Eosinophil progenitors in allergy and asthma - do they matter?

Insight into IL-5 as a Potential Target for the Treatment of Allergic Diseases

Interleukin-5 functions as a B-cell differentiation factor, but more importantly, in the context of this review, it plays a variety of roles in eosinophil biology, including eosinophil differentiation and maturation in the bone marrow, and facilitates eosinophil migration to tissue sites, usually in the context of an allergic reaction. Given the availability of selective anti-IL-5 drugs such as mepolizumab and reslizumab, as well as the IL-5 receptor antagonist benralizumab, it is worth investigating whether they could be used in some cases of allergic disease. Asthma has a well-documented involvement of IL-5 in its pathophysiology and has clear benefits in the case of anti-IL-5 therapy; therefore, current knowledge is presented to provide a reference point for the study of less-described diseases such as atopic dermatitis, chronic rhinosinusitis, chronic spontaneous urticaria, and its association with both IL-5 and anti-IL-5 treatment options. We then review the current literature on these diseases, explain where appropriate potential reasons why anti-IL-5 treatments are ineffective, and then point out possible future directions for further research.

Wogonoside Ameliorates Airway Inflammation and Mucus Hypersecretion via NF-κB/STAT6 Signaling in Ovalbumin-Induced Murine Acute Asthma

Asthma is recognized as a chronic respiratory illness characterized by airway inflammation and airway hyperresponsiveness. Wogonoside, a flavonoid glycoside, is reported to significantly alleviate the inflammation response and oxidative stress. Herein, this study aimed to investigate the therapeutic effect and underlying mechanism of wogonoside on airway inflammation and mucus hypersecretion in a murine asthma model and in human bronchial epithelial cells (16HBE). BALB/c mice were sensitized and challenged with ovalbumin (OVA). Pulmonary function and the number of cells in the bronchoalveolar lavage fluid (BALF) were examined. Pathological changes in lung tissue in each group were evaluated via hematoxylin and eosin and periodic acid-Schiff staining, and changes in levels of cytokines in BALF and of immunoglobulin E in serum were determined via an enzyme-linked immunosorbent assay. The expression of relevant genes in lung tissue was analyzed via real-time PCR. Western blotting and immunofluorescence were employed to detect the expression of relevant proteins in lung tissue and 16HBE cells. Treatment with 10 and 20 mg/kg wogonoside significantly attenuated the OVA-induced increase of inflammatory cell infiltration, mucus secretion, and goblet cell percentage and improved pulmonary function. Wogonoside treatment reduced the level of T-helper 2 cytokines including interleukin (IL)-4, IL-5, and IL-13 in BALF and of IgE in serum and decreased the mRNA levels of cytokines (IL-4, IL-5, IL-6, IL-13, and IL-1β and tumor necrosis factor-α), chemokines (CCL-2, CCL-11, and CCL-24), and mucoproteins (MUC5AC, MUC5B, and GOB5) in lung tissues. The expression of MUC5AC and the phosphorylation of STAT6 and NF-κB p65 in lung tissues and 16HBE cells were significantly downregulated after wogonoside treatment. Thus, wogonoside treatment may effectively decrease airway inflammation, airway remodeling, and mucus hypersecretion via blocking NF-κB/STAT6 activation.

Benralizumab in severe eosinophilic asthma in real life: confirmed effectiveness and contrasted effect on sputum eosinophilia versus exhaled nitric oxide fraction - PROMISE

Background

Randomised controlled trials have shown that benralizumab, an anti-interleukin-5 receptor monoclonal antibody, reduces exacerbations and oral corticosteroid dose and improves asthma control and lung function in severe eosinophilic asthma. The aim of this study was to confirm results of randomised controlled trials in real life in a population of 73 patients with severe eosinophilic asthma treated with benralizumab for at least 12 months.

Methods

Patients underwent careful monitoring of asthma exacerbations, exhaled nitric oxide fraction, lung function, asthma control and quality of life questionnaire responses and sputum induction, and gave a blood sample at baseline, after 6 months and then every year.

Results

We found significant reductions in exacerbations (by 92%, p<0.0001) and oral corticosteroid dose (by 83%, p<0.001) after 6 months that were maintained over time, with 78% of patients able to stop oral corticosteroid therapy. Patients improved their Asthma Control Test (ACT) score (from 11.7±5.1 to 16.9±5.35, p<0.0001), Asthma Control Questionnaire (ACQ) score (from 2.88±1.26 to 1.77±1.32, p<0.0001) and Asthma Quality of Life Questionnaire score (+1.04, p<0.0001) at 6 months and this was maintained during follow-up. Only 35% and 43% of patients reached asthma control according to an ACT score ≥20 and ACQ score <1.5, respectively. We observed stable post-bronchodilation lung function over time and a significant reduction in sputum eosinophil count, with 85% of patients exhibiting sputum eosinophil counts <3% after 6 months (p<0.01) with no effect on exhaled nitric oxide fraction.

Conclusion

In our real-life study, we confirm the results published in randomised controlled trials showing a sharp reduction in exacerbations and oral corticosteroid therapy, an improvement in asthma control and quality of life, and a dramatic reduction in sputum eosinophil count.

Subsets of Eosinophils in Asthma, a Challenge for Precise Treatment

The existence of eosinophils was documented histopathologically in the first half of the 19th century. However, the term “eosinophils” was first used by Paul Ehrlich in 1878. Since their discovery and description, their existence has been associated with asthma, allergies, and antihelminthic immunity. Eosinophils may also be responsible for various possible tissue pathologies in many eosinophil-associated diseases. Since the beginning of the 21st century, the understanding of the nature of this cell population has undergone a fundamental reassessment, and in 2010, J. J. Lee proposed the concept of “LIAR” (Local Immunity And/or Remodeling/Repair), underlining the extensive immunoregulatory functions of eosinophils in the context of health and disease. It soon became apparent that mature eosinophils (in line with previous morphological studies) are not structurally, functionally, or immunologically homogeneous cell populations. On the contrary, these cells form subtypes characterized by their further development, immunophenotype, sensitivity to growth factors, localization, role and fate in tissues, and contribution to the pathogenesis of various diseases, including asthma. The eosinophil subsets were recently characterized as resident (rEos) and inflammatory (iEos) eosinophils. During the last 20 years, the biological therapy of eosinophil diseases, including asthma, has been significantly revolutionized. Treatment management has been improved through the enhancement of treatment effectiveness and a decrease in the adverse events associated with the formerly ultimately used systemic corticosteroids. However, as we observed from real-life data, the global treatment efficacy is still far from optimal. A fundamental condition, “sine qua non”, for correct treatment management is a thorough evaluation of the inflammatory phenotype of the disease. We believe that a better understanding of eosinophils would lead to more precise diagnostics and classification of asthma subtypes, which could further improve treatment outcomes. The currently validated asthma biomarkers (eosinophil count, production of NO in exhaled breath, and IgE synthesis) are insufficient to unveil super-responders among all severe asthma patients and thus give only a blurred picture of the adepts for treatment. We propose an emerging approach consisting of a more precise characterization of pathogenic eosinophils in terms of the definition of their functional status or subset affiliation by flow cytometry. We believe that the effort to find new eosinophil-associated biomarkers and their rational use in treatment algorithms may ameliorate the response rate to biological therapy in patients with severe asthma.

IgE cross-linking induces activation of human and mouse mast cell progenitors

BACKGROUND

The concept of innate and adaptive effector cells that are repleted by maturing inert progenitor cell populations is changing. Mast cells develop from rare mast cell progenitors populating peripheral tissues at homeostatic conditions, or as a result of induced recruitment during inflammatory conditions.

OBJECTIVE

Because FcεRI-expressing mast cell progenitors are the dominating mast cell type during acute allergic lung inflammation in vivo, we hypothesized that they are activated by IgE cross-linking.

METHODS

Mouse peritoneal and human peripheral blood cells were sensitized and stimulated with antigen, or stimulated with anti-IgE, and the mast cell progenitor population analyzed for signs of activation by flow cytometry. Isolated peritoneal mast cell progenitors were studied before and after anti-IgE stimulation at single-cell level by time-lapse fluorescence microscopy. Lung mast cell progenitors were analyzed for their ability to produce IL-13 by intracellular flow cytometry in a mouse model of ovalbumin-induced allergic airway inflammation.

RESULTS

Sensitized mouse peritoneal mast cell progenitors demonstrate increased levels of phosphorylation of tyrosines on intracellular proteins (total tyrosine phosphorylation), and spleen tyrosine kinase (Syk) phosphorylation after antigen exposure. Anti-IgE induced cell surface-associated lysomal-associated membrane protein-1 (LAMP-1) in naive mast cell progenitors, and prompted loss of fluorescence signal and altered morphology of isolated cells loaded with lysotracker. In human mast cell progenitors, anti-IgE increased total tyrosine phosphorylation, cell surface-associated LAMP-1, and CD63. Lung mast cell progenitors from mice with ovalbumin-induced allergic airway inflammation produce IL-13.

CONCLUSIONS

Mast cell progenitors become activated by IgE cross-linking and may contribute to the pathology associated with acute allergic airway inflammation.

Novel mechanisms of action contributing to Benralizumab's potent anti-eosinophilic activity

Benralizumab is a humanised, anti-IL-5Rα monoclonal antibody with anti-eosinophilic activity. Lack of fucose (afucosylation) increases its affinity to CD16a and significantly enhances antibody-dependent cell-mediated cytotoxicity (ADCC) by NK cells. Although benralizumab proved clinically efficacious in clinical trials for patients with severe asthma and hypereosinophilic syndrome, in-depth characterisation of its anti-eosinophilic mechanisms of action remain elusive. Here, we further investigated the mechanisms involved in benralizumab's anti-eosinophilic activities. In the presence of NK cells benralizumab induced potent eosinophil apoptosis as demonstrated by the upstream induction of caspase 3/7 and upregulation of cytochrome C. In addition, we uncovered a previously unrecognised mechanism whereby benralizumab can induce eosinophil phagocytosis/efferocytosis by macrophages, a process called antibody-dependent cell phagocytosis (ADCP). Using live cell imaging we unravel the stepwise processes leading to eosinophil apoptosis and uptake by activated macrophages. Through careful observations of cellular co-culture assays we identified a novel role for macrophage derived TNF to further enhance benralizumab-mediated eosinophil apoptosis through activation of TNF-receptor 1 on eosinophils. TNF-induced eosinophil apoptosis was associated with Cytochrome C upregulation, mitochondrial membrane depolarisation, and increased caspase 3/7 activity. Moreover, activated NK cells were found to amplify this axis through the secretion of IFNγ, subsequently driving TNF expression by macrophages. Our data provide insights into the timely appearance of events leading to benralizumab-induced eosinophil apoptosis and suggest that additional mechanisms may contribute to the potent anti-eosinophilic activity of benralizumab in vivo Importantly, afucosylation of benralizumab strongly enhanced its potency for all mechanisms investigated.

Evidence for Asthma in the Lungs of Mice Inoculated with Different Doses of Toxocara canis

Toxocara canis, a common roundworm that mainly causes toxocariasis, is a zoonotic parasite found worldwide. Humans, an accidental host, can acquire T. canis infection through accidental ingestion of T. canis-embryonated egg-contaminated food, water, and soil, and by encapsulated larvae in a paratenic host's viscera or meat. Long-term residence of T. canis larvae in a paratenic host's lungs may induce pulmonary inflammation that contributes to lung injury, airway inflammatory hyperresponsiveness, and collagen deposition in mice and clinical patients. This study intended to investigate the relationship between T. canis infection and allergic asthma in BALB/c mice inoculated with high, moderate, and low doses of T. canis eggs for a 13-week investigation. The airway hyperresponsiveness (AHR) to methacholine, collagen deposition, cytokine levels, and pathological changes in lung tissues was assessed in infected mice at weeks 1, 5, and 13 postinfection. The cell composition in bronchoalveolar lavage fluid of infected mice was assessed at weeks 5 and 13 postinfection. Compared with uninfected control mice, all groups of T. canis-infected mice exhibited significant AHR, a dose-dependent increase in eosinophilic infiltration leading to multifocal interstitial and alveolar inflammation with abundant mucus secretion, and collagen deposition in which the lesion size increased with the infective dose. Infected mice groups also showed significant expressions of eotaxin and type 2 T-helper-dominant cytokines such as interleukin (IL)-4, IL-5, and IL-13. Overall, these results suggest that T. canis larval invasion of the lungs may potentially cause pulmonary inflammatory injury and could subsequently contribute to the development of allergic manifestations such as asthma.

Elevated Levels of Activated and Pathogenic Eosinophils Characterize Moderate-Severe House Dust Mite Allergic Rhinitis

Eosinophils play a critical role in the pathogenesis of allergic airway inflammation. However, the relative importance of eosinophil activation and pathogenicity in driving the progression of disease severity of allergic rhinitis (AR) remains to be defined. We aimed to assess the relation of activated and pathogenic eosinophils with disease severity of patients with AR. Peripheral blood and nasal samples were collected from patients with mild (n = 10) and moderate-severe (n = 21) house dust mite AR and healthy control subjects (n = 10) recruited prospectively. Expressions of activation and pathogenic markers on eosinophils in the blood and nose were analyzed by flow cytometry. The eosinophilic cation protein- (ECP-) releasing potential and the pro-Th2 function of blood eosinophils were compared between the mild and moderate-severe patients and healthy controls. Our results showed that the numbers of activated (CD44⁺ and CD69⁺) and pathogenic (CD101⁺CD274⁺) eosinophils in the blood and nose as well as blood eosinophil progenitors were increased in moderate-severe AR compared with the mild patients and healthy controls. In addition, the levels of activated and pathogenic eosinophils in the blood were positively correlated with the total nasal symptom score and serum ECP and eosinophil peroxidase (EPX) levels in patients with AR. Furthermore, the blood eosinophils obtained from the moderate-severe patients exhibited a higher potential of releasing ECP and EPX induced by CCL11 and of promoting Th2 responses than those from the mild patients and healthy controls. In conclusion, patients with moderate-severe AR are characterized by elevated levels of activated and pathogenic eosinophils, which are associated with higher production of ECP, EPX, and IL-4 in the peripheral blood.

The impact of the prostaglandin D2 receptor 2 and its downstream effects on the pathophysiology of asthma

Current research suggests that the prostaglandin D₂ (PGD₂ ) receptor 2 (DP₂ ) is a principal regulator in the pathophysiology of asthma, because it stimulates and amplifies the inflammatory response in this condition. The DP₂ receptor can be activated by both allergic and nonallergic stimuli, leading to several pro-inflammatory events, including eosinophil activation and migration, release of the type 2 cytokines interleukin (IL)-4, IL-5 and IL-13 from T helper 2 (Th2) cells and innate lymphoid cells type 2 (ILCs), and increased airway smooth muscle mass via recruitment of mesenchymal progenitors to the airway smooth muscle bundle. Activation of the DP₂ receptor pathway has potential downstream effects on asthma pathophysiology, including on airway epithelial cells, mucus hypersecretion, and airway remodelling, and consequently might impact asthma symptoms and exacerbations. Given the broad distribution of DP₂ receptors on immune and structural cells involved in asthma, this receptor is being explored as a novel therapeutic target.

Sympathetic Nerves Positively Regulate Eosinophil-Driven Allergic Conjunctivitis via α1-Adrenergic Receptor Signaling

Eosinophils are a major cause of tissue injury in allergic conjunctivitis. The biological nature of eosinophils in the conjunctiva and the mechanisms that control eosinophils' responses in allergic conjunctivitis are currently not completely understood. This study reports that conjunctival eosinophils comprise two populations-Siglec-F^int and Siglec-F^hi-in different life stages. Siglec-F^int eosinophils partly expressed CD34 and were in the immature (or steady) state. Siglec-F^hi eosinophils did not express CD34, sharply increased in number after short ragweed (SRW) pollen challenge, and were in the mature (or activated) state. Moreover, chemical sympathectomy by 6-hydroxydopamine reduced the recruitment and activation of eosinophils, whereas the activation of the sympathetic nerve system (SNS) with restraint stress accelerated the recruitment and activation of eosinophils in SRW-induced conjunctivitis. It was also found that two eosinophil populations expressed alpha-1a-adrenergic receptors (α1a-ARs); in SRW-induced conjunctivitis, treatment with an α1a-AR antagonist decreased eosinophil responses, whereas treatment with an α1a-AR agonist aggravated eosinophil responses. Thus, eosinophil responses in conjunctivitis are regulated by the SNS via α1a-AR signaling. SNS inputs or α1a-AR function may be potential targets for the treatment of allergic conjunctivitis.

Petiveria alliacea Suppresses Airway Inflammation and Allergen-Specific Th2 Responses in Ovalbumin-Sensitized Murine Model of Asthma

OBJECTIVE

To examine the effect of metanol extract of Petiveria alliacea (PM) on airway inflflammation in a murine model of chronic asthma.

METHODS

Two-month-old male BALB/c mice (n=6-8/group) were sensitized on days 0 and 14 by intraperitoneal injection of 20 μg ovalbumin (OVA). On day 25, the mice received an airway challenge with OVA (3%, w/v, in phosphate buffered saline). PM was administered orally by oral gavage to mice at doses of 100, 200 and 400 mg/kg body weight once daily from days 18 to 23. Control mice were orally administered phosphate buffered saline (PBS) to induce a model of asthma. At the end of the test, respiratory reactivity was assayed, the total cell number, interleukin-4 (IL-4), IL-5, IL-13, tumor necrosis factor-alpha (TNF-α) and reactive oxygen species (ROS) in the bronchoalveolar lavage fluid (BALF) were determined and the levels of serum IgE, intercellular cell adhesion molecule 1 (ICAM-1) and eotoxin were measured. In addition, lung tissue was used to qualify the IL-4, IL-5, IL-13, TNF-α and transforming growth factor beta 1 (TGF-β1). Histologic examination was performed to observe inflammatory cellular infiltration.

RESULTS

The administration of PM in comparison with the OVA-only treated group signifificantly attenuated the infifiltration of eosinophils and other inflflammatory cells (P<0.01). Airway resistance (RI) in the OVA-only induced group was significantly higher than that of the PBS control group (P<0.01) when methacholine was added. TNF-α, IgE, TGF-β1 and cytokine levels IL-4, IL-5, IL-13 in the BALF decreased compared to control mice (P<0.01 or P<0.05). PM treatment also inhibited the production of chemokines, eotaxin and ICAM-1 in BALF (P<0.01), which improved lung function. Histopathological examination revealed that the sensitized treated PM groups had significant lower in inflammatory scores similar to dexamethasone treatments and the untreated group.

CONCLUSION

Administration of PM could inhibit airway inflammation, regulate cytokines, chemokines and enhance pulmonary conditions in allergic murine model of asthma.

C‑C chemokine receptor type 3 gene knockout alleviates inflammatory responses in allergic rhinitis model mice by regulating the expression of eosinophil granule proteins and immune factors

The present study aimed to investigate the effects of C‑C chemokine receptor type 3 (CCR3) gene knockout on allergic rhinitis (AR) in mice, as well as the underlying molecular mechanisms. Ovalbumin was administrated to CCR3+/+ and CCR3‑/‑ BALB/c mice to establish an AR model. The mice were divided into four groups: i) Normal control (CG), ii) AR model (AR), iii) CCR3 knockout CG (CCR3‑/‑CG) and iv) AR model with CCR3 knockout (CCR3‑/‑AR). Histological sections of nasal mucosae were examined by hematoxylin and eosin staining, which revealed that CCR3 knockout suppressed the invasion of inflammatory cells and relieved the damage of nasal mucosae. Peripheral blood smear and nasal‑washing smears were evaluated by Wright's staining. Eosinophil (EOS) numbers in nasal mucosae, peripheral blood, and nasal washings of the various groups were ranked in the order: AR>CCR3‑/‑AR>CG>CCR3‑/‑. mRNA expression levels of CCR3, EOS peroxidase (EPO), EOS cationic protein (ECP), and major basic protein (MBP) in the peripheral serum and nasal washings were detected by reverse transcription‑polymerase chain reaction. Interferon‑γ (IFN‑γ), interleukin (IL)‑4, IL‑10, and immunoglobulin E (IgE) protein levels in the peripheral serum and nasal washings were investigated by ELISA. CCR3 mRNA expression was not detected in the CCR3‑/‑ and CCR3‑/‑AR groups, whereas expression levels in the AR group were markedly higher compared with expression in the CG group. Compared with the CG‑associated groups (i.e., the CG and CCR3‑/‑CG groups), the levels of EPO, ECP, MBP, IL‑4, and IgE were significantly increased in the AR‑associated groups (that is, R and CCR3‑/‑AR). In addition, the CCR3‑/‑AR group mice produced significantly lower levels of EPO, ECP, MBP, IL‑4 and IgE compared with the AR group, whereas the expression levels of IFN‑γ and IL‑10 were increased. CCR3 gene knockout may alleviate EOS invasion and the inflammatory response in AR model mice by reducing the expression levels of EPO, ECP, MBP, IL‑4, and IgE, and increasing the expression of IL‑10 and IFN‑γ.

Surgical and immune reconstitution murine models in bone marrow research: Potential for exploring mechanisms in sepsis, trauma and allergy

Bone marrow, the vital organ which maintains lifelong hemopoiesis, currently receives considerable attention, as a source of multiple cell types which may play important roles in repair at distant sites. This emerging function, distinct from, but closely related to, bone marrow roles in innate immunity and inflammation, has been characterized through a number of strategies. However, the use of surgical models in this endeavour has hitherto been limited. Surgical strategies allow the experimenter to predetermine the site, timing, severity and invasiveness of injury; to add or remove aggravating factors (such as infection and defects in immunity) in controlled ways; and to manipulate the context of repair, including reconstitution with selected immune cell subpopulations. This endows surgical models overall with great potential for exploring bone marrow responses to injury, inflammation and infection, and its roles in repair and regeneration. We review three different murine surgical models, which variously combine trauma with infection, antigenic stimulation, or immune reconstitution, thereby illuminating different aspects of the bone marrow response to systemic injury in sepsis, trauma and allergy. They are: (1) cecal ligation and puncture, a versatile model of polymicrobial sepsis; (2) egg white implant, an intriguing model of eosinophilia induced by a combination of trauma and sensitization to insoluble allergen; and (3) ectopic lung tissue transplantation, which allows us to dissect afferent and efferent mechanisms leading to accumulation of hemopoietic cells in the lungs. These models highlight the gain in analytical power provided by the association of surgical and immunological strategies.

Effects of chemokine receptor 3 gene silencing by RNA interference on eosinophils

The present study aimed to use RNA interference (RNAi) to silence chemokine receptor 3 (CCR3) and observe the effects on eosinophils (EOS) in mice with allergic rhinitis (AR). CCR3 small interfering RNA (siRNA) lentiviral vectors were transduced into purified EOS cells cultured in vitro. Reverse transcription-polymerase chain reaction (RT-PCR) and western blot analyses were also used to detect the efficiency of silencing, and flow cytometry was used to detect the EOS apoptosis rates. Experimental mice were grouped for nasal administration, and the lentivirus was then dispensed to AR mice. RT-PCR and western blots were performed to detect the expression levels of CCR3 mRNA and protein in EOS extracted from bone marrow, peripheral blood and nasal mucosa. Furthermore, flow cytometry was performed to detect changes to CD34-positive (CD34⁺) cells in each group. The CCR3 siRNA lentiviral vector exhibited high efficiency in silencing CCR3 mRNA and protein expression, inhibited growth and promoted apoptosis of EOS. In addition, the expression of CCR3 mRNA and protein in the bone marrow, peripheral blood and nasal mucosa of mice in the CCR3 siRNA treatment group were lower than those in the control group (P<0.05), whereas the number of CD34⁺ cells in the CCR3 siRNA treatment group was not significantly different compared with that in the control group (P>0.05). CCR3 RNAi could effectively silence the expression of CCR3 mRNA and protein both in vitro and in vivo, thus promoting apoptosis of EOS and inhibiting its growth, migration and invasion.

Monoclonal antibody therapy for the treatment of asthma and chronic obstructive pulmonary disease with eosinophilic inflammation

Eosinophils have been linked with asthma for more than a century, but their role has been unclear. This review discusses the roles of eosinophils in asthma and chronic obstructive pulmonary disease (COPD) and describes therapeutic antibodies that affect eosinophilia. The aims of pharmacologic treatments for pulmonary conditions are to reduce symptoms, slow decline or improve lung function, and reduce the frequency and severity of exacerbations. Inhaled corticosteroids (ICS) are important in managing symptoms and exacerbations in asthma and COPD. However, control with these agents is often suboptimal, especially for patients with severe disease. Recently, new biologics that target eosinophilic inflammation, used as adjunctive therapy to corticosteroids, have proven beneficial and support a pivotal role for eosinophils in the pathology of asthma. Nucala® (mepolizumab; anti-interleukin [IL]-5) and Cinquair® (reslizumab; anti-IL-5), the second and third biologics approved, respectively, for the treatment of asthma, exemplifies these new treatment options. Emerging evidence suggests that eosinophils may contribute to exacerbations and possibly to lung function decline for a subset of patients with COPD. Here we describe the pharmacology of therapeutic antibodies inhibiting IL-5 or targeting the IL-5 receptor, as well as other cytokines contributing to eosinophilic inflammation. We discuss their roles as adjuncts to conventional therapeutic approaches, especially ICS therapy, when disease is suboptimally controlled. These agents have achieved a place in the therapeutic armamentarium for asthma and COPD and will deepen our understanding of the pathogenic role of eosinophils.

Functional interleukin-33 receptors are expressed in early progenitor stages of allergy-related granulocytes

Interleukin-33 (IL-33) induces T helper type 2 (Th2) cytokine production and eosinophilia independently of acquired immunity, leading to innate immunity-mediated allergic inflammation. Allergy-related innate myeloid cells such as eosinophils, basophils and mast cells express the IL-33 receptor (IL-33R), but it is still unknown how IL-33 regulates allergic inflammation involving these cells and their progenitors. Here, we revealed that the functional IL-33R was expressed on eosinophil progenitors (EoPs), basophil progenitors (BaPs) and mast cell progenitors (MCPs). In the presence of IL-33, these progenitors did not expand, but produced a high amount of Th2 and pro-inflammatory cytokines such as IL-9, IL-13, IL-1β and IL-6. The amount of cytokines produced by these progenitors was greater than that by mature cells. In vivo, IL-33 stimulated the expansion of EoPs, but it was dependent upon the elevated serum IL-5 that is presumably derived from type 2 innate lymphoid cells that express functional IL-33R. These data collectively suggest that EoPs, BaPs and MCPs are not only the sources of allergy-related granulocytes, but can also be sources of allergy-related cytokines in IL-33-induced inflammation. Because such progenitors can differentiate into mature granulocytes at the site of inflammation, they are potential therapeutic targets in IL-33-related allergic diseases.

Precursor B Cells Increase in the Lung during Airway Allergic Inflammation: A Role for B Cell-Activating Factor

Background

B cells, key cells in allergic inflammation, differentiate in the bone marrow and their precursors include pro-B, pre-B and immature B cells. Eosinophil progenitor cells increase in the lung after allergen exposure. However, the existence and possible role of B cell precursors in the lung during allergic inflammation remains elusive.

Methods

A BALB/c mouse model of allergic airway inflammation was utilized to perform phenotypic and quantification analyses of pro-B and pre-B cells in the lung by flow cytometry. B cell maturation factors IL-7 and B cell-activating factor (BAFF) and their receptors (CD127 and BAFFR, BCMA, TACI, respectively) were also evaluated in the lung and serum. The effect of anti-BAFF treatment was investigated both in vivo (i.p. administration of BAFF-R-Ig fusion protein) and in vitro (colony forming cell assay). Finally, BAFF levels were examined in the bronchoalveolar lavage (BAL) of asthmatic patients and healthy controls.

Results

Precursor pro and pre-B cells increase in the lung after allergen exposure, proliferate in the lung tissue in vivo, express markers of chemotaxis (CCR10 and CXCR4) and co-stimulation (CD40, CD86) and are resistant to apoptosis (Bax). Precursor B cells express receptors for BAFF at baseline, while after allergen challenge both their ligand BAFF and the BCMA receptor expression increases in B cell precursors. Blocking BAFFR in the lung in vivo decreases eosinophils and proliferating precursor B cells. Blocking BAFFR in bone marrow cultures in vitro reduces pre-B colony formation units. BAFF is increased in the BAL of severe asthmatics.

Conclusion

Our data support the concept of a BAFF-mediated role for B cell precursors in allergic airway inflammation.

The binary toxin CDT enhances Clostridium difficile virulence by suppressing protective colonic eosinophilia

Clostridium difficile is the most common hospital acquired pathogen in the USA, and infection is, in many cases, fatal. Toxins A and B are its major virulence factors, but expression of a third toxin, known as C. difficile transferase (CDT), is increasingly common. An adenosine diphosphate (ADP)-ribosyltransferase that causes actin cytoskeletal disruption, CDT is typically produced by the major, hypervirulent strains and has been associated with more severe disease. Here, we show that CDT enhances the virulence of two PCR-ribotype 027 strains in mice. The toxin induces pathogenic host inflammation via a Toll-like receptor 2 (TLR2)-dependent pathway, resulting in the suppression of a protective host eosinophilic response. Finally, we show that restoration of TLR2-deficient eosinophils is sufficient for protection from a strain producing CDT. These findings offer an explanation for the enhanced virulence of CDT-expressing C. difficile and demonstrate a mechanism by which this binary toxin subverts the host immune response.

The LINA Study: Higher Sensitivity of Infant Compared to Maternal Eosinophil/Basophil Progenitors to Indoor Chemical Exposures

Purpose. Enhanced eosinophil/basophil (Eo/B) progenitor cell levels are known to be associated with allergic inflammation and atopy risk. The aim of the present study was to investigate the influence of different indoor exposures on the recruitment and differentiation of Eo/B progenitors in mother-child pairs. Methods. In 68 mother-child pairs of the LINA study peripheral blood mononuclear cells were used to assess Eo/B colony forming units (CFUs). Information about disease outcomes and indoor exposures was obtained from questionnaires. Indoor concentrations of volatile organic compounds (VOCs) were measured by passive sampling. Results. Infant's Eo/B CFUs were positively associated with exposure to tobacco smoke, disinfectants, or VOCs. In contrast, for maternal Eo/B CFUs, only a few associations were seen. Higher numbers of infant Eo/B CFUs were observed in children with wheezing symptoms within the second year of life. Conclusions. We demonstrate that infant's hematopoietic cells seem to respond with more sensitivity to environmental exposure compared to maternal cells. At least in infants, an activation of these hematopoietic cells by environmental exposure could contribute to an enhanced risk for the development of respiratory outcomes.

Eosinophilia in Pulmonary Disorders

Lung disease associated with marked peripheral blood eosinophilia is unusual and nearly always clinically significant. Once recognized, it is generally easy to manage, albeit with long-term systemic corticosteroids. A failure to respond to oral steroids in the context of good compliance suggests a malignant cause for the eosinophilia. An important development is the introduction of antieosinophil therapies, particularly those directed against the interleukin 5 pathway, which is hoped to provide benefit in the full spectrum of eosinophilic lung disease as well as asthma, reducing the burden of side effects and resultant comorbidities.

Histone deacetylation of memory T lymphocytes by You-Gui-Wan alleviates allergen-induced eosinophilic airway inflammation in asthma

Background

You-Gui pills (You-Gui-Wan; YGW) can promote T lymphocyte proliferation and differentiation, and restore Th1/Th2 balance in the treatment of asthma, but their mechanism of action is not fully known. This study aims to explore whether YGW can induce histone deacetylation or acetylation in memory T lymphocytes (Tm) for improvement of airway inflammation in asthma.

Methods

CD4⁺CD45RB^low cells, as Tm, were obtained by magnetic-activated cell sorting and flow cytometry from the spleens of BALB/c mice with ovalbumin (OVA)-induced asthma. Tm were cocultured with hydrocortisone (CORT; 1000 nM), serum containing low (0.225 g/kg), moderate (0.9 g/kg), or high (3.6 g/kg) doses of YGW, or medium only, and then adoptively transferred into naïve mice (n = 5 per group). Recipient mice were challenged with aerosolized OVA. The levels of IL-4, IL-5, IL-13, and IFN-γ in culture supernatants and bronchoalveolar lavage fluid (BALF) from the OVA-challenged mice were measured by ELISA. Histone deacetylase (HDAC) and histone acetyltransferase (HAT) activities and protein expressions of T-bet, GATA-3, and HDAC1–11 in lung tissue were measured by western blotting analyses. The alveolar eosinophilic inflammation index (AEII) was evaluated in the lungs of adoptive transfer recipient mice.

Results

YGW reduced inflammation and eosinophil infiltration into the lung tissues as evidenced by histology, with similar effects to those of CORT. High-, moderate-, and low-YGW increased HDAC (P < 0.0001, P = 0.0009 and P = 0.0253 respectively) and decreased HAT (P = 0.0001, P = 0.0000 and P = 0.0039, respectively) activities in dose-dependent manners in the lung tissues of adoptive transfer recipient mice. Increased histone deacetylation of Tm by YGW reduced the AEII by reducing GATA-3 (P = 0.014),IL-4 (P = 0.0004), IL-5 (P = 0.0067), and IL-13 (P = 0.0002), and inducing IFN-γ release (P = 0.0375). Moreover, YGW reduced inflammatory cytokines such as IL-4, IL-5, and IL-13 by upregulating the activities of HDAC7 (P = 0.003)/10 (P = 0.003), HDAC11 (P < 0.0001), and HDAC9–11 (P < 0.0001, P < 0.0001 and P < 0.0001, respectively), respectively, and increased IFN-γ release by increasing HDAC9 (P < 0.0001).

Conclusions

Histone deacetylation of Tm was observed during alleviation of allergen-induced eosinophilic airway inflammation in asthma by YGW.

The flavone eupatilin inhibits eotaxin expression in an NF-κB-dependent and STAT6-independent manner

The CC chemokine eotaxin contributes to epithelium-induced inflammation in airway diseases such as asthma. Eupatilin (5,7-dihydroxy-3',4',6'-trimethoxyflavone), a bioactive component of Artemisia asiatica Nakai (Asteraceae), is reported to inhibit the adhesion of eosinophils to bronchial epithelial cells. However, little is known about the molecular mechanism of eupatilin-induced attenuation of bronchial epithelium-induced inflammation. In this study, we investigated the effect of eupatilin on expression of eotaxin-1 (CCL11), a potent chemoattractant for eosinophils. Eupatilin significantly inhibited eotaxin expression in bronchial epithelial cells stimulated with TNF-α, while NF-κB and IκBα kinase (IKK) activities declined concurrently. Eupatilin also inhibited mitogen-activated protein kinase (MAPK) activity; however, all of these anti-inflammatory activities were reversed by MAPK overexpression. In contrast, eupatilin did not affect the signal transducer and activator of transcription 6 (STAT6) signalling in bronchial epithelial cells stimulated with IL-4. Furthermore, eupatilin significantly attenuated TNF-α-induced eosinophil migration. These results suggest that the eupatilin inhibits the signalling of MAPK, IKK, NF-κB and eotaxin-1 in bronchial epithelial cells, leading to inhibition of eosinophil migration.

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.

Zerumbone enhances the Th1 response and ameliorates ovalbumin-induced Th2 responses and airway inflammation in mice

Zerumbone is a sesquiterpene compound isolated from the rhizome of wild ginger, Zingiber zerumbet Smith. The rhizomes of the plant are used as a spice and traditional medicine. Zerumbone was shown to possess anticarcinogenic, anti-inflammatory, and antioxidant properties. However, the antiallergic activity and the underlying mechanism of zerumbone have not been reported. Herein, we investigated the immunomodulatory effects of zerumbone on antigen-presenting dendritic cells (DCs) in vitro and its potential therapeutic effects against ovalbumin (OVA)-induced T helper 2 (Th2)-mediated asthma in mice. In the presence of zerumbone, lipopolysaccharide-activated bone marrow-derived DCs enhanced T cell proliferation and Th1 cell polarization in an allogeneic mixed lymphocyte reaction. In animal experiments, mice were sensitized and challenged with OVA, and were orally treated with different doses of zerumbone after sensitization. Circulating titers of OVA-specific antibodies, airway hyperresponsiveness to methacholine, histological changes in lung tissues, the cell composition and cytokine levels in bronchoalveolar lavage fluid, and cytokine profiles of spleen cells were assessed. Compared to OVA-induced hallmarks of asthma, oral administration of zerumbone induced lower OVA-specific immunoglobulin E (IgE) and higher IgG2a antibody production, attenuated airway hyperresponsiveness, prevented eosinophilic pulmonary infiltration, and ameliorated mucus hypersecretion. Zerumbone treatment also reduced the production of eotaxin, keratinocyte-derived chemokine (KC), interleukin (IL)-4, IL-5, IL-10, and IL-13, and promoted Th1 cytokine interferon (IFN)-γ production in asthmatic mice. Taken together, these results suggest that zerumbone exhibits an antiallergic effect via modulation of Th1/Th2 cytokines in an asthmatic mouse model.

Mast cells' integrated actions with eosinophils and fibroblasts in allergic inflammation: implications for therapy

Mast cells (MCs) and eosinophils (Eos) are the key players in the development of allergic inflammation (AI). Their cross-talk, named the Allergic Effector Unit (AEU), takes place through an array of soluble mediators and ligands/receptors interactions that enhance the functions of both the cells. One of the salient features of the AEU is the CD48/2B4 receptor/ligand binding complex. Furthermore, MCs and Eos have been demonstrated to play a role not only in AI but also in the modulation of its consequence, i.e., fibrosis/tissue remodeling, by directly influencing fibroblasts (FBs), the main target cells of these processes. In turn, FBs can regulate the survival, activity, and phenotype of both MCs and Eos. Therefore, a complex three players, MCs/Eos/FBs interaction, can take place in various stages of AI. The characterization of the soluble and physical mediated cross talk among these three cells might lead to the identification of both better and novel targets for the treatment of allergy and its tissue remodeling consequences.

Effect of RNA interference therapy on the mice eosinophils CCR3 gene and granule protein in the murine model of allergic rhinitis

OBJECTIVE

To observe the clinical manifestations of allergic rhinitis mice and the expression changes of the eosinophils CCR3 and the granule protein mRNA in the bone marrow, peripheral blood and nasal lavage fluid.

METHODS

Twenty-four BALB/c mice were randomly divided into the control group, PBS therapy group, siRNA therapy group and the CCR3 siRNA therapy group (n=6). Allergic rhinitis model were sensitized and stimulated by ovalbunfin, and CCR3 siRNA therapy group were administered with CCR3 transnasally before stimulated. The levels of the eosinophils CCR3, MBP, ECP and EPO in bone marrow, peripheral blood and nasal lavage fluid were detected by RT-PCR.

RESULTS

Compared to the control group and CCR3 siRNA therapy group, the nasal mucosa of the PBS therapy group and siRNA therapy group developed epithalaxy, goblet cells hyperplasia, squamous epithelium metaplasia, epithelium necrosis, lamina propria and submucosa gland hyperplasia, vasodilatation, tissue edema, and the characterized eosinophil infiltration. RT-PCR indicated that the CCR3 mRNA, MBP, ECP and EPO expression in bone marrow, peripheral blood and nasal lavage fluid of the CCR3 siRNA therapy group was lower than the PBS therapy group and siRNA therapy group (P<0.05).

CONCLUSIONS

The RNA interference therapy to CCR3 by local administration pernasal can suppress the process of the development, migration and invasion of the allergic rhinitis eosinophil, thus can reduce the effect of eosinophils and then reduce the inflammation effect of the allergic rhinitis. It may be a new treatment for respiratory tract allergic inflammation.

Eosinophils as a pharmacological target for the treatment of allergic diseases

Eosinophils are innate immune cells and active players in inflammatory responses. Their activation and increased levels in the blood and at specific sites are associated with parasitic infections and several inflammatory conditions, notably allergic diseases in which eosinophils are considered to be damaging cells. Intervention targeting eosinophils is thought to prevent and/or limit irreversible organ damage and other eosinophil-associated disorders like hypereosinophilic syndromes, some cancers and autoimmune diseases. Several eosinophil-targeted therapeutic agents which block specific steps in eosinophil differentiation, migration and activation have recently been developed, showing encouraging results and new insights into their specific role in allergy. Here, we review some potentially effective drug compounds, their drawbacks and future prospective focusing on allergic diseases.

Balance of apoptotic cell death and survival in allergic diseases

Allergic diseases result from over-reaction of the immune system in response to exogenous allergens, where inflammatory cells have constantly extended longevity and contribute to an on-going immune response in allergic tissues. Here, we review disequilibrium in the death and survival of epithelial cells and inflammatory cells in the pathological processes of asthma, atopic dermatitis, and other allergic diseases.

IL-4 and IL-13 differentially regulate TLR-induced eosinophil-basophil differentiation of cord blood CD34+ progenitor cells

Intrauterine environmental exposures have been shown to influence neonatal immunity and subsequent allergic disease development. We have previously shown that fewer lipopolysaccharide (LPS)-stimulated eosinophil-basophil (Eo/B) colonies grow from cord blood (CB) of high-atopic risk infants, compared to low-atopic risk infants. In the present study, we investigated whether a surrogate ex vivo T_H2 milieu (i.e., either IL-4 or IL-13) could represent an underlying mechanism to explain our previous findings. CB CD34⁺ cells from healthy donors were cultured with IL-4 or IL-13 (in combination with LPS) and assessed for Eo/B differentiation using methylcellulose cultures and flow cytometry for related intracellular signalling pathways. Pharmacological inhibitors were added to the methylcellulose cultures to determine the effect of blocking intracellular signalling in CB CD34⁺ cells in relation to Eo/B colony forming unit (CFU) formation. Stimulation of CD34⁺ cells with IL-4, but not IL-13, reduced Eo/B CFU formation in the presence of LPS; this was found to be dependent on IL-4Rα and not IL-13Rα1. Additionally, IL-4 reduced the expression of ERK 1/2 after LPS stimulation, which was recovered by inhibition of IL-4Rα. While IL-13 did not have an inhibitory effect on ERK 1/2 expression, inhibition of ERK 1/2 significantly reduced Eo/B CFU formation. Thus, the responsiveness of CB CD34⁺ progenitor cells to LPS is differentially regulated by the T_H2 cytokines, IL-4 and IL-13. This may have implications for in utero interactions between placental-derived pro-allergic cytokines and neonatal progenitor cells influencing Eo/B-mediated inflammatory responses in early life.

Hematopoietic stem and progenitor cells in inflammation and allergy

Hematopoietic stem and progenitor cells contribute to allergic inflammation. Pro-inflammatory cytokines that are generated following allergen challenge can impact the differentiation of hematopoietic progenitor cells leading to increased production of effector cells such as eosinophils and basophils, which are key cells involved in the pathogenesis of allergic airway inflammation. Homing of stem cells to the lungs is associated with inflammatory and remodeling changes in asthmatics. Factors that modulate the differentiation and increased migration of stem cells to the site of inflammation in asthma remain to be defined. Stem cells can mature at the site of inflammation in response to inflammatory mediators and other components in the milieu. While the available data suggest that hematopoietic cells traffic to target tissues, the molecular factors underlying in situ differentiation have yet to be specified. Here, we critically evaluate the potential role of hematopoietic progenitors in contributing to the increased immune cell infiltrate in allergic asthma and the factors that drive their differentiation.

The eosinophil chemoattractant 5-oxo-ETE and the OXE receptor

5-Oxo-ETE (5-oxo-6,8,11,14-eicosatetraenoic acid) is formed from the 5-lipoxygenase product 5-HETE (5S-hydroxy-6,8,11,14-eicosatetraenoic acid) by 5-hydroxyeicosanoid dehydrogenase (5-HEDH). The cofactor NADP(+) is a limiting factor in the synthesis of 5-oxo-ETE because of its low concentrations in unperturbed cells. Activation of the respiratory burst in phagocytic cells, oxidative stress, and cell death all dramatically elevate both intracellular NADP(+) levels and 5-oxo-ETE synthesis. 5-HEDH is widely expressed in inflammatory, structural, and tumor cells. Cells devoid of 5-lipoxygenase can synthesize 5-oxo-ETE by transcellular biosynthesis using inflammatory cell-derived 5-HETE. 5-Oxo-ETE is a chemoattractant for neutrophils, monocytes, and basophils and promotes the proliferation of tumor cells. However, its primary target appears to be the eosinophil, for which it is a highly potent chemoattractant. The actions of 5-oxo-ETE are mediated by the highly selective OXE receptor, which signals by activating various second messenger pathways through the release of the βγ-dimer from Gi/o proteins to which it is coupled. Because of its potent effects on eosinophils, 5-oxo-ETE may be an important mediator in asthma, and, because of its proliferative effects, may also contribute to tumor progression. Selective OXE receptor antagonists, which are currently under development, could be useful therapeutic agents in asthma and other allergic diseases.

Toll-like receptor-mediated eosinophil-basophil differentiation: autocrine signalling by granulocyte-macrophage colony-stimulating factor in cord blood haematopoietic progenitors

Eosinophils are multi-functional leucocytes that play a role in inflammatory processes including allergy and infection. Although bone marrow (BM) inflammatory cells are the main source of eosinophil-basophil (Eo/B) differentiation-inducing cytokines, a recent role has been demonstrated for cytokine induction through Toll-like receptor (TLR)-mediated signalling in BM progenitors. Having previously demonstrated that cord blood (CB) progenitors induce Eo/B colony-forming units (CFU) after lipopolysaccharide (LPS) stimulation, we sought to investigate the intracellular mechanisms by which LPS induces Eo/B differentiation. Freshly isolated CD34-enriched human CB cells were stimulated with LPS (and/or pharmacological inhibitors) and assessed for alterations in haematopoietic cytokine receptor expression and signalling pathways by flow cytometry, Eo/B CFU in methylcellulose cultures, and cytokine secretion using Luminex assays. The LPS stimulation resulted in a significant increase in granulocyte-macrophage colony-stimulating factor (GM-CSF)-responsive, as opposed to interleukin-5-responsive, Eo/B CFU, which also correlated with significant increases in CD34(+) cell GM-CSFRα expression. Functionally, CB CD34(+) cells secrete abundant amounts of GM-CSF following LPS stimulation, via a p38 mitogen-activated protein kinase (MAPK)-dependent mechanism; this secretion was responsible for Eo/B CFU formation ex vivo, as shown by antibody blockade. We show for the first time that LPS stimulation of CB progenitor cells results in autocrine activation of p38 MAPK-dependent GM-CSF secretion facilitating Eo/B differentiation ex vivo. This work provides evidence that early life exposure to products of bacterial agents can modulate Eo/B differentiation, representing a novel mechanism by which progenitor cells can respond to microbial stimuli and so affect immune and inflammatory responses.

Pin1-FADD interactions regulate Fas-mediated apoptosis in activated eosinophils

Abnormally long-lived eosinophils (Eos) are the major inflammatory component of allergic responses in the lungs of active asthmatics. Eos recruited to the airways after allergen exposure produce and respond to IL-5 and GM-CSF, enhancing their survival. Prosurvival signaling activates Pin1, a peptidyl-prolyl cis-trans isomerase that binds to Bax and prevents its activation. How long-lived Eos, despite the continued presence of GM-CSF or IL-5, eventually undergo apoptosis to end allergic inflammation remains unclear. In this study, we show that Pin1 location, activity, and protein interactions are jointly influenced by Fas and the prosurvival cytokine IL-5. Fas signaling strongly induced the phosphorylation of FADD at Ser(194) and Pin1 at Ser(16), as well as their nuclear accumulation. Phospho-mimic Ser(194)Glu FADD mutants accelerated Eos apoptosis compared with wild-type or Ser(194)Ala mutants. Downstream of FADD phosphorylation, caspase 8, 9, and 3 cleavage, as well as Eos apoptosis induced by Fas, were reduced by constitutively active Pin1 and enhanced by Pin1 inhibition. Pin1 was activated by IL-5, whereas simultaneous IL-5 and anti-Fas treatment modestly reduced peptidyl isomerase activity but induced Pin1 to associate with FADD after its phosphorylation at Ser(194). Mechanistically, Pin1-mediated isomerization facilitated the subsequent dephosphorylation of Ser(194) FADD and maintenance of cytoplasmic location. In vivo-activated bronchoalveolar Eos obtained after allergen challenge showed elevated survival and Pin1 activity that could be reversed by anti-Fas. Therefore, our data suggest that Pin1 is a critical link between FADD-mediated cell death and IL-5-mediated prosurvival signaling.

Human versus mouse eosinophils: "that which we call an eosinophil, by any other name would stain as red"

The respective life histories of human subjects and mice are well defined and describe a unique story of evolutionary conservation extending from sequence identity within the genome to the underpinnings of biochemical, cellular, and physiologic pathways. As a consequence, the hematopoietic lineages of both species are invariantly maintained, each with identifiable eosinophils. This canonical presence nonetheless does not preclude disparities between human and mouse eosinophils, their effector functions, or both. Indeed, many books and reviews dogmatically highlight differences, providing a rationale to discount the use of mouse models of human eosinophilic diseases. We suggest that this perspective is parochial and ignores the wealth of available studies and the consensus of the literature that overwhelming similarities (and not differences) exist between human and mouse eosinophils. The goal of this review is to summarize this literature and in some cases provide experimental details comparing and contrasting eosinophils and eosinophil effector functions in human subjects versus mice. In particular, our review will provide a summation and an easy-to-use reference guide to important studies demonstrating that although differences exist, more often than not, their consequences are unknown and do not necessarily reflect inherent disparities in eosinophil function but instead species-specific variations. The conclusion from this overview is that despite nominal differences, the vast similarities between human and mouse eosinophils provide important insights as to their roles in health and disease and, in turn, demonstrate the unique utility of mouse-based studies with an expectation of valid extrapolation to the understanding and treatment of patients.

5,7-Dihydroxy-3,4,6-trimethoxyflavone inhibits intercellular adhesion molecule 1 and vascular cell adhesion molecule 1 via the Akt and nuclear factor-κB-dependent pathway, leading to suppression of adhesion of monocytes and eosinophils to bronchial epithelial cells

5,7-Dihydroxy-3',4',6'-trimethoxyflavone (eupatilin), the active pharmacological ingredient from Artemisia asiatica Nakai (Asteraceae), is reported to have a variety of anti-inflammatory properties in intestinal epithelial cells. However, little information is known about the molecular mechanism of eupatilin-induced attenuation of bronchial epithelial inflammation. This study investigates the role of eupatilin in the adhesion of inflammatory cells such as monocytes and eosinophils to bronchial epithelial cells. Stimulation of a human bronchial epithelial cell line (BEAS-2B) with tumour necrosis factor-α (TNF-α) increased the expression of surface adhesion molecules, including intercellular adhesion molecule 1 (ICAM-1) and vascular cell adhesion molecule 1 (VCAM-1), in which eupatilin significantly inhibited the expression of those adhesion molecules in a dose-dependent manner. Eupatilin suppressed the TNF-α-induced activation of IκBα and nuclear factor-κB (NF-κB) signals in BEAS-2B cells. The IκB kinase (IKK) activation was also significantly reduced in eupatilin-pre-treated BEAS-2B and primary normal human bronchial epithelial (NHBE) cells. However, eupatilin did not influence AP-1 activity in TNF-α-stimulated cells. Suppression of NF-κB signalling induced by eupatilin resulted in the inhibition of the expression of adhesion molecules and the adhesion of monocytes and eosinophils to BEAS-2B cells. Furthermore, eupatilin suppressed the phosphorylation of Akt in TNF-α-stimulated BEAS-2B and NHBE cells, leading to down-regulation of NF-κB activation and adhesion molecule expression and finally to suppression of the inflammatory cell adhesion to epithelial cells. These results suggest that eupatilin can inhibit the adhesion of inflammatory cells to bronchial epithelial cells via a signalling pathway, including activation of Akt and NF-κB, as well as expression of adhesion molecules.

CpG methylation at GATA elements in the regulatory region of CCR3 positively correlates with CCR3 transcription

DNA methylation may regulate gene expression by restricting the access of transcription factors. We have previously demonstrated that GATA-1 regulates the transcription of the CCR3 gene by dynamically interacting with both positively and negatively acting GATA elements of high affinity binding in the proximal promoter region including exon 1. Exon 1 has three CpG sites, two of which are positioned at the negatively acting GATA elements. We hypothesized that the methylation of these two CpGs sites might preclude GATA-1 binding to the negatively acting GATA elements and, as a result, increase the availability of GATA-1 to the positively acting GATA element, thereby contributing to an increase in GATA-1-mediated transcription of the gene. To this end, we determined the methylation of the three CpG sites by bisulfate pyrosequencing in peripheral blood eosinophils, cord blood (CB)-derived eosinophils, PBMCs, and cell lines that vary in CCR3 mRNA expression. Our results demonstrated that methylation of CpG sites at the negatively acting GATA elements severely reduced GATA-1 binding and augmented transcription activity in vitro. In agreement, methylation of these CpG sites positively correlated with CCR3 mRNA expression in the primary cells and cell lines examined. Interestingly, methylation patterns of these three CpG sites in CB-derived eosinophils mostly resembled those in peripheral blood eosinophils. These results suggest that methylation of CpG sites at the GATA elements in the regulatory regions fine-tunes CCR3 transcription.

Lactoferrin restrains allergen-induced pleurisy in mice

Objectives

The aim of this study was to assess the utility of lactoferrin (LF), a natural immunomodulator, to restrain allergen-induced pleurisy in mice.

Material and subjects

BALB/c female mice, 8- to 10-week old, weighing 24 g on average, were used.

Treatment

Mice were immunized intraperitoneally with 50 μg of ovalbumin (OVA) and the pleurisy was elicited 14 days later by intrapleural injection of 12.5 μg of OVA. LF was given 24 and 3 h before elicitation of the allergic reaction.

Methods

The cytokine levels in the pleural exudates were measured by immunoassays. The blood and pleural exudates smears were stained with Giemsa and May-Grünwald reagents and reviewed histologically. Lung sections were stained with eosin and hematoxylin for histological evaluation.

Results

Lactoferrin significantly decreased manifestation of pleurisy induced by OVA in a sensitized mouse model. In particular, the percentages of eosinophils in blood and pleural exudates were strongly diminished. The histological analysis of lungs revealed that LF diminished the development of pathological lesions, such as pulmonary edema, diffuse alveolar hemorrhage and hemosiderosis, which were found in the lungs after injection of the eliciting dose of OVA. LF also decreased the level of IL-5 secreted into the pleural fluid.

Conclusions

This is a first demonstration that LF significantly decreases antigen-specific pleurisy in a sensitized mouse model.

The Immunomodulatory Effect of You-Gui-Wan on Dermatogoides-pteronyssinus-Induced Asthma

The traditional Chinese medicine You-Gui-Wan (YGW) contains ten species of medicinal plants and has been used to improve health in remissive states of asthma for hundreds of years in Asia. However, little is known about the immunomodulatory mechanisms in vivo. Therefore, this study investigated the pathologic and immunologic responses to YGW in mice that had been repeatedly exposed to Dermatogoides-pteronyssinus (Der p). YGW reduced Der-p-induced airway hyperresponsiveness and total IgE in serum. It also inhibited eosinophil infiltration by downregulating the protein expression of IL-5 in serum and changed the Th2-bios in BALF by upregulating IL-12. Results of the collagen assay and histopathologic examination showed that YGW reduced airway remodeling in the lung. In addition, after YGW treatment there was a relative decrease in mRNA expression of TGF-β1, IL-13, eotaxin, RANTES, and MCP-1 in lung in the YGW group. The results of EMSA and immunohistochemistry revealed that YGW inhibited NF-κB expression in epithelial lung cells. YGW exerts its regulative effects in chronic allergic asthmatic mice via its anti-inflammatory activity and by inhibiting the progression of airway remodeling.

PTP1B deficiency exacerbates inflammation and accelerates leukocyte trafficking in vivo

It is reported that PTP1B limits cytokine signaling in vitro. However, PTP1B's function during inflammation in vivo is not known. In this report, we determined whether PTP1B deficiency affects allergic inflammation in vivo. Briefly, lungs of OVA-challenged PTP1B(-/-) mice had elevated numbers of eosinophils and eosinophil progenitors at 6 h after one OVA challenge and at 24 h after a third OVA challenge as compared with OVA-challenged wild-type mice. There was also an increase in numbers of CD11b(+)SiglecF(+)CD34(+)IL-5Rα(+) eosinophil progenitors in the bone marrow, peripheral blood, and spleens of OVA-challenged PTP1B(-/-) mice. Intravital microscopy revealed that, in OVA-challenged PTP1B(-/-) mice, blood leukocytes rapidly bound to endothelium (5-30 min), whereas, in wild-type mice, blood leukocytes bound to endothelium at the expected 6-18 h. Consistent with early recruitment of leukocytes, lung eotaxin and Th2 cytokine levels were elevated early in the PTP1B(-/-) mice. Interestingly, spleen leukocytes from PTP1B(-/-) mice exhibited an increased chemotaxis, chemokinesis, and transendothelial migration in vitro. In summary, PTP1B functions as a critical negative regulator to limit allergic responses.

Molecular and clinical rationale for therapeutic targeting of interleukin-5 and its receptor

Interleukin-5 is a Th2 homodimeric cytokine involved in the differentiation, maturation, migration, development, survival, trafficking and effector function of blood and local tissue eosinophils, in addition to basophils and mast cells. The IL-5 receptor (IL-5R) consists of an IL-5-specific α subunit that interacts in conformationally dynamic ways with the receptor's βc subunit, an aggregate of domains it shares with binding sites of IL-3 and granulocyte-macrophage colony-stimulating factor. IL-5 and IL-5R drive allergic and inflammatory immune responses characterizing numerous diseases, such as asthma, atopic dermatitis, chronic obstructive pulmonary disease, eosinophilic gastrointestinal diseases, hyper-eosinophilic syndrome, Churg-Strauss syndrome and eosinophilic nasal polyposis. Although corticosteroid therapy is the primary treatment for these diseases, a substantial number of patients exhibit incomplete responses and suffer side-effects. Two monoclonal antibodies have been designed to neutralize IL-5 (mepolizumab and reslizumab). Both antibodies have demonstrated the ability to reduce blood and tissue eosinophil counts. One additional monoclonal antibody, benralizumab (MEDI-563), has been developed to target IL-5R and attenuate eosinophilia through antibody-dependent cellular cytotoxicity. All three monoclonal antibodies are being clinically evaluated. Antisense oligonucleotide technology targeting the common βc IL-5R subunit is also being used therapeutically to inhibit IL-5-mediated effects (TPI ASM8). Small interfering RNA technology has also been used therapeutically to inhibit the expression of IL-5 in animal models. This review summarizes the structural interactions between IL-5 and IL-5R and the functional consequences of such interactions, and describes the pre-clinical and clinical evidence supporting IL-5R as a therapeutic target.

Dose-response effects of TPI ASM8 in asthmatics after allergen

BACKGROUND

TPI ASM8 contains two modified antisense oligonucleotides (AON) targeting the beta subunit (β(c) ) of the IL-3, IL-5, GM-CSF receptors and the chemokine receptor CCR3. A previous study suggested that TPI ASM8 had broader effects than just inhibition of eosinophils in asthmatics.

OBJECTIVE

We assessed whether TPI ASM8 caused a dose-dependent attenuation in the inflammatory and physiological changes after inhaled allergen challenge (AIC).

METHODS

This single-center, open-label, stepwise-ascending dose study was conducted in fourteen stable, mild allergic asthmatics. Following placebo AIC, subjects underwent AIC after 4 days treatment with 1, 2, and 4 mg BID and finally 8 mg once daily (OD) of TPI ASM8, inhaled via the I-Neb™ nebuliser. Treatments were separated by 2-3-week washout periods.

RESULTS

TPI ASM8 was safe and well tolerated at all doses. TPI ASM8 8 mg OD reduced eosinophils in sputum after AIC (by 60.9% at 7 h and 68.4% at 24 h post-AIC, P=0.016 and P=0.007, respectively). Additionally, TPI ASM8 8 mg OD significantly attenuated the early and late airway responses as shown by the reduction in the area under the curve by 45% (P=0.016) and 59%, (P=0.0015), respectively, the increase in eosinophil cationic protein (ECP) by up to 57% (P=0.021), and airway responsiveness to methacholine by more than 1 doubling dose (P=0.012). A dose-response relationship was noted, and efficacy was maintained with once per day administration.

CONCLUSIONS

TPI ASM8 attenuated a broad range of inflammatory and physiological changes after AIC, suggesting that CCR3, IL-3, and GM-CSF also are important targets for the management of asthma.

Regulator of calcineurin 1 (Rcan1) is required for the development of pulmonary eosinophilia in allergic inflammation in mice

The presence of eosinophils in the lung is often regarded as a defining feature of asthma. On allergen stimulation, numbers of eosinophils and their progenitors are increased in both the bone marrow and lungs. Eosinophil progenitors provide an ongoing supply of mature eosinophils. Here, we report that deficiency in the regulator of calcineurin 1 gene (Rcan1) leads to a near-complete absence of eosinophilia in ovalbumin-induced allergic asthma in mice. In the absence of Rcan1, bone marrow cells produce significantly fewer eosinophils in vivo and in vitro on interleukin-5 stimulation. Importantly, eosinophil progenitor populations are significantly reduced in both naïve and ovalbumin-challenged Rcan1(-/-) mice. Bone marrow cells from Rcan1(-/-) mice are capable of developing into fully mature eosinophils, suggesting that Rcan1 is required for eosinophil progenitor production but may not be necessary for eosinophil maturation. Thus, Rcan1 represents a novel contributor in the development of eosinophilia in allergic asthma through regulation of eosinophil progenitor production.

An alternate STAT6-independent pathway promotes eosinophil influx into blood during allergic airway inflammation

Background

Enhanced eosinophil responses have critical roles in the development of allergic diseases. IL-5 regulates the maturation, migration and survival of eosinophils, and IL-5 and eotaxins mediate the trafficking and activation of eosinophils in inflamed tissues. CD4⁺ Th2 cells are the main producers of IL-5 and other cells such as NK also release this cytokine. Although multiple signalling pathways may be involved, STAT6 critically regulates the differentiation and cytokine production of Th2 cells and the expression of eotaxins. Nevertheless, the mechanisms that mediate different parts of the eosinophilic inflammatory process in different tissues in allergic airway diseases remain unclear. Furthermore, the mechanisms at play may vary depending on the context of inflammation and microenvironment of the involved tissues.

Methodology/Principal Findings

We employed a model of allergic airway disease in wild type and STAT6-deficient mice to explore the roles of STAT6 and IL-5 in the development of eosinophilic inflammation in this context. Quantitative PCR and ELISA were used to examine IL-5, eotaxins levels in serum and lungs. Eosinophils in lung, peripheral blood and bone marrow were characterized by morphological properties. CD4⁺ T cell and NK cells were identified by flow cytometry. Antibodies were used to deplete CD4⁺ and NK cells. We showed that STAT6 is indispensible for eosinophilic lung inflammation and the induction of eotaxin-1 and -2 during allergic airway inflammation. In the absence of these chemokines eosinophils are not attracted into lung and accumulate in peripheral blood. We also demonstrate the existence of an alternate STAT6-independent pathway of IL-5 production by CD4⁺ and NK cells that mediates the development of eosinophils in bone marrow and their subsequent movement into the circulation.

Conclusions

These results suggest that different points of eosinophilic inflammatory processes in allergic airway disease may be differentially regulated by the activation of STAT6-dependent and -independent pathways.

Chronic allergen challenge induces pulmonary extramedullary hematopoiesis

Allergic inflammation is associated with increased generation and trafficking of inflammatory cells, especially eosinophils, to sites of inflammation. The effect of acute versus chronic airway allergen challenge on hematopoietic activity in the bone marrow (BM) and lungs was investigated using murine models of allergic airway inflammation. Acute allergen challenge induced proliferation of BM cells and significantly increased generation of eosinophil, but not multipotent, granulocyte-macrophage (GM), or B-lymphocyte progenitor cells. However, no hematopoietic activity was observed in the lungs. With chronic challenge, BM cells failed to proliferate, but exhibited increased capacity to generate multipotent as well as eosinophil, GM, and B-lymphocyte progenitors. In addition, increased generation of eosinophil- and GM-specific progenitors was observed in the lungs. Although no differences were observed in their ability to roll on BM endothelium in vitro or in vivo, CD34-enriched hematopoietic/stem progenitor cells (HSPCs) from chronic-, but not acute-, challenged mice demonstrated reduced migration across BM endothelial cells associated with decreased CXCR4 expression. Overall, these studies demonstrate that chronic allergen exposure can alter BM homing due to decreased transendothelial migration enabling noninteracting HSPCs to egress out of the BM and recruit to sites of inflammation such as the airways, resulting in extramedullary hematopoiesis.

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.

5-Oxo-ETE and the OXE receptor

5-Oxo-ETE is a product of the 5-lipoxygenase pathway that is formed by the oxidation of 5-HETE by 5-hydroxyeicosanoid dehydrogenase (5-HEDH). 5-HEDH is a microsomal NADP(+)-dependent enzyme that is highly selective for 5-HETE. 5-Oxo-ETE synthesis is regulated by intracellular NADP(+) levels and is dramatically increased under conditions that favor oxidation of NADPH to NADP(+) such as oxidative stress and the respiratory burst in phagocytic cells. 5-Oxo-ETE is a potent chemoattractant for eosinophils and has similar effects on neutrophils, basophils and monocytes. It elicits infiltration of eosinophils and, to a lesser extent, neutrophils into the skin after intradermal injection in humans. It also promotes the survival of tumor cells and has been shown to block the induction of apoptosis by 5-LO inhibitors. 5-Oxo-ETE acts by the G(i/o)-coupled OXE receptor, which was also known as TG1019, R527 and hGPCR48. Although the pathophysiological role of 5-oxo-ETE is not well understood, it may play important roles in asthma and allergic diseases, cancer, and cardiovascular disease. The availability of a selective antagonist would help to clarify the role of 5-oxo-ETE and may be of therapeutic benefit.