TLR9 gene region polymorphisms and susceptibility to tuberculosis in Vietnam

Recent advances in understanding the human host immune response in tuberculous meningitis

Tuberculous meningitis (TBM), the most severe form of tuberculosis, causes death in approximately 25% cases despite antibiotic therapy, and half of survivors are left with neurological disability. Mortality and morbidity are contributed to by a dysregulated immune response, and adjunctive host-directed therapies are required to modulate this response and improve outcomes. Developing such therapies relies on improved understanding of the host immune response to TBM. The historical challenges in TBM research of limited in vivo and in vitro models have been partially overcome by recent developments in proteomics, transcriptomics, and metabolomics, and the use of these technologies in nested substudies of large clinical trials. We review the current understanding of the human immune response in TBM. We begin with M. tuberculosis entry into the central nervous system (CNS), microglial infection and blood-brain and other CNS barrier dysfunction. We then outline the innate response, including the early cytokine response, role of canonical and non-canonical inflammasomes, eicosanoids and specialised pro-resolving mediators. Next, we review the adaptive response including T cells, microRNAs and B cells, followed by the role of the glutamate-GABA neurotransmitter cycle and the tryptophan pathway. We discuss host genetic immune factors, differences between adults and children, paradoxical reaction, and the impact of HIV-1 co-infection including immune reconstitution inflammatory syndrome. Promising immunomodulatory therapies, research gaps, ongoing challenges and future paths are discussed.

Host Genetic Impact on Infectious Diseases among Different Ethnic Groups

Infectious diseases such as malaria, tuberculosis (TB), human immunodeficiency virus (HIV), and the coronavirus disease of 2019 (COVID-19) are problematic globally, with high prevalence particularly in Africa, attributing to most of the death rates. There have been immense efforts toward developing effective preventative and therapeutic strategies for these pathogens globally, however, some remain uncured. Disease susceptibility and progression for malaria, TB, HIV, and COVID-19 vary among individuals and are attributed to precautionary measures, environment, host, and pathogen genetics. While studying individuals with similar attributes, it is suggested that host genetics contributes to most of an individual's susceptibility to disease. Several host genes are identified to associate with these pathogens. Interestingly, many of these genes and polymorphisms are common across diseases. This paper analyzes genes and genetic variations within host genes associated with HIV, TB, malaria, and COVID-19 among different ethnic groups. The differences in host-pathogen interaction among these groups, particularly of Caucasian and African descent, and which gene polymorphisms are prevalent in an African population that possesses protection or risk to disease are reviewed. The information in this review could potentially help develop personalized treatment that could effectively combat the high disease burden in Africa.

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.

Research progress on genetic control of host susceptibility to tuberculosis

The "Lübeck disaster", twins studies, adoptees studies, and other epidemiological observational studies have shown that host genetic factors play a significant role in determining the host susceptibility to Mycobacterium tuberculosis infection and pathogenesis of tuberculosis. From linkage analyses to genome-wide association studies, it has been discovered that human leucocyte antigen (HLA) genes as well as non-HLA genes (such as SLC11A1, VDR, ASAP1 as well as genes encoding cytokines and pattern recognition receptors) are associated with tuberculosis susceptibility. To provide ideas for subsequent studies about risk prediction of MTB infection and the diagnosis and treatment of tuberculosis, we review the research progress on tuberculosis susceptibility related genes in recent years, focusing on the correlation of HLA genes and non-HLA genes with the pathogenesis of tuberculosis. We also report the results of an enrichment analysis of the genes mentioned in the article. Most of these genes appear to be involved in the regulation of immune system and inflammation， and are also closely related to autoimmune diseases.

Human genetic background in susceptibility to tuberculosis

Tuberculosis (TB), especially in developing countries, is a major threat to human health. The pathogenesis of TB remains poorly understood, and <5%-10% of individuals infected with Mycobacterium tuberculosis (MTB) will develop clinical disease. The human genetic factors contributing to susceptibility or resistance to TB pathogenesis have been investigated by high-throughput and low-throughput association studies. Genetic polymorphisms of several genes including TLR, IGRM, VDR, ASAP1, AGMO, FOXP1, and UBLCP1 effect on the disease phenotype and also the outcome of TB treatment. Recently, microRNAs (miRNAs), which negatively regulated gene expression at the posttranscriptionally level, have gained increasing attention due to their altered expression in various human diseases, including some infections. They are crucial posttranscriptional regulators of immune response in both innate and adaptive immunity. It has been established in recent studies that the host immune response against MTB is regulated by many miRNAs, most of which are induced by MTB infection. Moreover, differential expression of miRNAs in TB patients may help distinguish between TB patients and healthy individuals or latent TB. In this review, we summarize and discuss the literature and highlight the role of selected single nucleotide polymorphisms and miRNAs that have been associated with TB infection.

Underwhelming or Misunderstood? Genetic Variability of Pattern Recognition Receptors in Immune Responses and Resistance to Mycobacterium tuberculosis

Human genetic control is thought to affect a considerable part of the outcome of infection with Mycobacterium tuberculosis (Mtb). Most of us deal with the pathogen by containment (associated with clinical "latency") or sterilization, but tragically millions each year do not. After decades of studies on host genetic susceptibility to Mtb infection, genetic variation has been discovered to play a role in tuberculous immunoreactivity and tuberculosis (TB) disease. Genes encoding pattern recognition receptors (PRRs) enable a consistent, molecularly direct interaction between humans and Mtb which suggests the potential for co-evolution. In this review, we explore the roles ascribed to PRRs during Mtb infection and ask whether such a longstanding and intimate interface between our immune system and this pathogen plays a critical role in determining the outcome of Mtb infection. The scientific evidence to date suggests that PRR variation is clearly implicated in altered immunity to Mtb but has a more subtle role in limiting the pathogen and pathogenesis. In contrast to 'effectors' like IFN-γ, IL-12, Nitric Oxide and TNF that are critical for Mtb control, 'sensors' like PRRs are less critical for the outcome of Mtb infection. This is potentially due to redundancy of the numerous PRRs in the innate arsenal, such that Mtb rarely goes unnoticed. Genetic association studies investigating PRRs during Mtb infection should therefore be designed to investigate endophenotypes of infection - such as immunological or clinical variation - rather than just TB disease, if we hope to understand the molecular interface between innate immunity and Mtb.

Innate Immune Pattern Recognition Receptors of Mycobacterium tuberculosis: Nature and Consequences for Pathogenesis of Tuberculosis

Innate immunity against Mycobacterium tuberculosis is a critical early response to prevent the establishment of the infection. Despite recent advances in understanding the host-pathogen dialogue in the early stages of tuberculosis (TB), much has yet to be learnt. The nature and consequences of this dialogue ultimately determine the path of infection: namely, either early clearance of M. tuberculosis, or establishment of M. tuberculosis infection leading to active TB disease and/or latent TB infection. On the frontline in innate immunity are pattern recognition receptors (PRRs), with soluble factors (e.g. collectins and complement) and cell surface factors (e.g. Toll-like receptors and other C-type lectin receptors (Dectin 1/2, Nod-like receptors, DC-SIGN, Mincle, mannose receptor, and MCL) that play a central role in recognising M. tuberculosis and facilitating its clearance. However, in a 'double-edged sword' scenario, these factors can also be involved in enhancement of pathogenesis as well. Furthermore, innate immunity is also a critical bridge in establishing the subsequent adaptive immune response, which is also responsible for granuloma formation that cordons off M. tuberculosis infection, establishing latency and acting as a reservoir for bacterial persistence and dissemination of future disease. This chapter discusses the current understanding of pattern recognition of M. tuberculosis by innate immunity and the role this plays in the pathogenesis and protection against TB.

N6-methylated adenine on the target sites of mamA from Mycobacterium bovis BCG enhances macrophage activation by CpG DNA in mice

CpG motifs in DNA sequences are recognized by Toll-like receptor 9 and activate immune cells. Bacterial genomic DNA (gDNA) has modified cytosine bases (5-methylcytosine [5 mC]) and modified adenine bases (6-methyladenine [6 mA]). 5 mC inhibits immune activation by CpG DNA; however, it is unclear whether 6 mA inhibits immune activation by CpG DNA. Mycobacterium bovis BCG (BCG) has three adenine methyltransferases (MTases) that act on specific target sequences. In this study, we examined whether the 6 mA at the target sites of adenine MTases affected the immunostimulatory activity of CpG DNA. Our results showed that only 6 mA located at the target sequence of mamA, an adenine MTase from BCG, enhanced interleukin (IL)-12p40 production from murine bone marrow-derived macrophages (BMDMs) stimulated with CpG DNA. Enhancement of IL-12p40 production in BMDMs was also observed when BMDMs were stimulated with CpG DNA ligated to oligodeoxynucleotides (ODNs) harboring 6 mA. Accordingly, we then evaluated whether gDNA from adenine MTase-deficient BCG was less efficient with regard to stimulation of BMDMs. Indeed, gDNA from a mamA-deficient BCG had less ability to activate BMDMs than that from wild-type BCG. We concluded from these results that adenine methylation on ODNs and bacterial gDNA may enhance immune activity induced by CpG DNA.

The Interplay of Human and Mycobacterium Tuberculosis Genomic Variability

Tuberculosis (TB), caused by the human pathogens Mycobacterium tuberculosis (Mtb) and Mycobacterium africanum, has plagued humanity for millennia and remains the deadliest infectious disease in the modern world. Mycobacterium tuberculosis and M. africanum can be subdivided phylogenetically into seven lineages exhibiting a low but significant degree of genomic diversity and preferential geographic distributions. Human genetic variability impacts all stages of TB pathogenesis ranging from susceptibility to infection with Mtb, progression of infection to disease, and the development of distinct clinical subtypes. The genetic study of severe childhood TB identified strong inborn single-gene errors revealing crucial pathways of vulnerability to TB. However, the identification of major TB-susceptibility genes on the population level has remained elusive. In particular, the replication of findings from candidate and genome-wide association studies across distinct human populations has proven difficult, thus hampering the characterization of reliable host molecular markers of susceptibility. Among the possible confounding factors of genetic association studies is Mtb genomic variability, which generally was not taken into account by human genetic studies. In support of this possibility, Mtb lineage was found to be a contributing factor to clinical presentation of TB and epidemiological spread of Mtb in exposed populations. The confluence of pathogen and human host genetic variability to TB pathogenesis led to the consideration of a possible coadaptation of Mtb strains and their human hosts, which should reveal itself in significant interaction effects between Mtb strain and TB-susceptibility/resistance alleles. Here, we present some of the most consistent findings of genetic susceptibility factors in human TB and review studies that point to genome-to-genome interaction between humans and Mtb lineages. The limited results available so far suggest that analyses considering joint human–Mtb genomic variability may provide improved power for the discovery of pathogenic drivers of the ongoing TB epidemic.

The pathogenesis of tuberculous meningitis

Tuberculosis (TB) remains a leading cause of death globally. Dissemination of TB to the brain results in the most severe form of extrapulmonary TB, tuberculous meningitis (TBM), which represents a medical emergency associated with high rates of mortality and disability. Via various mechanisms the Mycobacterium tuberculosis (M.tb) bacillus disseminates from the primary site of infection and overcomes protective barriers to enter the CNS. There it induces an inflammatory response involving both the peripheral and resident immune cells, which initiates a cascade of pathologic mechanisms that may either contain the disease or result in significant brain injury. Here we review the steps from primary infection to cerebral disease, factors that contribute to the virulence of the organism and the vulnerability of the host and discuss the immune response and the clinical manifestations arising. Priorities for future research directions are suggested.

Association of TLR8 and TLR9 polymorphisms with tuberculosis in a Chinese Han population: a case-control study

Background

Toll-like receptor (TLR) single nucleotide polymorphisms (SNPs) have been associated with regulation of TLR expression and development of active tuberculosis (TB). The objectives of this study were to determine whether TLR8 and TLR9 SNPs were associated with the development of latent TB infection (LTBI) and the subsequent pulmonary TB (PTB) in a Chinese Han population.

Methods

Two independent samples were enrolled. The first sample contained 584 TB cases and 608 controls; the second sample included 204 healthy controls, 201 LTBI subjects and 209 bacteria-confirmed active PTB patients. Three SNPs (rs3764880, rs187084 and rs5743836) were genotyped. The associations between the SNPs and risk of LTBI or PTB were investigated using unconditional logistic regression analysis.

Results

The A-allele of TLR8 rs3764880 SNP was protective against the development of TB in males (A vs G, OR = 0.58, 95%CI = 0.37–0.91). The AA genotype of rs3764880 SNP was found to increase the risk of PTB among females with an OR of 4.81 (1.11–20.85). The G allele of TLR9 SNP rs187084 was found to increase the risk of PTB (G vs A, P = 0.01, OR = 1.48, 95% CI = 1.10–2.00), the significance was also observed under dominant genetic models. The GA-genotype of TLR9 rs187084 SNP was found to increase the risk of PTB with an OR of 1.68 (1.07–2.65), but was found to decrease the risk of MTB infection with an OR = 0.64 (0.41–0.98). TLR9_rs5743836 SNP was excluded from the data analyses, because the minimum allele frequency was< 1%.

Conclusions

Our findings in two independent samples indicated that SNPs in TLR8 and TLR9 were associated with the development of TB, and highlight that SNPs may have different effects on disease pathogenesis and progression.

Diminished TLR2-TLR9 mediated CD4+ T cell responses are associated with increased inflammation in intraocular tuberculosis

Intraocular tuberculosis (IOTB) is amongst the leading causes of uveitis in tropical countries. Despite reports on involvement of proinflammatory cytokines, studies on innate immune responses in disease pathogenesis are lacking. Reports from animal models and patients with pulmonary tuberculosis indicate that defects in toll like receptor (TLR)2 and TLR9 signalling predispose them to tuberculosis. In this context, we investigated the role of TLR2, TLR4 and TLR9 in generation of CD4+ T effector (Teff) cell responses during IOTB. Firstly, the cells in vitreous fluids showed lower expression of TLR2 and TLR9 in IOTB as compared to non-uveitis and non-TB uveitis groups. Next, peripheral CD4+ Teff cells of subjects with IOTB showed decreased proliferative responses and lower induction of Tregs following TLR2 and TLR9 stimulation. Further, TLR9 ligation resulted in increased IFN-γ and IL-17a but decreased expression of IL-10 and TGF-β. Lastly, lower expression of genes involved in TLR9 signalling after direct TLR9 ligation was observed in IOTB. Collectively, our results show that a subdued response to direct TLR2 and TLR9 stimulation in CD4+ T cells is associated with increased proinflammatory responses in IOTB. These findings reveal an important link between innate immune signalling and ensuing adaptive immune responses in IOTB with implications in other forms of extrapulmonary tuberculosis.

Influence of Genetic Polymorphism Towards Pulmonary Tuberculosis Susceptibility

Tuberculosis (TB) is still remains the major threat for human health worldwide. Several case-control, candidate-gene, family studies and genome-wide association studies (GWAS) suggested the association of host genetic factors to TB susceptibility or resistance in various ethnic populations. Moreover, these factors modulate the host immune responses to tuberculosis. Studies have reported genetic markers to predict TB development in human leukocyte antigen (HLA) and non-HLA genes like killer immunoglobulin-like receptor (KIR), toll-like receptors (TLRs), cytokine/chemokines and their receptors, vitamin D receptor (VDR) and SLC11A1 etc. Highly polymorphic HLA loci may influence antigen presentation specificities by modifying peptide binding motifs. The recent meta-analysis studies revealed the association of several HLA alleles in particular class II HLA-DRB1 with TB susceptibility and valuable marker for disease development especially in Asian populations. Case-control studies have found the association of HLA-DR2 in some populations, but not in other populations, this could be due to an ethnic specific association of gene variants. Recently, GWAS conducted in case-control and family based studies in Russia, Chinese Han, Morocco, Uganda and Tanzania revealed the association of genes such as ASAP1, Alkylglycerol monooxygenase (AGMO), Forkhead BoxP1 (FOXP1), C-terminal domain phosphatase 1 (UBLCP1) and intergenic SNP rs932347C/T with TB. Whereas, SNP rs10956514A/G were not associated with TB in western Chinese Han and Tibetan population. In this review, we summarize the recent findings of genetic variants with susceptibility/resistance to TB.

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)].

Large-scale genomic analysis shows association between homoplastic genetic variation in Mycobacterium tuberculosis genes and meningeal or pulmonary tuberculosis

Background

Meningitis is the most severe manifestation of tuberculosis. It is largely unknown why some people develop pulmonary TB (PTB) and others TB meningitis (TBM); we examined if the genetic background of infecting M. tuberculosis strains may be relevant.

Methods

We whole-genome sequenced M. tuberculosis strains isolated from 322 HIV-negative tuberculosis patients from Indonesia and compared isolates from patients with TBM (n = 106) and PTB (n = 216). Using a phylogeny-adjusted genome-wide association method to count homoplasy events we examined phenotype-related changes at specific loci or genes in parallel branches of the phylogenetic tree. Enrichment scores for the TB phenotype were calculated on single nucleotide polymorphism (SNP), gene, and pathway level. Genetic associations were validated in an independent set of isolates.

Results

Strains belonged to the East-Asian lineage (36.0%), Euro-American lineage (61.5%), and Indo-Oceanic lineage (2.5%). We found no association between lineage and phenotype (Chi-square = 4.556; p = 0.207). Large genomic differences were observed between isolates; the minimum pairwise genetic distance varied from 17 to 689 SNPs. Using the phylogenetic tree, based on 28,544 common variable positions, we selected 54 TBM and 54 PTB isolates in terminal branch sets with distinct phenotypes. Genetic variation in Rv0218, and absence of Rv3343c, and nanK were significantly associated with disease phenotype in these terminal branch sets, and confirmed in the validation set of 214 unpaired isolates.

Conclusions

Using homoplasy counting we identified genetic variation in three separate genes to be associated with the TB phenotype, including one (Rv0218) which encodes a secreted protein that could play a role in host-pathogen interaction by altering pathogen recognition or acting as virulence effector.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-4498-z) contains supplementary material, which is available to authorized users.

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.

Tuberculous meningitis

Tuberculosis remains a global health problem, with an estimated 10.4 million cases and 1.8 million deaths resulting from the disease in 2015. The most lethal and disabling form of tuberculosis is tuberculous meningitis (TBM), for which more than 100,000 new cases are estimated to occur per year. In patients who are co-infected with HIV-1, TBM has a mortality approaching 50%. Study of TBM pathogenesis is hampered by a lack of experimental models that recapitulate all the features of the human disease. Diagnosis of TBM is often delayed by the insensitive and lengthy culture technique required for disease confirmation. Antibiotic regimens for TBM are based on those used to treat pulmonary tuberculosis, which probably results in suboptimal drug levels in the cerebrospinal fluid, owing to poor blood-brain barrier penetrance. The role of adjunctive anti-inflammatory, host-directed therapies - including corticosteroids, aspirin and thalidomide - has not been extensively explored. To address this deficit, two expert meetings were held in 2009 and 2015 to share findings and define research priorities. This Review summarizes historical and current research into TBM and identifies important gaps in our knowledge. We will discuss advances in the understanding of inflammation in TBM and its potential modulation; vascular and hypoxia-mediated tissue injury; the role of intensified antibiotic treatment; and the importance of rapid and accurate diagnostics and supportive care in TBM.

Persistent mycobacteria evade an antibacterial program mediated by phagolysosomal TLR7/8/MyD88 in human primary macrophages

Pathogenic mycobacteria reside in macrophages where they avoid lysosomal targeting and degradation through poorly understood mechanisms proposed to involve arrest of phagosomal maturation at an early endosomal stage. A clear understanding of how this relates to host defenses elicited from various intracellular compartments is also missing and can only be studied using techniques allowing single cell and subcellular analyses. Using confocal imaging of human primary macrophages infected with Mycobacterium avium (Mav) we show evidence that Mav phagosomes are not arrested at an early endosomal stage, but mature to a (LAMP1⁺/LAMP2⁺/CD63⁺) late endosomal/phagolysosomal stage where inflammatory signaling and Mav growth restriction is initiated through a mechanism involving Toll-like receptors (TLR) 7 and 8, the adaptor MyD88 and transcription factors NF-κB and IRF-1. Furthermore, a fraction of the mycobacteria re-establish in a less hostile compartment (LAMP1^-/LAMP2^-/CD63^-) where they not only evade destruction, but also recognition by TLRs, growth restriction and inflammatory host responses that could be detrimental for intracellular survival and establishment of chronic infections.

Mycobacterium avium is increasingly reported as a causative agent of non-tuberculous disease in immunocompromised patients and in individuals with underlying disease or using immunosuppressant drugs, with prevalence often higher than the more pathogenic M. tuberculosis in developed countries. Both M. avium and M. tuberculosis cause persistent infections by surviving inside host macrophages. Here, we identify from which compartment M. avium evoke inflammatory signaling in human primary macrophages, and the pattern-recognition receptors involved. In essence, we present three key findings: 1) M. avium phagosomes are not arrested at an early endosomal stage, but rather mature normally into phagolysosomes from where a fraction of the bacteria escape and re-establish in a new compartment. 2) In addition to avoiding degradation in phagolysosomes, by escaping M. avium also evade inflammatory signaling. 3) M. avium unable to escape is degraded in phagolysosomes and recognized by Toll-like receptors 7 and 8. Our results can contribute to new understanding of intracellular infections, and thus have vital clinical implications for development of novel anti-microbial strategies and host-targeted therapy to mycobacterial and other infectious diseases.

Human genetic factors in tuberculosis: an update

Tuberculosis (TB) is a major threat to human health, especially in many developing countries. Human genetic variability has been recognised to be of great relevance in host responses to Mycobacterium tuberculosis infection and in regulating both the establishment and the progression of the disease. An increasing number of candidate gene and genome-wide association studies (GWAS) have focused on human genetic factors contributing to susceptibility or resistance to TB. To update previous reviews on human genetic factors in TB we searched the MEDLINE database and PubMed for articles from 1 January 2014 through 31 March 2017 and reviewed the role of human genetic variability in TB. Search terms applied in various combinations were 'tuberculosis', 'human genetics', 'candidate gene studies', 'genome-wide association studies' and 'Mycobacterium tuberculosis'. Articles in English retrieved and relevant references cited in these articles were reviewed. Abstracts and reports from meetings were also included. This review provides a recent summary of associations of polymorphisms of human genes with susceptibility/resistance to TB.

New findings of Toll-like receptors involved in Mycobacterium tuberculosis infection

Tuberculosis (TB), an important issue in the present age, affects millions of people each year. The infectious agent of TB, Mycobacterium tuberculosis (Mtb), interacts with the immune system which prevents the development of this bacterium as much as possible. In fact, the receptors on the surface of immune cells identify the bacteria, one of which is Toll-like receptors (TLRs). Different TLRs including 2, 4, 9 and 8 play critical roles in tuberculosis infection. In this paper, we focused on the role of TLRs which interact with different components of Mtb and, consequently, prevent the entrance and influence of bacteria on the body.

Pattern recognition receptors and coordinated cellular pathways involved in tuberculosis immunopathogenesis: Emerging concepts and perspectives

Pattern Recognition Receptors (PRRs) play a central role in the recognition of numerous pathogens, including Mycobacterium tuberculosis, resulting in activation of innate and adaptive immune responses. Besides Toll Like Receptors, C-type Lectin Receptors and Nod Like Receptors are now being recognized for their involvement in inducing immune response against M. tuberculosis infection. Although, a functional redundancy of the PRRs has also been reported in many studies, emerging evidences support the notion that a cooperative and coordinated response generated by these receptors is critical to sustain the full immune control of M. tuberculosis infection. Many of the PRRs are now found to be involved in various cellular host defenses, such as inflammasome activation, phagosome biogenesis, endosomal trafficking, and antigen processing pathways that are all very critical for an effective immune response against M. tuberculosis. In support, polymorphism in several of these receptors has also been found associated with increased susceptibility to tuberculosis in humans. Nonetheless, increasing evidences also show that in order to enhance its intracellular survival, M. tuberculosis has also evolved multiple strategies to subvert and reprogram PPR-mediated immune responses. In light of these findings, this review analyzes the interaction of bacterial and host factors at the intersections of PRR signaling pathways that could provide integrative insights for the development of better vaccines and therapeutics for tuberculosis.

The SIGLEC14 null allele is associated with Mycobacterium tuberculosis- and BCG-induced clinical and immunologic outcomes

Humans exposed to Mycobacterium tuberculosis (Mtb) have variable susceptibility to tuberculosis (TB) and its outcomes. Siglec-5 and Siglec-14 are members of the sialic-acid binding lectin family that regulate immune responses to pathogens through inhibitory (Siglec-5) and activating (Siglec-14) domains. The SIGLEC14 coding sequence is deleted in a high proportion of individuals, placing a SIGLEC5-like gene under the expression of the SIGLEC14 promoter (the SIGLEC14 null allele) and causing expression of a Siglec-5 like protein in monocytes and macrophages. We hypothesized that the SIGLEC14 null allele was associated with Mtb replication in monocytes, T-cell responses to the BCG vaccine, and clinical susceptibility to TB. The SIGLEC14 null allele was associated with protection from TB meningitis in Vietnamese adults but not with pediatric TB in South Africa. The null allele was associated with increased IL-2 and IL-17 production following ex-vivo BCG stimulation of blood from 10 week-old South African infants vaccinated with BCG at birth. Mtb replication was increased in THP-1 cells overexpressing either Siglec-5 or Siglec-14 relative to controls. To our knowledge, this is the first study to demonstrate an association between SIGLEC expression and clinical TB, Mtb replication, or BCG-specific T-cell cytokines.

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.