Upregulation of IL-13 concentration in vivo by the IL13 variant associated with bronchial asthma

BACKGROUND

A substantial body of evidence exists to support the pivotal role of IL-13 in the pathogenesis of bronchial asthma. We recently found that a variant of the IL13 gene (Arg110Gln) is genetically associated with bronchial asthma, which is concordant with animal experiments using IL-13 in the development of asthma.

OBJECTIVE

To address whether the Gln110 variant of IL13 influences IL-13 function, contributing to the pathogenesis of bronchial asthma, we studied the functional properties of the variant.

METHODS

We generated 2 types of recombinant IL-13 proteins, the amino acids of which at 110 were arginine or glutamine, and analyzed the binding affinities with the IL-13 receptors, as well as the stability of the proteins. We further compared the relationship between the genotype and serum levels of IL-13.

RESULTS

The variant showed a lower affinity with the IL-13 receptor alpha2 chain, a decoy receptor, causing less clearance. The variant also demonstrated an enhanced stability in both human and mouse plasma. We further identified that asthmatic patients homozygous for the Gln110 variant have higher serum levels of IL-13 than those without the variant.

CONCLUSION

These results suggested that the variant might act as a functional genetic factor of bronchial asthma with a unique mechanism to upregulate local and systemic IL-13 concentration in vivo.

Genetic polymorphism of enzymes involved in xenobiotic metabolism and the risk of lung cancer

Chronic inhalation of cigarette smoke is a major risk factor for the development of lung cancer. It has been suggested that genetic susceptibility may contribute to the risk, because only a small portion of smokers develops the disease. Several polymorphisms that involve the metabolic activation or detoxification of carcinogens derived from cigarette smoke have been found to be associated with lung cancer risk. Many studies have focused on the relation between the distribution of polymorphic variants of different forms of the metabolic enzymes and lung cancer susceptibility. In this respect two groups of genetic polymorphisms of enzymes involved in xenobiotic metabolism, cytochrome P450 (CYP) and glutathione S-transferases (GSTs), have been discussed.CYP multigene superfamily consists of 10 subfamilies (CYP1-CYP10). A positive association between development of lung cancer and the mutant homozygous genotype ofCYP1A1 gene has been reported in several Japanese populations but such an association has not been observed in either Caucasians or African-Americans. The relation betweenCYP2D6 and lung cancer remains conflicting and inconclusive. Several polymorphisms have been identified at theCYP2E1 locus. No definitive link between the polymorphisms ofCYP2E1 and the risk of lung cancer has, however, been identified. The role of otherCYP2 isoforms in lung carcinogenesis has not been sufficiently investigated.GSTs form a superfamily of genes consisting of five distinct families, namedGSTA, GSTM, GSTP, GSTT andGSTS. The role ofGSTM, GSTT1 orGSTP1 polymorphism in modifying the lung cancer risk may be more limited than has been so far anticipated.Although some genetic polymorphisms discussed here have not shown significant increases/decreases in risk, individuals with differing genotypes may have different susceptibilities to lung cancer. Hopefully, in future studies it will be possible to screen for lung cancer using specific biomarkers.

Genetic variants of the receptors for thromboxane A2 and IL-4 in atopic dermatitis

Thromboxane A2 (TXA2) is an arachidonate metabolite which is considered to relate to chronic inflammation in atopic diseases characterized by elevated immunoglobulin E productivity. The elevation of immunoglobulin E levels involves many molecules including interleukin-4 (IL-4) and interleukin-4 receptor alpha chain (IL-4R alpha). To assess whether genetic variants of TXA2 receptor, IL-4 and IL-4R alpha genes relate to the elevation of serum immunoglobulin E levels in patients with atopic dermatitis (AD), we conducted an association study of genetic polymorphisms of TXA2 receptor (795C/T), IL-4 (-589C/T), and IL-4R alpha (Ile50Val) in a Japanese population (n = 789). The TXA2 receptor 795TT genotype strongly related to AD with high serum immunoglobulin E concentrations. AD patients with both TXA2 receptor 795TT genotype and the IL-4R alpha Ile50/Ile50 genotype showed the greatest immunoglobulin E concentrations. These results suggest TXA2 receptor polymorphism strongly interacts with IL-4R alpha polymorphism as a major determinant of high serum immunoglobulin E levels in AD.

IL-4 receptor alpha chain genetic polymorphism and total IgE levels in the English population: two-locus haplotypes are more informative than individual SNPs

The IL-4RA locus encodes for the alpha chain of the IL-4 receptor, and is both a functional and positional candidate gene for atopy and allergic disease. Recently Ober et al. have shown that the study of haplotypes at multiple loci in the IL-4RA gene could be more informative than the separate study of single nucleotide polymorphisms (SNPs). One hundred and fifty subjects affected by atopic asthma and 150 healthy control subjects were studied in the English population (Oxford district). Subjects and controls were genotyped for the Ile50Val, Ser478Pro and Gln551Arg polymorphism of the IL-4 receptor alpha chain. The distribution of haplotypes 50-478 shows a highly significant association with IgE levels. In particular, the haplotype Val50/Pro478 is much less frequent in subjects with IgE levels > 100 U mL-1 than in those with IgE levels < 100 U mL-1. Furthermore, the distribution of haplotype 50-551 shows a weak association with IgE levels that is lacking for 478-551 haplotypes. A lower frequency of the Val50/Pro478 haplotype is also observed among asthmatic subjects as compared to healthy controls. With regard to individual SNPs (50 478 and 551), no significant association has been observed with IgE levels or with asthma, thus confirming the higher informative value of the haplotype analysis as compared to separate study on SNPs.

Interleukin-4 and its alternatively spliced variant (IL-4delta2) in patients with atopic asthma

The interleukin-4 (IL-4) splice variant (IL-4delta2) is known to antagonize many biological activities of IL-4, and this challenges our understanding of the role of IL-4 in asthma. Studies that have used nonspecific antibodies, probes, and/or primers to quantify IL-4 in clinical samples would not have distinguished the expression of IL-4 from IL-4delta2. This is the first study to examine patients with chronic asthma and atopy for IL-4delta2 mRNA in their peripheral blood mononuclear cells without antigen stimulation, using a quantitative nested reverse-transcription polymerase chain reaction (RT-PCR) protocol. The median IL-4 mRNA copy number in cells from the patients with asthma was 2.8 logs higher than in a comparator group of patients with tuberculosis (p = 0.0005) and 4.5 logs higher (p = 0.0004) than in healthy control subjects. In contrast, IL-4delta2 expression in cells from patients with asthma was similar to that seen in cells from patients with tuberculosis. Hence, the median ratio of IL-4 to IL-4delta2 was 500-fold higher in the patients with asthma when compared with either patients with tuberculosis or healthy control subjects. The relative expression of IL-4 and IL-4delta2 may be a reason for the functional diversity of Th2 cells in different clinical conditions, and a hitherto unexplored mechanism for the pulmonary pathology in patients with atopic asthma.

Recent advances in understanding how interleukin 13 signals are involved in the pathogenesis of bronchial asthma

The prevalence of allergic disease has dramatically increased in recent decades, especially in urban and industrialized areas. Allergic diseases are disorders of the immune system, the results of complex interactions among various genetic and environmental factors. Among them, the important role of interleukin 13 (IL-13), a Th2-type cytokine, has recently emerged in the pathogenesis of bronchial asthma. Based on studies using mice, great attention has been paid to the direct effects of IL-13 on bronchial tissues. In this review, we describe recent advances in understanding the signal transduction mechanism of IL-13, the involvement of IL-13 signal-related genes as genetic factors in the pathogenesis of bronchial asthma, and the expression of IL-13 receptor on bronchial tissues. We describe potential strategies for targeting IL-13 signals to improve allergic states.

Genetic polymorphisms of CC chemokine receptor 3 in Japanese and British asthmatics

Whole genome scan analyses have revealed that chromosomal region 3p21-24, which contains a gene cluster of CC chemokine receptors such as CCR3, is possibly linked to asthma. Because CCR3 ligands play a pivotal role in the selective recruitment and activation of inflammatory cells in the asthmatic airway, the authors examined whether there is any association between asthma and the CCR3 gene polymorphisms. Three polymorphisms were identified using the single stranded conformational polymorphism method in Japanese (Asian) and British (Caucasian) subjects; one silent mutation T51C and two missense mutations G824A and T971C. These polymorphisms were examined in 391 Japanese subjects (210 asthmatics and 181 nonasthmatic controls) and 234 British subjects (142 asthmatics and 92 nonasthmatic controls). Asthma diagnosis was based on episodic symptoms, documented wheeze, and the presence of reversible airflow limitation. CCR3 T51C demonstrated a significant association with the diagnosis of asthma in the British population (odds ratio 2.35, p<0.01), but not in the Japanese population. Multiple logistic regression analysis also showed that CCR3 T51C was associated with asthma (odds ratio 2.83, p < 0.02), independent of atopic phenotypes such as high levels of total or house dust mite-specific immunoglobulin-E in serum. In conclusion, a significant association between asthma and CCR3 T51C polymorphism localized on chromosome 3p21 was found.

Imbalance production between interleukin-1beta (IL-1beta) and IL-1 receptor antagonist (IL-1Ra) in bronchial asthma

Genes of the IL-1 family encode three different peptides, IL-1alpha, IL-1beta, and IL-1Ra, respectively. IL-1 operates through IL-1RI, and is involved in airway inflammation in asthmatic subjects, whereas IL-1Ra appears to be a specific competitive inhibitor of IL-1. All genes are on chromosome 2q12-21 where genomewide searches have identified linkage for asthma. To test whether variants of IL-1 relate to asthma, we conducted a genetic association study in a Japanese population. We show that the A2 allele of IL1RN (encoding IL-1Ra) associates with nonatopic asthma [OR = 5.71, 95% CI: 1.63-19. 8, Pc = 0.007]. Both atopic and nonatopic asthmatics with the A2 allele had significantly lower serum IL-1Ra levels in both types of asthmatics. Peripheral blood cells from asthmatics with A2 alleles, however, produced as much IL-1 as did those with A1 homozygotes. Since Th1 and Th2 cytokines differentially regulate the ratio between IL-1beta and IL-1Ra, these findings suggest that dysregulation of IL-1beta/IL-1Ra, probably due to interaction between epithelium and immuno-competent cells in the airway, is important in asthma inflammation.

Atopy and the human IL-4 receptor alpha chain

BACKGROUND

Atopy is a common inherited disorder characterized by increased IgE responsiveness, but no functional analysis of the candidate genes related to atopy has been performed. IL-4 is important for B-cell production of IgE, and the human IL-4 receptor alpha chain (hIL-4Ralpha) is crucial for the binding and signal transduction of IL-4, so hIL-4Ralpha may be a candidate gene related to atopy.

OBJECTIVE

We examined the relationship between the variation at amino acid 50 of hIL-4Ralpha and atopic asthma.

METHODS

We performed a genetic study to investigate the relationship between the variation of amino acid 50 (isoleucine [Ile(50)] or valine [Val(50)]) and atopic asthma in a Japanese population and a functional study with the use of transfectants that expressed hIL4Ralpha bearing either Ile(50) or Val(50). Furthermore, we analyzed CD23 expression and IgE synthesis after IL-4 stimulation of peripheral blood mononuclear cells bearing either Ile(50) or Val(50).

RESULTS

The prevalence of Ile(50) was higher than that of Val(50) in individuals with atopic asthma, especially during childhood. In transfectants, germline epsilon transcription activity and Stat6 activity were upregulated by the Ile(50) variant, compared with Val(50), but receptor affinity for IL-4 was similar between the two. CD23 expression and IgE synthesis in response to IL-4 were augmented in Ile(50)-expressing peripheral mononuclear blood cells compared to cells expressing Val(50).

CONCLUSION

The Ile(50) variant of hIL-4Ralpha may be related to atopic asthma, particularly in children.

The Ile198Thr and Ala379Val variants of plasmatic PAF-acetylhydrolase impair catalytical activities and are associated with atopy and asthma

The platelet-activating factor (PAF) represents a phospholipid with complex biological functions, including involvement in inflammatory processes. The degrading enzyme PAF acetylhydrolase (PAFAH) represents a candidate for asthma and other atopic diseases. Two loss-of-function mutations of PAFAH are associated with severe asthma in Japanese individuals. Our aim was to look for further PAFAH variants in white populations, their possible association with atopic and asthmatic phenotypes, and their functional importance. We picked up three common variants in the PAFAH gene: Arg92His (exon 4), Ile198Thr (exon 7), and Ala379Val (exon 11). The known loss-of-function mutations were not seen. The variant allele Thr198 was found to be highly associated with total IgE concentrations in an atopic population (P=.009) and with "atopic asthma" in an asthmatic population (P=.008). The variant allele Val379 was found to be highly associated with "specific sensitization" in the atopic population (P=.002) and with "asthma" in the asthmatic population (P=.003). By use of recombinant PAFAH enzymes, the variant Val379 showed increased (14 microM) and Thr198 markedly increased (42 microM) KM values compared to the wild type (7 microM); furthermore, Vmax of Val379 was highly increased (132%). Thr198 and Val379 influence plasmatic PAFAH toward lower substrate affinities and therefore are very likely to prolong the activities of PAF. At the same time, they are associated with an increased risk to develop asthma and atopy. Thus, two PAFAH variants seem to play a key role in atopic and asthmatic processes in Caucasian populations.

Genetic variants of IL-13 signalling and human asthma and atopy

Asthma and atopy show epidemiological association and are biologically linked by T-helper type 2 (T(h)2) cytokine-driven inflammatory mechanisms. IL-4 operates through the IL-4 receptor (IL-4R, a heterodimer of IL-4Ralpha and either gammac or IL-13Ralpha1) and IL-13 operates through IL-13R (a heterodimer of IL-4Ralpha and IL-13Ralpha1) to promote IgE synthesis and IgE-based mucosal inflammation which typify atopy. Recent animal model data suggest that IL-13 is a central cytokine in promoting asthma, through the stimulation of bronchial epithelial mucus secretion and smooth muscle hyper-reactivity. We investigated the role of common genetic variants of IL-13 and IL-13Ralpha1 in human asthma, considering IgE levels. A novel variant of human IL-13, Gln110Arg, on chromosome 5q31, associated with asthma rather than IgE levels in case-control populations from Britain and Japan [peak odds ratio (OR) = 2.31, 95% CI 1.33-4.00]; the variant also predicted asthma and higher serum IL-13 levels in a general, Japanese paediatric population. Immunohistochemistry demonstrated that both subunits of IL-13R are prominently expressed in bronchial epithelium and smooth muscle from asthmatic subjects. Detailed molecular modelling analyses indicate that residue 110 of IL-13, the site of the charge-modifying variants Arg and Gln, is important in the internal constitution of the ligand and crucial in ligand-receptor interaction. A non-coding variant of IL-13Ralpha1, A1398G, on chromosome Xq13, associated primarily with high IgE levels (OR = 3. 38 in males, 1.10 in females) rather than asthma. Thus, certain variants of IL-13 signalling are likely to be important promoters of human asthma; detailed functional analysis of their actions is needed.

Variants of NOS1, NOS2, and NOS3 genes in asthmatics

Nitric oxide (NO) gas concentrations are higher in expired air in asthmatics. NO is synthesized by three isoforms of NO synthase (NOS) encoded by three distinct genes, NOS1, NOS2, and NOS3. Genome-wide searches have identified linkages to asthma on chromosomes 7, 12, and 17 where these three genes are localized. No association study, however, has been reported to date. To test whether variants of NOS1, NOS2, and NOS3 relate to asthma, a genetic association study was conducted in a British population (n = 300). Intragenic microsatellite variants of NOS1 were significantly associated with asthma [odds ratio (OR) = 2.08, 95% CI: 1.20-3.57 (95% CI), P = 0.008 (Pc = 0.048)], but not with IgE levels. Neither NOS2 nor NOS3 variants showed any association with asthma nor IgE levels. These findings suggest that NOS1 variants may be a significant contributor to asthma in a British population.

Nonpathogenic common variants of IFNGR1 and IFNGR2 in association with total serum IgE levels

Atopy is an immune disorder in which a Th2 dominant mechanism leads to high IgE levels and the clinical disorder asthma. It has been postulated that the Th1 cytokine IFNgamma, acting through its heterodimeric receptors, IFNgammaR1 and IFNgammaR2, in the induction/proliferation of Th1 cells, might suppress the Th2 responses that may underlie atopic asthma. However, neither murine nor human variants of IFNgamma associate with atopy. Several dysfunctional mutations have been identified in IFNgamma receptor genes (IFNGR1 and IFNGR2) in relation to severe and selective infections with poorly pathogenic organisms. However, little is known about common polymorphisms and their functional role in atopy. To test whether such variants of IFNGR1 and IFNGR2 relate to atopic asthma, we conducted a genetic association study in both British (n = 300) and Japanese (n = 200) populations. An intronic variant of IFNGR1 showed marginal association with total serum IgE levels in the British population compared with those with total IgE levels <30 IU/ml and those with >120-500 IU/ml [odds ratio = 2.00 (95% CI 1. 00-4.07), P = 0.048]. A coding variant, Gln64Arg of the IFNGR2, also associated with total serum IgE levels in the British population [chi(2) = 5.08, P = 0.024]. Further genetic and functional analyses are needed to clarify the role of variants of IFNgamma receptor genes in atopic immune disorder among different ethnic groups.

Variants of endothelin-1 and its receptors in atopic asthma

Endothelin-1 (ET-1) is a 21 amino acid peptide released from several types of bronchial cells. It operates through two types of receptors, type A(ET-RA) and type B(ET-RB) and has various activities in the pathophysiology of atopic asthma. These genes are localised on different chromosomes where genome-wide searches have identified linkage for atopic asthma, thus supporting the candidacy of ET-1 and its receptors for atopic asthma. A genetic association study was performed with variants of these three genes in both British (n = 300) and Japanese populations (n = 200). No significant association was found between variants of EDN1 and EDNRB genes, and atopic asthma in either population. However, variants of EDNRA gene showed a marginal association with atopy [odds = 0.39(95% CI: 0.17-0.89), p = 0.022, Pc = 0.066], especially with antigen specific IgE levels [odds = 0.31 (95% CI: 0.20-0.77), p = 0.006, Pc = 0.018] in the British population. These findings suggest that EDNRA is a major candidate locus for atopy on chromosome 4.

Chromosome 11q13 and atopic asthma

Asthma is a complex syndrome in which bronchial inflammation and smooth muscle hyperactivity lead to labile airflow obstruction. The commonest form of asthma is that due to atopy, which is an immune disorder where production of IgE to inhaled antigens leads to bronchial mucosal inflammation. The ultimate origins of asthma are interactive environmental and genetic factors. The genetics is acknowledged to be heterogeneous, and one chromosomal region of interest and controversy has been 11q13. To clarify the nature of the chromosome 11q13 effect in atopy and asthma, we conducted a genetic association study in subjects with marked atopic asthma and matched controls, which incorporated the study of 13 genetic variants over a distance of 10-12 cM and which took account of detailed immune and clinical phenotyping. Association with high IgE levels was limited to the interval flanked by D11S1335 and CD20 in a 0.8-Mb interval and was greatest for variants of Fc epsilonRIbeta and HTm4; these variants also associated with asthma (recurrent wheeze with labile airflow obstruction and need for regular inhaler treatment). At the more telomeric marker, D11S480, variants associated with asthma, but not with high IgE levels. The data might support the possibility of multiple loci relevant to atopic asthma on chromosome 11q13.

Cutting Edge: Dominant Effect of Ile50Val Variant of the Human IL-4 Receptor α-Chain in IgE Synthesis

Two variants of the IL-4R α-chain (IL-4Rα) gene have been recently identified in association with different atopic disorders. To clarify the etiological relationship between the two variants, we analyzed responsiveness to IL-4 of transfectants with four kinds of IL-4Rα carrying either Val or Ile at 50 and either Gln or Arg at 551. The substitution of Ile for Val augmented STAT6 activation, proliferation, and transcription activity of the Iε promoter by IL-4, whereas that of Arg for Gln did not change these IL-4 signals. Arg551 was not associated with atopic asthma in the Japanese population. CD23 expression and IgE synthesis by IL-4 were augmented in Ile50-bearing PBMC, compared with those bearing Val50. Taken together, substitution of Arg551 does not enhance the IL-4 signal for generation of germline ε transcript, whereas the substitution of Ile50 contributes to enhancement of IgE synthesis.