Single step high-throughput determination of Toll-like receptor 4 polymorphisms

A review of methods for detecting single-nucleotide polymorphisms in the Toll-like receptor gene family

The Toll-like receptors play an essential role in immunity through targeting the pathogen-associated molecular patterns. Nucleotide variations in TLR genes, especially single-nucleotide polymorphisms, have been shown to alter host immune susceptibility to several infections and diseases. Since TLR genes' polymorphisms can be a promising biomarker, ongoing investigations aim to develop, optimize and validate SNP detection methods. This review discusses various TLR SNP detection methods, either used extensively or occasionally, but having a vast potential in high-throughput settings. Methods such as PCR-restriction fragment length polymorphism, TaqMan^® assay, direct sequencing and matrix-assisted laser desorption ionization - time of flight mass spectroscopy MS are frequently used methods whereas Illumina GoldenGate^® assay, reverse hybridization technology, PCR-confronting two-pair primers, KBiosciences KASPar^® SNP assay, SNP stream^®, PCR-fluorescence hybridization and SNaPshot^® are powerful but sporadically used methods. We suggest that, for individual laboratories, the detection method of choice depends on a combination of factors such as throughput volume, reproducibility, feasibility and cost-effectiveness.

Postpartum Circulating Markers of Inflammation and the Systemic Acute-Phase Response After Early-Onset Preeclampsia

Preeclampsia is an inflammatory-mediated hypertensive disorder of pregnancy and seems to be an early indicator of increased cardiovascular risk, but mechanisms underlying this association are unclear. In this study, we identified levels of circulating inflammatory markers and dynamic changes in the systemic acute-phase response in 44 women with a history of severe early-onset preeclampsia, compared with 29 controls with only uneventful pregnancies at 1.5 to 3.5 years postpartum. Models used were in vivo seasonal influenza vaccination and in vitro whole-blood culture with T-cell stimulants and the toll-like receptor-4 ligand lipopolysaccharide. Outcome measures were C-reactive protein, interleukin-6 (IL-6), IL-18, fibrinogen, myeloperoxidase, and a panel of 13 cytokines representative of the innate and adaptive inflammatory response, in addition to established cardiovascular markers. The in vivo acute-phase response was higher for women with previous preeclampsia than that for controls without such a history, although only significant for C-reactive protein (P=0.04). Preeclampsia was associated with higher IL-1β (P<0.05) and IL-8 (P<0.01) responses to T-cell activation. Hierarchical clustering revealed 2 distinct inflammatory clusters associated with previous preeclampsia: an adaptive response cluster associated with increased C-reactive protein and IL-6 before and after vaccination, increased weight, and low high-density lipoprotein cholesterol; and a toll-like receptor-4 mediated the cluster associated with increased IL-18 before and after vaccination but not associated with other cardiovascular markers. Furthermore, we found interactions between previous preeclampsia, common TLR4 gene variants, and the IL-18 response to vaccination. In conclusion, preeclampsia is associated with alterations in the inflammatory response postpartum mostly independent of other established cardiovascular risk markers.

Maternal TLR4 and NOD2 gene variants, pro-inflammatory phenotype and susceptibility to early-onset preeclampsia and HELLP syndrome

BACKGROUND

Altered maternal inflammatory responses play a role in the development of preeclampsia and the hemolysis, elevated liver enzymes and low platelets (HELLP) syndrome. We examined whether allelic variants of the innate immune receptors Toll-like receptor 4 (TLR4) and nucleotide-binding oligomerization domain 2 (NOD2), that impair the inflammatory response to endotoxin, are related to preeclampsia and HELLP syndrome.

METHODS AND FINDINGS

We determined five common mutations in TLR4 (D299G and T399I) and NOD2 (R702W, G908R and L1007fs) in 340 primiparous women with a history of early-onset preeclampsia, of whom 177 women developed HELLP syndrome and in 113 women with a history of only uneventful pregnancies as controls. In addition, we assessed plasma levels of pro-inflammatory biomarkers C-reactive protein, interleukin-6, soluble intercellular adhesion molecule-1, fibrinogen and von Willebrand factor in a subset of 214 women included at least six months after delivery. After adjustment for maternal age and chronic hypertension, attenuating allelic variants of TLR4 were more common in women with a history of early-onset preeclampsia than in controls (OR 2.9 [95% CI 1.2-6.7]). Highest frequencies for TLR4 variants were observed in women who developed HELLP syndrome (adjusted OR 4.1 [95% CI 1.7-9.8]). In addition, high levels of interleukin-6 and fibrinogen were associated with a history of early-onset preeclampsia. Combined positivity for any of the TLR4 and NOD2 allelic variants and high levels of interleukin-6 was 6.9-fold more common in women with a history of early-onset preeclampsia (95% CI 2.1-23.2) compared to controls.

CONCLUSIONS

We observed an association of common TLR4 and NOD2 gene variants, and pro-inflammatory phenotype with a history of early-onset preeclampsia and HELLP syndrome. These findings suggest involvement of the maternal innate immune system in severe hypertensive disorders of pregnancy.

The interaction between HMGB1 and TLR4 dictates the outcome of anticancer chemotherapy and radiotherapy

For the last four decades, the treatment of cancer has relied on four treatment modalities, namely surgery, radiotherapy, cytotoxic chemotherapy, and hormonotherapy. Most of these therapies are believed to directly attack and eradicate tumor cells. The emerging concept that cancer is not just a disease of a tissue or an organ but also a host disease relies on evidence of tumor-induced immunosuppression and polymorphisms in genes involved in host protection against tumors. This theory is now gaining new impetus, based on our recent data showing that optimal therapeutic effects require the immunoadjuvant effect of tumor cell death induced by cytotoxic anticancer agents. Here, we show that the release of the high mobility group box 1 protein (HMGB1) by dying tumor cells is mandatory to license host dendritic cells (DCs) to process and present tumor antigens. HMGB1 interacts with Toll-like receptor 4 (TLR4) on DCs, which are selectively involved in the cross-priming of anti-tumor T lymphocytes in vivo. A TLR4 polymorphism that affects the binding of HMGB1 to TLR4 predicts early relapse after anthracycline-based chemotherapy in breast cancer patients. This knowledge may be clinically exploited to predict the immunogenicity and hence the efficacy of chemotherapeutic regimens.

Toll-like receptor 4-dependent contribution of the immune system to anticancer chemotherapy and radiotherapy

Conventional cancer treatments rely on radiotherapy and chemotherapy. Such treatments supposedly mediate their effects via the direct elimination of tumor cells. Here we show that the success of some protocols for anticancer therapy depends on innate and adaptive antitumor immune responses. We describe in both mice and humans a previously unrecognized pathway for the activation of tumor antigen-specific T-cell immunity that involves secretion of the high-mobility-group box 1 (HMGB1) alarmin protein by dying tumor cells and the action of HMGB1 on Toll-like receptor 4 (TLR4) expressed by dendritic cells (DCs). During chemotherapy or radiotherapy, DCs require signaling through TLR4 and its adaptor MyD88 for efficient processing and cross-presentation of antigen from dying tumor cells. Patients with breast cancer who carry a TLR4 loss-of-function allele relapse more quickly after radiotherapy and chemotherapy than those carrying the normal TLR4 allele. These results delineate a clinically relevant immunoadjuvant pathway triggered by tumor cell death.

Study of disease-relevant polymorphisms in the TLR4 and TLR9 genes: A novel method applied to the analysis of the Portuguese population

Toll-like receptors (TLRs) are cellular receptors that mediate recognition of microbial challenges and the subsequent inflammatory response. Genetic variations within these inflammation-associated genes may alter host-pathogen defence mechanisms affecting susceptibility towards infectious diseases. Taking into account the significance of these genes, we developed a simple and rapid method based in the bi-directional PCR amplification of specific alleles (Bi-PASA) for genotyping known sequence variants in TLR4 (Asp299Gly and Thr399Ile) and TLR9 (T-1237C) genes. This method allows genotype determination in a single reaction and is amenable to large-scale analysis. We used Bi-PASA to characterize the distribution of these polymorphisms in the Portuguese population. A total of 388 randomly selected blood donors of Portuguese origin (203 females and 185 males) were genotyped and allele frequencies were determined. Among the tested individuals, 11.1% and 10.8% were heterozygous for Asp299Gly and Thr399Ile, respectively. In what concerns the T-1237C variation in TLR9, the variant allele was present in 19.4% of the individuals tested. Besides confirming the usefulness of the Bi-PASA in polymorphism analysis, the data presented provide valuable information on TLR polymorphisms in the Portuguese population that can be used to stratify risk patients with increased susceptibility to infection.

Gingival epithelial cells heterozygous for Toll-like receptor 4 polymorphisms Asp299Gly and Thr399ile are hypo-responsive to Porphyromonas gingivalis

The Toll-like receptor (TLR)4 is the major sensor for bacterial lipopolysaccharide and its two common co-segregating polymorphisms, Asp299Gly and Thr399Ile, which occur at a frequency of between 6 and 10%, have been associated with infectious diseases, LPS hypo-responsiveness and cardiovascular disease. Porphyromonas gingivalis is a Gram-negative bacterium implicated in chronic periodontitis and is a known TLR4 and TLR2 agonist. We obtained two gingival epithelial cell primary cultures from subjects heterozygous for the TLR4 polymorphism Asp299Gly and compared response characteristics with similar cells from patients (four) with the wild-type TLR4 genes. Cytokine responses and transcriptome profiles of gingival epithelial cell primary culture cells to TNFalpha challenge were similar for all primary epithelial cell cultures. P. gingivalis challenge, however, gave markedly different responses for Asp299Gly heterozygous and wild-type epithelial cell cultures. The epithelial cells heterozygous for the TLR4 polymorphism Asp299Gly were functionally hypo-responsive, evidenced by differences in BD-2 mRNA expression, mRNA response profile by microarray analysis and by pro-inflammatory and chemokine cytokines at the protein and mRNA level. These findings emphasize variance in human epithelial cell TLRs, linked with Asp299Gly carriage, which results in a hypo-responsive epithelial cell phenotype less susceptible to Gram-negative diseases and associated systemic conditions.

Toll-like receptor (TLR) 4 polymorphism Asp299Gly is not associated with disease course in Dutch sarcoidosis patients

The aetiology of sarcoidosis, a systemic disorder characterized by the formation of non-caseating granulomas in variable organs, remains enigmatic. Clarification is hampered by heterogeneity in disease phenotypes and course, due partly to the influence of a variety of genetic and environmental factors. Multiple studies have pointed towards bacteria as possible causative agents. Toll-like receptors (TLR) are innate immunity receptors important in the immune response against pathogens. TLR-4, together with CD14 and MD-2, is an essential receptor for the recognition of lipopolysaccharide (LPS), unique to the cell wall of Gram-negative bacteria. Recently, an association between TLR-4 polymorphism Asp299Gly, leading to a change in the extracellular domain of the receptor and possible hyporesponsiveness to LPS, and a chronic course of sarcoidosis was found in German patients. In the present study this polymorphism was genotyped in 156 Dutch sarcoidosis patients and 200 healthy Dutch controls using dual-labelled fluorescent oligonucleotides. No differences were found in allelic distributions between patients and controls (P = 0.79) or within the different clinical entities of the sarcoidosis group (P = 0.44). Importantly, there were no differences between the Dutch and German sarcoidosis patients (P = 0.62). However, the allelic distribution of the Asp299Gly polymorphism differed significantly between both control groups (P = 0.04). This study highlights the importance of testing a reported gene association in a distinct population when performing genetic association studies.

Toll-like receptor 4 polymorphisms and idiopathic chromosomally normal miscarriage

BACKGROUND

Lipopolysaccharide (LPS or endotoxin) exposure resulting from microbial invasion of the endometrium disturbs the Th1/Th2 balance at the feto-maternal interface and has been linked to the risk of idiopathic miscarriage in a range of human and animal studies. Toll-like receptor 4 (TLR4) mediates LPS signalling, and the human TLR4 gene harbours two single-nucleotide polymorphisms (SNPs) known to reduce LPS responsiveness. We hypothesized that genetic variation altering TLR4 function may influence the risk of idiopathic pregnancy loss.

METHODS AND RESULTS

We examined fetal TLR4 genotypes in a case-control cohort of chromosomally normal miscarriages (n=96) and healthy term newborns (n=113). The allele frequencies of the Asp299Gly and Thr399Ile TLR4 SNPs were determined by quantitative PCR using DNA extracted from extraembryonic tissues and umbilical cord blood, respectively. TLR4 genotype frequencies were not significantly different between cases and controls.

CONCLUSIONS

There was no association between fetal TLR4 polymorphisms, Asp299Gly and Thr399Ile, known to blunt LPS responsiveness, and the risk of idiopathic, chromosomally normal miscarriage. Nevertheless, TLR4 or perhaps other LPS-binding chaperone molecules are biologically plausible candidate genes that may alter the risk of idiopathic miscarriage.

High-throughput genotyping with infrared fluorescence allele specific hybridization (iFLASH): A simple, reliable and low-cost alternative

OBJECTIVES

To develop and validate a novel genotyping approach, named infrared Fluorescence Allele Specific Hybridization (iFLASH), which combines the principles of allele specific oligonucleotide (ASO) hybridization with the advanced possibilities of infrared imaging.

DESIGN AND METHODS

As an example, we genotyped the 55L > M and the 192Q > R common genetic variants of the paraoxonase-1 gene in 92 DNA samples using the iFLASH technique, and validated the outcomes with the restriction fragment length polymorphism (RFLP) and TAQman genotyping assays.

RESULTS

There was a 100 percent agreement in genotype outcome among the three methods.

CONCLUSIONS

Although we found complete unity in genotype outcome, the iFLASH assay has essential advantages over the RFLP and TAQman genotyping assays. First, the iFLASH technique is capable of handling up to 1536 samples per assay, which makes it a suitable technique for high-throughput genotyping. Secondly, because the costs per assay are lower, high-throughput genotyping with iFLASH is affordable.