Allergen exposure-induced differences in CD34+ cell phenotype: relationship to eosinophilopoietic responses in different compartments

Eosinophil Lineage-Committed Progenitors as a Therapeutic Target for Asthma

Eosinophilic asthma is the most prevalent phenotype of asthma. Although most asthmatics are adequately controlled by corticosteroid therapy, a subset (5-10%) remain uncontrolled with significant therapy-related side effects. This indicates the need for a consideration of alternative treatment strategies that target airway eosinophilia with corticosteroid-sparing benefits. A growing body of evidence shows that a balance between systemic differentiation and local tissue eosinophilopoietic processes driven by traffic and lung homing of bone marrow-derived hemopoietic progenitor cells (HPCs) are important components for the development of airway eosinophilia in asthma. Interleukin (IL)-5 is considered a critical and selective driver of terminal differentiation of eosinophils. Studies targeting IL-5 or IL-5R show that although mature and immature eosinophils are decreased within the airways, there is incomplete ablation, particularly within the bronchial tissue. Eotaxin is a chemoattractant for mature eosinophils and eosinophil-lineage committed progenitor cells (EoP), yet anti-CCR3 studies did not yield meaningful clinical outcomes. Recent studies highlight the role of epithelial cell-derived alarmin cytokines, IL-33 and TSLP, (Thymic stromal lymphopoietin) in progenitor cell traffic and local differentiative processes. This review provides an overview of the role of EoP in asthma and discusses findings from clinical trials with various therapeutic targets. We will show that targeting single mediators downstream of the inflammatory cascade may not fully attenuate tissue eosinophilia due to the multiplicity of factors that can promote tissue eosinophilia. Blocking lung homing and local eosinophilopoiesis through mediators upstream of this cascade may yield greater improvement in clinical outcomes.

A sticky wicket: Defining molecular functions for CD34 in hematopoietic cells

The CD34 cell surface antigen is widely expressed in tissues on cells with progenitor-like properties and on mature vascular endothelia. In adult human bone marrow, CD34 marks hematopoietic stem and progenitor cells (HSPCs) starting from the bulk of hematopoietic stem cells with long-term repopulating potential (LT-HSCs) throughout expansion and differentiation of oligopotent and unipotent progenitors. CD34 protein surface expression is typically lost as cells mature into terminal effectors. Because of this expression pattern of HSPCs, CD34 has had a central role in the evaluation or selection of donor graft tissue in HSC transplant (HSCT). Given its clinical importance, it is surprising that the biological functions of CD34 are still poorly understood. This enigma is due, in part, to CD34's context-specific role as both a pro-adhesive and anti-adhesive molecule and its potential functional redundancy with other sialomucins. Moreover, there are also critical differences in the regulation of CD34 expression on HSPCs in humans and experimental mice. In this review, we highlight some of the more well-defined functions of CD34 in HSPCs with a focus on proposed functions most relevant to HSCT biology.

Role of local eosinophilopoietic processes in the development of airway eosinophilia in prednisone-dependent severe asthma

BACKGROUND

In severe asthmatics with persistent airway eosinophilia, blockade of interleukin-5 has significant steroid-sparing effects and attenuates blood and sputum eosinophilia. The contribution of local maturational processes of progenitors within the airways relative to the recruitment of mature cells from the peripheral circulation to the development of airway eosinophilia is not known. We hypothesize that local eosinophilopoiesis may be the predominant process that drives persistent airway eosinophilia and corticosteroid requirement in severe asthmatics.

OBJECTIVES

In a cross-sectional study, the number and growth potential of eosinophil-lineage-committed progenitors (EoP) were assayed in 21 severe eosinophilic asthmatics, 19 mild asthmatics, eight COPD patients and eight normal subjects. The effect of anti-IL-5 treatment on mature eosinophils and EoP numbers was made in severe eosinophilic asthmatics who participated in a randomized clinical trial of mepolizumab (substudy of a larger GSK sponsored global phase III trial, MEA115575) where subjects received mepolizumab (100 mg, n = 9) or placebo (n = 8), as six monthly subcutaneous injections.

RESULTS

Mature eosinophil and EoP numbers were significantly greater in the sputum of severe asthmatics compared with all other subject groups. In colony-forming assays, EoP from blood of severe asthmatics demonstrated a greater response to IL-5 than mild asthmatics. Treatment of severe asthmatics with mepolizumab significantly attenuated blood eosinophils and increased EoP numbers consistent with blockade of systemic eosinophilopoiesis. There was however no significant treatment effect on mature eosinophils, sputum EoP numbers or the prednisone maintenance dose.

CONCLUSIONS AND CLINICAL RELEVANCE

Patients with severe eosinophilic asthma have an exaggerated eosinophilopoeitic process in their airways. Treatment with 100 mg subcutaneous mepolizumab significantly attenuated systemic differentiation of eosinophils, but did not suppress local airway eosinophil differentiation to mature cells. Targeting IL-5-driven eosinophil differentiation locally within the lung maybe of relevance for optimal control of airway eosinophilia and asthma.

Recent advances in understanding eosinophil biology

With the advent of novel therapies targeting eosinophils, there has been renewed interest in understanding the basic biology of this unique cell. In this context, murine models and human studies have continued to highlight the role of the eosinophil in homeostatic functions and immunoregulation. This review will focus on recent advances in our understanding of eosinophil biology that are likely to have important consequences on the development and consequences of eosinophil-targeted therapies. Given the breadth of the topic, the discussion will be limited to three areas of interest: the eosinophil life cycle, eosinophil heterogeneity, and mechanisms of cell-cell communication.

Hematopoietic Processes in Eosinophilic Asthma

Airway eosinophilia is a hallmark of allergic asthma, and understanding mechanisms that promote increases in lung eosinophil numbers is important for effective pharmacotherapeutic development. It has become evident that expansion of hematopoietic compartments in the bone marrow (BM) promotes differentiation and trafficking of mature eosinophils to the airways. Hematopoietic progenitor cells egress the BM and home to the lungs, where in situ differentiation within the tissue provides an ongoing source of proinflammatory cells. In addition, hematopoietic progenitor cells in the airways can respond to locally derived alarmins to produce a panoply of cytokines, thereby themselves acting as effector proinflammatory cells that potentiate type 2 responses in eosinophilic asthma. In this review, we provide evidence for these findings and discuss novel targets for modulating eosinophilopoietic processes, migration, and effector function of precursor cells.

Clinical potential of oligonucleotide-based therapeutics in the respiratory system

The discovery of an ever-expanding plethora of coding and non-coding RNAs with nodal and causal roles in the regulation of lung physiology and disease is reinvigorating interest in the clinical utility of the oligonucleotide therapeutic class. This is strongly supported through recent advances in nucleic acids chemistry, synthetic oligonucleotide delivery and viral gene therapy that have succeeded in bringing to market at least three nucleic acid-based drugs. As a consequence, multiple new candidates such as RNA interference modulators, antisense, and splice switching compounds are now progressing through clinical evaluation. Here, manipulation of RNA for the treatment of lung disease is explored, with emphasis on robust pharmacological evidence aligned to the five pillars of drug development: exposure to the appropriate tissue, binding to the desired molecular target, evidence of the expected mode of action, activity in the relevant patient population and commercially viable value proposition.

In situ hematopoiesis: a regulator of TH2 cytokine-mediated immunity and inflammation at mucosal surfaces

Hematopoiesis refers to the development of blood cells in the body through the differentiation of pluripotent stem cells. Although hematopoiesis is a multifocal process during embryonic development, under homeostatic conditions it occurs exclusively within the bone marrow. There, a limited number of hematopoietic stem cells differentiate into a rapidly proliferating population of lineage-restricted progenitors that serve to replenish circulating blood cells. However, emerging reports now suggest that under inflammatory conditions, alterations in hematopoiesis that occur outside of the bone marrow appear to constitute a conserved mechanism of innate immunity. Moreover, recent reports have identified previously unappreciated pathways that regulate the egress of hematopoietic progenitor cells from the bone marrow, alter their activation status, and skew their developmental potential. These studies suggest that progenitor cells contribute to inflammatory response by undergoing in situ hematopoiesis (ISH). In this review, we highlight the differences between homeostatic hematopoiesis, which occurs in the bone marrow, and ISH, which occurs at mucosal surfaces. Further, we highlight factors produced at local sites of inflammation that regulate hematopoietic progenitor cell responses and the development of TH2 cytokine-mediated inflammation. Finally, we discuss the therapeutic potential of targeting ISH in preventing the development of inflammation at mucosal sites.

CD34+ eosinophil-lineage-committed cells in the mouse lung

Several studies suggest that eosinophil progenitor cells are capable of extramedullary proliferation but also enhance chronic inflammation via their own production of inflammatory and chemotactic mediators, thus augmenting the degree of inflammation by recruitment of more progenitors or mature effector cells, such as eosinophils at the site of inflammation. In this chapter, we provide methods focused on detecting eosinophil progenitor cells in the lung of allergen-challenged mice and how to monitor their proliferation capacity.

The effects of thymic stromal lymphopoietin and IL-3 on human eosinophil-basophil lineage commitment: Relevance to atopic sensitization

An important immunopathological hallmark of allergic disease is tissue eosinophilic and basophilic inflammation, a phenomenon which originates from hemopoietic progenitors (HP). The fate of HP is determined by local inflammatory cytokines that permit “in situ hemopoiesis,” which leads to the accumulation of eosinophils and basophils (Eo/B). Given that recent evidence supports a critical immunomodulatory role for thymic stromal lymphopoietin (TSLP) in allergic inflammation, as well as TSLP effects on CD34+ progenitor cytokine and chemokine secretion, we investigated the role of TSLP in mediating eosinophilo- and basophilopoiesis, the mechanisms involved, and the association of these processes with atopic sensitisation. In the studies presented herein, we demonstrate a direct role for TSLP in Eo/B differentiation from human peripheral blood CD34+ cells. In the presence of IL-3, TSLP significantly promoted the formation of Eo/B colony forming units (CFU) (including both eosinophils and basophils) from human HP (HHP), which was dependent on TSLP–TSLPR interactions. IL-3/TSLP-stimulated HHP actively secreted an array of cytokines/chemokines, key among which was TNFα, which, together with IL-3, enhanced surface expression of TSLPR. Moreover, pre-stimulation of HHP with IL-3/TNFα further promoted TSLP-dependent Eo/B CFU formation. HHP isolated from atopic individuals were functionally and phenotypically more responsive to TSLP than those from nonatopic individuals. This is the first study to demonstrate enhanced TSLP-mediated hemopoiesis ex vivo in relation to clinical atopic status. The capacity of HHP to participate in TSLP-driven allergic inflammation points to the potential importance of “in situ hemopoiesis” in allergic inflammation initiated at the epithelial surface.

Local proliferation and mobilization of CCR3(+) CD34(+) eosinophil-lineage-committed cells in the lung

Emerging evidence suggests that haematopoietic CD34(+) progenitor cells migrate from bone marrow (BM) to sites of allergen exposure where they can undergo further proliferation and final maturation, potentially augmenting the degree of tissue inflammation. In the current study we used a well-characterized mouse model of allergen-induced airway inflammation to determine the role of CCR3 receptor-ligand interactions in the migration and function of CD34(+) cells. Allergen exposure significantly increased BM, blood and airway CD34(+) CCR3(+) cells as well as airway CD34(+) CCR3(+) stem cell antigen-1-positive (Sca-1(+) ) and CD34(+) CD45(+) interleukin-5 receptor-α-positive (IL-5Rα(+) ) cells. A portion of the newly produced CD34(+) CCR3(+), Sca-1(+) CCR3(+) and IL-5Ralpha(+) lung cells showed a significant proliferative capacity in response to allergen when compared with saline-treated animals. In addition, in vitro colony formation of lung CD34(+) cells was increased by IL-5 or eotaxin-2 whereas eotaxin-2 had no effect on BM CD34(+) cells. Furthermore, both eotaxin-1 and eotaxin-2 induced migration of BM and blood CD34(+) CCR3(+) cells in vitro. These data suggest that the CCR3/eotaxin pathway is involved in the regulation of allergen-driven in situ haematopoiesis and the accumulation/mobilization of eosinophil-lineage-committed progenitor cells in the lung. Hence, targeting both IL-5 and CCR3-mediated signalling pathways may be required to control the inflammation associated with allergen-induced asthma.

Hemopoietic progenitors: the role of eosinophil/basophil progenitors in allergic airway inflammation

Progenitor cells play important roles in the physiology and homeostasis of the overall hemopoietic system. The majority of hemopoietic activity takes place in the bone marrow, under the influence of resident marrow stromal cells, accessory cells, and/or their products. This constitutes the complex network of the hemopoietic inductive microenvironment, which is crucial for providing signals necessary for the maintenance of populations of progenitors at varying stages of lineage commitment. Accumulation of eosinophils and basophils in tissues is characteristic of allergic inflammation. A large body of evidence now exists which confirms that these tissue inflammatory events are coincident with relevant changes in progenitors; it has thus been hypothesized that the observed changes in mature cell numbers occur directly or indirectly as a result of differentiation of lineage-committed eosinophil/basophil, and perhaps other, progenitor cells. Differentiation and maturation of hemopoietic cells have traditionally been thought to be restricted to the bone marrow microenvironment. More recently, evidence has accumulated to suggest that some hemopoietic cells present in allergic tissue may be recruited from the bone marrow, traffic through the peripheral circulation and into tissues to participate in the ongoing inflammatory process at these distal sites. The clinical administration of monotherapy with topical corticosteroids, oral cysteinyl leukotriene antagonists and cytokine antagonists such as antibodies to interleukin-5, suggest that suppression of hemopoietic contributions to allergic inflammation may be necessary for full control of allergic inflammation and disease manifestations. In addition to progenitors being targets of therapy, they may well determine how and whether allergic inflammation is generated in early life, thus serving as biomarkers of disease.

Haemopoietic processes in allergic disease: eosinophil/basophil development

Haemopoietic myeloid progenitors contribute to the ongoing recruitment of pro-inflammatory cells, such as eosinophils and basophils (Eo/B), to target tissue sites in allergic diseases. It is apparent that the development of allergic inflammation is critically dependent on the ability of the bone marrow to support the proliferation, differentiation and mobilization of haemopoietic progenitors. The haemopoietic inductive microenvironment in the bone marrow is crucial for providing signals necessary for maintenance of progenitor populations at varying stages of lineage commitment and permitting these cells to circulate in the bloodstream. Progenitors demonstrate responsiveness to specific cytokines, which varies with stage of differentiation. Pro-inflammatory signals, Th2 cytokines in particular, generated following allergen challenge, can impact on haemopoietic progenitor differentiation and mobilization, leading to accelerated Eo/B production. Allergen inhalation by allergic asthmatics induces a time-dependent change in cytokine levels within the bone marrow compartment, influencing differentiation of Eo/B progenitors, as evidenced by the relationship between increased bone marrow IL-5 levels and Eo/B production. It is proposed that inhaled allergen induces trafficking of IL-5-producing T lymphocytes to the bone marrow, further promoting eosinophilopoiesis through IL-5R signalling. In this manner, Th2 lymphocyte trafficking from the airway may regulate events occurring in the bone marrow. Negative regulators of Eo/B differentiation, including Th1 cytokines, may prove to be important for restoring homeostasis. Eo/B progenitors are also altered in cord blood of infants at risk of atopy and asthma, offering a potential biomarker for, and raising the possibility that Eo/B progenitors are directly involved in the development of allergic disease. For example, changes in the expression of haemopoietic cytokine receptors on cord blood progenitor cells are associated with maternal allergic sensitization, atopic risk and its development, suggesting that haemopoietic processes underlying the allergic phenotype may begin to evolve in the perinatal period.

Human airway smooth muscle promotes eosinophil differentiation

INTRODUCTION

Human airway smooth muscle (HASM) cells in culture synthesize cytokines and chemokines that may orchestrate the tissue homing and in situ differentiation of haemopoietic progenitor cells from the peripheral circulation.

OBJECTIVE

To study the effect of a supernatant from cultured HASM cells on the differentiative and transmigrational responses of haemopoietic progenitor cells.

METHODS

HASM cells were grown to confluence and stimulated with a cytomix of TNF-alpha, IL-1beta and IFN-gamma. Peripheral blood-derived progenitors from atopic asthmatics (n=12) and non-atopic controls (n=11) were grown in a methylcellulose culture with a supernatant from stimulated HASM cells to assess clonogenic potential. The ability of HASM cells to stimulate directional migration and adhesion to fibronectin of blood progenitors was also investigated.

RESULTS

HASM cells stimulated significant growth of eosinophil/basophil colony forming units (Eo/B CFUs) from blood progenitor cells from both groups of subjects. This activity was significantly attenuated in the presence of anti-IL-5 and anti-granulocyte macrophage-colony forming factor blocking antibodies and by pre-treatment with SB202190 [p38 mitogen-activated protein kinase (MAPK) inhibitor]. An src kinase (srcK) inhibitor (Pyrazolopyrimidine 1) was less effective at attenuating IL-5- and HASM-stimulated Eo/B CFU growth from both groups of subjects. Examination of the phosphorylation of these kinases in CD34(+) cells following co-incubation with the major constituents of HASM showed activation of p38 MAPK but not that of the srcK pathway. The HASM supernatant had no significant effect on the migrational and adhesive responses of haemopoietic progenitor cells in vitro.

CONCLUSION

We have shown that HASM cell-derived cytokines promote eosinophil differentiation that is dependent on p38 MAPK but not on the srcK pathway. This study shows that a major structural cell of the lungs, airway smooth muscle, has the capability to direct eosinophil differentiation and maturation from progenitor cells, which in turn may perpetuate an eosinophilic inflammation and consequently tissue remodelling in patients with chronic asthma.

Eosinophil progenitors in allergy and asthma - do they matter?

Allergic inflammation is associated with marked infiltration of eosinophils in affected tissues. The eosinophil is believed to be a key effector cells in allergen induced asthma pathogenesis. However, the role of eosinophils in the clinical manifestation of asthma has recently been questioned, since therapies directed against eosinophil infiltration (i.e. anti-interleukin-5) failed to improve clinical symptoms such as airways hyper-responsiveness (AHR) in patients with asthma. Although eosinophils in peripheral blood and the airways were largely depleted after anti-IL-5 treatment, residual eosinophilia in lung tissue persisted, which permits speculation that the remaining eosinophils may be sufficient to drive the asthma symptomatology. Furthermore, recent findings suggest that primitive eosinophil progenitor cells traffic from the bone marrow to sites of inflammation in response to allergen exposure. These progenitors may then differentiate in situ and thus provide an ongoing supply of mature pro-inflammatory cells and secretory mediators that augment the inflammatory response. In the present article, we will review the evidence for these findings, and discuss the rationale for targeting hematopoiesis and their migration pathways in the treatment of allergic diseases. Furthermore, this review will highlight the hypothesis that both IL-5- and CCR3-mediated signaling pathways may need to be targeted in order to control the inflammation and AHR associated with asthma.

Treatment with anti-CC chemokine receptor 3 monoclonal antibody or dexamethasone inhibits the migration and differentiation of bone marrow CD34 progenitor cells in an allergic mouse model

BACKGROUND

The migration and in situ differentiation of CD34(+) progenitors contribute to inflammatory eosinophilia in asthma and corticosteroids have been widely used in asthma. However, little is know about whether and how corticosteroids modulate the migration and differentiation of CD34(+) progenitors. This study was aimed to investigate the impact of anti-CC chemokine receptor 3 (CCR3) or dexamethasone on inflammatory eosinophilia in asthma and possible mechanism(s) underlying the action of dexamethasone or anti-CCR3 on migration and differentiation of CD34(+) progenitors in asthmatic context.

METHODS

Using an asthmatic mouse model, airway inflammation of anti-CCR3- or dexamethasone-treated mice and that of controls were characterized. And the migration and differentiation of CD34(+) progenitor cells were analyzed in vivo, ex vivo or in vitro.

RESULTS

Treatment with anti-CCR3 or dexamethasone significantly inhibited allergen-induced eosinophilia and CD34(+) progenitor cell infiltration in the lung, which was accompanied by lower levels of airway hyper-responsiveness and mucus production. Moreover, anti-CCR3 inhibited the eotaxin-mediated migration and IL-5/eotaxin-induced differentiation of CD34(+) progenitors in vitro. Dexamethasone was also shown to mitigate eotaxin-mediated migration and IL-5 or eotaxin-promoted differentiation of CD34(+) progenitor cells ex vivo, which were associated with the down-regulation of CCR3 expression on bone marrow progenitor cells.

CONCLUSIONS

Treatment with anti-CCR3 or dexamethasone can inhibit the migration and differentiation of CD34(+) progenitor cells by regulating the eotaxin/CCR3 axis in asthmatic mice. Our findings provide new insights into understanding the mechanism(s) underlying the action of dexamethasone and CCR3-mediated signaling in allergic inflammation and aid in the design of new immunotherapy for intervention of human asthma.

Regulation of functional phenotypes of cord blood derived eosinophils by gamma-secretase inhibitor

Eosinophils develop from stem cells in the bone marrow under the influence of hematopoietic cytokines, particularly IL-5. Previously, we have demonstrated that blockage of Notch signaling by a gamma-secretase inhibitor (GSI) promotes the differentiation of umbilical cord blood (UCB)-derived eosinophils. These highly major basic protein (MBP)-positive eosinophils cultured in the presence of the inhibitor lack the migratory response to eotaxin, although their CCR3 levels are similar to those of eosinophils cultured without the inhibitor. We investigated the mechanism underlying the differential responses of differentiating eosinophils and their functionalities in response to eosinophil-active cytokines in the presence and absence of GSI. UCB cells cultured for 4 weeks with hematopoietic cytokines in the presence or absence of GSI were monitored for extracellular signal-regulated kinase (ERK) phosphorylation, MBP expression, and functionality. Eosinophil differentiation from UCB cells was accompanied by activation of the ERK1/2 pathway during the 4-week culture period. In particular, strong ERK1/2 phosphorylation was observed in eosinophils during the final stage of culture when GSI was present. Consistent with this finding, ERK inhibition nullified the effect of GSI on eosinophil differentiation. Eosinophils cultured with GSI resembled airway eosinophils rather than peripheral blood eosinophils based on reduced IL-5Ralpha expression, blunted eosinophil cationic protein (ECP) degranulation, and decreased IL-13 and granulocyte macrophage-colony-stimulating factor production. These results suggest that Notch signaling regulates the terminal differentiation and subsequent effector phenotypes of eosinophils, partly through modulation of the ERK pathway. GSI has therapeutic potential for eosinophilic inflammatory diseases, such as asthma.

Regulatory role of CD8+ T lymphocytes in bone marrow eosinophilopoiesis

Background

There is a growing body of evidence to suggest that CD8⁺ T lymphocytes contribute to local allergen-induced eosinophilic inflammation. Since bone marrow (BM) responses are intricately involved in the induction of airway eosinophilia, we hypothesized that CD8⁺ T lymphocytes, as well as CD4⁺ T lymphocytes, may be involved in this process.

Methods

Several approaches were utilized. Firstly, mice overexpressing interleukin-5 (IL-5) in CD3⁺ T lymphocytes (NJ.1638; CD3^IL-5+ mice) were bred with gene knockout mice lacking either CD4⁺ T lymphocytes (CD4^-/-) or CD8⁺ T lymphocytes (CD8^-/-) to produce CD3^IL-5+ knockout mice deficient in CD4⁺ T lymphocytes (CD3^IL-5+/CD4^-/-) and CD8⁺ T lymphocytes (CD3^IL-5+/CD8^-/-), respectively. Secondly, CD3⁺, CD4⁺ and CD8⁺ T lymphocytes from naïve CD3^IL-5+ and C57BL/6 mice were adoptively transferred to immunodeficient SCID-bg mice to determine their effect on BM eosinophilia. Thirdly, CD3^IL-5+, CD3^IL-5+/CD8^-/- and CD3^IL-5+/CD4^-/- mice were sensitized and allergen challenged. Bone marrow and blood samples were collected in all experiments.

Results

The number of BM eosinophils was significantly reduced in CD3^IL-5+/CD8^-/- mice compared to CD3^IL-5+ mice and CD3^IL-5+/CD4^-/- mice. Serum IL-5 was significantly higher in CD3^IL-5+/CD4^-/- mice compared to CD3^IL-5+ mice but there was no difference in serum IL-5 between CD3^IL-5+/CD4^-/- and CD3^IL-5+/CD8^-/- mice. Adoptive transfer of CD8⁺, but not CD4⁺ T lymphocytes from naïve CD3^IL-5+ and C57BL/6 mice restored BM eosinophilia in immunodeficient SCID-bg mice. Additionally, allergen challenged CD3^IL-5+/CD8^-/- mice developed lower numbers of BM eosinophils compared to CD3^IL-5+ mice and CD3^IL-5+/CD4^-/- mice.

Conclusion

This study shows that CD8⁺ T lymphocytes are intricately involved in the regulation of BM eosinophilopoiesis, both in non-sensitized as well as sensitized and allergen challenged mice.

Airway allergen exposure stimulates bone marrow eosinophilia partly via IL-9

Background

Interleukin (IL)-9 is a Th2-derived cytokine with pleiotropic biological effects, which recently has been proposed as a candidate gene for asthma and allergy. We aimed to evaluate the therapeutic effect of a neutralizing anti-IL-9 antibody in a mouse model of airway eosinophilic inflammation and compared any such effect with anti-IL-5 treatment.

Methods

OVA-sensitized Balb/c mice were intraperitoneally pretreated with a single dose (100 μg) of an anti-mouse IL-9 monoclonal antibody (clone D9302C12) or its vehicle. A third group was given 50 μg of a monoclonal anti-mouse IL-5 antibody (TRFK-5) or its vehicle. Animals were subsequently exposed to OVA on five days via airways. Newly produced eosinophils were labelled using 5-bromo-2'-deoxyuridine (BrdU). BrdU⁺ eosinophils and CD34⁺ cell numbers were examined by immunocytochemistry. After culture and stimulation with OVA or PMA+IC, intracellular staining of IL-9 in bone marrow cells from OVA-exposed animals was measured by Flow Cytometry. The Mann-Whitney U-test was used to determine significant differences between groups.

Results

Anti-IL-9 significantly reduced bone marrow eosinophilia, primarily by decrease of newly produced (BrdU⁺) and mature eosinophils. Anti-IL-9 treatment also reduced blood neutrophil counts, but did not affect BAL neutrophils. Anti-IL-5 was able to reduce eosinophil numbers in all tissue compartments, as well as BrdU⁺ eosinophils and CD34⁺ progenitor cells, and in all instances to a greater extent than anti-IL-9. Also, FACS analysis showed that IL-9 is over-expressed in bone marrow CD4⁺ cells after allergen exposure.

Conclusions

Our data shows that a single dose of a neutralizing IL-9 antibody is not sufficient to reduce allergen-induced influx of newly produced cells from bone marrow to airways. However, in response to allergen, bone marrow cells over-express IL-9. This data suggest that IL-9 may participate in the regulation of granulocytopoiesis in allergic inflammation.

Allergen-induced traffic of bone marrow eosinophils, neutrophils and lymphocytes to airways

We evaluated whether bone marrow (BM) inflammatory cells have capacity to traffic into the airways following allergen exposure in a mouse model of allergen-induced airway inflammation. We also evaluated the effect of IL-5 overexpression on (i) the production of eosinophils in BM, (ii) the accumulation of eosinophils, neutrophils and lymphocytes in blood and airways and (iii) the changes in CD34+ cell numbers in BM, blood and airways. Bromodeoxyuridine (BrdU) was used to label cells produced during the exposure period. Furthermore, CD3 splenocytes were adoptively transferred to investigate the BM inflammatory response. Allergen exposure induced traffic of BM eosinophils, neutrophils and lymphocytes to the airways and increased the number of BrdU+ eosinophils, neutrophils, lymphocytes and CD34+ cells in BALf. IL-5 overexpression enhanced the eosinophilopoiesis and increased the presence of BrdU+ eosinophils and CD34+ cells in airways and enhanced the number of CD34+ cells in BM and blood after allergen exposure. Adoptive transfer of CD3 lymphocytes overexpressing IL-5 caused increased BM eosinophilia. In conclusion, allergen exposure induces traffic of not only newly produced eosinophils but also newly produced neutrophils and lymphocytes into the airways.

Allergen stimulates bone marrow CD34(+) cells to release IL-5 in vitro; a mechanism involved in eosinophilic inflammation?

The specific mechanisms that alter bone marrow (BM) eosinophilopoiesis in allergen-induced inflammation are poorly understood. The aims of this study were to evaluate (a) whether the number of BM CD34(+) cells is altered due to allergen sensitization and exposure in vivo and (b) whether BM CD34(+) cells produce and release interleukin (IL)-5, IL-3 and granulocyte macrophage-colony stimulating factor (GM-CSF) after stimulation in vitro. A mouse model of ovalbumin (OVA)-induced airway inflammation was used. Bone marrow CD34(+) cells were cultured in vitro and the cytokine release was measured by enzyme-linked immunosorbent assay. The IL-5-production from CD34(+) cells was confirmed by immunocytochemistry. Airway allergen exposure increased the number of BM CD34(+) cells (P = 0.01). Bone marrow CD34(+) cells produced IL-5 when stimulated with the allergen OVA in vitro, but not IL-3 or GM-CSF. Nonspecific stimulus with calcium ionophore and phorbol-myristate-acetate of BM CD34(+) cells caused release of IL-5, IL-3 and GM-CSF. The induced release of IL-5 was increased in alum-injected vs naive mice (P = 0.02), but was not affected by allergen sensitization and exposure. The release of IL-3 and GM-CSF was increased after allergen sensitization and exposure (P < 0.02). In conclusion, allergen can stimulate BM CD34(+) cells to produce IL-5 protein. It is likely that the CD34(+) cells have autocrine functions and thereby regulate the early stages of BM eosinophilopoiesis induced by airway allergen exposure. Alum, a commonly used adjuvant, enhances the release of IL-5 and may thereby enhance eosinophilopoiesis.