Functional Fcgamma receptor polymorphisms are associated with human allergy

Objective

IgG Fc receptors (FcγRs) play important roles in immune responses. It is not clear whether FcγR receptors play a role in human asthma and allergy. The aim of current study was to investigate whether functional single nucleotide polymorphisms (SNPs) of FcγR genes (FCGR) are associated with human asthma and allergy.

Methods

Functional SNPs of FCGR2A (FcγRIIA-131His>Arg, rs1801274), FCGR2B (FcγRIIB-187Ile>Thr, rs1050501), FCGR2C (FcγRIIC-13Gln>Stop, rs10917661), FCGR3A (FcγRIIIA-158Val>Phe, rs396991), and FCGR3B variants (FcγRIIIB NA1 and NA2) were genotyped in an asthma family cohort including 370 atopy positive, 239 atopy negative, and 169 asthma positive subjects. The genotype and phenotype data (asthma, bronchial hyper-responsiveness, and atopy) of subjects were analyzed using family-based association tests (FBAT) and logistic regression adjusted for age and sex.

Result

The FcγRIIA-131His>Arg SNP is significantly associated with atopy in a family-based association test (P = 0.00287) and in a logistic regression analysis (P = 0.0269, OR 0.732, 95% CI: 0.555–0.965). The FcγRIIA-131His (or rs1801274-A) allele capable of binding human IgG2 has a protective role against atopy. In addition, the rare FcγRIIB-187Thr (or rs1050501-C) allele defective for the receptor-mediated inhibitory signals is a risk factor for atopy (P = 0.0031, OR 1.758, 95% CI: 1.209–2.556) and IgE production (P<0.001). However, variants of activating FcγRIIIA (rs396991), and FcγRIIIB (NA1 and NA2), and FcγRIIC (rs10917661) are not associated with asthma, BHR, and atopy (P>0.05).

Conclusions

FcγRIIA and FcγRIIB functional polymorphisms may have a role in the pathogenesis of allergy.

The p110δ subunit of PI3K regulates bone marrow-derived eosinophil trafficking and airway eosinophilia in allergen-challenged mice

Trafficking and recruitment of eosinophils during allergic airway inflammation is mediated by the phosphatidylinositol 3-kinase (PI3K) family of signaling molecules. The role played by the p110δ subunit of PI3K (PI3K p110δ) in regulating eosinophil trafficking and recruitment was investigated using a selective pharmacological inhibitor (IC87114). Treatment with the PI3K p110δ inhibitor significantly reduced murine bone marrow-derived eosinophil (BM-Eos) adhesion to VCAM-1 as well as ICAM-1 and inhibited activation-induced changes in cell morphology associated with reduced Mac-1 expression and aberrant cell surface localization/distribution of Mac-1 and α4. Infused BM-Eos demonstrated significantly decreased rolling and adhesion in inflamed cremaster muscle microvessels of mice treated with IC87114 compared with vehicle-treated mice. Furthermore, inhibition of PI3K p110δ significantly attenuated eotaxin-1-induced BM-Eos migration and prevented eotaxin-1-induced changes in the cytoskeleton and cell morphology. Knockdown of PI3K p110δ with siRNA in BM-Eos resulted in reduced rolling, adhesion, and migration, as well as inhibition of activation-induced changes in cell morphology, validating its role in regulating trafficking and migration. Finally, in a mouse model of cockroach antigen-induced allergic airway inflammation, oral administration of the PI3K p110δ inhibitor significantly inhibited airway eosinophil recruitment, resulting in attenuation of airway hyperresponsiveness in response to methacholine, reduced mucus secretion, and expression of proinflammatory molecules (found in inflammatory zone-1 and intelectin-1). Overall, these findings indicate the important role played by PI3K p110δ in mediating BM-Eos trafficking and migration by regulating adhesion molecule expression and localization/distribution as well as promoting changes in cell morphology that favor recruitment during inflammation.

Serum metalloproteinase leukolysin (MMP-25/MT-6): a potential metabolic marker for atopy-associated inflammation

BACKGROUND

Leukolysin is a novel matrix metalloproteinase (MMP-25/MT-6) released mainly by granulocytic cells, primarily neutrophils, which are implicated in chronic airways inflammation.

OBJECTIVE

To determine if leukolysin might be a serum marker for atopic asthma or chronic obstructive pulmonary disease (COPD).

METHODS

Three study populations were evaluated: (1) nuclear families with medical history of atopic asthma (N=337), (2) married-in individuals from an independent study of asthma genetics (N=122) and (3) randomly selected males with diagnosis of COPD (N=100). Each person was screened for asthma or COPD symptoms, respiratory function by standardized spirometry and serum total IgE and leukolysin and anti-IL1 levels by immunoassay. Study groups (1 and 2) were also screened by skin prick test using a battery of 14 common aeroallergens. Heritability estimates for leukolysin and total IgE were made by variance components analysis.

RESULTS

For those without asthma or who had asthma defined as having symptoms, a physician's diagnosis and bronchial hyper-reactivity as demonstrated by reversibility in response to albuteral and/or bronchial reactivity as measured by a methacholine challenge, serum leukolysin levels were found to be higher for those with any positive skin test result. This paralleled trends for serum total IgE. In the nuclear families and COPD patients, serum leukolysin levels were significantly elevated for those who also had elevated total IgE levels (log[IgE]>2.0) compared with those with lower IgE (log[IgE]<2.0). Serum IL-1 levels correlated with the leukolycin levels. In contrast to IgE, leukolysin showed no apparent inherited component.

CONCLUSION

Among individuals with history of chronic airways inflammation (asthma and COPD) serum leukolysin may be a metabolic marker associated with chronic atopy-associated respiratory inflammation. Common factors may stimulate increased production or release of both leukolysin from myeloid cells and IgE from lymphoid cells.

Search for quantitative trait loci of atopy-associated immune responses using allergen-specific IgG1 as an "endophenotype"

Inherited atopic diseases of humans arise from adverse adaptive humoral responses to noninfectious environmental allergens. We previously reported that allergen-specific IgG1 provides more reliable heritability estimates for responses to allergens than total IgE. Genome scans were done for 91 Caucasian nuclear families with history of atopy for total IgE and IgG1 produced against a common major allergen from house dust mite, Der p 1. Suggestive associations for Der p 1-IgG1 production were found at 7 quantitative trait loci (QTL) (logarithm of the odds, LOD > or = 1.23; p < or = 0.009) with QTL-specific heritabilities of 73%-80%. Scans using total IgE found suggestive associations for 12 QTLs (LOD > or = 1.44; p < or = 0.004), but QTL-specific heritabilities only in the range of 30%-35%. Allergen-specific IgG1 is a suitable "endophenotype" to be used in searches for genes associated with atopy-associated humoral immune responses to common aeroallergens.

Asthma, atopy, and lung function among racially diverse, poor inner-urban Minneapolis schoolchildren

As part of an assessment of schoolchildren's environmental exposures and health, a probability sample of 136 children from diverse racial/ethnic backgrounds was drawn from grades 2-5 of two inner-urban Minneapolis schools (Whittier, Lyndale). Questionnaires were administered to a parent/guardian; blood samples for IgE and lung function tests were obtained. Overall adjusted rates for lifetime asthma (15.4%; 95%CI 9.3-21.5%), asthma in the last 12 months (13.6%; 7.8-19.4%), and current asthma medication use (10.5%; 5.3-15.7%) were higher than reported US national rates. Adjusted rates for lifetime physician-diagnosed asthma differed significantly among racial/ethnic groups (P<0.01): African-Americans (25.9%), White/Others (25.8%), Hispanics (9.3%), Somalis (1.8%), Asians (0%). Corresponding rates for atopy (total IgE>100 IU/mL or an allergen-specific IgE>0.35 IU/mL) were: African-Americans (66.6%), White/Others (100%), Hispanics (77.2%), Somalis (78.1%), Asians (81.8%). Lung function (FEV1, FVC) was analyzed by linear regression using log-transformed data: significant race-specific differences in lung function were found relative to White/Others (P<0.001 for each racial/ethnic group): African-Americans (FEV1 -16.5%, FVC -16.9%), Somalis (-22.7%, -26.8%), Hispanics (-12.2%, -11.4%) and Asians (-11.1%, -12.4%). Females had significantly lower FEV1 (-8.8%) and FVC (-11.0%) than males. An unexplained, significant difference in children's lung function was found between the two schools. A history of physician-diagnosed asthma was not associated with decreased lung function. Factors other than poverty, inner-urban living, and IgE levels (atopy) need to be considered in the development of childhood asthma.

Complement in asthma: sensitivity to activation and generation of C3a and C5a via the different complement pathways

Studies in rodent models suggested that complement may play a critical role in susceptibility to airway hyperresponsiveness (AHR) and as a mediator of bronchial obstruction and inflammation in asthma. Complement may participate in susceptibility to asthma because of an intrinsic abnormality in complement activation and generation of C3a, C5a, or other products that affect cellular responses, resulting in T(H)2 predominance and asthma susceptibility. Alternatively, an intrinsic abnormality in the cellular response to complement activation products could determine susceptibility to asthma. In this study, the authors investigated whether complement in patients with atopic asthma versus nonatopic controls possesses an increased propensity to become activated. Despite reports that total complement plasma levels in unchallenged asthmatics are normal, an abnormal sensitivity of complement to activation may exist if an isoform or a polymorphic variant of a complement protein was present and resulted in gain or loss of function without associated changes in total complement levels. Therefore, complement activation was induced in vitro in plasma of asthmatics and controls using activators of the classical, alternative, and lectin pathways and measured C3a, other C3 fragments, and C5a. For each pathway, similar amounts of generated fragments, as well as C3a/C3 and C5a/C5 ratios, were found in asthmatics and controls. Also, similar basal plasma levels of C3a and C5a were found in both groups; however, mannan-binding lectin (MBL) levels were moderately elevated in asthmatics. In conclusion, the results suggest that, in asthmatic patients, complement activation does not exhibit an abnormal sensitivity to activation by any of the known activation pathways.

The C523A beta2 adrenergic receptor polymorphism associates with markers of asthma severity in African Americans

Our goal was to explore associations between ss2 adrenergic receptor polymorphisms and markers of asthma severity in African American and Caucasian patients with asthma. Polymorphisms at loci -1023, -654, -47, 46, 79, 491, and 523 were genotyped and haplotypes were imputed in 143 African Americans and 336 Caucasians. C523A genotype associated with percentage of African Americans (but not of Caucasians) having an asthma exacerbation: AA, AC, and CC genotypes were 17, 29, and 40%, respectively (p = 0.018). Symptom scores, pulmonary function, and rescue inhaler use paralleled exacerbation prevalence. We conclude the 523 A allele modifies asthma severity in African Americans.

A genome-wide search for quantitative trait loci contributing to variation in seasonal pollen reactivity

BACKGROUND

Asthma and atopy represent complex traits for which genetic predisposition has been demonstrated. Pollen sensitivity, whether seasonal or chronic, appears to be a major contributor to the asthmatic phenotype.

OBJECTIVE

Regions of the genome contributing to skin test reactivity to 5 seasonal allergens are to be identified in a genome-wide scan. These regions may be distinct from those contributing to risk for asthma and/or atopy.

METHODS

In the Collaborative Study on the Genetics of Asthma, 4 sites collected 287 families with 2 or more members with asthma. Reactivity to individual pollens were determined on all family members. A genome scan was performed at 9-centiMorgan intervals, and skin test reactivity to 5 seasonal allergens was the focus of nonparametric genetic linkage analysis.

RESULTS

Chromosomal regions that exhibited suggestive linkage (logarithm of the odds >1.18; P < .01) to seasonal pollen reactivity were identified on chromosomes 13q34, 20p12, and 21q21. Evidence of ethnic differences in linkage to seasonal allergens was demonstrated, with support for linkage in African American subjects on chromosomes 8, 10, and 12, in European American subjects on chromosomes 14, 19, 20, and 22, and in Hispanics on chromosome 21. In all families, evidence for linkage of skin test reactivity for Betula, Lolium, and Artemisia was strongest in a region on chromosome 21 that contained the candidate gene, A Disintegrin And Metalloprotease domain 33 (ADAM33).

CONCLUSION

These results suggest both substantial genetic overlap and extensive heterogeneity in the genetic basis for the allergic response to seasonal allergens.

CD14 promoter polymorphisms in atopic families: implications for modulated allergen-specific immunoglobulin E and G1 responses

BACKGROUND

CD14 promoter DNA sequence polymorphisms for the endotoxin receptor gene have been implicated in modulating allergen-specific immunoglobulin (Ig)E responses in randomly selected individuals with atopy. We sought to determine if a single nucleotide polymorphism in the CD14 promoter region is associated with atopy in atopic families, and to assess its influence on serum levels of CD14 and allergen-specific IgE and IgG1 responses.

METHODS

We screened 367 members of 91 Caucasian nuclear families with a history of asthma for pulmonary function by spirometry, including methacholine challenge to detect bronchial hyperreactivity, and atopy by serum total IgE and skin prick test to 14 allergens. The CD14 promoter single nucleotide polymorphism was analyzed in DNA isolated from peripheral blood mononuclear cells to identify C/C, C/T and T/T genotypes. Serum tests were done for soluble CD14 (sCD14) and dust mite-specific antibody (Der p 1-IgG1).

RESULTS

Serum sCD14 levels were not associated with clinical phenotypes (asthma, bronchial hyperreactivity or atopy). However, sCD14 levels were inversely related to both allergen-specific IgE and Der p 1-IgG1 production, but only among those with evidence of atopic sensitization. Linear regression analysis, accounting for random family effects, demonstrated a higher production of allergen-specific IgE or Der p 1-IgG1 associated with the T/T genotype and a lower level of specific IgE and IgG1 production associated with sCD14 levels.

CONCLUSIONS

An element of the innate immune system (CD14) has profound effects upon modulating the acquired allergen-specific immunoglobulin responses among those with an inherited atopic predisposition.

The role of genetics in the development of asthma and atopy

PURPOSE OF REVIEW

The mapping of complex traits such as asthma and atopy is one of the most important and central areas of human genetics. This article will present an overview of the current status of genetic studies of asthma and atopy using genome screens and association studies that have occurred in the literature since January 2003.

RECENT FINDINGS

Many regions of the genome have been found to have linkage with the phenotypes of asthma and atopy. Over 70 variants in candidate genes have been reported to be associated with these phenotypes. The main regions these variants have been found are on chromosomes 2q, 5q, 6p, 11q, 12q, 16q and 17q. Five potential asthma susceptibility genes or complexes have been identified using a positional approach. These are ADAM33, DPP10, PHF11 and SETDB2, GPRA and SPINK5. It is evident that environmental factors will influence the expression of genes and the ultimate clinical phenotype of asthma and atopy.

SUMMARY

The development of asthma and atopy involves many genes and environmental factors. An understanding of their genetic basis has great implications for their management.

A coding polymorphism in the CYSLT2 receptor with reduced affinity to LTD4 is associated with asthma

BACKGROUND

Cysteinyl leukotrienes (CYSLTR) are potent biological mediators in the pathophysiology of asthma for which two receptors have been characterized, CYSLTR1 and CYSLTR2. The leukotriene modifying agents currently used to control bronchoconstriction and inflammation in asthmatic patients are CYSLTR1-specific leukotriene receptor antagonists. In this report, we investigated a possible role for therapeutic modulation of CYSLTR2 in asthma by investigating genetic association with asthma and further characterization of the pharmacology of a coding polymorphism.

METHODS

The association of CYSLTR2 polymorphisms with asthma was assessed by transmission disequilibrium test in two family-based collections (359 families from Denmark and Minnesota, USA and 384 families from the Genetics of Asthma International Network).

RESULTS

A significant association of the coding polymorphism, 601A>G, with asthma was observed (P = 0.003). We replicated these findings in a collection of 384 families from the Genetics of Asthma International Network (P = 0.04). The G allele is significantly under-transmitted to asthmatics, indicating a possible role for this receptor in resistance to asthma. The potency of cysteinyl leukotrienes at the wild-type CYSLTR2 and the coding polymorphism 601A>G were assessed using a calcium mobilization assay. The potency of LTC4 and LTE4 was similar for both forms of the receptor and LTB4 was inactive, however, LTD4 was approximately five-fold less potent on 601A>G compared to wild-type CYSLTR2.

CONCLUSIONS

Since 601A>G alters the potency of LTD4 and this variant allele may be associated with resistance to asthma, it is possible that modulation of the CYSLTR2 may be useful in asthma pharmacotherapy.

Evidence that negative feedback between antibody concentration and affinity regulates humoral response consolidation to a non-infectious antigen in infants

The dynamics of human antigen-specific immunoglobulin (Ig) responses in early life are not well characterized. We have previously observed an inverse relationship between allergen-specific Ig concentration and allergen-Ig-binding affinity in allergen-sensitive atopic adults, suggesting a possible feedback relationship between these variables. We prospectively studied children (6 months to 6 years) with and without atopic sensitization to the Der p 1 major allergen. Experimental results showed the following trends. (1) In both study groups, there was little change with age in average Der p 1-specific Ig (IgG1 or IgE) concentrations or allergen-Ig-binding affinities, and concentrations and affinities were independent. (2) Among individuals, however, there was a negative correlation between Ig concentration changes and affinity changes with age. (3) The rate of increase with age of the non-atopic Der p 1-IgG1 total binding capacity (Ig concentration x Ig affinity) paralleled that for the atopic Der p 1-IgE total binding capacity, and there was a comparable 'consolidation' of responses with age reflected by a narrowing of the variance of total binding capacity values. Except for the Ig classes involved, development of a humoral response to a non-infectious allergen is similarly regulated in atopic and non-atopic children, with Ig total binding capacity as the key regulatory variable. These results also suggest that there is a time-dependent feedback relationship between Ig concentrations and affinities that establishes an optimal Ig total binding capacity for a given environmental 'antigen load'. A theoretical model is proposed to account for this relationship.

Genome scan for loci linked to mite sensitivity: the Collaborative Study on the Genetics of Asthma (CSGA)

Mite sensitivity has been reported to be a major risk factor for asthma. As part of the Collaborative Study on the Genetics of Asthma (CSGA), a genome scan using mite reactivity (Dermatophagoides Pteronyssinus (Der p) and Dermatophagoides farinae (Der f)) as the phenotype was conducted. In 287 CSGA families, 122 were informative for linkage. Evidence supporting linkage was observed for regions on chromosome 19 (D19S591, lod=2.43, P=0.0008; D19S1037, lod=1.57, P=0.007) and chromosome 20 (D20S473/D20S604, lod=1.41, P=0.01). All three ethnic groups appeared to contribute to the evidence for linkage on chromosome 20. African-American families gave strongest support for linkage on chromosomes 3 (D3S2409, lod=1.33, P=0.01), 12 (D12S373, lod=1.51, P=0.008) and 18 (ATA82B02, lod=1.32, P=0.01). Caucasian families showed strong evidence for linkage on chromosome 19 (D19S591, lod=3.51, P=0.00006). Hispanic families supported linkage on chromosomes 11 (D11S1984, lod=1.56, P=0.007), 13 (D13S787, lod=1.30, P=0.01) and 20 (D20S470, lod=1.71, P=0.005). These results suggest that multiple genes may be involved in controlling skin reactivity to Dermatophoigoies.

Evidence for two independent distributions of serum immunoglobulin E in atopic families: cognate and non-cognate IgE

Genetic studies of IgE-mediated atopic disease have produced conflicting results, due largely to variable phenotype definitions. Total IgE concentrations and 14 allergen skin prick tests (SPT) were determined in 1099 members of families with history of atopy. Log10 [Total IgE] values were normally distributed in both atopic (SPT [+]) and non-atopic (SPT [-]) groups. The mean Log10 [Total IgE] value was higher in the atopic group, although the standard deviations of the distributions were the same. The mean Log10 [Total IgE] value of the non-atopic distribution was subtracted from the individual Log10 [Total IgE] values of the atopic group giving an allergen-specific fraction. There was a strong positive correlation between the specific IgE fraction and the number (#) SPT [+] results, defined as Cognate IgE. Among the atopics, subtracting the Cognate IgE value from total IgE yielded Non-Cognate IgE. The Cognate and Non-Cognate IgE distributions were statistically uncorrelated. Evidence is presented for two serum IgE fractions that are statistically and physiologically independent of one another in atopic families; a Cognate IgE fraction associated with atopic sensitization and a Non-Cognate IgE fraction unrelated to atopic disease. Elevated serum IgE is a consequence, not a predisposing cause, of allergen sensitization.

Random outcomes of allergen-specific responses in atopic families

BACKGROUND

Allergens are common non-infectious antigens to which people will mount T cell dependent humoral responses. Among genetically susceptible individuals, an antigen-specific response results involving the production of allergen-specific IgE (atopy).

OBJECTIVE

Determine if this susceptibility is manifested as an inherited, allergen-specific trait or a random response to allergens among susceptible people.

METHODS

We evaluated allergen-specific outcomes in 1099 members of families with positive atopic history (26 multi-generation and 112 nuclear families). Each was tested for sensitivity to 14 common allergens by standardized skin prick test (SPT), a marker of specific IgE production. Over 15,000 individual SPT's were evaluated. Among five randomly selected multi-generation families (N=163), semi-quantitative determinations of Amb a 1-specific IgA1,2 and IgG1-4 were determined in three groups: (A) Amb a SPT(+)/Amb a 1-IgE(+), (B) Amb a SPT(-)/Amb a 1-IgE(+), (C) Amb a SPT(-)/Amb a 1-IgE(-).

RESULTS

By rank correlation statistics, there were no discernible 'patterns' of specific SPT outcomes among any of the multi-generation families, suggesting that environmental exposure rather than allergen-specific inheritance determined the responses. This was confirmed among the nuclear families since the conditional SPT outcomes among children were independent of the SPT responses of their parents. Among five randomly selected multi-generation families, the relative proportionate concentrations of the Amb a 1-specific IgA and IgG subclasses were comparable, regardless of atopic sensitization to the ragweed allergen Amb a.

CONCLUSION

While the general propensity for atopy may be inherited, an individual's specific atopic outcome is a random variable independent of familial sensitization patterns.

Allergen skin test reaction patterns in children (</=10 years old) from atopic families suggest age-dependent changes in allergen-IgE binding in early life

BACKGROUND

Genetic studies of atopy rely upon evidence of abnormal IgE production, usually elevated total IgE or skin prick test (SPT) reactions. However, these measures may change with subject age.

METHODS

We screened 1,099 members of atopic families (aged 6-87 years) by serum total IgE and SPT for 14 allergens. For those SPT negative, we screened for Amb a 1- and Der p 1-specific IgE. Der p 1 IgE-Der p 1 allergen binding affinities were done on randomly selected subjects.

RESULTS

There were significantly fewer atopics </=10 years old (69.1%) compared to those >10 years old (75.8%) based upon any SPT-positive result. Children </=10 years had fewer SPT-positive reactions and smaller SPT wheal reaction areas. Yet, mean total IgE values were comparable to those of the older group. Screens for specific IgE showed no differences in proportions of atopics (</=10 years old = 83.1% and >10 years old = 82.3%). Among those SPT-positive for house dust mite extract, there was a positive correlation between Der p 1 binding affinity and the wheal area of the house dust mite extract. There was a positive correlation between the number of SPT-positive reactions and total IgE for both age groups. However, there was only a significant relationship between SPT-positive wheal area and total IgE for those >10 years old and no apparent relationship between wheal area and total IgE for those </=10 years old.

CONCLUSION

These results suggest that atopy-specific physiological mechanisms, primarily those involving allergen-IgE binding, change during the earliest years of life.

A genome-wide search for allergic response (atopy) genes in three ethnic groups: Collaborative Study on the Genetics of Asthma

Atopy is an IgE-mediated condition known to aggregate in families and is a major risk factor for asthma. As part of the Collaborative Study on the Genetics of Asthma (CSGA), a genome-wide scan for atopy, defined by skin sensitivity to one or more common environmental allergens, was conducted in 287 CSGA families (115 African American, 138 Caucasian and 34 Hispanic). Using a nonparametric genetic analysis approach, two regions were observed in the sample of all families that yielded multipoint lod scores >1.5 (chromosome 11q, lod=1.55 between D11S1986 and D11S1998; chromosome 20p between D20S473 and D20S604, lod=1.54). Modeling that included multiple genomic positions simultaneously indicated that four chromosomal regions accounted for the majority of evidence for linkage in the combined families. These four regions are on chromosomes 10p near D10S1412 (lod=0.94), 11q near D11S1986 (lod=1.76), 17q near D17S784 (lod=0.97) and 20p near D20S473 (lod=1.74). In the subset of pedigrees giving positive evidence for linkage on chromosome 11q, the evidence for linkage increased by lod scores greater than one in four other chromosomal regions: 5q (D5S1480, lod=1.65), 8p (D8S1113, lod=1.60), 12p (D12S372, lod=1.54) and 14q (D14S749, lod=1.70). These results suggest that several regions may harbor genes contributing to the risk for atopy and these may interact with one another in a complex manner.

Evidence for gene-environment interactions in a linkage study of asthma and smoking exposure

BACKGROUND

Asthma, a common and chronic disease of the airways, has a multifactorial cause involving both genetic and environmental factors. As a result, mapping genes that influence asthma susceptibility has been challenging.

OBJECTIVE

This study tests the hypothesis that inclusion of exposure to environmental tobacco smoke (ETS), a potential risk factor for asthma, would improve the ability to map genes for asthma.

METHODS

By using 144 white families from the Collaborative Study for the Genetics of Asthma, environmental information about exposure to ETS during infancy was incorporated into a genome-wide multipoint linkage analysis. Statistical significance of observed gene-environment interactions was assessed by means of simulation.

RESULTS

Three regions with nominal evidence for linkage when stratified on the basis of ETS exposure were identified (P <.01) and showed a significant increase from the baseline lod score (1p at 97 cM, D1S1669-D1S1665; 5q at 135 cM, D5S1505-D5S816; and 9q at 106 cM, D9S910; all P <.05). In addition, 2 other regions, although not meeting nominal significance after stratification on the basis of ETS exposure, showed a significant increase from baseline lod score when ETS was taken into account (1q at 240 cM, D1S549; 17p at 3 cM, D17S1308; all P <.01).

CONCLUSION

These results illustrate how evidence for linkage of asthma can depend on exposure to an environmental factor, such as ETS. Future linkage analyses should include information on suspected environmental factors for asthma to help target new candidate susceptibility genes for asthma.

Robustness into advanced age of atopy-specific mechanisms in atopy-prone families

We evaluated atopy-associated parameters in 1,099 people (aged 6-84 years) from families with history for atopy. All were tested for serum total immunoglobulin E (IgE) and allergen sensitivity by skin prick test. Specific IgE tests were done in randomly selected families. There was a decline with age in serum total IgE values, and relative atopy "incidence rates" were slightly lower among those older than 60 years. However, there was no change with age in sensitivity or severity of atopy. Among those sensitized to ragweed (Ambrosia artemisilfolia), there was no age-associated change in IgE levels specific to Amb a 1, a major allergen extracted from ragweed, and no change in the binding affinity of IgE for the Amb a 1 allergen. Among families with atopic histories, the underlying atopic mechanisms are particularly robust, and the atopic propensity remains into advanced age. In addition, established atopic responses may be focused in an immune system compartment either independent of or minimally influenced by T-cell activity.

Variable binding affinities for allergen suggest a 'selective competition' among immunoglobulins in atopic and non-atopic humans

Atopy is a persistent, aberrant humoral response to certain classes of proteins (allergens) characterized by the presence of allergen-specific IgE. Yet, in both atopic and non-atopic individuals, allergen-specific responses involving the IgA and IgG subclasses have been observed, which evidence does not support models suggesting inherited differences in sensitivity to certain protein classes. Using the major ragweed component Amb a 1 as a model allergen, we assessed the humoral responses in three groups of unrelated donors: (A) atopic, ragweed sensitive; (B) atopic, but not ragweed sensitive; (C) non-atopic. As expected, Amb a 1-specific IgE was present in group A only. However, there were essentially no differences in the relative proportions of Amb a 1-specific IgA(1,2) and IgG(1-4) among the groups. We also determined the Amb a 1 binding affinities for IgG(1) and IgG(4) in the three groups, and compared these to Amb a 1-specific IgE binding affinities in group A. Group A donors' Amb a 1-IgE had extremely high affinities (10(8) to 10(11)M(-1)), but their Amb a 1-IgG(1) and Amb a 1-IgG(4) affinities were significantly lower (10(7) to 10(10)M(-1)). The average IgG(4) binding affinities in groups B and C were slightly higher than that of IgG(4) in group A, although not statistically significant. However, the IgG(1) affinity for Amb a 1 among group C, non-atopic donors was significantly elevated and comparable to the IgE affinity observed in group A, ragweed atopics. Inhibition studies with allergen-specific IgE-free serum showed that all isotypes recognized the major epitopes seen by IgE. These results suggest that there may be a "selective competition" among isotypes for allergens that is driven by the ability to produce high affinity, allergen-specific immunoglobulins.

Genetics of asthma

As is becoming increasingly apparent, both atopy and asthma (however they are clinically defined) are a diverse group of related conditions, which are similarly disparate in their origins. Despite this, genetic factors are clearly operational. Speaking to their relatedness, linkages have been found between similar chromosomal sites for both atopy and asthma. Speaking to their divergence, there are also reports of the same phenotypes displaying linkage to different chromosomal areas. The likely explanation for this is that both the atopy and asthma phenotypes are polygenetic, requiring that multiple genes (some of them common to both) be expressed. For example, it may be that three genes, such as "a," "b," and "c," are involved in the development of skin test reactivity. Having only two of these genes, such as "a" and "b" or "b" and "c," alone does not result in the development of the defined phenotype of skin test reactivity. At the same time, it may be that to develop asthma one also needs three genes, such as "c", "d," and "e." One gene "c" involved in atopy inflammation is needed for both asthma and skin test reactivity. Genes "a" and "b" are also needed to be present for skin test reactivity, and a different set of genes, "d" and "e," are needed for asthma to develop. These genes "a" and "b" may be needed to localize the process in the skin and "d" and "e" to localize the process in the lung (Fig. 1). In addition to having the genetic predisposition for atopy and its associated conditions, environmental interactions are involved. Environmental conditions may be the initiating trigger and cause a shift in the balance between the protection and susceptibility of getting the clinical picture. In summary, atopy and asthma seem to be related conditions, involving both environmental and genetic factors, most likely consisting of multiple genes, which may interact with each other and the environment. A deeper [figure: see text] understanding of these genetic bases and the roles that environmental factors play in the development and manifestations of these conditions will provide better methods of diagnosis and treatment.

Evidence of an affinity threshold for IgE-allergen binding in the percutaneous skin test reaction

BACKGROUND

Atopy is an aberrant immune response involving allergen-specific IgE production, though serum IgE concentration is not an entirely reliable diagnostic tool, particularly for epidemiological and genetic studies. There is no clear correlation between IgE and other indicators of atopy such as skin prick tests (SPT)s, and physiological associations are difficult to justify in cases with detectable IgE but negative SPT results.

OBJECTIVE

IgE reflects the number of molecules available to produce an atopic response, but the degree of the response is determined by the binding strength (affinity) between receptor-bound IgE and the allergen. We sought to determine if there was an association between binding affinity and SPT results in people with histories of atopy.

METHODS

Standard SPTs (whole allergen extracts) were administered to people with histories of sensitivities to ragweed and house dust mite. The concentrations and affinities of serum allergen-specific IgEs were determined using the purified allergens Amb a 1 and Der p 1.

RESULTS

There was a positive correlation between weal area and allergen-specific IgE among SPT-positive donors. However, for those individuals with detectable amounts of allergen-specific IgE, there was considerable overlap of IgE values between SPT-positive and -negative groups. Among sensitized donors, IgE-allergen interactions were characterized by two or three specific reactions of very high affinity (K(A) range 10(8) -10(11) M). Negative SPT reactions were associated with lowered IgE binding affinities to major allergens. This delimited two groups with atopic disorders: specific IgE(+)/ SPT(+) and specific IgE(+)/SPT(-).

CONCLUSION

The product of antibody affinity and concentration, which we define as antibody capacity (CAP = K(A) x IgE), is more informative with regard to describing allergen sensitivity than antibody concentration alone. Antibody binding capacity provides physiological evidence of atopy in some subjects who do not test positively by common methods and suggests an affinity threshold to produce a positive SPT reaction.

Ethnic differences in asthma and associated phenotypes: collaborative study on the genetics of asthma

BACKGROUND

In the Collaborative Study on the Genetics of Asthma, 314 families with 2584 subjects were characterized for asthma and allergy.

OBJECTIVE

The purpose of this investigation was to examine clinical heterogeneity observed in asthma and allergic characteristics among 3 ethnic groups (African American, white, and Hispanic family members).

METHODS

Pulmonary function parameters and asthma associated phenotypes were compared among the ethnic groups.

RESULTS

In comparison with the other groups, African American sibling pairs had a significantly lower baseline FEV(1) percent of predicted (P =.0001) and a higher rate of skin test reactivity to cockroach allergen (P =.0001); Hispanic sibling pairs had significantly more skin reactivity overall (P =.001); and white sibling pairs had significantly lower total serum IgE (P <.05). In addition, there were significantly more relatives with asthma among the African American families than among the white and the Hispanic families (P =.001).

CONCLUSION

Although different environmental backgrounds should be considered, these clinical differences could be due to differences in genetic susceptibility among the ethnic groups, such as those suggested by our previous genome screen.

Genomewide screen and identification of gene-gene interactions for asthma-susceptibility loci in three U.S. populations: collaborative study on the genetics of asthma

The genomewide screen to search for asthma-susceptibility loci, in the Collaborative Study on the Genetics of Asthma (CSGA), has been conducted in two stages and includes 266 families (199 nuclear and 67 extended pedigrees) from three U.S. populations: African American, European American, and Hispanic. Evidence for linkage with the asthma phenotype was observed for multiple chromosomal regions, through use of several analytical approaches that facilitated the identification of multiple disease loci. Ethnicity-specific analyses, which allowed for different frequencies of asthma-susceptibility genes in each ethnic population, provided the strongest evidence for linkage at 6p21 in the European American population, at 11q21 in the African American population, and at 1p32 in the Hispanic population. Both the conditional analysis and the affected-sib-pair two-locus analysis provided further evidence for linkage, at 5q31, 8p23, 12q22, and 15q13. Several of these regions have been observed in other genomewide screens and linkage or association studies, for asthma and related phenotypes. These results were used to develop a conceptual model to delineate asthma-susceptibility loci and their genetic interactions, which provides a promising basis for initiation of fine-mapping studies and, ultimately, for gene identification.

Genome-wide linkage analyses of total serum IgE using variance components analysis in asthmatic families

Variance components models were used to analyze total IgE levels in families ascertained though the Collaborative Study of the Genetics of Asthma (CSGA) using a genome-wide array of polymorphic markers. While IgE levels are known to be associated with clinical asthma and recognized to be under strong genetic control (here the heritability was estimated at 44-60% in the three racial groups), specific genes influencing this trait are still largely unknown. Multipoint analysis of 323 markers yielded little indication of specific regions containing a trait locus controlling total serum IgE levels (adjusted for age and gender). Although a number of regions showed LOD statistics above 1.5 in Caucasian families (chromosome 4) and in African-American families (chromosomes 2 and 4), none yielded consistent evidence in all three racial groups. Analysis of total IgE adjusted for gender, age and Allergy Index (a quantitative score of skin test sensitivity to 14 common aeroallergens) was conducted on these data. In this analysis, a much stronger signal for a trait locus controlling adjusted log[total IgE] was seen on the telomeric end of chromosome 18, but only in Caucasian families. This region accounted for most of the genetic variation in log[total IgE], and may represent a quantitative trait locus for IgE levels independent of atopic response. Oligogenic analysis accounting simultaneously for the contribution of this locus on chromosome 18 and other chromosomal regions showing some evidence of linkage in these Caucasian families (on chromosomes 2, 4 and 20) failed to yield significant evidence for interaction.

Nedocromil sodium 2% ophthalmic solution for the treatment of ragweed pollen seasonal allergic conjunctivitis

PURPOSE

To determine the efficacy and safety of nedocromil sodium 2% ophthalmic solution in the treatment of seasonal allergic conjunctivitis.

METHODS

A combined analysis of two multicenter, randomized, comparative, double-masked, placebo-controlled clinical trials involving 261 patients diagnosed with seasonal allergic conjunctivitis was used. Patients were randomly assigned to receive either topical 2% nedocromil sodium or placebo twice daily for eight weeks. Diary card scores and clinician assessments of allergic symptoms were recorded throughout the study; efficacy was determined by comparing symptom severity at the peak pollen period with symptom severity at baseline. Clinician and patient evaluations of treatment effectiveness were used as secondary measurements of efficacy.

RESULTS

Patients treated with nedocromil sodium experienced improvement in allergy symptoms, with reductions in the summary symptom score, itch, redness, conjunctival injection, and conjunctival edema significantly (p<0.05) greater than those observed in the patients treated with placebo. Clinicians' and patients' opinions of nedocromil sodium treatment effectiveness were significantly (p<0.02) superior to those of placebo treatment effectiveness.

CONCLUSION

Nedocromil sodium is effective in the management of seasonal allergic conjunctivitis.

Characterization of polyclonal allergen-specific IgE responses by affinity distributions

Polyclonal IgE responses have been previously characterized by allergen-specific antibody levels and by identification of amino acid sequences related to immunodominant epitopes. However, the binding affinities related to these antibody families are not well known. Using sera from donors with known sensitivities to ragweed or house dust mite allergens, we studied the binding reactions between the purified allergens Amb a 1 and Der p 1 and allergen-specific IgE's by determining affinity distribution functions. The distributions of binding affinities only exhibited a few dominant reactions indicated by peaks in an affinity distribution display. In all the donors tested, there were two dominant peaks and in 2/3 of the cases there was a third peak for both Amb a 1 and Der p 1. We further characterized the polyclonal interactions between IgE and Der p 1 by inhibiting the specific binding of IgE using peptide fragments known to be constituents of Der p 1 epitopes. Each peptide inhibited only a single peak in the affinity distributions. It would appear that the peaks in the affinity distribution represent antibodies directed to single epitopes. These results suggest that in our atopic population the response is surprisingly uniform. The bulk of the IgE response (70-80%) is of high affinity (10(8)-10(11) M(-1)) and directed towards a few epitopes. The relative affinities towards epitopes seem to be determined by the structure of the epitope and not variations of individuals' immune responses.

Efficacy and safety of nedocromil sodium 2% ophthalmic solution b.i.d. in the treatment of ragweed seasonal allergic conjunctivitis

The efficacy and safety of twice-daily nedocromil sodium 2% ophthalmic solution and vehicle were compared in the treatment of ragweed seasonal allergic conjunctivitis. Two separate multicenter, randomized, double-masked, placebo-controlled studies were subjected to a combined analysis. Following a one-week baseline period during the beginning of the ragweed pollen season, 189 patients with seasonal allergic conjunctivitis received either nedocromil sodium or vehicle b.i.d. for eight weeks. Efficacy was evaluated by patient diary cards and clinical eye examinations. Safety was assessed by reports of adverse events. Compared with vehicle, nedocromil sodium produced significantly greater decreases in summary symptom score (p = 0.005), itch (p = 0.005), tearing (p = 0.004), overall eye condition (p = 0.001), and clinician-evaluated conjunctival edema (p = 0.018), and significantly better (p = 0.001), and patient (p = 0.001) opinions of treatment effectiveness at the peak pollen period. Additionally, the superiority of nedocromil sodium compared to vehicle approached statistical significance in redness reduction (p = 0.087) and clinician-evaluated conjunctival injection (p = 0.087). There were no serious treatment-related adverse events in either treatment group. In summary, nedocromil sodium 2% ophthalmic solution b.i.d. was found to be effective and to have a favorable safety profile in the treatment of seasonal allergic conjunctivitis.

Genetics of asthma and allergy

Asthma and allergies are complex conditions involving multiple steps and pathways, which are influenced by both genetic and environmental factors. The genes involved in these processes are just being identified. Most likely asthma is a result of several genes and their interaction with other genes as well as the environment. Management involves the proper diagnosis, modulating the genetic and environmental factors involved as well as interfering with the activated pathways. Using this approach will lead to a more rational method of managing individuals with allergies and asthma.

Approaches and issues in defining asthma and associated phenotypes map to chromosome susceptibility areas in large Minnesota families. The Collaborative Study for the Genetics of Asthma (CSGA)

Evidence for linkage of asthma and its associated phenotypes with susceptibility genes on chromosome 12 has been demonstrated in one group of Minnesota families. The evidence is strong in affected sib pairs and weakens in analysis of the large pedigrees. A second group of families provided little evidence for such linkage. A discrepancy has been demonstrated in different families. This may be due to several factors, including genetic heterogeneity and gene-gene, or gene-environmental interaction effects as well as the statistical power of the sample population used.

Evaluation of a non-chlorofluorocarbon formulation of cromolyn sodium (Intal) metered-dose inhaler versus the chlorofluorocarbon formulation in the treatment of adult patients with asthma: a controlled trial

BACKGROUND

Cromolyn sodium is a nonsteroidal inhaled antiinflammatory agent for the treatment of asthma. As with other pressurized aerosol medications, the metered-dose inhaler (MDI) formulation currently contains chlorofluorocarbon (CFC) propellants. Because of their harmful effects on the environment CFCs are now generally banned from production and use. Alternative propellants under production for MDIs include derivatives of hydrofluoroalkane (HFA). This study uses HFA-227 in an MDI formulation of cromolyn sodium.

OBJECTIVES

The objectives of the study were (1) to examine the efficacy and safety of an HFA formulation of cromolyn sodium (Intal) MDI and (2) to compare the HFA formulation with the CFC formulation.

METHODS

A multicenter, randomized, double-blind, placebo-controlled, parallel study with two active groups (HFA-cromolyn sodium [n = 113] and CFC-cromolyn sodium [n = 107]) and a placebo-treated group (n = 105).

RESULTS

Patients treated with either formulation of cromolyn sodium MDI showed a statistically significant (p < 0.05) improvement of 12% to 18% compared with placebo in symptom summary score, daytime asthma symptoms, and albuterol use. No statistically significant differences were observed in pulmonary function. Patient and physician opinions of overall effectiveness favored HFA-cromolyn sodium over placebo (p = 0.01), with no other significant between-treatment differences. No statistically significant differences existed among groups in the incidence of treatment-related adverse events.

CONCLUSION

The HFA formulation of cromolyn sodium MDI is a well- tolerated and active alternative treatment for asthma patients aged 12 years and more.

B-cell epitopes recognized by IgE from patients sensitive to Amb a 5

BACKGROUND

The response to allergens characterized by IgE-mediated hypersensitivity is selective. The search for the inherited contribution to atopy has among other things, focused on the linkage of sensitivity to the presence of specific alleles in the DR and DQ locus. More than 90% of the responders to Amb a 5, an allergen from ambrosia artemisifolia, are DR-2 positive. This relationship is logically linked to the T-cell epitope presentation by the HLA complex.

OBJECTIVES

This study aims to investigate a possible relationship between T-cell epitopes, B-cell epitopes and the alleles of the DR and DQ loci in Amb a 5 sensitive DR-2+ and DR-2- individuals.

METHODS

Inhibition of solid state Elisa assays by IgE-enriched and IgG-depleted, heated sera. The inhibition was carried out in checkerboard pattern, bidirectionally; A inhibits B and B inhibits A.

RESULTS

The B-cell epitopes defined by the inhibition pattern were all found to be conformational. Three different epitope patterns (A, B, C) were recognized. The IgE and IgG complexes were found in only one responder. The DR and DQ locus alleles were all sequenced. Although all the individuals studied responding to Amb a 5 show presence of alleles such as 1501, associated with DR-2, our data indicates no correlation between the B-cell epitopes recognized and the DR and DQ locus alleles. A well known, general T-cell motif was recognized in the known sequence of Amb a 5.

CONCLUSIONS

Our investigation suggests that the choice of B-cell recognition is regulated independently of a putative link between T-cell epitope recognition and the D locus.

Managing allergies in active people

Though exercise does not appear to cause allergies, active patients require special attention when allergies appear. Physical activity may increase contact with substances that cause hay fever, trigger asthma episodes, or result in contact dermatitis. Nonspecific irritants (like chlorine or air pollutants) and allergens often interact in the context of exercise, and strenuous activity may produce allergic-like symptoms that complicate the clinical picture. An athletic patient's exercise patterns and preferences should be kept in mind in evaluating allergies, devising treatment strategies, and choosing medication.

Absence of linkage between 5q markers and serum IgE levels in four large atopic families

BACKGROUND

Both genetic and environmental influences have been suggested to control the immunoglobulin (Ig)E response to allergens and, as a result, provide susceptibility to atopic disease. Two recent reports suggested that a major gene controlling basal IgE levels in humans was transmitted in a pattern consistent with autosomal recessive inheritance and was located on the long arm of chromosome 5 in the interleukin (IL)-4 gene complex.

OBJECTIVE

The purpose of this report is to evaluate evidence for linkage of IgE with polymorphic genetic markers in the candidate region of 5q in four large pedigrees originally selected for studies of atopy.

METHOD

Four large, highly characterized pedigrees in which IgE levels had been determined and genotypes at markers in the 5q candidate region were evaluated using both lod score and sib pair methods of analysis.

RESULTS

In these pedigrees, we reject close to moderate linkage (up to 5 cM) of an IgE locus with markers on 5q.

CONCLUSION

The genetic aspects of IgE regulation and its role in atopy remain controversial. The data suggest that should major genes be involved in the inheritance of atopy susceptibility, they are likely to be multiple in number and likely to involve interaction with other (exogenous) environmental exposures.

The affinity of allergen specific IgE and the competition between IgE and IgG for the allergen in Amb a V sensitive individuals

We have calibrated a solid state RAST assay with affinity purified allergen-specific IgE. We then utilized the calibrated assay to measure the average affinity of individual IgE-containing sera in terms of the average association constant < K > for purified allergen Amb a V. The binding data yielded linear reciprocal plots indicating that the range of affinities of the responding clones was narrow. The range of the average association constant for the IgE-Amb a V complex was 0.9-26 x 10(10) M-1. The average affinity of the corresponding IgG response in the same individual, estimated by inhibition studies of IgE binding, was 10(7) M-1 in one case and lower than 10(6) M-1 in all the other cases.