A frequent toll-like receptor (TLR)-2 polymorphism is a risk factor for coronary restenosis

Impact of Toll-Like Receptor 2 and 9 Gene Polymorphisms on COVID-19: Susceptibility, Severity, and Thrombosis

Background

Toll-like receptors (TLRs) play an important role in activation of innate and adaptive immune responses.

Aim

We aimed to detect the association between TLR2 rs5743708 G>A and TLR9 rs5743836 C>T variants and COVID-19 disease susceptibility, severity, and thrombosis by using neutrophil extracellular traps (NETs).

Subjects and Methods

We included 100 adult COVID-19 patients as well as 100 age- and gender-matched normal controls. Participants were genotyped for TLR2 rs5743708 and TLR9 rs5743836. Citrullinated Histone (H3) was detected as an indicator of NETs.

Results

The mutant (G/A and C/C) genotypes and (A and C) alleles of TLR2 rs5743708 and TLR9 rs5743836, respectively, have been significantly related to a higher risk of COVID-19 infection, representing a significant risk factor for the severity of COVID-19. There was no significant association between the two variants and citrullinated histone (H3).

Conclusion

TLR2 rs5743708 and TLR9 rs5743836 variants have been significantly related to a higher risk and severity of COVID-19 infection but had no effect on thrombus formation.

Polymorphism of CD14 Gene Is Associated with Adverse Outcome among Patients Suffering from Cardiovascular Disease

Background

The biological link between severe periodontitis and cardiovascular disease is well established. Both complex inflammatory diseases are influenced by genetic background. Therefore, the impact of genetic variations of receptors of the innate immune system-(Toll-like receptors (TLRs)) TLR2, TLR4, cluster of differentiation 14 (CD14), and the transcription factor nuclear factor-κΒ (NF-κB)-was investigated.

Materials and Methods

In this study (ClinicalTrials.gov identifier: NCT01045070), 1002 cardiovascular (CV) patients were included. In a 3-year follow-up period, new vascular events were assessed. SNPs in CD14 (rs2569190), NF-κΒ (rs28362491), TLR2 (rs5743708), and TLR4 (rs4986790) were genotyped. The impact of these genetic variants on severe periodontitis as well as on CV outcome was assessed.

Results

All investigated genetic variants were not associated with preexisting CV events or severe periodontitis in CV patients. In Kaplan-Meier survival analyses, the CT genotype of CD14 single-nucleotide polymorphism (SNP) rs2569190 was shown to be an independent predictor for combined CV endpoint (log rank: p = 0.035; cox regression; hazard ratio: 1.572; p = 0.044) as well as cardiovascular death (log rank: p = 0.019; cox regression; hazard ratio: 1.585; p = 0.040) after three years of follow-up.

Conclusions

SNPs in CD14, NF-κΒ, TLR2, and TLR4 are no risk modulators for preexisting CV events or severe periodontitis in CV patients. The CT genotype of CD14 SNP rs2569190 provides prognostic value for further CV events within 3 years of follow-up.

Toll-like receptors in immunity and inflammatory diseases: Past, present, and future

The immune system is a very diverse system of the host that evolved during evolution to cope with various pathogens present in the vicinity of environmental surroundings inhabited by multicellular organisms ranging from achordates to chordates (including humans). For example, cells of immune system express various pattern recognition receptors (PRRs) that detect danger via recognizing specific pathogen-associated molecular patterns (PAMPs) and mount a specific immune response. Toll-like receptors (TLRs) are one of these PRRs expressed by various immune cells. However, they were first discovered in the Drosophila melanogaster (common fruit fly) as genes/proteins important in embryonic development and dorso-ventral body patterning/polarity. Till date, 13 different types of TLRs (TLR1-TLR13) have been discovered and described in mammals since the first discovery of TLR4 in humans in late 1997. This discovery of TLR4 in humans revolutionized the field of innate immunity and thus the immunology and host-pathogen interaction. Since then TLRs are found to be expressed on various immune cells and have been targeted for therapeutic drug development for various infectious and inflammatory diseases including cancer. Even, Single nucleotide polymorphisms (SNPs) among various TLR genes have been identified among the different human population and their association with susceptibility/resistance to certain infections and other inflammatory diseases. Thus, in the present review the current and future importance of TLRs in immunity, their pattern of expression among various immune cells along with TLR based therapeutic approach is reviewed.

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TLRs are first described PRRs that revolutionized the biology of host-pathogen interaction and immune response

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The discovery of different TLRs in humans proved milestone in the field of innate immunity and inflammation

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The pattern of expression of all the TLRs expressed by human immune cells

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An association of various TLR SNPs with different inflammatory diseases

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Currently available drugs or vaccines based on TLRs and their future in drug targeting along with the role in reproduction, and regeneration

Association between Toll-like receptor 4 Asp299Gly polymorphism and coronary heart disease susceptibility

Published data on the association between Toll-like receptor 4 (TLR4) Asp299Gly polymorphism and coronary heart disease (CHD) susceptibility are inconclusive. To derive a more precise estimation of the relationship, a meta-analysis was performed. English-language studies were identified by searching PubMed and Embase databases (up to November 2016). All epidemiological studies were regarding Caucasians because no TLR4 Asp/Gly and Gly/Gly genotypes have been detected in Asians. A total of 20 case-control studies involving 14,416 cases and 10,764 controls were included in the meta-analysis. Overall, no significant associations were found between TLR4 Asp299Gly polymorphism and CHD susceptibility in the dominant model (OR=0.89; 95%CI=0.74 to 1.06; P=0.20) pooled in the meta-analysis. In the subgroup analysis by CHD, non-significant associations were found in cases compared to controls. When stratified by control source, no significantly decreased risk was found in the additive model or dominant model. The present meta-analysis suggests that the TLR4 Asp299Gly polymorphism was not associated with decreased CHD risk in Caucasians.

The Correlation of Increased CRP Levels with NFKB1 and TLR2 Polymorphisms in the Case of Morbid Obesity

Morbid obesity (MO) is associated with an increase in circulating levels of systemic acute phase proteins such as C-reactive protein (CRP). Toll-like receptor is possible candidate for inflammatory responses which is mainly mediated by NFKB1. The aim of this study was to investigate the relationship between NFKB1 and Toll-like receptor (TLR) 2 polymorphisms and the risk of MO in a Turkish population in the context of CRP serum levels which may contribute to susceptibility to the disease. We analysed the distribution of NFKB1-94 ins/del ATTG rs28362491 and TLR2 Arg753Gln rs5743708 polymorphisms using PCR-RFLP method and CRP serum levels using ELISA method in 213 MO and 200 healthy controls. The frequency of the ins/ins genotype and ins allele of rs28362491 was significantly higher in the patients compared to control group (P: 0.0309; P: 0.0421, respectively). Additionally, the frequency of GG genotype and G allele of rs5743708 was found to be statistically higher in the patient group (P: 0.0421; P < 0.0001, respectively). In addition, serum CRP levels (>20 mg/l) in MO patients with ins/ins genotype were significantly higher than in patients with del/ins genotype (P: 0.0309). Serum CRP levels were also higher in MO patients with GG genotype and G allele (P: 0.0001). According to combined analysis, the wild type of rs28362491 and rs5743708 polymorphisms (ins/ins/GG genotype) was also significantly higher in the patient group versus the control group when compared with the combined ins/ins/GA and del/ins/GA genotype (P < 0.0001). Therefore, our findings suggest that rs28362491 and rs5743708 polymorphisms were significantly associated with MO disease through acting by modulating serum CRP levels.

Clinical significance of the single nucleotide polymorphism TLR2 R753Q in heart transplant recipients at risk for cytomegalovirus disease

BACKGROUND

The toll-like receptor 2 (TLR2) is a significant component of innate immunity against cytomegalovirus (CMV) infection but information on the clinical significance of the single nucleotide polymorphism (SNP) (R753Q) is conflicting.

OBJECTIVES

The inconsistent observations of the immunological and clinical significance of the TLR2 R753Q polymorphism for CMV infection indicates the influence of confounders.

STUDY DESIGN

The presence of the TLR2 polymorphism was determined by a genotyping assay of 175 HTX patients and 281 healthy blood donors and evaluated in relation to selected virological and clinical parameters.

RESULTS

Relative frequency of TLR2 polymorphism was similar in HTX patients and blood donors (homozygous wild-type, 94.3% vs. 94.0%; heterozygous, 5.1% vs. 5.7%; homozygous mutated, <1%). CMV viremia was detectable in 108 (61.7%) of HTX patients. The TLR2 polymorphism was neither associated with occurrence or level of CMV infection nor with survival, graft failure or rejection, or CMV serostatus of patient before transplantation. Nevertheless, CMV viremia occurred in 83.1% of R+/D+, 77.1% of R+/D-, and 64.3% of R-/D+ patients. Time of first CMV viremia was in R-/D+ patients later than in CMV-seropositive patients (median, 182days versus 23 days; P<0.001) corresponding to the duration of antiviral prophylaxis in R-/D+ patients.

CONCLUSIONS

The TLR2 R753Q polymorphism is extremely rare in the general population and HTX patients. Screening for this risk factor of CMV disease may not be cost-effective in contrast to testing for CMV viremia.

Toll-like receptors mediating vascular malfunction: Lessons from receptor subtypes

Toll-like receptors (TLR) are a subfamily of pattern recognition receptors (PRR) implicated in a variety of vascular abnormalities. However, the pathophysiological role and the interplay between different TLR-mediated innate and adaptive immune responses during the development of vascular diseases remain largely unspecified. TLR are widely distributed in both immune and nonimmune cells in the blood vessel wall. The expressions and locations of TLR are dynamically regulated in response to distinct molecular patterns derived from pathogens or damaged host cells. As a result, the outcome of TLR signaling is agonist- and cell type-dependent. A better understanding of discrete TLR signaling pathways in the vasculature will provide unprecedented opportunities for the discovery of novel therapies in many inflammatory vascular diseases. The present brief review discusses the role of individual TLR in controlling cellular functions of the vascular system, by focusing on the inflammatory responses within the blood vessel wall which contribute to the development of hypertension and atherosclerosis.

Association of ACE insertion or deletion polymorphisms with the risk of coronary restenosis after percutaneous coronary intervention: A meta-analysis

OBJECTIVE

Previous case-control studies on the relationship between the angiotensin-converting enzyme (ACE) gene insertion/deletion (I/D) polymorphisms and coronary restenosis did not reach the same conclusion. In the present study, we aimed to further evaluate the relationship between the ACE gene I/D polymorphisms and coronary restenosis, after percutaneous coronary intervention (PCI).

METHODS

By searching PubMed, EMBase, the Chinese Biomedical Literature Database and Wanfang database, we selected 16 case-control studies related to ACE gene I/D polymorphism and coronary restenosis after PCI. To test for heterogeneity in each study, we utilized the Q-test and I(2) test. To merge the odds ratio (OR) and 95% CI, we utilized the random effects model during the analyses.

RESULTS

The present study included 4693 subjects: 1241 patients with coronary restenosis and 3452 without coronary restenosis. By meta-analysis, we found there was significant association of ACE gene I/D polymorphism with coronary restenosis (D allele versus I allele: OR = 1.92; 95% CI (1.40-2.43); p < 0.001). A subgroup analysis, by stratification according to ethnicity, also showed that this association was found not only in the Caucasian population ((D allele versus I allele: OR = 1.94; 95% CI (1.38-2.80); p < 0.001)), but also in the Asian population ((D allele versus I allele: OR = 1.83; 95% CI (1.05-3.20); p = 0.03)). After stratification according to age, we found that the D allele carriers have a higher risk for development of coronary restenosis in subjects < 60 years old (OR = 2.13; 95% CI: 1.40-3.24; p = 0.0004); while in the subjects ⩾ 60 years old, the association was present with bordering significance (OR = 1.48; 95%CI: 0.98-2.25; p = 0.06).

CONCLUSIONS

The present study suggested that the ACE gene I/D polymorphism was associated with coronary restenosis, regardless of age and ethnicity.

Human Cytomegalovirus miR-UL112-3p Targets TLR2 and Modulates the TLR2/IRAK1/NFκB Signaling Pathway

Human Cytomegalovirus (HCMV) encodes multiple microRNAs (miRNAs) whose functions are just beginning to be uncovered. Using in silico approaches, we identified the Toll-Like Receptor (TLR) innate immunity pathway as a possible target of HCMV miRNAs. Luciferase reporter assay screens further identified TLR2 as a target of HCMV miR-UL112-3p. TLR2 plays a major role in innate immune response by detecting both bacterial and viral ligands, including HCMV envelope proteins gB and gH. TLR2 activates a variety of signal transduction routes including the NFκB pathway. Furthermore, TLR2 plays an important role in controlling CMV infection both in humans and in mice. Immunoblot analysis of cells transfected with a miR-UL112-3p mimic revealed that endogenous TLR2 is down-regulated by miR-UL112-3p with similar efficiency as a TLR2-targeting siRNA (siTLR2). We next found that TLR2 protein level decreases at late times during HCMV infection and correlates with miR-UL112-3p accumulation in fibroblasts and monocytic THP1 cells. Confirming direct miR-UL112-3p targeting, down-regulation of endogenous TLR2 was not observed in cells infected with HCMV mutants deficient in miR-UL112-3p expression, but transfection of miR-UL112-3p in these cells restored TLR2 down-regulation. Using a NFκB reporter cell line, we found that miR-UL112-3p transfection significantly inhibited NFκB-dependent luciferase activity with similar efficiency as siTLR2. Consistent with this observation, miR-UL112-3p transfection significantly reduced the expression of multiple cytokines (IL-1β, IL-6 and IL-8) upon stimulation with a TLR2 agonist. Finally, miR-UL112-3p transfection significantly inhibited the TLR2-induced post-translational activation of IRAK1, a kinase located in the upstream section of the TLR2/NFκB signaling axis. To our knowledge, this is the first identified mechanism of TLR2 modulation by HCMV and is the first report of functional targeting of TLR2 by a viral miRNA. These results provide a novel mechanism through which a HCMV miRNA regulates the innate immune response by down-regulating TLR-2 expression.

TLR4 rs1927911, but not TLR2 rs5743708, is associated with atherosclerotic cerebral infarction in the Southern Han population: a case-control study

The objective of this study was to explore the association of toll-like receptor (TLR) 4 rs1927911 and TLR2 rs5743708 with atherosclerotic cerebral infarction (ACI) and their effects on blood pressure, fasting blood glucose, and blood lipids in the Han population of Hunan Province. TLR4 rs1927911 and TLR2 rs5743708 were detected by polymerase chain reaction and restriction fragment length polymorphism in 170 patients with ACI and 149 healthy controls. Our results indicated that the genotype and allele frequencies of TLR4 rs1927911 were significantly different between ACI patients and controls, whereas those of TLR2 rs5743708 were not significantly different between the 2 groups. For TLR4 rs1927911, blood pressure, fasting blood sugar, and serum lipid levels were not significantly different among different genotypes in the ACI and control groups. The rs1927911 polymorphism of the TLR4 gene may be a risk factor for ACI in the Southern Han population of Hunan Province; however, it may not be associated with blood pressure, fasting blood sugar, or blood lipids.

The effect of genetic polymorphisms of TLR2 and TLR4 in Turkish patients with coronary artery disease

Coronary artery disease (CAD), being a multifactorial disease process, has been suggested to be associated by the interaction of both environmental and genetic risk factors. Toll-like receptors (TLRs) are related to the receptors of the innate immune system which serves as the recognition of the conserved pathogen motifs and the activation of the signals that stimulate inflammatory genes. In this study, we investigated the relationship between the polymorphisms in the TLR2-Arg753Gly, TLR4-Asp299Gly and Thr399Ile gene and CAD. The study population consisted of 300 patients (149 men, 151 women) with angiographically documented CAD. The polymorphisms were genotyped by real time PCR. No association between TLR2-Arg677Trp or TLR4-Asp299Gly and -Thr399Ile gene polymorphisms and the presence or the severity of CAD was observed. On the other hand, the TLR2-Arg753Arg genotype seemed to have a protective effect against development of CAD (OR=0.17; 95% CI=0.04-0.83). Our findings suggest that TLR2-Arg753Gly polymorphism is associated with CAD susceptibility in Turkish patients.

Evaluation of Toll-Like receptor 2 and 4 RNA expression and the cytokine profile in postmenopausal women with metabolic syndrome

OBJECTIVE

To evaluate the gene expression of Toll-Like (TLR-2 and TLR-4) receptors and cytokine profile in postmenopausal women with or without metabolic syndrome (MetS).

METHODS

In this cross-sectional study, 311 Brazilian women (age≥45 years and amenorrhea≥12 months) were included. Women showing three or more of the following diagnostic criteria were diagnosed as positive for MetS: waist circumference>88 cm, triglycerides≥150 mg/dL, HDL cholesterol<50 mg/dL, blood pressure≥130/85 mmHg, and fasting glucose≥100 mg/dL. The expression of TLR-2 and TLR-4 in peripheral blood was evaluated by RNA extraction and subsequent real time PCR analysis. The cytokine profile, tumor necrosis factor alpha (TNF-α) and interleukins 1β, 6, and 10, were measured by ELISA.

RESULTS

The expression of TLR-2 RNA was demonstrated in 32.5% and TLR-4 in 20.6% of the subjects. There was no association between the expression of TLR-2 and TLR-4 and the presence or absence of MetS (P>0.05). A greater production of IL-6 was associated with TLR-2 and TLR-4 expressions and greater production of TNF-α was associated only with TLR-2 expression (P>0.05). Only the lower quartile of IL-10 was associated with the presence of the MetS (P>0.05).

CONCLUSIONS

TLR-2 and TLR-4 expressions were associated with increased pro-inflammatory cytokines, IL-6 and TNF-α, with no association with biomarkers of MetS. The low concentrations of IL-10 may suggest an anti-inflammatory modulation in postmenopausal women with MetS.

A micro RNA-146a polymorphism is associated with coronary restenosis

The association of the miRNA-146a polymorphism rs2910164 with atherosclerosis and restenosis was investigated. We found no association with atherosclerosis; however, we found a negative association for the G/C (P = 0.007) and a positive association for the C/C genotype with the risk of restenosis, which is the main drawback for cardiac surgery.

Attenuation of myocardial injury by HMGB1 blockade during ischemia/reperfusion is toll-like receptor 2-dependent

Genetic or pharmacological ablation of toll-like receptor 2 (TLR2) protects against myocardial ischemia/reperfusion injury (MI/R). However, the endogenous ligand responsible for TLR2 activation has not yet been detected. The objective of this study was to identify HMGB1 as an activator of TLR2 signalling during MI/R. C57BL/6 wild-type (WT) or TLR2(-/-)-mice were injected with vehicle, HMGB1, or HMGB1 BoxA one hour before myocardial ischemia (30 min) and reperfusion (24 hrs). Infarct size, cardiac troponin T, leukocyte infiltration, HMGB1 release, TLR4-, TLR9-, and RAGE-expression were quantified. HMGB1 plasma levels were measured in patients undergoing coronary artery bypass graft (CABG) surgery. HMGB1 antagonist BoxA reduced cardiomyocyte necrosis during MI/R in WT mice, accompanied by reduced leukocyte infiltration. Injection of HMGB1 did, however, not increase infarct size in WT animals. In TLR2(-/-)-hearts, neither BoxA nor HMGB1 affected infarct size. No differences in RAGE and TLR9 expression could be detected, while TLR2(-/-)-mice display increased TLR4 and HMGB1 expression. Plasma levels of HMGB1 were increased MI/R in TLR2(-/-)-mice after CABG surgery in patients carrying a TLR2 polymorphism (Arg753Gln). We here provide evidence that absence of TLR2 signalling abrogates infarct-sparing effects of HMGB1 blockade.

Association of a common TLR-6 polymorphism with coronary artery disease - implications for healthy ageing?

BACKGROUND

The pro-inflammatory status of the elderly triggers most of the age-related diseases such as cancer and atherosclerosis. Atherosclerosis, the leading cause world wide of morbidity and death, is an inflammatory disease influenced by life-style and genetic host factors. Stimuli such as oxLDL or microbial ligands have been proposed to trigger inflammation leading to atherosclerosis. It has recently been shown that oxLDL activates immune cells via the Toll-like receptor (TLR) 4/6 complex. Several common single nucleotide polymorphisms (SNPs) of the TLR system have been associated with atherosclerosis. To investigate the role of TLR-6 we analyzed the association of the TLR-6 SNP Pro249Ser with atherogenesis.

RESULTS

Genotyping of two independent groups with CAD, as well as of healthy controls revealed a significant association of the homozygous genotype with a reduced risk for atherosclerosis (odds ratio: 0.69, 95% CI 0.51-0.95, P = 0.02). In addition, we found a trend towards an association with the risk of restenosis after transluminal coronary angioplasty (odds ratio: 0.53, 95% CI 0.24-1.16, P = 0.12). In addition, first evidence is presented that the frequency of this protective genotype increases in a healthy population with age. Taken together, our results define a role for TLR-6 and its genetic variations in modulating the inflammatory response leading to atherosclerosis.

CONCLUSIONS

These results may lead to a better risk stratification, and potentially to an improved prophylactic treatment of high-risk populations. Furthermore, the protective effect of this polymorphism may lead to an increase of this genotype in the healthy elderly and may therefore be a novel genetic marker for the well-being during aging.

Lack of association between TLR4 Asp299Gly polymorphism and atherosclerosis: evidence from meta-analysis

INTRODUCTION

Toll like receptor 4 (TLR4) expression was found to increase markedly in human atherosclerotic lesions, notably on macrophages and endothelial cells. TLR4 Asp299Gly polymorphism was associated with a blunted receptor activity and a subsequently diminished inflammatory response, and may subsequently reduce atherosclerosis (AS) risk. However, the results of molecular epidemiological studies remained inconsistent.

MATERIALS AND METHODS

The PubMed, CNKI databases were searched for all articles available. The OR corresponding to the 95% confidence interval (95% CI) was used to assess the association between TLR4 Asp299Gly polymorphism and risk of AS.

RESULTS

15 case-control studies with 9,989 cases and 6,746 controls were available for this analysis. For control subjects, G allele frequency of TLR4 Asp299Gly polymorphism was ranging from 0.045 to 0.085. The G allele and the AG/GG genotypes were not associated with significantly risk of AS (OR=1.02, 95% CI=0.83 - 1.26 for G versus A and OR=0.96, 95% CI=0.80 - 1.15 for AG/GG versus AA, respectively) by random effects model.

CONCLUSION

These findings indicated that TLR4 Asp299Gly polymorphism may not play a role in AS development.

Association studies of gene polymorphisms in toll-like receptors 2 and 4 in Croatian patients with acute myocardial infarction

The aim of the study was to assess the frequency of SNP896A/G in the Toll-like receptor (TLR) 4 gene and SNP1350T/C in the TLR2 gene in patients with acute myocardial infarction (AMI) and to analyse the association of these SNPs with risk factors for atherosclerosis and clinical aspects of AMI in a sample of the Croatian population. We included 240 participants in the study: 120 AMI patients and 120 sex- and age-matched healthy blood donor controls. The SNP1350T/C variant in the TLR2 gene showed a lower frequency in the AMI patient group than in the control group (P = 0.033). The frequency of SNP896A/G variants in the TLR4 gene between the patients and the controls did not differ (P = 0.286). Significantly, fewer people had SNP1350T/C in the TLR2 gene (P = 0.003) among the participants with arterial hypertension than those without it. The frequency of SNP896A/G in TLR4 was the same in hypertensive patients compared with normotensive subjects (P = 0.088). SNP1350T/C in TLR2 was less frequent in the AMI patients and in those with hypertension. Thus, SNP1350T/C in TLR2 might play a protective role against AMI and arterial hypertension. The frequency of SNP896A/G in the TLR4 gene was not associated with AMI and arterial hypertension. Other risk factors for atherosclerosis and clinical aspects of myocardial infarction were not associated with the genotype distribution of the examined genes.

Restenosis after PCI. Part 1: pathophysiology and risk factors

Restenosis is a complex disease for which the pathophysiological mechanisms have not yet been fully elucidated, but are thought to include inflammation, proliferation, and matrix remodeling. Over the years, many predictive clinical, biological, (epi)genetic, lesion-related, and procedural risk factors for restenosis have been identified. These factors are not only useful in risk stratification of patients, they also contribute to our understanding of this condition. Furthermore, these factors provide evidence on which to base treatment tailored to the individual and aid in the development of novel therapeutic modalities. In this Review, we will evaluate the available evidence on the pathophysiological mechanisms of restenosis and provide an overview of the various risk factors, together with the possible clinical application of this knowledge.

Toll-like receptors and myocardial ischemia/reperfusion, inflammation, and injury

Cardiac ischemia/reperfusion (I/R) injury occurs in several important clinical contexts including percutaneous coronary interventions for acute myocardial ischemia, cardiac surgery in the setting of cardiopulmonary bypass, and cardiac transplantation. While the pathogenesis of I/R injury in these settings is multifactorial, it is clear that activation of the innate immune system and the resultant inflammatory response are important components of I/R injury. Toll-like receptor 4 (TLR4), originally identified as the sensor for bacterial lipopolysaccharide (LPS), has also been shown to serve as a sensor for endogenous molecules released from damaged or ischemic tissues. Accordingly, recent findings have demonstrated that TLR4 not only plays a central role as a mediator of cardiac dysfunction in sepsis, but also serves as a key mediator of myocardial injury and inflammation in the setting of I/R. Furthermore, TLR4 may play a role in the development of atherosclerotic lesions. Other studies have implicated TLR4 in the adverse remodeling that may occur after ischemic myocardial injury. This emerging body of literature, which is reviewed here, has provided new insight into the early molecular events that mediate myocardial injury and dysfunction in the setting of I/R injury.

The emerging role of innate immunity in the heart and vascular system: for whom the cell tolls

Recent studies suggest that the heart possesses an innate immune system that is intended to delimit tissue injury, as well as orchestrate homoeostatic responses, within the heart. The extant literature suggests that this intrinsic stress response system is mediated, at least in part, by a family of pattern recognition receptors, most notably the Toll-like receptors. Although the innate immune system provides a short-term adaptive response to tissue injury, the beneficial effects of this phylogenetically ancient system may be lost if innate immune signaling becomes sustained and/or excessive; in which case, the salutary effects of activation of these pathways are contravened by the known deleterious effects of inflammatory signaling. Herein, the biology of innate immune signaling in the heart is reviewed, as well as the literature suggesting that the innate immune system is involved in the pathogenesis of atherosclerosis, acute coronary syndromes, stroke, viral myocarditis, sepsis, ischemia/reperfusion injury, and heart failure. The review concludes by discussing new therapies that are being developed to modulate the innate immune system.

Genetic variants in TLR2 and TLR4 are associated with markers of monocyte activation: the Atherosclerosis Risk in Communities MRI Study

Markers of monocyte activation play a critical role in atherosclerosis, but little is known about the genetic influences on cellular levels. Therefore, we investigated the influence of genetic variants in monocyte differentiation antigen (CD14), toll-like receptor-4 (TLR4), toll-like receptor-2 (TLR2), and myeloperoxidase (MPO) on monocyte surface receptor levels. The study sample consisted of 1,817 members of a biracial cohort of adults from the Atherosclerosis Risk in Communities Carotid MRI Study. Monocyte receptors were measured using flow cytometry on fasting whole blood samples. TLR2 rs1816702 genotype was significantly associated with CD14+/TLR2+ percent of positive cells (%) and median fluorescence intensity (MFI) in whites but not in blacks (p < 0.001). Specifically, the presence of the minor T-allele was associated with increased receptor levels. In blacks, TLR4 rs5030719 was significantly associated with CD14+/TLR4+ monocytes (MFI) with mean ± SE intensities of 16.7 ± 0.05 and 16.0 ± 0.14 for GG and GT/TT genotypes, respectively (p < 0.001). Variants in TLR2 and TLR4 were associated with monocyte receptor levels of TLR2 and TLR4, respectively, in a biracial cohort of adults. To our knowledge, this is the first study to look at associations between variants in the toll-like receptor family and toll-like receptor levels on monocytes.

Genetic variation of TLR4 influences immunoendocrine stress response: an observational study in cardiac surgical patients

Introduction

Systemic inflammation (for example, following surgery) involves Toll-like receptor (TLR) signaling and leads to an endocrine stress response. This study aims to investigate a possible influence of TLR2 and TLR4 single nucleotide polymorphisms (SNPs) on perioperative adrenocorticotropic hormone (ACTH) and cortisol regulation in serum of cardiac surgical patients. To investigate the link to systemic inflammation in this context, we additionally measured 10 different cytokines in the serum.

Methods

A total of 338 patients admitted for elective cardiac surgery were included in this prospective observational clinical cohort study. Genomic DNA of patients was screened for TLR2 and TLR4 SNPs. Serum concentrations of ACTH, cortisol, interferon (IFN)-γ, interleukin (IL)-1β, IL-2, IL-4, IL-5, IL-6, IL-8, IL-10, tumor necrosis factor (TNF)-α and granulocyte macrophage-colony stimulating factor (GM-CSF) were determined before surgery, immediately post surgery and on the first postoperative day.

Results

Thirteen patients were identified as TLR2 SNP carriers, 51 as TLR4 SNP carriers and 274 patients as non-carriers. Basal levels of ACTH, cortisol and cytokines did not differ among groups. In all three groups a significant, transient perioperative rise of cortisol could be observed. However, only in the non-carrier group this was accompanied by a significant ACTH rise. TLR4 SNP carriers had significant lower ACTH levels compared to non-carriers (mean (95% confidence intervals)) non-carriers: 201.9 (187.7 to 216.1) pg/ml; TLR4 SNP carriers: 149.9 (118.4 to 181.5) pg/ml; TLR2 SNP carriers: 176.4 ((110.5 to 242.3) pg/ml). Compared to non-carriers, TLR4 SNP carriers showed significant lower serum IL-8, IL-10 and GM-CSF peaks (mean (95% confidence intervals)): IL-8: non-carriers: 42.6 (36.7 to 48.5) pg/ml, TLR4 SNP carriers: 23.7 (10.7 to 36.8) pg/ml; IL-10: non-carriers: 83.8 (70.3 to 97.4) pg/ml, TLR4 SNP carriers: 54.2 (24.1 to 84.2) pg/ml; GM-CSF: non-carriers: 33.0 (27.8 to 38.3) pg/ml, TLR4 SNP carriers: 20.2 (8.6 to 31.8) pg/ml). No significant changes over time or between the groups were found for the other cytokines.

Conclusions

Regulation of the immunoendocrine stress response during systemic inflammation is influenced by the presence of a TLR4 SNP. Cardiac surgical patients carrying this genotype showed decreased serum concentrations of ACTH, IL-8, IL-10 and GM-CSF. This finding might have impact on interpreting previous and designing future trials on diagnosing and modulating immunoendocrine dysregulation (for example, adrenal insufficiency) during systemic inflammation and sepsis.

The evolving role of inflammatory biomarkers in risk assessment after stent implantation

The main adverse reactions to coronary stents are in-stent restenosis (ISR) and stent thrombosis. Along with procedural factors, individual susceptibility to these events plays an important role. In particular, inflammatory status, as assessed by C-reactive protein levels, predicts the risk of ISR after bare-metal stent implantation, although it does not predict the risk of stent thrombosis. Conversely, C-reactive protein levels fail to predict the risk of ISR after drug-eluting stent (DES) implantation, although they appear to predict the risk of stent thrombosis. Of note, DES have abated ISR rates occurring in the classical 1-year window, but new concern is emerging regarding late restenosis and thrombosis. The pathogenesis of these late events seems to be related to delayed healing and allergic reactions to polymers, a process in which eosinophils seem to play an important role by enhancing restenosis and thrombosis. The identification of high-risk individuals based on biomarker assessment may be important for the management of patients receiving stent implantation. In this report, we review the evolving role of inflammatory biomarkers in predicting the risk of ISR and stent thrombosis.

A comprehensive genotype-phenotype interaction of different Toll-like receptor variations in a renal transplant cohort

To date, the impact of the TLR (Toll-like receptor) system on early and late kidney transplantation outcome, such as ARE (acute rejection episodes) or cardiovascular morbidity and mortality, has still not been elucidated conclusively. Genetically determined alterations in TLR expression exhibit a possibility to evaluate their role in transplantation. In the present study, we sought to determine a comprehensive genotype-phenotype association with early and late allograft outcomes. We studied 11 SNPs (single nucleotide polymorphisms) in TLR2, TLR3, TLR4, TLR5, TLR9 and within a co-molecule CD14 in 265 patients receiving their first kidney transplant and the association of these with the occurrence of DGF (delayed graft function), ARE or MACE (major adverse cardiovascular events). ARE were significantly more frequent in patients carrying the TLR3 TT/CT allele (43.8 compared with 25.8%; P=0.001) as were rates of DGF (21.4 compared with 12.0%; P=0.030). Furthermore, TLR9 was significantly involved in the occurrence of MACE (TLR9 -1237; P=0.030). Interestingly, there was no significant effect of any TLR polymorphism on graft survival or renal function and the incidence of any infection, including CMV (cytomegalovirus) infection. In conclusion, our present study in renal transplant recipients suggests that the TLR system may be involved in both acute rejection and MACE. Modulation of the TLR system may be a promising target in future therapeutic strategies.

Very low frequencies of Toll-like receptor 2 supposed-2029T and 2258A (RS5743708) mutant alleles in southern Brazilian critically ill patients: would it be a lack of worldwide-accepted clinical applications of Toll-like receptor 2 variants?

Toll-like receptor 2 (TLR2) is a recognition receptor for the widest repertoire of pathogen-associated molecular patterns. Two polymorphisms of TLR2 could be linked to reduced nuclear factor kappa-light-chain-enhancer of activated B cells (NF-kB) activation and to increased risk of infection (supposed-2029C>T and 2258G>A). We investigated the supposed-2029C>T and 2258G>A TLR2 polymorphisms in 422 critically ill patients of European origin from southern Brazil (295 with sepsis and 127 without sepsis) and reviewed 33 studies on these polymorphisms, conducting a quality assessment with a score system. Among our patients we found only one heterozygote (1/422) for the supposed-2029C>T and none for the 2258G>A (0/422) single nucleotide polymorphism (SNP). We were unable to find a clinical application of supposed-2029T and 2258A allele analyses in our southern Brazilian population. Our review detected that current TLR2 SNP assays had very controversial and contradictory results derived from reports with a variety of investigation quality criteria. We suggest that, if analyzed alone, the supposed-2029C>T and 2258G>A TLR2 SNP are not good candidates for genetic markers in studies that search for direct or indirect clinical applications between genotype and phenotype. Future efforts to improve the knowledge and to provide other simultaneous genetic markers might reveal a more effective TLR2 effect on the susceptibility to infectious diseases.

Toll-like receptors, tumor necrosis factor-α, and interleukin-10 gene polymorphisms in risk of pulmonary tuberculosis and disease severity

Toll-like receptors (TLRs) and cytokines play key roles in innate and adaptive immunity against Mycobacterium tuberculosis (M.TB). The aim of this study was to investigate whether the functional genetic variations at position 1805 G/T in TLR1, 2258 A/G in TLR2, -857 C/T, and -863 A/C in tumor necrosis factor-α (TNF-α), as well as -819 C/T in interleukin-10 (IL-10) confer susceptibility to pulmonary tuberculosis (PTB). We performed a hospital-based case-control study using 543 case patients and 544 controls. Multivariate logistic regression analysis revealed that the TT genotype of -857 C/T in TNF-α gene was significantly associated with lower risk of PTB, in comparison with other genotypes (odds ratios [OR] = 0.68, 95% confidence interval [CI] = 0.53-0.86, p = 0.001). Conversely, the genetic variants of -863 A/C in TNF-α gene was associated with susceptibility to PTB (OR = 2.42%, 95% CI = 1.28-4.59, p = 0.007) and clinical severity of disease (OR = 3.59%, 95% CI = 1.41-9.11, p = 0.007). Our results indicated that the variants in TNF-α gene were associated with susceptibility to PTB and clinical severity of disease, whereas no significance could be inferred from TLRs and IL-10 genes polymorphisms.

Enhanced TLR4 endothelial cell immunohistochemical expression in symptomatic carotid atherosclerotic plaques

BACKGROUND AND PURPOSE

Toll-like receptor-4 (TLR4) has been linked to the pathogenesis of atherosclerosis. Carotid atheroma endothelial cells (ECs) express TLR4, nevertheless correlations with cerebrovascular symptomatology, epidemiological and clinical variables remain unresolved.

METHODS

Carotid atherosclerotic plaques were obtained by standard carotid endarterectomy from 157 patients with carotid artery disease (84 asymptomatic - Group A, 73 symptomatic - Group B). TLR4 expression was detected by immunohistochemistry and TLR4 positivity, overexpression and intensity of immunostaining in ECs were correlated with cerebrovascular symptomatology, epidemiological and clinical variables.

RESULTS

A significant association was found between TLR4 positivity in ECs and the occurrence of any cerebrovascular event (overall response (OR): 2.85, 95% CI 1.33 - 6.11, p = 0.009). TLR4 overexpression and staining intensity in ECs were both significantly enhanced in symptomatic patients (p < 0.0001 and p = 0.003, respectively). These associations were stronger for the occurrence of a major cerebrovascular accident (CVA) compared with a transient ischemic attack (TIA) or amaurosis fugax. TLR4 expression in ECs was less prominent in statin users (OR: 0.25, 95%CI 0.1 - 0.58, p = 0.001], while it was enhanced in restenotic plaques compared with primary atherosclerotic lesions (p = 0.012).

CONCLUSIONS

TLR4 expression in ECs of carotid atheroma was enhanced in symptomatic patients with most commonly 'unstable' - 'more prone to rupture' carotid plaques.

Toll-like receptor-2 mediates inflammation and matrix degradation in human atherosclerosis

BACKGROUND

Inflammation and matrix degradation are the hallmarks of high-risk atherosclerosis that leads to myocardial infarction and stroke. Toll-like receptors (TLRs), key players in innate immunity, are upregulated in atherosclerotic lesions, but their functional role in human atherosclerosis is unknown. We explored the effects of blocking TLR-2, TLR-4, and myeloid differentiation primary response gene 88 (MyD88), a signaling adaptor shared by most TLRs and interleukin-1 receptor (IL-1R), in an in vitro model of human atherosclerosis.

METHODS AND RESULTS

Carotid endarterectomies were obtained from patients with symptomatic carotid disease. Cells were isolated via enzymatic tissue dissociation and cultured in the presence or absence of TLR signaling blockers. A dominant-negative form of MyD88 (MyD88(DN)) decreased the production of monocyte chemotactic protein-1/CCL2 (P=0.000), IL-8/CXCL8 (P=0.006), IL-6 (P=0.002), matrix metalloproteinase-1 (MMP-1; P=0.002), and MMP-3 (P=0.000), as well as nuclear factor-kappaB activation (P<0.05) in atheroma cell cultures. IL-1R antagonist, TLR-4 blocking antibodies, or overexpression of a dominant-negative form of the TLR-4 signaling adaptor TRIF-related adaptor molecule reduced nuclear factor-kappaB activity but did not have a broad impact on the production of the mediators studied. In contrast, TLR-2 neutralizing antibodies inhibited nuclear factor-kappaB activation (P<0.05) and significantly reduced monocyte chemotactic protein-1/CCL2 (P=0.000), IL-8/CXCL8 (P=0.009), IL-6 (P=0.000), and MMP-1 (P=0.000), MMP-2 (P=0.004), MMP-3 (P=0.000), and MMP-9 (P=0.006) production.

CONCLUSIONS

Our data indicate that TLR-2 signaling through MyD88 plays a predominant role in inflammation and matrix degradation in human atherosclerosis. TLR-2 blockade may represent a therapeutic strategy for atherosclerosis and its complications.

Toll-like receptor modulation: a novel therapeutic strategy in cardiovascular disease?

BACKGROUND

Toll-like receptors (TLRs) have been recently recognised as primary receptors in the innate immune system. Apart from initiating a prompt immune response against invading pathogens, TLRs are also considered to be an important link between innate immunity, inflammation and a variety of clinical disorders, including cardiovascular diseases. TLR signalling manipulation with novel drugs could offer important opportunities for cardiovascular disease modification.

OBJECTIVE

To present the latest knowledge supporting the involvement of TLRs in the pathogenesis and progress of cardiovascular diseases and explore the role of TLRs as potential targets for therapeutic intervention in cardiovascular territory.

METHODS

A review of the literature documenting implication of TLR signalling in cardiovascular disorders. Current progress in TLR-targeting drug development and the potential role of such a treatment strategy in cardiovascular disorders are discussed.

CONCLUSIONS

A growing body of evidence supports a role for TLRs in cardiovascular disease initiation and progression. Altering TLR signalling with novel drugs could be a beneficial therapeutic strategy for patients with cardiovascular disorders.

Immune interventions of human diseases through toll-like receptors

Toll-like receptors (TLRs) are the immune sensors for infections, triggering robust innate immune activation followed by protective adaptive immunity against various infectious diseases. Recent evidence, however, has suggested that TLRs are involved in the pathogenesis of many diseases, including not only infectious diseases but also autoimmune diseases, allergy and atherosclerosis. Therefore, prophylactic or therapeutic application of TLR-based immune interventions should be potent, but their safety must be demonstrated using experimental animal models as well as human resources, including analysis of single nucleotide polymorphisms. Here, we focus on recent advances in understanding of the protective and pathogenic roles of TLRs in human diseases.

Toll-like receptor and IL-12 signaling control susceptibility to contact hypersensitivity

Allergic contact hypersensitivity (CHS) is a T cell–mediated inflammatory skin disease. Interleukin (IL)-12 is considered to be important in the generation of the allergen-specific T cell response. Loss of IL-12 function in IL-12Rβ2–deficient mice, however, did not ameliorate the allergic immune response, suggesting alternate IL-12–independent pathways in the induction of CHS. Because exposure to contact allergens always takes place in the presence of microbial skin flora, we investigated the potential role of Toll-like receptors (TLRs) in the induction of CHS. Using mice deficient in TLR4, the receptor for bacterial lipopolysaccharide (LPS), IL-12 receptor (R) β2, or both, we show that the concomitant absence of TLR4 and IL-12Rβ2, but not the absence of TLR4 or IL-12Rβ2 alone, prevented DC-mediated sensitization, generation of effector T cells, and the subsequent CHS response to 2,4,6-trinitro-1-chlorobenzene (TNCB), oxazolone, and fluorescein isothiocyanate. Introduction of the TLR4 transgene into the TLR4/IL-12Rβ2 mutant restored the CHS inducibility, showing a requirement for TLR4 in IL-12–independent CHS induction. Furthermore, the concomitant absence of TLR2 and TLR4 prevented the induction of CHS to TNCB in IL-12–competent mice. Finally, CHS was inducible in germ-free wild-type and IL-12Rβ2–deficient mice, but not in germ-free TLR4/IL-12Rβ2 double deficient mice, suggesting that the necessary TLR activation may proceed via endogenous ligands.

Role of pattern-recognition receptors in cardiovascular health and disease

A role for PRRs (pattern-recognition receptors) in immune cell function is now well established. In macrophages and other immune cells, activation of TLRs (Toll-like receptors) and cytosolic NLRs [NOD (nucleotide oligomerization domain) proteins containing a leucine-rich repeat] results in the induction of genes and release of imunoregulator hormones including cytokines and NO (nitric oxide). In addition to immune cells, structural cells of the cardiovascular system including endothelial cells, vascular smooth muscle and cardiac myocytes express functional PRRs and sense PAMPs (pathogen-associated molecular patterns). Furthermore, bacteria and PAMPs activate the coagulation system and platelets. TLRs are now implicated in a range of cardiovascular diseases and syndromes including atherosclerosis and sepsis. Our group is working on the hypotheses that differences exist in how tissues of the cardiovascular system, including vessels, endothelium, heart and blood, sense pathogens compared with immune cells (principally macrophages) and that identifying such differences will reveal new therapeutic targets for the treatment of cardiovascular disease. We have identified examples of similarities and differences in how cardiovascular tissues and macrophages sense PAMPs. These findings will be discussed together with our interpretation of how this information may lead to new treatments.

Polymorphisms in Toll-like receptor genes and risk of cancer

Host genetic factors are emerging as key determinants of disease risk for many cancers. Identifying candidate genes is a major challenge that has to stem from a profound understanding of the pathophysiology of the disease. The Toll-like receptors are important members of the host's innate immune response and their genes have been found to be polymorphic. This genetic variation allows for a more intricate repertoire that enables the host to withstand microbial challenges. While this may be advantageous on a population level, there may be less favourable outcomes for individuals that harbour certain genotypes associated with excessive immune activation and inflammatory drive. The damage is often collateral and is manifest in organs where this chronic inflammation alters normal physiology. A classic example of this paradigm is the Helicobacter pylori-induced gastric cancer model. Another emerging model is prostate cancer where Toll-like receptor polymorphisms have also been found to play a role. In this review, we discuss polymorphisms in Toll-like receptors and give an insight into how they may influence risk of cancer.

The role of Toll-like receptors in non-infectious lung injury

The role of Toll-like receptors (TLRs) in pathogen recognition has been expeditiously advanced in recent years. However, investigations into the function of TLRs in non-infectious tissue injury have just begun. Previously, we and others have demonstrated that fragmented hyaluronan (HA) accumulates during tissue injury. CD44 is required to clear HA during tissue injury, and impaired clearance of HA results in unremitting inflammation. Additionally, fragmented HA stimulates the expression of inflammatory genes by inflammatory cells at the injury site. Recently, we identified that HA fragments require both TLR2 and TLR4 to stimulate mouse macrophages to produce inflammatory chemokines and cytokines. In a non-infectious lung injury model, mice deficient in both TLR2 and TLR4 show an impaired transepithelial migration of inflammatory cells, increased tissue injury, elevated lung epithelial cell apoptosis, and decreased survival. Lung epithelial cell overexpression of high molecular mass HA protected mice against acute lung injury and apoptosis, in part through TLR-dependent basal activation of NF-kappaB. The exaggerated injury in TLR2 and TLR4 deficient mice appears to be due to impaired HA-TLR interactions on epithelial cells. These studies identify that host matrix component HA and TLR interactions provide signals that initiate inflammatory responses, maintain epithelial cell integrity, and promote recovery from acute lung injury.

Toll-like receptor 2 and 4 gene polymorphisms in generalized aggressive periodontitis

BACKGROUND

Toll-like receptors (TLRs) recognize exogenous ligands such as lipopolysaccharide and bacterial lipoprotein during the immune responses to pathogens. The aim of the present study was to investigate whether TLR2 and TLR4 gene polymorphisms are related to susceptibility to generalized aggressive periodontitis (GAgP).

METHODS

A total of 245 subjects were included in the present study. Genomic DNA was obtained from the peripheral blood of 90 patients with GAgP and 155 periodontally healthy subjects. Probing depth, clinical attachment loss, plaque accumulation, and bleeding on probing were recorded. The TLR2 gene Arg753Gln and Arg677Trp polymorphisms and TLR4 gene Asp299Gly and Thr399Ile polymorphisms were genotyped by the polymerase chain reaction-restriction fragment length polymorphism method. The data were analyzed by chi2 and Mann-Whitney U tests and logistic regression analysis.

RESULTS

There was no significant difference in the distribution of TLR2 and TLR4 genotypes and allele frequencies between GAgP patients and healthy subjects (P > 0.05). The TLR2 753Gln allele was found in 3.9% of the GAgP patients compared to 6.1% in the healthy group. The GAgP patients and healthy subjects did not show homozygosity for the TLR2 mutant alleles. The TLR2 677Trp mutant allele was not found in any of the subjects; 2.2% of the GAgP patients and 2.9% of the periodontally healthy subjects were identified as having the TLR4 299Gly polymorphic allele. With regard to the TLR4 399Ile polymorphic allele, 1.1% of the GAgP patients and 2.3% of the periodontally healthy subjects had this allele.

CONCLUSIONS

The present study failed to find any significant association between the TLR polymorphisms and GAgP, potentially because of the small sample size. To the best of our knowledge, this was the first study to examine the prevalence of these polymorphisms in a Turkish population with aggressive periodontitis.

Innate immunity, macrophage activation, and atherosclerosis

Inflammation underpins the development of atherosclerosis. Initiation and progression of vascular inflammation involves a complex cellular network, with macrophages as major contributors. Activated macrophages produce proinflammatory mediators, bridge innate and adaptive immunity, regulate lipid retention, and participate directly in vascular repair and remodeling. Recent efforts to elucidate molecular mechanisms involved in the regulation of vascular inflammation in atherosclerosis have implicated several families of innate immune recognition receptors in inflammatory activation during the course of this disease. This article reviews our current understanding of innate immune recognition receptors, signaling pathways, and putative ligands implicated in activation of macrophages in the disease. In its final section, we propose a model for the role of macrophages in bridging inflammation and atherosclerosis from the perspective of innate immune recognition and activation.

Mechanisms of disease: Toll-like receptors in cardiovascular disease

The innate immune system detects highly conserved, relatively invariant structural motifs of pathogens. Toll-like receptors (TLRs) have been identified as the primary innate immune receptors. TLRs distinguish between different patterns of pathogens and activate a rapid innate immune response; however, TLRs can also be activated by host-derived molecules. In addition to being expressed in immune cells, TLRs are expressed in other tissues, such as those of the cardiovascular system. TLRs could, therefore, be a key link between cardiovascular disease development and the immune system. Indeed, evidence that TLR activation contributes to the development and progression of atherosclerosis, cardiac dysfunction in sepsis, and congestive heart failure, is convincing. Although much has been learned about TLR activation in cellular components of the cardiovascular system, the role individual TLR family members have in the pathophysiology of cardiovascular diseases and hence in clinical practice remains to be defined. Here we review the rapid progress that has been made in this field, which has improved our understanding of vascular as well as myocardial TLR function in basic and clinical science.

Toll-like receptor 9-stimulated monocyte chemoattractant protein-1 is mediated via JNK-cytosolic phospholipase A2-ROS signaling

Monocyte chemoattractant protein-1 (MCP-1) influences monocyte migration into sites of inflammation. This study highlights the importance of cytosolic phospholipase A2 (cPLA2)-mediated reactive oxygen species (ROS) signaling processes in the regulation of MCP-1 release as a result of toll-like receptor (TLR) activation. In macrophages, activation of TLR9 induced MCP-1 and cPLA2-phosphorylated arachidonic acid (AA) release. Inhibition of cPLA2 blocked CpG-induced MCP-1 and AA release. Although CpG stimulates phosphorylation of ERK, p38 and JNK, only inhibition of the JNK signaling pathways attenuated MCP-1 release, suggesting that the TLR9-mediated MCP-1 release was dependent upon the JNK pathway. TLR9 activation also stimulated ROS generation, while inhibition of NADPH oxidases (Noxs) blocked CpG-induced MCP-1 release. The CpG treatment increased macrophage Nox1 mRNA level, however it had no effect on macrophage Nox2 mRNA level. Overall, these results suggest that CpG enhances ROS generation through cPLA2-dependent pathways, which results in MCP-1 release.

Reducing the toll of inflammatory lung disease

Toll-like receptors (TLRs) are pivotal in human response to microbial stimuli. Their activation and signaling underpin much of the observed epidemiologic data generated by the hygiene hypothesis, and their contribution to infectious exacerbations of airways disease is likely to be highly important. Our growing knowledge in this field will have a significant impact on the understanding of the pathogenesis of inflammatory diseases, and TLR-based therapies are already in early clinical trials to modify atopic disease severity.

Relationship between Toll-like receptor 2 polymorphism and cytomegalovirus disease after liver transplantation

BACKGROUND

Experimental data suggest that cytomegalovirus (CMV) initiates innate immunity through the activation of Toll-like receptor 2 (TLR2). To assess the clinical relevance of this experimental observation, we assessed the association between the specific single-nucleotide polymorphism that results in the substitution of arginine for glutamine in position 753 of TLR2 (the TLR2 Arg753Gln polymorphism) and CMV replication and disease after liver transplantation.

METHODS

Ninety-two liver transplant recipients with chronic hepatitis C were screened for the presence of the TLR2 Arg753Gln polymorphism. CMV load was determined in serially collected blood samples using CMV DNA polymerase chain reaction. Kaplan-Meier estimation and univariable and multivariable stepwise Cox proportional hazard models were used to assess associations.

RESULTS

The degree of CMV replication, as measured by CMV load, was significantly higher in patients who were homozygous (mean maximum viral load, 37,059 copies/mL) and heterozygous (mean maximum viral load, 29,718 copies/mL) for this polymorphism, compared with patients without the TLR2 Arg753Gln polymorphism (mean maximum viral load, 3252 copies/mL; P=.003). Kaplan-Meier survival analysis demonstrated an association between being homozygous for the TLR2 Arg753Gln polymorphism and CMV disease (P=.04). A multivariate Cox proportional hazard model demonstrated a trend towards a higher risk of CMV disease among patients who were homozygous for the TLR2 Arg753Gln polymorphism (hazard ratio, 1.91 [95% confidence interval, 0.91-3.40]; P=.08) after adjusting for patient age, CMV serostatus, and allograft rejection.

CONCLUSIONS

TLR2 Arg753Gln polymorphism is possibly associated with CMV replication and disease after liver transplantation. This novel clinical observation supports the potential role of TLR2 in the immunologic control of CMV infection in humans.