Toll-like receptor 2 gene polymorphisms, pulmonary tuberculosis, and natural killer cell counts

Human Toll-like receptor 2 genetic polymorphisms with tuberculosis susceptibility: A systematic review and meta-analysis

BACKGROUND

Toll-like receptor 2 (TLR2) is a crucial factor in the development of tuberculosis. However, no studies have explored the association between TLR2 polymorphisms and tuberculosis susceptibility.

OBJECTIVES

This study aimed to explore the correlation between tuberculosis susceptibility and TLR2 polymorphisms (rs3804099, rs3804100, rs1898830, rs5743708, rs121917864, and (-196-174) del).

METHODS

All relevant online databases including PubMed, CNKI, WANFANG DATA, and METSTR-FMRS were systematically searched. STATA17.0 (Stata Corp LP, College Station, Texas, USA) was used.

RESULTS

A total of 37 studies, covering six polymorphisms and comprising 9,474 cases and 10,295 controls, were included in this analysis. rs3804099(C vs T: OR = 1.00, 95 % CI: 0.93-1.08, CC + TC vs TT: OR = 1.04, 95 % CI: 0.98-1.10), rs3804100 (C vs T: OR = 1.19, 95 % CI: 0.93-1.07, CC + TC vs TT: OR = 0.97, 95 % CI: 0.89-1.06), rs1898830(G vs A: OR = 0.90, 95 % CI: 0.81-1.00, GG + AG vs AA: OR = 0.87, 95 % CI: 0.67-1.12), (-196 ∼174) del polymorphism (Del vs Ins: OR = 0.93,95 % CI: 0.76-1.14, DD + DI vs II: OR = 0.92,95 % CI: 0.72-1.17).

CONCLUSIONS

This study indicated that only the TLR2 rs5743708 polymorphism exhibited a significant association with a higher tuberculosis risk, while TLR2 rs3804099, rs3804100, rs1898830, rs121917864, and (-196-174) del polymorphisms were not associated with tuberculosis susceptibility.

Association of Toll-like Receptors 1, 2, 4, 6, 8, 9 and 10 Genes Polymorphisms and Susceptibility to Pulmonary Tuberculosis in Sudanese Patients

Background

Genetic factors are important contributors to the development of a wide range of complex disease. Polymorphisms in genes encoding for toll-like receptors (TLRs) usually influence the efficiency of the immune response to infection and are associated with disease susceptibility and progression. Therefore, we aim to describe the first association between TLR1, TLR2, TLR4 TLR6, TLR8, TLR9 and TLR10 genes polymorphisms and susceptibility to pulmonary tuberculosis (PTB) in Sudanese patients.

Methodology

Here we performed a case study which included 160 tuberculosis patients and 220 healthy matched controls from Sudan. In the study population, we evaluated the possible association between 86 markers in TLR1, TLR2, TLR4 TLR6, TLR8, TLR9 and TLR10 genes polymorphisms and susceptibility to PTB disease in Sudanese population using polymerase chain reaction and restriction fragment length polymorphism (PCR-RFLP).

Results

From our results it appeared that in the PTB population the TLR1 (rs5743557, rs4833095, rs5743596), TLR2 (rs5743704, rs5743708, rs3804099), TLR4 (rs4986790, rs4986791), TLR6 (rs5743810), TLR8 (rs3764879, rs3764880), TLR9 (rs352165, rs352167, rs187084) and TLR10 (rs4129009) were significantly more often encountered (p<0.0001) than in the control population and were associated with PTB in the Sudanese population. For the other polymorphisms tested, no association with PTB was found in the population tested.

Conclusion

The work describes novel mutations in TLR1, TLR2, TLR4, TLR6, TLR8, TLR9 and TLR10 genes and their association with PTB infection in Sudanese population. These results will enhance our ability to determine the risk of developing the disease by targeting specific TLR pathways to reduce the severity of the disease. Future studies are needed in a larger sample to replicate our findings and understand the mechanism of association of TLR polymorphism in PTB.

Evaluation of peripheral lymphocyte subsets in acne vulgaris patients before and after systemic isotretinoin treatment

OBJECTIVES

Isotretinoin (ISO) is a retinoic acid-derived molecule which is very efficient in the treatment of acne vulgaris (AV). Little is known regarding alterating affects of systemic ISO on immune system.

SUBJECTS

AND METHODS

Thirty-two patients with moderate and severe AV with indications for systemic ISO treatment were recruited. The evaluation of peripheral blood lymphocyte subsets was made on treatment initiation and at the end of the therapy by flow cytometry.

RESULTS

CD16/56+ natural killer (NK) cell levels were higher in patients with severe acne compared to moderate acne (P = 0.009). CD45RA+ (naive) cell levels decreased significantly after systemic ISO treatment; the mean percentage was 66.9 ± 6.5 which decreased to 63.9 ± 7.5 after treatment (P = 0.013). CD19+ cell levels were also significantly increased; mean percentage (%) and absolute cell counts were 8.0 ± 3.1 and 161.3 ± 7.36 cells/μl which increased to 10 ± 2.7 and 227.7 ± 108.7 cells/μl, at the end of treatment, respectively (P = 0.007, P = 0.011).

CONCLUSIONS

NK cell count may be a parameter related to acne severity. Systemic ISO may have an inhibitory effect on naïve T cells. Finally, systemic ISO seems to stimulate mature B-cell proliferation.

Arg753Gln Polymorphisms in the Toll-Like Receptor 2 Gene are Associated with Cytomegalovirus Infection in Egyptian Bone Marrow Recipients

BACKGROUND

Previous studies have shown that cytomegalovirus (CMV) induced innate immune response via activation of Toll-like receptor 2 (TLR2). The association between CMV among specific single-nucleotide polymorphisms (SNPs) in the TLR2 gene was also investigated.

OBJECTIVE

This study investigated the relationship between specific SNPs in the TLR2 gene (G>A), TLR2-Arg753Gln (rs5743708), and CMV replication after bone marrow transplantation.

METHODS

The TLR2-Arg753Gln SNP was genotyped in 181 patients after bone marrow transplantation: 83 and 98 patients with and without CMV infection, respectively. CMV load was determined in serially collected blood samples using real-time PCR. Genotyping was performed using specific sequence primer PCR (SSP-PCR), and the results were confirmed by restriction fragment length polymorphism (RFLP) analysis of the PCR-amplified fragments for GG (wild type), GA and AA identification.

RESULTS

Roughly, 85% of the patients screened for the presence of the TLR2-Arg753Gln were GG homozygous, and 15% were GA heterozygous; no patients were homozygous for the mutant allele (A). The GA heterozygous allele was more frequent in the CMV-infected group after bone marrow transplantation.

CONCLUSION

To our knowledge, this is a novel observation that supports the notion that the functional missense mutation (TLR2-Arg753Gln polymorphism) is possibly associated with CMV replication after bone marrow transplantation. This suggests a role for TLR2 in the innate immune response of human CMV infection in Egyptian bone marrow recipients.

Higher Levels of Serum TLR2 and TLR4 in Patients with Hashimoto's Thyroiditis

OBJECTIVE

Hashimoto's thyroiditis (HT) is an autoimmune disorder caused by the interaction between genes and environmental triggers. HT is the most common endocrine disorder, as well as the most common cause of hypothyroidism. Autoimmunity plays a crucial role in the pathogenesis of HT and recent studies suggest that Toll-like receptor (TLR) signals lead to increased inflammatory response. The aim of our study is to investigate whether TLR-2 and TLR-4 levels and gene polymorphisms contribute to the damaged immune response leading to HT.

METHODS

Using the polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method, single-nucleotide polymorphisms (SNPs) of TLR2 gene Arg677Trp, Arg753Gln, 196-174 del and TLR4 gene Asp299Gly, Thr399Ile were studied in 100 patients with HT and 100 healthy controls. Also, we investigated serum levels of TLR-2 and TLR-4 in the immunopathogenesis of HT. TLR-2 and TLR-4 serum levels were found to be significantly higher in HT patients than the control group. However, no statistical significance was found between patient and control groups in terms of genotype frequencies and allele frequency distribution of TLR2 gene Arg677Trp, Arg753Gln, 196-174 del and TLR4 gene Asp299Gly, Thr399Ile polymorphisms.

RESULT

TLR2 gene Arg677Trp, Arg753Gln, 196-174 del and TLR4 gene Asp299Gly, Thr399Ile polymorphism do not appear to have a role in the development of HT disease. However, in our study, serum levels of TLR-2 and TLR-4 were found to be higher in HT patients than control groups.

CONCLUSION

These findings suggest that TLR-2 and TLR-4 play an important role in the immunopathologic mechanism of disease by causing an increase in proinflammatory response.

The association of inflammasome and TLR2 gene polymorphisms with susceptibility to tuberculosis in the Han Taiwanese population

Pulmonary tuberculosis (TB) caused by Mycobacterium tuberculosis (Mtb) is a global public health concern. Although inflammasome and the toll-like receptor 2 (TLR2) genes play an important role in host defense against Mtb, the associations of polymorphisms in these genes with TB risk are incompletely understood. A total of 230 TB patients and 213 individuals without TB were enrolled in this study. A significant difference in the frequencies of different AIM2 rs2276405 genotypes between the non-TB and TB groups was detected. When the patients were stratified by gender or age, significant differences in genotype frequencies at NLRP3 rs34298354 in men and in non-aged (≤65-year-old) subjects and at IFI16 rs1772408 in women were found. OR analysis showed that the TC rs34298354 genotype in NLRP3 was associated with reduced risk of TB. In women, the AG rs1772408 genotype in IFI16 was associated with decreased TB risk. Haplotype analysis showed that, in comparison with the most common haplotype (T-T) of rs3804099-rs3804100 in the TLR2 gene, the C-T haplotype was associated with an increased risk for TB. Our study indicates that rs34298354 in NLRP3 and rs1772408 in IFI16 protect individuals from TB, and that the less common TLR2 haplotype is associated with increased TB susceptibility.

Interaction of H. pylori with toll-like receptor 2-196 to -174 ins/del polymorphism is associated with gastric cancer susceptibility in southern China

BACKGROUND

Genetic polymorphisms of Toll-like receptors play important roles in gastric carcinogenesis. The aim of this study was to determine the role of TLR2-196 to -174 ins/del polymorphism in gastric cancer susceptibility and prognosis.

METHODS

This study included 520 people from southern China. Samples were genotyped by the allele-specific polymerase chain reaction, among which 10% were randomly selected for sequencing. The serological method was used to determine Helicobacter pylori.

RESULTS

The TLR2 genotype was not associated with the risk of H. pylori infection. The del/del genotype exhibited significantly higher gastric cancer risk (adjusted OR 2.59, 95% CI 1.33‒5.07) than that of the ins/ins genotype. Further stratification analyses demonstrated that the del/del genotype was associated with a risk of intestinal gastric cancer (adjusted OR 2.62, 95% CI 1.34-5.14). In addition, the presence of the del/del genotype and the H. pylori infection conferred a synergistic effect (OR 3.04, 95% CI 1.33‒6.98) for the development of gastric cancer. The del/del genotype was not associated with a poor prognosis in gastric cancer patients.

CONCLUSION

The del/del genotype is associated with an increased gastric cancer risk in the southern Chinese population. However, TLR2 polymorphism is neither associated with H. pylori infection, nor with a poor prognosis.

Association of VDR gene polymorphisms and 22 bp deletions in the promoter region of TLR2Δ22 (-196-174) with increased risk of pulmonary tuberculosis: A case-control study in tea garden communities of Assam

BACKGROUND

A high number of pulmonary tuberculosis (PTB) cases have been reported from tea garden communities of Assam. Till date, no molecular epidemiological study was performed to investigate the association of candidate gene(s) with the risk PTB in this region. The present case-control study was aimed to investigate the association of vitamin D receptor (VDR) gene polymorphisms and 22 bp deletion in the promoter region of toll-like receptor 2 (TLR2) gene with the risk of PTB in tea garden communities of Assam.

METHODS

Genotyping of VDR polymorphisms and TLR2Δ22 (-196-174) gene was carried out for 169 PTB cases and 227 apparently healthy community controls using blood samples by PCR-RFLP followed by DNA sequencing. For association study, both univariate and multivariate logistic regression analyses were performed.

RESULTS

This study has shown that BsmI and FokI polymorphisms of VDR gene significantly associated with an increased risk of PTB (AOR = 3.58, 95% CI = 1.64-7.80, P < .01 for B/b genotype of BsmI and AOR = 2.44, 95% CI = 1.40-4.24, P < .01 for F/f genotype of FokI polymorphism). No significant association of TaqI and ApaI polymorphism of VDR gene was found with the risk of PTB. Moreover, this study has revealed that person carrying deletion allele in their TLR2Δ22 (-196-174) gene is significantly associated with an increased risk of PTB having b/b or F/f genotypes in BsmI or FokI polymorphisms of VDR gene.

CONCLUSION

This study has revealed that BsmI and FokI polymorphisms of VDR gene significantly associated with an increased risk of PTB.

Association of Toll like receptor 2 and 9 gene variants with pulmonary tuberculosis: exploration in a northern Indian population

Tuberculosis (TB) is a disease of global importance. There is an increasing recognition of the role of Toll like receptors, important pattern recognition receptors of host immune system, in determining the susceptibility or resistance to TB in various populations. In an attempt to examine the importance of Toll like receptors in immune response to Mycobacterium tuberculosis infection, we explored two variants each of TLR2 and TLR9 in a population residing in Uttar Pradesh, India. Genotyping was performed to detect -196 to -174 del polymorphism and G2258A SNP (Arg753Gln, rs5743708) in TLR2 gene and -T1237C (rs5743836) and G2848A (rs352140) SNP in TLR9 gene in patients with pulmonary TB and healthy controls. The A allele of G2848A SNP in TLR9 gene was found with a marginally higher frequency among TB patients as compared to healthy controls, suggesting that A allele at position 2848 of TLR9 gene may be associated with susceptibility to TB in North Indian population [p = 0.05, Mantel-Haenszel OR = 1.34, 95% CI (1.0-1.82)].

Importance of common TLR2 genetic variants on clinical phenotypes and risk in tuberculosis disease in a Western Chinese population

OBJECTIVES

Abundant studies have suggested that TLR2 genetic variants involve in susceptibility to TB infection. We tried to verified the hypothesis that TLR2 genetic loci effect on the susceptibility to TB in the Western Chinese population.

METHODS

A total 1109 individuals (634 TB patients and 475 healthy controls) were genotyped for rs3804099, rs3804100 and rs76112010 by using a custom-by-design 2x48-Plex SNP scan TM Kit. The statistical analysis between candidate 3 SNPs and risk and phenotypes of TB were conducted in this study. Significant SNPs were further interrogated in relation to TB susceptibility to TB infection and clinical phenotypes.

RESULTS

None of the three genetic loci (rs3804099, rs3804100 and rs76112010) showed statistically significant differences between all TB cases and healthy controls in genotype, allele frequencies and genetic models (all p > 0.05). Statistical comparisons of retreatment TB cases and healthy controls or primary cases revealed that rs3804099 was significantly associated with the increased risk of developing TB in Western Chinese population. For genotypes frequencies, the subgroups of retreatment TB group versus healthy control group analysis and retreatment TB group versus primary TB group analysis results showed the p = 0.041 and p = 0.002 respectively. For recessive model, the subgroup of retreatment TB group versus healthy control group and retreatment TB group versus primary TB group analyses showed the p = 0.028 and P = 0.002 after Bonferroni correction respectively. Furthermore, analysis of the genotypes of rs76112010 in relation to clinical phenotypes of active TB using the dominant model demonstrated that it was strongly correlated with different hematological parameters (Erythrocyte P = 0.043, Hemoglobin P = 0.047, Hematocrit P = 0.027).

CONCLUSION

Our study presented the significant associations of rs3804099 with TB susceptibility in the retreatment TB subgroup analysis. Our study proposed that common TLR2 genetic variants may influence TB development and disease phenotypes in Western Chinese population.

Genomics of human pulmonary tuberculosis: from genes to pathways

Purpose of review

Tuberculosis (TB), caused by Mycobacterium tuberculosis (MTB), remains a major public health threat globally. Several lines of evidence support a role for host genetic factors in resistance/susceptibility to TB disease and MTB infection. However, results across candidate gene and genome-wide association studies (GWAS) are largely inconsistent, so a cohesive genetic model underlying TB risk has not emerged.

Recent Findings

Despite the difficulties in identifying consistent genetic associations, genetic studies of TB and MTB infection have revealed a few well-documented loci. These well validated genes are presented in this review, but there remains a large gap in how these genes translate into better understanding of TB. To address this, we present a pathway based extension of standard association analyses, seeding the results with the best validated genes from candidate gene and GWAS studies.

Summary

Several pathways were significantly enriched using pathway analyses that may help to explain population patterns of TB risk. In conclusion, we advocate for novel approaches to the study of host genetic analysis of TB that extend traditional association approaches.

Histone H3K14 hypoacetylation and H3K27 hypermethylation along with HDAC1 up-regulation and KDM6B down-regulation are associated with active pulmonary tuberculosis disease

The aim of this study is to determine the roles of global histone acetylation (Ac)/methylation (me), their modifying enzymes, and gene-specific histone enrichment in active pulmonary tuberculosis (TB) disease. Global histone H3K27me3, H3K27me2, H3K9me3, H3K9Ac, and H3K14Ac expressions, and their modifying enzyme expressions, including KDM1A, KDM6B, EZH2, HDAC1, and HDAC2, were assessed in blood leukocytes from 81 patients with active pulmonary TB disease and 44 matched healthy subjects (HS). TLR2, TNF-α, IFN-γ, and IL12B-specific histone enrichment of peripheral blood mononuclear cells was measured by chromatin immunoprecipitation method. We found that Global H3K14Ac was decreased and H3K27me2 was increased in TB patients as compared with that in HS. TB patients with low H3K14Ac had lower one-year survival. Global H3K27me3 was increased in TB patients with high bacterial burden, or systemic symptoms as compared with that in those without the attribute or HS. HDAC1 gene/protein expressions were increased in TB patients as compared with that in HS, whereas KDM6B gene/protein expressions were decreased. Global H3K27me2, HDAC1 and KDM6B protein expressions were all reversed to normal after 6-month anti-TB treatment. TNF-α/IL12B promoter-specific H3K14Ac and TNF-α/IL12B/IFN-γ promoter-specific H3K27me2 enrichment were all decreased in 10 TB patients as compared with that in 10 HS. Among them, IL12B-specific H3K27me2 enrichment was reversed to normal after treatment, while the other 4 remained depressed. In conclusions, H3K14 hypoacetylation and H3K27 hypermethylation play a role in the development of active pulmonary TB disease or its clinical phenotypes, probably through up-regulation of HDAC1 and down-regulation of KDM6B, respectively.

Population structure and infectious disease risk in southern Africa

The KhoeSan populations are the earliest known indigenous inhabitants of southern Africa. The relatively recent expansion of Bantu-speaking agropastoralists, as well as European colonial settlement along the south-west coast, dramatically changed patterns of genetic diversity in a region which had been largely isolated for thousands of years. Owing to this unique history, population structure in southern Africa reflects both the underlying KhoeSan genetic diversity as well as differential recent admixture. This population structure has a wide range of biomedical and sociocultural implications; such as changes in disease risk profiles. Here, we consolidate information from various population genetic studies that characterize admixture patterns in southern Africa with an aim to better understand differences in adverse disease phenotypes observed among groups. Our review confirms that ancestry has a direct impact on an individual's immune response to infectious diseases. In addition, we emphasize the importance of collaborative research, especially for populations in southern Africa that have a high incidence of potentially fatal infectious diseases such as HIV and tuberculosis.

The Role of Host Genetics (and Genomics) in Tuberculosis

Familial risk of tuberculosis (TB) has been recognized for centuries. Largely through studies of mono- and dizygotic twin concordance rates, studies of families with Mendelian susceptibility to mycobacterial disease, and candidate gene studies performed in the 20th century, it was recognized that susceptibility to TB disease has a substantial host genetic component. Limitations in candidate gene studies and early linkage studies made the robust identification of specific loci associated with disease challenging, and few loci have been convincingly associated across multiple populations. Genome-wide and transcriptome-wide association studies, based on microarray (commonly known as genechip) technologies, conducted in the past decade have helped shed some light on pathogenesis but only a handful of new pathways have been identified. This apparent paradox, of high heritability but few replicable associations, has spurred a new wave of collaborative global studies. This review aims to comprehensively review the heritability of TB, critically review the host genetic and transcriptomic correlates of disease, and highlight current studies and future prospects in the study of host genomics in TB. An implicit goal of elucidating host genetic correlates of susceptibility to Mycobacterium tuberculosis infection or TB disease is to identify pathophysiological features amenable to translation to new preventive, diagnostic, or therapeutic interventions. The translation of genomic insights into new clinical tools is therefore also discussed.

Functional polymorphisms of the TLR7 and TLR8 genes contribute to Mycobacterium tuberculosis infection

Tuberculosis (TB) has recently re-emerged as a major global public health threat and Mycobacterium tuberculosis (MTB) is a highly successful pathogen that evolved remarkable strategies to establish persistent infection. There is strong evidence that host genetic factors influence individual susceptibility to TB. In this study, we evaluated the associations between the TLR7 and TLR8 genetic polymorphisms and TB susceptibility in Chinese individuals. The results demonstrated that the frequency of the TLR8-129C allele was higher in male patients with pulmonary TB than in healthy controls (22.9% vs. 6.8%, p < 0.001). Based on haplotype analysis, the frequency of the TLR7 IVS2-151A/TLR8 -129C haplotype increased the risk for TB infection compared to the wild-type allele (TLR7 IVS2-151A/TLR8 -129G), with OR = 3.23 (95% CI = 1.58-6.61; p = 0.001). An ex vivo phagocytosis assay that examined the functional effects of these polymorphisms on the defense against MTB revealed higher phagocytosis in monocytes from males with the TLR7 IVS2-151A/TLR8 -129C genotype than in those with the wild-type allele (73.0 ± 20.3% versus 34.6 ± 8.1%; p = 0.03). In addition, mRNA expression and cytokine production were analyzed in the whole blood of male healthy volunteers stimulated with inactivated MTB ex vivo. TNFα production was lower in TLR7 IVS2-151A/TLR8 -129C subjects than in those with the wild-type allele (578.4 ± 90.3 pg/ml versus 1043 ± 136 pg/ml; p = 0.03), and the expression of TLR7 was significantly impaired (0.8 ± 0.1 folds, p = 0.05) after MTB stimulation. In conclusion, these findings provide evidence that TLR7 and TLR8 genetic polymorphisms are associated with susceptibility to MTB infection, and the link is shaped by less effective MTB phagocytosis and impaired TLR signaling.

Acute Exposure to Crystalline Silica Reduces Macrophage Activation in Response to Bacterial Lipoproteins

Numerous studies have examined the relationship between alveolar macrophages (AMs) and crystalline silica (SiO2) using in vitro and in vivo immunotoxicity models; however, exactly how exposure to SiO2 alters the functionality of AM and the potential consequences for immunity to respiratory pathogens remains largely unknown. Because recognition and clearance of inhaled particulates and microbes are largely mediated by pattern recognition receptors (PRRs) on the surface of AM, we hypothesized that exposure to SiO2 limits the ability of AM to respond to bacterial challenge by altering PRR expression. Alveolar and bone marrow-derived macrophages downregulate TLR2 expression following acute SiO2 exposure (e.g., 4 h). Interestingly, these responses were dependent on interactions between SiO2 and the class A scavenger receptor CD204, but not MARCO. Furthermore, SiO2 exposure decreased uptake of fluorescently labeled Pam2CSK4 and Pam3CSK4, resulting in reduced secretion of IL-1β, but not IL-6. Collectively, our data suggest that SiO2 exposure alters AM phenotype, which in turn affects their ability to uptake and respond to bacterial lipoproteins.

TLR1, 2, 4, 6 and 9 Variants Associated with Tuberculosis Susceptibility: A Systematic Review and Meta-Analysis

BACKGROUND

Studies investigating the influence of toll-like receptor (TLR) polymorphisms and tuberculosis susceptibility have yielded varying and often contradictory results in different ethnic groups. A meta-analysis was conducted to investigate the relationship between TLR variants and susceptibility to tuberculosis, both across and within specific ethnic groups.

METHODS

An extensive database search was performed for studies investigating the relationship between TLR and tuberculosis (TB) susceptibility. Data was subsequently extracted from included studies and statistically analysed.

RESULTS

32 articles involving 18907 individuals were included in this meta-analysis, and data was extracted for 14 TLR polymorphisms. Various genetic models were employed. An increased risk of TB was found for individuals with the TLR2 rs3804100 CC and the TLR9 rs352139 GA and GG genotypes, while decreased risk was identified for those with the AG genotype of TLR1 rs4833095. The T allele of TLR6 rs5743810 conferred protection across all ethnic groups. TLR2 rs5743708 subgroup analysis identified the A allele to increase susceptibility to TB in the Asian ethnic group, while conferring protection in the Hispanic group. The T allele of TLR4 rs4986791 was also found to increase the risk of TB in the Asian subgroup. All other TLR gene variants investigated were not found to be associated with TB in this meta-analysis.

DISCUSSION

Although general associations were identified, most TLR variants showed no significant association with TB, indicating that additional studies investigating a wider range of pattern recognition receptors is required to gain a better understanding of this complex disease.

Genetic polymorphisms of CCL1 rs2072069 G/A and TLR2 rs3804099 T/C in pulmonary or meningeal tuberculosis patients

CCL1, one of the members of the CC chemokine family, is an inflammatory mediator that stimulates the migration of human monocytes. CCL1 expression is induced by Mycobacterium tuberculosis and TLR ligands in macrophage. TLR2 plays critical role in host immune response against M. tuberculosis infection by regulating the macrophage activation and cytokine secretion. M. tuberculosis causes different clinical forms of tuberculosis (TB) disease. Single-nucleotide polymorphisms (SNPs) in the CCL1 gene and TLR2 gene may be associated with the development of different clinical forms of TB, depending on the different immune mechanisms. This study was to evaluate the possible association between CCL1 rs2072069 G/A or/and TLR2 rs3804099 T/C (T597C) polymorphisms and pulmonary tuberculosis (PTB) or/and tuberculous meningitis (TBM) in a sample of the Chinese adult population. A case-control study was designed to compare the allele frequency and genotype distribution between control (n=386) and TB (n=341) who had either PTB (n=230) or TBM (n=111). The genotype typing was performed using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) technique. TLR2 variant genotype 597CC was associated with susceptibility to PTB rather than to TBM. In the male PTB subgroup, 597CC genotype was identified in a higher rate, compared with male control subgroup. This study demonstrates that T597C polymorphism of TLR2 is a risk factor for susceptibility to PTB rather than to TBM in a sample of Chinese adult population. Patient gender may affect the outcome of M. tuberculosis infection. TLR2 gene may influence the development of PTB and TBM by different immune mechanisms.

The involvement of NADPH oxidase-mediated ROS in cytokine secretion from macrophages induced by Mycobacterium tuberculosis ESAT-6

The 6-kDa early secretory antigenic target (ESAT-6) of Mycobacterium tuberculosis is strongly correlated with subversion of innate immune responses against invading mycobacteria. To understand the role of ESAT-6 in macrophage response against M. tuberculosis, the effects of ESAT-6 on macrophage generation of reactive oxygen species (ROS) and production of cytokines were studied. ESAT-6-induced macrophage secretion of monocyte chemoattractant protein-1 and TNF-α was found in a time- and dose-dependent manner. Signaling inhibition experiments indicate that NF-κB activation mediated by p38/JNK mitogen-activated protein kinase (MAPK) was involved in ESAT-6-triggered cytokine production. Moreover, TLR2 was engaged in ESAT-6-stimulated macrophage activation via rapidly induced ROS production and regulated activation of JNK/p38 MAPKs and NF-κB. More importantly, NADPH oxidase-mediated ROS generation is required during this process. Our study has identified a novel signal transduction pathway involving NADPH-ROS-JNK/p38-NF-κB in ESAT-6-induced cytokine production from macrophages. These findings provide an important evidence to understand the pathogenesis of M. tuberculosis infection in the modulation of the immune response.

Frequency of P2RX7 A1513C and TLR2 -196 to -174 ins/del in healthy Polish individuals

Polymorphisms within genes coding innate immune response proteins are involved in genetic susceptibility to various conditions. We investigated the frequency of P2RX7 A1513C and TLR2 -196 to -174 ins/del polymorphisms in healthy Polish population. Frequency of minor alleles was relatively similar to the pattern presented by Caucasian populations while it differed significantly when compared to non-European populations, which could be a result of variable selection pressure put upon studied alleles or hindered gene flow between populations.

Aberrant Toll-like receptor 2 promoter methylation in blood cells from patients with pulmonary tuberculosis

OBJECTIVES

Toll-like receptor 2 (TLR2) is a major mediator of innate immunity against tuberculosis (TB). This study aimed to determine if TLR2 promoter DNA methylation is associated with pulmonary TB.

METHODS

The DNA methylation levels of 20 CpG sites over the TLR2 promoter region and TLR2 gene/protein expressions of immune cells of the blood were examined in 99 sputum culture-positive pulmonary TB patients and 77 healthy subjects (HS).

RESULTS

TB patients had higher methylation levels over five CpG sites (3, 7, 9, 13, and 18), lower TLR2 gene expression, lower TLR2 expression on monocyte, higher TLR2 expression on NK cell, and higher serum TNF-α/IFN-γ levels than HS after adjusting for confounding factors. Patients with a high bacillary load had lower methylation levels at CpG-15, -17, and -20. Patients with drug-resistant TB had higher CpG-18 methylation levels and lower TLR2 expression on NK cell. Patients with far advanced lesion on chest radiograph had higher serum TNF-α level and higher TLR2 expression on NK cell. Patients with a high TLR2 expression on NK cell had lower one-year survival. CpG-18 methylation level, TLR2 expressions on monocyte/NK cell, and TNF-α/IFN-γ levels were all reversed to normal after 6-month anti-TB treatment.

CONCLUSIONS

Aberrant methylation of certain CpG sites over TLR2 promoter region is associated with active pulmonary TB or its phenotypes, probably through the down-regulation of TLR2 expression.

Genetic polymorphisms in the Toll-like receptor signalling pathway in Helicobacter pylori infection and related gastric cancer

BACKGROUND

Gastric cancer (GC) is a progressive process initiated by Helicobacter pylori-induced inflammation. Initial recognition of H. pylori involves Toll-like receptors (TLRs), central molecules in the host inflammatory response. Here, we investigated the association between novel polymorphisms in genes involved in the TLR signalling pathway, including TLR2, TLR4, LBP, MD-2, CD14 and TIRAP, and risk of H. pylori infection and related GC.

METHODS

A case-control study comprising 310 ethnic Chinese individuals (87 non-cardia GC cases and 223 controls with functional dyspepsia) was conducted. Twenty-five polymorphisms were detected by MALDI-TOF mass spectrometry, PCR, PCR-RFLP and real-time PCR.

RESULTS

Seven polymorphisms showed significant associations with GC (TLR4 rs11536889, TLR4 rs10759931, TLR4 rs1927911, TLR4 rs10116253, TLR4 rs10759932, TLR4 rs2149356 and CD14 -260 C/T). In multivariate analyses, TLR4 rs11536889 remained a risk factor for GC (OR: 3.58, 95% CI: 1.20-10.65). TLR4 rs10759932 decreased the risk of H. pylori infection (OR: 0.59, 95% CI: 0.41-0.86). Statistical analyses assessing the joint effect of H. pylori infection and the selected polymorphisms revealed strong associations with GC (TLR2, TLR4, MD-2, LBP and TIRAP polymorphisms).

CONCLUSIONS

Novel polymorphisms in TLR2, TLR4, MD-2, LBP, CD14 and TIRAP, genes encoding important molecules of the TLR signalling pathway, showed clear associations with H. pylori-related GC in Chinese.

Antitubercular therapy in patients with cirrhosis: Challenges and options

Tuberculosis (TB) has been a human disease for centuries. Its frequency is increased manyfold in patients with liver cirrhosis. The gold standard of TB management is a 6-mo course of isoniazid, rifampicin, pyrazinamide and ethambutol. Although good results are seen with this treatment in general, the management of patients with underlying cirrhosis is a challenge. The underlying depressed immune response results in alterations in many diagnostic tests. The tests used for latent TB have many flaws in this group of patients. Three of four first-line antitubercular drugs are hepatotoxic and baseline liver function is often disrupted in patients with underlying cirrhosis. Frequency of hepatotoxicity is increased in patients with liver cirrhosis, frequently leading to severe liver failure. There are no established guidelines for the treatment of TB in relation to the severity of liver disease. There is no consensus on the frequency of liver function tests required or the cut-off used to define hepatotoxicity. No specific treatment exists for prevention or treatment of hepatotoxicity, making monitoring even more important. A high risk of multidrug-resistant TB is another major worry due to prolonged and interrupted treatment.

The genetics of innate immunity sensors and human disease

Since their discovery, innate immunity microbial sensors have been increasingly studied and shown to play a critical role in innate responses to microbes in several experimental in vitro, ex vivo, and animal models. However, their role in the human response to infection in natural conditions has just started to be deciphered, by means of clinical studies of primary immunodeficiencies and epidemiological genetic studies. Here, we summarize the major findings concerning the genetic diversity of the various families of microbial sensors in humans, and of other molecules involved in the signaling pathways they trigger. Specifically, we review the genetic associations, revealed by both clinical and epidemiological genetics studies, of microbial sensors from five different families: Toll-like receptors, C-type lectin receptors, NOD-like receptors, RIG-I-like receptors, and cytosolic DNA sensors. In particular, we consider the relationships between variation at the genes encoding these molecules and susceptibility to and the severity of infectious diseases and other clinical conditions associated with immune dysfunction, including autoimmunity, inflammation, allergy, and cancer. Despite the fact that the genetic links between innate immunity sensors and human disorders remain still limited, human genetics studies are increasingly improving our understanding of the genuine functions of microbial sensors and downstream signaling molecules in the natural setting.

Variants in toll-like receptor 9 gene influence susceptibility to tuberculosis in a Mexican population

BACKGROUND

The control of Mycobacterium tuberculosis (Mtb) infection begins with the recognition of mycobacterial structural components by toll like receptors (TLRs) and other pattern recognition receptors. Our objective was to determine the influence of TLRs polymorphisms in the susceptibility to develop tuberculosis (TB) in Amerindian individuals from a rural area of Oaxaca, Mexico with high TB incidence.

METHODS

We carried out a case-control association community based study, genotyping 12 polymorphisms of TLR2, TLR4, TLR6 and TLR9 genes in 90 patients with confirmed pulmonary TB and 90 unrelated exposed but asymptomatic household contacts.

RESULTS

We found a significant increase in the frequency of the allele A of the TLR9 gene polymorphism rs352139 (A>G) in the group of TB patients (g.f. = 0.522) when compared with controls (g.f. = 0.383), (Pcorr = 0.01, OR = 1.75). Under the recessive model (A/G + A/A vs G/G) this polymorphism was also significantly associated with TB (Pcorr = 0.01, OR= 2.37). The association of the SNP rs352139 was statistically significant after adjustment by age, gender and comorbidities by regression logistic analysis (Dominant model: p value = 0.016, OR = 2.31; Additive model: p value = 0.023, OR = 1.68). The haplotype GAA of TLR9 SNPs was also associated with TB susceptibility (Pcorr = 0.02). Differences in the genotype or allele frequencies of TLR2, TLR4 and TLR6 polymorphisms between TB patients and healthy contacts were not detected.

CONCLUSIONS

Our study suggests that the allele A of the intronic polymorphism rs352139 on TLR9 gene might contribute to the risk of developing TB in Mexican Amerindians.

Role of Toll-like receptor 2 (-196 to -174) polymorphism in susceptibility to pulmonary tuberculosis in Pakistani population

Tuberculosis (TB) is a global public health problem and a source of preventable deaths each year, with 8.8 million new cases of TB and 1.6 million deaths worldwide. Pakistan ranks sixth on the list of 22 high-burden tuberculosis countries in the world. The transitions from infection to clinical disease are very few signifying that host-defence factors could lead to the development of active disease. Toll-like receptor (TLR) 2 polymorphisms have been associated with regulation of TLR expression and development of active TB. In this study, blood samples of 187 subjects including 100 healthy and 87 TB positive were collected from three districts of Pakistan. DNA was extracted from blood and TLR 2 (-196 to -174del) polymorphism was analysed by polymerase chain reaction (PCR). The results suggest that the frequency of -196 to -174del/del polymorphism of TLR2 was significantly higher in TB-positive patients compared with healthy. Results revealed that (-196 to -174del) polymorphism may increase the susceptibility to TB in healthy population of Pakistan. Moreover, males with heterozygous genotype (I/D) are more prone to TB than females with the same genotype. The occurrence of TB infection has been found positively associated with the age, suggesting that the population within the range of 21-45 years is more susceptible to Mycobacterium tuberculosis than other age groups studied. A significant association is also observed between smoking and the chances of developing TB, confirming that smoking strongly promotes its incidence.

Receptor-mediated recognition of mycobacterial pathogens

Mycobacteria are a genus of bacteria that range from the non-pathogenic Mycobacterium smegmatis to Mycobacterium tuberculosis, the causative agent of tuberculosis in humans. Mycobacteria primarily infect host tissues through inhalation or ingestion. They are phagocytosed by host macrophages and dendritic cells. Here, conserved pathogen-associated molecular patterns (PAMPs) on the surface of mycobacteria are recognized by phagocytic pattern recognition receptors (PRRs). Several families of PRRs have been shown to non-opsonically recognize mycobacterial PAMPs, including membrane-bound C-type lectin receptors, membrane-bound and cytosolic Toll-like receptors and cytosolic NOD-like receptors. Recently, a possible role for intracellular cytosolic PRRs in the recognition of mycobacterial pathogens has been proposed. Here, we discuss currentideas on receptor-mediated recognition of mycobacterial pathogens by macrophages and dendritic cells.

Toll-like receptor -1, -2, and -6 polymorphisms and pulmonary tuberculosis susceptibility: a systematic review and meta-analysis

Background

A large number of studies have investigated whether polymorphisms in the Toll-like receptor (TLR) genes are implicated in susceptibility to tuberculosis (TB) in different populations. However, the results are inconsistent and inconclusive.

Methods

A literature search was conducted using the PubMed, EMBASE, Medline (Ovid), ISI Web of Knowledge and Chinese National Knowledge Infrastructure (CNKI). A meta-analysis on the associations between the TLR1 G1805T, TLR2 T597C, T1350C, G2258A, and TLR6 C745T polymorphisms and TB risk was carried out by comparison using different genetic models.

Results

In total, 16 studies from 14 articles were included in this review. In meta-analysis, significant associations were observed between the TLR2 2258AA (AA vs. AG+AG, OR 5.82, 95% CI 1.30–26.16, P = 0.02) and TLR6 745TT (TT vs. CT+CC, OR 0.61, 95% CI 0.39–0.97, P = 0.04) polymorphisms and TB risk. In the subgroup analysis by ethnicity, Africans and American Hispanic subjects with the TLR1 1805T allele had an increased susceptibility, whereas Asian and European subjects with the TLR2 2258A allele had an increased susceptibility to TB.

Conclusions

The meta-analysis indicated that TLR2 G2258A is associated with increased TB risk, especially in Asians and Europeans. TLR1 G1805T is associated with increased TB in Africans and American Hispanics. TLR6 C745T is associated with decreased TB risk. Our systematic review and meta-analysis reported an interesting preliminary conclusion, but this must be validated by future large-scale and functional studies in different populations.

Genetic polymorphisms in Toll-like receptors among pediatric patients with renal parenchymal infections of different clinical severities

Background

Although several studies have suggested single gene defects or variations in the genes associated with host immune response could confer differences in susceptibility to urinary pathogen invasion, no studies have examined the genetic polymorphisms in various toll-like receptors (TLRs) that activate innate immune responses in pediatric renal parenchymal infections of different clinical severities, namely acute pyelonephritis and the clinically more severe disease, acute lobar nephronia.

Methodology

Patients who fulfilled the diagnostic criteria for acute pyelonephritis (APN) and acute lobar nephronia (ALN) without underlying diseases or structural anomalies, except for vesicoureteral reflux (VUR), were enrolled. Genotyping of the single nucleotide polymorphisms (SNPs) in the genes encoding TLR-1, TLR-2, TLR-4, TLR-5, and TLR-6 was performed by matrix-assisted laser desorption/ionization time-of-flight-based mini-sequencing analysis.

Principal Findings

A total of 16 SNPs were selected for genotyping. Analysis of 96 normal and 48 patients’ samples revealed that only four SNPs had heterozygosity rates >0.01. These SNPs were selected for further investigation. Hardy-Weinberg equilibrium was satisfied for the observed genotype frequencies. Statistically significant differences in the genotype frequency of TLR-2 (rs3804100, T1350C) between controls and ALN or (APN+ALN) combined group were identified using the recessive model with the correction for multiple-SNP testing. Further genotype pattern frequency analysis in TLR-2 SNPs (rs3804099 and rs3804100) showed significantly reduced occurrence of the rare allele homozygote (CC+CC) in the no-VUR subgroup of APN and ALN cases.

Conclusions

As the inflammatory responses in ALN patients are more severe than those in APN patients (higher CRP levels, longer duration of fever after antibiotic treatment), these findings suggest that the genetic variant in TLR-2 (rs3804100, T1350C) may protect the host from severe urinary tract infections as ALN.

Toll-like receptor 2 in promoting angiogenesis after acute ischemic injury

Angiogenesis is an important mechanism that protects tissue against necrosis following acute ischemic injury. The aim of this study was to investigate whether the Toll-like receptor 2 (TLR2) signaling pathway is involved in angiogenesis following ischemic injury by cell migration and lymphocyte invasion assays in vitro, and a mouse model of hindlimb ischemia by ligation in vivo, respectively. To assess the potential role of TLR2 activation in endothelial cell permeability, HUVECs were pretreated with Pam3CSK4 and analyzed using wound repair and transwell assays. The results showed that the TLR2 agonist induced human umbilical vein endothelial cell (HUVEC) migration and increased the permeability of HUVECs to lymphocyte. The lymphocyte invasion of TLR2 knockout (TLR2-/-) mice was inhibited as compared to that of wild-type (WT) mice. In the mouse model of hindlimb ischemia by ligation, blood perfusion of operated limbs was significantly lower in TLR2-/- compared to WT mice, 7 and 14 days after ligation. TLR2-/- mice showed a decreased CD31 expression in ischemic gastrocnemius at 7 and 14 days after ligation, reduced interleukin-6 (IL-6) level and lowered tumor necrosis factor-α (TNF-α) levels. These findings demonstrated that TLR2 activation promotes cell migration, cell permeability and the lymphocyte invasion of endothelial cells. TLR2 activation promotes angiogenesis in vivo, which may be associated with the serum of TNF-α levels and IL-6 release.

Genomic perspectives in inter-individual adverse responses following nanomedicine administration: The way forward

The underlying mechanism of intravenous infusion-related adverse reactions inherent to regulatory-approved nanomedicines still remains elusive. There are substantial inter-individual differences in observed adverse reactions, which may include cardiovascular, broncho-pulmonary, muco-cutaneous, neuro-psychosomatic and autonomic manifestations. Although nanomedicine-mediated triggering of complement activation has been suggested to be a significant contributing factor to these adverse events, complement activation may still proceed in non-responders. Whether these reactions share similar immunological mechanisms and underpinning genetic factors with drug hypersensitivity syndrome remains to be investigated. Genetic association studies could be a powerful tool to dissect causative factors and reveal the multiple molecular pathways that induce infusion related adverse reactions. It is envisaged that such research may lead to the design of reliable in vitro profiling tests for risk assessment and treatment decisions, thereby revolutionizing the practice of medicine with nanopharmaceuticals. Such procedures may further improve regulatory approval processes for nanomedicines currently in the pipeline and decrease the overall cost of health care. Here we discuss some key innate immunity genes and their polymorphisms in relation to nanomedicine infusion-mediated symptomatic responses.

Cellular and humoral mechanisms involved in the control of tuberculosis

Mycobacterium tuberculosis (Mtb) infection is a major international public health problem. One-third of the world's population is thought to have latent tuberculosis, a condition where individuals are infected by the intracellular bacteria without active disease but are at risk for reactivation, if their immune system fails. Here, we discuss the role of nonspecific inflammatory responses mediated by cytokines and chemokines induced by interaction of innate receptors expressed in macrophages and dendritic cells (DCs). We also review current information regarding the importance of several cytokines including IL-17/IL-23 in the development of protective cellular and antibody-mediated protective responses against Mtb and their influence in containment of the infection. Finally, in this paper, emphasis is placed on the mechanisms of failure of Mtb control, including the immune dysregulation induced by the treatment with biological drugs in different autoimmune diseases. Further functional studies, focused on the mechanisms involved in the early host-Mtb interactions and the interplay between host innate and acquired immunity against Mtb, may be helpful to improve the understanding of protective responses in the lung and in the development of novel therapeutic and prophylactic tools in TB.

Surrogate markers of infection: interrogation of the immune system

Infectious diseases remain the greatest causes of morbidity and mortality in global terms. As much of the burden occurs in the developing world, limited access to diagnostic testing has hampered the diagnosis and treatment of these conditions, while, in the developed world, the cost of managing infectious diseases remains considerable. Despite the size of the problem there remains an ongoing need for tests that improve diagnostic sensitivity and specificity, provide more rapid diagnoses, are available for point-of-care testing in remote regions, and can help inform therapeutic decision-making by identifying resistance patterns or patient outcomes. This article discusses the background to biomarker development for infectious diseases, some current assays that are providing useful information regarding the host's response to infection (using examples such as Cytomegalovirus and Mycobacterium tuberculosis), as well as likely future technologies and their limitations.

The toll-like receptor 2 (TLR2) -196 to -174 del/ins polymorphism affects viral loads and susceptibility to hepatocellular carcinoma in chronic hepatitis C

Chronic hepatitis C virus (HCV) infection is a major risk factor for hepatocellular carcinoma (HCC). HCV proteins core and NS3 can bind to toll-like receptor 2 (TLR2) and trigger inflammatory responses. Polymorphisms in the TLR2 gene predispose to various forms of malignancy but have not been studied in HCV-associated HCC. Here, we investigated whether single nucleotide polymorphisms (SNPs), rs4696480, rs5743708, rs5743704 and the -196 to -174 del/ins polymorphism of the TLR2 gene affect the risk for HCC in chronic hepatitis C. The study involved 189 and 192 HCV genotype 1 infected patients with and without HCC, respectively, as well as 347 healthy controls. TLR2 alleles were determined by hybridization probe assays and allele-specific short fragment polymerase chain reaction on a LightCycler system. All TLR2 polymorphisms matched the Hardy-Weinberg equilibrium in each study group. Although TLR2 SNPs showed no effect, the frequency of the TLR2 -196 to -174 del allele was significantly higher in patients with HCV-associated HCC (22.5%) than in HCV-infected patients without HCC (15.6%, p = 0.016) and healthy controls (15.3%, p = 0.003). HCV-infected carriers of a TLR2 -196 to -174 del allele had significantly higher HCV viral loads than TLR2 -196 to -174 ins/ins homozygous patients (p = 0.031). Finally, in carriers of the TLR2 -196 to -174 del allele, stimulation of monocytes resulted in significantly lower TLR2 expression levels and interleukin-8 (IL-8) induction than in individuals with the TLR2 -196 to -174 ins/ins genotype (p < 0.05). Our data suggest the TLR2 -196 to -174 del allele to affect HCV viral loads and to increase the risk for HCC in HCV genotype1-infected patients.

Human TLRs and IL-1Rs in host defense: natural insights from evolutionary, epidemiological, and clinical genetics

Toll-like receptors (TLRs) and interleukin-1 receptors (IL-1Rs) have TIR intracellular domains that engage two main signaling pathways, via the TIR-containing adaptors MyD88 (which is not used by TLR3) and TRIF (which is used only by TLR3 and TLR4). Extensive studies in inbred mice in various experimental settings have attributed key roles in immunity to TLR- and IL-1R-mediated responses, but what contribution do human TLRs and IL-1Rs actually make to host defense in the natural setting? Evolutionary genetic studies have shown that human intracellular TLRs have evolved under stronger purifying selection than surface-expressed TLRs, for which the frequency of missense and nonsense alleles is high in the general population. Epidemiological genetic studies have yet to provide convincing evidence of a major contribution of common variants of human TLRs, IL-1Rs, or their adaptors to host defense. Clinical genetic studies have revealed that rare mutations affecting the TLR3-TRIF pathway underlie herpes simplex virus encephalitis, whereas mutations in the TIR-MyD88 pathway underlie pyogenic bacterial diseases in childhood. A careful reconsideration of the contributions of TLRs and IL-1Rs to host defense in natura is required.

Innate immune recognition of Mycobacterium tuberculosis

Tuberculosis (TB), caused by Mycobacterium tuberculosis (MTB), is a major health problem, with 10 million new cases diagnosed each year. Innate immunity plays an important role in the host defense against M. tuberculosis, and the first step in this process is recognition of MTB by cells of the innate immune system. Several classes of pattern recognition receptors (PPRs) are involved in the recognition of M. tuberculosis, including Toll-like receptors (TLRs), C-type lectin receptors (CLRs), and Nod-like receptors (NLRs). Among the TLR family, TLR2, TLR4, and TLR9 and their adaptor molecule MyD88 play the most prominent roles in the initiation of the immune response against tuberculosis. In addition to TLRs, other PRRs such as NOD2, Dectin-1, Mannose receptor, and DC-SIGN are also involved in the recognition of M. tuberculosis. Human epidemiological studies revealed that genetic variation in genes encoding for PRRs and downstream signaling products influence disease susceptibility, severity, and outcome. More insight into PRRs and the recognition of mycobacteria, combined with immunogenetic studies in TB patients, does not only lead to a better understanding of the pathogenesis of tuberculosis but also may contribute to the design of novel immunotherapeutic strategies.

Mycobacterium tuberculosis lipoproteins directly regulate human memory CD4(+) T cell activation via Toll-like receptors 1 and 2

The success of Mycobacterium tuberculosis as a pathogen relies on its ability to regulate the host immune response. M. tuberculosis can manipulate adaptive T cell responses indirectly by modulating antigen-presenting cell (APC) function or by directly interacting with T cells. Little is known about the role of M. tuberculosis molecules in direct regulation of T cell function. Using a biochemical approach, we identified lipoproteins LprG and LpqH as major molecules in M. tuberculosis lysate responsible for costimulation of primary human CD4(+) T cells. In the absence of APCs, activation of memory CD4(+) T cells with LprG or LpqH in combination with anti-CD3 antibody induces Th1 cytokine secretion and cellular proliferation. Lipoprotein-induced T cell costimulation was inhibited by blocking antibodies to Toll-like receptor 2 (TLR2) and TLR1, indicating that human CD4(+) T cells can use TLR2/TLR1 heterodimers to directly respond to M. tuberculosis products. M. tuberculosis lipoproteins induced NF-κB activation in CD4(+) T cells in the absence of TCR co-engagement. Thus, TLR2/TLR1 engagement alone by M. tuberculosis lipoprotein triggered intracellular signaling, but upregulation of cytokine production and proliferation required co-engagement of the TCR. In conclusion, our results demonstrate that M. tuberculosis lipoproteins LprG and LpqH participate in the regulation of adaptive immunity not only by inducing cytokine secretion and costimulatory molecules in innate immune cells but also through directly regulating the activation of memory T lymphocytes.