The role of CD23 on allergen-induced IgE levels, pulmonary eosinophilia and bronchial hyperresponsiveness in mice

FCER2 T2206C variant associated with FENO levels in asthmatic children using inhaled corticosteroids: The PACMAN study

BACKGROUND

The FCER2 gene, via encoding of the CD23 receptor, plays an important role in the regulation of IgE responses. A genetic variant of the FCER2 gene (T2206C) was previously shown to be associated with IgE levels in asthmatic children. IgE sensitization has also been linked to increased levels of fractional exhaled nitric oxide (FENO).

OBJECTIVE

To investigate whether the FCER2 T2206C variant influences FENO levels in asthmatic children with a reported use of inhaled corticosteroids (ICS).

METHODS

This cross-sectional study involved 593 asthmatic children with a reported use of ICS, availability of FENO measurements and genotyping data on the FCER2 T2206C variant (rs28364072). An additive genetic model was assumed, and the association between the FCER2 T2206C variant and the log-transformed (ln) FENO levels was evaluated using linear regression analysis, adjusted for age, sex, adapted British Thoracic Society (BTS) treatment steps and atopy.

RESULTS

The mean age of the population was 9.1 ± 2.2 years, and the median of FENO levels was 13.0 ppb with an interquartile range (IQR) of (8.0-27.5 ppb). The minor allele (G) frequency of rs28364072 was 29.6%, and each extra copy of the G allele was significantly associated with a lower level of the geometric mean of FENO (log scale, β = -0.12, 95% CI: -0.23, -0.02).

CONCLUSION AND CLINICAL RELEVANCE

Our results showed that the FCER2 T2206C variant was significantly associated with lower FENO levels in carriers of the G allele. Nevertheless, this SNP contributed little to the variability in FENO levels in this patient population. Our findings contribute to the present knowledge on FENO in asthmatic children; however, future replication studies are required to establish the role of this gene in relation to FENO.

Preschool wheeze, genes and treatment

Preschool wheeze is a common but poorly understood cause of respiratory morbidity that is both distinct from and overlaps with infantile bronchiolitis and school age asthma. Attempts at classification by epidemiology, pathophysiology, therapeutic response and clinical phenotype are imperfect and yet fundamental to both treatment choice and research design. The four main therapeutic classes for preschool wheeze, namely beta₂ agonists, anticholinergics, corticosteroids and leukotriene modifiers are employed with variable and often scanty evidence base, with evidence for a genetic influence on response variations. The article will discuss the pharmacogenetics of the various options, summarise current treatment recommendations, and explore future research directions.

Approaches to target IgE antibodies in allergic diseases

IgE is the antibody isotype found at the lowest concentration in the circulation. However IgE can undeniably play an important role in mediating allergic reactions; best exemplified by the clinical benefits of anti-IgE monoclonal antibody (omalizumab) therapy for some allergic diseases. This review will describe our current understanding of the interactions between IgE and its main receptors FcεRI and CD23 (FcεRII). We will review the known and potential functions of IgE in health and disease: in particular, its detrimental roles in allergic diseases and chronic spontaneous urticaria, and its protective functions in host defense against parasites and venoms. Finally, we will present an overview of the drugs that are in clinical development or have therapeutic potential for IgE-mediated allergic diseases.

Cockroach protease allergen induces allergic airway inflammation via epithelial cell activation

Protease allergens are known to enhance allergic inflammation but their exact role in initiation of allergic reactions at mucosal surfaces still remains elusive. This study was aimed at deciphering the role of serine protease activity of Per a 10, a major cockroach allergen in initiation of allergic inflammation at mucosal surfaces. We demonstrate that Per a 10 increases epithelial permeability by disruption of tight junction proteins, ZO-1 and occludin, and enhances the migration of Monocyte derived dendritic cell precursors towards epithelial layer as exhibited by trans-well studies. Per a 10 exposure also leads to secretion of IL-33, TSLP and intracellular Ca²⁺ dependent increase in ATP levels. Further, in vivo experiments revealed that Per a 10 administration in mice elevated allergic inflammatory parameters along with high levels of IL-33, TSLP, IL-1α and uric acid in the mice lungs. We next demonstrated that Per a 10 cleaves CD23 (low affinity IgE receptor) from the surface of PBMCs and purified B cells and CD25 (IL-2 receptor) from the surface of PBMCs and purified T cells in an activity dependent manner, which might favour Th2 responses. In conclusion, protease activity of Per a 10 plays a significant role in initiation of allergic airway inflammation at the mucosal surfaces.

Inhibition of CD23-mediated IgE transcytosis suppresses the initiation and development of allergic airway inflammation

The epithelial lining of the airway tract and allergen-specific IgE are considered essential controllers of inflammatory responses to allergens. The human low affinity IgE receptor, CD23 (FcɛRII), is capable of transporting IgE or IgE-allergen complexes across the polarized human airway epithelial cell (AEC) monolayer in vitro. However, it remains unknown whether the CD23-dependent IgE transfer pathway in AECs initiates and facilitates allergic inflammation in vivo, and whether inhibition of this pathway attenuates allergic inflammation. To this end, we show that in wild-type (WT) mice, epithelial CD23 transcytosed both IgE and ovalbumin (OVA)-IgE complexes across the airway epithelial barrier, whereas neither type of transcytosis was observed in CD23 knockout (KO) mice. In chimeric mice, OVA sensitization and aerosol challenge of WT/WT (bone-marrow transfer from the WT to WT) or CD23KO/WT (CD23KO to WT) chimeric mice, which express CD23 on radioresistant airway structural cells (mainly epithelial cells) resulted in airway eosinophilia, including collagen deposition and a significant increase in goblet cells, and increased airway hyperreactivity. In contrast, the absence of CD23 expression on airway structural or epithelial cells, but not on hematopoietic cells, in WT/CD23KO (the WT to CD23KO) chimeric mice significantly reduced OVA-driven allergic airway inflammation. In addition, inhalation of the CD23-blocking B3B4 antibody in sensitized WT mice before or during airway challenge suppressed the salient features of asthma, including bronchial hyperreactivity. Taken together, these results identify a previously unproven mechanism in which epithelial CD23 plays a central role in the development of allergic inflammation. Further, our study suggests that functional inhibition of CD23 in the airway is a potential therapeutic approach to inhibit the development of asthma.

Helminth-induced CD19+CD23hi B cells modulate experimental allergic and autoimmune inflammation

Numerous population studies and experimental models suggest that helminth infections can ameliorate immuno-inflammatory disorders such as asthma and autoimmunity. Immunosuppressive cell populations associated with helminth infections include Treg and alternatively-activated macrophages. In previous studies, we showed that both CD4⁺CD25⁺ Treg, and CD4^– MLN cells from Heligmosomoides polygyus-infected C57BL/6 mice were able to transfer protection against allergic airway inflammation to sensitized but uninfected animals. We now show that CD4^–CD19⁺ MLN B cells from infected, but not naïve, mice are able to transfer a down-modulatory effect on allergy, significantly suppressing airway eosinophilia, IL-5 secretion and pathology following allergen challenge. We further demonstrate that the same cell population can alleviate autoimmune-mediated inflammatory events in the CNS, when transferred to uninfected mice undergoing myelin oligodendrocyte glycoprotein_(p35–55)-induced EAE. In both allergic and autoimmune models, reduction of disease was achieved with B cells from helminth-infected IL-10^−/− donors, indicating that donor cell-derived IL-10 is not required. Phenotypically, MLN B cells from helminth-infected mice expressed uniformly high levels of CD23, with follicular (B2) cell surface markers. These data expand previous observations and highlight the broad regulatory environment that develops during helminth infections that can abate diverse inflammatory disorders in vivo.

Protease inhibitors in respiratory disease: focus on asthma and chronic obstructive pulmonary disease

Respiratory diseases, such as asthma and chronic obstructive pulmonary disease (COPD), are a major health burden on society and current treatment modalities for these diseases have not significantly changed over the past 40 years. The only major pharmacological advancement for the treatment of these diseases has been to increase the duration of action of bronchodilators (asthma: salmeterol; COPD: tiotropium bromide) and glucocorticosteroids (asthma: fluticasone propionate) and, increasingly, to formulate these agents in the same delivery device. Despite our increasing understanding of the cell and molecular biology of these diseases, the development of novel treatments remains beyond the reach of the scientific community. Proteases are a family of proteins with diverse biological activity, which are found in abundance within the airways of asthma and COPD, and have been implicated in the pathogenesis of these diseases. The targeting of proteases, including mast cell tryptase, neutrophil elastase and matrix metalloprotease with low-molecular-weight inhibitors, has highlighted the potential role of these enzymes in mediating certain aspects of the disease process in preclinical studies. Several challenges remain regarding the development of protease inhibitors, including the synthesis of highly potent and specific inhibitors, and target validation in man.

Increased serum ADAM8 concentration in patients with drug-induced eosinophilic pneumonia-ADAM8 expression depends on a the allergen route of entry

BACKGROUND

ADAM8 (a disintegrin and a metalloprotease 8) has been linked to asthma and eosinophilic pneumonia (EP). ADAM8 cleaves a variety of substrates and is a sheddase for CD23, the low affinity IgE receptor. The concentration of soluble ADAM8 (sADAM8) is increased in bronchoalveolar lavage fluid (BALF) from patients with smoking-induced acute eosinophilic pneumonia (AEP) and chronic eosinophilic pneumonia (CEP), but not drug-induced EP (Drug-EP). In AEP, the BALF sADAM8 concentration significantly correlates with the soluble CD23 concentration (sCD23).

METHODS

To evaluate the involvement of ADAM8 in the pathogenesis of eosinophilic pneumonia, we measured the concentrations of sADAM8 and its substrate, soluble CD23 (sCD23), in serum from patients with AEP, CEP, and Drug-EP. We also measured the change in the sADAM8 concentration after a provocation test.

RESULTS

In contrast to the BALF findings, serum sADAM8 concentrations were increased in Drug-EP (mean+/-SEM; 639.6+/-49.15) and serum ADAM8 levels correlated positively with the serum sCD23 levels in patients with Drug-EP (P=0.0080, R(2)=0.8465). Serum sADAM8 concentrations were also increased in AEP (409+/-76.91) and CEP (644.7+/-87.03). Serum ADAM8 concentrations were also elevated after the provocation test.

CONCLUSION

Serum ADAM8 concentrations were elevated in Drug-EP, although the sADAM8 concentrations were not increased in the BALF in Drug-EP. Thus, the pathogenesis of AEP and Drug-EP may be distinct with regard to allergen exposure; AEP may be caused by the inhalation of antigens, whereas Drug-EP may be caused by bloodstream antigens. These findings indicate that ADAM8 levels reflect the route of eosinophilic inflammation in EP.

Molecular blocking of CD23 supports its role in the pathogenesis of arthritis

Background

CD23 is a differentiation/activation antigen expressed by a variety of hematopoietic and epithelial cells. It can also be detected in soluble forms in biological fluids. Initially known as the low-affinity receptor for immunoglobulin E (FcεRII), CD23 displays various other physiologic ligands such as CD21, CD11b/c, CD47-vitronectin, and mannose-containing proteins. CD23 mediates numerous immune responses by enhancing IgE-specific antigen presentation, regulating IgE synthesis, influencing cell differentiation and growth of both B- and T-cells. CD23-crosslinking promotes the secretion of pro-inflammatory mediators from human monocytes/macrophages, eosinophils and epithelial cells. Increased CD23 expression is found in patients during allergic reactions and rheumatoid arthritis while its physiopathologic role in these diseases remains to be clarified.

Methodology/Principal Findings

We previously generated heptapeptidic countrestructures of human CD23. Based on in vitro studies on healthy and arthritic patients' cells, we showed that CD23-specific peptide addition to human macrophages greatly diminished the transcription of genes encoding inflammatory cytokines. This was also confirmed by significant reduction of mediator levels in cell supernatants. We also show that CD23 peptide decreased IgE-mediated activation of both human and rat CD23⁺ macrophages. In vivo studies in rat model of arthritis showed that CD23-blocking peptide ameliorates clinical scores and prevent bone destruction in a dose dependent manner. Ex-vivo analysis of rat macrophages further confirmed the inhibitory effect of peptides on their activation. Taken together our results support the role of CD23 activation and subsequent inflammatory response in arthritis.

Conclusion

CD23-blocking peptide (p30A) prevents the activation of monocytes/macrophages without cell toxicity. Thus, targeting CD23 by antagonistic peptide decreases inflammatory markers and may have clinical value in the treatment of human arthritis and allergic reactions involving CD23.

A role for MC3R in modulating lung inflammation

In this study we set out to ascertain whether melanocortin peptides could be potential therapeutic agents in allergic and non-allergic models of lung inflammation by identifying the receptor(s) involved using a molecular, genetic and pharmacological approach. Western blot analyses revealed expression of the melanocortin receptor (MCR) type 1 and 3 on alveolar macrophages from wild-type mice. Alveolar macrophage incubation, with the selective MC3R agonist [D-TRP(8)]-gamma-MSH and pan-agonist alpha-MSH but not the selective MC1R agonist MS05, led to an increase in cAMP in wild-type macrophages. This increase occurred also in macrophages taken from recessive yellow (e/e; bearing a mutant and inactive MC1R) mice but not from MC3R-null mice. In an allergic model of inflammation, the pan-agonist alpha-MSH and selective MC3R agonist [D-TRP(8)]-gamma-MSH displayed significant attenuation of both eosinophil and lymphocyte accumulation but not IL-5 levels in wild-type and recessive yellow e/e mice. However in MC3R-null mice, alpha-MSH failed to cause a significant inhibition in these parameters, highlighting a preferential role for MC3R in mediating the anti-inflammatory effects of melanocortins in this model. Utilising a non-allergic model of LPS-induced lung neutrophilia, the pan-agonist alpha-MSH and selective MC3R agonist [D-TRP(8)]-gamma-MSH displayed significant attenuation of neutrophil accumulation and inhibition of TNF-alpha release. Thus, this study highlights that melanocortin peptides inhibit leukocyte accumulation in a model of allergic and non-allergic inflammation and this protective effect is associated with activation of the MC3R. The inhibition of leukocyte accumulation is via inhibition of TNF-alpha in the non-allergic model of inflammation but not IL-5 in the allergic model. These data have highlighted the potential for selective MC3R agonists as novel anti-inflammatory therapeutics in lung inflammation.

Influence of age on the development of immunological lung response in intrauterine undernourishment

OBJECTIVE

We investigated the effect of intrauterine undernourishment on some features of asthma using a model of allergic lung inflammation in rats. The effects of age at which the rats were challenged (5 and 9 wk) were also evaluated.

METHODS

Intrauterine undernourished offspring were obtained from dams that were fed 50% of the nourished diet of counterparts and were immunized at 5 and 9 wk of age. They were tested for immunoglobulin E anti-ova titers (by passive cutaneous anaphylaxis), cell count in the bronchoalveolar fluid, leukotriene concentration, airway reactivity, mucus production, and blood corticosterone and leptin concentrations 21 d after immunologic challenge.

RESULTS

Intrauterine undernourishment significantly reduced the antigen-specific immunoglobulin E production, inflammatory cell infiltration into airways, mucus secretion, and production of leukotrienes B(4)/C(4) in the lungs in both age groups compared with respective nourished rats. The increased reactivity to methacholine that follows antigen challenge was not affected by intrauterine undernourishment. Corticosterone levels increased with age in the undernourished rats' offspring, but not in the nourished rats' offspring. Undernourished offspring already presented high levels of corticosterone before inflammatory stimulus and were not modified by antigen challenge. Leptin levels increased with challenge in the nourished rats but not in the undernourished rats and could not be related to corticosterone levels in the undernourished rats.

CONCLUSION

Intrauterine undernourishment has a striking and age-dependent effect on the offspring, reducing lung allergic inflammation.

Allergic airways disease develops after an increase in allergen capture and processing in the airway mucosa

Airway mucosal dendritic cells (AMDC) and other airway APCs continuously sample inhaled Ags and regulate the nature of any resulting T cell-mediated immune response. Although immunity develops to harmful pathogens, tolerance arises to nonpathogenic Ags in healthy individuals. This homeostasis is thought to be disrupted in allergic respiratory disorders such as allergic asthma, such that a potentially damaging Th2-biased, CD4(+) T cell-mediated inflammatory response develops against intrinsically nonpathogenic allergens. Using a mouse model of experimental allergic airways disease (EAAD), we have investigated the functional changes occurring in AMDC and other airway APC populations during disease onset. Onset of EAAD was characterized by early and transient activation of airway CD4(+) T cells coinciding with up-regulation of CD40 expression exclusively on CD11b(-) AMDC. Concurrent enhanced allergen uptake and processing occurred within all airway APC populations, including B cells, macrophages, and both CD11b(+) and CD11b(-) AMDC subsets. Immune serum transfer into naive animals recapitulated the enhanced allergen uptake observed in airway APC populations and mediated activation of naive allergen-specific, airway CD4(+) T cells following inhaled allergen challenge. These data suggest that the onset of EAAD is initiated by enhanced allergen capture and processing by a number of airway APC populations and that allergen-specific Igs play a role in the conversion of normally quiescent AMDC subsets into those capable of inducing airway CD4(+) T cell activation.

FCER2: a pharmacogenetic basis for severe exacerbations in children with asthma

BACKGROUND

Although inhaled corticosteroids (ICSs) generally protect against severe exacerbations in asthma, they may result in elevated IgE levels, which are associated with exacerbations.

OBJECTIVE

To determine whether variation in the low-affinity IgE receptor gene, FCER2, is associated with severe exacerbations defined as emergency department visits and/or hospitalizations in patients with asthma on ICSs.

METHODS

We resequenced, then genotyped 10 FCER2 single nucleotide polymorphisms (SNPs) in 311 children randomized to inhaled budesonide as part of the Childhood Asthma Management Program. We evaluated the association of FCER2 variants with IgE levels and presence or absence of severe exacerbations over the 4-year clinical trial. We also evaluated differences in cellular expression of the novel FCER2 SNP, T2206C.

RESULTS

In white subjects, 3 FCER2 SNPs were significantly associated (P < .05) with elevated 4-year IgE level; each was also associated with increased severe exacerbations. Final multivariable models demonstrated associations between T2206C and severe exacerbations in both white and African American children (hazard ratio, 3.95; 95% CI, 1.64-9.51; and hazard ratio, 3.08; 95% CI, 1.00-9.47), despite ICS use. Interaction models supported a true gene-environment effect in white subjects (interaction P = .004). T2206C was also associated with decreased FCER2 expression (P = .02).

CONCLUSION

FCER2 predicts the likelihood of treatment protocol success in asthma. The associations of T2206C with IgE level, severe exacerbations, and FCER2 expression may provide a mechanistic basis for the observed findings.

CLINICAL IMPLICATIONS

Genetic variation in FCER2 may help form a prognostic model for ICS response in asthma.

Elevated soluble ADAM8 in bronchoalveolar lavage fluid in patients with eosinophilic pneumonia

BACKGROUND

ADAM (a disintegrin and metalloprotease) family members, characterized by a metalloprotease and a disintegrin domain, are membrane-anchored glycoproteins involved in proteolysis and cell adhesion. ADAM8 might have an important role in allergic inflammation. It can cleave a variety of substrates and is a sheddase for VCAM-1 and CD23, the low-affinity IgE receptors.

METHODS

To evaluate the contribution of ADAM8 to the pathogenesis of eosinophilic pneumonia (EP), we measured the concentrations of soluble ADAM8 (sADAM8) and its substrates, soluble VCAM-1 (sVCAM-1) and soluble CD23 (sCD23), in bronchoalveolar lavage fluid from patients with smoking-induced acute eosinophilic pneumonia (AEP), chronic idiopathic eosinophilic pneumonia (CEP), and drug-induced eosinophilic pneumonia (drug-EP).

RESULTS

The sADAM8 and sVCAM-1 concentrations were increased in AEP and CEP. The sCD23 concentration was elevated in AEP. In AEP, but not CEP, the sADAM8 concentration significantly correlated with those of both sVCAM and sCD23.

CONCLUSION

The pathogenesis of AEP, CEP, and drug-EP was distinct with regard to ADAM8. Our results are the first to associate ADAM8 with eosinophilic responses and lung inflammation in humans.

The level of IgE produced by a B cell is regulated by norepinephrine in a p38 MAPK- and CD23-dependent manner

Although the causes of asthma vary, the severity of the disease correlates with the level of IgE produced. In this study we show that mice produced less IgE when they were depleted of the neurotransmitter norepinephrine (NE) before the administration of Ag. The suppression was prevented when a beta2-adrenergic receptor (beta2AR)-selective agonist was administered, suggesting that NE stimulated the beta2AR to regulate the level of an IgE response in vivo. Although the cell targeted by NE to produce this effect in vivo is unknown, we show in vitro that the level of IgE increased on a per cell basis without an effect on class switch recombination when NE stimulated the beta2AR on a B cell directly. The beta2AR-induced increase in IgE depended on p38 MAPK but not protein kinase A activation, was due to an increased rate of mature IgE mRNA transcription, and was lost when beta2AR-deficient B cells were used. Also, CD23 transcription was increased in a p38 MAPK-dependent manner and resulted in an increased level of soluble CD23 (sCD23). The beta2AR-induced increase in sCD23 was associated with IgE up-regulation and possibly interacted with CD21/CD19. Using B cells from respective knockout mice, data showed that the beta2AR-induced increase in IgE depended on B cell expression of CD23, CD21, and CD19. These findings suggest that at least one mechanism by which endogenous B cell activity in vivo is regulated by NE involves stimulation of the beta2AR on the B cell alone to increase the level of IgE produced in a p38 MAPK- and sCD23-dependent manner.

Immunoglobulin E: role in asthma and allergic disease: lessons from the clinic

The role of immunoglobulin E (IgE) in allergic asthmatic disease is well established. Allergen-specific IgE binds to its cognate receptors, thus triggering a series of cellular events. These events include presentation of antigen by dendritic cells and the degranulation of mast cells and basophils to release numerous factors that play an integral part in potentiating the disease symptoms. Studies in the mouse indicate that a reduction in IgE levels could lead to significant attenuation of the allergic inflammatory response associated with diseases such as asthma, making IgE a target for the development of new therapeutic agents. Omalizumab (Xolair), a recombinant humanised monoclonal anti-IgE antibody that blocks the interaction of IgE with its receptors, is the first anti-IgE agent to undergo clinical development. Several clinical studies have been performed in adults and children with moderate-to-severe allergic asthma to evaluate the efficacy and safety of this agent, but which have also enabled an insight into the role of IgE in human disease. IgE plays a significant role in a number of allergic conditions including allergic rhinitis and allergies to various substances. Recent data suggests that local IgE production may occur in mucosal tissues and that locally significant concentrations of IgE, not reflected by serum IgE concentrations, indicate that it may play a role in non-atopic as well as atopic disease.

Early exposure to a nonhygienic environment alters pulmonary immunity and allergic responses

The hygiene hypothesis suggests that early life exposure to a nonhygienic environment that contains endotoxin reduces the risk of developing allergic diseases. The mechanisms underlying the hygiene hypothesis are unclear and may involve subtle immune system interactions that occur during maturation. Experimental objectives of this study were to use a novel animal model to test the hygiene hypothesis and to characterize early life immune system responses to a nonhygienic environment. Mice were reared in corn dust, a grain-processing byproduct with a high-endotoxin content and microbial products or in a low-endotoxin environment. The influence of early or later life exposure to corn dust on a subsequent allergen stimulus (ovalbumin) was assessed by bronchoalveolar lavage (BAL) cell analysis, lung histology, serum IgE, and BAL cytokine measurements. The influence of the corn dust environment on the developing pulmonary immune system was assessed by BAL cell analysis and immunostaining of lung tissue. The corn dust environment contained significantly more endotoxin ( P < 0.001), and the dust exposures attenuated the cellular inflammatory response to ovalbumin in the adult mouse ( P < 0.01) but did not reduce serum IgE levels or alter baseline BAL fluid proinflammatory cytokine levels. The corn dust environment did not induce significant neutrophilia in lavage fluid but significantly increased the number of antigen-presenting cells in alveolar walls early in life by ∼37%. In conclusion, exposure to a nonhygienic environment did not induce significant airway neutrophilia, yet altered the population of immunologically active cells in the lung and reduced subsequent allergic inflammation.

What targets have knockouts revealed in asthma?

There have been numerous studies of mice rendered genetically deficient of various genes in the context of allergic inflammatory airway disease. These studies have provided invaluable information about basic immune processes, but have also been considered to be useful in predicting novel pharmacological targets. In this review, the effect of a wide range of individual knockouts (KO) on the development of asthma-like pathologies in mice is compiled and considered. How the results of these studies compare with effects of agents that interfere with the function of each gene product, where known, is also described. Finally, a personal view of the utility of these studies in drug development is presented.

Pharmacological characterisation of the adenosine receptor mediating increased ion transport in the mouse isolated trachea and the effect of allergen challenge

The effect of adenosine on transepithelial ion transport was investigated in isolated preparations of murine trachea mounted in Ussing chambers. The possible regulation of adenosine receptors in an established model of allergic airway inflammation was also investigated. Mucosally applied adenosine caused increases in short-circuit current (I(SC)) that corresponded to approximately 50% of the response to the most efficacious secretogogue, ATP (delta I(SC) 69.5 +/- 6.7 microA cm2). In contrast, submucosally applied adenosine caused only small (<20%) increases in I(SC), which were not investigated further. The A1-selective (N6-cyclopentyladenosine, CPA, 1 nM-10 microM), A2A-selective (2-p-(2-carboxyethyl)phenethylamino-5'-N-ethylcarboxoamido adenosine; CGS 21680; 0.1-100 microM) and A3-selective (1-deoxy-1-[6-[[(3-iodophenyl)-methyl]amino]-9H-purin-9-yl]-N-methyl-beta-D-ribofuranuronamide; IB-MECA; 30 nM-100 microM) adenosine receptor agonists were either equipotent or less potent than adenosine, suggesting that these receptors do not mediate the response to adenosine. The A1 receptor selective antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX; 10 nM-1 microM) caused a rightward shift of the adenosine concentration-effect curve only at 1 microM. The mixed A2A/A2B receptor antagonist 4-(2-[7-amino-2-(2-furyl)[1,2,4]triazolo[2,3-a][1,3,5]triazin-5-ylamino]ethyl)phenol (ZM 241385) also caused rightward shift of the adenosine concentration-effect curve, again only at micromolar concentrations, suggestive of the involvement of A2B receptors. In preparations from animals sensitised to ovalbumin and challenged over 3 days with aerosol ovalbumin, a decrease in baseline I(SC) was observed and responses to ATP were diminished. Similarly, the amplitude of responses to adenosine were attenuated although there was no change in potency. These results suggest that the A2B receptor mediates the I(SC) response to adenosine in the mouse trachea. This receptor does not appear to be regulated in a standard asthma model.

Immunomodulation in asthma: a distant dream or a close reality?

The search for new treatments of asthma or any other disease for that matter is an infinite exercise. The scope for discovering new forms of treatment has increased now more than ever due to a better understanding of the molecular pathogenesis of the disease. Regulation of biomolecular or immunological events could occur at numerous points in the disease pathogenesis. This review describes the strategies to regulate the inappropriate immune responses that are elicited after exposure to an allergen. One such successful therapy is treatment with omalizumab, the anti-IgE antibody. Other therapies include cytokine antagonists, transcription factor antagonists, immunostimulatory DNA therapy, cytokine therapy and anti-T cell strategies. All these agents have been shown to be promising and could serve as an alternative approach to the treatment of asthma and maybe other allergic diseases.

Soluble CD23 and interleukin-1 receptor antagonist in human asthmatics following antigen challenge

Two postulated intrinsic anti-inflammatory mechanisms in asthma include the low affinity IgE receptor, or CD23, and interleukin 1 receptor antagonist (IL-1ra). We investigated the role these mediators play in the asthmatic response by measuring local levels in human asthmatics before and after segmental allergen challenge and examined the effect of inhaled corticosteroids on soluble CD23 and IL-1ra levels. Ten subjects underwent bronchoscopy at baseline and 24 hours after antigen challenge. Prior to challenge and every 12 hours afterward subjects received beclomethasone 252 microg or placebo. Fluid was analyzed for sCD23 and IL-1ra using ELISA immunoassays. Eosinophil percentages significantly increased at 24 hours following antigen challenge. sCD23 levels were generally undetectable at baseline and increased significantly following antigen challenge. IL-1ra levels increased 28-fold in the late-phase response. Beclomethasone significantly reduced the late-phase eosinophil percentage at 24 hours compared with placebo but did not attenuate late-phase sCD23 or IL-1ra levels. Our data showed a significant rise in the levels of two mediators thought to play an important role in the attenuation of the asthmatic response. The finding that steroid treatment did not enhance these levels suggests that this may be an independent approach to asthma therapy that should be investigated.

Hyper IgE in New Zealand black mice due to a dominant-negative CD23 mutation

Immunoglobulin E (IgE) plays a critical role in both resistance to parasitic infection and allergy to environmental antigens. The IgE response is in turn regulated by the B-cell co-receptor CD23, and CD23-deficient mice show exaggerated IgE responses and airway hyper-responsiveness. In this report, we show that New Zealand black (NZB) mice express a variant CD23 allele, with mutations in both the C-lectin-binding domain and stalk region, which fails to bind IgE at high affinity and has reduced expression on the cell surface. Expression of the variant CD23 chain interferes with trimerisation of the receptor and has a dominant-negative effect leading to reduced IgE binding in crosses between NZB and other strains. Genetic mapping shows that the variant CD23 leads to an exaggerated primary IgE response, which is independent of other strain-specific effects. These results suggest that NZB mice or mice carrying the variant allele will be useful models for studying both allergy and quantitative traits associated with atopy. The exaggerated IgE response provides an explanation for the natural resistance of NZB mice to parasitic infection by Leishmania.

Anti-immunoglobulin E therapy for asthma

The role of immunoglobulin E (IgE) in allergic asthmatic disease is well established. Allergen-specific IgE binds to its cognate receptors, thus triggering a series of cellular events. These events include presentation of antigen by dendritic cells and the degranulation of mast cells and basophils to release numerous factors that play an integral part in potentiating the disease symptoms. Studies in the mouse indicate that a reduction in IgE levels could lead to significant attenuation of the allergic inflammatory response associated with diseases such as asthma, making IgE a target for the development of new therapeutic agents. Omalizumab (Xolair, a recombinant humanized monoclonal anti-IgE antibody that blocks the interaction of IgE with its receptors, is the first anti-IgE agent to undergo clinical development. Several clinical studies have been performed in adults and children with moderate-to-severe allergic asthma to evaluate the efficacy and safety of this agent. Treatment with omalizumab was well tolerated and showed clinical benefit in terms of a reduction in the frequency and number of asthma exacerbation episodes and lower usage of corticosteroids and other medications to control disease, along with improved quality of life. Such findings indicate that omalizumab represents a promising new treatment option for allergic asthma.

Lack of the transcriptional coactivator OBF-1 prevents the development of systemic lupus erythematosus-like phenotypes in Aiolos mutant mice

Here we show that mice lacking the zinc finger transcription factor Aiolos develop the symptoms of human systemic lupus erythematosus (SLE), which is characterized by the production of anti-dsDNA Ab and immune complex-mediated glomerulonephritis. This finding indicates that normal Aiolos function is necessary to maintain immune homeostasis and suppress the development of systemic autoimmune disease and implicates Aiolos as a possible candidate gene for SLE. Interestingly, Aiolos-null mice can no longer mount autoimmune reactions and completely fail to develop SLE when they are deficient for the B cell-specific transcription coactivator OBF-1. The lack of OBF-1 reverses several Aiolos mutant mouse phenotypes, such as B cell hyperproliferation, high expression of activation marker on B cells, and spontaneous germinal center formation. Unexpectedly, B cell development at the immature B cell stage is severely impaired in the bone marrow of Aiolos/OBF-1 double-deficient mice, demonstrating the key role of these factors in the transition from pre-B to immature B cells. Our results indicate that B cells play a crucial role in the development of SLE in Aiolos mutant mice and might be useful for the strategy of SLE treatment.

Chronic exposure to innocuous antigen in sensitized mice leads to suppressed airway eosinophilia that is reversed by granulocyte macrophage colony-stimulating factor

In this study we investigated the impact of chronic allergen exposure on airway inflammation and humoral responses in sensitized mice. We observed marked eosinophilia in the bronchoalveolar lavage, lung tissue, and peripheral blood after 2 wk of exposure. In contrast, eosinophilia was markedly reduced by 3 wk and completely resolved by 4 wk of exposure, despite the continued presence of Ag. Decreases in airway eosinophilia were associated with a robust humoral response. We observed that levels of OVA-specific IgE, IgG1, and IgG2a increased during the course of exposure. To assess whether continuous exposure to Ag impacts the ability of the lung to respond to subsequent Ag challenge, mice were exposed to either 2 or 4 wk of OVA in the context of GM-CSF. All groups were then rested for 28 days and exposed to OVA on three consecutive days. We observed a significant decrease in airway eosinophilia and IL-5 expression in the bronchoalveolar lavage and serum in mice initially exposed to 4 wk of OVA, compared with animals exposed to 2 wk only. However, in both groups expression of B7.2 on dendritic cells as well as CD25, CD69, and T1/ST2 on CD4(+) T cells was enhanced, suggesting immune activation. Delivery of rGM-CSF fully restored airway eosinophilia. This study shows that exposure to innocuous Ag alone does not lead to persistent eosinophilic airway inflammation, but rather to abrogated eosinophilia. This suppression can be reversed by GM-CSF.

Expression of CD21 and CD23 during human fetal development

Neonates produce lower levels of IgE compared with adults. Diminished IL-4 production and impaired up-regulation of CD40L by neonatal T cells could explain this, however other regulators of IgE production, such as CD21 and CD23, could contribute to reduced circulating IgE levels during fetal development. Heparinized blood samples were collected from adults and from the umbilical cord at premature and term births. Whole blood flow cytometry was used to assess the percentage of T (CD3(+)) and B (CD19(+)) lymphocytes expressing CD21 and/or CD23 at 26-29 (n = 3), 30-33 (n = 7), 34-37 (n = 5), and >37 (n = 11) wk of gestation, as well as in adults (n = 15). Plasma-soluble CD21 was also measured. At term, the percentage of CD21(+) and CD23(+) B cells was comparable to the adult, however, the percentage of cells positive for each of these surface antigens was decreased significantly before term. The percentage of T cells expressing CD21 from all gestations was significantly higher than the adult and the percentage positive decreased with increasing gestational age. Conversely, soluble CD21 levels increased with increasing gestation to be comparable to the adult by term. Thus, it is unlikely that altered expression of CD21 and CD23 on B cells contributes to the low level of IgE in the neonatal circulation unless functional differences occur or a lack of processing to the soluble form is important in regulating IgE production. However the abundance of CD21-positive T cells could alter the T- and B-cell interaction necessary for IgE switching by B cells and, thereby, especially with impaired IL-4 production, limit IgE production.

Inhalation of a harmless antigen (ovalbumin) elicits immune activation but divergent immunoglobulin and cytokine activities in mice

BACKGROUND

Exposure to aerosolized harmless antigen such as ovalbumin (OVA) has previously been shown to induce inhalation tolerance, a state characterized by inhibition of IgE synthesis and airway inflammation, upon secondary immunogenic antigen encounter. Immune events associated with this phenomenon are still poorly understood.

OBJECTIVE

The aim of this study was to investigate cellular and molecular mechanisms underlying this state of 'unresponsiveness'.

METHODS

After initial repeated OVA exposure, mice were subjected to a protocol of antigen-induced airway inflammation, encompassing two intraperitoneal injections of OVA adsorbed to aluminium hydroxide followed by airway challenge. We assessed immune events in the draining lymph nodes after sensitization, and in the lungs after challenge.

RESULTS

In animals initially exposed to OVA, we observed, at the time of sensitization, considerable expansion of T cells, many of which expressed the activation markers CD69 and CD25, as well as increased numbers of antigen-presenting cells, particularly B cells. While these animals produced low levels of IgE, the observed elevated levels of IgG1 signified isotype switching. Splenocytes and lymph node cells from OVA-exposed mice produced low levels of IL-4, IL-5, IL-13 and IFN-gamma, indicating aborted effector function of both T helper (Th)2- and Th1-associated cytokines. Real time quantitative polymerase chain reaction (PCR) (TaqMan) analysis of costimulatory molecules in the lungs after in vivo challenge showed that B7.1, B7.2, CD28 and CTLA-4 mRNA expression was low in animals initially exposed to OVA. Ultimately, these events were associated with abrogated airway inflammation and attenuated airway hyper-responsiveness. The decreased inflammation was antigen-specific and independent of IL-10 or IFN-gamma.

CONCLUSION

Initial exposure to OVA establishes a programme that prevents the generation of intact, fully functional inflammatory responses upon secondary antigen encounter. The absence of inflammation, however, is not associated with categorical immune unresponsiveness.

IgE regulation and roles in asthma pathogenesis

Asthma and the predisposition to produce IgE are inherited as linked traits in families. In patients IgE levels correlate with asthma severity and bronchial hyperresponsiveness. The concept that IgE plays a critical role in asthma pathogenesis has driven the development of IgE blockers, which are currently being introduced into clinical use. This review focuses on the mechanisms whereby IgE participates both in immediate hypersensitivity responses in the airways and in the induction of chronic allergic bronchial inflammation. The molecular genetic events that give rise to IgE production by B cells and the cellular and cytokine factors that support IgE production in the bronchial mucosal microenvironment are discussed. It is clear that much remains to be learned regarding the roles of IgE in asthma and the genetic and environmental influences that lead to its production. Over the next few years, the emerging experience with anti-IgE in patients will provide a more complete understanding of the mechanisms whereby IgE contributes to disease, as well as the therapeutic potential of its inhibition.

Cytokines in airway inflammation

With over 50 potential asthma mediators, cytokines are the latest group of substances which have been investigated for their potential role in this disease. The use of murine models of allergic inflammation has facilitated the investigation of the role of individual cytokines in this response. The use of targeted gene disruption, overexpression of genes and monoclonal antibodies directed against cytokines have allowed a detailed examination of the role cytokines play in IgE production, eosinophil recruitment and bronchial hyperresponsiveness, which are the characteristic features of the asthma phenotype. Despite the introduction of this new methodology, conflicting reports relating to the role of cytokines in allergic inflammation, highlight the complexity of allergic inflammation and challenge the notion that a single cytokine can explain the asthma phenotype.