TB, or not TB: that is the question -- does TLR signaling hold the answer?

Role of pattern recognition receptors in sensing Mycobacterium tuberculosis

Mycobacterium tuberculosis is one of the major invasive intracellular pathogens causing most deaths by a single infectious agent. The interaction between host immune cells and this pathogen is the focal point of the disease, Tuberculosis. Host immune cells not only mount the protective action against this pathogen but also serve as the primary niche for growth. Thus, recognition of this pathogen by host immune cells and following signaling cascades are key dictators of the disease state. Immune cells, mainly belonging to myeloid cell lineage, recognize a wide variety of Mycobacterium tuberculosis ligands ranging from carbohydrate and lipids to proteins to nucleic acids by different membrane-bound and soluble pattern recognition receptors. Simultaneous interaction between different host receptors and pathogen ligands leads to immune-inflammatory response as well as contributes to virulence. This review summarizes the contribution of pattern recognition receptors of host immune cells in recognizing Mycobacterium tuberculosis and subsequent initiation of signaling pathways to provide the molecular insight of the specific Mtb ligands interacting with specific PRR, key adaptor molecules of the downstream signaling pathways and the resultant effector functions which will aid in identifying novel drug targets, and developing novel drugs and adjuvants.

Nicotine Modulates MyD88-Dependent Signaling Pathway in Macrophages during Mycobacterial Infection

Recently, we reported that cigarette smoking, and especially nicotine, increases susceptibility to mycobacterial infection and exacerbates inflammation in patients with Crohn’s disease (CD). The macrophagic response to Mycobacterium avium subspecies paratuberculosis (MAP) in CD and Mycobacteria tuberculosis (MTB) continues to be under investigation. The role of toll-like-receptors (TLRs) and cytoplasmic adaptor protein (MyD88) in proinflammatory response during Mycobacterial infection has been suggested. However, the mechanism of how nicotine modulates macrophage response during infection in CD and exacerbates inflammatory response remain unclear. In this study, we elucidated the mechanistic role of nicotine in modulating MyD88-dependent/TLR pathway signaling in a macrophage system during mycobacterial infection. The data demonstrated that MAP infection in THP-1 derived macrophages was mediated through TLR2 and MyD88 leading to increase in IL-8 in expression and production. On the other hand, LPS-representing, Gram-negative bacteria mediated macrophage response through TLR4. Blocking TLR2 and TLR4 with antagonists voided the effect of MAP, and LPS, respectively in macrophages and reversed response with decrease in expression of iNOS, TNF-α and IL-8. Interestingly, nicotine in infected macrophages significantly (1) downregulated TLR2 and TLR4 expression, (2) activated MyD88, (3) increased M1/M2 ratio, and (4) increased expression and secretion of proinflammatory cytokines especially IL-8, as seen in CD smokers. We also discovered that blocking macrophages during MAP infection with MyD88 antagonist significantly decreased response which illustrates the key role for MyD88 during infection. Surprisingly, dual treatment of MAP-infected macrophages with MyD88 antagonist and nicotine absolutely impaired immune response and decreased MAP viability, which clearly validate the inflammatory role of nicotine in macrophages through TLR2/MyD88 pathway during infection. This is the first report to describe the mechanism by which nicotine modulates TLR2/MyDD88 and exacerbates inflammation in CD smokers associated with infection.

Severity of bovine tuberculosis is associated with innate immune-biased transcriptional signatures of whole blood in early weeks after experimental Mycobacterium bovis infection

Mycobacterium bovis, the causative agent of bovine tuberculosis, is a pathogen that impacts both animal and human health. Consequently, there is a need to improve understanding of disease dynamics, identification of infected animals, and characterization of the basis of immune protection. This study assessed the transcriptional changes occurring in cattle during the early weeks following a M. bovis infection. RNA-seq analysis of whole blood-cell transcriptomes revealed two distinct transcriptional clusters of infected cattle at both 4- and 10-weeks post-infection that correlated with disease severity. Cattle exhibiting more severe disease were transcriptionally divergent from uninfected animals. At 4-weeks post-infection, 25 genes had commonly increased expression in infected cattle compared to uninfected cattle regardless of disease severity. Ten weeks post-infection, differential gene expression was only observed when severely-affected cattle were compared to uninfected cattle. This indicates a transcriptional divergence based on clinical status following infection. In cattle with more severe disease, biological processes and cell type enrichment analyses revealed overrepresentation of innate immune-related processes and cell types in infected animals. Collectively, our findings demonstrate two distinct transcriptional profiles occur in cattle following M. bovis infection, which correlate to clinical status.

MAL adaptor (TIRAP) S180L polymorphism and severity of disease among tuberculosis patients

OBJECTIVE

Though several genetic variants have been recognized to be associated with susceptibility to Tuberculosis (TB) infection and disease, a recent observation on the association of TIRAP C975T (S180L) variants with TB disease severity in mice model prompted us to assess their relevance in humans. In addition, TIRAP variants have also been reported to be associated with varied circulating Interferon-gamma induced protein (IP-10) levels. We investigated the association of TIRAP variants with severity of TB disease and IP-10 production in humans, which may be useful in predicting poor clinical outcome.

METHODS

Culture positive symptomatic adult pulmonary TB (PTB) patients enrolled between August 2014 and October 2017 were included in this investigation. Allelic discrimination PCR and conventional IP-10 quantification methods were employed for genotyping and IP-10 measurement followed by statistical investigations to analyse patients' variables.

RESULTS

Among 211 participants, C/C allele was identified in 70% (n = 147); 26% (n = 55) and 4% (n = 9) had C/T and T/T alleles respectively. There was no significant association between TIRAP variants and smear grade, chest-X-ray score, symptom severity score and circulating IP-10 levels. However, significant association was observed between i) circulating IP-10 levels and time to Mycobacterium Growth Indicator Tube (MGIT) culture conversion (p =0.032); ii) smear grade among active TB patients and circulating IP-10 levels (p =0 .032).

CONCLUSIONS

Although mice experiments showed promising results with more severe disease in C/C and T/T individuals, we did not observe any such association in humans.

microRNAs in Mycobacterial Infection: Modulation of Host Immune Response and Apoptotic Pathways

Our current knowledge of mycobacterial infections in humans has progressively increased over the past few decades. The infection of Mycobacterium tuberculosis causes tuberculosis (TB) disease, which has reasoned for excessive morbidity and mortality worldwide, and has become a foremost issue of health problem globally. Mycobacterium leprae, another member of the family Mycobacteriaceae, is responsible for causing a chronic disease known as leprosy that mainly affects mucosa of the upper respiratory tract, skin, peripheral nerves, and eyes. Ample amount of existing data suggests that pathogenic mycobacteria have skilled in utilizing different mechanisms to escape or offset the host immune responses. They hijack the machinery of immune cells through the modulation of microRNAs (miRs), which regulate gene expression and immune responses of the host. Evidence shows that miRs have now gained considerable attention in the research, owing to their involvement in a broad range of inflammatory processes that are further implicated in the pathogenesis of several diseases. However, the knowledge of functions of miRs during mycobacterial infections remains limited. This review summarises recent findings of differential expression of miRs, which are used to good advantage by mycobacteria in offsetting host immune responses generated against them.

Identification of genes associated with susceptibility to Mycobacterium avium ssp. paratuberculosis (Map) tissue infection in Holstein cattle using gene set enrichment analysis-SNP

Multiple genome-wide association analyses have investigated susceptibility to bovine paratuberculosis, but few loci have been identified across independent cattle populations. A SNP-based gene set enrichment analysis (GSEA-SNP) allows expanded identification of genes with moderate effects on a trait through the enrichment of gene sets instead of identifying only few loci with large effects. Therefore, the objective of this study was to identify genes that were moderately associated with Mycobacterium avium ssp. paratuberculosis (Map) tissue infection using GSEA-SNP in Holstein cattle from the Pacific Northwest (PNW; n = 205) and from the PNW and Northeast (PNW+NE; n = 245) which were previously genotyped with the Illumina BovineSNP50 BeadChip. The GSEA-SNP utilized 4389 gene sets from five databases. For each annotated gene in the UMD3.1 assembly (n = 19,723), the most significant SNP within each gene and its surrounding region (10 kb up- and downstream) was selected as a proxy for that gene. Any gene set with a normalized enrichment score > 2.5 was considered enriched. Thirteen gene sets (8 PNW GSEA-SNP; 5 PNW+NE) were enriched in these analyses and all have functions that relate to nuclear factor kappa beta. Nuclear factor kappa beta is critical to gut immune responses, implicated in host immune responses to other mycobacterial diseases, and has established roles in inflammation as well as cancer. Gene sets and genes moderately associated with Map infection could be used in genomic selection to allow producers to select for less susceptible cattle, lower the prevalence of the disease, and reduce economic losses.

Impaired toll like receptor 9 response in pulmonary tuberculosis

BACKGROUND & AIM

Innate immune responses are important in susceptibility to pulmonary tuberculosis (TB). In order to test the hypothesis that Toll-like receptor (TLR) 2 function would be abnormal in patients with active pulmonary TB we compared the cytokine responses of peripheral blood mononuclear cells (PBMC) to innate immune ligands in a case-control study.

METHODS

PBMC from 19 untreated pulmonary TB patients, 17 healthy controls, and 11 treated pulmonary TB patients, were cultured for 24h with TLR 2 ligand (PAM-CSK) and other TLR ligands (muramyl dipeptide, flagellin, lipopolysaccharide (LPS), CpG oligodeoxynucleotide (CpG-ODN)). Interleukin-8 (IL-8) was estimated in the supernatant by ELISA. Messenger RNA expression for inflammatory cytokines was quantitated using real time PCR.

RESULTS

The important findings were (1) reduced PBMC secretion of IL-8 in response to all ligands in active TB; (2) normal to increased PBMC secretion of IL-8 in response to all ligands except CpG ODN (TLR 9 ligand) in TB patients who had recovered; (3) absence of difference in mRNA expression for a consortium of inflammatory pathway genes between healthy controls, active pulmonary tuberculosis and treated pulmonary tuberculosis patients.

CONCLUSION

There was a generalized post-translational suppression of the IL-8 response to innate immune ligands in active TB. There appears to be a defect of TLR 9 signaling in patients with tuberculosis, the nature of which needs to be further explored.

Lactoferrin: A Modulator for Immunity against Tuberculosis Related Granulomatous Pathology

There is great need for a therapeutic that would limit tuberculosis related pathology and thus curtail spread of disease between individuals by establishing a "firebreak" to slow transmission. A promising avenue to increase current therapeutic efficacy may be through incorporation of adjunct components that slow or stop development of aggressive destructive pulmonary pathology. Lactoferrin, an iron-binding glycoprotein found in mucosal secretions and granules of neutrophils, is just such a potential adjunct therapeutic agent. The focus of this review is to explore the utility of lactoferrin to serve as a therapeutic tool to investigate "disruption" of the mycobacterial granuloma. Proposed concepts for mechanisms underlying lactoferrin efficacy to control immunopathology are supported by data generated based on in vivo models using nonpathogenic trehalose 6,6'-dimycolate (TDM, cord factor).

Admixture mapping of tuberculosis and pigmentation-related traits in an African-European hybrid cattle population

Admixture mapping affords a powerful approach to genetic mapping of complex traits and may be particularly suited to investigation in cattle where many breeds and populations are hybrids of the two divergent ancestral genomes, derived from Bos taurus and Bos indicus. Here we design a minimal genome wide SNP panel for tracking ancestry in recent hybrids of Holstein–Friesian and local Arsi zebu in a field sample from a region of high bovine tuberculosis (BTB) endemicity in the central Ethiopian highlands. We first demonstrate the utility of this approach by mapping the red coat color phenotype, uncovering a highly significant peak over the MC1R gene and a second peak with no previously known candidate gene. Secondly, we exploit the described differential susceptibility to BTB between the ancestral strains to identify a region in which Bos taurus ancestry associates, at suggestive significance, with skin test positivity. Interestingly, this association peak contains the toll-like receptor gene cluster on chromosome 6. With this work we have shown the potential of admixture mapping in hybrid domestic animals with divergent ancestral genomes, a recurring condition in domesticated species.

Analysis of Toll-like receptors, iNOS and cytokine profiles in patients with pulmonary tuberculosis during anti-tuberculosis treatment

Toll-like receptors (TLRs) play an important role in mycobacterial infection, although little is known about the roles of these receptors, cytokines and nitric oxide during anti-tuberculosis treatment. Our objective was to evaluate the mRNA and cell surface expression of TLR2 and TLR4; inducible nitric oxide synthase (iNOS) expression; and cytokine Th1, Th2 and Th17 profiles in pulmonary tuberculosis patients at different time points of anti-tuberculosis treatment. Peripheral blood mononuclear cells (PBMCs) were obtained from PPD⁺ healthy controls and from patients receiving anti-tuberculosis treatment. Gene expression quantification was performed by qPCR, cell surface expression was assessed using flow cytometry, and cytokine quantification was conducted using the CBA technique. The treated patients presented higher gene expression and higher numbers of receptors on the cell surface of lymphocytes and monocytes than did control individuals. IL-12 and IFN-γ levels increased after the start of treatment, whereas TNF-α levels were reduced. TGF-β presented the highest levels during treatment. IL-10 and IL-17 expression and production tended to increase during treatment. iNOS gene expression was reduced throughout treatment in patients. Our results suggest that anti-tuberculosis treatment modulates the immune response, inducing an increase in the expression of TLRs and pro- and anti-inflammatory cytokines to combat bacteria and reduce the inflammatory process.

Heterozygosity at the A625C polymorphic site of the MyD88 gene is associated with Mycobacterium bovis infection in cattle

The study demonstrates that in cattle, animals heterozygous at the MyD88 A625C polymorphic marker have a 5-fold reduced risk for active pulmonary tuberculosis (odds ratio [OR] = 0.19; P = 6 × 10(-12)). The reduced risk, however, does not extend to animals with latent pulmonary tuberculosis (OR = 0.83; P = 0.40). Heterozygosity at the A625C single nucleotide polymorphism is associated with intermediate levels of tumor necrosis factor alpha, gamma interferon, and nitric oxide synthase (NOS). Accordingly, deficiency as well as overexpression of proinflammatory cytokines or NOS favor tuberculosis, while heterozygosity provides the animals with the optimal level of inflammation.

An information-gain approach to detecting three-way epistatic interactions in genetic association studies

Background

Epistasis has been historically used to describe the phenomenon that the effect of a given gene on a phenotype can be dependent on one or more other genes, and is an essential element for understanding the association between genetic and phenotypic variations. Quantifying epistasis of orders higher than two is very challenging due to both the computational complexity of enumerating all possible combinations in genome-wide data and the lack of efficient and effective methodologies.

Objectives

In this study, we propose a fast, non-parametric, and model-free measure for three-way epistasis.

Methods

Such a measure is based on information gain, and is able to separate all lower order effects from pure three-way epistasis.

Results

Our method was verified on synthetic data and applied to real data from a candidate-gene study of tuberculosis in a West African population. In the tuberculosis data, we found a statistically significant pure three-way epistatic interaction effect that was stronger than any lower-order associations.

Conclusion

Our study provides a methodological basis for detecting and characterizing high-order gene-gene interactions in genetic association studies.

Mycobacterial signaling through toll-like receptors

Studies over the past decade have helped to decipher molecular networks dependent on Toll-like receptor (TLR) signaling, in mycobacteria-infected macrophages. Stimulation of TLRs by mycobacteria and their antigenic components rapidly induces intracellular signaling cascades involved in the activation of nuclear factor-κB and mitogen-activated protein kinase pathways, which play important roles in orchestrating proinflammatory responses and innate defense through generation of a variety of antimicrobial effector molecules. Recent studies have provided evidence that mycobacterial TLR-signaling cross talks with other intracellular antimicrobial innate pathways, the autophagy process and functional vitamin D receptor (VDR) signaling. In this article we describe recent advances in the recognition, responses, and regulation of mycobacterial signaling through TLRs.

Genome-wide transcriptional profiling of peripheral blood leukocytes from cattle infected with Mycobacterium bovis reveals suppression of host immune genes

BACKGROUND

Mycobacterium bovis is the causative agent of bovine tuberculosis (BTB), a pathological infection with significant economic impact. Recent studies have highlighted the role of functional genomics to better understand the molecular mechanisms governing the host immune response to M. bovis infection. Furthermore, these studies may enable the identification of novel transcriptional markers of BTB that can augment current diagnostic tests and surveillance programmes. In the present study, we have analysed the transcriptome of peripheral blood leukocytes (PBL) from eight M. bovis-infected and eight control non-infected age-matched and sex-matched Holstein-Friesian cattle using the Affymetrix® GeneChip® Bovine Genome Array with 24,072 gene probe sets representing more than 23,000 gene transcripts.

RESULTS

Control and infected animals had similar mean white blood cell counts. However, the mean number of lymphocytes was significantly increased in the infected group relative to the control group (P = 0.001), while the mean number of monocytes was significantly decreased in the BTB group (P = 0.002). Hierarchical clustering analysis using gene expression data from all 5,388 detectable mRNA transcripts unambiguously partitioned the animals according to their disease status. In total, 2,960 gene transcripts were differentially expressed (DE) between the infected and control animal groups (adjusted P-value threshold ≤ 0.05); with the number of gene transcripts showing decreased relative expression (1,563) exceeding those displaying increased relative expression (1,397). Systems analysis using the Ingenuity® Systems Pathway Analysis (IPA) Knowledge Base revealed an over-representation of DE genes involved in the immune response functional category. More specifically, 64.5% of genes in the affects immune response subcategory displayed decreased relative expression levels in the infected animals compared to the control group.

CONCLUSIONS

This study demonstrates that genome-wide transcriptional profiling of PBL can distinguish active M. bovis-infected animals from control non-infected animals. Furthermore, the results obtained support previous investigations demonstrating that mycobacterial infection is associated with host transcriptional suppression. These data support the use of transcriptomic technologies to enable the identification of robust, reliable transcriptional markers of active M. bovis infection.

Tuberculosis immunity: opportunities from studies with cattle

Mycobacterium tuberculosis and M. bovis share >99% genetic identity and induce similar host responses and disease profiles upon infection. There is a rich history of codiscovery in the development of control measures applicable to both human and bovine tuberculosis (TB) including skin-testing procedures, M. bovis BCG vaccination, and interferon-γ release assays. The calf TB infection model offers several opportunities to further our understanding of TB immunopathogenesis. Recent observations include correlation of central memory immune responses with TB vaccine efficacy, association of SIRPα⁺ cells in ESAT-6:CFP10-elicited multinucleate giant cell formation, early γδ T cell responses to TB, antimycobacterial activity of memory CD4⁺ T cells via granulysin production, association of specific antibody with antigen burden, and suppression of innate immune gene expression in infected animals. Partnerships teaming researchers with veterinary and medical perspectives will continue to provide mutual benefit to TB research in man and animals.

Toll-like receptors in innate immunity and infectious diseases

The protective ability of host defense system is largely dependent on germ-line encoded pattern-recognition receptors (PRRs). These PRRs respond to a variety of exogenous pathogens or endogenous danger signals, by recognizing some highly conserved structures such as pathogen-associated molecular patterns (PAMPs) and danger/damage associated molecular patterns (DAMPs). The most studied PRRs are Toll-like receptors (TLRs). Activation of TLRs triggers production of inflammatory cytokines and type I interferons (IFNs) via myeloid differentiation primary response gene 88 (MyD88)-dependent or -independent signaling respectively, thereby modulating innate and adaptive immunity, as well as inflammatory responses. This review introduces the classification, structure, and specific ligands of TLRs, and focuses on their signal pathways and biological activities, as well as clinical relevance. These studies of TLRs in the innate immune system have implications for the prevention and treatment of a variety of infectious diseases, including tuberculosis (TB), microbial keratitis, and hepatitis B and C.

Influence of serum on the immune recognition of a synthetic lipopeptide mimetic of the 19-kDa lipoprotein from Mycobacterium tuberculosis

The innate immune response provides a critical first-line defense against Mycobacterium tuberculosis, an intracellular pathogen that represents a major health threat world-wide. A synthetic lipopeptide (LP) mimicking the lipid moiety of the cell-wall associated 19-kDa lipoprotein from M. tuberculosis has recently been assigned an important role in the induction of an antibacterial immune response in host macrophages. Here, we present experimental data on the biological activities and the biophysical mechanisms underlying cell activation by synthetic 19-kDa M. tuberculosis-derived lipopeptide (Mtb-LP). Investigation of the geometry of the LP (i.e. the molecular conformation and supramolecular aggregate structure) and the preference for membrane intercalation provide an explanation for the biological activities of the mycobacterial LP. Cell activation by low concentrations of Mtb-LP was enhanced by the lipopolysaccharide—binding protein and CD14. However, surprisingly, we found that activation of human macrophages to induce pro- as well as antiinflammatory mediators (tumor necrosis factor(TNF)-α, Interleukin(IL)-6, IL-8, and IL-10) in response to the Mtb-LP is strongly reduced in the presence of serum. This observation could be confirmed for the immune response of murine macrophages which showed a strongly enhanced TNF-α release in the absence of serum, suggesting that the molecular mechanisms of immune recognition of the Mtb-LP are tailored to the ambient conditions of the lung.

A role for glycogen synthase kinase-3 in antagonizing mycobacterial immune evasion by negatively regulating IL-10 induction

Mtb dysregulates monocyte/macrophage functions to produce a large amount of the immunosuppressive cytokine IL-10. An important function of IL-10 in promoting Mtb survival is the suppression of antigen presentation of monocytes/macrophages to T cells. This dampens the host immune responses and provides an opportunity for immune evasion. GSK3 has been shown to control the balance between pro- and anti-inflammatory cytokine productions. Here, we investigated whether GSK3 regulates IL-10 expression and mediates a protective role upon live mycobacterial challenge using BCG as a model. Our results showed that BCG increased Akt phosphorylation and inhibited GSK3 activity, resulting in increased IL-10 production. We confirmed further that suppression of GSK3 activities by a specific chemical inhibitor strongly enhanced BCG-induced IL-10 production. We also showed that IL-10 secreted by BCG-infected human PBMo was a major suppressor of subsequent IFN-gamma production by PBMC and HLA-DR expression on PBMo in response to BCG. Neutralization of PBMo-secreted IL-10 by anti-IL-10 antibodies restored the IFN-gamma production and HLA-DR surface expression. Taken together, GSK3 negatively regulates mycobacteria-induced IL-10 production in human PBMo. The kinase may play a role in restoring IFN-gamma secretions and subsequent antigen presentation in response to mycobacterial infection. In conclusion, our results suggest a significant role for GSK3 in guarding against mycobacterial evasion of immunity via IL-10 induction in the host.

RP105 facilitates macrophage activation by Mycobacterium tuberculosis lipoproteins

RP105, phylogenetically related to Toll-like receptor (TLR)-4, is reported to facilitate B cell activation by the TLR4-agonist lipopolysaccharide (LPS)--but to limit LPS-induced cytokine production by antigen-presenting cells. Here, we show that the role of RP105 extends beyond LPS recognition and that RP105 positively regulates macrophage responses to Mycobacterium tuberculosis (Mtb) lipoproteins. Mtb-infected RP105(-/-) mice exhibited impaired proinflammatory cytokine responses associated with enhanced bacterial burden and increased lung pathology. The Mtb 19 kDa lipoprotein induced release of tumor necrosis factor in a manner dependent on both TLR2 and RP105, and macrophage activation by Mtb lacking mature lipoproteins was not RP105 dependent. Thus, mycobacterial lipoproteins are RP105 agonists. RP105 physically interacted with TLR2, and both RP105 and TLR2 were required for optimal macrophage activation by Mtb. Our data identify RP105 as an accessory molecule for TLR2, forming part of the receptor complex for innate immune recognition of mycobacterial lipoproteins.

Antigen stimulation of peripheral blood mononuclear cells from Mycobacterium bovis infected cattle yields evidence for a novel gene expression program

Background

Bovine tuberculosis (BTB) caused by Mycobacterium bovis continues to cause substantial losses to global agriculture and has significant repercussions for human health. The advent of high throughput genomics has facilitated large scale gene expression analyses that present a novel opportunity for revealing the molecular mechanisms underlying mycobacterial infection. Using this approach, we have previously shown that innate immune genes in peripheral blood mononuclear cells (PBMC) from BTB-infected animals are repressed in vivo in the absence of exogenous antigen stimulation. In the present study, we hypothesized that the PBMC from BTB-infected cattle would display a distinct gene expression program resulting from exposure to M. bovis. A functional genomics approach was used to examine the immune response of BTB-infected (n = 6) and healthy control (n = 6) cattle to stimulation with bovine tuberculin (purified protein derivative – PPD-b) in vitro. PBMC were harvested before, and at 3 h and 12 h post in vitro stimulation with bovine tuberculin. Gene expression changes were catalogued within each group using a reference hybridization design and a targeted immunospecific cDNA microarray platform (BOTL-5) with 4,800 spot features representing 1,391 genes.

Results

250 gene spot features were significantly differentially expressed in BTB-infected animals at 3 h post-stimulation contrasting with only 88 gene spot features in the non-infected control animals (P ≤ 0.05). At 12 h post-stimulation, 56 and 80 gene spot features were differentially expressed in both groups respectively. The results provided evidence of a proinflammatory gene expression profile in PBMC from BTB-infected animals in response to antigen stimulation. Furthermore, a common panel of eighteen genes, including transcription factors were significantly expressed in opposite directions in both groups. Real-time quantitative reverse transcription PCR (qRT-PCR) demonstrated that many innate immune genes, including components of the TLR pathway and cytokines were differentially expressed in BTB-infected (n = 8) versus control animals (n = 8) after stimulation with bovine tuberculin.

Conclusion

The PBMC from BTB-infected animals exhibit different transcriptional profiles compared with PBMC from healthy control animals in response to M. bovis antigen stimulation, providing evidence of a novel gene expression program due to M. bovis exposure.

Innate gene repression associated with Mycobacterium bovis infection in cattle: toward a gene signature of disease

Background

Bovine tuberculosis is an enduring disease of cattle that has significant repercussions for human health. The advent of high-throughput functional genomics technologies has facilitated large-scale analyses of the immune response to this disease that may ultimately lead to novel diagnostics and therapeutic targets. Analysis of mRNA abundance in peripheral blood mononuclear cells (PBMC) from six Mycobacterium bovis infected cattle and six non-infected controls was performed. A targeted immunospecific bovine cDNA microarray with duplicated spot features representing 1,391 genes was used to test the hypothesis that a distinct gene expression profile may exist in M. bovis infected animals in vivo.

Results

In total, 378 gene features were differentially expressed at the P ≤ 0.05 level in bovine tuberculosis (BTB)-infected and control animals, of which 244 were expressed at lower levels (65%) in the infected group. Lower relative expression of key innate immune genes, including the Toll-like receptor 2 (TLR2) and TLR4 genes, lack of differential expression of indicator adaptive immune gene transcripts (IFNG, IL2, IL4), and lower BOLA major histocompatibility complex – class I (BOLA) and class II (BOLA-DRA) gene expression was consistent with innate immune gene repression in the BTB-infected animals. Supervised hierarchical cluster analysis and class prediction validation identified a panel of 15 genes predictive of disease status and selected gene transcripts were validated (n = 8 per group) by real time quantitative reverse transcription PCR.

Conclusion

These results suggest that large-scale expression profiling can identify gene signatures of disease in peripheral blood that can be used to classify animals on the basis of in vivo infection, in the absence of exogenous antigenic stimulation.

Disifin (sodium tosylchloramide) and Toll-like receptors (TLRs): evolving importance in health and diseases

Disifin has emerged as a unique and very effective agent used in disinfection of wounds, disinfection of surfaces, materials and water, and other substances contaminated with almost every type of pathogenic microorganism ranging from viruses, bacteria, fungi and yeast, and, very possibly, protozoan parasites, as well. The major active component of Disifin is tosylchloramide sodium (chloramine T). However, the mechanism by which Disifin suppresses the activities of pathogenic microbial agents remains enigmatic. The molecular mechanisms, and the receptors and the signal transducing pathways responsible for the biological effects of Disifin are largely unknown. Despite considerable advances, enormous investigative efforts and large resources invested in the research on infectious diseases, microbial infection still remains a public health problem in many parts of the world. The exact nature of the pathogenic agents responsible for many infectious diseases, and the nature of the receptors mediating the associated inflammatory events are incompletely understood. Recent advances in understanding the molecular basis for mammalian host immune responses to microbial invasion suggest that the first line of defense against microbes is the recognition of pathogen-associated molecular patterns (PAMPs) by a family of transmembrane pattern-recognizing and signal transducing receptor proteins called Toll-like receptors (TLRs). The TLR family plays an instructive role in innate immune responses against microbial pathogens, as well as the subsequent induction of adaptive immune responses. TLRs mediate recognition and inflammatory responses to a wide range of microbial products and are crucial for effective host defense by eradication of the invading pathogens. Now, recent updates demonstrated the ability of Disifin-derived products, Disifin-Animal and Disifin-Pressant to effectively suppress the progression and activities of Chikungunya fever and that of avian influenza A virus [A/cardialis/Germany/72, H7N1: the agent of a highly pathogenic avian influenza (HPAI)] infection, respectively. Overall, the above findings led me to suggest that Disifin and TLRs may mechanistically overlap in the processes of executing their functions against pathogenic microbial organisms. Thus, elucidating and better understanding of the molecular underpinnings responsible for the biochemical effects of Disifin-products, and the nature and mode of the interaction(s) of Disifin with TLRs in the process of exerting their biological effects may open a novel dimension in the research of infectious diseases, which may provide novel therapeutic targets for the prevention and treatment of a wide range of infectious diseases.

The pathogen recognition sensor, NOD2, is variably expressed in patients with pulmonary tuberculosis

Background

NOD2, an intracellular pathogen recognition sensor, modulates innate defences to muropeptides derived from various bacterial species, including Mycobacterium tuberculosis (MTB). Experimentally, NOD2 attenuates two key putative mycobactericidal mechanisms. TNF-α synthesis is markedly reduced in MTB-antigen stimulated-mononuclear cells expressing mutant NOD2 proteins. NOD2 agonists also induce resistance to apoptosis, and may thus facilitate the survival of MTB in infected macrophages. To further define a role for NOD2 in disease pathogenesis, we analysed NOD2 transcriptional responses in pulmonary leucocytes and mononuclear cells harvested from patients with pulmonary tuberculosis (PTB).

Methods

We analysed NOD2 mRNA expression by real-time polymerase chain-reaction in alveolar lavage cells obtained from 15 patients with pulmonary tuberculosis and their matched controls. We compared NOD2 transcriptional responses, in peripheral leucocytes, before and after anti-tuberculous treatment in 10 patients. In vitro, we measured NOD2 mRNA levels in MTB-antigen stimulated-mononuclear cells.

Results

No significant differences in NOD2 transcriptional responses were detected in patients and controls. In some patients, however, NOD2 expression was markedly increased and correlated with toll-like-receptor 2 and 4 expression. In whole blood, NOD2 mRNA levels increased significantly after completion of anti-tuberculosis treatment. NOD2 expression levels did not change significantly in mononuclear cells stimulated with mycobacterial antigens in vitro.

Conclusion

There are no characteristic NOD2 transcriptional responses in PTB. Nonetheless, the increased levels of NOD2 expression in some patients with severe tuberculosis, and the increases in expression levels within peripheral leucocytes following treatment merit further studies in selected patient and control populations.

The potential of Mycobacterium to protect against allergy and asthma

The increase in the global incidence of atopic disease and asthma during the past few decades has been ascribed to environmental factors, including the reduction in exposure to serious infections. The hypothetical framework to explain the inverse relationship between infections and atopic disease and asthma has been called the "hygiene hypothesis." Animal and experimental models have identified Mycobacteria as important potential candidates in the hygiene hypothesis by demonstrating that exposure to Mycobacteria or mycobacterial proteins led to subsequent reduction in different atopic manifestations. Although there are epidemiological studies in support, they have not always been consistent. In this review we appraise epidemiologic evidence on the inverse relationship between mycobacterial exposure and atopic disease, explore the immunological mechanisms involved and evidence that this effect may be dose-dependent, and discuss the challenges facing the use of Mycobacteria as vaccine for prevention of atopic disease.

CD45 negatively regulates tumour necrosis factor and interleukin-6 production in dendritic cells

CD45 is known to regulate signalling through many different surface receptors in diverse haemopoietic cell types. Here we report for the first time that CD45-/- bone marrow dendritic cells (BMDC) are more activated than CD45+/+ cells and that tumour necrosis factor (TNF) and interleukin-6 (IL-6) production by BMDC and splenic dendritic cells (sDC), is increased following stimulation via Toll-like receptor (TLR)3 and TLR9. Nuclear factor-kappaB activation, an important downstream consequence of TLR3 and TLR9 signalling, is also increased in CD45-/- BMDC. BMDC of CD45-/- mice also produce more TNF and IL-6 following stimulation with the cytokines TNF and interferon-alpha. These results show that TLR signalling is increased in CD45-/- dendritic cells and imply that CD45 is a negative regulator of TLR and cytokine receptor signalling in dendritic cells.

The beta-glucan receptor dectin-1 functions together with TLR2 to mediate macrophage activation by mycobacteria

Pattern recognition receptors (PRRs) play an essential role in a macrophage's response to mycobacterial infections. However, how these receptors work in concert to promote this macrophage response remains unclear. In this study, we used bone marrow-derived macrophages isolated from mannose receptor (MR), complement receptor 3 (CR3), MyD88, Toll-like receptor 4 (TLR4), and TLR2 knockout mice to examine the significance of these receptors in mediating a macrophage's response to a mycobacterial infection. We determined that mitogen-activated protein kinase (MAPK) activation and tumor necrosis factor-alpha (TNF-alpha) production in macrophage infected with Mycobacterium avium or M smegmatis is dependent on myeloid differentiation factor 88 (MyD88) and TLR2 but not TLR4, MR, or CR3. Interestingly, the TLR2-mediated production of TNF-alpha by macrophages infected with M smegmatis required the beta-glucan receptor dectin-1. A similar requirement for dectin-1 in TNF-alpha production was observed for macrophages infected with M bovis Bacillus Calmette-Guerin (BCG), M phlei, M avium 2151-rough, and M tuberculosis H37Ra. The limited production of TNF-alpha by virulent M avium 724 and M tuberculosis H37Rv was not dependent on dectin-1. Furthermore, dectin-1 facilitated interleukin-6 (IL-6), RANTES (regulated on activation, normal T expressed and secreted), and granulocyte colony-stimulating factor (G-CSF) production by mycobacteria-infected macrophages. These are the first results to establish a significant role for dectin-1, in cooperation with TLR2, to activate a macrophage's proinflammatory response to a mycobacterial infection.

Human host genetic factors in nontuberculous mycobacterial infection: lessons from single gene disorders affecting innate and adaptive immunity and lessons from molecular defects in interferon-gamma-dependent signaling

Mendelian defects in interferon-gamma (IFN-gamma) signaling most commonly lead to infection with nontuberculous mycobacteria. Mutations have been identified in the genes encoding IFN-gamma-receptor-1, IFN-gamma-receptor-2 and Stat-1. Partial and complete deficiencies in signaling are found, leading to parallel clinical, pathological, and cellular phenotypes. These rare defects have led to better molecular and mechanistic understanding of the role of IFN-gamma in the human immune system.

Distinct toll-like receptor expression in monocytes and T cells in chronic HCV infection

AIM: Hepatitis C virus often establishes chronic infections. Recent studies suggest that viral and bacterial infections are more common in HCV-infected patients compared to controls. Pathogens are recognized by Toll-like receptors (TLRs) to shape adaptive and innate immune responses.

METHODS: In this study, to assess the ability of HCV-infected host to recognize invading pathogens, we investigated Toll-like receptor expression in innate (monocytes) and adaptive (T cells) immune cells by real-time PCR.

RESULTS: We determined that RNA levels for TLRs 2, 6. 7, 8, 9 and 10 mRNA levels were upregulated in both monocytes and T cells in HCV-infected patients compared to controls. TLR4 was only upregulated in T lymphocytes, while TLR5 was selectively increased in monocytes of HCV-infected patients. MD-2, a TLR4 co-receptor, was increased in patients’ monocytes and T cells while CD14 and MyD88 were increased only in monocytes.

CONCLUSION: Our data reveal novel details on TLR expression that likely relates to innate recognition of pathogens and immune defense in HCV-infected individuals.

Toll-like receptors and chronic lung disease

TLRs (Toll-like receptors) comprise a family of proteins whose function is principally to facilitate the detection of, and response to, pathogens. Protozoa, helminths, viruses, bacteria and fungi can all activate TLR signalling, and these signals have important roles in the activation of host defence. TLRs may also respond to products of tissue damage, providing them with roles in infective and sterile inflammation. Their role as detectors of pathogens and pathogen-associated molecules provides molecular mechanisms to underpin the observations leading to the hygiene hypothesis. Targeting of TLR signalling has implications in the control of infection, vaccine design, desensitization to allergens and down-regulation of inflammation. This review will explore TLR history, molecular signalling and the potential roles of TLRs in chronic lung disease.

MyD88 is pivotal for the early inflammatory response and subsequent bacterial clearance and survival in a mouse model of Chlamydia pneumoniae pneumonia

Chlamydia pneumoniae is the causative agent of respiratory tract infections and a number of chronic diseases. Here we investigated the involvement of the common TLR adaptor molecule MyD88 in host responses to C. pneumoniae-induced pneumonia in mice. MyD88-deficient mice were severely impaired in their ability to mount an acute early inflammatory response toward C. pneumoniae. Although the bacterial burden in the lungs was comparable 5 days after infection, MyD88-deficient mice exhibited only minor signs of pneumonia and reduced expression of inflammatory mediators. MyD88-deficient mice were unable to up-regulate proinflammatory cytokines and chemokines, demonstrated delayed recruitment of CD8+ and CD4+ T cells to the lungs, and were unable to clear the pathogen from their lungs at day 14. At day 14 the MyD88-deficent mice developed a severe, chronic lung inflammation with elevated IL-1beta and IFN-gamma leading to increased mortality, whereas wild-type mice as well as TLR2- or TLR4-deficient mice recovered from acute pneumonia and did not show delayed bacterial clearance. Thus, MyD88 is essential to recognize C. pneumoniae infection and initiate a prompt and effective immune host response against this organism leading to clearance of bacteria from infected lungs.

Transforming Growth Factor-β Differentially Inhibits MyD88-dependent, but Not TRAM- and TRIF-dependent, Lipopolysaccharide-induced TLR4 Signaling

Transforming growth factor-beta1 (TGF-beta1) is a multifunctional, potent anti-inflammatory cytokine produced by many cell types that regulates cell proliferation, apoptosis, and immune responses. Toll-like receptors (TLRs) recognize various pathogen-associated molecular patterns and are therefore a pivotal component of the innate immune system. In this study we show that TGF-beta1 blocks the NF-kappaB activation and cytokine release that is stimulated by ligands for TLRs 2, 4, and 5. We further show that TGF-beta1 can specifically interfere with TLR2, -4, or -5 ligand-induced responses involving the adaptor molecule MyD88 (myeloid differentiation factor 88) but not the TRAM/TRIF signaling pathway by decreasing MyD88 protein levels in a dose- and time-dependent manner without altering its mRNA expression. The proteasome inhibitor epoxomicin abolished the MyD88 degradation induced by TGF-beta1. Furthermore, TGF-beta1 resulted in ubiquitination of MyD88 protein, suggesting that TGF-beta1 facilitates ubiquitination and proteasomal degradation of MyD88 and thereby attenuates MyD88-dependent signaling by decreasing cellular levels of MyD88 protein. These findings importantly contribute to our understanding of molecular mechanisms mediating anti-inflammatory modulation of immune responses by TGF-beta1.