Lys694Arg polymorphism leads to blunted responses to LPS by interfering TLR4 with recruitment of MyD88

TLR4 polymorphisms such as Asp299Gly and Thr399Ile related to Gram-negative sepsis have been reported to result in significantly blunted responsiveness to LPS. Our study group previously screened other TLR4 polymorphic variants by checking the NF-κB activation in comparison to wild type (WT) TLR4 in human embryonic kidney 293T cells. In this study, we found that the Lys694Arg (K694R) polymorphism reduced the activation of NF-κB, and the production of downstream inflammatory factors IL-1, TNF-α and IL-6, representing the K694R polymorphism, led to blunted responsiveness to LPS. Then, we examined the influence of the K694R polymorphism on total and cell-surface TLR4 expression by Western blotting and flow cytometry, respectively, but observed no differences between the K694R polymorphism and WT TLR4. We also used co-immunoprecipitation to determine the interaction of the K694R polymorphism and WT TLR4 with their co-receptor myeloid differentiation factor 2 (MD2) and their downstream signal adaptor MyD88. We found that K694R reduced the recruitment of MyD88 in TLR4 signalling but had no impact on the interaction with MD2.     

Toll-like receptor 4 Asp299Gly/Thr399Ile polymorphisms are a risk factor for Candida bloodstream infection

Toll-like receptor (TLR)-4 is an important pattern recognition receptor for Candida albicans, playing a role in innate host defense. We investigated whether there is an association between the TLR4 Asp299Gly or TLR4 Thr399Ile polymorphism, and the occurrence of Candida bloodstream infection. We performed a case-control study, involving 43 patients with a Candida bloodstream infection and 166 healthy individuals. TLR4 Asp299Gly and Thr399Ile polymorphisms were assessed, as well as cytokine production after stimulation of peripheral blood mononuclear cells (PBMC) with Candida albicans. We observed that the prevalence of TLR4 Asp299Gly polymorphism was found to be higher in patients with Candida bloodstream infection than in controls (26% versus 10%; OR 3.0; 95%CI 1.3-6.9). All patients bearing the Asp299Gly polymorphism were also positive for the Thr399Ile allele, a linkage well described in literature. IL-10 production was higher in C. albicans-stimulated PBMC from volunteers bearing the TLR4 Asp299Gly polymorphism, and a similar tendency was observed in TLR4 Asp299Gly heterozygous patients who had recovered from candidemia. These findings show that the TLR4 Asp299Gly/Thr399Ile polymorphisms are associated with an increased susceptibility to Candida bloodstream infections, and an increased production of IL-10 is probably involved in this effect.     

Functional consequences of toll-like receptor 4 polymorphisms

Toll-like receptor 4 (TLR4) is an important pathogen recognition receptor that recognizes mainly lipopolysaccharide (LPS) of Gram-negative bacteria, but also structures from fungal and mycobacterial pathogens, as well as endogenous ligands. Two nonsynonymous polymorphisms of TLR4, Asp299Gly and Thr399Ile, have been suggested to alter the function of the receptor. Some, but not all, studies have proposed that these polymorphisms lead to reduced cytokine response and increased susceptibility to Gram-negative infections. In this review, we compare studies that assessed the effect of the Asp299Gly and Thr399Ile polymorphisms on susceptibility to Gram-negative infections and examine the phenotypic consequences of these polymorphisms. In addition, we review the geographical distribution of TLR4 polymorphisms and present a model for evolutionary pressures on the TLR4 genetic make-up.     

TLR4 and TLR9 polymorphism: Probable role in susceptibility among the population of Bihar for Indian visceral leishmaniasis

Genetic variations in the host TLRs genes play an important role in susceptibility and/or resistance to visceral leishmaniasis by altering the host-pathogen interaction. In this study, we investigated the association between polymorphisms of TLR4 (Asp299Gly, Thr399Ile) and TLR-9 (T-1237C), with susceptibility to visceral leishmaniasis. A bi-directional PCR amplification of specific alleles technique was used to characterize the distribution of TLR4 (Asp299Gly and Thr399Ile) and TLR9 (T-1237C) polymorphisms. A total of 60 samples were randomly selected from confirmed visceral leishmaniasis patients and 24 endemic healthy volunteers. The samples were genotyped and allele frequencies were determined. We observed that TLR4 Asp299Gly and Thr399Ile genotypes were more frequent in visceral leishmaniasis patients (10% and 15% respectively) compared to controls (4.2% and 8.3% respectively). However, the differences were not significant in TLR4 Asp299Gly and Thr399Ile alleles and genotypes. In the case of TLR9, we observed the frequency of T1237C genotype was higher in visceral leishmaniasis patients (43.3%) than in healthy controls (33.3%). Statistically significant differences were observed in TLR9 T1237C alleles and genotypes. We concluded that TLR9 T1237C, but not TLR4, gene polymorphisms can be regarded as contributors to visceral leishmaniasis susceptibility among the Indian population of Bihar state.     

CD14-159 and -260 gene polymorphisms are associated with HBV-related cirrhotic injury in Chinese Han patients

The present study aimed to investigate the association between TLR4 mutations (Asp299Gly and Thr399Ile) and CD14 polymorphisms (base pair -159 and -260) with HBV-related cirrhosis in Chinese Han patients. By use of a polymerase chain reaction-based restriction fragment length polymorphism (PCR-RFLP) analysis technique, we genotyped Toll-like receptor 4 (TLR4) Asp299Gly and Thr399Ile and CD14-159 and -260 polymorphisms in 110 HBV-related cirrhotic patients and 110 healthy controls from the Chinese Han population. We found significant differences in the genotypes and allele frequencies of CD14-159 (but not -260) between healthy controls and liver cirrhotic patients, and both the CD14-159 and -260 genotypes were significantly different among Child-Pugh grades in cirrhotic patients. No TLR4 Asp299Gly and Thr399Ile mutations were detected in any cirrhotic patients or healthy controls in the Chinese Han population. These findings indicated that the polymorphisms of CD14, but not TLR4 Asp299Gly and Thr399Ile mutations, may be an important genetic factor for HBV-related cirrhotic injury in the Chinese Han population.     

TLR4基因多态性与感染性ARDS易感性的相关性研究

目的研究Toll样受体4(TLR4)基因Asp299Gly、Thr399Ile多态性与感染性急性呼吸窘迫综合征(ARDS)的关系。方法采用多聚酶链反应-限制性片段长度多态性(PCR-RFLP)方法,对40例感染性ARDS患者和50名健康人进行TLR4等位基因Asp299Gly和Thr399Ile的基因型检测。结果在感染性ARDS患者和健康体检者中,TLR4受体基因Asp299Gly、Thr399Ile两位点的基因型之间差异无统计学意义(χ2=0.043,P=0.635;χ2=0.071,P=0.583)。结论感染性ARDS患者的TLR4基因Asp299Gly和Thr399Ile多态性与感染性ARDS发病无显著相关性。     

Analysis of TLR4 polymorphic variants: new insights into TLR4/MD-2/CD14 stoichiometry, structure, and signaling

TLR4 is the signal-transducing receptor for structurally diverse microbial molecules such as bacterial LPS, respiratory syncytial virus fusion (F) protein, and chlamydial heat shock protein 60. Previous studies associated two polymorphic mutations in the extracellular domain of TLR4 (Asp(299)Gly and Thr(399)Ile) with decreased LPS responsiveness. To analyze the molecular basis for diminished responsiveness, site-specific mutations (singly or coexpressed) were introduced into untagged and epitope (Flag)-tagged wild-type (WT) TLR4 expression vectors to permit a direct comparison of WT and mutant signal transduction. Coexpression of WT TLR4, CD14, and MD-2 expression vectors in HEK293T cells was first optimized to achieve optimal LPS-induced NF-kappaB reporter gene expression. Surprisingly, transfection of cells with MD-2 at high input levels often used in the literature suppressed LPS-induced signaling, whereas supraoptimal CD14 levels did not. Under conditions where WT and polymorphic variants were comparably expressed, significant differences in NF-kappaB activation were observed in response to LPS and two structurally unrelated TLR4 agonists, chlamydial heat shock protein 60 and RSV F protein, with the double, cosegregating mutant TLR4 exhibiting the greatest deficiency. Overexpression of Flag-tagged WT and mutant vectors at input levels resulting in agonist-independent signaling led to equivalent NF-kappaB signaling, suggesting that these mutations in TLR4 affect appropriate interaction with agonist or coreceptor. These data provide new insights into the importance of stoichiometry among the components of the TLR4/MD-2/CD14 complex. A structural model that accounts for the diminished responsiveness of mutant TLR4 polymorphisms to structurally unrelated TLR4 agonists is proposed.     

Lack of association between TLR4 Asp299Gly and Thr399Ile polymorphisms and sepsis susceptibility: a meta-analysis

Sepsis, a condition of systemic inappropriate inflammation response to the invasion of microorganisms, results in considerable morbidity and mortality in patients. Some, but not all, epidemiological studies have suggested that Toll-like receptor 4 (TLR4) polymorphisms, Asp299Gly and Thr399Ile, may influence the risk of at-risk patients for sepsis. Our work tried to further study the association of the two common polymorphisms with sepsis susceptibility by performing a meta-analysis of previous data. Electronic searches of MEDLINE, EMBASE and Web of Science databases were performed. Original observational studies dealing with the association between polymorphisms Asp299Gly and/or Thr399Ile and sepsis risk were selected. Pooled odds ratios (ORs) and 95% confidence intervals (CIs) were calculated with random-effects model or fixed-effects model based on the heterogeneity analysis. Seventeen studies including 2212 cases and 3880 controls were included with most subjects of Caucasian ethnicity. The odds ratio for the association of Asp299Gly polymorphism with sepsis risk was 1.22 (95% CI: 0.90-1.65, P=0.21), and the association of Thr399Ile polymorphism was 1.16 (95%CI: 0.70-1.91, P=0.57). Subgroup analysis and sensitivity analysis did not change the results. Our meta-analysis revealed that the two common TLR4 polymorphisms, Asp299Gly and Thr399Ile, have no strong association with the likelihood of sepsis in Caucasian populations. Further studies are needed to investigate the effect of genetic networks and their mutual interactions in TLR4 signaling pathway on sepsis susceptibility.     

Association between TLR2 and TLR4 Gene Polymorphisms and the Susceptibility to Inflammatory Bowel Disease: A Meta-Analysis

BackgroundThe associations between toll-like receptor 2 (TLR2) and toll-like receptor 4(TLR4) polymorphisms and inflammatory bowel disease (IBD) susceptibility remain controversial. A meta-analysis was performed to assess these associations.MethodsA systematic search was performed to identify all relevant studies relating TLR2 and TLR4 polymorphisms and IBD susceptibility. Odds ratios (ORs) and 95% confidence intervals (CIs) were calculated. Subgroup analyses were performed by ethnicity and publication quality.ResultsThirty-eight eligible studies, assessing 10970 cases and 7061 controls were included. No TLR2 Arg677Trp polymorphism was found. No significant association was observed between TLR2 Arg753Gln polymorphism and Crohn’s disease (CD) or ulcerative colitis (UC) in all genetic models. Interestingly, TLR4 Asp299Gly polymorphism was significantly associated with increased risk of CD and UC in all genetic models, except for the additive one in CD. In addition, a statistically significant association between TLR4 Asp299Gly polymorphism and IBD was observed among high quality studies evaluating Caucasians, but not Asians. Associations between TLR4 Thr399Ile polymorphisms and CD risk were found only in the allele and dominant models. The TLR4 Thr399Ile polymorphism was associated with UC risk in pooled results as well as subgroup analysis of high quality publications assessing Caucasians, in allele and dominant models.ConclusionsThe meta-analysis provides evidence that TLR2 Arg753Gln is not associated with CD and UC susceptibility in Asians; TLR4 Asp299Gly is associated with CD and UC susceptibility in Caucasians, but not Asians. TLR4 Thr399Ile may be associated with IBD susceptibility in Caucasians only. Additional well-powered studies of Asp299Gly and other TLR4 variants are warranted.     

Relationship between the TLR2 and TLR4 gene polymorphisms with a predisposition to certain urogenital infections

The distribution of the TLR2 Arg753Gln, TLR4 Asp299Gly and TLR4 Thr399Ile polymorphisms among residents of Poltavsky region was studied. The relationship between these polymorphisms and the presence of diseases caused by urogenital infections was also studied. The population control group was a random sample of residents of Poltavsky region (n = 299); the group of patients with urogenital diseases consisted of 156 individuals. PCR and subsequent restriction analysis were used to enable the genotyping of the following TLR polymorphisms in these groups: Arg753Gln, Asp299Gly, and TLR4 Thr399Ile. We found a statistically significant correlation between the presence of allele A of the TLR2 gene (p = 0.0018) and allele G of the TLR4 gene (p = 0.085) and the presence of urogenital diseases.     

The Asp299Gly polymorphism alters TLR4 signaling by interfering with recruitment of MyD88 and TRIF

Asp(299)Gly (D299G) and, to a lesser extent, Thr(399)Ile (T399I) TLR4 polymorphisms have been associated with gram-negative sepsis and other infectious diseases, but the mechanisms by which they affect TLR4 signaling are unclear. In this study, we determined the impact of the D299G and T399I polymorphisms on TLR4 expression, interactions with myeloid differentiation factor 2 (MD2), LPS binding, and LPS-mediated activation of the MyD88- and Toll/IL-1R resistance domain-containing adapter inducing IFN-β (TRIF) signaling pathways. Complementation of human embryonic kidney 293/CD14/MD2 transfectants with wild-type (WT) or mutant yellow fluorescent protein-tagged TLR4 variants revealed comparable total TLR4 expression, TLR4-MD2 interactions, and LPS binding. FACS analyses with anti-TLR4 Ab showed only minimal changes in the cell-surface levels of the D299G TLR4. Cells transfected with D299G TLR4 exhibited impaired LPS-induced phosphorylation of p38 and TANK-binding kinase 1, activation of NF-κB and IFN regulatory factor 3, and induction of IL-8 and IFN-β mRNA, whereas T399I TLR4 did not cause statistically significant inhibition. In contrast to WT TLR4, expression of the D299G mutants in TLR4(-/-) mouse macrophages failed to elicit LPS-mediated induction of TNF-α and IFN-β mRNA. Coimmunoprecipitation revealed diminished LPS-driven interaction of MyD88 and TRIF with the D299G TLR4 species, in contrast to robust adapter recruitment exhibited by WT TLR4. Thus, the D299G polymorphism compromises recruitment of MyD88 and TRIF to TLR4 without affecting TLR4 expression, TLR4-MD2 interaction, or LPS binding, suggesting that it interferes with TLR4 dimerization and assembly of intracellular docking platforms for adapter recruitment.     

Relationship of TLR2 and TLR4 gene polymorphism with a penchant for individual urogenital infections

We investigated the population prevalence of polymorphisms of Arg753Gln TLR2gene, and Asp299Gly, Thr399Ile TLR4 genes among people living in the Poltava region, as well as data communication polymorphisms with the presence of diseases caused by urogenital infections. The group of population control was a random sample of residents of the Poltava region (n = 299). The group of patients with urogenital diseases included 156 people. Genotyping of these groups TLR2 Arg753Gln polymorphism and the gene TLR4 Asp299Gly, Thr399Ile was performed using PCR and subsequent restriction analysis. Statistically significant association of allele A ofgene TLR2 (p = 0.0018) and allele G of gene TLR4 (p = 0.085) with the presence of urogenital diseases was confirmed.     

TLR4 and TLR9 polymorphisms are not associated with either rheumatoid arthritis or systemic lupus erythematosus in Mexican patients

Toll-like receptor (TLR)-mediated signaling pathways induce a proinflammatory microenvironment to eradicate pathogens. However, in rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE), TLRs can promote chronic inflammation. It has been shown that some TLR4 and TLR9 single nucleotide polymorphisms (SNPs) are risk factors for RA and SLE, but these findings have not been replicated in all populations; thus, results are inconclusive. We evaluated the TLR4 Asp299Gly, Thr399Ile,???1892G/A SNPs, and the TLR9 Pro545Pro SNP to assess potential associations with RA and SLE in Mexican patients. This study included 474 patients with RA, 283 patients with SLE, and 424 healthy controls. We used a 5′ nuclease allelic discrimination assay to genotype individuals for the four TLR4 and TLR9 polymorphisms. We found that the genotype or allelic frequencies of the TLR4 Asp299Gly, Thr399Ile,???1892G/A, and TLR9 Pro545Pro polymorphisms were similar between patients and controls. We found no association under different genetic models. A haplotype analysis of TLR4 showed no association with either RA or SLE. We found no significant differences in the allelic or genotypic frequencies of TLR4 Asp299Gly, Thr399IIe,???1892G/A, or TLR9 Pro545Pro between patients and controls. These findings suggested that these variants are not risk factors for RA or SLE in Mexican patients.

     

TLR4 polymorphisms mediate impaired responses to respiratory syncytial virus and lipopolysaccharide

Severe bronchiolitis following respiratory syncytial virus (RSV) infection occurs in only a small subset of infected infants and the basis for variations in disease severity is not understood. Innate immune responses to RSV are mediated by TLR-4, and the (299)Gly and (399)Ile alleles of the TLR4 gene have been linked epidemiologically with increased severity of RSV disease in children. We hypothesized that cellular immune responses to RSV mediated by these variant forms of the receptor are defective relative to responses mediated via the common form of the receptor. Human bronchial epithelial cells were transfected with TLR4 constructs encoding the common TLR4 gene sequence ((299)Asp/(399)Thr), or the (299)Gly or (399)Ile alleles, and cytokine responses to in vitro RSV challenge were analyzed in the different transfected cells. Follow-up studies compared RSV-induced responses in PBMC from children expressing these same TLR4 genotypes. Human bronchial epithelial expressing (299)Gly or (399)Ile displayed normal levels of intracellular TLR4 but failed to efficiently translocate the receptor to the cell surface. This was associated with reduced NF-kappaB signaling post-TLR4 engagement, reduced production of IFNs, IL-8, IL-10, IL-12p35, IL-18, and CCL8, and the absence of acute-phase TNF-alpha. These findings were mirrored by blunted PBMC responses to RSV in children expressing the same TLR4 variants. Compromised first-line defense against RSV at the airway-epithelial surface of children expressing these TLR4 variants may thus confer increased susceptibility to severe infections with this virus.     

TLR4 Asp299Gly and Thr399Ile Polymorphisms: No Impact on Human Immune Responsiveness to LPS or Respiratory Syncytial Virus

Background

A broad variety of natural environmental stimuli, genotypic influences and timing all contribute to expression of protective versus maladaptive immune responses and the resulting clinical outcomes in humans. The role of commonly co-segregating Toll-like receptor 4 (TLR4) non-synonymous single nucleotide polymorphisms Asp299Gly and Thr399Ile in this process remains highly controversial. Moreover, what differential impact these polymorphisms might have in at risk populations with respiratory dysfunction, such as current asthma or a history of infantile bronchiolitis, has never been examined. Here we determine the importance of these polymorphisms in modulating LPS and respiratory syncytial virus (RSV) - driven cytokine responses. We focus on both healthy children and those with clinically relevant respiratory dysfunction.

Methodology

To elucidate the impact of TLR4 Asp299Gly and Thr399Ile on cytokine production, we assessed multiple immune parameters in over 200 pediatric subjects aged 7–9. Genotyping was followed by quantification of pro- and anti-inflammatory cytokine responses by fresh peripheral blood mononuclear cells upon acute exposure to LPS or RSV.

Principal Findings

In contrast to early reports, neither SNP influenced immune responses evoked by LPS exposure or RSV infection, as measured by the intermediate phenotype of pro- and anti-inflammatory cytokine responses to these ubiquitous agents. There is no evidence of altered sensitivity in populations with “at risk” clinical phenotypes.

Conclusions/Significance

Genomic medicine seeks to inform clinical practice. Determination of the TLR4 Asp299Gly/Thr399Ile haplotype is of no clinical benefit in predicting the nature or intensity of cytokine production in children whether currently healthy or among specific at-risk groups characterized by prior infantile broncholitis or current asthma.     

Toll-like receptor 4 polymorphisms predispose to cutaneous leishmaniasis

The clinical spectrum of cutaneous leishmaniasis (CL) is extremely variable. Studies in experimental leishmaniasis have revealed a role for TLR4 in control of infection. In the present study the associations between TLR4 mutations (Asp299Gly and Thr399Ile) with outcome of CL have been investigated. Genotyping for Asp299Gly and Thr399Ile was performed in patients with chronic (N?=?22) and acute (N?=?61) CL, asymptomatic (N?=?45) and healthy leishmanin skin test negative individuals (N?=?75). The results showed the frequency of the Asp299Gly genotype was increased in patients with chronic disease (OR 25.3, 95% CI 5.2-115.6, P?相似文献   

High variability of TLR4 gene in different ethnic groups in Iran

Infectious diseases exert a constant evolutionary pressure on the innate immunity genes. TLR4, an important member of the TLR family, specifically recognizes conserved structures of various infectious pathogens. Two functional TLR4 polymorphisms, Asp299Gly and Thr399Ile, modulate innate host defense against infections, and their prevalence between various populations has been proposed to be influenced by local infectious pressures. If this assumption is true, strong local infectious pressures would lead to a homogeneous pattern of these ancient TLR4 polymorphisms in geographically-close populations, while a weak selection or genetic drift may result in a diverse pattern. We evaluated TLR4 polymorphisms in 15 ethnic groups in Iran, to assess whether infections exerted selective pressures on different haplotypes containing these variants. The Iranian subpopulations displayed a heterogeneous pattern of TLR4 polymorphisms, comprising various percentages of Asp299Gly and Thr399Ile, alone or in combination. The Iranian sample, as a whole, showed an intermediate mixed pattern when compared with commonly-found patterns in Africa, Europe, Eastern Asia and the Americas. These findings suggest a weak, or absent, selection pressure on TLR4 polymorphisms in the Middle-East that does not support the assumption of an important role of these polymorphisms in the host defense against local pathogens.     

Polymorphisms in vitamin D receptor,toll-like receptor 2 and Toll-Like receptor 4 genes links with Dengue susceptibility

Host genetic factors are known to determine disease susceptibility in dengue virus infection. Therefore, in this study association of gene polymorphisms of Vitamin D Receptor [rs731236 (Taq) and rs7975232 (Apa1)], Toll-like receptor 2 [rs5743708 (Arg735Gln) and rs5743704 (Pro631His)] and Toll-like receptor 4 [rs4986790A/G(Asp299Gly13843) and rs4986791 C/T(Thr399Ile)] were studied in cases with dengue as compared to controls. Total 98 cases of confirmed dengue virus infection and 98 age, sex and geographically matched healthy controls were enrolled and their genetic polymorphisms for the above mentioned regions were studied by Sanger sequencing. Mutant genotypes CC of VDR rs731236 (Taq1) [(OR 3.808, p value =0.02, CI 1.160-12.498)], GG of VDR rs7975232 (Apa1) [(OR 3.485, p value =0.02, CI 1.162-10.45)] and heterozygous genotypes of TLR4 rs4986790 A/G Asp299Gly [OR 2.40, p value= 0.02, CI 1.12-5.14], TLR4 rs4986791 C/T Thr399Ile [OR 2.09, p value=0.02, CI 1.12-5.14] were found to be significantly more in cases with dengue virus infection as compared to the controls. Also, at these positions mutant alleles were observed in significantly higher number of cases than controls. The values for C allele at VDR rs731236 (Taq1) were OR 1.86, p value 0.009, CI 1.162-3.001; for allele G at rs7975232( Apa1) were OR 2.71, p value 0.006, CI 1.196-2.98 for allele G at TLR4s rs4986790 A/G Asp299Gly were OR 2.35, p value 0.009, CI 1.23-4.50 and for allele T at rs4986791 C/T Thr399Ile were OR 2.36, p value=0.006, CI 1.28-4.38. VDR and TLR4 but not TLR2 gene polymorphisms were found to be associated with dengue susceptibility in Indian population.     

Association of TLR4 polymorphisms with symptomatic respiratory syncytial virus infection in high-risk infants and young children

Respiratory syncytial virus (RSV) is a leading cause of infant mortality worldwide. Although anti-RSV Ab prophylaxis has greatly reduced infant mortality in the United States, there is currently no vaccine or effective antiviral therapy. RSV fusion (F) protein activates cells through TLR4. Two single nucleotide polymorphisms (SNPs) encoding Asp299Gly and Thr399Ile substitutions in the TLR4 ectodomain were previously associated with TLR4 hyporesponsiveness and increased susceptibility to bacterial infection. Prevalence of these SNPs was analyzed in a case series of 105 DNA samples extracted from archived nasal lavage samples from high-risk infants/young children with confirmed RSV disease who participated in two seminal clinical trials for anti-RSV prophylaxis. Frequencies of TLR4 SNPs in the case series were compared with those of literature controls, healthy adults, infants, and young children who presented with symptoms of respiratory infections (but not preselected for high risk for RSV). Both SNPs were highly associated with symptomatic RSV disease in this largely premature population (p < 0.0001), with 89.5% and 87.6% of cases being heterozygous for Asp299Gly and Thr399Ile polymorphisms versus published control frequencies of 10.5% and 6.5%, respectively. The other two control groups had similarly low frequencies. Our data suggest that heterozygosity of these two extracellular TLR4 polymorphisms is highly associated with symptomatic RSV disease in high-risk infants and support a dual role for TLR4 SNPs in prematurity and increased susceptibility to RSV not revealed by analysis of either alone.     

Functional consequences of the Asp299Gly Toll-like receptor-4 polymorphism

Toll-like receptor-4 (TLR4) is a pattern-recognition receptor not only for exogenous ligands such as lipopolysaccharide (LPS) of Gram-negative bacteria, but also for endogenous ligands such as fibronectin, heat shock proteins and hyaluronan oligosaccharides. The Asp299Gly allele of the TLR4 gene has been associated with increased risk for severe infections, but reduced progression of atherosclerosis. We have investigated the consequences of the presence of Asp299Gly polymorphism after stimulation of mononuclear cells with lipopolysaccharide (LPS), the non-LPS TLR4 microbial stimuli Aspergillus fumigatus and Cryptococcus neoformans, and the endogenous TLR4 ligand heat shock protein 60. No differences in either production of the proinflammatory cytokine TNF or the antiinflammatory cytokine interleukin-10 were observed between volunteers with the wild-type allele, volunteers heterozygous for the Asp299Gly allele and one volunteer homozygous for the TLR4 variant. In conclusion, the presence of the Asp299Gly TLR4 polymorphism does not result in defective pro and antiinflammatory cytokine production after stimulation with either exogenous (LPS and non-LPS) or endogenous TLR4 ligands, and alternative explanations are likely to be responsible for the epidemiological data showing associations with inflammatory conditions. In addition, this is the first study to demonstrate that even homozygosity for the Asp299Gly mutation does not confer hyporesponsiveness to stimulation with TLR4 stimuli.