TLR4 mutations are associated with endotoxin hyporesponsiveness in humans

Abstract

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, underlies the variability in airway responsiveness to inhaled LPS in humans. 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.

The role of the Toll receptor pathway in susceptibility to inflammatory bowel diseases

“…The OR associated with each variant are virtually identical, and a previous study indicates that both alleles appear to have an effect on NFKB1 activation and IL1a expression. 38 These findings are supported by recent evidence that both TLR4 299Gly and TLR4 399Ile demonstrate decreased responsiveness to LPS and other TLR4 ligands in an in vitro reconstituted TLR4 signaling apparatus when compared to the TLR4 proteins bearing the major allele of each SNP (TLR4 Asp299 and TLR4 Thr399 ). 47 A construct containing both minor alleles had a significantly lower response to TLR4 stimulation than all other constructs, and all of these differences in responses were noted to be dependent on the stochiometry of TLR4, MD-2 and CD14.…”

“…Interestingly, it has been reported that the TLR4 299Gly variant leads to decreased airway responsiveness to inhaled LPS, decreased NFKB1 activation and decreased in vitro IL1a expression in airway epithelial cells. 38 However, several other groups report no significant evidence for a functional difference in ex vivo or in vitro characterization of cytokine expression by peripheral blood mononuclear cells between subjects having either the Asp or Gly allele at position 299. [39][40][41][42][43][44][45] It should be noted, however, that binding of the TLR4 receptor leads to more than just the activation of NFkB1.…”

Toll-like receptor 6 gene (TLR6): single-nucleotide polymorphism frequencies and preliminary association with the diagnosis of asthma

“…Additionally, two missense mutations of the TLR4 gene (Asp299Gly and Thr399Ile) have been associated with a decreased response to inhaled endotoxin in humans. 16 In turn, endotoxin exposure confers protection on the development of allergy and asthma. 17 While no prior studies have evaluated this effect in our gene of interest, TLR6, both TLR6 and TLR4 elicit similar cytokine responses upon exposure to bacteria, 18 suggesting that alterations in TLR6 may result in a phenotype similar to that of TLR4.…”

The TLR4 +896 polymorphism is not associated with lipopolysaccharide hypo-responsiveness in leukocytes

“…[13][14][15] Although several groups have shown a correlation between carrier status for the coding polymorphisms in TLR4 and alterations in LPS signaling, [13][14][15] other investigators have not. 20,22 Our observations suggest that any effect of the variant allele is minimal as we did not observe differences in MAPK IL-6 (pg/ml) c Figure 3 Whole-blood LPS induced proinflammatory cytokine production does not differ based on donor TLR4 genotype.…”

“…The TLR4 þ 896 variant (G allele) confers an alteration to the extracellular domain of the TLR4 receptor. Carriers have been reported to have an impaired response to bacterial endotoxin exposure compared to wild-type controls, [13][14][15][16] and they may be at increased risk for Gram negative infections and septic shock, and mortality from systemic inflammatory response syndrome (SIRS). [17][18][19] However, other in vivo and clinical studies have shown inconsistencies in the link between coding SNPs in the TLR4 gene and the inflammatory response.…”