Systemic eosinophil response induced by respiratory syncytial virus

Respiratory syncytial virus (RSV) is a common cause of lower respiratory tract disease (LRTD) in infants. Eosinophils have been suggested to play a role in the disease pathogenesis of LRTD. Inflammation can induce functional and morphological alterations of peripheral blood granulocytes. In patients with RSV LRTD, we aimed to investigate the eosinophil activation status by analysing surface markers. In vitro stimulation of eosinophils with cytokines leads to up-regulation of CD11b and priming markers recognized by the recently developed priming markers A17 and A27, whereas interleukin (IL)-5Ralpha is being down-regulated. In 51 patients and 10 controls we examined the expression of these surface markers on eosinophils in moderate to severe RSV-induced LRTD patients at the time of admission and 6 weeks later during the convalescence phase. RSV-patients were characterized by a higher eosinophil CD11b expression compared to controls. Although basal A17 and A27 expression was not increased, we observed a significantly higher expression of these priming epitopes on N-formyl-methionyl-leucyl-phenylalanine (fMLP)-stimulated cells of RSV patients compared with cells of controls, indicative of prior in vivo priming. Furthermore, IL-5Ralpha expression was down-regulated on peripheral blood eosinophils of these patients. Follow-up blood samples showed normalization of all markers but CD11b, which was persistently increased. Utilizing cellular markers, we observed that peripheral blood eosinophils from infants with RSV LRTD are in a more activated state compared to eosinophils of controls, which normalizes only partially during convalescence.

Multifactor dimensionality reduction reveals gene-gene interactions associated with multiple sclerosis susceptibility in African Americans

Multiple sclerosis (MS) is a common disease of the central nervous system characterized by inflammation, myelin loss, gliosis, varying degrees of axonal pathology, and progressive neurological dysfunction. Multiple sclerosis exhibits many of the characteristics that distinguish complex genetic disorders including polygenic inheritance and environmental exposure risks. Here, we used a highly efficient multilocus genotyping assay representing variation in 34 genes associated with inflammatory pathways to explore gene-gene interactions and disease susceptibility in a well-characterized African-American case-control MS data set. We applied the multifactor dimensionality reduction (MDR) test to detect epistasis, and identified single-IL4R(Q576R)- and three-IL4R(Q576R), IL5RA(-80), CD14(-260)- locus association models that predict MS risk with 75-76% accuracy (P<0.01). These results demonstrate the importance of exploring both main effects and gene-gene interactions in the study of complex diseases.

Asymmetric usage of antagonist charged residues drives interleukin-5 receptor recruitment but is insufficient for receptor activation

The cyclic peptide AF17121 (VDECWRIIASHTWFCAEE) is a library-derived antagonist for human Interleukin-5 receptor alpha (IL5Ralpha). We have previously demonstrated that AF17121 mimics Interleukin-5 (IL5) by binding in a region of IL5Ralpha that overlaps the IL5 binding epitope. In the present study, to explore the functional importance of the amino acid residues of AF17121 required for effective binding to, and antagonism of, IL5Ralpha, each charged residue was subjected to site-directed mutagenesis and examined for IL5Ralpha interaction by using a surface plasmon resonance biosensor. One residue, Arg(6), was found to be essential for receptor antagonism; its replacement with either alanine or lysine completely abolished the interaction between AF17121 and IL5Ralpha. Other charged residues play modulatory roles. One class consists of the N-terminal acidic cluster (Asp(2) and Glu(3)) for which alanine replacement decreased the association rate. A second class consists of His(11) and the C-terminal acidic cluster (Glu(17) and Glu(18)) for which alanine replacement increased the dissociation rate. Binding model analysis of the mutants of the latter class of residues indicated the existence of conformational rearrangement during the interaction. On the basis of these results, we propose a model in which Arg(6) and N-terminal acidic residues drive the encounter complex, while Arg(6), His(11), and C-terminal acidic residues are involved in stabilizing the final complex. These data argue that the charged residues of AF17121 are utilized asymmetrically in the pathway of inhibitor-receptor complex formation to deactivate the receptor function. The results also help focus emerging models for the mechanism by which IL5 activates the IL5Ralpha-betac receptor system.

Cytokine recognition by human interleukin 5 receptor

The activation of interleukin 5 (IL-5) receptor is a dynamic process that depends on specific interaction of IL-5 with IL-5 receptor alpha, the formation of oligomeric receptor complexes with receptor beta, and the initiation of cytoplasmic phosphorylation events. These steps culminate in the triggering of a cellular response. Important advances have been made recently in understanding the molecular mechanisms of cytokine recognition, receptor assembly, and signal triggering. Cytokine recognition can be envisioned by relating structure to function in IL-5 and IL-5 receptor alpha. A pair of charge-complementary regions plays an essential role in the specific interaction between IL-5 receptor alpha and IL-5. Moreover, peptide library methodology has led to the discovery of IL-5 receptor alpha antagonists that mimic key elements in IL-5 receptor recognition. Because IL-5 has been implicated in the pathology of eosinophil-related inflammatory diseases, revealing the key recognition elements of IL-5, IL-5 mimetic peptides, and IL-5 receptor alpha could help drive the design of new compounds for therapeutic treatment against allergic inflammatory diseases such as asthma.

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.

Receptor Epitope Usage by an Interleukin-5 Mimetic Peptide

The cyclic peptide AF17121 is a library-derived antagonist for human interleukin-5 (IL5) receptor alpha (IL5Ralpha) and inhibits IL5 activity. Our previous results have demonstrated that the sixth arginine residue of the peptide is crucial for the inhibitory effect and that several acidic residues in the N- and C-terminal regions also make a contribution, although to a lesser extent (Ruchala, P., Varadi, G., Ishino, T., Scibek, J., Bhattacharya, M., Urbina, C., Van Ryk, D., Uings, I., and Chaiken, I. (2004) Biopolymers 73, 556-568). However, the recognition mechanism of the receptor has remained unresolved. In this study, AF17121 was fused to thioredoxin by recombinant DNA techniques and examined for IL5Ralpha interaction using a surface plasmon resonance biosensor method. Kinetic analysis revealed that the dissociation rate of the peptide.receptor complex is comparable with that of the cytokine.receptor complex. The fusion peptide competed with IL5 for both biological function and interaction with IL5Ralpha, indicating that the binding sites on the receptor are shared by AF17121 and IL5. To define the epitope residues for AF17121, we defined its binding footprint on IL5Ralpha by alanine substitution of Asp(55), Asp(56), Glu(58), Lys(186), Arg(188), and Arg(297) of the receptor. Marked effects on the interaction were observed in all three fibronectin type III domains of IL5Ralpha, in particular Asp(55), Arg(188), and Arg(297) in the D1, D2, and D3 domains, respectively. This footprint represents a significant subset of that for IL5 binding. The fact that AF17121 mimics the receptor binding capability of IL5 but antagonizes biological function evokes several models for how IL5 induces activation of the multisubunit receptor system.

Increased eosinophil-lineage committed progenitors in the lung of allergen-challenged mice

BACKGROUND

There is increasing evidence that hemopoietic progenitor cells may traffic from bone marrow to sites of allergen exposure in asthma and undergo in situ differentiation, contributing to ongoing airway inflammation. However, the isolation and detailed phenotyping of true CD34 + progenitors from lung tissue during an allergen-induced airway eosinophilia has not been performed.

OBJECTIVE

We attempted to isolate and investigate the in vivo kinetics of hemopoietic progenitor cells and production of eosinophilopoietic mediators in the lung.

METHODS

In a mouse model of allergic airway inflammation, cells were extracted from lung tissue by enzymatic digestion. Total (CD34 + 45 + ) and eosinophil lineage committed (CD34 + 45 + IL-5Ralpha + ) progenitors were enumerated by flow cytometry. Outcome measurements were made 2, 6, 12, 24, 48, and 72 hours and 7 and 14 days after allergen challenge.

RESULTS

Compared with saline control, CD34 + 45 + progenitors were elevated between 6 and 48 hours ( P < .05), attenuated by 72 hours and subsequently increased by 14 days ( P > .05). CD34 + 45 + IL-5Ralpha + progenitors were transiently elevated at 6 hours ( P < .05) before a return to preallergen levels by 12 hours and a subsequent increase at 14 days ( P < .05). Bronchoalveolar lavage eosinophils were increased at 2 hours, peaking at 72 hours ( P < .00625) and declining by 14 days. Both IL-5 and eotaxin levels were increased by 2 hours, peaking at 12 hours ( P < .05) and 24 hours ( P < .05), respectively.

CONCLUSION

We propose that the increase in CD34 + 45 + IL-5Ralpha + cells and the eosinophilopoietic mediators IL-5 and eotaxin in the lung after allergen exposure may promote in situ differentiation of eosinophils that contribute to ongoing allergic airway inflammation.

Differential control of eosinophil survival by glucocorticoids

Glucocorticoids are effective drugs for eosinophil-related disorders, such as asthma and allergy. Previous studies have demonstrated that glucocorticoids increase eosinophil apoptosis and block the survival effect of submaximal concentrations of interleukin-5 (IL-5). We investigated the effect of glucocorticoids on eosinophil survival in the presence of a higher concentration of IL-5 (1 ng/ml), comparable to IL-5 levels in bronchoalveolar lavage and sputum specimens from patients with asthma. In contrast to incubation in the presence of submaximal concentrations of IL-5, the addition of dexamethasone (DEX) to media containing 1 ng/ml IL-5 led to a significant increase in eosinophil cell viability from 58 +/- 6.9% to 87 +/- 2.4% ( p < 0.005) after 72 hours in culture. We found that RU486 blocked the DEX effect on cell viability confirming that glucocorticoid receptor functions are required. We investigated the possibility that the glucocorticoid enhancement of eosinophil survival may be due to an effect on IL-5 receptor expression. Our results show that the IL-5 associated decrease in IL-5 receptor alpha-subunit expression was blocked significantly after 24 hrs in culture with media containing IL-5 plus DEX compared to IL-5 alone. It is tempting to speculate that the observed glucocorticoid enhancement of eosinophil survival in the presence of elevated concentrations of IL-5 could be a mechanism that contributes to glucocorticoid resistance in asthma.

Soluble interleukin-5 receptor alpha is increased in acute exacerbation of chronic obstructive pulmonary disease

BACKGROUND

During chronic obstructive pulmonary disease (COPD) exacerbations (AE-COPD), an influx of eosinophils into the bronchial mucosa has been described. Eosinophilic cationic protein (ECP) and soluble interleukin-5 receptor alpha (sIL5Ralpha) are secreted by eosinophils and increased in eosinophilic airway diseases.

METHODS

We studied ECP and sIL5Ralpha expression in patients with COPD compared to healthy controls and smokers and investigated a possible association to viral exacerbations of COPD. Expression of sIL5Ralpha in serum was analyzed by ELISA and ECP by the Uni-Cap system. Induced sputum from patients with COPD was analyzed for six different respiratory viruses by nested PCR.

RESULTS

ECP and sIL5Ralpha were significantly elevated in AE-COPD subjects (n = 54) compared to healthy controls (n = 11, p = 0.018). Furthermore, there was a significant increase in sIL5Ralpha, but not in ECP, in 30 patients with virus-associated AE-COPD compared to smokers without COPD (n = 16) and healthy controls. The increase in FEV(1) after resolution of the AE-COPD correlated with the decrease in sIL5Ralpha (r = 0.269, p = 0.034).

CONCLUSIONS

sIL5Ralpha is increased in AE-COPD and not affected by smoking like ECP. sIL5Ralpha is increased in patients with virus-associated AE-COPD compared to smokers and controls. Concentrations of sIL5Ralpha mirror changes in the clinical status and lung function. These data support the involvement of eosinophils in acute exacerbations of COPD.

[The effects of anti-inflammatory and anti-asthmatic agents on CD34+ hematopoietic cells in bone marrow of asthmatic mice]

OBJECTIVE

To observe the effects of glucocorticoids and cysteinyl leukotrienes 1 receptor antagonist on CD(34)(+) hematopoietic cells, and to study the rationality of a bone marrow-targeting anti-inflammatory strategy.

METHODS

Twenty-four BALB/c mice were sensitized and challenged by 1% ovalbumin (OVA) to establish the asthmatic model. Asthmatic mice were challenged by 1% OVA and divided into 4 groups: fed by sterile saline (group A), prednisone (group B), montelukast (group C) and prednisone plus montelukast (group D) respectively for two consecutive weeks. The mice were killed at 24 h after the last challenge, then bronchoalveolar lavage fluid (BALF), peripheral blood and bone marrow were prepared. Eosinophils in peripheral blood and BALF, nucleate cells in BALF, peripheral blood and bone marrow were counted. The percentage of CD(34)(+) cells, CD(4)(+), CD(8)(+) T lymphocyte to nucleate cells in peripheral blood and bone marrow were counted by flow cytometry. Immunocytochemistry and in situ hybridization were employed to detect the hematopoietic cells expression of CD(34)(+) and IL-5Ralpha mRNA in bone marrow (CD(34)(+) IL-5Ralpha mRNA(+) cells).

RESULTS

The number of EOS in BALF and peripheral blood and the number of CD(34)(+) cells in peripheral blood and bone marrow in group A were [(18.3 +/- 1.3) x 10(5)/L], [(2.5 +/- 0.4) x 10(8)/L], [(9.6 +/- 5.1) x 10(7)/L] and [(7.7 +/- 3.2) x 10(7)/femur] respectively, compared with the corresponding indices in group B [(4.6 +/- 1.7) x 10(5)/L, (1.5 +/- 0.3) x 10(8)/L, (3.9 +/- 2.1) x 10(7)/L, (3.3 +/- 1.8) x 10(7)/femur] and group D [(3.7 +/- 1.4) x 10(5)/L, (1.7 +/- 0.3) x 10(8)/L, (4.1 +/- 1.8) x 10(7)/L, (2.2 +/- 0.7) x 10(7)/femur]; the differences all were significant (all P < 0.01). The number of bone marrow CD(34)(+) IL-5Ralpha mRNA(+) in group B and D were (23 +/- 7)% and (21 +/- 4)%, as compared with the corresponding index in group A [(37 +/- 4)%], the differences were significant (P < 0.01); the number of eosinophils in BALF in group C was (12.2 +/- 1.1) x 10(5)/L, as compared with the corresponding index in group A [(18.3 +/- 1.3) x 10(5)/L], the difference was significant (P < 0.05).

CONCLUSIONS

Prednisone probably inhibits the proliferation, differentiation and emigration of CD(34)(+) cells in the bone marrow of asthmatic mice, and inhibits eosinophilopoiesis in bone marrow, eosinophil migration into peripheral blood and recruitment to the airways. Montelukast may suppress eosinophil infiltrating into lungs of asthmatic mice, but it does not inhibit the proliferation and emigration of CD(34)(+) cells and does not show apparent synergistic effect with prednisone.

Kinetic interaction analysis of human interleukin 5 receptor alpha mutants reveals a unique binding topology and charge distribution for cytokine recognition

Human interleukin 5 receptor alpha (IL5Ralpha) comprises three fibronectin type III domains (D1, D2, and D3) in the extracellular region. Previous results have indicated that residues in the D1D2 domains are crucial for high affinity interaction with human interleukin 5 (IL5). Yet, it is the D2D3 domains that have sequence homology with the classic cytokine recognition motif that is generally assumed to be the minimum cytokine-recognizing unit. In the present study, we used kinetic interaction analysis of alanine-scanning mutational variants of IL5Ralpha to define the residues involved in IL5 recognition. Soluble forms of IL5Ralpha variants were expressed in S2 cells, selectively captured via their C-terminal V5 tag by anti-V5 tag antibody immobilized onto the sensor chip and examined for IL5 interaction by using a sandwich surface plasmon resonance biosensor method. Marked effects on the interaction kinetics were observed not only in D1 (Asp(55), Asp(56), and Glu(58)) and D2 (Lys(186) and Arg(188)) domains, but also in the D3 (Arg(297)) domain. Modeling of the tertiary structure of IL5Ralpha indicated that these binding residues fell into two clusters. The first cluster consists of D1 domain residues that form a negatively charged patch, whereas the second cluster consists of residues that form a positively charged patch at the interface of D2 and D3 domains. These results suggest that the IL5 x IL5Ralpha system adopts a unique binding topology, in which the cytokine is recognized by a D2D3 tandem domain combined with a D1 domain, to form an extended cytokine recognition interface.

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.