Interleukin-13 mediates airways hyperreactivity through the IL-4 receptor-alpha chain and STAT-6 independently of IL-5 and eotaxin

Interleukin (IL)-13 is a central mediator of the processes underlying the induction of airways hyperreactivity (AHR) in the allergic lung. However, the mechanisms by which IL-13 induces AHR and the associated role of inflammatory infiltrates as effector cells has not been fully elucidated. In this investigation, we show that intratracheal administration of IL-13 induces AHR in the presence and absence of inflammation. The initial AHR response (peak, 6 to 24 h; preinflammatory phase [PIP]) was dissociated from inflammation (eosinophilia) and mucus hypersecretion but was critically regulated by signaling through the IL-4 receptor alpha chain (IL-4Ralpha) and signal transducers and activators of transcription (STAT)-6. The second response (> 24 h, inflammatory phase [IP]) was characterized by an amplified AHR, eosinophil accumulation, and mucus hypersecretion. These features of the IP were not observed in IL-4Ralpha- or STAT-6-deficient mice. To determine the role of eosinophils in the induction of IP AHR and mucus hypersecretion, we administered IL-13 to IL-5-, eotaxin-, and IL-5/eotaxin- deficient mice. IL-13-mediated eosinophil accumulation was significantly attenuated (but not ablated) in IL-5-, eotaxin-, or IL-5/eotaxin-deficient mice. However, IL-13-induced AHR and mucus secretion occurred independently of IL-5 and/or eotaxin. These findings demonstrate that IL-13 can induce AHR independently of these eosinophil regulatory cytokines and mucus hypersecretion. Furthermore, IL-13-induced AHR, eosinophilia, and mucus production are critically dependent on the IL-4Ralpha chain and STAT-6.

IL-13 induces eosinophil recruitment into the lung by an IL-5- and eotaxin-dependent mechanism

BACKGROUND

IL-13 induces several characteristic features of asthma, including airway eosinophilia, airway hyperresponsiveness, and mucus overproduction; however, the mechanisms involved are largely unknown.

OBJECTIVE

We hypothesized that IL-13-induced inflammatory changes in the lung were dependent in part on IL-5 and eotaxin, two eosinophil-selective cytokines.

METHODS

Recombinant murine IL-13 was repeatedly administered to the lung by intranasal delivery until the characteristic features of asthma developed. To analyze the role of IL-5 and eotaxin, we subjected eotaxin gene-targeted, IL-5 gene-targeted, eotaxin/IL-5-double-deficient, IL-5 transgenic, and wild-type mice of the Balb/C background to the experimental regime.

RESULTS

The induction of IL-13-mediated airway eosinophilia was found to occur independently of eosinophilia in the blood or bone marrow, indicating that IL-13-induced airway inflammation is primarily mediated by local effects of IL-13 in the lung. Eosinophil recruitment into both the lung tissue and bronchoalveolar lavage fluid was markedly attenuated in IL-5-deficient mice in comparison with wild-type controls. Accordingly, IL-13 delivery to IL-5 transgenic mice resulted in a large increase in airway eosinophils in comparison with wild-type mice. Interestingly, IL-13-induced eosinophilia in the bronchoalveolar lavage fluid of eotaxin-deficient mice was not impaired; however, these same mice failed to mount a significant tissue eosinophilia in response to IL-13. Finally, IL-13-induced mucus production was not affected by the presence of IL-5 or eotaxin, suggesting that IL-13-induced mucus secretion is mechanistically dissociated from airway eosinophilia.

CONCLUSION

Selective components of the IL-13-induced asthma phenotype--airway eosinophilia but not mucus secretion--are differentially regulated by IL-5 and eotaxin. IL-5 is required for IL-13 to induce eosinophilia throughout the lung, whereas eotaxin regulates the distribution of airway eosinophils.

Tryptase 4, a new member of the chromosome 17 family of mouse serine proteases

Genomic blot analysis raised the possibility that uncharacterized tryptase genes reside on chromosome 17 at the complex containing the three genes that encode mouse mast cell protease (mMCP) 6, mMCP-7, and transmembrane tryptase (mTMT). Probing of GenBank's expressed sequence tag data base with these three tryptase cDNAs resulted in the identification of an expressed sequence tag that encodes a portion of a novel mouse serine protease (now designated mouse tryptase 4 (mT4) because it is the fourth member of this family). 5'- and 3'-rapid amplification of cDNA ends approaches were carried out to deduce the nucleotide sequence of the full-length mT4 transcript. This information was then used to clone its approximately 5.0-kilobase pair gene. Chromosome mapping analysis of its gene, sequence analysis of its transcript, and comparative protein structure modeling of its translated product revealed that mT4 is a new member of the chromosome 17 family of mouse tryptases. mT4 is 40-44% identical to mMCP-6, mMCP-7, and mTMT, and this new serine protease has all of the structural features of a functional tryptase. Moreover, mT4 is enzymatically active when expressed in insect cells. Due to its 17-mer hydrophobic domain at its C terminus, mT4 is a membrane-anchored tryptase more analogous to mTMT than the other members of its family. As assessed by RNA blot, reverse transcriptase-polymerase chain reaction, and/or in situ hybridization analysis, mT4 is expressed in interleukin-5-dependent mouse eosinophils, as well as in ovaries and testes. The observation that recombinant mT4 is preferentially retained in the endoplasmic reticulum of transiently transfected COS-7 cells suggests a convertase-like role for this integral membrane serine protease.

A pathological function for eotaxin and eosinophils in eosinophilic gastrointestinal inflammation

Although eosinophils have been implicated in the pathogenesis of gastrointestinal disorders, their function has not been established. Using a murine model of oral antigen-induced eosinophil-associated gastrointestinal disease, we report the pathological consequences of eosinophilic inflammation and the involvement of eotaxin and eosinophils. Exposure of mice to enteric-coated antigen promotes an extensive T helper 2-associated eosinophilic inflammatory response involving the esophagus, stomach, small intestine and Peyer's patches as well as the development of gastric dysmotility, gastromegaly and cachexia. Electron microscopy shows eosinophils in proximity to damaged axons, which indicated that eosinophils were mediating a pathologic response. In addition, mice deficient in eotaxin have impaired eosinophil recruitment and are protected from gastromegaly and cachexia. These results establish a critical pathological function for eotaxin and eosinophils in gastrointestinal allergic hypersensitivity.

Distinct spatial requirement for eosinophil-induced airways hyperreactivity

T helper (Th)-2-derived cytokines and their involvement in the recruitment and activation of inflammatory cells crucially orchestrate asthma pathogenesis. A notable cellular component of this allergy-induced inflammation is the eosinophil. However, whether the eosinophil is an obligatory mediator for enhancing airways hyperreactivity (AHR) to cholinergic stimuli, a watershed of the asthmatic lung, is somewhat controversial. In this investigation we have endeavoured to define the spatial requirements for IL-4 and IL-13, and the downstream effector molecules, IL-5 and the CC chemokine eotaxin, for the recruitment of eosinophils and the development of AHR in a murine model of allergic pulmonary disease. These studies are of particular importance considering clinical trials, with either the soluble IL-4Ralpha subunit or a humanized anti-IL-5 antibody, are being conducted. Interestingly, our studies show that depletion of both IL-4 and IL-13 is necessary to ablate pulmonary eosinophilia and AHR, and that this may be attributed to the role these cytokines play in regulating the expression of the eosinophil- activating molecules, IL-5 and eotaxin. While it is clear that depletion of IL-5 diminishes pulmonary eosinophilia, we demonstrate in BALB/c mice that a deficiency in both IL-5 and eotaxin is necessary to abolish both the trafficking of eosinophils to the lung and AHR. However, in contrast to the neutrophil-rich inflammation observed in mice deficient in both IL-4 and IL-13, inflammation per se in mice deficient in both IL-5 and eotaxin is significantly attenuated. This suggests that asthma immunotherapy may be better directed towards the eosinophil- activating molecules IL-5 and eotaxin, rather than towards pleiotrophic molecules such IL-4 and IL-13, which are additionally important in modulating alternative inflammatory responses.

Interleukin-5-mediated allergic airway inflammation inhibits the human surfactant protein C promoter in transgenic mice

Allergen challenge in the lung of humans and animals is associated with surfactant dysfunction, but the mechanism of this effect has not been established. By using a murine model of asthma we now report the effect of allergen-induced airway inflammation on the expression of transgenes regulated by the human surfactant protein (hSP)-C promoter. The hSP-C 3.7-kilobase pair promoter was used to direct the expression of eotaxin, an eosinophil-selective chemokine, into the lungs of several transgenic lines. As expected, the transgenic mice expressed increased amounts of eotaxin mRNA and protein compared with wild-type mice. Surprisingly, following allergen challenge, there was a marked down-regulation of transgene mRNA in three independent transgenic lines. The down-regulation was in contrast to other related proteins such as endogenous eotaxin and surfactant protein D levels, which were both increased following allergen challenge. Consistent with specific down-regulation of the eotaxin transgene, there was no increase in pulmonary eosinophil levels in the transgenic mice above that found in wild-type mice. Analysis of hSP-C transgenic mice with distinct reporter genes and 3'-untranslated regions revealed that allergen challenge was directly affecting the hSP-C promoter. We hypothesized that allergen-induced down-regulation of the hSP-C promoter was related to the eosinophilic inflammation. To test this, we blocked eosinophilic inflammation in the lungs by treating mice with neutralizing antiserum against interleukin-5. Interestingly, this treatment also blocked allergen-induced inhibition of the hSP-C promoter. These results establish that allergic airway inflammation is associated with up-regulation of the surfactant proteins primarily involved in immunity, whereas down-regulation of the surfactant protein primarily involved in maintaining airway patency. Furthermore, the marked down-regulation of the hSP-C promoter is interleukin-5-dependent, implying a critical role for eosinophilic inflammation. These results suggest that alterations in surfactant protein levels may contribute to immune and airway dysfunction in asthma.

Elemental signals regulating eosinophil accumulation in the lung

In this review we identify the elemental signals that regulate eosinophil accumulation in the allergic lung. We show that there are two interwoven mechanisms for the accumulation of eosinophils in pulmonary tissues and that these mechanisms are linked to the development of airways hyperreactivity (AHR). Interleukin-(IL)-5 plays a critical role in the expansion of eosinophil pools in both the bone marrow and blood in response to allergen provocation of the airways. Secondly, IL-4 and IL-13 operate within the allergic lung to control the transmigration of eosinophils across the vascular bed into pulmonary tissues. This process exclusively promotes tissue accumulation of eosinophils. IL-13 and IL-4 probably act by activating eosinophil-specific adhesion pathways and by regulating the production of IL-5 and eotaxin in the lung compartment. IL-5 and eotaxin co-operate locally in pulmonary tissues to selectively and synergistically promote eosinophilia. Thus, IL-5 acts systemically to induce eosinophilia and within tissues to promote local chemotactic signals. Regulation of IL-5 and eotaxin levels within the lung by IL-4 and IL-13 allows Th2 cells to elegantly co-ordinate tissue and peripheral eosinophilia. Whilst the inhibition of either the IL-4/IL-13 or IL-5/eotaxin pathways resulted in the abolition of tissue eosinophils and AHR, only depletion of IL-5 and eotaxin concurrently results in marked attenuation of pulmonary inflammation. These data highlight the importance of targeting both IL-5 and CCR3 signalling systems for the resolution of inflammation and AHR associated with asthma.

Gastrointestinal eosinophils

The gut-associated lymphoid tissue (GALT) is composed of lymphocytes residing in Peyer's patches, lamina propria, and intraepithelial compartments. In addition to these features which distinguish GALT from other peripheral sites of the immune system, the gastrointestinal immune system is also composed of resident eosinophils. Eosinophils are generally considered to be peripheral blood leukocytes that have an important pro-inflammatory role in various immune disorders. Although most research concerning this cell has focused on understanding its trafficking and function in the blood and lung, recent studies have also started to elucidate its regulation and function in the gastrointestinal tract. Interestingly, eosinophil numbers in the gastrointestinal tract are substantially higher than in other tissues. At baseline (healthy conditions), most eosinophils reside in the lamina propria in the stomach and intestine. Eosinophil homing to these sites occurs during embryonic development and their levels in perinatal mice are comparable to those in adults, indicating that their homing is not dependent upon the presence of intestinal flora. Furthermore, eosinophil localization to the lamina propria at baseline is critically regulated by eotaxin, a chemokine constitutively expressed throughout the gastrointestinal tract. Although eotaxin is required for eosinophil homing, its expression in the esophagus is not sufficient for eosinophil accumulation, since this organ is devoid of eosinophils at baseline. During Th2-associated inflammatory conditions (e.g. interleukin (IL)-5 overexpression or oral allergen challenge), marked increases of eosinophils occur not only in the lamina propria but also in Peyer's patches. The accumulation of Peyer's patch eosinophils, which mainly occurs in the outer cortex and interfollicular regions, is critically regulated by IL-5 and less significantly by eotaxin, suggesting the involvement of other eosinophil chemokines in this lymphoid compartment. Preliminary investigations have shown that gastrointestinal eosinophils express the alpha4beta7 integrin and that this molecule is responsible, in part, for eosinophil homing. In summary, eosinophils are resident cells of the gastrointestinal immune system whose levels can be induced by antigen exposure under Th2 conditions, in a manner that is critically regulated by eotaxin and IL-5. We propose that eosinophils are integral members of the gastrointestinal immune system and are likely to be important in innate, regulatory and inflammatory immune responses.

An etiological role for aeroallergens and eosinophils in experimental esophagitis

Eosinophil infiltration into the esophagus is observed in diverse diseases including gastroesophageal reflux and allergic gastroenteritis, but the processes involved are largely unknown. We now report an original model of experimental esophagitis induced by exposure of mice to respiratory allergen. Allergen-challenged mice develop marked levels of esophageal eosinophils, free eosinophil granules, and epithelial cell hyperplasia, features that mimic the human disorders. Interestingly, exposure of mice to oral or intragastric allergen does not promote eosinophilic esophagitis, indicating that hypersensitivity in the esophagus occurs with simultaneous development of pulmonary inflammation. Furthermore, in the absence of eotaxin, eosinophil recruitment is attenuated, whereas in the absence of IL-5, eosinophil accumulation and epithelial hyperplasia are ablated. These results establish a pathophysiological connection between allergic hypersensitivity responses in the lung and esophagus and demonstrate an etiologic role for inhaled allergens and eosinophils in gastrointestinal inflammation.

Murine eotaxin-2: a constitutive eosinophil chemokine induced by allergen challenge and IL-4 overexpression

The generation of tissue eosinophilia is governed in part by chemokines; initial investigation has identified three chemokines in the human genome with eosinophil selectivity, referred to as eotaxin-1, -2, and -3. Elucidation of the role of these chemokines is dependent in part upon analysis of murine homologues; however, only one murine homologue, eotaxin-1, has been identified. We now report the characterization of the murine eotaxin-2 cDNA, gene and protein. The eotaxin-2 cDNA contains an open reading frame that encodes for a 119-amino acid protein. The mature protein, which is predicted to contain 93 amino acids, is most homologous to human eotaxin-2 (59.1% identity), but is only 38.9% identical with murine eotaxin-1. Northern blot analysis reveals three predominant mRNA species and highest constitutive expression in the jejunum and spleen. Additionally, allergen challenge in the lung with Aspergillus fumigatus or OVA revealed marked induction of eotaxin-2 mRNA. Furthermore, eotaxin-2 mRNA was strongly induced by both transgenic over-expression of IL-4 in the lung and administration of intranasal IL-4. Analysis of eotaxin-2 mRNA expression in mice transgenic for IL-4 but genetically deficient in STAT-6 revealed that the IL-4-induced expression was STAT-6 dependent. Recombinant eotaxin-2 protein induced dose-dependent chemotactic responses on murine eosinophils at concentrations between 1-1000 ng/ml, whereas no activity was displayed on murine macrophages or neutrophils. Functional analysis of recombinant protein variants revealed a critical role for the amino terminus. Thus, murine eotaxin-2 is a constitutively expressed eosinophil chemokine likely to be involved in homeostatic, allergen-induced, and IL-4-associated immune responses.

Analysis of the CC chemokine receptor 3 gene reveals a complex 5' exon organization, a functional role for untranslated exon 1, and a broadly active promoter with eosinophil-selective elements

To understand the regulation of CC chemokine receptor 3 (CCR3) expression, its gene structure and promoter have been characterized. The CCR3 gene contains 4 exons that give rise to multiple messenger RNA (mRNA) species by alternative splicing. Exon 1 is present in all transcripts, whereas exon 2 or 3 is present at low frequency (< 10%). Exon 4 contains the open reading frame and 11 bp of the 5' untranslated region. Northern analysis revealed 4 species of CCR3 mRNA. Direct sequencing revealed that the first 1 kb of the promoter and exon 1 contained only one mutation in 19 individuals, indicating that the CCR3 promoter and exon 1 are conserved between individuals. The first 1.6 kb of the 5' flanking region of exon 1 contained promoter elements including a TATA box and motifs for myeloid transcription factors and had strong promoter activity in eosinophilic, lymphoid, myeloid, and respiratory epithelial cell lines. Deletion analysis revealed differential regulation of the CCR3 promoter in eosinophilic and epithelial cells suggesting the presence of lineage-specific elements. Interestingly, exon 1 enhanced the activity of the promoter and this effect was especially prominent in eosinophilic cells. Thus, the human CCR3 gene has a complex 5' exon structure, a conserved promoter with strong activity in multiple cell types, and a functional 5' untranslated exon.

Peyer's patch eosinophils: identification, characterization, and regulation by mucosal allergen exposure, interleukin-5, and eotaxin

The gastrointestinal immune system is traditionally thought to be composed of lymphocytes located within Peyer's patches and the lamina propria. We have recently reported that eosinophils also reside in the gastrointestinal tract during healthy states, in particular, within the lamina propria, and that these cells substantially increase after oral allergen exposure. We now demonstrate the presence of eosinophils in Peyer's patches and characterize the signals that regulate the accumulation of eosinophils in Peyer's patches. In contrast to the lamina propria, intestinal Peyer's patches have very low levels of eosinophils under healthy states. However, elevated levels of interleukin-5 (IL-5), generated by transgenic or pharmacologic approaches, result in a dramatic increase in eosinophil levels in Peyer's patches. Most eosinophils are located in the outer cortex and interfollicular regions of the Peyer's patches. To dissect the mechanism of eosinophil trafficking to Peyer's patches, the role of eotaxin was examined. Mice transgenic for IL-5 and genetically deficient in eotaxin were found to have reduced levels of eosinophils in Peyer's patches compared with IL-5-transgenic mice. To prove that eosinophils also traffic to Peyer's patches in wild-type mice, allergic hypersensitivity was induced and Peyer's patches were examined. Exposure to mucosal allergen promoted marked accumulation of eosinophils in Peyer's patches and this process was attenuated in eotaxin-deficient mice. In summary, these data demonstrate that elevated levels of IL-5 and mucosal allergen exposure promote eotaxin-dependent eosinophil trafficking to Peyer's patches. These studies suggest that eosinophils may cooperate with lymphocytes in the development of mucosal immune responses in the gastrointestinal tract. (Blood. 2000;96:1538-1544)

A critical role for eotaxin in experimental oral antigen-induced eosinophilic gastrointestinal allergy

Despite marked advances in the understanding of allergic responses, the mechanisms regulating gastrointestinal allergy are not very well understood. We have developed a model of antigen-induced eosinophil-associated gastrointestinal allergy and characterized the role of eotaxin and IL-5. Challenge of allergen-sensitized mice with oral allergen, in the form of enteric-coated beads, resulted in marked allergen-specific IgG(1) and IgE, Th(2)-type (IL-4 and IL-5) cytokine production, and eosinophil accumulation in the blood and small intestine. In the genetic absence of eotaxin, a chemokine constitutively expressed in the gastrointestinal tract, eosinophil recruitment into the small intestine was ablated, and these mice developed enhanced eosinophil accumulation in the blood compared with wild-type mice. Interestingly, in the absence of IL-5, allergen challenge promoted partial eosinophil accumulation into the small intestine and a decline in circulating eosinophil levels. Collectively, these results establish that the accumulation of gastrointestinal eosinophils is antigen induced, can occur independent of IL-5, and provides a molecular mechanism to explain the dichotomy between peripheral blood and tissue eosinophilia. Furthermore, eotaxin is identified as a critical regulator of antigen-induced eosinophilic inflammation in the gastrointestinal tract.

Postnatal mammary gland development requires macrophages and eosinophils

Interactions between mammary epithelial and mesenchymal cells including fibroblasts and adipocytes are crucial for the proper postnatal development of the mammary ductal tree. Often overlooked, however, are the migrant cells that enter tissues at different stages of development. In this paper we identify two such cell types, macrophages and eosinophils, that are recruited around the growing terminal end buds (TEBs) during postnatal development. An important role for leukocytes in mammary gland ductal outgrowth is first demonstrated by depleting mice of leukocytes using sub-lethal (gamma)-irradiation. This treatment results in a curtailment of mammary gland epithelial development that is completely rescued by bone-marrow transplantation, concurrent with a restoration of macrophage and eosinophil recruitment around the growing ducts. Using mice homozygous for a null mutation in the gene for CSF1 (Csfm(op)/Csfm(op)), the major growth factor for macrophages, we show that in the absence of CSF1, the population of macrophages in mammary glands is depleted. In this mutant, the formation of TEBs, their outgrowth into the fat pad and the branching of the resultant ducts are all impaired. Similarly, by using mice homozygous for a null mutation in the gene for eotaxin, a major chemokine for local recruitment of eosinophils in tissue, we identify eotaxin as the necessary and sufficient chemokine responsible for eosinophil recruitment around TEBs. In the absence of eosinophils, mammary gland branch formation and to a lesser extent TEB formation are reduced. Our data show that CSF1-regulated macrophages, in collaboration with eotaxin-regulated eosinophils, have essential and complementary functions in regulating the branching morphogenesis of the mammary gland.

The effect of IL-5 and eotaxin expression in the lung on eosinophil trafficking and degranulation and the induction of bronchial hyperreactivity

The mechanisms regulating the selective migration and degranulation of eosinophils in the asthmatic lung and the subsequent development of airways hyperreactivity (AHR) have not been fully delineated. In this investigation, we have employed a novel transgene model to facilitate the dissection of the contributions of IL-5 and/or eotaxin to eosinophil function in the absence of complex tissue signals derived from the allergic lung. Gene transfer of IL-5 and/or eotaxin to the lungs of naive mice induced a pronounced and selective airways eosinophilia, but did not result in eosinophil degranulation or AHR. Airways eosinophilia occurred independently of the induction of a blood eosinophilia, but was markedly augmented by the coexpression of both cytokines and/or by the transient mobilization of eosinophils from the bone marrow by the administration of i.v. IL-5. However, for eosinophil degranulation and AHR to occur, the inhalation of Ag was required in association with IL-5 and eotaxin expression. Investigations in IL-5-deficient mice linked eosinophilia, and not solely IL-5 and eotaxin, with the induction of AHR. Furthermore, eosinophil degranulation and AHR were dependent on CD4+ T cells. Importantly, this investigation shows that IL-5 regulates eosinophilia within the lung as well as in the circulation and also amplifies eotaxin-induced chemotaxis in the airway compartment. Moreover, the interplay between these cytokines, CD4+ T cells, and factors generated by Ag inhalation provides fundamental signals for eosinophil degranulation and the induction of AHR.

Molecular analysis of CCR-3 events in eosinophilic cells

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

The R576 IL-4 receptor alpha allele correlates with asthma severity

BACKGROUND

Atopic disorders, including asthma, are very prevalent, affecting up to 40% of populations, and their incidence is on the rise. Although environmental factors are important in the development of atopy, there is a strong genetic predisposition. Several genes and chromosomal regions have been linked to atopy and asthma, supporting the polygenic nature of these disorders. IL-4 and IL-13 are T(H)2 cytokines with numerous activities that contribute to allergic inflammation and asthma. Both IL-4 and IL-13 use the IL-4 receptor alpha chain (IL-4Ralpha) as a component of their respective receptor systems. Allelic variants of IL-4Ralpha have been reported, and the R576IL-4Ralpha allele was recently shown to be a risk factor for atopy.

OBJECTIVE

We sought to determine whether the R576 allele was associated with the prevalence or clinical severity of asthma.

METHODS

We developed a rapid, reliable, PCR-based assay to screen individuals for the R576IL-4Ralpha allele and used this assay to genotype prospectively recruited individuals with asthma (n = 149) and control subjects (n = 57).

RESULTS

There was a strong association of R576IL-4Ralpha with the prevalence and clinical severity of asthma. In a prospective cohort, homozygosity for R576 was significantly increased in individuals with asthma (n = 149, P =.03; relative risk 8.2) compared with controls (n = 57). Furthermore, 1 or 2 copies R576IL-4Ralpha correlated with asthma severity establishing a genotype-phenotype relationship and suggesting a gene dosage effect.

CONCLUSIONS

Thus R576IL-4Ralpha acts as an allergic asthma susceptibility and disease-modifying gene and may serve as a clinically useful marker of asthma severity.