Toll-like receptor 4 variants reduce airway response in human subjects at high endotoxin levels in a swine facility (original) (raw)
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TLR4 mutations are associated with endotoxin hyporesponsiveness in humans
Nature Genetics, 2000
There is much variability between individuals in the response to inhaled toxins, but it is not known why certain people develop disease when challenged with environmental agents and others remain healthy. To address this, we investigated whether TLR4 (encoding the toll-like receptor-4), which has been shown to affect lipopolysaccharide (LPS) responsiveness in mice 1,2 , underlies the variability in airway responsiveness to inhaled LPS in humans 3 . Here we show that common, co-segregating missense mutations (Asp299Gly and Thr399Ile) affecting the extracellular domain of the TLR4 receptor are associated with a blunted response to inhaled LPS in humans. Transfection of THP-1 cells demonstrates that the Asp299Gly mutation (but not the Thr399Ile mutation) interrupts TLR4-mediated LPS signalling. Moreover, the wild-type allele of TLR4 rescues the LPS hyporesponsive phenotype in either primary airway epithelial cells or alveolar macrophages obtained from individuals with the TLR4 mutations. Our findings provide the first genetic evidence that common mutations in TLR4 are associated with differences in LPS responsiveness in humans, and demonstrate that gene-sequence changes can alter the ability of the host to respond to environmental stress.
Polymorphisms in Toll-Like Receptor 4 Are Not Associated with Asthma or Atopy-related Phenotypes
American Journal of Respiratory and Critical Care Medicine, 2002
Toll-like receptor 4 (TLR4) is the principal receptor for bacterial cant interindividual variability in response to endotoxin has endotoxin recognition, and functional variants in the gene confer long been recognized (4, 5). Arbour and colleagues have endotoxin-hyporesponsiveness in humans. Furthermore, there is recently demonstrated that common polymorphisms in the evidence that endotoxin exposure during early life is protective coding region of the TLR4 gene are responsible for a substanagainst the development of atopy and asthma, although this relatial portion of this variability (6). Specifically, a substitution tionship remains poorly understood. It is therefore possible that of glycine for asparginine at amino acid position 259 (D259G) genetic variation in the TLR4 locus contributes to asthma susceptiresults in reduction in cell surface expression of TLR4 and bility. In this study we characterize the genetic diversity in the TLR4 subsequent disruption of LPS-mediated signaling. Furtherlocus and test for association between the common genetic variants more, subjects heterozygous for D259G demonstrate a blunted and asthma-related phenotypes. In a cohort of 90 ethnically diverse bronchoconstrictor response to inhaled LPS, suggesting a subjects, we resequenced the TLR4 locus and identified a total of dominant genetic effect. A second amino acid variant, a sub-29 single nucleotide polymorphisms. We assessed five common stitution of threonine for isoleucine at position 359 (T359I), polymorphisms for evidence of association with asthma in two large which is in tight linkage disequilibrium (LD) with D259G, family-based cohorts: a heterogeneous North American cohort (589 also demonstrated in vitro LPS-hyporesponsive effects. There families), and a more homogenous population from northeastern is evidence that these functional variants are important deter-Quebec, Canada (167 families). Using the transmission-disequilibminants of health and disease, including sepsis susceptibility rium test, we found no evidence of association for any of the polymorphisms tested, including two functional variants. Furthermore, and atherogenesis (7, 8). Smirnova and colleagues have resewe found no evidence for association between the TLR4 variants quenced the complete coding region of TLR4 in 348 individuand four quantitative intermediate asthma-and atopy-related pheals of diverse ethnic origin and identified 10 additional amino notypes. Based on these results, we found no evidence that genetic acid variants of extremely low frequency (9). Although funcvariation in TLR4 contributes to asthma susceptibility. tional data regarding these rare variants is currently unavailable, this excess number of rare variants suggests that weakly purifying selective forces influence variation at the TLR4 netic association cohort of 499 infants at high risk of developing asthma dem-Recherche sur la Nature et les Technologies du Québec. C.G. is a Chercheur onstrated that higher household endotoxin levels were associ-Boursier of the Fonds pour la Recherche en Santé du Québec. ated with an increased risk of persistent wheeze during the Correspondence and requests for reprints should be addressed to Benjamin A. first year of life (16). Household endotoxin level is also sig-Raby, M.D., Channing Laboratory, Brigham and Women's Hospital, 181 Longnificantly associated with asthma severity among dust mitesensitive children (17). The role of endotoxin in the develop-
TLR4 gene dosage contributes to endotoxin-induced acute respiratory inflammation
Journal of Leukocyte Biology, 2006
Toll-like receptor (TLR)4 is critical for endotoxin recognition and cellular responses. Using Tlr4 transgenic mice, we investigated the influence of Tlr4 gene dosage on acute respiratory response to endotoxin. Transgenic mice expressing three, six, or 30 copies of Tlr4, control, and Tlr4deficient mice received intranasal administration of lipopolysaccharide (LPS; 10 ug), and the airway response was analyzed by plethysmography, lung histology, cell recruitment, cytokine and chemokine secretion and protein leakage into the bronchoalveolar space. We demonstrate that overexpression of Tlr4 augmented a LPS-induced bronchoconstrictive effect, as well as tumor necrosis factor and CXC chemokine ligand 1 (keratinocytederived chemokine) production. Neutrophil recruitment, microvascular and alveolar epithelial injury with protein leak in the airways, and damage of the lung microarchitecture were Tlr4 gene dosedependently increased. Therefore, the TLR4 expression level determines the extent of acute pulmonary response to inhaled endotoxin, and TLR4 may thus be a valuable target for immunointervention in acute lung inflammation as a result of endotoxins. J. Leukoc. Biol. 80: 451-457; 2006.
Toll-like receptor 4 polymorphism and severity of atopy in asthmatics
Genes and Immunity, 2004
Endotoxin exposure may have a protective effect against asthma and atopy. An Asp299Gly polymorphism in the Toll-like receptor 4 (TLR4) gene reduces responsiveness to endotoxin. This study determined the effect of TLR4 polymorphism on the risk and severity of asthma and atopy. In all, 336 UK Caucasian families with Z2 affected sibs (physician's diagnosis of asthma and current medication use) and 179 Caucasians without asthma or a family history of asthma were genotyped using ARMS-PCR. No association of the TLR4 polymorphism was found with the risk of developing asthma, either in parent-affected sibling trios, or in case-control analyses (P40.05). In the first affected asthmatic siblings, the atopy severity score (based on size and number of positive skin-prick tests and specific IgE) was higher in those with the Asp/Gly or Gly/Gly genotypes (mean 1.8, s.d. 1.1, n¼39) compared to those with the Asp/Asp genotype (mean 1.2, s.d. 1.0, n¼279) (P¼0.003, t-test). No associations were found with total IgE, FEV 1 % predicted, slope of FEV 1 response to methacholine or asthma severity score (P40.05). This study confirms the previously observed lack of association of TLR4 polymorphisms with asthma. In contrast, the findings suggest that genetically determined hyporesponsiveness to endotoxin may increase atopy severity.
Clinical Immunology, 2006
Mutations (Asp299Gly and Thr399Ile) in the human Toll-like receptor 4 (hTLR4) gene are reportedly associated with hyporesponsiveness to inhaled LPS in humans. It was hypothesized that normal volunteers with these hTLR4 mutations would manifest altered physiological responses to intravenous LPS administration. Human subjects (n = 57) were administered LPS (2 ng/kg) intravenously and monitored for vital signs (temperature, heart rate, mean arterial pressure). Blood-derived genomic DNA samples were evaluated using PCR to detect hTLR4 and TLR2 mutations. Heterozygous hTLR4 mutations were identified in 8 of the 57 subjects studied. Subjects with hTLR4 mutations demonstrated similar responses to LPS administration. The moderate systemic inflammatory response produced by intravenous LPS administration in human subjects is not modulated by the presence of heterozygous mutations in the hTLR4 gene. D a v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m w w w . e l s e v i e r . c o m / l o c a t e / y c l i m
Pediatric Allergy and Immunology, 2014
Background: We investigated the interaction between genetic variants in endotoxin signalling pathway and domestic endotoxin exposure in relation to asthma presence, and amongst children with asthma, we explored the association of these genetic variants and endotoxin exposure with hospital admissions due to asthma exacerbations. Methods: In a case-control study, we analysed data from 824 children (417 asthmatics, 407 controls; age 5-18 yr). Amongst asthmatics, we extracted data on hospitalization for asthma exacerbation from medical records. Endotoxin exposure was measured in dust samples collected from homes. We included 26 single-nucleotide polymorphisms (SNPs) in the final analysis (5 CD14, 7LY96 and 14 TLR4). Results: Two variants remained significantly associated with hospital admissions with asthma exacerbations after correction for multiple testing: for CD14 SNP rs5744455, carriers of T allele had decreased risk of repeated hospital admissions compared with homozygotes for C allele [OR (95% CI), 0.42 (0.25-0.88), p = 0.01, False Discovery Rate (FDR) p = 0.02]; for LY96 SNP rs17226566, C-allele carriers were at a lower risk of hospital admissions compared with T-allele homozygotes [0.59 (0.38-0.90), p = 0.01, FDR p = 0.04]. We observed two interactions between SNPs in CD14 and LY96 with environmental endotoxin exposure in relation to hospital admissions due to asthma exacerbation which remained significant after correction for multiple testing (CD14 SNPs rs2915863 and LY96 SNP rs17226566). Conclusion: Amongst children with asthma, genetic variants in CD14 and LY96 may increase the risk of hospital admissions with acute exacerbations. Polymorphisms in endotoxin pathway interact with domestic endotoxin exposure in further modification of the risk of hospitalization.
Endotoxins, asthma, and allergic immune responses
Toxicology, 2000
Asthma severity depends to a great extent on the levels of endotoxin present in the microenvironment. Although favouring a Th1 cytokine response that could be beneficial to the asthmatic, lipopolysaccharide (LPS) aggravates bronchopulmonary inflammation by several mechanisms. These include neutrophil and eosinophil recruitment, and release by activated macrophages of pro-inflammatory cytokines and nitric oxide. LPS exerts its biological actions through its interaction with CD14. The genetic locus of CD14 is close to the genomic region controlling levels of IgE. A polymorphism in the CD14 promoter region seems to favour high serum IgE levels. Genetic influences may thus control circulating levels of sCD14 and by this mechanism modulate Th1/Th2 balance and IgE synthesis. LPS exposure, although hazardous to the asthmatic, seems to exert a role in the maturation of the immune system in children towards a Th1-skewed pattern.