Neutrophil mobilization and clearance in the bone marrow

Bone marrow-targeted liposomal carriers

INTRODUCTION

Bone marrow-targeted drug delivery systems appear to offer a promising strategy for advancing diagnostic, protective and/or therapeutic medicine for the hematopoietic system. Liposome technology can provide a drug delivery system with high bone marrow targeting that is mediated by specific phagocytosis in bone marrow.

AREA COVERED

This review focuses on a bone marrow-specific liposome formulation labeled with technetium-99 m. Interspecies differences in bone marrow distribution of the bone marrow-targeted formulation are emphasized. This review provides a liposome technology to target bone marrow. In addition, the selection of proper species for the investigation of bone marrow targeting is suggested.

EXPERT OPINION

It can be speculated that the bone marrow macrophages have a role in the delivery of lipids to the bone marrow as a source of energy and for membrane biosynthesis or in the delivery of fat-soluble vitamins for hematopoiesis. This homeostatic system offers a potent pathway to deliver drugs selectively into bone marrow tissues from blood. High selectivity of the present bone marrow-targeted liposome formulation for bone marrow suggests the presence of an active and specific mechanism, but specific factors affecting the uptake of the bone marrow mononuclear phagocyte system are still unknown. Further investigation of this mechanism will increase our understanding of factors required for effective transport of agents to the bone marrow, and may provide an efficient system for bone marrow delivery for therapeutic purposes.

Neutrophil survival and c-kit(+)-progenitor proliferation in Staphylococcus aureus-infected skin wounds promote resolution

Polymorphonuclear neutrophils (PMNs) are critical for the formation, maintenance, and resolution of bacterial abscesses. However, the mechanisms that regulate PMN survival and proliferation during the evolution of an abscess are not well defined. Using a mouse model of Staphylococcus aureus abscess formation within a cutaneous wound, combined with real-time imaging of genetically tagged PMNs, we observed that a high bacterial burden elicited a sustained mobilization of PMNs from the bone marrow to the infected wound, where their lifespan was markedly extended. A continuous rise in wound PMN number, which was not accounted for by trafficking from the bone marrow or by prolonged survival, was correlated with the homing of c-kit(+)-progenitor cells from the blood to the wound, where they proliferated and formed mature PMNs. Furthermore, by blocking their recruitment with an antibody to c-kit, which severely limited the proliferation of mature PMNs in the wound and shortened mouse survival, we confirmed that progenitor cells are not only important contributors to PMN expansion in the wound, but are also functionally important for immune protection. We conclude that the abscess environment provides a niche capable of regulating PMN survival and local proliferation of bone marrow-derived c-kit(+)-progenitor cells.

Effect of an extract based on the medicinal mushroom Agaricus blazei Murill on expression of cytokines and calprotectin in patients with ulcerative colitis and Crohn's disease

An immunomodulatory extract (AndoSan™) based on the medicinal mushroom Agaricus blazei Murill (AbM) has shown to reduce blood cytokine levels in healthy volunteers after 12 days' ingestion, pointing to an anti-inflammatory effect. The aim was to study whether AndoSan™ had similar effects on cytokines in patients with ulcerative colitis (UC) and Crohn's disease (CD). Calprotectin, a marker for inflammatory bowel disease (IBD), was also measured. Patients with CD (n = 11) and with UC (n = 10) consumed 60 ml/day of AndoSan™. Patient blood plasma was harvested before and after 6 h LPS (1 ng/ml) stimulation ex vivo. Plasma and faecal calprotectin levels were analysed using ELISA and 17 cytokines [IL-2, IFN-γ, IL-12 (Th1), IL-4, IL-5, IL-13 (Th2), IL-7, IL-17, IL-1β, IL-6, TNF-α, IL-8, MIP-1β, MCP-1, G-CSF, GM-CSF and IL-10] by multiplex assay. After 12 days' ingestion of AndoSan™, baseline plasma cytokine levels in UC was reduced for MCP-1 (40%) and in LPS-stimulated blood for MIP-1β (78%), IL-6 (44%), IL-1β (41%), IL-8 (30%), G-CSF (29%), MCP-1 (18%) and GM-CSF (17%). There were corresponding reductions in CD: IL-2 (100%), IL-17 (55%) and IL-8 (29%) and for IL-1β (35%), MIP-1β (30%), MCP-1 (22%), IL-8 (18%), IL-17 (17%) and G-CSF (14%), respectively. Baseline concentrations for the 17 cytokines in the UC and CD patient groups were largely similar. Faecal calprotectin was reduced in the UC group. Ingestion of an AbM-based medicinal mushroom by patients with IBD resulted in interesting anti-inflammatory effects as demonstrated by declined levels of pathogenic cytokines in blood and calprotectin in faeces.

Phagocytosis and digestion of pH-sensitive fluorescent dye (Eos-FP) transfected E. coli in whole blood assays from patients with severe sepsis and septic shock

The function of phagocytic and antigen presenting cells is of crucial importance to sustain immune competence against infectious agents as well as malignancies. We here describe a reproducible procedure for the quantification of phagocytosis by leukocytes in whole blood. For this, a pH-sensitive green-fluorescent protein- (GFP) like dye (Eos-FP) is transfected into infectious microroganisms. After UV-irradiation, the transfected bacteria emit green (≈5160 nm) and red (≈581 nm) fluorescent light at 490 nm excitation. Since the red fluorescent light is sensitive to acidic pH, the phagocytosed bacteria stop emitting red fluorescent light as soon as the phagosomes fuse with lysosomes. The green fluorescence is maintained in the phagolysosome until pathogen degradation is completed. Fluorescence emission can be followed by flow cytometry with filter settings documenting fluorescence 1 (FL 1, FITC) and fluorescence 2 (FL 2, phycoerythrin, PE). Eos-FP transfected bacteria can also be traced within phagocytes using microscopical techniques. A standardized assay has been developed which is suitable for clinical studies by providing clinicians with syringes pre-filled with fixed and appropriately UV-irradiated Eos-FP E. coli (TruCulture™). After adding blood or body fluids to these containers and starting the incubation at 37°C, phagocytosis by granulocytes proceeds over time. Cultures can be terminated at a given time by lysing red blood cells followed by flow cytometry. A pilot study demonstrated that Eos-FP E. coli phagocytosis and digestion was up-regulated in the majority of patients with either severe sepsis or septic shock as compared to healthy donors (p < 0.0001 after o/n incubation). Following treatment with recombinant human granulocyte colony-stimulating factor (rhG-CSF) in selected patients with sepsis, phagolysosome fusion appeared to be accelerated.

G-CSF-mediated thrombopoietin release triggers neutrophil motility and mobilization from bone marrow via induction of Cxcr2 ligands

Emergency mobilization of neutrophil granulocytes (neutrophils) from the bone marrow (BM) is a key event of early cellular immunity. The hematopoietic cytokine granulocyte-colony stimulating factor (G-CSF) stimulates this process, but it is unknown how individual neutrophils respond in situ. We show by intravital 2-photon microscopy that a systemic dose of human clinical-grade G-CSF rapidly induces the motility and entry of neutrophils into blood vessels within the tibial BM of mice. Simultaneously, the neutrophil-attracting chemokine KC (Cxcl1) spikes in the blood. In mice lacking the KC receptor Cxcr2, G-CSF fails to mobilize neutrophils and antibody blockade of Cxcr2 inhibits the mobilization and induction of neutrophil motility in the BM. KC is expressed by megakaryocytes and endothelial cells in situ and is released in vitro by megakaryocytes isolated directly from BM. This production of KC is strongly increased by thrombopoietin (TPO). Systemic G-CSF rapidly induces the increased production of TPO in BM. Accordingly, a single injection of TPO mobilizes neutrophils with kinetics similar to G-CSF, and mice lacking the TPO receptor show impaired neutrophil mobilization after short-term G-CSF administration. Thus, a network of signaling molecules, chemokines, and cells controls neutrophil release from the BM, and their mobilization involves rapidly induced Cxcr2-mediated motility controlled by TPO as a pacemaker.

Measuring whole-body neutrophil redistribution using a dedicated whole-body counter and ultra-low doses of 111Indium

BACKGROUND

There is increasing interest in the 'homing' of neutrophils to bone marrow. The aim of this study was to measure the whole-body redistribution of (111) In using a whole-body counter following the administration of ultra-small activities of (111) In-labelled neutrophils.

METHODS

The detectors of a dedicated whole-body counter were fitted with lead collimators. Whole-body (111) In distribution was recorded at 45 min, 24 h, and 2, 4, 7 and 10 days after administration of (111) In-labelled neutrophils (0·29-0·74 MBq) in eight healthy non-smokers, five healthy smokers, eight patients with inactive bronchiectasis, three with asthma and nine with chronic obstructive pulmonary disease (COPD).

RESULTS

Intravascular 45-min (111) In-labelled neutrophil recovery was not significantly different between groups, ranging from 33 (SD 8%) in healthy smokers to 45 (14%) in healthy non-smokers (P > 0·05). Peaks were identified on the whole body count profile corresponding to the chest, upper abdomen (liver/spleen) and pelvis (bone marrow). (111) In distribution changed between 45 min and 24 h and then remained stable thereafter. Peak chest counts increased ∼ 1·5-fold between 45 min and 24 h, whereas upper abdominal peak counts decreased by ∼ 25% with no significant inter-group differences. The increment in pelvic counts (∼ 2·7-fold) was similar between groups, except COPD patients, in whom it was 2·04 (0·35; P < 0·02 vs. healthy participants).

CONCLUSIONS

Assuming neutrophils are distributed only between blood, liver, spleen and bone marrow, the data suggest that marrow pools 25% and destroys 67% of circulating neutrophils, rising in COPD to 40% and 80%, respectively, possibly as a result of the effects on marrow of chronic hypoxaemia.

Discovery of a CXCR4 agonist pepducin that mobilizes bone marrow hematopoietic cells

The G protein-coupled receptor (GPCR), chemokine CXC-type receptor 4 (CXCR4), and its ligand, CXCL12, mediate the retention of polymorphonuclear neutrophils (PMNs) and hematopoietic stem and progenitor cells (HSPCs) in the bone marrow. Agents that disrupt CXCL12-mediated chemoattraction of CXCR4-expressing cells mobilize PMNs and HSPCs into the peripheral circulation and are therapeutically useful for HSPC collection before autologous bone marrow transplantation (ABMT). Our aim was to develop unique CXCR4-targeted therapeutics using lipopeptide GPCR modulators called pepducins. A pepducin is a synthetic molecule composed of a peptide derived from the amino acid sequence of one of the intracellular (IC) loops of a target GPCR coupled to a lipid tether. We prepared and screened a small CXCR4-targeted pepducin library and identified several pepducins with in vitro agonist activity, including ATI-2341, whose peptide sequence derives from the first IC loop. ATI-2341 induced CXCR4- and G protein-dependent signaling, receptor internalization, and chemotaxis in CXCR4-expressing cells. It also induced dose-dependent peritoneal recruitment of PMNs when administered i.p. to mice. However, when administered systemically by i.v. bolus, ATI-2341 acted as a functional antagonist and dose-dependently mediated release of PMNs from the bone marrow of both mice and cynomolgus monkeys. ATI-2341-mediated release of granulocyte/macrophage progenitor cells from the bone marrow was confirmed by colony-forming assays. We conclude that ATI-2341 is a potent and efficacious mobilizer of bone marrow PMNs and HSPCs and could represent a previously undescribed therapeutic approach for the recruitment of HSPCs before ABMT.

A WHIM-sical zebrafish

In this issue of Blood, Walters and colleagues describe an elegant model of WHIM syndrome in the zebrafish embryo. By allowing the movement of WHIM neutrophils to be observed in live animals, this model dramatically illustrates the dynamics of the interaction between the neutrophil chemokine receptor CXCR4 and its receptor ligand (stromal-derived factor-1 [SDF-1], also known as CXCL12) in th hallmark of WHIM-excessive neutrophil adhesion to the marrow stroma.

Targeting granulocyte apoptosis: mechanisms, models, and therapies

The inflammatory process is a complex series of tightly controlled cellular and biochemical events initiated by the immune system, which has evolved to eliminate or contain infectious agents and to repair damaged tissue. Apoptosis is essential for the clearance of potentially injurious inflammatory cells, such as neutrophils, eosinophils, and basophils, and the subsequent efficient resolution of inflammation. In this review, we aim to cover key features of the granulocyte life-cycle ranging from their differentiation within the bone marrow to their maturation and ultimate clearance, with a focus on granulocyte apoptosis and macrophage efferocytosis. We further aim to discuss current and emerging models of inflammation and suggest novel ways of terminating or resolving deleterious inflammatory responses with a specific view to the translation of these strategies into fully realized, pro-resolution therapies.

Live imaging of neutrophil motility in a zebrafish model of WHIM syndrome

CXCR4 is a G protein-coupled chemokine receptor that has been implicated in the pathogenesis of primary immunodeficiency disorders and cancer. Autosomal dominant gain-of-function truncations of CXCR4 are associated with warts, hypo-gammaglobulinemia, infections, and myelokathexis (WHIM) syndrome, a primary immunodeficiency disorder characterized by neutropenia and recurrent infections. Recent progress has implicated CXCR4-SDF1 (stromal cell-derived factor 1) signaling in regulating neutrophil homeostasis, but the precise role of CXCR4-SDF1 interactions in regulating neutrophil motility in vivo is not known. Here, we use the optical transparency of zebrafish to visualize neutrophil trafficking in vivo in a zebrafish model of WHIM syndrome. We demonstrate that expression of WHIM mutations in zebrafish neutrophils induces neutrophil retention in hematopoietic tissue, impairing neutrophil motility and wound recruitment. The neutrophil retention signal induced by WHIM truncation mutations is SDF1 dependent, because depletion of SDF1 with the use of morpholino oligonucleotides restores neutrophil chemotaxis to wounds. Moreover, localized activation of a genetically encoded, photoactivatable Rac guanosine triphosphatase is sufficient to direct migration of neutrophils that express the WHIM mutation. The findings suggest that this transgenic zebrafish model of WHIM syndrome may provide a valuable tool to screen for agents that modify CXCR4-SDF1 retention signals.

Genome-wide association identifies OBFC1 as a locus involved in human leukocyte telomere biology

Telomeres are engaged in a host of cellular functions, and their length is regulated by multiple genes. Telomere shortening, in the course of somatic cell replication, ultimately leads to replicative senescence. In humans, rare mutations in genes that regulate telomere length have been identified in monogenic diseases such as dyskeratosis congenita and idiopathic pulmonary fibrosis, which are associated with shortened leukocyte telomere length (LTL) and increased risk for aplastic anemia. Shortened LTL is observed in a host of aging-related complex genetic diseases and is associated with diminished survival in the elderly. We report results of a genome-wide association study of LTL in a consortium of four observational studies (n = 3,417 participants with LTL and genome-wide genotyping). SNPs in the regions of the oligonucleotide/oligosaccharide-binding folds containing one gene (OBFC1; rs4387287; P = 3.9 x 10(-9)) and chemokine (C-X-C motif) receptor 4 gene (CXCR4; rs4452212; P = 2.9 x 10(-8)) were associated with LTL at a genome-wide significance level (P < 5 x 10(-8)). We attempted replication of the top SNPs at these loci through de novo genotyping of 1,893 additional individuals and in silico lookup in another observational study (n = 2,876), and we confirmed the association findings for OBFC1 but not CXCR4. In addition, we confirmed the telomerase RNA component (TERC) as a gene associated with LTL (P = 1.1 x 10(-5)). The identification of OBFC1 through genome-wide association as a locus for interindividual variation in LTL in the general population advances the understanding of telomere biology in humans and may provide insights into aging-related disorders linked to altered LTL dynamics.

Host genetics in granuloma formation: human-like lung pathology in mice with reciprocal genetic susceptibility to M. tuberculosis and M. avium

Development of lung granulomata is a hallmark of infections caused by virulent mycobacteria, reflecting both protective host response that restricts infection spreading and inflammatory pathology. The role of host genetics in granuloma formation is not well defined. Earlier we have shown that mice of the I/St strain are extremely susceptible to Mycobacterium tuberculosis but resistant to M. avium infection, whereas B6 mice show a reversed pattern of susceptibility. Here, by directly comparing: (i) characteristics of susceptibility to two infections in vivo; (ii) architecture of lung granulomata assessed by immune staining; and (iii) expression of genes encoding regulatory factors of neutrophil influx in the lung tissue, we demonstrate that genetic susceptibility of the host largely determines the pattern of lung pathology. Necrotizing granuloma surrounded by hypoxic zones, as well as a massive neutrophil influx, develop in the lungs of M. avium-infected B6 mice and in the lungs of M. tuberculosis-infected I/St mice, but not in the lungs of corresponding genetically resistant counterparts. The mirror-type lung tissue responses to two virulent mycobacteria indicate that the level of genetic susceptibility of the host to a given mycobacterial species largely determines characteristics of pathology, and directly demonstrate the importance of host genetics in pathogenesis.

Effects of sepsis on neutrophil chemotaxis

PURPOSE OF REVIEW

Neutrophil recruitment to sites of infection is a critical element of the innate immune response. In patients with sepsis, this response is dysregulated, with exuberant inflammation being followed by a state of profound immune suppression, including inhibition of neutrophil recruitment. This review examines mechanisms underlying suppression of neutrophil migration during sepsis.

RECENT FINDINGS

Mechanisms governing neutrophil chemotactic function in sepsis are complex. Bacterial products, cytokines, and chemokines can modulate neutrophil migratory responses during sepsis via induction of cytoskeletal changes, inhibition of polymorphonuclear leukocyte (PMN)-endothelial cell interactions, and alterations in G protein-coupled receptor expression or signaling. Impaired chemotactic responses can occur as a result of dysregulated PMN Toll-like receptor signaling. Other recently identified inhibitory mechanisms include exposure to elevated temperatures, activation of the anti-inflammatory nuclear transcription factor peroxisome proliferator-activated receptor-gamma, and suppression of PMN-endothelial interactions due to nitric oxide and its metabolites. Finally, circulating microparticles released in sepsis exert important immunomodulatory effects on PMN adherence and transmigration.

SUMMARY

Neutrophil recruitment is a coordinated process that is altered at multiple stages during sepsis, culminating in defective innate immunity and increased risk of infection in these patients. Defining mechanisms involved and strategies to interrupt these deleterious responses requires further investigation.

Bone marrow-targeted liposomal carriers: a feasibility study in nonhuman primates

BACKGROUND & AIMS

Recently, we described a novel surface-modified lipid vesicle formulation (liposome) that had very high targeting to bone marrow in normal rabbits. Because the bone marrow is the site of hematopoiesis, bone marrow-targeted drug-delivery systems have many potential applications. In this study we investigated whether these bone marrow-targeted vesicles are also similarly effective for bone marrow targeting in rhesus monkeys, a primate animal model that is more relevant to humans.

MATERIALS & METHODS

The preformed vesicles encapsulating 30 mM glutathione were labeled with technetium-99m ((99m)Tc) for scintigraphic imaging. The vesicles were 216 +/- 21 nm in diameter with a negative surface charge composed of DPPC, cholesterol, anionic amphiphile and poly(ethylene glycol)-DSPE (1:1:0.2:0.013 molar ratio).

RESULTS

The whole-body images of rhesus monkeys receiving intravenous (99m)Tc vesicles revealed high uptake of the (99m)Tc vesicles in bone marrow. Based on image analysis, we estimated that approximately 70% of the injected dose of the (99m)Tc vesicles was taken up by the bone marrow.

CONCLUSION

This finding increases the feasibility of using this bone marrow-specific drug-delivery system for clinical applications.

Integrin and chemokine receptor gene expression in implant-adherent cells during early osseointegration

The mechanisms of early cellular recruitment and interaction to titanium implants are not well understood. The aim of this study was to investigate the expression of pro-inflammatory cytokines, chemokines and adhesion markers during the first 24 h of implantation. Anodically oxidized and machined titanium implants were inserted in rat tibia. After 3, 12, and 24 h the implants were unscrewed and analyzed with quantitative polymerase chain reaction. Immunohistochemistry and scanning electron microscopy revealed different cell types, morphology and adhesion at the two implant surfaces. A greater amount of cells, as indicated by higher expression of small subunit ribosomal RNA (18S), was detected on the oxidized surface. Higher expression of CXC chemokine receptor-4 (at 12 h) and integrins, alphav (at 12 h), beta1 (at 24 h) and beta2 (at 12 and 24 h) was detected at the oxidized surfaces. Significantly higher tumor necrosis factor-alpha (at 3 h) and interleukin-1beta (at 24 h) expression was demonstrated for the machined surface. It is concluded that material surface properties rapidly modulate the expression of receptors important for the recruitment and adhesion of cells which are crucial for the inflammatory and regenerative processes at implant surfaces in vivo.

Fifth complement cascade protein (C5) cleavage fragments disrupt the SDF-1/CXCR4 axis: further evidence that innate immunity orchestrates the mobilization of hematopoietic stem/progenitor cells

OBJECTIVE

Having previously demonstrated that the complement system modulates mobilization of hematopoietic stem/progenitor cells (HSPC) in mice, we investigated the involvement of C5 cleavage fragments (C5a/(desArg)C5a) in human HSPC mobilization.

MATERIALS AND METHODS

C5 cleavage fragments in the plasma were evaluated by enzyme-linked immunosorbent assay using human anti-(desArg)C5a antibody, and expression of the C5a/(desArg)C5a receptor (CD88) in hematopoietic cells by flow cytometry. We also examined the chemotactic responses of hematopoietic cells to C5 cleavage fragments and expression of stromal cell-derived factor-1 (SDF-1)-degrading proteases that perturb retention of HSPC in bone marrow, namely matrix metalloproteinase (MMP)-9, membrane type (MT) 1-MMP, and carboxypeptidase M.

RESULTS

We found that plasma levels of (desArg)C5a are significantly higher in patients who are good mobilizers and correlate with CD34(+) cell and white blood cell counts in mobilized peripheral blood. C5 cleavage fragments did not chemoattract myeloid progenitors (colony-forming unit granulocyte-macrophage), but (desArg)C5a did strongly chemoattract mature nucleated cells. Consistently, CD88 was not detected on CD34(+) cells, but appeared on more mature myeloid precursors, monocytes, and granulocytes. Moreover, granulocyte colony-stimulating factor-mobilized peripheral blood mononuclear cells and polymorphonuclear cells had a significantly higher percentage of cells expressing CD88 than nonmobilized peripheral blood. Furthermore, C5a stimulation of granulocytes and monocytes decreased CXCR4 expression and chemotaxis toward an SDF-1 gradient and increased secretion of MMP-9 and expression of MT1-MMP and carboxypeptidase M.

CONCLUSION

C5 cleavage fragments not only induce a highly proteolytic microenvironment in human bone marrow, which perturbs retention through the CXCR4/SDF-1 axis, but also strongly chemoattracts granulocytes, promoting their egress into mobilized peripheral blood, which is crucial for subsequent mobilization of HSPC.

Inflammatory monocytes but not neutrophils are necessary to control infection with Toxoplasma gondii in mice

Previous studies have suggested that both inflammatory monocytes and neutrophils are important for controlling acute toxoplasmosis in the mouse model. To test the role of these cell types, we used monoclonal antibody (MAb) RB6-8C5 to deplete both subsets of cells or MAb 1A8 to selectively remove neutrophils. RB6-8C5 MAb-treated mice succumbed to oral infection with Toxoplasma gondii, similar to Ccr2(-/-) mice, which are deficient in monocyte recruitment but have normal neutrophils. In contrast, mice treated with MAb 1A8 controlled parasite replication and survived acute infection. Ccr2(-/-) mice suffered from acute ileitis and inflammation in the spleen that was associated with a lack of inflammatory monocytes and elevated numbers of neutrophils. RB6-8C5 MAb-treated C57BL/6 mice also suffered from intestinal pathology and splenic damage, although this was less extensive due to the reduced numbers of neutrophils. Neutrophil-depleted infected wild-type mice displayed no pathological changes, compared to untreated infected controls. Collectively, these observations demonstrate the critical role of inflammatory monocytes during the acute infection with the parasite T. gondii and reveal that neutrophils are not protective but rather contribute to the pathology.

B cells delay neutrophil migration toward the site of stimulus: tardiness critical for effective bacillus Calmette-Guérin vaccination against tuberculosis infection in mice

Mutations in the btk gene encoding Bruton's tyrosine kinase cause X-linked immune deficiency, with impaired B lymphocyte function as the major phenotype. Earlier, we demonstrated that CBA/N-xid mice, unlike the wild-type CBA mice, were not protected by bacillus Calmette-Guérin (BCG) vaccination against tuberculosis infection. Because IFN-gamma-producing T cells and activated macrophages are key elements of antituberculosis protection, it remained unclear how the mutation predominantly affecting B cell functions interferes with responses along the T cell-macrophage axis. In this study, we show that B cell deficiency leads to an abnormally rapid neutrophil migration toward the site of external stimulus. Using adoptive cell transfers and B cell genetic knockout, we demonstrate a previously unappreciated capacity of B cells to downregulate neutrophil motility. In our system, an advanced capture of BCG by neutrophils instead of macrophages leads to a significant decrease in numbers of IFN-gamma-producing T cells and impairs BCG performance in X-linked immune-deficient mice. The defect is readily compensated for by the in vivo neutrophil depletion.

Citrullination of CXCL8 increases this chemokine's ability to mobilize neutrophils into the blood circulation

BACKGROUND

During the first line defense of an infected host, circulating neutrophils invade the inflamed tissue, whereas mature neutrophils from the bone marrow pool migrate into the blood circulation and from there reinforce tissue infiltration. The CXC chemokine CXCL8, also know as interleukin-8, is a potent attractant of neutrophils. Recently, we discovered a new natural post-translational modification of CXCL8, i.e. the deimination of arginine into citrulline by peptidylarginine deiminases.

DESIGN AND METHODS

The ability to provoke leukocytosis was assessed by intravenous administration of citrullinated CXCL8 in rabbits. Adsorption of citrullinated CXCL8 to the Duffy antigen/receptor for chemokines on human or rabbit erythrocytes was evaluated using a competitive binding assay. Finally, surface expression of adhesion molecules was studied after stimulating neutrophils with citrullinated CXCL8.

RESULTS

Citrullination of CXCL8 significantly increased this chemokine's ability to recruit neutrophils into the blood circulation. In addition, the competitive binding properties of CXCL8 for the Duffy antigen/receptor for chemokines were impaired upon citrullination. Since the Duffy antigen/receptor for chemokines is an important scavenging receptor for CXCL8 in the blood stream, citrullination may delay CXCL8 clearance from the circulation. Furthermore, the shedding of CD62L (L-selectin) and the upregulation of CD11b (beta2-integrin) protein expression on CXCL8-induced neutrophils were improved by deimination of CXCL8, possibly contributing to the neutrophil egress from the bone marrow. Conversely, surface expression of CD15, the neutrophilic ligand of endothelial selectins, was equally well upregulated by intact and citrullinated CXCL8.

CONCLUSIONS

These data show that citrullination of CXCL8 enhances leukocytosis, possibly through impaired chemokine clearance from the blood circulation and prolonged presentation to the bone marrow.