in myelocytes, Metamyelocytes, and band cells. Immunohistochemistry and subcellular fractionation demonstrated that ficolin-1 is primarily localized in gelatinase granules but also in highly exocytosable gelatinase-poor granules, not described previously. Ficolin-1 is released from neutrophil granules by stimulation with fMLP or PMA, and the majority becomes associated with the surface membrane of the cells and can be detected by flow cytometry. Our studies show that neutrophils are a major source of ficolin-1, which can be readily exocytosed by stimulation.

  • the secretory leukocyte protease inhibitor slpi and the secondary granule protein lactoferrin are synthesized in myelocytes colocalize in subcellular fractions of neutrophils and are coreleased by activated neutrophils
    Journal of Leukocyte Biology, 2008
    Co-Authors: Lars C Jacobsen, Jack Cowland, Niels Borregaard, Ole E Sorensen, Kim Theilgaardmonch
    Abstract:

    The secretory leukocyte protease inhibitor (SLPI) re-establishes homeostasis at sites of infection by virtue of its ability to exert antimicrobial activity, to suppress LPS-induced cellular immune responses, and to reduce tissue damage through inhibition of serine proteases released by polymorphonuclear neutrophil granulocytes (PMNs). Microarray analysis of bone marrow (BM) populations highly enriched in promyelocytes, myelocytes/Metamyelocytes (MYs), and BM neutrophils demonstrates a transient, high mRNA expression of SLPI and genuine secondary granule proteins (GPs) in MYs. Consistent with this finding, immunostaining of BM cells showed SLPI and the secondary GP lactoferrin (LF) to be present in cells from the myelocyte stage and throughout neutrophil differentiation. Subcellular fractionation studies demonstrated the colocalization of SLPI and LF in subcellular fractions highly enriched in secondary granules. Finally, exocytosis studies demonstrated a corelease of SLPI and LF within minutes of activation. Collectively, these findings strongly indicate that SLPI is localized in secondary granules of PMNs. However, the amount of SLPI detected in PMNs is low compared with primary keratinocytes stimulated by growth factors involved in wound healing. This implicates that neutrophil-derived SLPI might not contribute essentially to re-establishment of homeostasis at sites of infection but rather, exert physiologically relevant intracellular activities. These might include the protection of secondary GPs against proteolytic activation and/or degradation by proteases, which might be dislocated to secondary granules at minute amounts as a consequence of spillover.

Jack Cowland - One of the best experts on this subject based on the ideXlab platform.

  • mirna 130a regulates c ebp e expression during granulopoiesis
    Blood, 2014
    Co-Authors: Maria Torp Larsen, Niels Borregaard, Mattias Hager, Andreas Glenthoj, Fazila Asmar, Stine N Clemmensen, Helena Morajensen, Jack Cowland
    Abstract:

    CCAAT/enhancer binding protein-e (C/EBP-e) is considered a master transcription factor regulating terminal neutrophil maturation. It is essential for expression of secondary granule proteins, but it also regulates proliferation, cell cycle, and maturation during granulopoiesis. Cebpe(-/-) mice have incomplete granulocytic differentiation and increased sensitivity toward bacterial infections. The amount of C/EBP-e messenger RNA (mRNA) increases with maturation from myeloblasts with peak level in myelocytes (MC)/Metamyelocytes (MM), when the cells stop proliferating followed by a decline in more mature cells. In contrast, C/EBP-e protein is virtually detectable only in the MC/MM population, indicating that expression in more immature cells could be inhibited by microRNAs (miRNAs). We found that miRNA-130a (miR-130a) regulates C/EBP-e protein expression in both murine and human granulocytic precursors. Overexpression of miR-130a in a murine cell line downregulated C/EBP-e protein and lactoferrin (Ltf), cathelicidin antimicrobial protein (Camp), and lipocalin-2 (Lcn2) mRNA expression giving rise to cells with a more immature phenotype, as seen in the Cebpe(-/-) mouse. Introduction of a C/EBP-e mRNA without target site for miR-130a restored both C/EBP-e production, expression of Camp and Lcn2, and resulted in the cells having a more mature phenotype. We conclude that miR-130a is important for the regulation of the timed expression of C/EBP-e during granulopoiesis.

  • microrna profiling in human neutrophils during bone marrow granulopoiesis and in vivo exudation
    PLOS ONE, 2013
    Co-Authors: Jack Cowland, Niels Borregaard, Corinna Cavan Pedersen, Kim Theilgaardmonch, Christoffer Hother, Mattias Hager, Maria Torp Larsen
    Abstract:

    The purpose of this study was to describe the microRNA (miRNA) expression profiles of neutrophils and their precursors from the initiation of granulopoiesis in the bone marrow to extravasation and accumulation in skin windows. We analyzed three different cell populations from human bone marrow, polymorphonuclear neutrophil (PMNs) from peripheral blood, and extravasated PMNs from skin windows using the Affymetrix 2.0 platform. Our data reveal 135 miRNAs differentially regulated during bone marrow granulopoiesis. The majority is differentially regulated between the myeloblast/promyelocyte (MB/PM) and myelocyte/Metamyelocyte (MC/MM) stages of development. These 135 miRNAs were divided into six clusters according to the pattern of their expression. Several miRNAs demonstrate a pronounced increase or reduction at the transition between MB/PM and MC/MM, which is associated with cell cycle arrest and the initiation of terminal differentiation. Seven miRNAs are differentially up-regulated between peripheral blood PMNs and extravasated PMNs and only one of these (miR-132) is also differentially regulated during granulopoiesis. The study indicates that several different miRNAs participate in the regulation of normal granulopoiesis and that miRNAs might also regulate activities of extravasated neutrophils. The data present the miRNA profiles during the development and activation of the neutrophil granulocyte in healthy humans and thus serves as a reference for further research of normal and malignant granulocytic development.

  • ficolin 1 is present in a highly mobilizable subset of human neutrophil granules and associates with the cell surface after stimulation with fmlp
    Journal of Leukocyte Biology, 2009
    Co-Authors: Sara Rørvig, Jack Cowland, Christian Honoré, Larsinge Larsson, Sophie Ohlsson, Corinna Cavan Pedersen, Lars C Jacobsen, Niels Borregaard
    Abstract:

    Ficolins are soluble molecules that bind carbohydrate present on the surface of microorganisms and function as recognition molecules in the lectin complement pathway. Three ficolins have been identified in humans: ficolin-1, ficolin-2, and ficolin-3. Ficolin-1 is synthesized in monocytes and type II alveolar epithelial cells. Ficolin-1 has been shown to be present in secretory granules of human neutrophils, but it is not known which subset of the neutrophils' secretory granules harbors ficolin-1. To determine the exact subcellular localization of ficolin-1 in neutrophils, recombinant ficolin-1 was expressed in Chinese hamster ovary cells and used for generation of polyclonal antibodies. This allowed detection of ficolin-1 in subcellular fractions of human neutrophils by ELISA, by Western blotting, and by immunohistochemistry. Real-time PCR examination of normal human bone marrow showed FCN1 gene expression largely in myelocytes, Metamyelocytes, and band cells with a profile quite similar to that of gelatinase. In accordance with this, biosynthesis studies of neutrophils precursor cells showed that ficolin-1 was primarily synthesized in myelocytes, Metamyelocytes, and band cells. Immunohistochemistry and subcellular fractionation demonstrated that ficolin-1 is primarily localized in gelatinase granules but also in highly exocytosable gelatinase-poor granules, not described previously. Ficolin-1 is released from neutrophil granules by stimulation with fMLP or PMA, and the majority becomes associated with the surface membrane of the cells and can be detected by flow cytometry. Our studies show that neutrophils are a major source of ficolin-1, which can be readily exocytosed by stimulation.

  • the secretory leukocyte protease inhibitor slpi and the secondary granule protein lactoferrin are synthesized in myelocytes colocalize in subcellular fractions of neutrophils and are coreleased by activated neutrophils
    Journal of Leukocyte Biology, 2008
    Co-Authors: Lars C Jacobsen, Jack Cowland, Niels Borregaard, Ole E Sorensen, Kim Theilgaardmonch
    Abstract:

    The secretory leukocyte protease inhibitor (SLPI) re-establishes homeostasis at sites of infection by virtue of its ability to exert antimicrobial activity, to suppress LPS-induced cellular immune responses, and to reduce tissue damage through inhibition of serine proteases released by polymorphonuclear neutrophil granulocytes (PMNs). Microarray analysis of bone marrow (BM) populations highly enriched in promyelocytes, myelocytes/Metamyelocytes (MYs), and BM neutrophils demonstrates a transient, high mRNA expression of SLPI and genuine secondary granule proteins (GPs) in MYs. Consistent with this finding, immunostaining of BM cells showed SLPI and the secondary GP lactoferrin (LF) to be present in cells from the myelocyte stage and throughout neutrophil differentiation. Subcellular fractionation studies demonstrated the colocalization of SLPI and LF in subcellular fractions highly enriched in secondary granules. Finally, exocytosis studies demonstrated a corelease of SLPI and LF within minutes of activation. Collectively, these findings strongly indicate that SLPI is localized in secondary granules of PMNs. However, the amount of SLPI detected in PMNs is low compared with primary keratinocytes stimulated by growth factors involved in wound healing. This implicates that neutrophil-derived SLPI might not contribute essentially to re-establishment of homeostasis at sites of infection but rather, exert physiologically relevant intracellular activities. These might include the protection of secondary GPs against proteolytic activation and/or degradation by proteases, which might be dislocated to secondary granules at minute amounts as a consequence of spillover.

  • the transcriptional program of terminal granulocytic differentiation
    Blood, 2004
    Co-Authors: Kim Theilgaardmonch, Jack Cowland, Lars C Jacobsen, Rehannah Borup, Thomas Rasmussen, Malene Digmann Bjerregaard, Finn Cilius Nielsen, Niels Borregaard
    Abstract:

    To characterize the transcriptional program that governs terminal granulocytic differentiation in vivo, we performed comprehensive microarray analyses of human bone marrow populations highly enriched in promyelocytes (PMs), myelocytes/Metamyelocytes (MYs), and neutrophils (bm-PMNs). These analyses identified 11 310 genes involved in differentiation, of which 6700 were differentially regulated, including previously unidentified effector proteins and surface receptors of neutrophils. Differentiation of PMs toward MYs was accompanied by a marked decline of proliferative and general cellular activity as defined by down-regulation of E2 promoter binding factor (E2F) target genes; cyclin dependent kinases 2, 4, and 6; and various metabolic, proteasomal, and mitochondrial genes. Expression patterns of apoptosis genes indicated death control by the p53 pathway in PMs and by death receptor pathways in bm-PMNs. Effector proteins critical for host defense were expressed successively throughout granulocytic differentiation, whereas receptors and receptor ligands essential for the activation of the host defense program were terminally up-regulated in bm-PMNs. The up-regulation of ligand-receptor pairs, which are defined inducers as well as target genes of nuclear factor-kappa B (NF-kappa B), suggests a constitutive activation of NF-kappa B in bm-PMNs by autocrine loops. Overall, these results define a granulocytic differentiation model governed by a highly coordinated fail-safe program, which promotes completion of differentiation before cells gain responsiveness toward activating stimuli that accompany infections.

Poels, Lambert G. - One of the best experts on this subject based on the ideXlab platform.

Kim Theilgaardmonch - One of the best experts on this subject based on the ideXlab platform.

  • microrna profiling in human neutrophils during bone marrow granulopoiesis and in vivo exudation
    PLOS ONE, 2013
    Co-Authors: Jack Cowland, Niels Borregaard, Corinna Cavan Pedersen, Kim Theilgaardmonch, Christoffer Hother, Mattias Hager, Maria Torp Larsen
    Abstract:

    The purpose of this study was to describe the microRNA (miRNA) expression profiles of neutrophils and their precursors from the initiation of granulopoiesis in the bone marrow to extravasation and accumulation in skin windows. We analyzed three different cell populations from human bone marrow, polymorphonuclear neutrophil (PMNs) from peripheral blood, and extravasated PMNs from skin windows using the Affymetrix 2.0 platform. Our data reveal 135 miRNAs differentially regulated during bone marrow granulopoiesis. The majority is differentially regulated between the myeloblast/promyelocyte (MB/PM) and myelocyte/Metamyelocyte (MC/MM) stages of development. These 135 miRNAs were divided into six clusters according to the pattern of their expression. Several miRNAs demonstrate a pronounced increase or reduction at the transition between MB/PM and MC/MM, which is associated with cell cycle arrest and the initiation of terminal differentiation. Seven miRNAs are differentially up-regulated between peripheral blood PMNs and extravasated PMNs and only one of these (miR-132) is also differentially regulated during granulopoiesis. The study indicates that several different miRNAs participate in the regulation of normal granulopoiesis and that miRNAs might also regulate activities of extravasated neutrophils. The data present the miRNA profiles during the development and activation of the neutrophil granulocyte in healthy humans and thus serves as a reference for further research of normal and malignant granulocytic development.

  • the secretory leukocyte protease inhibitor slpi and the secondary granule protein lactoferrin are synthesized in myelocytes colocalize in subcellular fractions of neutrophils and are coreleased by activated neutrophils
    Journal of Leukocyte Biology, 2008
    Co-Authors: Lars C Jacobsen, Jack Cowland, Niels Borregaard, Ole E Sorensen, Kim Theilgaardmonch
    Abstract:

    The secretory leukocyte protease inhibitor (SLPI) re-establishes homeostasis at sites of infection by virtue of its ability to exert antimicrobial activity, to suppress LPS-induced cellular immune responses, and to reduce tissue damage through inhibition of serine proteases released by polymorphonuclear neutrophil granulocytes (PMNs). Microarray analysis of bone marrow (BM) populations highly enriched in promyelocytes, myelocytes/Metamyelocytes (MYs), and BM neutrophils demonstrates a transient, high mRNA expression of SLPI and genuine secondary granule proteins (GPs) in MYs. Consistent with this finding, immunostaining of BM cells showed SLPI and the secondary GP lactoferrin (LF) to be present in cells from the myelocyte stage and throughout neutrophil differentiation. Subcellular fractionation studies demonstrated the colocalization of SLPI and LF in subcellular fractions highly enriched in secondary granules. Finally, exocytosis studies demonstrated a corelease of SLPI and LF within minutes of activation. Collectively, these findings strongly indicate that SLPI is localized in secondary granules of PMNs. However, the amount of SLPI detected in PMNs is low compared with primary keratinocytes stimulated by growth factors involved in wound healing. This implicates that neutrophil-derived SLPI might not contribute essentially to re-establishment of homeostasis at sites of infection but rather, exert physiologically relevant intracellular activities. These might include the protection of secondary GPs against proteolytic activation and/or degradation by proteases, which might be dislocated to secondary granules at minute amounts as a consequence of spillover.

  • arginase 1 is expressed in myelocytes Metamyelocytes and localized in gelatinase granules of human neutrophils
    Blood, 2007
    Co-Authors: Lars C Jacobsen, Erik Ilsø Christensen, Kim Theilgaardmonch, Niels Borregaard
    Abstract:

    Arginase 1 (ARG1) metabolizes arginine, thus reducing the availability of arginine as a substrate for nitric oxide synthase (NOS). The decreased production of nitric oxide (NO) by NOS and the production of ornithine by ARG1 affect immune responses and tissue regeneration at sites of infection, respectively. We here demonstrate that ARG1 is synthesized in myelocytes/Metamyelocytes and is stored in gelatinase granules. In accordance with this, activated neutrophils coreleased ARG1 and gelatinase to the extracellular environment on stimulation with phorbol-12-myristate 13-acetate (PMA), formyl-methionyl-leucyl-phenylalanine (fMLP), or tumor necrosis factor α (TNF-α). Overall, these findings define ARG1 as a genuine gelatinase granule protein and support a model in which activated neutrophils release ARG1 at sites of infection to modulate immune responses and promote tissue regeneration.

  • the transcriptional program of terminal granulocytic differentiation
    Blood, 2004
    Co-Authors: Kim Theilgaardmonch, Jack Cowland, Lars C Jacobsen, Rehannah Borup, Thomas Rasmussen, Malene Digmann Bjerregaard, Finn Cilius Nielsen, Niels Borregaard
    Abstract:

    To characterize the transcriptional program that governs terminal granulocytic differentiation in vivo, we performed comprehensive microarray analyses of human bone marrow populations highly enriched in promyelocytes (PMs), myelocytes/Metamyelocytes (MYs), and neutrophils (bm-PMNs). These analyses identified 11 310 genes involved in differentiation, of which 6700 were differentially regulated, including previously unidentified effector proteins and surface receptors of neutrophils. Differentiation of PMs toward MYs was accompanied by a marked decline of proliferative and general cellular activity as defined by down-regulation of E2 promoter binding factor (E2F) target genes; cyclin dependent kinases 2, 4, and 6; and various metabolic, proteasomal, and mitochondrial genes. Expression patterns of apoptosis genes indicated death control by the p53 pathway in PMs and by death receptor pathways in bm-PMNs. Effector proteins critical for host defense were expressed successively throughout granulocytic differentiation, whereas receptors and receptor ligands essential for the activation of the host defense program were terminally up-regulated in bm-PMNs. The up-regulation of ligand-receptor pairs, which are defined inducers as well as target genes of nuclear factor-kappa B (NF-kappa B), suggests a constitutive activation of NF-kappa B in bm-PMNs by autocrine loops. Overall, these results define a granulocytic differentiation model governed by a highly coordinated fail-safe program, which promotes completion of differentiation before cells gain responsiveness toward activating stimuli that accompany infections.

Jan Ake Lindgren - One of the best experts on this subject based on the ideXlab platform.

  • inverse relationship between myeloid maturation and leukotriene c4 synthase expression in normal and leukemic myelopoiesis consistent overexpression of the enzyme in myeloid cells from patients with chronic myeloid leukemia
    Experimental Hematology, 2003
    Co-Authors: Susanne Tornhamre, Leif Stenke, Anna Granzelius, Mikael Sjolinder, Barbro Nasmanglaser, Cecilia Roos, Susanne Widell, Jan Ake Lindgren
    Abstract:

    Abstract Objective Leukotriene (LT) C 4 synthase (LTC 4 S) is the key enzyme in the biosynthesis of LTC 4 , which has been reported to stimulate the growth of human myeloid progenitor cells and is specifically overproduced in chronic myeloid leukemia (CML). The aim of this study was to clarify the expression of LTC 4 S during normal and leukemic myelopoiesis and to investigate the correlation between abnormal LTC 4 S expression in CML myeloid cells and the activity of the disease-specific tyrosine kinase p210 BCR-ABL. Materials and Methods Immature and mature myeloid cell subpopulations were isolated with magnetic cell sorting from healthy volunteer bone marrow (n = 11) and CML patient peripheral blood (n = 8), respectively. The cells were subjected to analysis of LTC 4 S protein expression and activity. Expression of LTC 4 S was investigated in CD16 + neutrophils from CML patients before and after 1 month of medication with imatinib mesylate (STI571), which is a specific inhibitor of p210 BCR-ABL. Results Among normal cells, the highest enzyme activity was observed in the most immature, CD34 + progenitor cell-enriched and CD15 + myelocyte-enriched fractions. Subsequently, LTC 4 S activity decreased with increasing maturity, with only negligible amounts of LTC 4 produced in CD16 + neutrophils. LTC 4 S was expressed at the protein level in the immature myeloid cell fractions but not in CD16 + cells. In CML cells, LTC 4 S activity and expression were consistently elevated. Thus, the CML CD34 + and CD15 + cell fractions, as well as the CD11b + myelocyte/Metamyelocyte-enriched fractions, produced 6 to 10 times as much LTC 4 as the corresponding normal cells. Again, enzyme expression was highest in the most immature cells, although evident LTC 4 S expression and activity remained in CML CD16 + neutrophils. Interestingly, treatment of five CML patients with imatinib mesylate down-regulated the abnormal neutrophil LTC 4 S expression and activity. Conclusions Expression of LTC 4 S in immature myelopoid cells is in line with a role for this enzyme in myelopoiesis. In addition, consistent overexpression of LTC 4 S in CML and the correlation to p210 BCR-ABL activity suggests that LTC 4 S may be involved in leukemic pathogenesis.