Linkage between IgE receptor-mediated histamine releasability from basophils and gene marker of chromosome 11q13

Association and functional relevance of E237G, a polymorphism of the high-affinity immunoglobulin E-receptor beta chain gene, to airway hyper-responsiveness

BACKGROUND

The hyper-sensitivity reaction of IgE, with its high-affinity receptors (FcepsilonRI), is central to the phenomenon of atopic diseases.

OBJECTIVE

To evaluate the genetic effects of non-synonymous single-nucleotide polymorphisms (SNPs) of FcepsilonRI on intermediate phenotypes of asthma, i.e. atopy and airway hyper-responsiveness (AHR), in the Korean general population.

SUBJECTS AND METHODS

Atopy and AHR were evaluated in a cohort of 2055 subjects, aged 10-18 years, using skin prick tests (SPTs) for common aeroallergens and total serum IgE and methacholine bronchial provocation tests. All FcepsilonRI-alpha, FcepsilonRI-beta, and FcepsilonRI-gamma gene exons of 24 healthy subjects were sequenced to locate informative non-synonymous SNPs (minor allele frequency>2%). Informative SNPs were then scored, using the high-throughput single base extension method. Relative risk (RR) was determined by multiple logistic regression analysis, after adjusting for confounding factors. The functional relevance of non-synonymous SNPs was analysed using the sorting intolerant from tolerant (SIFT) program.

RESULTS

The SNP search found only one informative non-synonymous SNP in FcepsilonRI-beta: E237G (minor allele frequency=0.21). The positive rate of AHR was lower among subjects with the 237*E allele than among those with 237*G [RR (95% confidence interval)=0.41 (0.19-0.89); P=0.01]. However, the E237G substitution was not associated with either a positive SPT response or total serum IgE levels. Sequence evolution analysis predicted that the E237G variation is an intolerant amino acid substitution, with functional importance.

CONCLUSION

In the Korean general population, AHR is significantly associated with the E237G polymorphism of FcepsilonRI-beta, which results in an intolerant amino acid substitution.

Immunoglobulin E (IgE)-mediated cross-reactivity between mesquite pollen proteins and lima bean, an edible legume

Immunoglobulin E (IgE)-mediated food allergy often develops as a consequence of allergic sensitization to pollen proteins. Mesquite (Prosopis juliflora) tree pollen is reported to be cross-reactive with other pollen species, but little has been reported on its cross-reactivity with plant-derived foods belonging to the same/different families. The present study investigates the in vitro cross-reactivity of mesquite pollen and lima bean (Phaseolus lunatus), an edible seed belonging to the Leguminosae family. Of 110 patients (asthma, rhinitis or both) tested intradermally, 20 showed marked positive reactions with Prosopis pollen extract. Of these, 12 patients showed elevated specific IgE to Prosopis pollen extract alone and four to both Phaseolus and pollen extract. In vitro cross-reactivity was investigated using inhibition assays [enzyme-linked immunosorbent assay (ELISA) inhibition, immunoblot inhibition], histamine release and lymphoproliferation. P. lunatus extract could inhibit IgE binding to P. juliflora in a dose-dependent manner, requiring 400 ng of protein for 50% inhibition in ELISA assay. Immunoblot and immunoblot inhibition demonstrated the presence of 20, 26, 35, 66 and 72 kDa as shared IgE binding components between the two extracts. Histamine release, peripheral blood mononuclear cells proliferation and interleukin (IL)-4 levels also suggested allergenic cross-reactivity. In conclusion, there is humoral and cellular cross-reactivity between Prosopis pollen and Phaseolus seed allergens.

A_16_C haplotype in the FcepsilonRIbeta gene confers a higher risk for atopic asthma in the Indian population

We conducted a case-control study aimed at identifying polymorphisms and haplotypes in the FcepsilonRIbeta gene associated with asthma and its associated phenotypes such as serum IgE levels. A G/A polymorphism in intron 2, a (CA)n repeat polymorphism in intron 5, and a C/T polymorphism in 3'-UTR, encompassing a length of 8.74 Kb, were genotyped, and haplotypes were generated for unrelated patients and healthy volunteers in two independent cohorts. A significant association was observed at the level of alleles and genotypes studied with asthma independently in the two cohorts (p < 0.05). A change in CC_AA genotype combination to a non-CC_AA genotype was associated with reduced risk for asthma. Interestingly, a three-locus haplotype, A_16_C, was found to be significantly associated with asthma (p = 10(-5) in cohort A and p = 0.004 in cohort B). On the other hand, the haplotype G_18_T was found to be negatively associated with asthma (p = 0.007 in cohort A and p = 0.0004 in cohort B). This is the first study identifying a haplotype A_16_C that predisposes individuals to asthma in the Indian population.

The role of the FcepsilonRI beta-chain in allergic diseases

The high affinity receptor for IgE, FcepsilonRI, is a multimeric surface receptor that is expressed exclusively as a tetramer on rodent cells, but exists as a tetramer or trimer on human cells. The tetrameric form is expressed on effector cells of allergic responses such as mast cells and basophils and is composed of an IgE-binding alpha-subunit, a beta-subunit and a gamma-subunit dimer. Complexes lacking the beta-subunit are found on human antigen-presenting cells. On mast cells and basophils, FcepsilonRI is essential for IgE-mediated acute allergic reactions. Crosslinking of FcepsilonRI by IgE and multivalent antigen induces a signaling cascade that culminates in the release of preformed mediators and the synthesis of lipid mediators and cytokines. The beta-subunit functions as an amplifier of FcepsilonRI expression and signaling. As a consequence, strongly enhanced mast cell effector functions and in vivo allergic reactions can be observed in the presence of FcepsilonRIbeta. In contrast, a truncated beta-isoform (betaT) that is produced by alternative splicing acts as an inhibitor of FcepsilonRI surface expression. Thus, by producing two proteins with antagonistic functions, the FcepsilonRIbeta gene could serve as a potent regulator of allergic responses. In addition, the genomic region encompassing the beta-chain has been linked to atopy and a number of polymorphisms within the FcepsilonRIbeta gene are associated with various atopic diseases. It remains to be elucidated how these polymorphisms might affect the allergic phenotype. These functions of the beta-chain together with the described genetic linkages to atopy make it a candidate for a role in the pathophysiology of allergic diseases.

LD mapping of maternally and non-maternally derived alleles and atopy in FcepsilonRI-beta

Polymorphisms in the beta chain of the high affinity receptor for IgE (Fc epsilon RI-beta, MS4A2) are consistently associated with traits underlying asthma and atopy (immunoglobulin E-mediated allergy). However, the causal variants and haplotypes underlying disease have not yet been identified. Maternal effects, with association confined to maternally derived alleles, have been shown in some studies but not in others. We have therefore extended the known sequence and systematically detected polymorphisms across an 18.1 Kb genomic region that includes Fc epsilon RI-beta. Association testing in two panels of subjects showed the presence of single-nucleotide polymorphisms (SNPs) affecting prick skin tests and specific IgE responses in several clusters. Stepwise analyses indicated that the clusters represent independent effects. Interferon regulatory factor 2 (IRF-2) sites were altered by significantly associated SNPs in two regions. Strong association to maternally derived alleles was seen in one panel of subjects and not in the other. Maternal and non-maternally derived associations tended to share the same SNP clusters, but associations were stronger in the presence of maternal effects. Two regions of increased CpG concentration were identified in Fc epsilon RI-beta. One of these approximated a SNP cluster that showed strong association and maternal effects, providing a potential substrate for epigenetic effects.

Allergen-specific conventional immunotherapy decreases immunoglobulin E-mediated basophil histamine releasability

BACKGROUND

Allergen-specific immunotherapy has proven to be clinically effective in the treatment of patients with atopic asthma; however, the mechanisms are still unclear. Several noted immunological changes include an increase of the allergen-specific IgG antibody, a reduction in the allergen-specific IgE antibody subsequent to transient increase, an allergen-specific T cell shift in cytokine production from Th2 to Th1, and a decrease in quantity and activity of basophils and mast cells.

OBJECTIVE

To analyse the changes of basophil histamine release in response to IgE-mediated and non-IgE-mediated stimuli before and after conventional house-dust mite immunotherapy in children who suffer from atopic asthma.

METHODS

Fourteen Dermatophagoides farinae (Df) sensitive asthmatic children with conventional immunotherapy were examined. Basophil histamine releasability was measured 0 months (just before immunotherapy), 4 months and 9 months after immunotherapy. Basophils were stimulated with Df and goat anti-human IgE antibody as IgE-mediated stimuli; and formyl-Met-Leu-Phe (fMLP) and calcium ionophore A23187 as non-IgE-mediated stimuli. Accordingly, the asthma symptom score was used to assess clinical outcome and the skin test reactivity to Df was measured.

RESULTS

In contrast to pre-immunotherapy activity, 4 and 9 months after immunotherapy there were significant decreases in histamine release by Df and by anti-IgE antibody. The histamine release by fMLP and by calcium ionophore showed no significant changes after immunotherapy. Histamine release by Df demonstrated significant correlation to that by anti-IgE antibody and by fMLP, yet there was no observable correlation between histamine release by Df and by calcium ionophore. The asthma symptom score decreased significantly 4 and 9 months after immunotherapy and showed significant correlation with histamine release by Df. The skin test reactivity (allergen/histamine ratio) remained constant 4 months after immunotherapy, but decreased significantly 9 months after immunotherapy.

CONCLUSION

Basophils have the potential to play an important role in the early clinical improvement of conventional immunotherapy in children with atopic asthma, which may be a result of the decreased IgE-mediated histamine releasability during immunotherapy.

Coding single nucleotide polymorphism in the high-affinity immunoglobulin E receptor b chain (FcepsilonRI-beta) gene is associated with immunoglobulin E receptor-mediated histamine release from basophils

BACKGROUND

Our previous work on linkage analysis showed that histamine release from basophils to anti-IgE stimuli was linked to the gene marker of chromosome 11q13, where the beta chain of the high-affinity receptor for IgE (FcepsilonRI-beta) is located.

OBJECTIVE

To evaluate the association between FcepsilonRI-mediated histamine release from basophils and four bi-allelic single nucleotide polymorphisms of the FcepsilonRI-beta gene.

METHODS

Phenotypes of asthma, such as maximal histamine release from basophils and atopy, were measured from 80 randomly recruited asthmatic children. Polymorphisms of the FcepsilonRI-beta gene were determined by PCR-based methods.

RESULTS

The polymorphism in exon 7, resulting in Glu to Gly substitution, was significantly associated with histamine release from basophils to anti-IgE stimuli, but not with total IgE levels and skin test responses to aeroallergens.

CONCLUSION

This study supports a role for the FcepsilonRI-beta gene in the expression of high affinity IgE receptor-mediated histamine release from basophils.

Association of beta2-adrenoreceptor polymorphisms with nocturnal cough among atopic subjects but not with atopy and nonspecific bronchial hyperresponsiveness

BACKGROUND

The reports from in vitro studies that beta(2)-adre-nergic receptor (B2AR) polymorphisms are associated with agonist-promoted downregulation have evoked considerable research interest for the roles of these polymorphisms to the pathogenesis of asthma.

OBJECTIVE

We sought to evaluate the association between asthma phenotypes and B2AR polymorphisms at 2 sites (Arg16 --> Gly16 and Gln27 --> Glu27) in the general population.

METHODS

Four hundred forty unrelated Korean adults were randomly selected, and asthma phenotypes were determined with a questionnaire, immunoassay, skin prick testing, and methacholine bronchial provocation testing. Genotypes of B2AR polymorphisms were determined with PCR-based methods.

RESULTS

No significant association was found between B2AR alleles and haplotypes and total IgE levels, skin test responses to aeroallergens, and bronchial responsiveness to methacholine. Among the atopic subjects, however, numbers of both Arg16 alleles and Arg16-Gln27 haplotypes were negatively associated with nocturnal cough, and in contrast, Gly16-Gln27 was positively associated with it.

CONCLUSION

B2AR polymorphisms may play an important role in the expression of nocturnal cough in atopic subjects but not in the expression of atopy and bronchial hyperresponsiveness in a general population.

Human mast cell progenitors in peripheral blood from atopic subjects with high IgE levels

BACKGROUND

It remains unclear whether the number of circulating mast cell progenitors is increased in patients with atopic diseases. Distinct genotypes are reported to affect mast cell/basophil activation.

OBJECTIVE

We compared the number and function of mast cell progenitors present in the peripheral blood from donors with normal IgE (IgE < 400 U/mL) and those with atopic dermatitis accompanied by high serum IgE (IgE > 5000 U/mL).

METHODS

Purified peripheral blood cells were cultured in serum-free methylcellulose containing stem cell factor (SCF), IL-6 plus IL-3. Fresh methylcellulose containing the cytokines was layered over every 2 weeks. The cultured mast cells were retrieved from the methylcellulose and were functionally analysed.

RESULTS

Mast cell colonies were distinguished at 6 weeks of culture as other colony types had been degenerated. The number of mast cell colony-forming cells varied depending on donors and was not significantly increased in peripheral blood from the hyper-IgE atopic patients. A significant inversed correlation was found between the number of mast cells per one colony and the ages of donors. The cultured mast cells derived from atopic patients and those from normal IgE donors equally expressed Fc epsilon RI and released histamine through Fc epsilon RI, although IL-4 priming in vitro markedly enhanced the function of mast cells regardless of donors.

CONCLUSIONS

These results indicate that the number of circulating mast cell progenitors may be regulated by unknown individual factors unrelated to IgE levels. Mast cell function may be regulated largely by environmental factors, such as IL-4, but not determined by their progenitors' genotypes.