Polymorphisms of endotoxin pathway and endotoxin exposure: in vitro IgE synthesis and replication in a birth cohort.

BACKGROUND: Genetic variants in endotoxin signaling pathway are important in modulating the effect of environmental endotoxin on asthma and atopic phenotypes. Our objective was to determine the single nucleotide polymorphisms (SNPs) in the endotoxin signaling pathway that may influence in vitro IgE synthesis and to investigate the relationship between these variants and endotoxin exposure in relation to the development of asthma and atopy in a birth cohort. METHODS: Peripheral blood mononuclear cells from 45 children with asthma were stimulated with 2 and 200 ng/ml lipopolysaccharide in vitro and IgE was measured in the culture supernatants. Children were genotyped for 121 SNPs from 30 genes in the endotoxin signaling pathway. Variants with a dose-response IgE production in relation to lipopolysaccharide (LPS) were selected for replication in a population-based birth cohort, in which we investigated the interaction between these SNPs and endotoxin exposure in relation to airway hyper-responsiveness, wheeze, and atopic sensitization. RESULTS: Twenty-one SNPs in nine genes (CD14, TLR4, IRF3, TRAF-6, TIRAP, TRIF, IKK-1, ST-2, SOCS1) were found to modulate the effect of endotoxin on in vitro IgE synthesis, with six displaying high linkage disequilibrium. Of the remaining 15 SNPs, for seven we found significant relationships between genotype and endotoxin exposure in the genetic association study in relation to symptomatic airway hyper-responsiveness (CD14-rs2915863 and rs2569191, TRIF-rs4807000), current wheeze (ST-2-rs17639215, IKK-1-rs2230804, and TRIF-rs4807000), and atopy (CD14-rs2915863 and rs2569192, TRAF-6-rs5030411, and IKK-1-rs2230804). CONCLUSIONS: Variants in the endotoxin signaling pathway are important determinants of asthma and atopy. The genotype effect is a function of the environmental endotoxin exposure.

Methylation of IL-2 promoter at birth alters the risk of asthma exacerbations during childhood.

BACKGROUND: Epigenetic modifications may have a role in asthma susceptibility. OBJECTIVE: To investigate whether epigenetic modification at birth of a CpG site necessary for the regulation of IL-2 transcription (IL-2 Site1) is associated with the development of asthma during childhood. METHODS: Methylation of IL-2 Site1 was assessed in cord blood from 303 children (225 with atopic mothers); as controls, we measured methylation of a site not important in the transcription of IL-2 (IL-2 Site7) and methylation of the LINE-1 repetitive element. Children were followed to the age of 8 years. Information on severe asthma exacerbations and hospital admissions was collected from child's primary care medical record. To account for potential confounding by bronchiolitis, we used exacerbations/hospitalizations after age 1 year as primary outcomes. RESULTS: There were 49 severe exacerbations amongst 33 children, and 22 hospital admissions amongst 11 children. The risk of asthma exacerbation increased 1.07-fold (95% CI 1.01-1.14, P = 0.03) and the risk of hospital admission increased 1.12-fold (95% CI 1.04-1.20, P = 0.002) for each one per cent increase in IL-2 Site1 methylation. Children who were admitted to hospital at any time-point had significantly higher IL-2 Site1 methylation than children not admitted to hospital (P = 0.007). There was a significant interaction between age at exacerbation (P = 0.03) or hospital admission (P = 0.02) and methylation, with the effect of methylation increasing with increasing age. Methylation of the control IL-2 Site7 or LINE-1 was not a significant predictor of asthma exacerbations/hospital admission, and we found no association between IL-2 Site1 methylation and hospital admissions for other reasons (0.99 [0.92-1.06]). Cord blood mononuclear cell phytohemagglutinin-stimulated lymphoproliferative responses decreased significantly with increasing IL-2 Site1 methylation (P < 0.001). CONCLUSIONS: Increasing methylation in cord blood of a functional CpG site in the IL-2 promoter is associated with increased likelihood of severe asthma exacerbations and hospital admissions for asthma/wheeze between ages of 2 and 8 years.