Molecular mechanisms regulating persistent Mycobacterium tuberculosis infection

Expression and Clinical Significance of lncRNA NEAT1 in Patients with Spinal Tuberculosis

Background

Spinal tuberculosis (STB) often leads to irreversible neurological injury, resulting in serious social and economic problems. With the emergence of drug resistance, the management becomes even more challenging, given the treatment courses are generally longer for skeletal than pulmonary tuberculosis (PTB). The development and validation of nonsputum biomarkers for diagnosis and tailoring of treatment duration to enable personalized and evidence-based management of such diseases to improve treatment outcomes is being called for globally. Studies have demonstrated that lncRNA NEAT1 was highly expressed in pulmonary tuberculosis (TB) and was related to its progression and recovery. However, the expression and clinical significance of lncRNA NEAT1 in STB remains unclear.

Methods

The relative expression of lncRNA NEAT1 was quantified by relative real-time reverse transcription PCR (RT-PCR). The prognostic value was assessed by receiver-operating characteristic (ROC) curve analysis. Pearson and Spearman correlation coefficient and chi-square test were used to analyze the correlation between the lncRNA NEAT1 expression and the clinical characteristics. Univariate and multivariate logistic regression analyses were used to analyze independent predictors of STB recurrence.

Results

Compared with normal healthy individuals, the expression level of lncRNA NEAT1 in peripheral blood and granulomatous tissues of STB patients was significantly increased. The results of the in vitro Mycobacterium tuberculosis- (Mtb-) infected cell model showed that the expression level of lncRNA NEAT1 was significantly upregulated in macrophages infected with Mtb, and the difference was statistically significant compared with Mtb-uninfected group. The expression level of lncRNA NEAT1 in granulomatous tissue of STB was significantly higher than that in peripheral blood. The expression of lncRNA NEAT1 was related to segments of the lesions, paraspinal abscesses, anti-TB treatment, drug resistance, interleukin-6 (IL-6), C-reactive protein (CRP), and erythrocyte sedimentation rate (ESR). Multivariate analysis results showed that relatively high expression of lncRNA NEAT1_1, the shorter transcript of the NEAT1 gene, was an independent prognostic factor of STB outcome.

Conclusion

LncRNA NEAT1 was highly expressed in peripheral blood mononuclear cells (PBMCs) and granulomatous tissue from patients with STB, as well as in Mtb-infected THP-1 cell lines. LncRNA NEAT1 expression was significantly associated with clinical characteristics (paraspinal abscesses, segments of the lesions and anti-TB treatment, IL-6, CRP, and ESR) of patients in STB. Increased expression of lncRNA NEAT1_1 predicted good prognosis of STB and might become a prognostic biomarker for STB.

Regionally Distinct Immune and Metabolic Transcriptional Responses in the Bovine Small Intestine and Draining Lymph Nodes During a Subclinical Mycobacterium avium subsp. paratuberculosis Infection

Mycobacterium avium subsp. paratuberculosis (MAP) is the causative infectious agent of Johne’s disease (JD), an incurable granulomatous enteritis affecting domestic livestock and other ruminants around the world. Chronic MAP infections usually begin in calves with MAP uptake by Peyer’s patches (PP) located in the jejunum (JE) and ileum (IL). Determining host responses at these intestinal sites can provide a more complete understanding of how MAP manipulates the local microenvironment to support its long-term survival. We selected naturally infected (MAPinf, n=4) and naive (MAPneg, n=3) cows and transcriptionally profiled the JE and IL regions of the small intestine and draining mesenteric lymph nodes (LN). Differentially expressed (DE) genes associated with MAP infection were identified in the IL (585), JE (218), jejunum lymph node (JELN) (205), and ileum lymph node (ILLN) (117). Three DE genes (CD14, LOC616364 and ENSBTAG00000027033) were common to all MAPinf versus MAPneg tissues. Functional enrichment analysis revealed immune/disease related biological processes gene ontology (GO) terms and pathways predominated in IL tissue, indicative of an activated immune response state. Enriched GO terms and pathways in JE revealed a distinct set of host responses from those detected in IL. Regional differences were also identified between the mesenteric LNs draining each intestinal site. More down-regulated genes (52%) and fewer immune/disease pathways (n=5) were found in the ILLN compared to a higher number of up-regulated DE genes (56%) and enriched immune/disease pathways (n=13) in the JELN. Immunohistochemical staining validated myeloid cell transcriptional changes with increased CD172-positive myeloid cells in IL and JE tissues and draining LNs of MAPinf versus MAPneg cows. Several genes, GO terms, and pathways related to metabolism were significantly DE in IL and JE, but to a lesser extent (comparatively fewer enriched metabolic GO terms and pathways) in JELN suggesting distinct regional metabolic changes in IL compared to JE and JELN in response to MAP infection. These unique tissue- and regional-specific differences provides novel insight into the dichotomy in host responses to MAP infection that occur throughout the small intestine and mesenteric LN of chronically MAP infected cows.

Inhalable nanoparticles delivery targeting alveolar macrophages for the treatment of pulmonary tuberculosis

Pulmonary tuberculosis is a highly prevalent respiratory disease that affects approximately a quarter of the world's population. The drug treatment protocol for tuberculosis is complex because the Mycobacterium tuberculosis (M. tuberculosis) invades macrophages and begins to infect. Thus treatment usually includes combination therapy with several drugs such as rifampicin, pyrazinamide, isoniazid, and ethambutol over a long dosing period. Therefore, drug-delivery technologies have been developed to improve patient compliance with medication, reduce adverse effects, and increase effectiveness of the treatment. In the present review, we have discussed recent inhalable nanopharmaceutical systems for the treatment of pulmonary tuberculosis and investigated their design and effectiveness. We examined the underlying processes and characteristics of spray-drying technology and studied the formulation of a dry carrier using spray-drying method. Moreover, we reviewed various research articles on pulmonary delivery of nanoparticles using these carriers, and studied their alveolar macrophage targeting ability and therapeutic effects. Further, we appraised the effectiveness of nanoparticle inhalation therapy for the treatment of pulmonary tuberculosis and its potential as a treatment strategy for lung diseases.

Role of resuscitation promoting factors in reactivation of latent tuberculosis during high glucose conditions employing human granuloma in vitro model

BACKGROUND

Diabetes aggravates the risk of tuberculosis (TB) through impairment of immunity which may lead to the activation of latent tuberculosis (LTBI). LTBI serves as a homeostatic state where host does not develop any symptoms of the disease as host immune system assist in the containment of infection leading to granuloma formation. However, the compromised immunity imbalances this equilibrium which further leads to reactivation of LTBI. The aim of this study was to assess if hyperglycemia like conditions contribute towards activation of latent tuberculosis.

MATERIAL/METHODS

In vitro granuloma model was developed using peripheral blood monocytic cells (PBMCs) under normal and high glucose conditions and the characteristics of dormancy i.e. tolerance towards rifampicin, loss of acid fastness were monitored. Further, activation was assessed by expression analysis of various resuscitation promoting factors rpfA-E.

RESULTS

Granuloma formation was not observed in the presence of high glucose. The gene expression of hspX was downregulated whereas the expression of rpfA-E genes was upregulated under high glucose conditions after 48 h of glucose treatment. The expression of rpfD gene remained upregulated till 72 h of glucose treatment.

CONCLUSION

High glucose concentrations impede the granuloma formation and may lead to activation of latent tubercle bacilli through resuscitation promoting factors. Thus, rpfs represent an important targets for new interventions that can abate the burden from co-pathogenesis of tuberculosis and diabetes.

A TLR2-Activating Fraction From Mycobacterium abscessus Rough Variant Demonstrates Vaccine and Diagnostic Potential

Mycobacterium abscessus is a prevalent pathogenic mycobacterium in cystic fibrosis (CF) patients and one of the most highly drug resistant mycobacterial species to antimicrobial agents. It possesses the property to transition from a smooth (S) to a rough (R) morphotype, thereby influencing the host innate immune response. This transition from the S to the R morphotype takes place in patients with an exacerbation of the disease and a persistence of M. abscessus. We have previously shown that the exacerbation of the Toll-like receptor 2 (TLR2)-mediated inflammatory response, following this S to R transition, is essentially due to overproduction of bacilli cell envelope surface compounds, which we were able to extract by mechanical treatment and isolation by solvent partition in a fraction called interphase. Here, we set up a purification procedure guided by bioactivity to isolate a fraction from the R variant of M. abscessus cells which exhibits a high TLR2 stimulating activity, referred to as TLR2-enriched fraction (TLR2eF). As expected, TLR2eF was found to contain several lipoproteins and proteins known to be stimuli for TLR2. Vaccination with TLR2eF showed no protection toward an M. abscessus aerosol challenge, but provided mild protection in ΔF508 mice and their FVB littermates when intravenously challenged by M. abscessus. Interestingly however, antibodies against TLR2eF compounds were detected during disease in CF patients. In conclusion, we show the potential for compounds in TLR2eF as vaccine and diagnostic candidates, in order to enhance diagnosis, prevent and/or treat M. abscessus-related infections.

Multiple differences in pathogen-host cell interactions following a bacterial host shift

Novel disease emergence is often associated with changes in pathogen traits that enable pathogen colonisation, persistence and transmission in the novel host environment. While understanding the mechanisms underlying disease emergence is likely to have critical implications for preventing infectious outbreaks, such knowledge is often based on studies of viral pathogens, despite the fact that bacterial pathogens may exhibit very different life histories. Here, we investigate the ability of epizootic outbreak strains of the bacterial pathogen, Mycoplasma gallisepticum, which jumped from poultry into North American house finches (Haemorhous mexicanus), to interact with model avian cells. We found that house finch epizootic outbreak strains of M. gallisepticum displayed a greater ability to adhere to, invade, persist within and exit from cultured chicken embryonic fibroblasts, than the reference virulent (R_low) and attenuated (R_high) poultry strains. Furthermore, unlike the poultry strains, the house finch epizootic outbreak strain HF_1994 displayed a striking lack of cytotoxicity, even exerting a cytoprotective effect on avian cells. Our results suggest that, at epizootic outbreak in house finches, M. gallisepticum was particularly adept at using the intra-cellular environment, which may have facilitated colonisation, dissemination and immune evasion within the novel finch host. Whether this high-invasion phenotype is similarly displayed in interactions with house finch cells, and whether it contributed to the success of the host shift, remains to be determined.

Inhalable nanotherapeutics to improve treatment efficacy for common lung diseases

Respiratory illnesses are prevalent around the world, and inhalation-based therapies provide an attractive, noninvasive means of directly delivering therapeutic agents to their site of action to improve treatment efficacy and limit adverse systemic side effects. Recent trends in medicine and nanoscience have prompted the development of inhalable nanomedicines to further enhance effectiveness, patient compliance, and quality of life for people suffering from lung cancer, chronic pulmonary diseases, and tuberculosis. Herein, we discuss recent advancements in the development of inhalable nanomaterial-based drug delivery systems and analyze several representative systems to illustrate their key design principles that can translate to improved therapeutic efficacy for prevalent respiratory diseases. This article is categorized under: Therapeutic Approaches and Drug Discovery > Nanomedicine for Respiratory Disease.

Mycobacterium tuberculosis thymidylate kinase antigen assays for designating incipient, high-risk latent M.tb infection

BACKGROUND

Precise designation of high risk forms of latent Mycobacterium tuberculosis-M.tb infections (LTBI) is impossible. Delineation of high-risk LTBI can, however, allow for chemoprophylaxis and curtail majority cases of active tuberculosis (ATB). There is epidemiological evidence to support the view that LTBI in context of HIV-1 co-infection is high-risk for progression to ATB relative to LTBI among HIV-ve persons. We recently showed that assays of M.tb thymidylate kinase (TMKmt) antigen and host specific IgG can differentiate ATB from LTBI and or no TB (NTB, or healthy controls). In this study, we aimed to expose the differential levels of TMKmt Ag among HIV+ve co-infected LTBI relative to HIV-ve LTBI as a strategy to advance these assays for designating incipient LTBI.

METHODS

TMKmt host specific IgM and IgG detection Enzyme Immuno-Assays (EIA) were conducted on 40 TB exposed house-hold contacts (22 LTBI vs. 18 no TB (NTB) by QunatiFERON-TB GOLD®); and TMKmt Ag detection EIA done on 82 LTBI (46 HIV+ve vs 36 HIV-ve) and 9 NTB (American donors). Purified recombinant TMKmt protein was used as positive control for the Ag assays.

RESULTS

IgM levels were found to be equally low across QuantiFERON-TB GOLD® prequalified NTB and TB exposed house-hold contacts. Higher TMKmt host specific IgG trends were found among TB house-hold contacts relative to NTB controls. TMKmt Ag levels among HIV+ve LTBI were 0.2676 ± 0.0197 (95% CI: 0.2279 to 0.3073) relative to 0.1069 ± 0.01628 (95% CI: 0.07385 to 0.14) for HIV-ve LTBI (supporting incipient nature of LTBI in context of HIV-1 co-infection). NTB had TMKmt Ag levels of 0.1013 ± 0.02505 (5% CI: 0.0421 to 0.1606) (intimating that some were indeed LTBI).

CONCLUSIONS

TMKmt Ag levels represent a novel surrogate biomarker for high-risk LTBI, while host-specific IgG can be used to designate NTB from LTBI.

Anaerobic Mycobacterium tuberculosis Cell Death Stems from Intracellular Acidification Mitigated by the DosR Regulon

Mycobacterium tuberculosis is a strict aerobe capable of prolonged survival in the absence of oxygen. We investigated the ability of anaerobic M. tuberculosis to counter challenges to internal pH homeostasis in the absence of aerobic respiration, the primary mechanism of proton efflux for aerobic bacilli. Anaerobic M. tuberculosis populations were markedly impaired for survival under a mildly acidic pH relative to standard culture conditions. An acidic environmental pH greatly increased the susceptibilities of anaerobic bacilli to the collapse of the proton motive force by protonophores, to antimicrobial compounds that target entry into the electron transport system, and to small organic acids with uncoupling activity. However, anaerobic bacilli exhibited high tolerance against these challenges at a near-neutral pH. At a slightly alkaline pH, which was near the optimum intracellular pH, the addition of protonophores even improved the long-term survival of bacilli. Although anaerobic M. tuberculosis bacilli under acidic conditions maintained 40% lower ATP levels than those of bacilli under standard culture conditions, ATP loss alone could not explain the drop in viability. Protonophores decreased ATP levels by more than 90% regardless of the extracellular pH but were bactericidal only under acidic conditions, indicating that anaerobic bacilli could survive an extreme ATP loss provided that the external pH was within viable intracellular parameters. Acidic conditions drastically decreased the anaerobic survival of a DosR mutant, while an alkaline environment improved the survival of the DosR mutant. Together, these findings indicate that intracellular acidification is a primary challenge for the survival of anaerobic M. tuberculosis and that the DosR regulon plays a critical role in sustaining internal pH homeostasis.IMPORTANCE During infection, M. tuberculosis bacilli are prevalent in environments largely devoid of oxygen, yet the factors that influence the survival of these severely growth-limited and metabolically limited bacilli remain poorly understood. We determined how anaerobic bacilli respond to fluctuations in environmental pH and observed that these bacilli were highly susceptible to stresses that promoted internal acidic stress, whereas conditions that promoted an alkaline internal pH promoted long-term survival even during severe ATP depletion. The DosR regulon, a major regulator of general hypoxic stress, played an important role in maintaining internal pH homeostasis under anaerobic conditions. Together, these findings indicate that in the absence of aerobic respiration, protection from internal acidification is crucial for long-term M. tuberculosis survival.

Characterization of a secretory hydrolase from Mycobacterium tuberculosis sheds critical insight into host lipid utilization by M. tuberculosis

Mycobacterium tuberculosis causes tuberculosis in humans and predominantly infects alveolar macrophages. To survive inside host lesions and to evade immune surveillance, this pathogen has developed many strategies. For example, M. tuberculosis uses host-derived lipids/fatty acids as nutrients for prolonged persistence within hypoxic host microenvironments. M. tuberculosis imports these metabolites through its respective transporters, and in the case of host fatty acids, a pertinent question arises: does M. tuberculosis have the enzyme(s) for cleavage of fatty acids from host lipids? We show herein that a previously uncharacterized membrane-associated M. tuberculosis protein encoded by Rv2672 is conserved exclusively in actinomycetes, exhibits both lipase and protease activities, is secreted into macrophages, and catalyzes host lipid hydrolysis. In light of these functions, we annotated Rv2672 as mycobacterial secreted hydrolase 1 (Msh1). Furthermore, we found that this enzyme is up-regulated both in an in vitro model of hypoxic stress and in a mouse model of M. tuberculosis infection, suggesting that the pathogen requires Msh1 under hypoxic conditions. Silencing Msh1 expression compromised the ability of M. tuberculosis to proliferate inside lipid-rich foamy macrophages but not under regular culture conditions in vitro, underscoring Msh1's importance for M. tuberculosis persistence in lipid-rich microenvironments. Of note, this is the first report providing insight into the mechanism of host lipid catabolism by an M. tuberculosis enzyme, augmenting our current understanding of how M. tuberculosis meets its nutrient requirements under hypoxic conditions.

Thioridazine Alters the Cell-Envelope Permeability of Mycobacterium tuberculosis

The increasing occurrence of multidrug resistant tuberculosis exerts a major burden on treatment of this infectious disease. Thioridazine, previously used as a neuroleptic, is active against extensively drug resistant tuberculosis when added to other second- and third-line antibiotics. By quantitatively studying the proteome of thioridazine-treated Mycobacterium tuberculosis, we discovered the differential abundance of several proteins that are involved in the maintenance of the cell-envelope permeability barrier. By assessing the accumulation of fluorescent dyes in mycobacterial cells over time, we demonstrate that long-term drug exposure of M. tuberculosis indeed increased the cell-envelope permeability. The results of the current study demonstrate that thioridazine induced an increase in cell-envelope permeability and thereby the enhanced uptake of compounds. These results serve as a novel explanation to the previously reported synergistic effects between thioridazine and other antituberculosis drugs. This new insight in the working mechanism of this antituberculosis compound could open novel perspectives of future drug-administration regimens in combinational therapy.

PE_PGRS30 of Mycobacterium tuberculosis mediates suppression of proinflammatory immune response in macrophages through its PGRS and PE domains

The success of Mycobacterium tuberculosis as a pathogen relies on its ability to survive inside macrophages and evade host immune mechanisms. M. tuberculosis employs multiple strategies to confer resistance against immune system including inhibition of phago-lysosomal fusion, modulation of cytokine responses and granuloma formation. PE_PGRS proteins, uniquely present in pathogenic mycobacteria, are cell surface molecules that are suggested to interact with host cells. PE_PGRS proteins have also been implicated in its pathogenesis. In the present study, immuno-regulatory property of Rv1651c-encoded PE_PGRS30 protein was explored. Infection of PMA-differentiated human THP-1 macrophages with Mycobacterium smegmatis harbouring pVV(1651c) resulted in reduced production of IL-12, TNF-α and IL-6, as compared to infection with M. smegmatis harbouring the control plasmid pVV16. No differential effect was observed on bacterial persistence inside macrophages or on macrophage mortality upon infection with the two recombinant strains. Infection of THP-1 macrophages with recombinant M. smegmatis expressing deletion variants of PE_PGRS30 indicated that anti-inflammatory function of the protein is possessed by its PGRS and PE domains while the C-terminal domain, when expressed alone, displayed antagonistic effect in terms of TNF-α secretion. These results suggest that PE_PGRS30 interferes with macrophage immune functions important for activation of adaptive T-cell responses.

Mechanisms of Phenotypic Rifampicin Tolerance in Mycobacterium tuberculosis Beijing Genotype Strain B0/W148 Revealed by Proteomics

The "successful" Russian clone B0/W148 of Mycobacterium tuberculosis Beijing is well-known for its capacity to develop antibiotic resistance. During treatment, resistant mutants can occur that have inheritable resistance to specific antibiotics. Next to mutations, M. tuberculosis has several mechanisms that increase their tolerance to a variety of antibiotics. Insights in the phenotypic mechanisms that contribute to drug tolerance will increase our understanding of how antibiotic resistance develops in M. tuberculosis. In this study, we examined the (phospho)proteome dynamics in M. tuberculosis Beijing strain B0/W148 when exposed to a high dose of rifampicin; one of the most potent first-line antibiotics. A total of 2,534 proteins and 191 phosphorylation sites were identified, and revealed the differential regulation of DosR regulon proteins, which are necessary for the development of a dormant phenotype that is less susceptible to antibiotics. By examining independent phenotypic markers of dormancy, we show that persisters of in vitro rifampicin exposure entered a metabolically hypoactive state, which yields rifampicin and other antibiotics largely ineffective. These new insights in the role of protein regulation and post-translational modifications during the initial phase of rifampicin treatment reveal a shortcoming in the antituberculosis regimen that is administered to 8-9 million individuals annually.

Mycobacterium aurum is Unable to Survive Mycobacterium tuberculosis Latency Associated Stress Conditions: Implications as Non-suitable Model Organism

Mycobacterium tuberculosis manages to remain latent in the human body regardless of extensive chemotherapy. Complete eradication of tuberculosis (TB) requires treatment strategies targeted against latent form of infection, in addition to the current regimen of antimycobacterials. Many in vitro and in vivo models have been proposed to imitate latent TB infection, yet none of them is able to completely mimic latent infection state of M. tuberculosis. Highly infectious nature of the pathogen requiring BSL3 facilities and its long generation time further add to complications. M. aurum has been proposed as an important model organism for high throughput screening of drugs and exhibits high genomic similarity with that of M. tuberculosis. Thus, the present study was undertaken to explore if M. aurum could be used as a surrogate organism for studies related to M. tuberculosis latent infection. M. aurum was subjected to in vitro conditions of oxygen depletion, lack of nutrients and acidic stress encountered by latent M. tuberculosis bacteria. CFU count of M. aurum cells along with any change in cell shape and size was recorded at regular intervals during the stress conditions. M. aurum cells were unable to survive for extended periods under all three conditions used in the study. Thus, our studies suggest that M. aurum is not a suitable organism to mimic M. tuberculosis persistent infection under in vitro conditions, and further studies are required on different species for the establishment of a fast growing species as a suitable model for M. tuberculosis persistent infection.

A lacZ Reporter-Based Strategy for Rapid Expression Analysis and Target Validation of Mycobacterium tuberculosis Latent Infection Genes

We report a novel lacZ fusion vector and demonstrate its utility for expression analysis of genes associated with Mycobacterium tuberculosis latent infection. The vector contains E. coli (oriE) and mycobacterial (oriM) origins of replication, a kanamycin resistance gene (Km(r)) as selection marker, and a lacZ reporter gene in fusion with MCS for cloning of upstream regulatory sequence of the desired genes. β-galactosidase activity of the vector was standardized for expression analysis under latent mycobacterial conditions using Phsp60, a constitutive mycobacterial promoter, utilizing Mycobacterium smegmatis as model organism. Validation of the vector was done by cloning and expression analysis of PhspX (alpha crystalline) and Picl (isocitrate lyase), promoters from two of the genes shown to be involved in M. tuberculosis persistence. Both genes showed appreciable levels of β-galactosidase expression under hypoxia-induced persistent conditions in comparison to their actively replicating state. Expression analysis of a set of hypothetical genes was also done, of which Rv0628c showed increased expression under persistent conditions. The reported fusion vector and the strategy can be effectively used for short listing and validation of drug targets deduced from various non-conclusive approaches such as bioinformatics and microarray analysis against latent/persistent form of mycobacterial infection.

Calmodulin-like protein from M. tuberculosis H37Rv is required during infection

M. tuberculosis constitutes very sophisticated signaling systems that convert the environment signals into appropriate cellular response and helps the bacilli to overcome the onslaught of host defence mechanisms. Although mycobacterial two-component systems and STPKs have gained lot of attention as virulence factors, mycobacterial calcium signaling has not been very well studied. Calcium signaling has been the primary mechanism in eukaryotes for regulation of kinases, however in prokaryotes auto-phosphorylation of number of kinases has been reported. We have previously reported a small calmodulin-like-protein (CAMLP) from M. tuberculosis regulating enzymes of heterogeneous origin. To understand its role in both viability and virulence, we have assessed the effect of reduced expression of CAMLP coding gene Rv1211 on M. tb growth in vitro and ex vivo. Further, we have also studied the expression profile of Rv1211 in various conditions simulating host microenvironments. Our results highlight the possible role of CAMLP in growth and survival of M. tb during infection.

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.

Diversity of disease in childhood pulmonary tuberculosis

Many factors can influence the dynamic balance that exists between the host and the pathogen (M. tuberculosis), but the host immune response seems to be the most important. This is illustrated by the vulnerability of immune-compromised individuals to develop tuberculosis and by the age-related spectrum of disease witnessed in immune-competent children. This age-related spectrum of disease reflects the ontogeny of the host immune response towards M. tuberculosis. Renewing our focus on the ontogeny of the immune response in children might provide valuable insights to direct future research regarding tuberculosis prevention, vaccine development and treatment.

Discovery and evaluation of novel inhibitors of mycobacterium protein tyrosine phosphatase B from the 6-Hydroxy-benzofuran-5-carboxylic acid scaffold

Mycobacterium tuberculosis (Mtb) protein tyrosine phosphatase B (mPTPB) is a virulence factor secreted by the pathogen and mediates mycobacterial survival in macrophages by targeting host cell immune responses. Consequently, mPTPB represents an exciting new target to combat tuberculosis (TB) infection. We describe a medicinal chemistry oriented approach that transforms a benzofuran salicylic acid scaffold into a highly potent (IC(50) = 38 nM) and selective mPTPB inhibitor (>50 fold against a large panel of PTPs). Importantly, the inhibitor is capable of reversing the altered host immune responses induced by the bacterial phosphatase and restoring the macrophage's full capacity to secrete IL-6 and undergo apoptosis in response to interferon-γ stimulation, validating the concept that chemical inhibition of mPTPB may be therapeutically useful for novel TB treatment. The study further demonstrates that bicyclic salicylic acid pharmacophores can be used to deliver PTP inhibitors with high potency, selectivity, and cellular efficacy.

Human granuloma in vitro model, for TB dormancy and resuscitation

Tuberculosis (TB) is responsible for death of nearly two million people in the world annually. Upon infection, Mycobacterium tuberculosis (Mtb) causes formation of granuloma where the pathogen goes into dormant state and can live for decades before resuscitation to develop active disease when the immune system of the host is weakened and/or suppressed. In an attempt to better understand host-pathogen interactions, several groups have been developing in vitro models of human tuberculosis granuloma. However, to date, an in vitro granuloma model in which Mtb goes into dormancy and can subsequently resuscitate under conditions that mimic weakening of the immune system has not been reported. We describe the development of a biomimetic in vitro model of human tuberculosis granuloma using human primary leukocytes, in which the Mtb exhibited characteristics of dormant mycobacteria as demonstrated by (1) loss of acid-fastness, (2) accumulation of lipid bodies (3) development of rifampicin-tolerance and (4) gene expression changes. Further, when these micro granulomas were treated with immunosuppressant anti-tumor necrosis factor-alpha monoclonal antibodies (anti-TNFα mAbs), resuscitation of Mtb was observed as has been found in humans. In this human in vitro granuloma model triacylglycerol synthase 1deletion mutant (Δtgs1) with impaired ability to accumulate triacylglycerides (TG), but not the complemented mutant, could not go into dormancy. Deletion mutant of lipY, with compromised ability to mobilize the stored TG, but not the complemented mutant, was unable to come out of dormancy upon treatment with anti-TNFα mAbs. In conclusion, we have developed an in vitro human tuberculosis granuloma model that largely exhibits functional features of dormancy and resuscitation observed in human tuberculosis.

Emerging role of lipid droplets in host/pathogen interactions

Lipid droplets (LDs) are highly dynamic cell organelles involved in energy homeostasis and membrane trafficking. Here, we review how select pathogens interact with LDs. Several RNA viruses use host LDs at different steps of their life cycle. Some intracellular bacteria and parasites usurp host LDs or encode their own lipid biosynthesis machinery, thus allowing production of LDs independently of their host. Although many mechanistic details of host/pathogen LD interactions are unknown, a picture emerges in which the unique cellular architecture and energy stored in LDs are important in the replication of diverse pathogens.

The role of ABC efflux pump, Rv1456c-Rv1457c-Rv1458c, from Mycobacterium tuberculosis clinical isolates in China

Recently the ATP-binding cassette (ABC) efflux pumps have been proved to be a major component of drug resistance in Mycobacterium tuberculosis. The objective of this study was to investigate the expression profiles of Rv1456c-Rv1457c-Rv1458c efflux system in clinical isolates of M. tuberculosis and its involvement in drug-resistance mechanisms. Significantly increased mRNA expression of Rv1456c, Rv1457c, and Rv1458c appeared among the clinical isolates (P < 0.05), which are resistant to at least one of the four first-line drugs including rifampin, isoniazid, streptomycin, and ethambutol. In addition, overexpression of this efflux system was more frequently found in multidrug-resistant and extensively drug-resistant M. tuberculosis strains. Therefore, Rv1456c-Rv1457c-Rv1458c efflux pumps may play an important role in drug resistance of treatment of M. tuberculosis. Further investigation of this gene may lead to the development of countermeasures against M. tuberculosis drug resistance.

Diagnostic luciferase reporter phage assay for active and non-replicating persistors to detect tubercle bacilli from sputum samples

Diagnosis of latent tuberculosis infection is a myth for want of a simple, direct tool. Simulation of hypoxic environment was done to create a novel hypothetical model for persistence using processed sputum samples. The adaptation of tubercle bacilli to hypoxic environment seems to be influenced by pre-existing clinical status of the patients at the time of sputum collection, resulting in varied growth pattern. Bacilli from 36 samples did not get adapted to latency of which 15 samples were from patients in whom the disease was well established and the tubercle bacilli in them probably did not experience any stress whatsoever. Similarly, 10 of the 37 samples showing the presence of cultivable cells in both aerobic and anaerobic conditions were from patients who had relapsed. The bacilli in these samples had been probably experiencing stress and thus were ready to adapt to the hypoxic environment. Diagnostic luciferase reporter phage assay for non-replicating persistors (DLRPA-NRP) identified 30 additional positives which failed to grow on Lowenstein-Jensen medium. Presence of viable bacilli in these samples was confirmed by reverse transcriptase-PCR (RT-PCR) for 16S rRNA indicating either the improved sensitivity of the assay to detect actively growing bacilli or its ability to detect non-replicating persistors. The utility of LRP assay to detect both dormant and active tubercle bacilli was explored in this work and was optimized using lysis inhibition to diagnose tuberculosis with rapidity, improved sensitivity and specificity. DLRPA-NRP, a rapid growth based assay is thus developed to detect both dormant and actively growing tubercle bacilli.

Mycobacterium tuberculosis uses host triacylglycerol to accumulate lipid droplets and acquires a dormancy-like phenotype in lipid-loaded macrophages

Two billion people are latently infected with Mycobacterium tuberculosis (Mtb). Mtb-infected macrophages are likely to be sequestered inside the hypoxic environments of the granuloma and differentiate into lipid-loaded macrophages that contain triacylglycerol (TAG)-filled lipid droplets which may provide a fatty acid-rich host environment for Mtb. We report here that human peripheral blood monocyte-derived macrophages and THP-1 derived macrophages incubated under hypoxia accumulate Oil Red O-staining lipid droplets containing TAG. Inside such hypoxic, lipid-loaded macrophages, nearly half the Mtb population developed phenotypic tolerance to isoniazid, lost acid-fast staining and accumulated intracellular lipid droplets. Dual-isotope labeling of macrophage TAG revealed that Mtb inside the lipid-loaded macrophages imports fatty acids derived from host TAG and incorporates them intact into Mtb TAG. The fatty acid composition of host and Mtb TAG were nearly identical suggesting that Mtb utilizes host TAG to accumulate intracellular TAG. Utilization of host TAG by Mtb for lipid droplet synthesis was confirmed when fluorescent fatty acid-labeled host TAG was utilized to accumulate fluorescent lipid droplets inside the pathogen. Deletion of the Mtb triacylglycerol synthase 1 (tgs1) gene resulted in a drastic decrease but not a complete loss in both radiolabeled and fluorescent TAG accumulation by Mtb suggesting that the TAG that accumulates within Mtb is generated mainly by the incorporation of fatty acids released from host TAG. We show direct evidence for the utilization of the fatty acids from host TAG for lipid metabolism inside Mtb. Taqman real-time PCR measurements revealed that the mycobacterial genes dosR, hspX, icl1, tgs1 and lipY were up-regulated in Mtb within hypoxic lipid loaded macrophages along with other Mtb genes known to be associated with dormancy and lipid metabolism.

Two billion people are latently infected with Mycobacterium tuberculosis (Mtb). Cure and possible eradication of tuberculosis are limited by the lack of availability of any drug that can kill dormant Mtb. Understanding of the processes critical for dormancy and a reliable dormancy model suitable for high throughput screening of chemicals will help to discover drugs that can kill dormant Mtb. Storage of lipids for utilization as energy source is critically needed for dormancy. In the human lung, Mtb-infected macrophages are sequestered inside the hypoxic environments of the physical enclosure called granuloma in which Mtb becomes dormant. None of the currently used cell culture models of Mtb infection mimic this situation. We developed a model that mimics the environment inside the human granuloma by incubating Mtb-infected macrophages under hypoxia. We found that, under these conditions, macrophages accumulate lipid droplets and Mtb within these macrophages acquire a dormancy phenotype. We report how the pathogen inside the macrophages utilizes the host lipids to store lipids within the pathogen and acquire the hallmark traits of dormant Mtb. Thus, our novel model of Mtb dormancy may enable better understanding of the metabolic processes vital for the dormant pathogen and help to discover drugs that can kill latent pathogens.

Genes and regulatory networks involved in persistence of Mycobacterium tuberculosis

The causative agent of tuberculosis, Mycobacterium tuberculosis, is one of the most successful of human pathogens. It can evade the host immune response and establish a persistent infection or enter a dormant state within the host which can be reactivated if the host becomes immuno-compromised. Both of these features are major obstacles to tuberculosis eradication. Dormancy and reactivation of M. tuberculosis are tightly coordinated dynamic processes involving numerous genes and their products. Molecular mechanisms underlying M. tuberculosis persistence may provide an opportunity for the discovery of effective drug targets for tuberculosis control. Here, we review the genes required for M. tuberculosis persistence and propose a regulatory network for the action of these genes using text mining. This should provide fresh insights into the persistence mechanisms of M. tuberculosis and suggest candidates for new drug targets and immune intervention.

Primary transcriptomes of Mycobacterium avium subsp. paratuberculosis reveal proprietary pathways in tissue and macrophages

Background

Mycobacterium avium subsp. paratuberculosis (MAP) persistently infects intestines and mesenteric lymph nodes leading to a prolonged subclinical disease. The MAP genome sequence was published in 2005, yet its transcriptional organization in natural infection is unknown. While prior research analyzed regulated gene sets utilizing defined, in vitro stress related or advanced surgical methods with various animal species, we investigated the intracellular lifestyle of MAP in the intestines and lymph nodes to understand the MAP pathways that function to govern this persistence.

Results

Our transcriptional analysis shows that 21%, 8% and 3% of the entire MAP genome was represented either inside tissues, macrophages or both, respectively. Transcripts belonging to latency and cell envelope biogenesis were upregulated in the intestinal tissues whereas those belonging to intracellular trafficking and secretion were upregulated inside the macrophages. Transcriptomes of natural infection and in vitro macrophage infection shared genes involved in transcription and inorganic ion transport and metabolism. MAP specific genes within large sequence polymorphisms of ancestral M. avium complex were downregulated exclusively in natural infection.

Conclusions

We have unveiled common and unique MAP pathways associated with persistence, cell wall biogenesis and virulence in naturally infected cow intestines, lymph nodes and in vitro infected macrophages. This dichotomy also suggests that in vitro macrophage models may be insufficient in providing accurate information on the events that transpire during natural infection. This is the first report to examine the primary transcriptome of MAP at the local infection site (i.e. intestinal tissue). Regulatory pathways that govern the lifecycle of MAP appear to be specified by tissue and cell type. While tissues show a "shut-down" of major MAP metabolic genes, infected macrophages upregulate several MAP specific genes along with a putative pathogenicity island responsible for iron acquisition. Many of these regulatory pathways rely on the advanced interplay of host and pathogen and in order to decipher their message, an interactome must be established using a systems biology approach. Identified MAP pathways place current research into direct alignment in meeting the future challenge of creating a MAP-host interactome.

PepD participates in the mycobacterial stress response mediated through MprAB and SigE

Currently, one-third of the world's population is believed to be latently infected with Mycobacterium tuberculosis. The mechanisms by which M. tuberculosis establishes latent infection remain largely undefined. mprAB encodes a two-component signal transduction system required by M. tuberculosis for aspects of persistent infection. MprAB regulates a large and diverse group of genetic determinants in response to membrane stress, including the extracytoplasmic function (ECF) sigma factor sigE and the HtrA-like serine protease pepD. Recent studies have demonstrated that PepD functions as both a protease and chaperone in vitro. In addition, inactivation of pepD alters the virulence of M. tuberculosis in a mouse model system of infection. Here, we demonstrate that PepD plays an important role in the stress response network of Mycobacterium mediated through MprAB and SigE. In particular, we demonstrate that the protease activity of PepD requires the PDZ domain, in addition to the catalytic serine at position 317. pepD expression initiates from at least three promoters in M. tuberculosis, including one that is regulated by SigE and is located upstream of the mprA coding sequence. Deletion of pepD or mprAB in Mycobacterium smegmatis and M. tuberculosis alters the stress response phenotypes of these strains, including increasing sensitivity to SDS and cell wall antibiotics and upregulating the expression of stress-responsive determinants, including sigE. Taking these data together, we hypothesize that PepD utilizes its PDZ domain to recognize and process misfolded proteins at the cell membrane, leading to activation of the MprAB and SigE signaling pathways and subsequent establishment of a positive feedback loop that facilitates bacterial adaptation.

A systems perspective of host-pathogen interactions: predicting disease outcome in tuberculosis

The complex web of interactions between the host immune system and the pathogen determines the outcome of any infection. A computational model of this interaction network, which encodes complex interplay among host and bacterial components, forms a useful basis for improving the understanding of pathogenesis, in filling knowledge gaps and consequently to identify strategies to counter the disease. We have built an extensive model of the Mycobacterium tuberculosis host-pathogen interactome, consisting of 75 nodes corresponding to host and pathogen molecules, cells, cellular states or processes. Vaccination effects, clearance efficiencies due to drugs and growth rates have also been encoded in the model. The system is modelled as a Boolean network. Virtual deletion experiments, multiple parameter scans and analysis of the system's response to perturbations, indicate that disabling processes such as phagocytosis and phagolysosome fusion or cytokines such as TNF-alpha and IFN-gamma, greatly impaired bacterial clearance, while removing cytokines such as IL-10 alongside bacterial defence proteins such as SapM greatly favour clearance. Simulations indicate a high propensity of the pathogen to persist under different conditions.

A novel in vitro multiple-stress dormancy model for Mycobacterium tuberculosis generates a lipid-loaded, drug-tolerant, dormant pathogen

BACKGROUND

Mycobacterium tuberculosis (Mtb) becomes dormant and phenotypically drug resistant when it encounters multiple stresses within the host. Inability of currently available drugs to kill latent Mtb is a major impediment to curing and possibly eradicating tuberculosis (TB). Most in vitro dormancy models, using single stress factors, fail to generate a truly dormant Mtb population. An in vitro model that generates truly dormant Mtb cells is needed to elucidate the metabolic requirements that allow Mtb to successfully go through dormancy, identify new drug targets, and to screen drug candidates to discover novel drugs that can kill dormant pathogen.

METHODOLOGY/PRINCIPAL FINDINGS

We developed a novel in vitro multiple-stress dormancy model for Mtb by applying combined stresses of low oxygen (5%), high CO(2) (10%), low nutrient (10% Dubos medium) and acidic pH (5.0), conditions Mtb is thought to encounter in the host. Under this condition, Mtb stopped replicating, lost acid-fastness, accumulated triacylglycerol (TG) and wax ester (WE), and concomitantly acquired phenotypic antibiotic-resistance. Putative neutral lipid biosynthetic genes were up-regulated. These genes may serve as potential targets for new antilatency drugs. The triacylglycerol synthase1 (tgs1) deletion mutant, with impaired ability to accumulate TG, exhibited a lesser degree of antibiotic tolerance and complementation restored antibiotic tolerance. Transcriptome analysis with microarray revealed the achievement of dormant state showing repression of energy generation, transcription and translation machineries and induction of stress-responsive genes. We adapted this model for drug screening using the Alamar Blue dye to quantify the antibiotic tolerant dormant cells.

CONCLUSIONS/SIGNIFICANCE

The new in vitro multiple stress dormancy model efficiently generates Mtb cells meeting all criteria of dormancy, and this method is adaptable to high-throughput screening for drugs that can kill dormant Mtb. A critical link between storage-lipid accumulation and development of phenotypic drug-resistance in Mtb was established. Storage lipid biosynthetic genes may be appropriate targets for novel drugs that can kill latent Mtb.

Theoretical basis for reducing time-lines to the determination of positive Mycobacterium tuberculosis cultures using thymidylate kinase (TMK) assays

BACKGROUND

In vitro culture of pathogens on growth media forms a "pillar" for both infectious disease diagnosis and drug sensitivity profiling. Conventional cultures of Mycobacterium tuberculosis (M.tb) on Lowenstein Jensen (LJ) medium, however, take over two months to yield observable growth, thereby delaying diagnosis and appropriate intervention. Since DNA duplication during interphase precedes microbial division, "para-DNA synthesis assays" could be used to predict impending microbial growth. Mycobacterial thymidylate kinase (TMKmyc) is a phosphotransferase critical for the synthesis of the thymidine triphosphate precursor necessary for M.tb DNA synthesis. Assays based on high-affinity detection of secretory TMKmyc levels in culture using specific antibodies are considered. The aim of this study was to define algorithms for predicting positive TB cultures using antibody-based assays of TMKmyc levels in vitro.

METHODS AND RESULTS

Systems and chemical biology were used to derive parallel correlation of "M.tb growth curves" with "TMKmyc curves" theoretically in four different scenarios, showing that changes in TMKmyc levels in culture would in each case be predictive of M.tb growth through a simple quadratic curvature, |tmk| = at2+ bt + c, consistent with the "S" pattern of microbial growth curves. Two drug resistance profiling scenarios are offered: isoniazid (INH) resistance and sensitivity. In the INH resistance scenario, it is shown that despite the presence of optimal doses of INH in LJ to stop M.tb proliferation, bacilli grow and the resulting phenotypic growth changes in colonies/units are predictable through the TMKmyc assay. According to our current model, the areas under TMKmyc curves (AUC, calculated as the integral integral(at2+ bt + c)dt or approximately 1/3 at3+ 1/2 bt2+ct) could directly reveal the extent of prevailing drug resistance and thereby aid decisions about the usefulness of a resisted drug in devising "salvage combinations" within resource-limited settings, where second line TB chemotherapy options are limited.

CONCLUSION

TMKmyc assays may be useful for reducing the time-lines to positive identification of Mycobacterium tuberculosis (M.tb) cultures, thereby accelerating disease diagnosis and drug resistance profiling. Incorporating "chemiluminiscent or fluorescent" strategies may enable "photo-detection of TMKmyc changes" and hence automation of the entire assay.

Monocyte-dependent oncostatin M and TNF-alpha synergize to stimulate unopposed matrix metalloproteinase-1/3 secretion from human lung fibroblasts in tuberculosis

Leukocyte-derived matrix metalloproteinases (MMP) are implicated in the tissue destruction characteristic of tuberculosis (TB). The contribution of lung stromal cells to MMP activity in TB is unknown. Oncostatin M (OSM) is an important stimulus to extrapulmonary stromal MMP induction, but its role in regulation of pulmonary MMP secretion or pathophysiology of TB is unknown. We investigated OSM secretion from Mycobacterium tuberculosis (Mtb)-infected human monocytes/macrophages and the networking effects of such OSM on lung fibroblast MMP secretion. Mtb increased monocyte OSM secretion dose dependently in vitro. In vivo tuberculous granulomas immunostained positively for OSM. Further, conditioned media from Mtb-infected monocytes (CoMTb) induced monocyte OSM secretion (670 +/- 55 versus 166 +/- 14 pg/mL in controls), implicating an autocrine loop. Mtb-induced OSM secretion was prostaglandin (PG) sensitive, and required activation of surface G-protein coupled receptors. OSM induction was ERK MAP kinase dependent, p38-requiring but JNK-independent. OSM synergized with TNF-alpha, a key cytokine in TB granuloma formation, to stimulate pulmonary fibroblast MMP-1/-3 secretion, while suppressing secretion of tissue inhibitors of metalloproteinases-1/-2. In summary, Mtb infection of monocytes results in PG-dependent OSM secretion, which synergizes with TNF-alpha to drive functionally unopposed fibroblast MMP-1/-3 secretion, demonstrating a previously unrecognized role for OSM in TB.

5-tert-butyl-N-pyrazol-4-yl-4,5,6,7-tetrahydrobenzo[d]isoxazole-3-carboxamide derivatives as novel potent inhibitors of Mycobacterium tuberculosis pantothenate synthetase: initiating a quest for new antitubercular drugs

Pantothenate synthetase (PS) is one of the potential new antimicrobial targets that may also be useful for the treatment of the nonreplicating persistent forms of Mycobacterium tuberculosis. In this Letter we present a series of 5- tert-butyl- N-pyrazol-4-yl-4,5,6,7-tetrahydrobenzo[ d]isoxazole-3-carboxamide derivatives as novel potent Mycobacterium tuberculosis PS inhibitors, their in silico molecular design, synthesis, and inhibitory activity.

The two chorismate mutases from both Mycobacterium tuberculosis and Mycobacterium smegmatis: biochemical analysis and limited regulation of promoter activity by aromatic amino acids

Chorismate mutase (CM) catalyzes the rearrangement of chorismate to prephenate in the biosynthetic pathway that forms phenylalanine and tyrosine in bacteria, fungi, plants, and apicomplexan parasites. Since this enzyme is absent from mammals, it represents a promising target for the development of new antimycobacterial drugs, which are needed to combat Mycobacterium tuberculosis, the causative agent of tuberculosis. Until recently, two putative open reading frames (ORFs), Rv0948c and Rv1885c, showing low sequence similarity to CMs have been described as "conserved hypothetical proteins" in the M. tuberculosis genome. However, we and others demonstrated that these ORFs are in fact monofunctional CMs of the AroQ structural class and that they are differentially localized in the mycobacterial cell. Since homologues to the M. tuberculosis enzymes are also present in Mycobacterium smegmatis, we cloned the coding sequences corresponding to ORFs MSMEG5513 and MSMEG2114 from the latter. The CM activities of both ORFs was determined, as well as their translational start sites. In addition, we analyzed the promoter activities of three M. tuberculosis loci related to phenylalanine and tyrosine biosynthesis under a variety of conditions using M. smegmatis as a surrogate host. Our results indicate that the aroQ (Rv0948c), *aroQ (Rv1885c), and fbpB (Rv1886c) genes from M. tuberculosis are constitutively expressed or subjected to minor regulation by aromatic amino acids levels, especially tryptophan.

Sphingosine 1-phosphate promotes antigen processing and presentation to CD4+ T cells in Mycobacterium tuberculosis-infected monocytes

Sphingosine 1-phosphate (S1P) has recently been described to induce antimycobacterial activity. The present study analyses the role played by S1P in antigen presentation of monocytes and in the next activation of Mycobacterium tuberculosis (MTB)-specific CD4+ T cell response. Results reported herein show that S1P stimulation of MTB-infected monocytes (i) inhibits intracellular mycobacterial growth, (ii) enhances phagolysosome maturation and the transit of mycobacteria in MHC class II compartments, (iii) increases the frequency of MTB-specific CD4+CD69+ T cells, expressing the inflammatory homing receptor CCR5, derived from tuberculosis patients and PPD+, BCG naïve, healthy subjects, and (iv) induces IFN-gamma production in CD4+CD69+CCR5+ T cells derived from PPD+ healthy individuals, only. Altogether, these results show that S1P promotes antigen processing and presentation in monocytes, increases the frequency of MTB-specific CD4+ T cells and can regulate IFN-gamma production by antigen specific CD4+ T cells in the course of active disease.

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.

Intracellular signalling cascades regulating innate immune responses to Mycobacteria: branching out from Toll-like receptors

Toll-like receptors (TLRs) recognize Mycobacterium tuberculosis (Mtb) or Mtb components and initiate mononuclear phagocyte responses that influence both innate and adaptive immunity. Recent studies have revealed the intracellular signalling cascades involved in the TLR-initiated immune response to mycobacterial infection. Although both TLR2 and TLR4 have been implicated in host interactions with Mtb, the relationship between specific mycobacterial molecules and various signal transduction pathways is not well understood. This review will discuss recent studies indicating critical roles for mycobacteria and mycobacterial components in regulation of mitogen-activated protein kinases and related signal transduction pathways that govern the outcome of infection and antibacterial defence. To better understand the roles of infection-induced signalling cascades in molecular pathogenesis, future studies are needed to clarify mechanisms that integrate the multiple signalling pathways that are activated by engagement of TLRs by both individual mycobacterial molecules and whole mycobacteria. These efforts will allow for the development of novel diagnostic and therapeutic modalities for tuberculosis that targets the intracellular signalling pathways permitting the replication of this nefarious pathogen.

Identification of a diacylglycerol acyltransferase gene involved in accumulation of triacylglycerol in Mycobacterium tuberculosis under stress

Mycobacterium tuberculosis under stress stores triacylglycerol (TG). There are 15 genes in M. tuberculosis that belong to a novel family of TG synthase genes (tgs), but it is not known which of them is responsible for this accumulation of TG. In this paper, it is reported that M. tuberculosis H37Rv accumulated TG under acidic, static or hypoxic growth conditions, or upon treatment with NO, whereas TG accumulation was drastically reduced in the tgs1 (Rv3130c) disrupted mutant. Complementation with tgs1 restored this TG accumulation. C(26) was a major fatty acid in this TG, indicating that the TGS1 gene product uses C(26) fatty acid, which is known to be produced by the mycobacterial fatty acid synthase. TGS1 expressed in Escherichia coli preferred C(26 : 0)-CoA for TG synthesis. If TG storage is needed for the long-term survival of M. tuberculosis under dormant conditions, the tgs1 product could be a suitable target for antilatency drugs.

Transcriptional autoregulation byMycobacterium tuberculosisPhoP involves recognition of novel direct repeat sequences in the regulatory region of the promoter

The PhoP-PhoR two-component system is essential for virulence and intracellular growth of Mycobacterium tuberculosis (MTB) in human and mouse macrophages or in mice. Here, PhoP and truncated PhoR sensor proteins were shown to participate in phosphotransfer reactions using conserved residues characteristic of two-component signaling systems. beta-Galactosidase activity originating from phoP promoter-lacZ construct was inhibited in presence of PhoP, suggesting transcriptional auto-inhibition by the response regulator. In vitro binding of PhoP is consistent with the in vivo transcriptional repression, indicating phosphorylation-independent assembly of the transcription initiation complex at elevated concentrations of PhoP. DNaseI protection studies reveal a consensus recognition sequence within the phoP promoter that includes three 9-bp direct repeat units. Each repeat unit adjusts to the consensus (1)AC(T)/(G)(T)/(G)(T)/(G)P(y)AP(u)C(9). Alteration in the sequence of the newly-identified direct repeat units relieved phoP transcriptional repression in presence of PhoP, suggesting that PhoP represses its own expression by sequence-specific interaction(s) with the repeat units. Together, these results identify so far unknown PhoP-regulated genetic determinants in the regulatory region of the phoP promoter that are central to understanding of how PhoP may possibly function as a global regulator in MTB.

Contribution of respiratory burst activity to innate immune function and the effects of disease status and agent on chemiluminescence responses by ruminant phagocytes in vitro

The mechanisms of interaction between phagocytes and different bacteria that help resolve lung infections or contribute to lung pathology are poorly defined. Alveolar phagocytes (resident macrophages and recruited neutrophils) make a major contribution to innate immunity by mounting a respiratory burst that helps kill internalised bacteria. However, this ability may be altered during or after exposure to infection. This review considers the application and limitations of a variety of analytical methods for oxygen-dependent mechanisms of respiratory burst in phagocytes initiated by soluble and particulate activators. Particular reference is given to the study in vitro of phagocytes from healthy and diseased ruminants during either natural infection with Mycobacterium avium paratuberculosis or experimental infection with Pasteurella multocida or Mannheimia haemolytica.

Effects of diesel particles on the control of intracellular mycobacterial growth by human macrophagesin vitro

Changes that may modify the capacity of macrophages to control mycobacterial growth could favour the reactivation of bacillary proliferation within protective granulomas developed in response to mycobacterial infection. There is increasing evidence that diesel exhaust particles (DEPs) could suppress some macrophage functions, but it is not known whether DEPs may alter macrophage mycobactericidal activity. The aim of this study was to assess the effect of DEPs on the mycobactericidal activity of human mononuclear phagocytes in vitro. Human monocytes from healthy donors were cultured for 3 days in the presence or absence of DEPs or carbon black particles (CBPs), and then infected with a Mycobacterium bovis bacillus Calmette-Guérin reporter strain expressing luciferase activity. DEPs were rapidly internalized by monocyte-derived macrophages without cytotoxic effect. Mycobactericidal activity of cells exposed to DEPs was not different from that of cells cultured in their absence or in the presence of CBPs. Although our study was restricted to the mycobactericidal activity of human macrophages in vitro, the results indicate that DEPs do not directly influence the first line of defence against microorganisms. Whether exposure to DEPs influences the adaptive immune response against mycobacterial infections remains to be determined.

The crystal structure of Rv0793, a hypothetical monooxygenase from M.␣tuberculosis

Mycobacterium tuberculosis infects millions worldwide. The Structural Genomics Consortium for M. tuberculosis has targeted all genes from this bacterium in hopes of discovering and developing new therapeutic agents. Open reading frame Rv0793 from M. tuberculosis was annotated with an unknown function. The 3-dimensional structure of Rv0793 has been solved to 1.6 A resolution. Its structure is very similar to that of Streptomyces coelicolor ActVA-Orf6, a monooxygenase that participates in tailoring of polyketide antibiotics in the absence of a cofactor. It is also similar to the recently solved structure of YgiN, a quinol monooxygenase from Escherichia coli. In addition, the structure of Rv0793 is similar to several structures of other proteins with unknown function. These latter structures have been determined recently as a result of structural genomic projects for various bacterial species. In M. tuberculosis, Rv0793 and its homologs may represent a class of monooygenases acting as reactive oxygen species scavengers that are essential for evading host defenses. Since the most prevalent mode of attack by the host defense on M. tuberculosis is by reactive oxygen species and reactive nitrogen species, Rv0793 may provide a novel target to combat infection by M. tuberculosis.

Recombinant interleukin-4-treated macrophages, epithelioid cell surrogates, harbor and arrest Mycobacterium avium multiplication in vitro

Our group has previously described that murine peritoneal macrophages treated in vitro for 7 days with recombinant interleukin-4 (rIL-4) acquire morphological and functional characteristics of epithelioid cells (ECs) found in granulomatous lesions. Although EC function has not been clarified so far, it has been suggested that these cells could present antigens and control multiplication of mycobacteria. These aspects have been addressed here using in vitro EC surrogates. Using immunocytochemistry and immunofluorescence methods, we have observed an increased expression of CD11b, CD54, CD86 and CD40 molecules on rIL-4-treated macrophages when compared to untreated ones. Cytokine-treated cells were less phagocytic for latex beads (P<0.03) and more pinocytic for dextran particles than untreated macrophages. T-cell lymphoproliferation assays using ovalbumin (OVA) and Mycobacterium avium as antigens showed that both cultured macrophages were equally efficient as antigen presenting cells (APCs). However, M. avium antigens were better presented in vivo by EC surrogates (P<0.01). Both macrophage cultures were similarly infected by M. avium. However, while the infection level was maintained in the cytokine-treated population, untreated macrophages showed a progressive increase in the number of bacilli/cell with time (P<0.01) and a reduction of about 65% in cell population. After 96 h of M. avium infection, untreated cells secreted higher amounts of tumor necrosis factor-alpha (P<0.005) while rIL-4-treated macrophages showed higher, although not significant, transforming growth factor-beta production. Also, EC surrogates produced less nitric oxide than control macrophages (P<0.05). Hence, EC surrogates restrain M. avium growth and act as APCs in vitro and in vivo.

A novel lipase belonging to the hormone-sensitive lipase family induced under starvation to utilize stored triacylglycerol in Mycobacterium tuberculosis

Twenty-four putative lipase/esterase genes of Mycobacterium tuberculosis H37Rv were expressed in Escherichia coli and assayed for long-chain triacylglycerol (TG) hydrolase activity. We show here that the product of Rv3097c (LIPY) hydrolyzed long-chain TG with high specific activity. LIPY was purified after solubilization from inclusion bodies; the enzyme displayed a K(m) of 7.57 mM and V(max) of 653.3 nmol/mg/min for triolein with optimal activity between pH 8.0 and pH 9.0. LIPY was inhibited by active serine-directed reagents and was inactivated at temperatures above 37 degrees C. Detergents above their critical micellar concentrations and divalent cations inhibited the activity of LIPY. The N-terminal half of LIPY showed sequence homology with the proline glutamic acid-polymorphic GC-rich repetitive sequences protein family of M. tuberculosis. The C-terminal half of LIPY possesses amino acid domains homologous with the hormone-sensitive lipase family and the conserved active-site motif GDSAG. LIPY shows low sequence identity with the annotated lipases of M. tuberculosis and with other bacterial lipases. We demonstrate that hypoxic cultures of M. tuberculosis, which had accumulated TG, hydrolyzed the stored TG when subjected to nutrient starvation. Under such conditions, lipY was induced more than all lipases, suggesting a central role for it in the utilization of stored TG. We also show that in the lipY-deficient mutant, TG utilization was drastically decreased under nutrient-deprived condition. Thus, LIPY may be responsible for the utilization of stored TG during dormancy and reactivation of the pathogen.

Synovial Chlamydia trachomatis up regulates expression of a panel of genes similar to that transcribed by Mycobacterium tuberculosis during persistent infection

BACKGROUND

Synovial tissues in patients with Chlamydia associated arthritis are persistently infected by C trachomatis, an organism for which genetic manipulation is not possible. M tuberculosis also engages in persistent infection, and because this bacterium is genetically tractable many groups have been able to define transcriptional characteristics of mycobacterial growth and persistence.

OBJECTIVE

To investigate whether the pattern of gene expression underlying chlamydial persistence is similar to that underlying mycobacterial persistence.

METHODS

194 genes in M tuberculosis that are transcriptionally up regulated to support in vivo growth and persistence of that organism have previously been identified. Each of those genes was compared with the C trachomatis genome to identify orthologues. Expression of selected chlamydial orthologues so identified was assessed by real time RT-PCR in an in vitro model of chlamydial persistence and synovial tissues from patients who were PCR positive for C trachomatis at that site.

RESULTS

67 C trachomatis genes were identified as being orthologous to mycobacterial persistence related genes, representing 35% of the genes tested. The chlamydial orthologues fell into similar metabolic and other categories as those in M tuberculosis. Expression of a majority of selected chlamydial orthologues was strongly up regulated in an in vitro model of chlamydial persistence and in synovial tissues of relevant patients, compared with their expression during active infection.

CONCLUSIONS

These observations provide new insight into the molecular genetic basis underlying chlamydial persistence, and indicate that this information can be obtained, in some instances, by extrapolating observations made in other biological systems and/or organisms.

Expression and characterization of the carboxyl esterase Rv3487c from Mycobacterium tuberculosis

Rv3487c (lipF), a member of the lipase family of Mycobacterium tuberculosis, is related to virulence of this pathogen. Real-time RT-PCR analysis indicated that Rv3487c was induced at low pH in M. tuberculosis cultured in vitro. The gene of Rv3487c was cloned and expressed as fusion protein in Escherichia coli. After removal of the N-terminal domain of the fusion partner by enterokinase treatment, the effect of pH, temperature, and detergents on the purified enzyme activity and stability was characterized. Rv3487c could efficiently hydrolyze short chain esters. The catalytic triad of Rv3487c consists of residues Ser90, Glu189, and His219 as demonstrated by amino acid sequence alignment, three-dimensional modeling, and site-directed mutagenesis.

Recent advances towards identification of new drug targets for Mycobacterium tuberculosis

Mycobacterium tuberculosis is a very successful pathogen that remains a leading infectious killer worldwide. The global situation has become precarious due to various factors such as the variable efficacy of the Bacille Calmette-Guerin (BCG) vaccine, drug resistance, delay in diagnosis, association with HIV, and other factors, creating a long-lasting reservoir of impending disease and infection. Surprisingly, no new drugs have been developed in the past 30 years. The release of the complete genome sequence of M. tuberculosis and the availability of advanced genetic tools have provided the powerful repertoire of potential drug targets that are now in hand and can be explored in a more rational and directional manner. In this review, the authors highlight some possible therapeutic targets in M. tuberculosis. The gene products involved in various processes, such as mycobacterial cell wall synthesis, ability to acquire or obtain essential nutrients, persistence, transcription regulation, energy metabolism and others, such as the PE-PGRS family and culture filtrate proteins, would be potential targets for the development of new drugs. Apart from these categories, the importance of signal transduction events in the virulence of mycobacteria is discussed in relation to their potential as therapeutic targets. The potential of all of these therapeutic targets should be investigated together with the potential of being able to synthesise future chemotherapeutic agents.

Identifying control mechanisms of granuloma formation during M. tuberculosis infection using an agent-based model

Infection with Mycobacterium tuberculosis is a major world health problem. An estimated 2 billion people are presently infected and the disease causes approximately 3 million deaths per year. After bacteria are inhaled into the lung, a complex immune response is triggered leading to the formation of multicellular structures termed granulomas. It is believed that the collection of host granulomas either contain bacteria resulting in a latent infection or are unable to do so, leading to active disease. Thus, understanding granuloma formation and function is essential for improving both diagnosis and treatment of tuberculosis. Granuloma formation is a complex spatio-temporal system involving interactions of bacteria, specific immune cells, including macrophages, CD4+ and CD8+ T cells, as well as immune effectors such as chemokine and cytokines. To study this complex dynamical system we have developed an agent-based model of granuloma formation in the lung. This model combines continuous representations of chemokines with discrete agent representations of macrophages and T cells in a cellular automata-like environment. Our results indicate that key host elements involved in granuloma formation are chemokine diffusion, prevention of macrophage overcrowding within the granuloma, arrival time, location and number of T cells within the granuloma, and an overall host ability to activate macrophages. Interestingly, a key bacterial factor is its intracellular growth rate, whereby slow growth actually facilitates survival.

Mucosal immunization against respiratory bacterial pathogens

Bacterial respiratory diseases remain a major cause of morbidity and mortality throughout the world. The young and the elderly are particularly susceptible to the pathogens that cause these diseases. Therapeutic approaches remain dependent upon antibiotics contributing to the persistent increases in antibiotic resistance. The main causes of respiratory disease discussed in this review are Mycobacterium tuberculosis, Corynebacterium diphtheriae, Bordatella pertussis, Streptococcus pneumoniae, non-typeable Haemophilus influenzae, Moraxella catarrhalis and Pseudomonas aeruginosa. All these organisms initiate disease at the mucosal surface of the respiratory tract and thus the efficacy of the host's response to infection needs to be optimal at this site. Vaccines available for diseases caused by many of these pathogens have limitations in accessibility or efficacy, highlighting the need for improvements in approaches and products. The most significant challenges in both therapy and prevention of disease induced by bacteria in the respiratory tract remain the development of non-injectable vaccines and delivery systems/immunization regimens that improve mucosal immunity.