A kinetic model of bone marrow neutrophil production that characterizes late phenotypic maturation

Acute inflammatory stimuli rapidly mobilize neutrophils from the bone marrow by shortening postmitotic maturation time and releasing younger neutrophils; however, the kinetics of this change in maturation time remains unknown. We propose a kinetic model that examines the rate of change in neutrophil average age at exit from the bone marrow during active mobilization to quantify this response and use this model to examine the temporal profile of late neutrophil phenotypic maturation. Total and CD10(-)/CD16(low) circulating neutrophils were quantified in cardiac surgery patients during extracorporeal circulation (ECC). Net growth in the circulating neutrophil pool occurred during the procedural (0.04 +/- 0.02 x 10(9) x l(-1) x min(-1)), warming (0.14 +/- 0.02 x 10(9) x l(-1) x min(-1)), and weaning (0.12 +/- 0.06 x 10(9) x l(-1) x min(-1)) phases of ECC. When applied to our differential equation mathematical model, these results predict that neutrophil average age at exit from the bone marrow decreased continually during ECC, resulting in average neutrophil release 8.44 +/- 2.20 h earlier during the weaning phase than at the beginning of ECC sampling. Modeling of concurrent changes in CD10(-)/CD16(low) neutrophil numbers indicates that CD10 expression is directly related to neutrophil mean age and predicts that the proportion of mobilizable postmitotic neutrophils that are CD10(+) increases from 64 to 81% during these sampled 8.4 h of maturation.     

Neutrophil Recruitment to Lymph Nodes Limits Local Humoral Response to Staphylococcus aureus

Neutrophils form the first line of host defense against bacterial pathogens. They are rapidly mobilized to sites of infection where they help marshal host defenses and remove bacteria by phagocytosis. While splenic neutrophils promote marginal zone B cell antibody production in response to administered T cell independent antigens, whether neutrophils shape humoral immunity in other lymphoid organs is controversial. Here we investigate the neutrophil influx following the local injection of Staphylococcus aureus adjacent to the inguinal lymph node and determine neutrophil impact on the lymph node humoral response. Using intravital microscopy we show that local immunization or infection recruits neutrophils from the blood to lymph nodes in waves. The second wave occurs temporally with neutrophils mobilized from the bone marrow. Within lymph nodes neutrophils infiltrate the medulla and interfollicular areas, but avoid crossing follicle borders. In vivo neutrophils form transient and long-lived interactions with B cells and plasma cells, and their depletion augments production of antigen-specific IgG and IgM in the lymph node. In vitro activated neutrophils establish synapse- and nanotube-like interactions with B cells and reduce B cell IgM production in a TGF- β1 dependent manner. Our data reveal that neutrophils mobilized from the bone marrow in response to a local bacterial challenge dampen the early humoral response in the lymph node.     

Annexin A1 regulates neutrophil clearance by macrophages in the mouse bone marrow

Under homeostatic conditions, a proportion of senescent CXCR4(hi) neutrophils home from the circulation back to the bone marrow, where they are phagocytosed by bone marrow macrophages. In this study, we have identified an unexpected role for the anti-inflammatory molecule annexin A1 (AnxA1) as a critical regulator of this process. We first observed that AnxA1(-/-) mice have significantly increased neutrophil numbers in their bone marrow while having normal levels of GM and G colony-forming units, monocytes, and macrophages. Although AnxA1(-/-) mice have more neutrophils in the bone marrow, a greater proportion of these cells are senescent, as determined by their higher levels of CXCR4 expression and annexin V binding. Consequently, bone marrow neutrophils from AnxA1(-/-) mice exhibit a reduced migratory capacity in vitro. Studies conducted in vitro also show that expression of AnxA1 is required for bone marrow macrophages, but not peritoneal macrophages, to phagocytose apoptotic neutrophils. Moreover, in vivo experiments indicate a defect in clearance of wild-type neutrophils in the bone marrow of AnxA1(-/-) mice. Thus, we conclude that expression of AnxA1 by resident macrophages is a critical determinant for neutrophil clearance in the bone marrow.     

Regulation of innate immunity by inositol 1,3,4,5-tetrakisphosphate

Many neutrophil functions are mediated by PtdIns(3,4,5)P3 that exerts its role by mediating protein translocation via binding to their PH-domains. Inositol 1,3,4,5-tetrakisphosphate (Ins(1,3,4,5)P4) binds the same PH domain, competes for its binding to PtdIns(3,4,5)P3, and thus negatively regulates PtdIns(3,4,5)P3 signaling. In neutrophils, chemoattractant stimulation triggers rapid elevation in Ins(1,3,4,5)P4 level. Depletion of Ins(1,3,4,5)P4 by deleting InsP3KB, the major enzyme producing Ins(1,3,4,5)P4 in neutrophils, augments PtdIns(3,4,5)P3 downstream signals, leading to enhanced sensitivity to chemoattractant stimulation, elevated superoxide production, and enhanced neutrophil recruitment to inflamed peritoneal cavity. InsP3KB gene is also expressed in hematopoietic stem/progenitor cells. In InsP3KB null mice, the bone marrow granulocyte monocyte progenitor (GMP) population is expanded and the proliferation of GMP cells is accelerated. As results, neutrophil production in the bone marrow is enhanced and peripheral blood neutrophil count is elevated. Ins(1,3,4,5)P4 also plays a role in maintaining neutrophil survival. Depletion of Ins(1,3,4,5)P4 leads to accelerated neutrophil spontaneous death. Finally, InsP3KB and Ins(1,3,4,5)P4 are essential components in bacterial killing by neutrophils. Despite of the augmented neutrophil recruitment, the clearance of bacteria in the InsP3KB knockout mice is significantly impaired. Collectively, these findings establish InsP3KB and its product Ins(1,3,4,5)P4 as essential modulators of neutrophil function and innate immunity.     

Neutrophil mobilization from the bone marrow during polymicrobial sepsis is dependent on CXCL12 signaling

Neutrophils are essential for successful host eradication of bacterial pathogens and for survival to polymicrobial sepsis. During inflammation, the bone marrow provides a large reserve of neutrophils that are released into the peripheral circulation where they traverse to sites of infection. Although neutrophils are essential for survival, few studies have investigated the mechanisms responsible for neutrophil mobilization from the bone marrow during polymicrobial sepsis. Using a cecal ligation and puncture model of polymicrobial sepsis, we demonstrated that neutrophil mobilization from the bone marrow is not dependent on TLR4, MyD88, TRIF, IFNARα/β, or CXCR2 pathway signaling during sepsis. In contrast, we observed that bone marrow CXCL12 mRNA abundance and specific CXCL12 levels are sharply reduced, whereas splenic CXCR4 mRNA and cell surface expression are increased during sepsis. Blocking CXCL12 activity significantly reduced blood neutrophilia by inhibiting bone marrow release of granulocytes during sepsis. However, CXCL12 inhibition had no impact on the expansion of bone marrow neutrophil precursors and hematopoietic progenitors. Bone marrow neutrophil retention by CXCL12 blockade prevented blood neutrophilia, inhibited peritoneal neutrophil accumulation, allowed significant peritoneal bacterial invasion, and increased polymicrobial sepsis mortality. We concluded that changes in the pattern of CXCL12 signaling during sepsis are essential for neutrophil bone marrow mobilization and host survival but have little impact on bone marrow granulopoiesis.     

Elimination of senescent neutrophils by TNF-related apoptosis-inducing [corrected] ligand

Neutrophils are phagocytic effectors which are produced in the bone marrow and released into the circulation. Thereafter, they are either recruited to sites of inflammation or rapidly become senescent, return to the bone marrow, and undergo apoptosis. Stromal cell-derived factor 1 (SDF-1) coordinates the return of senescent neutrophils to the bone marrow by interacting with CXCR4 that is preferentially expressed on senescent neutrophils. We demonstrate that CXCR4 ligation by SDF-1 or other CXCR4 agonists significantly increases the expression of both TNF-related apoptosis-inducing [corrected] ligand (TRAIL) and of the death-inducing TRAIL receptors on neutrophils, which confers an acquired sensitivity to TRAIL-mediated death and results in TRAIL-dependent apoptosis. In vivo administration of TRAIL antagonists results in neutrophilic accumulation within the bone marrow and a reduction in neutrophil apoptosis; conversely recombinant TRAIL administration reduced neutrophil number within bone marrow. Thus, SDF-1 ligation of CXCR4 causes the parallel processes of chemotaxis and enhanced TRAIL and TRAIL death receptor expression, resulting in apoptosis of senescent neutrophils upon their return to the bone marrow.     

Activation of granulocyte cytotoxic function by purified mouse colony-stimulating factors

Highly purified mouse colony-stimulating factors (CSF) were tested for their effect on neutrophil cytotoxic function in a homologous antibody-dependent cell-mediated cytotoxicity (ADCC) assay in which TNP-coupled mouse thymoma cells coated with mouse anti-TNP antibodies were used as targets, and purified normal mouse bone marrow neutrophils or induced peritoneal neutrophils were used as effector cells. Biochemically pure granulocyte-macrophage (GM)- and granulocyte (G)-CSF enhanced the cytotoxic activity of neutrophils obtained from both sources, allowing them to kill target cells at low antibody concentrations. Furthermore, GM- and G-CSF showed an additive effect, suggesting either the presence of separate receptors for GM- and G-CSF or of separate subsets of neutrophils. Induced peritoneal neutrophils showed a higher level of basal cytotoxic activity than did bone marrow neutrophils, suggesting neutrophil activation in vivo, but both reached similar levels of cytotoxicity upon maximal stimulation with CSF. In addition, CSF was found to be cross-reactive between mouse and human species in their enhancement of neutrophil cytotoxicity. By testing purified mouse CSF on human neutrophils, it could be shown that G-CSF and GM-CSF are functionally distinct molecules, because only G-CSF enhanced ADCC by human neutrophils. These experiments show that the purified factors that control the production of neutrophils by progenitor cells in vitro also activate differentiated neutrophils to carry out their cytotoxic activity in a more effective manner.     

Function and regulation of the neutrophil MEL-14 antigen in vivo: comparison with LFA-1 and MAC-1

The CD11/18 (LFA-1, Mac-1) molecules participate in neutrophil adhesion to cultured endothelium in vitro and are critical for effective neutrophil localization into inflamed tissues in vivo. More recently, the MEL-14 Ag, which was first defined as a lymphocyte homing receptor, has also been implicated in inflammatory neutrophil extravasation. Here we compare the regulation and function of these adhesion molecules on neutrophils during the in vivo inflammatory response. The MEL-14 Ag is expressed at high levels on bone marrow and peripheral blood neutrophils, but is lost on neutrophils isolated from the thioglycollate-inflamed peritoneal cavity. In contrast, Mac-1 is up-regulated on inflammatory neutrophils and little change is seen in the level of LFA-1 expression. In vitro activation of bone marrow neutrophils with PMA or leukotriene B4 results in a dose dependent increase in Mac-1 and decrease in MEL-14 Ag expression within 1 h after treatment, thus reflecting what is found during inflammation in vivo. Neutrophils activated in vitro or in vivo (MEL-14Low, Mac-1Hi) do not home to inflammatory sites in vivo, correlating with the loss of the MEL-14 Ag and the increased Mac-1 expression. Anti-LFA-1, anti-Mac-1, or MEL-14 antibody given i.v. suppress neutrophil accumulation within the inflamed peritoneum (38%, 30%, and 37% of medium control, respectively) without affecting the levels of circulating neutrophils. However, when FITC-labeled cells are precoated with the mAb and injected i.v., only MEL-14 inhibits extravasation into the inflamed peritoneum (25% of medium control). Finally, in ex vivo adhesion assays of neutrophil binding to high endothelial venules in inflamed-lymph node frozen sections MEL-14 inhibits greater than 90%. anti-LFA-1 20 to 30% and anti-Mac-1 less than 10% of the binding of bone marrow neutrophils to inflamed-lymph node high endothelial venules. These results confirm that both the MEL-14 antigen and Mac-1/LFA-1 are important in neutrophil localization to inflamed sites in vivo, but suggest that their roles in endothelial cell interactions are distinct.     

Neutrophil maturation and activation determine anatomic site of clearance from circulation

The long-term disposition of circulating neutrophils and the site of disappearance from circulation remain unclear. We investigated neutrophil localization in mice using (111)In-labeled murine peripheral blood neutrophils, mature bone marrow neutrophils, and peritoneal exudate neutrophils to track in vivo localization of these different cell populations. Infused peripheral neutrophils were found to localize equally between liver and marrow sites by 4 h (31.2 +/- 1.9 vs. 31.9 +/- 1.8%), whereas exudate neutrophils predominantly localized to liver (42.0 +/- 1.1%) and marrow-derived neutrophils to the marrow (65.9 +/- 6.6%) where they were found to localize predominantly in the hematopoietic cords. Stimulation of marrow neutrophils before infusion caused a shift in localization from marrow to liver, and subsequent induction of an inflammatory site after infusion and marrow sequestration led to remobilization of infused marrow neutrophils but not of peripheral neutrophils. These results indicate that the marrow participates in removing neutrophils from circulation, with evidence supporting both storage and perhaps disposal functions. Furthermore, models for circulating neutrophil homeostasis should consider that the site of retention is governed by the maturation and activation states of the cell.     

High concentrations of alpha-defensins in plasma and bronchoalveolar lavage fluid of patients with acute respiratory distress syndrome

alpha-Defensins, antimicrobial peptides localized in neutrophils, participate in tissue damage through their cytotoxic effects in neutrophil-mediated pulmonary diseases. Neutrophils play an important role in the pathogenesis of acute respiratory distress syndrome (ARDS). We measured alpha-defensins levels in plasma and bronchoalveolar lavage fluid (BALF) of ARDS patients to assess the kinetics of alpha-defensins in ARDS. Plasma alpha-defensins levels were higher in ARDS patients than in control subjects, and BALF levels were also higher in ARDS patients than in control subjects. In ARDS, BALF alpha-defensins levels correlated with those of interleukin (IL)-8, and plasma alpha-defensins levels also correlated with Lung Injury Score. Peripheral neutrophil alpha-defensins contents were higher in ARDS than the control. IL-8 dose-dependently stimulated alpha-defensins release from cultured neutrophils and these levels were higher in ARDS than the control. Reverse-phase high performance liquid chromatography showed high plasma levels of pro-defensins, precursors of alpha-defensins from the bone marrow in ARDS, although alpha-defensins in peripheral and BALF neutrophils were mature type. In conclusion, high plasma alpha-defensins in ARDS patients result from the release of pro-defensins from bone marrow, rather than mature alpha-defensins from neutrophils that accumulate in the alveolar space. The alpha-defensins contents of peripheral neutrophils in ARDS are higher and easier to release than control.     

G-CSF Control of Neutrophils Dynamics in the Blood

White blood cell neutrophil is a key component in the fast initial immune response against bacterial and fungal infections. Granulocyte colony stimulating factor (G-CSF) which is naturally produced in the body, is known to control the neutrophils production in the bone marrow and the neutrophils delivery into the blood. In oncological practice, G-CSF injections are widely used to treat neutropenia (dangerously low levels of neutrophils in the blood) and to prevent the infectious complications that often follow chemotherapy. However, the accurate dynamics of G-CSF neutrophil interaction has not been fully determined and no general scheme exists for an optimal G-CSF application in neutropenia. Here we develop a two-dimensional ordinary differential equation model for the G-CSF—neutrophil dynamics in the blood. The model is built axiomatically by first formally defining from the biology the expected properties of the model, and then deducing the dynamic behavior of the resulting system. The resulting model is structurally stable, and its dynamical features are independent of the precise form of the various rate functions. Choosing a specific form for these functions, three complementary parameter estimation procedures for one clinical (training) data set are utilized. The fully parameterized model (6 parameters) provides adequate predictions for several additional clinical data sets on time scales of several days. We briefly discuss the utility of this relatively simple and robust model in several clinical conditions. Dedicated to Lee Segel who guided us to apply mathematics for the benefit of mankind—a teacher, a colleague, a friend. L.A. Segel passed away on 31 January 2005.     

Homeostatic regulation of blood neutrophil counts

Blood neutrophil counts are determined by the differentiation and proliferation of precursor cells, the release of mature neutrophils from the bone marrow, margination, trafficking and transmigration through the endothelial lining, neutrophil apoptosis, and uptake by phagocytes. This brief review summarizes the regulation of blood neutrophil counts, which is in part controlled by G-CSF, IL-17, and IL-23. Neutrophils are retained in the bone marrow through interaction of CXCL12 with its receptor CXCR4. The relevance of this mechanism is illustrated by rare diseases in which disrupting the desensitization of CXCR4 results in failure to release mature neutrophils from bone marrow. Although blood neutrophil numbers in inbred mouse strains and individual human subjects are tightly controlled, their large variation among outbred populations suggests genetic factors. One example is benign ethnic neutropenia, which is found in some African Americans. Reduced and elevated neutrophil counts, even within the normal range, are associated with excess all-cause mortality.     

Bone marrow-derived cells require a functional glucose 6-phosphate transporter for normal myeloid functions

Glycogen storage disease type Ib (GSD-Ib) is caused by a deficiency in the ubiquitously expressed glucose 6-phosphate transporter (Glc-6-PT). Glc-6-PT activity has been shown to be critical in the liver and kidney where a deficiency disrupts glucose homeostasis. GSD-Ib patients also have defects in the neutrophil respiratory burst, chemotaxis, and calcium flux. They also manifest neutropenia, but whether Glc-6-PT deficiency in the bone marrow underlies myeloid dysfunctions in GSD-Ib remains controversial. To address this, we transferred bone marrow from Glc-6-PT-deficient (Glc-6-PT(-/-)) mice to wild-type mice to generate chimeric mice (BM-Glc-6-PT(-/-)). As a control, we also transferred bone marrow between wild-type mice (BM-Glc-6-PT(+/+)). While BM-Glc-6-PT(+/+) mice have normal myeloid functions, BM-Glc-6-PT(-/-) mice manifest myeloid abnormalities characteristic of Glc-6-PT(-/-) mice. Both have impairments in their neutrophil respiratory burst, chemotaxis response, and calcium flux activities and exhibit neutropenia. In the bone marrow of BM-Glc-6-PT(-/-) and Glc-6-PT(-/-) mice, the numbers of myeloid progenitor cells are increased, while in the serum there is an increase in granulocyte colony-stimulating factor and chemokine KC levels. Moreover, in an experimental model of peritoneal inflammation, local production of KC and the related chemokine macrophage inflammatory protein-2 is decreased in both BM-Glc-6-PT(-/-) and Glc-6-PT(-/-) mice along with depressed peritoneal neutrophil accumulation. The neutrophil recruitment defect was less severe in BM-Glc-6-PT(-/-) mice than in Glc-6-PT(-/-) mice. These findings demonstrate that Glc-6-PT expression in bone marrow and neutrophils is required for normal myeloid functions and that non-marrow Glc-6-PT activity also influences some myeloid functions.     

Inhibitors of elastase and cathepsin G in Chédiak-Higashi (beige) neutrophils

Previous studies have established that mature neutrophils from the peritoneal cavity, blood, and bone marrow of beige (Chédiak-Higashi syndrome) mice essentially lack activities of two lysosomal proteinases: elastase and cathepsin G. There are, however, significant levels of each enzyme in early neutrophil precursors in bone marrow. In the present experiments, it was found that the addition of extracts from mature beige neutrophils to extracts of normal neutrophils or to purified human neutrophil elastase and cathepsin G resulted in a significant inhibition of elastase and cathepsin G G activities. 125I-Labeled human neutrophil elastase formed high molecular mass complexes at 64 and 52 kDa on sodium dodecyl sulfate-polyacrylamide gel electrophoresis when added to beige neutrophil extracts. The molecular masses of the inhibitor-125I-elastase complexes suggested that the molecular masses of the inhibitors are approximately 36 and 24 kDa, respectively. These results were confirmed by gel filtration on Superose 12 under nondenaturing conditions. Cathepsin G was inhibited only by the 36-kDa component. The inhibitors formed a covalent complex with the active sites of elastase and cathepsin G. No inhibitory activity was present in mature neutrophil extracts of genetically normal mice or in extracts of bone marrow of beige mice. These results thus represent an unusual example of an enzyme deficiency state caused by the presence of excess inhibitors. Inactivation of neutrophil elastase and cathepsin G in mature circulating and tissue neutrophils may contribute to the increased susceptibility of Chédiak-Higashi patients to infection.     

Neutrophils Contribute to Excess Serum BAFF Levels and Promote CD4+ T Cell and B Cell Responses in Lupus-Prone Mice

Despite increased frequencies of neutrophils found in autoimmune diseases such as systemic lupus erythematosus (SLE), how they contribute to disease pathogenesis and the mechanisms that affect the accumulation of neutrophils are poorly understood. The aim of this study was to identify factors in autoantibody-mediated autoimmunity that controls the accumulation of spleen resident neutrophils and to determine whether neutrophils contribute to abnormal B cell responses. Increased levels of the cytokine BAFF have been linked to loss of B cell tolerance in autoimmunity, but the cellular source responsible for excess BAFF is unknown. B cell maturation antigen (BCMA) is a receptor for BAFF and is critical for the survival of bone marrow plasma cells. Paradoxically, BCMA deficiency exacerbates the formation of autoantibody-secreting plasma cells in spleens of lupus-prone mice and the reasons for this effect are not understood. Here we analyzed the phenotype, localization and function of neutrophils in spleens of healthy mice and congenic lupus-prone mice, and compared mice sufficient or deficient in BCMA expression. Neutrophils were found to be significantly increased in frequency and activation status in spleens of lupus-prone mice when BCMA was absent. Furthermore, neutrophils localized within T cell zones and enhanced CD4⁺ T cell proliferation and IFNγ production through the production of BAFF. Reduced BAFF and IFNγ serum levels, decreased frequencies of IFNγ-producing T cells, germinal center B cells, and autoantibody production after neutrophil depletion indicated the involvement of neutrophils in these autoimmune traits. Thus, we have identified a novel role for BCMA to control excess BAFF production in murine lupus through restraining the accumulation of BAFF-producing neutrophils. Our data suggests that devising therapeutic strategies to reduce neutrophils in autoimmunity may decrease BAFF levels and ameliorate disease.     

Stress-induced effects, which inhibit host defenses, alter leukocyte trafficking

Acute cold restraint stress (ACRS) has been reported to suppress host defenses against Listeria monocytogenes, and this suppression was mediated by beta1-adrenoceptors (β1-ARs). Although ACRS appears to inhibit mainly early innate immune defenses, interference with leukocyte chemotaxis and the involvement of β1-AR (or β2-AR) signaling had not been assessed. Thus, the link between sympathetic nerve stimulation, release of neurotransmitters, and changes in blood leukocyte profiles, including oxidative changes, following ACRS was evaluated. The numbers of leukocyte subsets in the blood were differentially affected by β1-ARs and β2-ARs following ACRS; CD3⁺ (CD4 and CD8) T-cells were shown to be decreased following ACRS, and the T cell lymphopenia was mediated mainly through a β2-AR mechanism, while the decrease in CD19⁺ B-cells was influenced through both β1- and β2-ARs, as assessed by pharmacological and genetic manipulations. In contrast to the ACRS-induced loss of circulating lymphocytes, the number of circulating neutrophils was increased (i.e., neutrophilia), and this neutrophilia was mediated through β1-ARs. The increase in circulating neutrophils was not due to an increase in serum chemokines promoting neutrophil emigration from the bone marrow; rather it was due to neutrophil release from the bone marrow through activation of a β1-AR pathway. There was no loss of glutathione in any of the leukocyte subsets suggesting that there was minimal oxidative stress; however, there was early production of nitric oxide and generation of some protein radicals. Premature egress of neutrophils from bone marrow is suggested to be due to norepinephrine induction of nitric oxide, which affects the early release of neutrophils from bone marrow and lessens host defenses.     

Bone marrow neutrophil aging in sickle cell disease mice is associated with impaired osteoblast functions

Bone loss is a common complication in individuals with sickle cell disease (SCD). The mechanism(s) of bone loss in SCD subjects has not been fully investigated, and there are no targeted therapies to prevent or treat compromised bone health in this population. Recent studies showed that depletion of gut microbiota with antibiotics significantly reduced the number of aged neutrophils, thereby dramatically improved the inflammation-related organ damages in SCD mice. Since neutrophils, abundantly present in bone marrow (BM), regulate bone cells, and BM neutrophils, induced by inflammatory cytokines, are associated with a low number of osteoblasts (OBs), we hypothesize that neutrophil aging in the BM of SCD mice impairs OB function. Flow cytometry analysis showed BM neutrophil aging was significantly increased in SCD mice that was reduced with antibiotic treatment. In vitro co-culture of calvarial OBs from control (Ctrl) mice with BM neutrophils from Ctrl or SCD mice showed that BM neutrophils from SCD mice inhibit OB function but was rescued when neutrophils were from antibiotic-treated SCD mice. In summary, there is an accumulation of aged neutrophils in BM from SCD mice that may contribute to impaired OB function, and antibiotic treatment is able to partially rescue impaired OB function by decreasing neutrophil aging in the BM of SCD mice.     

Deficiency of Src homology 2-containing phosphatase 1 results in abnormalities in murine neutrophil function: studies in motheaten mice

Neutrophils, an essential component of the innate immune system, are regulated in part by signaling pathways involving protein tyrosine phosphorylation. While protein tyrosine kinase functions in regulating neutrophil behavior have been extensively investigated, little is known about the role for specific protein tyrosine phosphatases (PTP) in modulating neutrophil signaling cascades. A key role for Src homology 2 domain-containing phosphatase 1 (SHP-1), a PTP, in neutrophil physiology is, however, implied by the overexpansion and inappropriate activation of granulocyte populations in SHP-1-deficient motheaten (me/me) and motheaten viable (me(v)/me(v)) mice. To directly investigate the importance of SHP-1 to phagocytic cell function, bone marrow neutrophils were isolated from both me/me and me(v)/me(v) mice and examined with respect to their responses to various stimuli. The results of these studies revealed that both quiescent and activated neutrophils from motheaten mice manifested enhanced tyrosine phosphorylation of cellular proteins in the 60- to 80-kDa range relative to that detected in wild-type congenic control neutrophils. MOTHEATEN: neutrophils also demonstrated increased oxidant production, surface expression of CD18, and adhesion to protein-coated plastic. Chemotaxis, however, was severely diminished in the SHP-deficient neutrophils relative to control neutrophils, which was possibly attributable to a combination of defective deadhesion and altered actin assembly. Taken together, these results indicate a significant role for SHP-1 in modulating the tyrosine phosphorylation-dependent signaling pathways that regulate neutrophil microbicidal functions.