Membrane-bound and soluble alpha IL-5 receptor mRNA in the bronchial mucosa of atopic and nonatopic asthmatics

A novel whole blood gene expression signature for asthma, dermatitis, and rhinitis multimorbidity in children and adolescents

BACKGROUND

Allergic diseases often occur in combination (multimorbidity). Human blood transcriptome studies have not addressed multimorbidity. Large-scale gene expression data were combined to retrieve biomarkers and signaling pathways to disentangle allergic multimorbidity phenotypes.

METHODS

Integrated transcriptomic analysis was conducted in 1233 participants with a discovery phase using gene expression data (Human Transcriptome Array 2.0) from whole blood of 786 children from three European birth cohorts (MeDALL), and a replication phase using RNA Sequencing data from an independent cohort (EVA-PR, n = 447). Allergic diseases (asthma, atopic dermatitis, rhinitis) were considered as single disease or multimorbidity (at least two diseases), and compared with no disease.

RESULTS

Fifty genes were differentially expressed in allergic diseases. Thirty-two were not previously described in allergy. Eight genes were consistently overexpressed in all types of multimorbidity for asthma, dermatitis, and rhinitis (CLC, EMR4P, IL5RA, FRRS1, HRH4, SLC29A1, SIGLEC8, IL1RL1). All genes were replicated the in EVA-PR cohort. RT-qPCR validated the overexpression of selected genes. In MeDALL, 27 genes were differentially expressed in rhinitis alone, but none was significant for asthma or dermatitis alone. The multimorbidity signature was enriched in eosinophil-associated immune response and signal transduction. Protein-protein interaction network analysis identified IL5/JAK/STAT and IL33/ST2/IRAK/TRAF as key signaling pathways in multimorbid diseases. Synergistic effect of multimorbidity on gene expression levels was found.

CONCLUSION

A signature of eight genes identifies multimorbidity for asthma, rhinitis, and dermatitis. Our results have clinical and mechanistic implications, and suggest that multimorbidity should be considered differently than allergic diseases occurring alone.

Biological functions and therapeutic opportunities of soluble cytokine receptors

Cytokines control the immune system by regulating the proliferation, differentiation and function of immune cells. They activate their target cells through binding to specific receptors, which either are transmembrane proteins or attached to the cell-surface via a GPI-anchor. Different tissues and individual cell types have unique expression profiles of cytokine receptors, and consequently this expression pattern dictates to which cytokines a given cell can respond. Furthermore, soluble variants of several cytokine receptors exist, which are generated by different molecular mechanisms, namely differential mRNA splicing, proteolytic cleavage of the membrane-tethered precursors, and release on extracellular vesicles. These soluble receptors shape the function of cytokines in different ways: they can serve as antagonistic decoy receptors which compete with their membrane-bound counterparts for the ligand, or they can form functional receptor/cytokine complexes which act as agonists and can even activate cells that would usually not respond to the ligand alone. In this review, we focus on the IL-2 and IL-6 families of cytokines and the so-called Th2 cytokines. We summarize for each cytokine which soluble receptors exist, were they originate from, how they are generated, and what their biological functions are. Furthermore, we give an outlook on how these soluble receptors can be exploited for therapeutic purposes.

Eosinophil cytolysis on Immunoglobulin G is associated with microtubule formation and suppression of rho-associated protein kinase signalling

BACKGROUND

The presence of eosinophils in the airway is associated with asthma severity and risk of exacerbations. Cell-free eosinophil granules are found in tissues in eosinophilic diseases, including asthma. This suggests that eosinophils have lysed and released cellular content, likely harming tissues.

OBJECTIVE

The present study explores the mechanism of CD32- and αMß2 integrin-dependent eosinophil cytolysis of IL3-primed blood eosinophils seeded on heat-aggregated immunoglobulin G (HA-IgG).

METHODS

Cytoskeletal events and signalling pathways potentially involved in cytolysis were assessed using inhibitors. The level of activation of the identified events and pathways involved in cytolysis was measured. In addition, the links between these identified pathways and changes in degranulation (exocytosis) and adhesion were analysed.

RESULTS

Cytolysis of IL3-primed eosinophils was dependent on the production of reactive oxygen species (ROS) and downstream phosphorylation of p-38 MAPK. In addition, formation of microtubule (MT) arrays was necessary for cytolysis and was accompanied by changes in MT dynamics as measured by phosphorylation status of stathmin and microtubule-associated protein 4 (MAP4), the latter of which was regulated by ROS production. Reduced ROCK signalling preceded cytolysis, which was associated with eosinophil adhesion and reduced migration.

CONCLUSION AND CLINICAL RELEVANCE

In this CD32- and αMß2 integrin-dependent adhesion model, lysing eosinophils exhibit reduced migration and ROCK signalling, as well as both MT dynamic changes and p-38 phosphorylation downstream of ROS production. We propose that interfering with these pathways would modulate eosinophil cytolysis and subsequent eosinophil-driven tissue damage.

Omalizumab reduces bronchial mucosal IgE and improves lung function in non-atopic asthma

Omalizumab therapy of non-atopic asthmatics reduces bronchial mucosal IgE and inflammation and preserves/improves lung function when disease is destabilised by staged withdrawal of therapy.

18 symptomatic, non-atopic asthmatics were randomised (1:1) to receive omalizumab or identical placebo treatment in addition to existing therapy for 20 weeks. Bronchial biopsies were collected before and after 12–14 weeks of treatment, then the patients destabilised by substantial, supervised reduction of their regular therapy. Primary outcome measures were changes in bronchial mucosal IgE+ cells at 12–14 weeks, prior to regular therapy reduction, and changes in lung function (forced expiratory volume in 1 s) after destabilisation at 20 weeks. Quality of life was also monitored.

Omalizumab but not placebo therapy significantly reduced median total bronchial mucosal IgE+ cells (p<0.01) but did not significantly alter median total mast cells, plasma cells, B lymphocytes, eosinophils and plasmablasts, although the latter were difficult to enumerate, being distributed as disperse clusters. By 20 weeks, lung function declined in the placebo-treated patients but improved in the omalizumab treated patients, with significant differences in absolute (p=0.04) and % predicted forced expiratory volume in 1 s (p=0.015).

Omalizumab therapy of non-atopic asthmatics reduces bronchial mucosal IgE+ mast cells and improves lung function despite withdrawal of conventional therapy.

Local IgE in non-allergic rhinitis

Local allergic rhinitis (LAR) is characterized by the presence of a nasal Th2 inflammatory response with local production of specific IgE antibodies and a positive response to a nasal allergen provocation test (NAPT) without evidence of systemic atopy. The prevalence has been shown to be up to 25% in subjects affected with rhinitis with persistence, comorbidity and evolution similar to allergic rhinitis. LAR is a consistent entity that does not evolve to allergic rhinitis with systemic atopy over time although patients have significant impairment in quality of life and increase in the severity of nasal symptoms over time. Lower airways can be also involved. The diagnosis of LAR is based mostly on demonstration of positive response to NAPT and/or local synthesis of specific IgE. Allergens involved include seasonal or perennial such as house dusts mites, pollens, animal epithelia, moulds (alternaria) and others. Basophils from peripheral blood may be activated by the involved allergens suggesting the spill over of locally synthesized specific IgE to the circulation. LAR patients will benefit from the same treatment as allergic patients using antihistamines, inhaled corticosteroids and IgE antagonists. Studies on immunotherapy are ongoing and will determine its efficacy in LAR in terms of symptoms improvement and evolution of the natural course of the disease.

Against all odds: anti-IgE for intrinsic asthma?

For many years, pathogenetic concepts and the results of clinical trials supported the view that anti-IgE treatment is specifically effective in allergic asthma. However, there is now growing clinical and mechanistic evidence suggesting that treatment with the anti-IgE antibody omalizumab can be effective in patients with intrinsic asthma. Therefore, large and well-controlled clinical trials with anti-IgE are urgently warranted in patients with intrinsic asthma. In addition, there is a need to find new biomarkers which can identify patients with asthma who respond to anti-IgE treatment.

A genetic effect of IL-5 receptor α polymorphism in patients with aspirin-exacerbated respiratory disease

Persistent eosinophil activation in both the upper and lower airway mucosa is a central feature of aspirin-exacerbated respiratory disease (AERD). Eosinophil activation and survival are profoundly influenced by interleukin 5 (IL-5) and its receptor, IL-5R. In patients susceptible to allergic disorders, IL-5 receptor α (IL5RA) polymorphisms have been reported; however, an association with AERD remains unclear. We hypothesize that IL5RA polymorphisms may contribute to eosinophil activation in AERD patients. We recruited 139 AERD patients, 171 aspirin-tolerant asthma patients and 160 normal controls. IL5RA polymorphisms (−5993G>A, −5567C>G and −5091G>A) were genotyped and functional activity of polymorphism was assessed by luciferase reporter assay and electrophoretic mobility shift assay (EMSA). There was no significant difference in the genotype frequency of the three polymorphisms among the three groups. AERD patients carrying the AA genotype at −5993G>A had a significantly higher presence of serum-specific immunoglobulin E (IgE) to staphylococcal enterotoxin A (P=0.008) than those with the GG/GA genotype. In vitro, the −5993A allele had a higher promoter activity compared with the −5993G allele in human mast cell (HMC-1; P=0.030) and human promyelocytic leukemia (HL-60; P=0.013) cells. In EMSA, a −5993A probe produced a specific shifted band than the −5993G had. These findings suggest that a functional polymorphism in IL5RA may contribute to eosinophil and mast cell activation along with specific IgE responses to staphylococcal enterotoxin A in AERD patients.

Increased serum-soluble interleukin-5 receptor alpha level precedes the development of eczema in children

Interleukin-5 receptor α-subunit expression may be implicated in the development of allergic diseases. In a population-based birth cohort, we investigated the relationship between IL-5Rα and the development of allergic phenotypes in childhood, using soluble IL-5Rα (s-IL-5Rα) as a marker. Children (n = 510) were followed from birth and assessed at age 3, 5 and 8. Based on the onset and resolution of symptoms, we assigned children into the following wheeze and eczema phenotypes: never, transient, persistent, intermittent and late-onset. Specific IgE to common allergens, s-IL-5Rα (ELISA) and urinary eosinophilic protein X (U-EPX) levels was measured at age 5. s-IL-5Rα was significantly higher among atopic compared to non-atopic children (pg/ml, geometric means [95% CI], 152.4 [126.0-184.5] vs. 103.4 [94.0-113.9], p < 0.0001). While we found no association between s-IL-5Rα and current eczema at age 5, there was a significant association between eczema phenotypes and s-IL-5Rα (multiple anova model adjusted for gender and atopy, F = 2.56, p = 0.04). After adjustment for multiple comparisons, we found that children with late-onset eczema had significantly higher s-IL-5Rα compared to those who have never had eczema (mean difference [95% CI], 2.41 [1.03-5.62], p = 0.04) and those with intermittent eczema (2.63 [1.08-6.41], p = 0.02), with no difference between children who have never had eczema and other eczema phenotypes. We found no such association for wheeze phenotypes. There was a weak correlation between s-IL-5Rα and U-EPX (r = 0.16, p < 0.0001). Increased serum s-IL-5Rα level at age 5 was associated with contemporaneous atopic sensitization and with subsequent development of eczema by age 8.

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.

Effects of omalizumab on markers of inflammation in patients with allergic asthma

Asthma is a chronic inflammatory disease of the airways in which immunoglobulin E (IgE) plays a key role by activating a variety of inflammatory cells through interactions with FcepsilonRI and FcepsilonRII receptors. The role of IgE in allergic inflammation provided the rationale for developing omalizumab, a humanized monoclonal anti-IgE antibody, for patients with moderate-to-severe or severe allergic asthma. The reductions in circulating levels of IgE resulting from omalizumab treatment leads to reductions in FcepsilonRI expression on mast cells, basophils and dendritic cells. This combined effect results in attenuation of several markers of inflammation, including peripheral and bronchial tissue eosinophilia and levels of granulocyte macrophage colony stimulating factor, interleukin (IL)-2, IL-4, IL-5 and IL-13. By blocking IgE binding to its receptors and diminishing dendritic cell FcepsilonRI receptor expression, omalizumab may also reduce allergen presentation to T cells and the production of Th2 cytokines. The anti-inflammatory effects of omalizumab may, therefore, explain the reductions in asthma exacerbations and symptoms seen in clinical trials in patients with moderate-to-severe or severe, persistent, inadequately controlled allergic 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.

Interleukin-5 does not influence differential transcription of transmembrane and soluble isoforms of IL-5R alpha in vivo

Interleukin-5 (IL-5) promotes signal transduction and expansion of eosinophil colonies in bone marrow via interactions with its heterodimeric receptor (IL-5R). Two variants encoding soluble forms of the alpha subunit (sIL-5R alpha) have been described, although the signals promoting and/or limiting differential transcription remain to be clarified.

OBJECTIVES

Our intent was to explore the role of IL-5 in regulating differential transcription of these splice variants in vivo.

METHODS

We have designed a quantitative reverse transcriptase-polymerase chain reaction assay to detect transcripts encoding the transmembrane, soluble 1 and 2 forms of IL-5R alpha in two strains of wild-type (BALB/c and C57BL/6) and corresponding IL-5 gene-deleted mice. Wild-type mice respond to S. mansoni infection with a gradual increase in serum IL-5 and eosinophilia, which is not observed in IL-5 gene-deleted mice.

RESULTS AND CONCLUSIONS

We find that IL-5 is not necessary for differential splicing to occur in vivo, as all three forms of the IL-5R alpha are detected in both strains of IL-5 gene-deleted mice, with ratios of transcript expression (transmembrane : soluble 1 : soluble 2) that were indistinguishable from their wild-type counterparts. Differential splicing does vary markedly between strains, potentially because of local effects of strain-specific polymorphisms.

Structural changes in airway diseases: characteristics, mechanisms, consequences, and pharmacologic modulation

In airway diseases such as asthma and COPD, specific structural changes may be observed, very likely secondary to an underlying inflammatory process. Although it is still controversial, airway remodeling may contribute to the development of these diseases and to their clinical expression and outcome. Airway remodeling has been described in asthma in various degrees of severity, and correlations have been found between such features as increase in subepithelial collagen or proteoglycan deposits and airway responsiveness. Although the clinical significance of airway remodeling remains a matter of debate, it has been suggested as a potential target for treatments aimed at reducing asthma severity, improving its control, and possibly preventing its development. To date, drugs used to treat airway diseases have a little influence on airway structural changes. More research should be done to identify key changes, valuable treatments, and proper interventional timing to counteract these changes. The potential of novel therapeutic agents to reverse or prevent airway remodeling is an exciting avenue and warrants further evaluation.

Association analysis of interleukin 5 receptor alpha subunit (IL5RA) polymorphisms and asthma

The alpha subunit of interleukin 5 receptor (IL5RA) on chromosome 3p26-p24 is known to regulate the development and function of eosinophils. In an effort to discover additional polymorphism(s) in genes whose variant(s) have been implicated in asthma, we investigated the genetic polymorphisms in IL5RA to evaluate the gene as a potential candidate for a host genetic study of asthma. By direct DNA sequencing in 24 individuals, we identified 22 sequence variants within exons and flanking regions including a 1.5-kb promoter region of IL5RA; 10 common polymorphic sites were selected for genotyping in our asthma cohort (n = 587). Two haplotype blocks were identified in a Korean population. Statistical analysis revealed that one promoter SNP, c.-5993A > G, and one ins/del polymorphism in intron 3, c.-480_482insdelGTT, showed significant association with the risk of asthma development. The genetic effects of c.-5993A>G and c.-480_482insdelGTT on asthma were more apparent among atopic subjects. Our findings suggest that polymorphisms in IL5RA might be among the genetic risk factors for asthma development, especially in atopic populations. IL5RA variant/haplotype information identified in this study will provide valuable information for strategies for the control of asthma.

Interleukin-5 reduces the expression of uteroglobin-related protein (UGRP) 1 gene in allergic airway inflammation

Airway inflammation is thought to play a major role in the pathogenesis of bronchial asthma. The precise role of individual inflammatory cells, mediator and asthma related genes in allergic lung diseases is not completely understood. The uteroglobin-related protein (UGRP) 1 was proposed to be an asthma candidate gene and play a role in regulating lung inflammation, however its precise function in the airways remains obscure. In this investigation, we used a mouse model of allergic airway inflammation to establish a relationship between UGRP 1 and IL-5 in airway inflammation. Ovalbumin (OVA) challenged mice demonstrate eosinophilia in airway tissues and high levels of IL-5 in bronchoalveolar lavage (BAL) fluid analogous to that found in bronchial asthma. Interestingly, these "OVA-challenged" mice show down-regulation of Ugrp1 expression as compared with the control group. Regression analysis further demonstrates a significant negative correlation between Ugrp1 mRNA expression in the lung and IL-5 levels in BAL fluid with r = 0.948 and P < 0.0001 when IL-5 levels were normalized by log transformation. Intranasal instillation of IL-5 to mice revealed an inhibitory effect of IL-5 on the expression of Ugrp1 mRNA. Together, these results indicate an involvement of IL-5 in the down-regulation of Ugrp1 expression in airway inflammation such as allergic asthma disease.

Relationship between Asthma and Rhinitis: Epidemiologic, Pathophysiologic, and Therapeutic Aspects

Over the last few years, the evidence of links between rhinitis and asthma has been strengthened. This has led to the introduction of the concept of united airway disease. Rhinitis and asthma appear to be interrelated at the epidemiologic level and at the pathophysiologic level. This article reviews current epidemiologic and pathophysiologic evidence of the relationship between rhinitis and asthma and discusses the effect of treatment of one site on the other site.

IL-5 and thromboxane A2 receptor gene polymorphisms are associated with decreased pulmonary function in Korean children with atopic asthma

BACKGROUND

Asthmatic airways undergo chronic inflammatory cell infiltration by T cells and eosinophils, which results in sustained airway hyperresponsiveness. IL-5 is important for eosinophil-induced airway inflammation and airway hyperresponsiveness. Thromboxane A2 and its receptor, TBXA2R, are involved in constriction of respiratory smooth muscles and may play a role in thickening and remodeling of airways, which contributes to the severity of asthma. The relationship between IL-5 and TBXA2R gene polymorphisms and pulmonary function in children with asthma has rarely been examined.

OBJECTIVE

To determine whether IL-5 (T-746C) and TBXA2R (T924C) gene polymorphisms are associated with asthma phenotype and pulmonary function in Korean children with atopic and nonatopic asthma.

METHODS

We conducted an association study between known polymorphisms of IL-5 (T-746C) and TBXA2R (T924C) and asthma phenotype and the parameters of atopy and pulmonary function in atopic and nonatopic Korean children with asthma. The subjects were 240 atopic children with asthma, 70 nonatopic children with asthma, and 106 nonatopic healthy children. Asthma phenotypes and bronchial responsiveness to methacholine were determined by a physician. IL-5 and TBXA2R gene polymorphisms were determined by genotyping by using PCR-RFLP assays.

RESULTS

The genotype frequencies of IL-5 and TBXA2R polymorphisms did not differ between healthy controls and atopic or nonatopic children with asthma. A significant association was observed between the IL-5 polymorphism and forced expiratory flow at 25% to 75% of forced vital capacity (FEF 25-75% ; %; P = .002), and between the TBXA2R polymorphism and FEV 1 (%; P = .035) and FEF 25-75% (%; P = .042) in children with atopic asthma, whereas no such association between the polymorphisms and lung function was observed in nonatopic or control children. In atopic children with asthma, we identified a significant gene-gene interaction in that the combination of the IL-5 (T-746C) and TBXA2R (T924C) mutant alleles was shown to be associated with reduced pulmonary function as determined by FEF 25-75% (%) measurement.

CONCLUSION

The current study indicates that IL-5 (T-746C) and TBXA2R (T924C) polymorphisms alone are associated with spirometric markers of asthma severity, whereas they are not associated with presence of asthma per se. In addition, the data suggest that an interaction between IL-5 and TBXA2R genes may contribute to the severity of asthma, especially atopic asthma. These results suggest that IL-5 and TBXA2R genes may be disease-modifying genes in Korean children with atopic asthma.

Phenotypes of asthma revisited upon the presence of atopy

Immunological studies claimed that atopic and non-atopic asthma share more similarities than differences. However, these two phenotypes of asthma are considered to be distinguishable upon distinct clinical patterns, which were not systematically assessed before in a large population. We studied characteristics discriminating atopic from non-atopic asthma among 751 asthmatic patients and 80 factors were analysed in univariate and multivariate analysis. Age, age of onset of asthma, female/male ratio were higher in non-atopic (n=200) than in atopic (n=551) asthmatics. Familial asthma, seasonal symptoms, rhinitis, conjunctivitis, allergen-triggered symptoms, improvement in altitude, exercise-induced asthma were associated with atopy. Non-atopic asthmatics displayed lower FEV(1) and FVC. Smoking was more frequent and asthma was more severe in these patients. Younger age, early onset, male sex, rhinitis and smoking were independent factors discriminating atopic from non-atopic asthma. This study establishes in a large population of asthmatics that although similarities exist between atopic and non-atopic asthma, two clinical phenotypes can still distinguish both kinds of asthma.

Interferon-gamma inhibits in vitro mobilization of eosinophils by interleukin-5

BACKGROUND

Th2 cytokines play pivotal roles in allergic inflammation, including eosinophilia, and their actions are antagonized by Th1 cytokines, conferring them therapeutic potential.

METHODS

In this study, we examined the ability of a number of cytokines to suppress the activation of eosinophils that function as effector cells for allergic airway diseases.

RESULTS

Interleukin (IL)-5, IL-6, and tumor necrosis factor (TNF) induced an eosinophil shape change, whereas interferon (IFN)-gamma significantly inhibited the shape change. Other cytokines, including IL-1beta, IL-4, IL-10 and IL-13, had little or only slightly enhancing or reducing effects on the shape change. We further analyzed the IFN-gamma effect, showing that pretreatment with IFN-gamma strongly suppressed IL-5-induced eosinophil shape change, and cycloheximide (CHX) abrogated the suppression by IFN-gamma, suggesting that new protein synthesis is required for the inhibitory effect by this cytokine. In agreement with these results, IFN-gamma blocked the eosinophil migration and ERK phophorylation induced by IL-5, and the addition of CHX restored eosinophil chemotaxis.

CONCLUSIONS

Collectively, IFN-gamma may attenuate eosinophilic inflammation by directly negating eosinophil mobilization.

Quantitative real time polymerase chain reaction for measurement of human interleukin-5 receptor alpha spliced isoforms mRNA

Background

Expression of human Interleukin-5 receptor alpha (hIL-5Rα) is controlled by alternative splicing, which generates two different transcripts encoding a membrane-anchored and a soluble form of the receptor, respectively. Although the study of the expression and regulation of hIL-5Rα is of crucial importance in the field of immunological processing, methods and techniques until now described lack sufficient sensitivity for detection of small differences in the expression of these isoforms. The aim of this study was to develop a reliable and sensitive real-time quantitative PCR assay to analyse the expression level of each isoform.

Methods

For the quantitative real-time PCR assay, two standard curves specific for each splice variant were constructed. PCR amplifications were performed on CDNA from peripheral blood, eosinophilic chronic rhinosinusitis and normal nasal tissue using a common forward and two specific reverse primers, in combination with SYBR Green I as the detection format.

Results and conclusion

We have developed an accurate and reliable assay for quantification of interleukin-5 receptor alpha mRNA isoforms over a broad dynamic range of input molecules. Importantly, excess of one isoform did not influence accurate quantification of the other isoform. Quantification of hIL-5Rα variants in human samples demonstrated an overexpression of both membrane-anchored and soluble encoding variants in eosinophilic chronic rhinosinusitis tissue and peripheral blood in patients with eosinophilic chronic rhinosinusitis compared to healthy subjects. The implementation of this assay will allow a better understanding of the regulatory mechanisms of the hIL-5Rα gene and hence its role in the pathogenesis of chronic inflammatory diseases.

Allergic and nonallergic forms of atopic diseases

Atopic dermatitis, allergic rhinitis, and asthma are atopic diseases that develop on a complex genetic background, the so-called atopic diathesis. Although they target different organs, in most patients they are characterized by the presence of elevated total serum IgE levels. However, a subgroup of atopic patients exhibits normal IgE levels and mechanisms contributing to the so-called "intrinsic" or "nonallergic form" have been the matter of intensive research work in the last years. Because of the rapid advancements in the research field of atopic diseases, it now becomes possible for the first time to delineate a new disease classification of allergic and nonallergic subtypes of atopic diseases, thereby bringing hope to the clinician for a more specific treatment approach for each subgroup of these patients.

Effect of SCH55700, a humanized anti-human interleukin-5 antibody, in severe persistent asthma: a pilot study

Antagonizing the effect of interleukin (IL)-5 is a potential new treatment strategy in allergic disorders. We evaluated the safety, biological activity, and pharmacokinetics of SCH55700, a humanized anti-human IL-5 antibody, in subjects with severe persistent asthma treated with oral or high doses of inhaled steroids. In a double-blind, randomized, multicenter trial, a rising single dose of SCH55700 (0.03 mg/kg [n = 2], 0.1 mg/kg [n = 4], 0.3 mg/kg [n = 6], or 1.0 mg/kg [n = 12]) or placebo (n = 8) was administered intravenously. SCH55700 dose dependently reduced circulating eosinophil counts. At a dose of 1.0 mg/kg, the decrease remained significant up to Day 30 [(0.07 +/- 0.01) x 10(9)/L versus (0.23 +/- 0.04) x 10(9)/L at baseline] (mean +/- SEM) (p = 0.05). After administration of SCH55700 at 0.3 and 1.0 mg/kg, a trend toward improvement in baseline FEV1 was observed, which reached significance 24 hours after the 0.3-mg/kg dose (p = 0.019 versus placebo). No significant changes occurred in other clinical indices of disease activity. Adverse events were not different between active treatment and placebo. We conclude that SCH55700 is a biologically active anti-human IL-5 antibody that can be safely used in severe steroid-treated asthma. Its therapeutic potential needs to be addressed in specifically designed efficacy trials.

T helper type 2 cytokine receptors and associated transcription factors GATA-3, c-MAF, and signal transducer and activator of transcription factor-6 in induced sputum of atopic asthmatic patients

BACKGROUND

It is well-known that the expression of T helper (Th) type 2 cytokines such as interleukin (IL)-4 and IL-5, and their receptors, is up-regulated within the airways of allergic asthmatic patients. Furthermore, higher numbers of cells producing GATA-3, c-MAF, and signal transducer and activator of transcription factor (STAT)-6, which are transcription factors (TFs) that are implicated in the regulation and signaling of the Th2 cytokines, have been observed in bronchial biopsy specimens from asthmatic patients but not in those of healthy control subjects.

METHODS

We examined whether these mediators also can be detected in induced sputum. Immunoreactivity for IL-4Ralpha, IL-5Ralpha, GATA-3, c-MAF, and STAT-6 was investigated in samples of induced sputum from asthmatic patients (n = 8) and healthy control subjects (n = 8).

RESULTS

Our results showed that the numbers of cells expressing IL-4 receptor alpha (Ralpha) and IL-5Ralpha were higher in samples from asthmatic patients compared to those of control subjects (p < 0.01). More cells exhibiting GATA-3, c-MAF, and STAT-6 immunoreactivity also were found in asthmatic patients vs those in control subjects (p < 0.005). Furthermore, the expression of STAT-6 and IL-4Ralpha, GATA-3 and IL-5Ralpha, and c-MAF with both IL-4Ralpha and IL-5Ralpha was correlated (p < 0.05).

CONCLUSIONS

This study demonstrated that induced sputum provides sufficient sensitivity for examining the pathways of cytokine signaling, cytokine receptor signaling, and intracellular signaling. Furthermore, these data show correlations between the expression of Th2 cytokine receptors and associated TFs in the human lung, which has not been documented previously.

Decreased expression of membrane IL-5 receptor alpha on human eosinophils: I. Loss of membrane IL-5 receptor alpha on airway eosinophils and increased soluble IL-5 receptor alpha in the airway after allergen challenge

IL-5 is a key cytokine for eosinophil maturation, recruitment, activation, and possibly the development of inflammation in asthma. High concentrations of IL-5 are present in the airway after Ag challenge, but the responsiveness of airway eosinophils to IL-5 is not well characterized. The objectives of this study were to establish, following airway Ag challenge: 1) the expression of membrane (m)IL-5Ralpha on bronchoalveolar lavage (BAL) eosinophils; 2) the responsiveness of these cells to exogenous IL-5; and 3) the presence of soluble (s)IL-5Ralpha in BAL fluid. To accomplish these goals, blood and BAL eosinophils were obtained from atopic subjects 48 h after segmental bronchoprovocation with Ag. There was a striking reduction in mIL-5Ralpha on airway eosinophils compared with circulating cells. Furthermore, sIL-5Ralpha concentrations were elevated in BAL fluid, but steady state levels of sIL-5Ralpha mRNA were not increased in BAL compared with blood eosinophils. Finally, BAL eosinophils were refractory to IL-5 for ex vivo degranulation, suggesting that the reduction in mIL-5Ralpha on BAL eosinophils may regulate IL-5-mediated eosinophil functions. Together, the loss of mIL-5Ralpha, the presence of sIL-5Ralpha, and the blunted functional response (degranulation) of eosinophils to IL-5 suggest that when eosinophils are recruited to the airway, regulation of their functions becomes IL-5 independent. These observations provide a potential explanation for the inability of anti-IL-5 therapy to suppress airway hyperresponsiveness to inhaled Ag, despite a reduction in eosinophil recruitment.

Allergic vs nonallergic asthma: what makes the difference?

BACKGROUND

The aim of this work was to describe clinical similarities and differences between allergic and nonallergic asthmatics, notably concerning the nasosinusal involvement.

METHODS

A total of 165 asthmatics (122 allergics and 43 nonallergics) and 193 controls (40 allergics and 153 nonallergics), recruited in the frame of EGEA study (Epidemiological study on the Genetics and Environment of Asthma, bronchial hyperresponsiveness and atopy), were included. Asthmatics were included on the basis of positive answer to four standardized items. To establish differences and similarities between allergic and nonallergic asthmatics, general characteristics (age, sex, smoking habits, history of hay fever and allergic dermatitis), history of asthma, severity and nasosinusal involvement were examined. Clinical assessment was based on the answers to a detailed questionnaire, and spirometry.

RESULTS

Greater age, female sex, sinusal polyposis, and FEV1 below 80% of the predicted value increased the risk of displaying a nonallergic type of asthma, whereas history of hay fever, seasonal exacerbation of asthma, and asthma duration lowered this risk. Unexpectedly, we found no difference in terms of rhinitic symptoms between both groups, probably resulting from distinct causes.

CONCLUSION

These results give new insights into the contrasts between clinical features of allergic and nonallergic asthma. The terminology of extrinsic asthma was first introduced by Rackeman in 1947 (1) and referred to the triggering role of allergens in asthma. By symmetry, he described intrinsic asthma as a disease characterized by later onset in life, female predominance, higher degree of severity, and more frequent association to nasosinusal polyposis. As these asthmatics were not improved by conventional treatment, this author considered their disease as caused by a nonallergic, unknown phenomenon. It is now widely admitted that nonallergic asthma can be objectively distinguished from allergic asthma based on negative skin tests to usual aeroallergens. On the other hand, positive skin test shows a tendency to produce IgE antibodies in response to low doses of allergens. "Atopy" and "atopic" are the terms used to describe this clinical trait and predisposition (2). Allergic clinical manifestations of atopy are of various types, for example rhinitis and asthma. Nowadays the terminology of "extrinsic" and "intrinsic" asthma should no longer be used, and should be replaced by the terminology of "allergic" or "nonallergic" asthma (2).

Retinoic acid modulates IL-5 receptor expression and selectively inhibits eosinophil-basophil differentiation of hemopoietic progenitor cells

BACKGROUND

IL-5 plays a central role in eosinophil and basophil differentiation, exerting its effects through the IL-5 receptor (IL-5Ralpha). Currently, little is known concerning regulation of IL-5Ralpha expression in the context of commitment of hemopoietic progenitor cells to the eosinophil and basophil lineages.

OBJECTIVE

Because all-trans retinoic acid (ATRA) is known to modulate some aspects of hemopoietic differentiation, we examined the effects of ATRA on eosinophil-basophil differentiation and IL-5Ralpha expression.

METHODS

Progenitor cells were obtained from bone marrow aspirates and cord blood samples. Enriched populations of CD34(+) cells were isolated by means of positive immunomagnetic selection with MACS beads.

RESULTS

In semisolid methylcellulose cultures of normal human bone marrow, ATRA (10(-6) mol/L) selectively suppressed eosinophil-basophil colony-forming units but had no effect on granulocyte-macrophage colony-forming units. Similarly, ATRA (10(-6) mol/L) inhibited eosinophil-basophil differentiation of cord blood CD34(+) cells in liquid culture, whereas neutrophil differentiation proceeded without impediment. Most importantly, these effects of ATRA (10(-8) to 10(-6) mol/L) on CD34(+) cells were associated with a dose-dependent inhibition of IL-5Ralpha but no change in GM-CSF receptor expression, as detected with flow cytometry.

CONCLUSIONS

These findings indicate that retinoids can differentially regulate expression of IL-5Ralpha, but not GM-CSF receptor, and that these effects have functional consequences in vitro on eosinophil and basophil differentiation.

Increased detection of interleukin-5 in sputum by addition of protease inhibitors

The measurement of interleukin (IL)-5 in sputum is problematic, with interfering factors affecting immunoassay. The authors investigated whether sputum proteases could be acting as interfering factors by studying the effect of protease inhibitors (PI) on sputum IL-5 measurement. Induced sputa from 20 subjects with asthma were divided into aliquots, processed with and without protease inhibitors (in low and high concentrations) and the levels of IL-5 (spiked and endogenous) measured by enzyme immunoassay were compared. The concentration of sputum IL-5 was significantly increased by PI, with median (interquartile range) levels processed with no, low and high PI concentrations being 0 (0), 41.8 (75.6) and 66.1 (124.4) pg x mL(-1), respectively. There was also a significant increase in percentage recovery of spiked IL-5. Although high concentrations of PI reduced cell viability, there was no effect on total or differential cell counts and low concentrations of PI had no effect on cell counts or viability. Levels of endogenous interleukin-5 in sputum of asthmatic subjects can be significantly increased by the addition of protease inhibitors, and samples which would be regarded as negative for interleukin-5 without protease inhibitors may instead have considerable amounts of interleukin-5 detected.

Pathophysiological mechanisms of asthma. Application of cell and molecular biology techniques

Asthma is a common increasing and relapsing disease that is associated with genetic and environmental factors such as respiratory viruses and allergens. It causes significant morbidity and mortality. The changes occurring in the airways consist of a chronic eosinophilic and lymphocytic inflammation, together with epithelial and structural remodeling and proliferation, and altered matrix proteins, which underlie airway wall narrowing and bronchial hyperresponsiveness (BHR). Several inflammatory mediators released from inflammatory cells such as histamine and cysteinyl-leukotrienes induce bronchoconstriction, mucus production, plasma exudation, and BHR. Increased expression of T-helper 2 (Th2)-derived cytokines such as interleukin-4 and 5 (IL-4, 5) have been observed in the airway mucosa, and these may cause IgE production and terminal differentiation of eosinophils. Chemoattractant cytokines (chemokines) such as eotaxin may be responsible for the chemoattraction of eosinophils to the airways. The initiating events are unclear but may be genetically determined and may be linked to the development of a Th2-skewed allergen-specific immunological memory. The use of molecular biology techniques on tissues obtained from asthmatics is increasing our understanding of the pathophysiology of asthma. With the application of functional genomics and the ability to transfer or delete genes, important pathways underlying the cause if asthma will be unraveled. The important outcome of this is that new preventive and curative treatments may ensue.

Neutralizing monoclonal antibodies can potentiate IL-5 signaling

IL-5 is a major determinant in the survival, differentiation and effector-functions of eosinophils. It mediates its effect upon binding and activation of a membrane bound receptor (R), composed of a ligand-specific alpha-chain and a beta-chain, shared with the receptors for IL-3 and granulocyte-macrophage colony-stimulating factor. We have generated and mapped the epitopes of three monoclonal antibodies (mAb) directed against this cytokine: the strong neutralizing mAb 5A5 and 1E1, and the very weak neutralizing mAb H30. We found that H30 as well as 5A5 can increase proliferation above the level induced by human (h)IL-5 alone, in a JAK-2-dependent manner, and at every sub-optimal hIL-5 concentration analyzed. This effect is dependent on mAb-mediated cross-linking of IL-5R complexes, and is only observed on cell lines expressing a hybrid human/mouse IL-5Ralpha-chain. We discuss these findings in view of the stoichiometric and topological requirements for an activated IL-5R. Since humanized anti-IL-5 mAb are currently in clinical testing, our findings imply that such mAb should be carefully evaluated for their potentiating effects.

TH2 cytokine-associated transcription factors in atopic and nonatopic asthma: evidence for differential signal transducer and activator of transcription 6 expression

BACKGROUND

The expression of IL-4 and IL-5 is increased in patients with atopic asthma compared with control subjects and correlates with indices of pulmonary function. In nonatopic asthma the expression of IL-4, unlike IL-5, fails to correlate with pulmonary function, and compared with their atopic counterparts, these patients have fewer cells expressing IL-4 receptor (IL-4R). As such, a deficiency in the IL-4 signaling pathway may be implicated in nonatopic asthma. The transcription factors GATA-3 and cMAF mediate IL-4 and IL-5 synthesis, whereas signal transducer and activator of transcription 6 (STAT-6) is critical for IL-4R signaling.

OBJECTIVE

This study examines the expression profile of these transcription factors in asthma, according to atopic status.

METHODS

With immunocytochemistry, the expression of GATA-3, cMAF, and STAT-6 protein was determined in sections of bronchial biopsy specimens from patients with atopic asthma (n = 7), patients with nonatopic asthma (n = 8), and control subjects (n = 8).

RESULTS

Higher numbers of cells expressing GATA-3 and cMAF were observed in patients with atopic and those with nonatopic asthma than in control subjects and patients with tuberculosis (P <.001). There were also more STAT-6-immunoreactive cells in patients with atopic and those with nonatopic asthma than in control subjects (P <.0001, P <.05). Notably, however, fewer cells expressing STAT-6 protein were observed in nonatopic versus atopic asthma (P <.0001).

CONCLUSIONS

These results demonstrate the upregulation of GATA-3 and cMAF in both variants of asthma and indicate that reduced IL-4R signaling, because of lower STAT-6 expression, may be a feature of nonatopic asthma.

New anti-asthma therapies: suppression of the effect of interleukin (IL)-4 and IL-5

Asthma is currently defined as a chronic inflammatory disorder of the airways. The central role of allergen-specific Th2 cells in the regulation of this mucosal airway inflammation has been highlighted. Hence, there is large interest in the therapeutic potential of an anti-Th2 cell approach. One of the strategies which has been developed, is to inhibit the effect of interleukin (IL)-4 or IL-5, two main Th2 cell derived cytokines. Interleukin-4 is pivotal in the pathogenesis of allergic disorders through its wide range of effects. An important observation, especially during secondary antigen exposure, is the possible redundancy with IL-13. Both cytokines share common elements in their receptor and intracellular signalling pathway. As a result, compounds can be developed that selectively inhibit the effect of either IL-4 or IL-13, or alternatively, by interfering with the common pathway, inhibit the effect of both cytokines. Eosinophils are generally seen as a particularly harmful element in the allergic inflammation. The importance of IL-5 on eosinophil biology has clearly been established. Conversely, in man, the biological effects of IL-5 are largely limited to eosinophil function. Therefore, IL-5 antagonists offer the unique opportunity of selectively neutralizing the effect of eosinophils. Several strategies have now been developed that successfully inhibit the biological effect of interleukin-4 or interleukin-5. Some of these compounds have proven to be biologically active in man. The challenge now is to establish their therapeutic role in asthma.

Antisense inhibition of membrane-bound human interleukin-5 receptor-alpha chain does not affect soluble receptor expression and induces apoptosis in TF-1 cells

Binding of human interleukin-5 (HuIL-5) to its membrane-anchored receptor (IL-5R) triggers multiple signaling pathways, cellular proliferation, and maturational responses, as well as protection from apoptosis. In contrast, soluble forms of the HuIL-5R have been shown to inhibit IL-5 signaling and, therefore, may represent naturally occurring negative regulators of IL-5 function. Because of the central role of IL-5 in promoting eosinophilia and airway hyperresponsiveness in animal models of asthma, antisense oligonucleotides specific either for the membrane form alone or for sequences shared between both the membrane and soluble forms of the HuIL-5Ralpha ligand binding chain were designed. The activities of these oligonucleotides were characterized in IL-5R-expressing erythroleukemic TF-1 cells. Herein we report that an antisense oligonucleotide targeted to a sequence unique to the alternatively spliced membrane-bound form of the HuIL-5Ralpha chain has been developed that selectively inhibits membrane, but not soluble, mRNA isoform expression. Both this membrane-specific oligonucleotide and an antisense oligonucleotide targeted to sequence common to both membrane and soluble isoforms were found to potently suppress cell surface IL-5Ralpha levels and IL-5-mediated cell survival by inducing apoptosis similar to IL-5 withdrawal. Thus, these oligonucleotides represent unique genetic agents with therapeutic potential for diseases with an eosinophilic component.

Eosinophilopoiesis in a murine model of allergic airway eosinophilia: involvement of bone marrow IL-5 and IL-5 receptor alpha

The airway inflammation in asthma is dominated by eosinophils. The aim of this study was to elucidate the contribution of newly produced eosinophils in airway allergic inflammation and to determine mechanisms of any enhanced eosinophilopoiesis. OVA-sensitized BALB/c mice were repeatedly exposed to allergen via airway route. Newly produced cells were identified using a thymidine analog, 5-bromo-2'-deoxyuridine, which is incorporated into DNA during mitosis. Identification of IL-5-producing cells in the bone marrow was performed using FACS. Bone marrow CD3+ cells were enriched to evaluate IL-5-protein release in vitro. Anti-IL-5-treatment (TRFK-5) was given either systemically or directly to the airways. IL-5R-bearing cells were localized by immunocytochemistry. Repeated airway allergen exposure caused prominent airway eosinophilia after three to five exposures, and increased the number of immature eosinophils in the bone marrow. Up to 78% of bronchoalveolar lavage (BAL) granulocytes were 5-bromo-2'-deoxyuridine positive. After three allergen exposures, both CD3+ and non-CD3 cells acquired from the bone marrow expressed and released IL-5-protein. Anti-IL-5 given i.p. inhibited both bone marrow and airway eosinophilia. Intranasal administration of anti-IL-5 also reduced BAL eosinophilia, partly via local effects in the airways. Bone marrow cells, but not BAL eosinophils, displayed stainable amounts of the IL-5R alpha-chain. We conclude that the bone marrow is activated by airway allergen exposure, and that newly produced eosinophils contribute to a substantial degree to the airway eosinophilia induced by allergen. Airway allergen exposure increases the number of cells expressing IL-5-protein in the bone marrow. The bone marrow, as well as the lung, are possible targets for anti-IL-5-treatment.

Interleukin-9 enhances interleukin-5 receptor expression, differentiation, and survival of human eosinophils

Interleukin-9 (IL-9) has been implicated in the pathogenesis of allergic disorders. To examine the interaction between IL-9 and eosinophils, we evaluated mature peripheral blood eosinophils for their expression of the specific α-subunit of the IL-9 receptor (IL-9R–α). The expression of IL-9R–α by human eosinophils was detected at the messenger RNA (mRNA) and protein levels by reverse transcriptase–polymerase chain reaction (RT-PCR), flow cytometry, and immunocytochemical analysis, respectively. Functional analyses demonstrated that recombinant human (rh)IL-9 inhibited in vitro peripheral blood human eosinophil apoptosis in a concentration-dependent manner. We then examined the role of IL-9 in eosinophil differentiation using the human cord blood CD34+cells and human promyelocytic leukemia cells (HL-60). The addition of IL-9 to CD34+ cells cultured in IL-3 and IL-5 enhanced eosinophil development, and IL-9 alone induced the expression of IL-5R–α. IL-9 also up-regulated the IL-5R–α chain cell surface expression during terminal eosinophil differentiation of the HL-60 cell line. Our findings suggest that IL-9 may potentiate in vivo eosinophil function by increasing their survival and IL-5–mediated differentiation and maturation. Taken together, these results suggest a mechanism by which IL-9 potentiates airway and tissue eosinophilia.

Interleukin-9 enhances interleukin-5 receptor expression, differentiation, and survival of human eosinophils

Interleukin-9 (IL-9) has been implicated in the pathogenesis of allergic disorders. To examine the interaction between IL-9 and eosinophils, we evaluated mature peripheral blood eosinophils for their expression of the specific α-subunit of the IL-9 receptor (IL-9R–α). The expression of IL-9R–α by human eosinophils was detected at the messenger RNA (mRNA) and protein levels by reverse transcriptase–polymerase chain reaction (RT-PCR), flow cytometry, and immunocytochemical analysis, respectively. Functional analyses demonstrated that recombinant human (rh)IL-9 inhibited in vitro peripheral blood human eosinophil apoptosis in a concentration-dependent manner. We then examined the role of IL-9 in eosinophil differentiation using the human cord blood CD34+cells and human promyelocytic leukemia cells (HL-60). The addition of IL-9 to CD34+ cells cultured in IL-3 and IL-5 enhanced eosinophil development, and IL-9 alone induced the expression of IL-5R–α. IL-9 also up-regulated the IL-5R–α chain cell surface expression during terminal eosinophil differentiation of the HL-60 cell line. Our findings suggest that IL-9 may potentiate in vivo eosinophil function by increasing their survival and IL-5–mediated differentiation and maturation. Taken together, these results suggest a mechanism by which IL-9 potentiates airway and tissue eosinophilia.

Induced sputum: validity of fluid-phase IL-5 measurement

BACKGROUND

IL-5 measurement in the fluid phase of induced sputum is considered to be important in the assessment of asthma, but the validity of these measurements is uncertain.

OBJECTIVE

We investigated the validity of sputum IL-5 measurements through a series of spiking experiments and examined the effect of dithiothreitol (DTT) on these measurements.

METHODS

Induced sputum from 26 asthmatic subjects was spiked with IL-5 and processed, and the percentage of recovery was measured by means of immunoassay. In 6 of the 26 samples the effect of adding albumin to the processing fluids was studied. In 3 separate samples radiolabeled IL-5 was added, and the recovery measured by means of gamma counting and immunoassay were compared. In addition, the effect of DTT on the immunoassay was examined.

RESULTS

The mean +/- SD recovery of spiked IL-5 was 26.1% +/- 14.6% measured by means of immunoassay; adding albumin increased the recovery to 47.7% +/- 8.0% (P <.001). The mean recovery measured by means of gamma counting was 84.8% +/- 5.7% (P <.001); adding albumin had no effect on recovery. DTT had no significant effect on IL-5 measurement.

CONCLUSION

The validity of IL-5 measurement by means of current methods is poor. The discrepancy in recovery as measured by gamma counting compared with immunoassay suggests that there is a problem with the recognition of IL-5 epitopes by immunoassay in induced sputum. This cannot be attributed to DTT but may be due to other interfering substances present in sputum, such as sputum proteases, soluble receptors, or autoantibodies.

Advances in immunopharmacology of asthma

Asthma is a chronic inflammatory disease characterized by airway hyperresponsiveness and recurrent reversible airway obstruction. As there appears to be a preponderance of T-helper 2 (Th2) cells over Th1 cells in asthma, more attention has been focused on the role of Th2-derived cytokines such as interleukin (IL)-4 and IL-5 and their corresponding signaling pathways in the pathophysiology of the disease. These complex pathways may involve the activation of signal transducers and activators of transcription (STATs) and nuclear factor-kappaB (NF-kappaB). On the other hand, immunoglobulin (Ig) E-mediated mechanisms and the protein tyrosine kinase signaling cascade are important in triggering the release of mediators from inflammatory cells. In spite of all of these, host regulatory mechanisms exist to limit the inflammation. An increase in the 3', 5'-cyclic adenosine monophosphate (cAMP) level generally suppresses the activities of immune and inflammatory cells, and the level of cAMP is closely regulated by a family of phosphodiesterases (PDEs). Heparin, a glycosaminoglycan released exclusively from mast cells, also is believed to possess anti-inflammatory actions. Many new therapeutic agents have been developed either to attenuate the pro-inflammatory processes in asthma or to augment the host anti-inflammatory mechanisms. In this article, we discuss the immunopharmacology of several of these agents, which include heparin and inhibitors of PDEs, tyrosine kinases, and NF-kappaB, as well as antibodies and soluble receptors directed against IgE, IL-4, and IL-5.

The pathology of chronic asthma

Our understanding of the pathophysiology of asthma has undergone great advances in the past decade, particularly with the recognition of cytokines and the roles they may take in orchestrating the local immune response. With this information, it has been possible to target new therapeutic entities such as cytokine or chemokine receptors. Eosinophils and T lymphocytes have a special place in the inflammatory and structural alterations contributing to the asthmatic diathesis. It is possible that phenotype subsets of these cells exist and they hold the key to perpetuation of immunologic and physiologic abnormalities in asthma.

Interleukin 5 regulates the isoform expression of its own receptor α-subunit

The receptor for interleukin 5 (IL-5) consists of a cytokine-specific  chain (IL-5R) and a signaling β chain, which is shared with interleukin 3 (IL-3) and granulocyte-macrophage colony-stimulating factor (GM-CSF). These 3 cytokines can act in eosinophil development and activation in vitro, but gene deletion or antibody blocking of IL-5 largely ablates eosinophilic responses in models of allergic disease or helminth infection. We investigated factors acting in differential IL-5R gene splicing to generate either the membrane-anchored isoform (TM-IL-5R) which associates with the common β chain to allow IL-5 responsiveness, or a secreted, antagonist variant (SOL-IL-5R). In a murine myeloid cell line (FDC-P1), transfected with minigenes allowing expression of either IL-5R variant, IL-5 itself, but not IL-3 or GM-CSF, stimulated a reversible switch toward expression of TM-IL-5R. A switch from predominantly soluble isoform to TM-IL-5R messenger RNA (mRNA) expression was also seen during IL-5-driven eosinophil development from human umbilical cord blood-derived CD34+ cells; this was accompanied by surface expression of IL-5R and acquisition of functional responses to IL-5. IL-3 and GM-CSF also supported eosinophil development and up-regulation of TM-IL-5R mRNA in this system, but this was preceded by expression of IL-5 mRNA and was inhibited by monoclonal antibody to IL-5. These data suggest IL-5-specific signaling, not shared by IL-3 and GM-CSF, leading to a switch toward up-regulation of functional IL-5R and, furthermore, that IL-3 and GM-CSF-driven eosinophil development is dependent on IL-5, providing an explanation for the selective requirement of IL-5 for expansion of the eosinophil lineage.

IL-5: biology and potential therapeutic applications

IL-5 is the predominant cytokine associated with antigen-induced eosinophilic inflammation in the lung. The activation of Th-2 cells leads to the production of IL-5. The pro-eosinophilic effects of IL-5 include: (1) enhanced replication and differentiation of eosinophilic myelocytes; (2) enhanced degranulation of eosinophils; (3) prolonged survival time of eosinophils: and (4) enhanced adhesion of eosinophils. The effects of IL-5 are mediated via the interaction of IL-5 with receptors (IL-5R) that are expressed on the eosinophil cell membrane. Intracellular signalling produced by occupation of the IL-5R by IL-5 occurs via the JAK-STAT system. IL-5 is a 45 kDa glycoprotein consisting of two identical polypeptide chains. The 5'-promoter region of the IL-5 gene contains elements that are down-regulated by glucocorticoids. Anti-IL-5 reagents have the potential to suppress IL-5 activity without the side effects of glucocorticoids. Studies using monoclonal antibodies (mAbs) against IL-5 have established the feasibility of suppressing eosinophilic inflammation by specifically blocking IL-5 activity. Studies with antisense IL-5 are beginning to provide the basis for non-glucocorticoid, sequence-specific oligonucleotide inhibitors of IL-5. Research has begun on the development of mAbs and antisense oligonucleotide inhibitors of IL-5 that can be inhaled and applied topically.

Evidence for local eosinophil differentiation within allergic nasal mucosa: inhibition with soluble IL-5 receptor

Eosinophil differentiation occurs within the bone marrow in response to eosinopoietic cytokines, particularly IL-5. Recently, however, eosinophil precursors (CD34/IL-5Ralpha+ cells) and IL-5 mRNA+ cells have been identified within the lungs of asthmatics, indicating that a population of eosinophils may differentiate in situ. In this report, we examined the presence of eosinophil precursors within allergic nasal mucosa and examined whether they undergo local differentiation following ex vivo stimulation. We cultured human nasal mucosa obtained from individuals with seasonal allergic rhinitis with either specific allergen, recombinant human IL-5 (rhIL-5), or allergen + soluble IL-5Ralpha (sIL-5Ralpha), shown to antagonize IL-5 function. Simultaneous immunocytochemistry and in situ hybridization demonstrated that there were fewer cells coexpressing CD34 immunoreactivity and IL-5Ralpha mRNA following culture with allergen or rhIL-5, compared with medium alone. Immunostaining revealed that the number of major basic protein (MBP) immunoreactive cells (eosinophils) was higher within tissue stimulated with allergen or rhIL-5, compared with unstimulated tissue. In situ hybridization detected an increase in IL-5 mRNA+ cells in sections from tissue cultured with allergen, compared with medium alone. These effects were not observed in tissue cultured with a combination of allergen and sIL-5Ralpha. Colocalization analysis indicated this expression to be mainly, but not exclusively, T cell (44%) and eosinophil (10%) derived. Our findings suggest that a subset of eosinophils may differentiate locally within allergic nasal mucosa, in what appears to be a highly IL-5-dependent fashion, and imply that this process might be regulated in vivo by endogenous production of sIL-5Ralpha.

Molecular pathology of allergic disease: I: lower airway disease

Asthma is a complex disorder associated with eosinophil infiltration and the activation of T lymphocytes within the airways. Recent advances in the pathophysiologic mechanisms of asthma point to the importance of eosinophil-basophil progenitor cells and a family of transcription factors that underlie the development of T(H)2-type responses. Further research is needed to address the development of chronic inflammatory changes, the role of profibrotic cytokines, and especially their reliance on eosinophils in the lungs.

Primary Peripheral Blood Eosinophils Rapidly Degrade Transfected Granulocyte-Macrophage Colony-Stimulating Factor mRNA

Despite increasing interest, very little information exists regarding gene regulatory mechanisms employed by eosinophils. This largely stems from the difficulty in transfecting these primary cells. In this study, we demonstrate that peripheral blood eosinophils (PBEos) can be successfully transfected with both GM-CSF cDNA and mRNA and reporter constructs by particle-mediated gene transfer. The transfection efficiency was 1.2% based on green fluorescent protein-positive cells. Promoter studies revealed CMV-driven expression vectors were initially active but rapidly quenched, while viral long terminal repeats had greater activity, indicating that certain viral constructs may be relatively poor to direct the production of transgenic proteins in PBEos. Exogenous GM-CSF mRNA was readily delivered and detected by Northern blot, permitting determination of its t1/2 in the absence of transcriptional poisons. These data show PBEos rapidly degraded GM-CSF mRNA with a t1/2 of 8 min. Mutant GM-CSF mRNAs, lacking the AUUUA motifs, were more stable, but were still rapidly degraded, suggesting the existence of accessory, destabilizing elements. We were able to measure minute amounts of intracellular GM-CSF after the transfection of mutant GM-CSF mRNA, but extracellular cytokine was below the sensitivity of our ELISA. However, the presence of secreted GM-CSF was established by in vitro, survival bioassay. In conclusion, the existence of this new technology should allow detailed studies of eosinophil-specific transcriptional and posttranscriptional regulation.

Advances in the immunobiology of eosinophils and their role in disease

Eosinophils play a protective role in host immunity to infections by parasitic worms and, detrimentally, are involved in the pathophysiology of asthma and other allergic diseases. Airway inflammation is central to the pathology of asthma and is characterized by infiltration of the bronchial mucosa by large numbers of proinflammatory cells, amongst which the eosinophil is prominent despite being a minority constituent of circulating leukocytes. Crucial steps in eosinophilic inflammation include augmented production of eosinophils in the bone marrow, their increased release into the circulation, and their selective accumulation in the conducting airways. The eosinophil has a potent armory of proinflammatory mediators, including cytotoxic granule proteins, cytokines and lipid mediators with considerable potential to initiate and sustain an inflammatory response. Thus there is much interest in the elucidation of the mechanisms responsible for eosinophil accumulation, persistence, activation and ultimate fate. This article reviews our current understanding of the role of the eosinophil in human disease and the immunobiology of this important proinflammatory cell.