Increased mature and immature CCR3 messenger RNA+ eosinophils in bone marrow from patients with atopic asthma compared with atopic and nonatopic control subjects

Neolignans from the Arils of Myristica fragrans as Potent Antagonists of CC Chemokine Receptor 3

CC chemokine receptor 3 (CCR3) is expressed selectively in eosinophils, basophils, and some Th2 cells and plays a major role in allergic diseases. A methanol extract from the arils of Myristica fragrans inhibited CC chemokine ligand 11-induced chemotaxis in CCR3-expressing L1.2 cells at 100 μg/mL. From this extract, eight new neolignans, maceneolignans A-H (1-8), were isolated, and their stereostructures were elucidated from their spectroscopic values and chemical properties. Of those constituents, compounds 1, 4, 6, and 8 and (+)-erythro-(7S,8R)-Δ(8')-7-hydroxy-3,4-methylenedioxy-3',5'-dimethoxy-8-O-4'-neolignan (11), (-)-(8R)-Δ(8')-3,4-methylenedioxy-3',5'-dimethoxy-8-O-4'-neolignan (17), (+)-licarin A (20), nectandrin B (25), verrucosin (26), and myristicin (27) inhibited CCR3-mediated chemotaxis at a concentration of 1 μM. Among them, 1 (EC50 1.6 μM), 6 (1.5 μM), and 8 (1.4 μM) showed relatively strong activities, which were comparable to that of a synthetic CCR3 selective antagonist, SB328437 (0.78 μM).

Mast Cell-Activated Bone Marrow Mesenchymal Stromal Cells Regulate Proliferation and Lineage Commitment of CD34(+) Progenitor Cells

BACKGROUND

Shortly after allergen exposure, the number of bone marrow (BM) and circulating CD34(+) progenitors increases. We aim to analyze the possible mechanism whereby the allergic reaction stimulates BM to release these effector cells in increased numbers. We hypothesize that mast cells (MCs) may play a predominant role in this process.

OBJECTIVE

To examine the effect of IgE-activated MCs on BM mesenchymal stromal cells which regulate proliferation and differentiation of CD34(+) progenitors.

METHODS

Primary MCs were derived from CD34(+) precursors and activated with IgE/anti-IgE. BM mesenchymal stromal cells were co-cultured with CD34(+) progenitor cells and stimulated with IL-1/TNF or IgE/anti-IgE-activated MCs in Transwell system.

RESULTS

BM mesenchymal stromal cells produce low level of thymic stromal lymphopoietin (TSLP) under steady state conditions, which is markedly increased by stimulation with proinflammatory cytokines IL-1 and TNF or IgE-activated MCs. The latter also triggers bone marrow-derived mesenchymal stromal cells production of G-CSF, and GM-CSF while inhibiting SDF-1. MC-activated mesenchymal stromal cells stimulate CD34(+) cells to proliferate and to regulate their expression of early allergy-associated genes.

CONCLUSION AND CLINICAL RELEVANCE

This in vitro study indicates that IgE-activated MCs trigger BM mesenchymal stromal cells to release TSLP and hematopoietic growth factors and to regulate the proliferation and lineage commitment of CD34(+) precursor cells. The data predict that the effective inhibition of MCs should impair mobilization and accumulation of allergic effector cells and thereby reduce the severity of allergic diseases.

Targeting chemokine receptors in allergic disease

The directed migration of cells in response to chemical cues is known as chemoattraction, and plays a key role in the temporal and spatial positioning of cells in lower- and higher-order life forms. Key molecules in this process are the chemotactic cytokines, or chemokines, which, in humans, constitute a family of approx. 40 molecules. Chemokines exert their effects by binding to specific GPCRs (G-protein-coupled receptors) which are present on a wide variety of mature cells and their progenitors, notably leucocytes. The inappropriate or excessive generation of chemokines is a key component of the inflammatory response observed in several clinically important diseases, notably allergic diseases such as asthma. Consequently, much time and effort has been directed towards understanding which chemokine receptors and ligands are important in the allergic response with a view to therapeutic intervention. Such strategies can take several forms, although, as the superfamily of GPCRs has historically proved amenable to blockade by small molecules, the development of specific antagonists has been has been a major focus of several groups. In the present review, I detail the roles of chemokines and their receptors in allergic disease and also highlight current progress in the development of relevant chemokine receptor antagonists.

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.

Use of biologicals as immunotherapy in asthma and related diseases

Recent advances in our understanding of the immune-mediated inflammatory pathways in asthma and other allergic diseases have resulted in the development of novel biological compounds for the treatment of these conditions. These compounds offer an advantage over glucocorticosteroid therapy by specifically targeting components of the immunologic cascade, thereby allowing patients to reduce or discontinue their glucocorticosteroid treatment. Another potential advantage of biological compounds is that they may provide additional anti-inflammatory benefits, over and above those provided by glucocorticosteroid therapy, for patients who continue to have evidence of refractory asthma. The anti-IgE monoclonal antibody omalizumab is already being used for the treatment of allergic asthma and a number of other biological therapies are currently in various stages of clinical development. The purpose of this review is to summarize the data from these studies and to provide a rationale for the use of these compounds in asthma and related allergic airway diseases.

A single nucleotide polymorphism in the CCR3 gene ablates receptor export to the plasma membrane

BACKGROUND

The chemokine receptor CCR3 orchestrates the migration of eosinophils, basophils, T(H)2 lymphocytes, and mast cells during the allergic response, with CCR3 blockade a potential means of therapeutic intervention. Non-synonymous single nucleotide polymorphisms (SNPs) within the ccr3 gene have previously been described, with little information regarding their effects on CCR3 function.

OBJECTIVE

To characterize the effects of nonsynonymous SNPs within the ccr3 gene.

METHODS

Site-directed mutagenesis was used to generate N-terminally tagged mutant CCR3 constructs corresponding to reported SNPs. Cell transfectants expressing either wild-type or mutant CCR3 were studied by flow cytometry, Western blotting, and confocal microscopy and examined for their ability to migrate to the CC chemokine ligand CCL11/eotaxin.

RESULTS

An L324P mutant CCR3 protein corresponding to the previously identified T971C SNP was not expressed at the cell surface, and cells remained unresponsive to CCL11 in chemotaxis assays. Confocal microscopy confirmed that L324P-CCR3 had a predominantly intracellular distribution compared with wild-type CCR3. A L324A variant of CCR3 had an identical phenotype to the L324P mutant, suggesting that L324 per se is critical for successful trafficking of nascent CCR3 to the cell membrane. The processes involved appear to be specific for CCR3, because an identical mutation in the homologous receptor CCR1 had minor effects.

CONCLUSION

Trafficking to the cell surface of nascent CCR3 is critically dependent on a C-terminal leucine residue, suggestive of specific mechanisms for CCR3 export. Manipulation of these mechanisms may suggest novel means of antagonizing CCR3 function in the treatment of allergy.

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.

Gastrointestinal eosinophils in health, disease and functional disorders

Eosinophils are potent innate immune cells that home to the gastrointestinal tract where they participate in host immunity to luminal pathogens, and help to maintain intestinal epithelial homeostasis. However, these cells are now recognized to have key functions in the pathogenesis of numerous other disorders of the gastrointestinal tract, including primary eosinophilic gastrointestinal disease, common functional conditions, such as dyspepsia, and also in gastrointestinal disorders in patients with allergic disease. We are just beginning to understand the potential pathological role of eosinophils in gastrointestinal disease, and it is increasingly likely that gastroenterologists and histopathologists will need to account for the presence of gastrointestinal eosinophils and relate their presence to gastrointestinal symptoms. This Review discusses the role of gastrointestinal eosinophils in health and disease, including their associations with functional and allergic disorders.

A novel CC-chemokine receptor 3 antagonist, Ki19003, inhibits airway eosinophilia and subepithelial/peribronchial fibrosis induced by repeated antigen challenge in mice

CC-chemokine receptor 3 (CCR3) is a chemokine receptor for which major ligands, CC-chemokine ligand (CCL) 11, CCL24, and CCL26, are known to be involved in chemotaxis for eosinophils. In the present study, we evaluated the effect of a low molecular weight CCR3-receptor antagonist, Ki19003 (4-[[5-(2,4-dichlorobenzylureido)pentyl][1-(4-chlorophenyl)ethyl]amino]butanoic acid), on airway remodeling in a mouse model of allergic asthma. BALB/c mice were sensitized twice by intraperitoneal injection of ovalbumin (OA) and exposed daily to 1% OA for 3 weeks. Twenty-four hours after the final antigen challenge, bronchoalveolar lavage and histological examinations were carried out. Ki19003 clearly inhibited antigen-induced increase in the number of eosinophils in bronchoalveolar lavage fluid (BALF), but did not affect the number of other cell types examined in this study. Ki19003 also inhibited the increased production of transforming growth factor-beta1 in BALF and the amount of hydroxyproline in the lungs in a dose-dependent manner. Furthermore, Ki19003 significantly attenuated allergen-induced subepithelial and peribronchial fibrosis. These findings indicate that CCR3 antagonism prevents not only the infiltration of eosinophils into the airways but also the development of allergen-induced subepithelial and peribronchial fibrosis. Therefore, a CCR3 antagonist may be useful in the treatment of airway remodeling, especially subepithelial and peribronchial fibrosis, in allergic asthma.

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.

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.

Genetic effect of CCR3 and IL5RA gene polymorphisms on eosinophilia in asthmatic patients

BACKGROUND

Eosinophilic infiltration and peripheral blood eosinophilia in asthma require the cooperation of eosinophil-specific cytokines and chemokines and their receptors.

OBJECTIVE

We investigated the association of polymorphisms in CCR3 and IL5RA with asthma susceptibility or peripheral blood eosinophilia and the effects of the polymorphisms on receptor expression.

METHODS

Polymorphisms in CCR3 and IL5RA were identified and genotyped in 576 asthmatic patients and 180 healthy control subjects. CCR3 and IL-5 receptor alpha (IL-5R alpha) protein expression on eosinophils was measured by means of flow cytometry.

RESULTS

Although polymorphisms in CCR3 were not associated with asthma susceptibility, the CCR3 haplotype ht2 showed a negative gene dose effect on the eosinophil count (P = .003-.009). IL5RA c.-5091G>A was weakly associated with eosinophil count. The effects of ht2 were greater when paired with IL5RA c.-5091A (P = .001-.002). CCR3 protein expression was higher on eosinophils of asthmatic patients without ht2 than in those with ht2. Asthmatic patients with the IL5RA c.-5091A allele showed higher IL-5R alpha expression than those who were homozygous for the G allele.

CONCLUSION

The genetic association between CCR3 polymorphisms and the number of circulating eosinophils was revealed as a novel finding. These associations were more pronounced when the CCR3 polymorphisms were paired with polymorphisms in IL5RA. The protein expression levels of CCR3 and IL-5R alpha on peripheral blood eosinophils are associated with the polymorphisms on their own genes.

CLINICAL IMPLICATIONS

The identification of single nucleotide polymorphisms and haplotypes of CCR3 and IL5RA might be useful in developing markers for intermediate phenotypes of eosinophil number and in designing strategies to control diseases related to hypereosinophilia.

Dendritic cells in allergic airway inflammation

Dendritic cells (DCs) are primary antigen-presenting cells involved in interactions with T cells leading to the proliferation of TH1 or TH2 cell types. In asthma, predominance of TH2 cells appears to be responsible for disease pathogenesis. Differentiation of TH2 cells is driven by a variety of factors such as the expression of high levels of costimulatory molecules, the cytokine profile, and the subset of DCs. Many inflammatory cells involved in the pathogenesis of asthma either directly or indirectly modulate DC function. Traditional treatments for asthma decrease the number of airway DCs in animals as well as in patients with asthma. Immunomodulators including interleukin (IL)-10, transforming growth factor (TGF)-beta, cytosine-phosphate-guanosine-containing oligodeoxynucleotides (CpG-ODN), 1alpha,25-dihydroxyvitamin D3, and fetal liver tyrosine kinase 3 ligand (Flt3L) are involved in the modulation of the function of DCs. Based on the critical review of the interaction between DCs and other inflammatory cells, we propose that activation of T cells by DCs and sensitization to inhaled allergen and resulting airway inflammation are dependent on plasmacytoid and myeloid subset of lung DCs to induce an immune response or tolerance and are tightly regulated by T-regulatory cells. Effects of various therapeutic agents to modulate the function of lung myeloid DCs have been discussed.

Effect of inhaled interleukin-5 on eosinophil progenitors in the bronchi and bone marrow of asthmatic and non-asthmatic volunteers

BACKGROUND

Asthma is characterized by increases in mature eosinophils and their progenitors within the bronchus and bone marrow. IL-5 plays a key role in eosinophil development in the bone marrow and at the site of allergic inflammation. We therefore studied the effects of nebulized IL-5 on eosinophils, their progenitors and in situ haemopoiesis within the airway and bone marrow.

METHODS

Nine atopic asthmatics and 10 non-atopic non-asthmatic control volunteers inhaled 10 microg of IL-5 or placebo via a nebulizer in a double-blind, randomized, cross-over study. Bronchoscopy, bone marrow aspiration and peripheral blood sampling were performed 24 h after nebulization. Four weeks later, volunteers inhaled the alternative solution and underwent a repeat bronchoscopy and bone marrow aspiration.

RESULTS

Inhalation of IL-5 significantly decreased CD34(+)/IL-5Ralpha mRNA(+) cells within the bronchial mucosa and the percentage of CD34(+) cells that were CCR3(+) within the bone marrow of atopic asthmatic, but not control, volunteers. Inhalation of IL-5 also induced a significant increase in bronchial mucosal eosinophils in the non-atopic non-asthmatic control volunteers, but not in the asthmatics. IL-5 had no effect on spirometry or airways hyper-reactivity in either group.

CONCLUSIONS

Inhaled IL-5 modulated eosinophil progenitor numbers in both the airways and bone marrow of asthmatics and induced local eosinophilia in non-asthmatics.

Effects of inhaled eotaxin on airway function and inflammatory cell influx in sensitised and non-sensitised guinea pigs

Eotaxin is a chemokine that has high potency and selectivity as a chemoattractant agent for eosinophils, signalling exclusively through the CCR3 receptor. Eotaxin is upregulated in the lungs within 3 h of antigen challenge, levels peak at 6 h in lung tissue and bronchoalveolar (BAL) fluid, and fall within 12 h of exposure. This study aimed to look at the effect(s) of eotaxin inhalation on airway function in guinea pigs, to determine if the expected inflammatory cell (eosinophil) infiltration could induce airway hyperreactivity (AHR) and a bronchoconstrictor response equivalent to the late asthmatic response (LAR) seen after antigen challenge. Animals were sensitised with 100 microg/ml OA with a dose on days 1 and 5. Airway responses to inhaled eotaxin (10 or 20 microg/ml) were determined by whole body plethysmography as the change in specific airway conductance (sGaw). Inhaled histamine (1mM) was used to investigate AHR, and cell influx was determined by BAL. Senitised animals exposed to 10 microg/ml eotaxin did not reveal a bronchoconstrictor response or AHR and cellular infiltration to the lungs was not evident 24 h after exposure. Both sensitised and non-sensitised animals exposed to 20 microg/ml eotaxin however revealed a significant bronchoconstrictor response 6h post-challenge, with reductions in sGaw of -27.0+/-6.6% and -32.3+/-6.8%, respectively. Both groups also displayed a bronchoconstrictor response to inhaled histamine 24h after exposure, indicating AHR, and a significant increase in both total and differential cell counts. Sensitised animals, however, revealed a significant increase in cell influx compared to non-sensitised animals. Nebulised eotaxin can reveal a LAR, AHR to inhaled histamine, and cellular infiltration to the lungs, possibly via the mobilisation of eosinophils from the bone marrow, and their subsequent recruitment to the airways.

Chemokine receptor expression and function in childhood acute lymphoblastic leukemia of B-lineage

Scanty information is available on chemokine receptor expression and function in childhood B-lineage acute lymphoblastic leukemia (ALL). Thirteen pro-B, 17 early pre-B, 12 pre-B, and 9 B-ALL/Burkitt lymphoma (BL) pediatric cases were tested for CXCR1 to CXCR5 and CCR1 to CCR7 expression. CXCR2, CXCR3, and CXCR4 were expressed in the majority of cases, while the other receptors were variably expressed or absent. CXCR4 mediated chemotaxis of all leukemic cell subtypes. Freshly isolated CCR7(+) early pre-B-ALL cells migrated to CCL19, whereas CCR7(+) pro-B- and pre-B-ALL cells were attracted by CCL19 only following culture with soluble recombinant CD40 ligand.

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.

The role of chemokines and chemokine receptors in eosinophil activation during inflammatory allergic reactions

Chemokines are important chemotactic cytokines that play a fundamental role in the trafficking of leukocytes to sites of inflammation. They are also potent cell-activating factors, inducing cytokine and histamine release and free radical production, a fact that makes them particularly important in the pathogenesis of allergic inflammation. The action of chemokines is regulated at the level of agonist production and processing as well as at the level of receptor expression and coupling. Therefore, an analysis of the ligands must necessarily consider receptors. Eosinophils are target cells involved in the allergic inflammatory response since they are able to release a wide variety of mediators including CC and CXC chemokines and express their receptors. These mediators could damage the airway epithelial cells and might be important to stimulate other cells inducing an amplification of the allergic response. This review focuses on recently emerging data pertaining to the importance of chemokines and chemokine receptors in promoting eosinophil activation and migration during the allergic inflammatory process. The analysis of the function of eosinophils and their chemokine receptors during allergic inflammation might be a good approach to understanding the determinants of asthma severity and to developing novel therapies.

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

We hypothesized that the allergen-induced increased number of airway eosinophils results from increased recruitment of eosinophils from bone marrow (BM) and local development of CD34(+) cells into eosinophils. We also assumed that the phenotype of airway eosinophils depends on whether these cells have differentiated within BM or airway. C57BL/6 mice were sensitized and subsequently exposed to ovalbumin (OVA) on 5 consecutive days. Newly produced cells were labeled with a thymidine analog. Clonogenic activity and interleukin 5 (IL-5) release from bronchoalveolar lavage fluid (BALf) CD34(+) cells were evaluated by using cell-culture techniques. Allergen exposure induces increase in CD135(+) primitive myeloid progenitors within the BM CD34(+) cell population, without significant changes in total number of CD34(+) cells or newly produced CD34(+) cells. CD34(+)/IL-5R alpha(+) cells in the first stage of cell differentiation were found only in BM, arguing that early commitment of CD34(+) cells into the eosinophil lineage is restricted to the BM compartment. Allergen exposure induces a shift in differentiation of BM, blood, and BALf eosinophillineage-committed CD34(+) cells toward mature eosinophils and recruitment of these cells via blood into airway. We further demonstrate in vitro that ability to multiply persists in BALf CD34(+) cells but not CD34(-) cells, likely via autocrine IL-5 release and IL-5-induced up-regulation of IL-5R alpha.

Regulation of eosinophilopoiesis in a murine model of asthma

Eosinophilic inflammation plays a key role in tissue damage that characterizes asthma. Eosinophils are produced in bone marrow and recent observations in both mice and humans suggest that allergen exposure results in increased output of eosinophils from hemopoietic tissue in individuals with asthma. However, specific mechanisms that alter eosinophilopoiesis in this disease are poorly understood. The current study used a well-characterized murine animal model of asthma to evaluate alterations of eosinophil and eosinophil progenitor cells (CFU-eo) in mice during initial sensitization to allergen and to determine whether observed changes in either cell population were regulated by T lymphocytes. Following the first intranasal installation of OVA, we observed sequential temporal elevation of eosinophils in bone marrow, blood, and lung. In immunocompetent BALB/c mice, elevation of bone marrow eosinophils was accompanied by transient depletion of CFU-eo in that tissue. CFU-eo rebounded to elevated numbers before returning to normal baseline values following intranasal OVA exposure. In T cell-deficient BALB/c nude (BALB/c(nu/nu)) mice, CFU-eo were markedly elevated following allergen sensitization, in the absence of bone marrow or peripheral blood eosinophilia. These data suggest that eosinophilia of asthma results from alterations in two distinct hemopoietic regulatory mechanisms. Elevation of eosinophil progenitor cells in the bone marrow is T cell independent and likely results from altered bone marrow stromal cell function. Differentiation of eosinophil progenitor cells and phenotypic eosinophilia is T cell dependent and does not occur in athymic nude mice exposed to intranasal allergen.

Allergen-induced fluctuation in CC chemokine receptor 3 expression on bone marrow CD34+ cells from asthmatic subjects: significance for mobilization of haemopoietic progenitor cells in allergic inflammation

There is increasing evidence that primitive progenitors migrate from the bone marrow (BM) via the peripheral circulation to tissue sites where they undergo in situ differentiation to provide a continued source of effector cells, such as eosinophils, during an allergic inflammatory response. To study mechanisms of progenitor cell mobilization in allergic reactions, we investigated fluctuations in the expression of the eotaxin receptor, CC chemokine receptor 3 (CCR3), on CD34+ cells from stable asthmatics following allergen (i.e. antigen) challenge. BM aspirates were taken from seven early responder (ER) and 10 dual responder (DR) asthmatics who, following antigen challenge developed only an early bronchoconstrictor response and an early and late- bronchoconstrictor response, respectively. Expression of CCR3 was detected on primitive (CD34+ cells) and eosinophil-lineage committed progenitors (CD34+ interleukin-5 receptor alpha-subunit+ cells) by flow cytometry and confirmed by co-localization of CCR3 messenger RNA to CD34 immunopositive cells using in situ hybridization. When preantigen levels were compared to 24-hr postantigen levels, significant increases in BM CD34+ CCR3+ cells were detected in DR, who also developed a significant sputum and blood eosinophilia and increased methacholine airway responsiveness. In contrast, a significant attenuation of BM CD34+ CCR3+ cells was observed in ER. In a dose-dependent manner eotaxin, but not interleukin (IL)-5, stimulated CD34+ progenitor cell migration in vitro. This migrational response to eotaxin was abrogated by anti-CCR3 monoclonal antibody and primed by preincubation with IL-5. We propose that fluctuations in CCR3 expression on human BM CD34+ cells may facilitate chemokine-mediated progenitor cell mobilization to the peripheral circulation and the resultant development of pulmonary eosinophilia, a cardinal feature of asthma.

Anti-IL-5 (mepolizumab) therapy induces bone marrow eosinophil maturational arrest and decreases eosinophil progenitors in the bronchial mucosa of atopic asthmatics

BACKGROUND

Eosinophils develop from CD34(+) progenitors under the influence of IL-5. Atopic asthmatic individuals have increased numbers of mature eosinophils and eosinophil pro-genitors within their bone marrow and bronchial mucosa. We have previously reported that anti-IL-5 monoclonal antibody treatment decreases total bone marrow and bronchial mucosal eosinophil numbers in asthma.

OBJECTIVE

Using an anti-IL-5 monoclonal antibody, we examined the role of IL-5 in eosinophil development within the bone marrow and bronchial mucosa in asthma.

METHODS

Blood, bone marrow, and airway mucosal biopsy specimens were examined before and after anti-IL-5 (mepolizumab) treatment of asthmatic individuals in a double-blind, placebo-controlled trial. Numbers of mature and immature eosinophils were measured by histologic stain (bone marrow myelocytes, metamyelocytes, and mature eosinophils), flow cytometry (bone marrow and blood CD34(+)/IL-5Ralpha(+) cells), enumeration of bone marrow-derived eosinophil/basophil colony-forming units in methylcellulose culture, and sequential immunohistochemistry and in situ hybridization (bronchial mucosal CD34(+)/IL-5Ralpha mRNA(+) cells).

RESULTS

Mepolizumab decreased mature eosinophil numbers in the bone marrow by 70% (P =.017) in comparison with placebo and decreased numbers of eosinophil myelocytes and metamyelocytes by 37% (P =.006) and 44% (P =.003), respectively. However, mepolizumab had no effect on numbers of blood or bone marrow CD34(+), CD34(+)/IL-5Ralpha(+) cells, or eosinophil/basophil colony-forming units. There was a significant decrease in bronchial mucosal CD34(+)/IL-5Ralpha mRNA(+) cell numbers in the anti-IL-5 treated group (P =.04).

CONCLUSION

These data suggest that anti-IL-5 therapy might induce partial maturational arrest of the eosinophil lineage in the bone marrow. The reduction in airway CD34(+)/IL-5 mRNA(+) cell numbers suggests that IL-5 might also be required for local tissue eosinophilopoiesis.

Constitutive overexpression of IL-5 induces extramedullary hematopoiesis in the spleen

The differentiation of eosinophils from hematopoietic precursors and their subsequent maturation, chemotaxis, and activation is primarily regulated by interleukin-5 (IL-5). To examine the effect of chronic IL-5 exposure on hematopoiesis, IL-5 transgenic (IL-5trg) mice and wild-type BALB/c (WT) mice were examined. In comparison to WT mice, a significant alteration in bone marrow hematopoiesis was observed in IL-5trg mice. Although the total number of myeloid progenitors in the bone marrow of IL-5trg mice was not significantly altered, the number of long-term culture-initiating cells (LTC-ICs) was 1.5-fold lower than that observed in WT mice. Furthermore, IL-5trg mice failed to demonstrate hematopoietic activity in long-term bone marrow cultures, which correlated with a significant decrease in the number of bone marrow mesenchymal/stromal progenitor (MSP) cells in these mice. In comparison to WT mice, a 10-fold decrease was observed in the number of fibroblast colony-forming units (CFU-Fs) in IL-5trg bone marrow. Hematopoietic activity of IL-5trg bone marrow cells was rescued by cultivation on preestablished layers of bone marrow-derived stromal cells. However, in contrast to bone marrow, increased hematopoietic activity was observed in the spleen and peripheral blood of IL-5trg mice. Likewise, the numbers of LTC-ICs and granulocyte-macrophage, macrophage, eosinophil, B-lymphocyte progenitors in the peripheral blood and spleen of IL-5trg mice were approximately 20-fold higher than in WT mice. A significant increase in CFU-F numbers was also observed in the spleens of IL-5trg mice compared with WT mice. Overall, our results suggest that constitutive overexpression of IL-5 can potentially induce colonization of spleen with MSP cells, which provides the necessary microenvironment for establishment of hematopoiesis in extramedullary sites.

Eosinophil's role remains uncertain as anti-interleukin-5 only partially depletes numbers in asthmatic airway

The role of eosinophils as effector cells in asthma pathogenesis has been questioned since an anti-interleukin (IL)-5 monoclonal antibody (mepolizumab), which depleted blood and sputum eosinophils, failed to inhibit allergen-induced bronchoconstriction and airway hyperresponsiveness. However, the effect of IL-5 blockade on tissue eosinophils was not examined. We sought to determine whether mepolizumab depletes airway tissue eosinophils and their products. Twenty-four patients with mild asthma received three intravenous doses of either 750 mg of mepolizumab or placebo in a randomized, double-blind, parallel-group fashion over 20 weeks. Mepolizumab produced a median decrease from baseline of 55% for airway eosinophils (interquartile range, 29-89%; p = 0.009 versus placebo), 52% for bone marrow eosinophils (45-76%, p = 0.003), and 100% for blood eosinophils (range, 67-100%, p = 0.02). Mepolizumab had no appreciable effect on bronchial mucosal staining of eosinophil major basic protein. There were no significant changes in clinical measures of asthma (airway hyperresponsiveness, FEV1, and peak flow recordings) between the mepolizumab and placebo-treated groups. Anti-IL-5 treatment reduces but does not deplete airway or bone marrow eosinophils. The role of the eosinophil remains uncertain. Further clinical studies in asthma with more effective antieosinophil strategies are required.

Eotaxin protein levels and airway pathology in a mouse model for allergic asthma

Eotaxin is a chemokine implicated in eosinophil trafficking and may be involved in the development of airway hyperresponsiveness. The role of eotaxin in a mouse model for allergic asthma was investigated. Challenging ovalbumin-sensitised mice with ovalbumin aerosol leads to airway hyperresponsiveness and airway eosinophilia 24 h after the last challenge. Furthermore, eotaxin concentrations were markedly increased in lungs and broncho-alveolar lavage fluid of ovalbumin-challenged mice compared to vehicle treated mice. This could mean that eotaxin is implicated in the pathology of this model. To further investigate the role of eotaxin in this murine model for allergic asthma, the ovalbumin response was modulated by either treatment with eotaxin antibodies or additional eotaxin, to suppress or promote the development of airway hyperresponsiveness and inflammation. Administration of eotaxin antibodies or an additional intravenous eotaxin injection did not alter the development of ovalbumin-induced airway hyperresponsiveness and eosinophilia. In conclusion, eotaxin concentrations were increased in a murine model for allergic airway inflammation. However, anti-eotaxin antibodies or additive intravenous murine eotaxin did not influence airway inflammation and hyperresponsiveness in this mouse model for allergic asthma.

Intranasal fluticasone propionate inhibits allergen induced bone marrow eosinophilia in mice

Local corticosteroids are currently the most efficient safe anti-allergic treatment, which attenuate eosinophilic tissue inflammation through several mechanisms. We evaluated the effect of local airways corticosteroid on repeated allergen exposure-induced bone marrow activation and airway eosinophilia using the number of eosinophils in bone marrow, bronchoalveolar lavage fluid (BALf) and airways tissue as study end-points. Male BALB/c mice were sensitized by intraperitoneal injections of aluminum-precipitated ovalbumin (OVA) on two different days (5 days apart). Eight days after the second sensitization, the animals were challenged intranasally with OVA or phosphate-buffered saline (PBS) on 5 consecutive days. Concomitantly with challenges mice were treated with fluticasone propionate or respective vehicle. OVA exposures induced a significant increase in eosinophil numbers in bone marrow, BALf and airways tissue (P<0.005). Treatment with fluticasone propionate significantly reduced the increase of absolute number of mature bone marrow eosinophils (P=0.014) and showed a tendency towards decrease in the immature bone marrow eosinophil number (P=0.057) compared to controls. However, fluticasone propionate had no significant effect on BALf and airways tissue eosinophils (P=0.28 and 0.07, respectively). In this murine allergy model intranasal corticosteroid reduced number of bone marrow mature eosinophils, but did not significantly affect airways cell populations.

Human mast cell progenitors in peripheral blood from atopic subjects with high IgE levels

BACKGROUND

It remains unclear whether the number of circulating mast cell progenitors is increased in patients with atopic diseases. Distinct genotypes are reported to affect mast cell/basophil activation.

OBJECTIVE

We compared the number and function of mast cell progenitors present in the peripheral blood from donors with normal IgE (IgE < 400 U/mL) and those with atopic dermatitis accompanied by high serum IgE (IgE > 5000 U/mL).

METHODS

Purified peripheral blood cells were cultured in serum-free methylcellulose containing stem cell factor (SCF), IL-6 plus IL-3. Fresh methylcellulose containing the cytokines was layered over every 2 weeks. The cultured mast cells were retrieved from the methylcellulose and were functionally analysed.

RESULTS

Mast cell colonies were distinguished at 6 weeks of culture as other colony types had been degenerated. The number of mast cell colony-forming cells varied depending on donors and was not significantly increased in peripheral blood from the hyper-IgE atopic patients. A significant inversed correlation was found between the number of mast cells per one colony and the ages of donors. The cultured mast cells derived from atopic patients and those from normal IgE donors equally expressed Fc epsilon RI and released histamine through Fc epsilon RI, although IL-4 priming in vitro markedly enhanced the function of mast cells regardless of donors.

CONCLUSIONS

These results indicate that the number of circulating mast cell progenitors may be regulated by unknown individual factors unrelated to IgE levels. Mast cell function may be regulated largely by environmental factors, such as IL-4, but not determined by their progenitors' genotypes.

Recombinant food allergens

Allergenic (glyco)proteins are the elicitors of food allergies and can cause acute severe hypersensitivity reactions. Recombinant food allergens are available in standardised quantity and constant quality. Therefore, they offer new perspectives to overcome current difficulties in the diagnosis, treatment and investigation of food allergies. This review summarises the expression strategies and characteristics of more than 40 recombinant food allergens that have been produced until today. Their IgE-binding properties are compared to those of their natural counterparts, in addition their application as diagnostic tools, the generation of hypoallergenic recombinant isoforms and mutants for therapeutic purposes, the determination of epitopes and cross-reactive structures are described.

Analysis of eosinophils and myeloid progenitor responses to modified forms of MPIF-2

Myeloid progenitor inhibitory factor (MPIF)-2 is a beta-chemokine with select and potent activities on eosinophils and myeloid progenitors. In the beta-chemokine family, biological activity is modulated by differential processing of the amino-terminus. Here, for MPIF-2, we describe the biological activities of NH(2)-terminal deletion mutants and compare regions necessary for eosinophil and myeloid progenitor activities. Five MPIF-2 proteins with deletions at the amino-terminus were produced in Escherichia coli and assayed for calcium mobilization, chemotaxis and receptor binding activities on eosinophils, and for their ability to inhibit colony formation of human myeloid bone marrow progenitors. For eosinophils, deletion of the first two amino acids did not markedly alter activity, while subsequent truncations result in a complete loss of activity. One of the MPIF-2 mutants, MPIF-2 (P30-R99) was converted from an agonist to an antagonist of eotaxin, MPIF-2 and MCP-4 functional responses in eosinophil calcium flux and chemotaxis assays. Surprisingly, while displaying a complete loss of agonist activity toward eosinophils, MPIF-2 (P30-R99) retains ability to inhibit human bone marrow myeloid progenitor cell colony formation. In addition, processing at the amino terminus of MPIF-2 in vivo, may result in a chemokine with altered biological activities.

IL-5 production by bone marrow stromal cells: implications for eosinophilia associated with asthma

BACKGROUND

Eosinophil infiltration of bronchial tissue is a hallmark of asthma. Recruitment of eosinophils into pulmonary tissue is dependent on the presence of IL-5. In addition, IL-5 plays a significant role in the differentiation, proliferation, and maturation of eosinophil progenitor cells in the bone marrow before recruitment into the lung. The contribution of bone marrow eosinophil production to eosinophilia associated with asthma is poorly understood.

OBJECTIVE

The aims of this study were to determine whether bone marrow stromal cells produce IL-5 and to determine whether IL-5 production by stromal cells is upregulated by IL-1, an inflammatory cytokine associated with asthma.

METHODS

IL-5 messenger (m)RNA from bone marrow stromal cells was amplified by RT-PCR and sequenced. Stromal cells were lysed, and IL-5 protein production was measured by ELISA. Upregulation of stromal cell IL-5 transcription, translation, and functional effect on eosinophil differentiation was evaluated after stimulation with recombinant IL-1alpha and IL-1beta and compared with untreated cells.

RESULTS

Bone marrow stromal cells transcribe and translate IL-5. The nucleotide sequence of IL-5 mRNA from stromal cells was identical to that previously reported for murine T cells. IL-5 mRNA abundance in stromal cells increased with increasing cell confluence in culture. IL-5 mRNA and protein levels were upregulated by exposure of stromal cells to the inflammatory cytokines IL-1alpha and IL-1beta. Exposure of stromal cells to IL-1 resulted in increased eosinophil differentiation in coculture experiments with nonadherent bone marrow cells.

CONCLUSION

The production of IL-5 mRNA and protein by bone marrow stromal cells is a novel finding that has implications for both normal eosinophilopoiesis and development of the accelerated eosinophil production associated with asthma.

Chemokine receptors and their role in inflammation and infectious diseases

Chemokines are small peptides that are potent activators and chemoattractants for leukocyte subpopulations and some nonhemopoietic cells. Their actions are mediated by a family of 7-transmembrane G-protein–coupled receptors, the size of which has grown considerably in recent years and now includes 18 members. Chemokine receptor expression on different cell types and their binding and response to specific chemokines are highly variable. Significant advances have been made in understanding the regulation of chemokine receptor expression and the intracellular signaling mechanisms used in bringing about cell activation. Chemokine receptors have also recently been implicated in several disease states including allergy, psoriasis, atherosclerosis, and malaria. However, most fascinating has been the observation that some of these receptors are used by human immunodeficiency virus type 1 in gaining entry into permissive cells. This review will discuss structural and functional aspects of chemokine receptor biology and will consider the roles these receptors play in inflammation and in infectious diseases.

Chemokine receptors and their role in inflammation and infectious diseases

Chemokines are small peptides that are potent activators and chemoattractants for leukocyte subpopulations and some nonhemopoietic cells. Their actions are mediated by a family of 7-transmembrane G-protein–coupled receptors, the size of which has grown considerably in recent years and now includes 18 members. Chemokine receptor expression on different cell types and their binding and response to specific chemokines are highly variable. Significant advances have been made in understanding the regulation of chemokine receptor expression and the intracellular signaling mechanisms used in bringing about cell activation. Chemokine receptors have also recently been implicated in several disease states including allergy, psoriasis, atherosclerosis, and malaria. However, most fascinating has been the observation that some of these receptors are used by human immunodeficiency virus type 1 in gaining entry into permissive cells. This review will discuss structural and functional aspects of chemokine receptor biology and will consider the roles these receptors play in inflammation and in infectious diseases.

Molecular analysis of CCR-3 events in eosinophilic cells

CCR-3 is a major receptor involved in regulating eosinophil trafficking. Initial analysis of chemokine receptors has demonstrated unique receptor events in different cell types, indicating the importance of investigating CCR-3 events in eosinophilic cell lines. We now report that the eosinophilic cell line, acute myelogenous leukemia (AML) 14.3D10, expresses eosinophil granule proteins and eotaxin, but has no detectable expression of eosinophil chemokine receptors. Treatment of the cell line with butyric acid and IL-5 results in a dose-dependent synergistic induction of CCR-3 and, to a lesser extent, CCR-1 and CCR-5. Interestingly, using a luciferase reporter construct under the control of the hCCR-3 promoter, the uninduced and induced cells display high, but comparable, levels of promoter activity. Differentiated AML cells developed enhanced functional activation, as indicated by adhesion to respiratory epithelial cells and chemokine-induced transepithelial migration. Chemokine signaling did not inhibit adenylate cyclase activity even though calcium transients were blocked by pertussis toxin. Additionally, chemokine-induced calcium transients were inhibited by pretreatment with PMA, but not forskolin. Eotaxin treatment of differentiated AML cells resulted in marked down-modulation of CCR-3 expression for at least 18 h. Receptor internalization was not dependent upon chronic ligand exposure and was not accompanied by receptor degradation. Thus, CCR-3 is a late differentiation marker on AML cells and uses a signal transduction pathway involving rapid and prolonged receptor internalization, calcium transients inhibitable by protein kinase C but not protein kinase A, and the paradoxical lack of inhibition of adenylate cyclase activity.

Clinical spectrum of food allergy in children in Australia and South-East Asia: identification and targets for treatment

The prevalence of atopic diseases is increasing worldwide for reasons that are not clear. Food allergies are the earliest manifestations of atopy. This review defines the foods most commonly involved in allergic reactions and identifies an emerging group of syndromes in which food allergy is involved. A study of the frequency of food allergies in Australia and South-East Asia has recently shown that egg, cow's milk and peanut are the most common food allergens in Australia, but there were divergent results from different regions of South-East Asia. It is not clear whether the differences in reactivity to foods are due to genetic or cultural factors, but the findings raise the possibility that genetic susceptibility to food allergy may operate at the T-cell level modulated by the major histocompatibility complex. The Melbourne Milk Allergy Study defined a wide range of clinical symptoms and syndromes that could be reproduced by dietary challenge. A subsequent analysis of the infants with hypersensitivity to cow's milk and other multiple food proteins identified a new syndrome, multiple food protein intolerance of infancy. Food challenges demonstrated reactions developing slowly days after commencement of low-allergen soy formula or extensively hydrolysed formula. Follow-up at the age of 3 years showed that most children with this disorder tolerated most foods apart from cow's milk, egg and peanut. Atopic dermatitis affects about 18% of infants in the first 2 years of life. In a community-based study we have shown a very strong association (RR 3.5) between atopic dermatitis and infants with immunoglobulin E allergy to cow's milk, egg or peanut. Family studies on these infants have shown a link between atopic dermatitis and the genomic region 5q31 adjacent to the interleukin-4 gene cluster. Infantile colic (distress) affects 15-40% of infants in the first 4 months of life. Many theories of causation have been proposed, but a study from our centre showed that dietary modification, particularly that of breastfeeding mothers whose infants present with colic before the age of 6 weeks, alleviated symptoms. Colic associated with vomiting has been attributed to gastro-oesophageal reflux (GOR). This has been considered primarily a motility disorder, but a secondary form resulting from food protein intolerance has been described recently. We have also recently identified a group of infants with distressed behaviour attributed to GOR who have failed to respond to H2-receptor antagonists, prokinetic agents and multiple formula changes. Symptoms resolved on commencement of an elemental amino acid-based formula. In two-thirds of the patients, symptoms relapsed when challenged with low-allergen soy formula or extensively hydrolysed formula. We propose that a period of food protein intolerance is a part of the normal development of the immune system as it encounters common dietary proteins in infancy and early childhood. Future targets for research are development of appropriate dietary and management strategies for these entities and identification of genetic markers for these disorders.