The 16-kDa alpha-crystallin (Acr) protein of Mycobacterium tuberculosis is required for growth in macrophages

Humoral correlates of protection against Mycobacterium tuberculosis following intravenous BCG vaccination in rhesus macaques

Altering Bacille Calmette-Guérin (BCG) immunization from low-dose intradermal (i.d.) to high-dose intravenous (i.v.) vaccination provides a high level of protection against Mycobacterium tuberculosis (Mtb). In addition to strong T cell immunity, i.v. BCG drives robust humoral immune responses that track with bacterial control. However, given the near-complete protection afforded by high-dose i.v. BCG immunization, a precise correlate of protection was difficult to define. Here we leveraged plasma and bronchoalveolar lavage fluid (BAL) from a cohort of rhesus macaques that received decreasing doses of i.v. BCG and aimed to define correlates of immunity following Mtb challenge. We show an i.v. BCG dose-dependent induction of mycobacterial-specific humoral immune responses. Antibody responses at peak immunogenicity predicted bacterial control post-challenge. Multivariate analyses revealed antibody-mediated complement and natural killer (NK) cell-activating humoral networks as key signatures of protective immunity. This work extends our understanding of humoral biomarkers and potential mechanisms of i.v. BCG-mediated protection against Mtb.

Stealing survival: Iron acquisition strategies of Mycobacteriumtuberculosis

Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis (TB), faces iron scarcity within the host due to immune defenses. This review explores the importance of iron for Mtb and its strategies to overcome iron restriction. We discuss how the host limits iron as an innate immune response and how Mtb utilizes various iron acquisition systems, particularly the siderophore-mediated pathway. The review illustrates the structure and biosynthesis of mycobactin, a key siderophore in Mtb, and the regulation of its production. We explore the potential of targeting siderophore biosynthesis and uptake as a novel therapeutic approach for TB. Finally, we summarize current knowledge on Mtb's iron acquisition and highlight promising directions for future research to exploit this pathway for developing new TB interventions.

Predicting bacterial fitness in Mycobacterium tuberculosis with transcriptional regulatory network-informed interpretable machine learning

Mycobacterium tuberculosis (Mtb) is the causative agent of tuberculosis disease, the greatest source of global mortality by a bacterial pathogen. Mtb adapts and responds to diverse stresses such as antibiotics by inducing transcriptional stress-response regulatory programs. Understanding how and when these mycobacterial regulatory programs are activated could enable novel treatment strategies for potentiating the efficacy of new and existing drugs. Here we sought to define and analyze Mtb regulatory programs that modulate bacterial fitness. We assembled a large Mtb RNA expression compendium and applied these to infer a comprehensive Mtb transcriptional regulatory network and compute condition-specific transcription factor activity profiles. We utilized transcriptomic and functional genomics data to train an interpretable machine learning model that can predict Mtb fitness from transcription factor activity profiles. We demonstrated that this transcription factor activity-based model can successfully predict Mtb growth arrest and growth resumption under hypoxia and reaeration using only RNA-seq expression data as a starting point. These integrative network modeling and machine learning analyses thus enable the prediction of mycobacterial fitness under different environmental and genetic contexts. We envision these models can potentially inform the future design of prognostic assays and therapeutic intervention that can cripple Mtb growth and survival to cure tuberculosis disease.

Antibodies as key mediators of protection against Mycobacterium tuberculosis

Tuberculosis (TB) is caused by infection with the bacterial pathogen Mycobacterium tuberculosis (M.tb) in the respiratory tract. There was an estimated 10.6 million people newly diagnosed with TB, and there were approximately 1.3 million deaths caused by TB in 2022. Although the global prevalence of TB has remained high for decades and is an annual leading cause of death attributed to infectious diseases, only one vaccine, Bacillus Calmette-Guérin (BCG), has been approved so far to prevent/attenuate TB disease. Correlates of protection or immunological mechanisms that are needed to control M.tb remain unknown. The protective role of antibodies after BCG vaccination has also remained largely unclear; however, recent studies have provided evidence for their involvement in protection against disease, as biomarkers for the state of infection, and as potential predictors of outcomes. Interestingly, the antibodies generated post-vaccination with BCG are linked to the activation of innate immune cascades, providing further evidence that antibody effector functions are critical for protection against respiratory pathogens such as M.tb. In this review, we aim to provide current knowledge of antibody application in TB diagnosis, prevention, and treatment. Particularly, this review will focus on 1) The role of antibodies in preventing M.tb infections through preventing Mtb adherence to epithelium, antibody-mediated phagocytosis, and antibody-mediated cellular cytotoxicity; 2) The M.tb-directed antibody response generated after vaccination and how humoral profiles with different glycosylation patterns of these antibodies are linked with protection against the disease state; and 3) How antibody-mediated immunity against M.tb can be further explored as early diagnosis biomarkers and different detection methods to combat the global M.tb burden. Broadening the paradigm of differentiated antibody profiling and antibody-based detection during TB disease progression offers new directions for diagnosis, treatment, and preventative strategies. This approach involves linking the aforementioned humoral responses with the disease state, progression, and clearance.

Gene Regulatory Mechanism of Mycobacterium Tuberculosis during Dormancy

Tuberculosis (TB), caused by Mycobacterium tuberculosis (Mtb) complex, is a zoonotic disease that remains one of the leading causes of death worldwide. Latent tuberculosis infection reactivation is a challenging obstacle to eradicating TB globally. Understanding the gene regulatory network of Mtb during dormancy is important. This review discusses up-to-date information about TB gene regulatory networks during dormancy, focusing on the regulation of lipid and energy metabolism, dormancy survival regulator (DosR), White B-like (Wbl) family, Toxin-Antitoxin (TA) systems, sigma factors, and MprAB. We outline the progress in vaccine and drug development associated with Mtb dormancy.

Enhancing the sequence coverage of nanodiamond-extracted early secretory proteins from the Mycobacterium tuberculosis complex

The unambiguous identification of protein species requires high sequence coverage. In this study, we successfully improved the sequence coverage of early secretory 10 kDa cell filtrate protein (CFP-10) and 6 kDa early secretory antigenic target (ESAT-6) proteins from the Mycobacterium tuberculosis complex (MTC) in broth culture media with the use of the 4-chloro-α-cyanocinnamic acid (Cl-CCA) matrix. Conventional matrices, α-cyano-hydroxy-cinnamic acid (CHCA) and 2,5-dihydroxybenzoic acid (DHB), were also used for comparison. After nanodiamond (ND) extraction, the sequence coverage of the CFP-10 protein was 87% when CHCA and DHB matrices were used, and the ESAT-6 protein was not detected. On the other hand, the sequence coverage for ND-extracted CFP-10 and ESAT-6 could reach 94% and 100%, respectively, when the Cl-CCA matrix was used and with the removal of interference from bovine serum albumin (BSA) protein and α-crystallin (ACR) protein. Matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) was also adopted to analyze the protein mass spectra. A total of 6 prominent ion signals were observed, including ESAT-6 protein peaks at mass-to-charge ratios (m/z) of ∼7931, ∼7974, ∼9768, and ∼9813 and CFP-10 protein peaks at m/z of ∼10 100 and ∼10 660. The ESAT-6 ion signals were always detected concurrently with CFP-10 ion signals, but CFP-10 ion signals could be detected alone without the ESAT-6 ion signals. Furthermore, the newly found ESAT-6 peaks were also confirmed using a Mag-Beads-Protein G kit with an ESAT-6 antibody to capture the ESAT-6 protein, which was also consistent with the sequence coverage analysis.

Lysine acetylation of Hsp16.3: Effect on its structure, chaperone function and influence towards the growth of Mycobacterium tuberculosis

Hsp16.3 plays a vital role in the slow growth of Mycobacterium tuberculosis via its chaperone function. Many secretory proteins, including Hsp16.3 undergo acetylation in vivo. Seven lysine (K) residues (K64, K78, K85, K114, K119, K132 and K136) in Hsp16.3 are acetylated inside pathogen. However, how lysine acetylation affects its structure, chaperone function and pathogen's growth is still elusive. We examined these aspects by executing in vitro chemical acetylation (acetic anhydride modification) and by utilizing a lysine acetylation mimic mutant (Hsp16.3-K64Q/K78Q/K85Q/K114Q/K119Q/K132Q/K136Q). Far- and near-UV CD measurements revealed that the chemically acetylated proteins(s) and acetylation mimic mutant has altered secondary and tertiary structure than unacetylated/wild-type protein. The chemical modification and acetylation mimic mutation also disrupted the oligomeric assembly, increased surface hydrophobicity and reduced stability of Hsp16.3, as revealed by GF-HPLC, 4,4'-dianilino-1,1'-binaphthyl-5,5'-disulfonic acid binding and urea denaturation experiments, respectively. These structural changes collectively led to an enhancement in chaperone function (aggregation and thermal inactivation prevention ability) of Hsp16.3. Moreover, when the H37Rv strain expressed the acetylation mimic mutant protein, its growth was slower in comparison to the strain expressing the wild-type/unacetylated Hsp16.3. Altogether, these findings indicated that lysine acetylation improves the chaperone function of Hsp16.3 which may influence pathogen's growth in host environment.

Genetically encoded transcriptional plasticity underlies stress adaptation in Mycobacterium tuberculosis

Transcriptional regulation is a critical adaptive mechanism that allows bacteria to respond to changing environments, yet the concept of transcriptional plasticity (TP) - the variability of gene expression in response to environmental changes - remains largely unexplored. In this study, we investigate the genome-wide TP profiles of Mycobacterium tuberculosis (Mtb) genes by analyzing 894 RNA sequencing samples derived from 73 different environmental conditions. Our data reveal that Mtb genes exhibit significant TP variation that correlates with gene function and gene essentiality. We also find that critical genetic features, such as gene length, GC content, and operon size independently impose constraints on TP, beyond trans-regulation. By extending our analysis to include two other Mycobacterium species -- M. smegmatis and M. abscessus -- we demonstrate a striking conservation of the TP landscape. This study provides a comprehensive understanding of the TP exhibited by mycobacteria genes, shedding light on this significant, yet understudied, genetic feature encoded in bacterial genomes.

Evaluation of cytokine profiles related to Mycobacterium tuberculosis latent antigens using a whole-blood assay in the Philippines

Introduction

There is no useful method to discriminate between latent tuberculosis infection (LTBI) and active pulmonary tuberculosis (PTB). This study aimed to investigate the potential of cytokine profiles to discriminate between LTBI and active PTB using whole-blood stimulation with Mycobacterium tuberculosis (MTB) antigens, including latency-associated antigens.

Materials and methods

Patients with active PTB, household contacts of active PTB patients and community exposure subjects were recruited in Manila, the Philippines. Peripheral blood was collected from the participants and used for whole-blood stimulation (WBS) with either the early secretory antigenic target and the 10-kDa culture filtrate protein (ESAT-6/CFP-10), Rv3879c or latency-associated MTB antigens, including mycobacterial DNA-binding protein 1 (MDP-1), α-crystallin (Acr) and heparin-binding hemagglutinin (HBHA). Multiple cytokine concentrations were analyzed using the Bio-Plex™ multiplex cytokine assay.

Results

A total of 78 participants consisting of 15 active PTB patients, 48 household contacts and 15 community exposure subjects were eligible. The MDP-1-specific IFN-γ level in the active PTB group was significantly lower than that in the household contact group (p < 0.001) and the community exposure group (p < 0.001). The Acr-specific TNF-α and IL-10 levels in the active PTB group were significantly higher than those in the household contact (TNF-α; p = 0.001, IL-10; p = 0.001) and community exposure (TNF-α; p < 0.001, IL-10; p = 0.01) groups. However, there was no significant difference in the ESAT-6/CFP-10-specific IFN-γ levels among the groups.

Conclusion

The patterns of cytokine profiles induced by latency-associated MTB antigens using WBS have the potential to discriminate between LTBI and active PTB. In particular, combinations of IFN-γ and MDP-1, TNF-α and Acr, and IL-10 and Acr are promising. This study provides the first demonstration of the utility of MDP-1-specific cytokine responses in WBS.

Antimicrobial activity of carvacrol and its derivatives on Mycobacterium spp.: systematic review of preclinical studies

Background: The scope of the study was to analyze original preclinical studies on the antimicrobial effects of carvacrol and derivatives on the Mycobacterium genus. Materials & methods: According to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses statement, four databases (PubMed, Web of Science, SCOPUS and EMBASE) were searched. Results: The search retrieved 392 records, of which 11 papers were selected. Heterogeneity in the techniques and mycobacterial targets was observed. Carvacrol demonstrated synergistic antimycobacterial activity with rifampicin against multidrug-resistant Mycobacterium tuberculosis on membranes and biofilms. In silico approaches showed specific targets in mycobacteria, by inhibition and molecular docking assays, on the enzyme chorismate mutase and the heat shock protein 16.3. Conclusion: Carvacrol has been shown to be a scaffold candidate for future molecules with activity against mycobacteria.

Antigen identification strategies and preclinical evaluation models for advancing tuberculosis vaccine development

In its myriad devastating forms, Tuberculosis (TB) has existed for centuries, and humanity is still affected by it. Mycobacterium tuberculosis (M. tuberculosis), the causative agent of TB, was the foremost killer among infectious agents until the COVID-19 pandemic. One of the key healthcare strategies available to reduce the risk of TB is immunization with bacilli Calmette-Guerin (BCG). Although BCG has been widely used to protect against TB, reports show that BCG confers highly variable efficacy (0-80%) against adult pulmonary TB. Unwavering efforts have been made over the past 20 years to develop and evaluate new TB vaccine candidates. The failure of conventional preclinical animal models to fully recapitulate human response to TB, as also seen for the failure of MVA85A in clinical trials, signifies the need to develop better preclinical models for TB vaccine evaluation. In the present review article, we outline various approaches used to identify protective mycobacterial antigens and recent advancements in preclinical models for assessing the efficacy of candidate TB vaccines.

Mucosal and systemic antigen-specific antibody responses correlate with protection against active tuberculosis in nonhuman primates

BACKGROUND

Increasing evidence supports that antibodies can protect against active tuberculosis (TB) but knowledge of potentially protective antigens, especially in the airways, is limited. The main objective of this study was to identify antigen-specific airway and systemic immunoglobulin isotype responses associated with the outcome of controlled latent Mycobacterium tuberculosis (Mtb) infection (LTBI) versus uncontrolled infection (TB) in nonhuman primates.

METHODS

In a case-control design, using non-parametric group comparisons with false discovery rate adjustments, we assessed antibodies in 57 cynomolgus macaques which, following low-dose airway Mtb infection, developed either LTBI or TB. We investigated airway and systemic IgG, IgA, and IgM responses in paired bronchoalveolar lavage and plasma samples prior to, two-, and 5-6-months post Mtb infection using an antigen-unbiased approach with Mtb glycan and proteome-wide microarrays.

FINDINGS

Macaques that developed LTBI (n = 36) had significantly increased airway and plasma IgA reactivities to specific arabinomannan (AM) motifs prior to Mtb infection compared to those that developed TB (n = 21; p < 0.01, q < 0.05). Furthermore, LTBI macaques had higher plasma IgG reactivity to protein MTB32A (Rv0125) early post Mtb infection (p < 0.05) and increasing airway IgG responses to some proteins over time.

INTERPRETATION

Our results support a protective role of pre-existing mucosal (lung) and systemic IgA to specific Mtb glycan motifs, suggesting that prior exposure to nontuberculous mycobacteria could be protective against TB. They further suggest that IgG to Mtb proteins early post infection could provide an additional protective mechanism. These findings could inform TB vaccine development strategies.

FUNDING

NIH/NIAID AI117927, AI146329, and AI127173 to JMA.

Antibodies as clinical tools for tuberculosis

Tuberculosis (TB) is a leading cause of morbidity and mortality worldwide. Global research efforts to improve TB control are hindered by insufficient understanding of the role that antibodies play in protective immunity and pathogenesis. This impacts knowledge of rational and optimal vaccine design, appropriate diagnostic biomarkers, and development of therapeutics. Traditional approaches for the prevention and diagnosis of TB may be less efficacious in high prevalence, remote, and resource-poor settings. An improved understanding of the immune response to the causative agent of TB, Mycobacterium tuberculosis (Mtb), will be crucial for developing better vaccines, therapeutics, and diagnostics. While memory CD4+ T cells and cells and cytokine interferon gamma (IFN-g) have been the main identified correlates of protection in TB, mounting evidence suggests that other types of immunity may also have important roles. TB serology has identified antibodies and functional characteristics that may help diagnose Mtb infection and distinguish between different TB disease states. To date, no serological tests meet the World Health Organization (WHO) requirements for TB diagnosis, but multiplex assays show promise for improving the sensitivity and specificity of TB serodiagnosis. Monoclonal antibody (mAb) therapies and serum passive infusion studies in murine models of TB have also demonstrated some protective outcomes. However, animal models that better reflect the human immune response to Mtb are necessary to fully assess the clinical utility of antibody-based TB prophylactics and therapeutics. Candidate TB vaccines are not designed to elicit an Mtb-specific antibody response, but evidence suggests BCG and novel TB vaccines may induce protective Mtb antibodies. The potential of the humoral immune response in TB monitoring and control is being investigated and these studies provide important insight into the functional role of antibody-mediated immunity against TB. In this review, we describe the current state of development of antibody-based clinical tools for TB, with a focus on diagnostic, therapeutic, and vaccine-based applications.

Prolonged survival of a patient with active MDR-TB HIV co-morbidity: insights from a Mycobacterium tuberculosis strain with a unique genomic deletion

Coinfection of HIV and multidrug-resistant tuberculosis (MDR-TB) presents significant challenges in terms of the treatment and prognosis of tuberculosis, leading to complexities in managing the disease and impacting the overall outcome for TB patients. This study presents a remarkable case of a patient with MDR-TB and HIV coinfection who survived for over 8 years, despite poor treatment adherence and comorbidities. Whole genome sequencing (WGS) of the infecting Mycobacterium tuberculosis (Mtb) strain revealed a unique genomic deletion, spanning 18 genes, including key genes involved in hypoxia response, intracellular survival, immunodominant antigens, and dormancy. This deletion, that we have called "Del-X," potentially exerts a profound influence on the bacterial physiology and its virulence. Only few similar deletions were detected in other non-related Mtb genomes worldwide. In vivo evolution analysis identified drug resistance and metabolic adaptation mutations and their temporal dynamics during the patient's treatment course.

Genetically encoded transcriptional plasticity underlies stress adaptation in Mycobacterium tuberculosis

Transcriptional regulation is a critical adaptive mechanism that allows bacteria to respond to changing environments, yet the concept of transcriptional plasticity (TP) remains largely unexplored. In this study, we investigate the genome-wide TP profiles of Mycobacterium tuberculosis (Mtb) genes by analyzing 894 RNA sequencing samples derived from 73 different environmental conditions. Our data reveal that Mtb genes exhibit significant TP variation that correlates with gene function and gene essentiality. We also found that critical genetic features, such as gene length, GC content, and operon size independently impose constraints on TP, beyond trans-regulation. By extending our analysis to include two other Mycobacterium species -- M. smegmatis and M. abscessus -- we demonstrate a striking conservation of the TP landscape. This study provides a comprehensive understanding of the TP exhibited by mycobacteria genes, shedding light on this significant, yet understudied, genetic feature encoded in bacterial genomes.

Genetically encoded transcriptional plasticity underlies stress adaptation in Mycobacterium tuberculosis

Transcriptional regulation is a critical adaptive mechanism that allows bacteria to respond to changing environments, yet the concept of transcriptional plasticity (TP) remains largely unexplored. In this study, we investigate the genome-wide TP profiles of Mycobacterium tuberculosis (Mtb) genes by analyzing 894 RNA sequencing samples derived from 73 different environmental conditions. Our data reveal that Mtb genes exhibit significant TP variation that correlates with gene function and gene essentiality. We also found that critical genetic features, such as gene length, GC content, and operon size independently impose constraints on TP, beyond trans-regulation. By extending our analysis to include two other Mycobacterium species -- M. smegmatis and M. abscessus -- we demonstrate a striking conservation of the TP landscape. This study provides a comprehensive understanding of the TP exhibited by mycobacteria genes, shedding light on this significant, yet understudied, genetic feature encoded in bacterial genomes.

Humoral correlates of protection against Mycobacterium tuberculosis following intravenous Bacille Calmette-Guérin vaccination in rhesus macaques

Altering the route of Bacille Calmette-Guérin (BCG) immunization from low-dose intradermal vaccination to high-dose intravenous (IV) vaccination resulted in a high level of protection against Mycobacterium tuberculosis ( Mtb ) infection, providing an opportunity to uncover immune correlates and mechanisms of protection. In addition to strong T cell immunity, IV BCG vaccination was associated with a robust expansion of humoral immune responses that tracked with bacterial control. However, given the near complete protection afforded by high-dose IV BCG immunization, a precise correlate of immune protection was difficult to define. Here we leveraged plasma and bronchoalveolar lavage fluid (BAL) from a cohort of rhesus macaques that received decreasing doses of IV BCG and aimed to define the correlates of immunity across macaques that experienced immune protection or breakthrough infection following Mtb challenge. We show an IV BCG dose-dependent induction of mycobacterial-specific humoral immune responses, both in the plasma and in the airways. Moreover, antibody responses at peak immunogenicity significantly predicted bacterial control following challenge. Multivariate analyses revealed antibody-mediated complement and NK cell activating humoral networks as key functional signatures associated with protective immunity. Collectively, this work extends our understanding of humoral biomarkers and potential mechanisms of IV BCG mediated protection against Mtb .

Mycobacterial Heat Shock Proteins in Sarcoidosis and Tuberculosis

Pathological similarities between sarcoidosis (SA) and tuberculosis (TB) suggest the role of mycobacterial antigens in the etiopathogenesis of SA. The Dubaniewicz group revealed that not whole mycobacteria, but Mtb-HSP70, Mtb-HSP 65, and Mtb-HSP16 were detected in the lymph nodes, sera, and precipitated immune complexes in patients with SA and TB. In SA, the Mtb-HSP16 concentration was higher than that of Mtb-HSP70 and that of Mtb-HSP65, whereas in TB, the Mtb-HSP16 level was increased vs. Mtb-HSP70. A high Mtb-HSP16 level, induced by low dose-dependent nitrate/nitrite (NOx), may develop a mycobacterial or propionibacterial genetic dormancy program in SA. In contrast to TB, increased peroxynitrite concentration in supernatants of peripheral blood mononuclear cell cultures treated with Mtb-HSP may explain the low level of NOx detected in SA. In contrast to TB, monocytes in SA were resistant to Mtb-HSP-induced apoptosis, and CD4+T cell apoptosis was increased. Mtb-HSP-induced apoptosis of CD8+T cells was reduced in all tested groups. In Mtb-HSP-stimulated T cells, lower CD8+γδ+IL-4+T cell frequency with increased TNF-α,IL-6,IL-10 and decreased INF-γ,IL-2,IL-4 production were present in SA, as opposed to an increased presence of CD4+γδ+TCR cells with increased TNF-α,IL-6 levels in TB, vs. controls. Mtb-HSP modulating the level of co-stimulatory molecules, regulatory cells, apoptosis, clonal deletion, epitope spread, polyclonal activation and molecular mimicry between human and microbial HSPs may also participate in the induction of autoimmunity, considered in SA. In conclusion, in different genetically predisposed hosts, the same antigens, e.g., Mtb-HSP, may induce the development of TB or SA, including an autoimmune response in sarcoidosis.

Highly conserved protein Rv1211 in Mycobacterium tuberculosis is a natively unfolded protein that binds to a calmodulin antagonist, trifluoperazine

Rv1211 is a conserved hypothetical protein in Mycobacterium tuberculosis and is required for the growth and pathogenesis of the bacteria. The protein has been suggested as a calmodulin-like calcium-binding protein with an EF-hand motif and as a target of trifluoperazine, a calmodulin antagonist in eukaryotes that inhibits mycobacterial growth. Here, we expressed the recombinant protein of Rv1211 and performed structural and biochemical studies of Rv1211 and its interaction with Ca²⁺ or trifluoperazine. Surprisingly, Rv1211 exhibited an elution property typical of a natively unfolded protein. Subsequent circular dichroism experiments with temperature elevation and trifluoroethanol treatment showed that Rv1211 has unfolded structure. Additional NMR experiment confirmed the unfolded state of the protein and further showed that it does not bind to Ca²⁺. Still, Rv1211 did bind to trifluoperazine, as evidenced by the two-dimensional NMR spectra of ¹⁵N-labeled Rv1211. However, there were no peak shifts upon binding, showing that Rv1211 retained its unfolded state even after the trifluoperazine binding. The residues involved in the binding were clustered in the C-terminal region, as identified by the sequence assignment. Isothermal titration calorimetry showed that the K_d of trifluoperazine-Rv1211 binding is 41 μM and that the stoichiometry is 1 : 2 (Rv1211: trifluoperazine). Our results argue against the suggestion of Rv1211 as a Ca²⁺-binding calmodulin-like protein, and show that Rv1211 is a natively unfolded protein that binds to trifluoperazine. In addition, our results suggest the evidence of the "Fuzziness" in the Rv1211-trifluoperazine interaction that differs from the conventional binding-induced folding of natively unfolded proteins.

The Iron Response of Mycobacterium tuberculosis and Its Implications for Tuberculosis Pathogenesis and Novel Therapeutics

Most pathogenic bacteria require iron for growth. However, this metal is not freely available in the mammalian host. Due to its poor solubility and propensity to catalyze the generation of reactive oxygen species, host iron is kept in solution bound to specialized iron binding proteins. Access to iron is an important factor in the outcome of bacterial infections; iron limitation frequently induces virulence and drives pathogenic interactions with host cells. Here, we review the response of Mycobacterium tuberculosis to changes in iron availability, the relevance of this response to TB pathogenesis, and its potential for the design of new therapeutic interventions.

Role of ATP-Small Heat Shock Protein Interaction in Human Diseases

Adenosine triphosphate (ATP) is an important fuel of life for humans and Mycobacterium species. Its potential role in modulating cellular functions and implications in systemic, pulmonary, and ocular diseases is well studied. Plasma ATP has been used as a diagnostic and prognostic biomarker owing to its close association with disease’s progression. Several stresses induce altered ATP generation, causing disorders and illnesses. Small heat shock proteins (sHSPs) are dynamic oligomers that are dominantly β-sheet in nature. Some important functions that they exhibit include preventing protein aggregation, enabling protein refolding, conferring thermotolerance to cells, and exhibiting anti-apoptotic functions. Expression and functions of sHSPs in humans are closely associated with several diseases like cataracts, cardiovascular diseases, renal diseases, cancer, etc. Additionally, there are some mycobacterial sHSPs like Mycobacterium leprae HSP18 and Mycobacterium tuberculosis HSP16.3, whose molecular chaperone functions are implicated in the growth and survival of pathogens in host species. As both ATP and sHSPs, remain closely associated with several human diseases and survival of bacterial pathogens in the host, therefore substantial research has been conducted to elucidate ATP-sHSP interaction. In this mini review, the impact of ATP on the structure and function of human and mycobacterial sHSPs is discussed. Additionally, how such interactions can influence the onset of several human diseases is also discussed.

Peptide-Based Vaccines for Tuberculosis

Tuberculosis (TB) is an infectious disease caused by Mycobacterium tuberculosis. As a result of the coronavirus disease 2019 (COVID-19) pandemic, the global TB mortality rate in 2020 is rising, making TB prevention and control more challenging. Vaccination has been considered the best approach to reduce the TB burden. Unfortunately, BCG, the only TB vaccine currently approved for use, offers some protection against childhood TB but is less effective in adults. Therefore, it is urgent to develop new TB vaccines that are more effective than BCG. Accumulating data indicated that peptides or epitopes play essential roles in bridging innate and adaptive immunity and triggering adaptive immunity. Furthermore, innovations in bioinformatics, immunoinformatics, synthetic technologies, new materials, and transgenic animal models have put wings on the research of peptide-based vaccines for TB. Hence, this review seeks to give an overview of current tools that can be used to design a peptide-based vaccine, the research status of peptide-based vaccines for TB, protein-based bacterial vaccine delivery systems, and animal models for the peptide-based vaccines. These explorations will provide approaches and strategies for developing safer and more effective peptide-based vaccines and contribute to achieving the WHO's End TB Strategy.

Robust IgM responses following intravenous vaccination with Bacille Calmette-Guérin associate with prevention of Mycobacterium tuberculosis infection in macaques

Development of an effective tuberculosis (TB) vaccine has suffered from an incomplete understanding of the correlates of protection against Mycobacterium tuberculosis (Mtb). Intravenous (i.v.) vaccination with Bacille Calmette-Guérin (BCG) provides nearly complete protection against TB in rhesus macaques, but the antibody response it elicits remains incompletely defined. Here we show that i.v. BCG drives superior antibody responses in the plasma and the lungs of rhesus macaques compared to traditional intradermal BCG administration. While i.v. BCG broadly expands antibody titers and functions, IgM titers in the plasma and lungs of immunized macaques are among the strongest markers of reduced bacterial burden. IgM was also enriched in macaques that received protective vaccination with an attenuated strain of Mtb. Finally, an Mtb-specific IgM monoclonal antibody reduced Mtb survival in vitro. Collectively, these data highlight the potential importance of IgM responses as a marker and mediator of protection against TB.

Insights into the molecular determinants involved in Mycobacterium tuberculosis persistence and their therapeutic implications

The establishment of persistent infections and the reactivation of persistent bacteria to active bacilli are the two hurdles in effective tuberculosis treatment. Mycobacterium tuberculosis, an etiologic tuberculosis agent, adapts to numerous antibiotics and resists the host immune system causing a disease of public health concern. Extensive research has been employed to combat this disease due to its sheer ability to persist in the host system, undetected, waiting for the opportunity to declare itself. Persisters are a bacterial subpopulation that possesses transient tolerance to high doses of antibiotics. There are certain inherent mechanisms that facilitate the persister cell formation in Mycobacterium tuberculosis, some of those had been characterized in the past namely, stringent response, transcriptional regulators, energy production pathways, lipid metabolism, cell wall remodeling enzymes, phosphate metabolism, and proteasome protein degradation. This article reviews the recent advancements made in various in vitro persistence models that assist to unravel the mechanisms involved in the persister cell formation and to hunt for the possible preventive or treatment measures. To tackle the persister population the immunodominant proteins that express specifically at the latent phase of infection can be used for diagnosis to distinguish between the active and latent tuberculosis, as well as to select potential drug or vaccine candidates. In addition, we discuss the genes engaged in the persistence to get more insights into resuscitation and persister cell formation. The in-depth understanding of persistent cells of mycobacteria can certainly unravel novel ways to target the pathogen and tackle its persistence.

Huete S, Vincent AT, Sismeiro O, Legendre R, Varet H, Bussotti G, Lorioux C, Lechat P, Coppée JY, Veyrier FJ, Picardeau M, Benaroudj N. The oxidative stress response of pathogenic Leptospira is controlled by two peroxide stress regulators which putatively cooperate in controlling virulence

Pathogenic Leptospira are the causative agents of leptospirosis, the most widespread zoonotic infectious disease. Leptospirosis is a potentially severe and life-threatening emerging disease with highest burden in sub-tropical areas and impoverished populations. Mechanisms allowing pathogenic Leptospira to survive inside a host and induce acute leptospirosis are not fully understood. The ability to resist deadly oxidants produced by the host during infection is pivotal for Leptospira virulence. We have previously shown that genes encoding defenses against oxidants in L. interrogans are repressed by PerRA (encoded by LIMLP_10155), a peroxide stress regulator of the Fur family. In this study, we describe the identification and characterization of another putative PerR-like regulator (LIMLP_05620) in L. interrogans. Protein sequence and phylogenetic analyses indicated that LIMLP_05620 displayed all the canonical PerR amino acid residues and is restricted to pathogenic Leptospira clades. We therefore named this PerR-like regulator PerRB. In L. interrogans, the PerRB regulon is distinct from that of PerRA. While a perRA mutant had a greater tolerance to peroxide, inactivating perRB led to a higher tolerance to superoxide, suggesting that these two regulators have a distinct function in the adaptation of L. interrogans to oxidative stress. The concomitant inactivation of perRA and perRB resulted in a higher tolerance to both peroxide and superoxide and, unlike the single mutants, a double perRAperRB mutant was avirulent. Interestingly, this correlated with major changes in gene and non-coding RNA expression. Notably, several virulence-associated genes (clpB, ligA/B, and lvrAB) were repressed. By obtaining a double mutant in a pathogenic Leptospira strain, our study has uncovered an interplay of two PerRs in the adaptation of Leptospira to oxidative stress with a putative role in virulence and pathogenicity, most likely through the transcriptional control of a complex regulatory network.

Latent tuberculosis: interaction of virulence factors in Mycobacterium tuberculosis

Tuberculosis (TB) remains a prominent health concern worldwide. Besides extensive research and vaccinations available, attempts to control the pandemic are cumbersome due to the complex physiology of Mycobacterium tuberculosis (Mtb). Alongside the emergence of drug-resistant TB, latent TB has worsened the condition. The tubercle bacilli are unusually behaved and successful with its strategies to modulate genes to evade host immune system and persist within macrophages. Under latent/unfavorable conditions, Mtb conceals itself from immune system and modulates its genes. Among many intracellular modulated genes, important are those involved in cell entry, fatty acid degradation, mycolic acid synthesis, phagosome acidification inhibition, inhibition of phagosome-lysosome complex and chaperon protein modulation. Though the study on these genes date back to early times of TB, an insight on their inter-relation within and to newly evolved genes are still required. This review focuses on the findings and discussions on these genes, possible mechanism, credibility as target for novel drugs and repurposed drugs and their interaction that enables Mtb in survival, pathogenesis, resistance and latency.

Aptamer-Based Diagnostic Systems for the Rapid Screening of TB at the Point-of-Care

The transmission of Tuberculosis (TB) is very rapid and the burden it places on health care systems is felt globally. The effective management and prevention of this disease requires that it is detected early. Current TB diagnostic approaches, such as the culture, sputum smear, skin tuberculin, and molecular tests are time-consuming, and some are unaffordable for low-income countries. Rapid tests for disease biomarker detection are mostly based on immunological assays that use antibodies which are costly to produce, have low sensitivity and stability. Aptamers can replace antibodies in these diagnostic tests for the development of new rapid tests that are more cost effective; more stable at high temperatures and therefore have a better shelf life; do not have batch-to-batch variations, and thus more consistently bind to a specific target with similar or higher specificity and selectivity and are therefore more reliable. Advancements in TB research, in particular the application of proteomics to identify TB specific biomarkers, led to the identification of a number of biomarker proteins, that can be used to develop aptamer-based diagnostic assays able to screen individuals at the point-of-care (POC) more efficiently in resource-limited settings.

Intricate Genetic Programs Controlling Dormancy in Mycobacterium tuberculosis

Mycobacterium tuberculosis (MTB) displays the remarkable ability to transition in and out of dormancy, a hallmark of the pathogen’s capacity to evade the immune system and exploit susceptible individuals. Uncovering the gene regulatory programs that underlie the phenotypic shifts in MTB during disease latency and reactivation has posed a challenge. We develop an experimental system to precisely control dissolved oxygen levels in MTB cultures in order to capture the transcriptional events that unfold as MTB transitions into and out of hypoxia-induced dormancy. Using a comprehensive genome-wide transcription factor binding map and insights from network topology analysis, we identify regulatory circuits that deterministically drive sequential transitions across six transcriptionally and functionally distinct states encompassing more than three-fifths of the MTB genome. The architecture of the genetic programs explains the transcriptional dynamics underlying synchronous entry of cells into a dormant state that is primed to infect the host upon encountering favorable conditions.

Mycobacterium tuberculosis (MTB) persists within the host by counteracting disparate stressors including hypoxia. Peterson et al. report a transcriptional program that coordinates sequential state transitions to drive MTB in and out of hypoxia-induced dormancy. Among varied properties, this program encodes advanced preparedness to infect the host in favorable conditions.

Genome-scale analyses of transcriptional start sites in Mycobacterium marinum under normoxic and hypoxic conditions

Background

Hypoxic stress plays a critical role in the persistence of Mycobacterium tuberculosis (Mtb) infection, but the mechanisms underlying this adaptive response remain ill defined.

Material and methods

In this study, using M. marinum as a surrogate, we analyzed hypoxic responses at the transcriptional level by Cappable-seq and regular RNA-seq analyses.

Results

A total of 6808 transcriptional start sites (TSSs) were identified under normoxic and hypoxic conditions. Among these TSSs, 1112 were upregulated and 1265 were downregulated in response to hypoxic stress. Using SigE-recognized consensus sequence, we identified 59 SigE-dependent promoters and all were upregulated under hypoxic stress, suggesting an important role for SigE in this process. We also compared the performance of Cappable-seq and regular RNA-seq using the same RNA samples collected from normoxic and hypoxic conditions, and confirmed that Cappable-seq is a valuable approach for global transcriptional regulation analyses.

Conclusions

Our results provide insights and information for further characterization of responses to hypoxia in mycobacteria, and prove that Cappable-seq is a valuable approach for global transcriptional studies in mycobacteria.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07572-8.

Mucosal Therapy of Multi-Drug Resistant Tuberculosis With IgA and Interferon-γ

New evidence has been emerging that antibodies can be protective in various experimental models of tuberculosis. Here, we report on protection against multidrug-resistant Mycobacterium tuberculosis (MDR-TB) infection using a combination of the human monoclonal IgA 2E9 antibody against the alpha-crystallin (Acr, HspX) antigen and mouse interferon-gamma in mice transgenic for the human IgA receptor, CD89. The effect of the combined mucosal IgA and IFN-γ; treatment was strongest (50-fold reduction) when therapy was applied at the time of infection, but a statistically significant reduction of lung bacterial load was observed even when the therapy was initiated once the infection had already been established. The protection involving enhanced phagocytosis and then neutrophil mediated killing of infected cells was IgA isotype mediated, because treatment with an IgG version of 2E9 antibody was not effective in human IgG receptor CD64 transgenic mice. The Acr antigen specificity of IgA antibodies for protection in humans has been indicated by their elevated serum levels in latent tuberculosis unlike the lack of IgA antibodies against the virulence-associated MPT64 antigen. Our results represent the first evidence for potential translation of mucosal immunotherapy for the management of MDR-TB.

A multiple T cell epitope comprising DNA vaccine boosts the protective efficacy of Bacillus Calmette-Guérin (BCG) against Mycobacterium tuberculosis

Background

Approximately 80% - 90% of individuals infected with latent Mycobacterium tuberculosis (Mtb) remain protected throughout their life-span. The release of unique, latent-phase antigens are known to have a protective role in the immune response against Mtb. Although the BCG vaccine has been administered for nine decades to provide immunity against Mtb, the number of TB cases continues to rise, thereby raising doubts on BCG vaccine efficacy. The shortcomings of BCG have been associated with inadequate processing and presentation of its antigens, an inability to optimally activate T cells against Mtb, and generation of regulatory T cells. Furthermore, BCG vaccination lacks the ability to eliminate latent Mtb infection. With these facts in mind, we selected six immunodominant CD4 and CD8 T cell epitopes of Mtb expressed during latent, acute, and chronic stages of infection and engineered a multi-epitope-based DNA vaccine (C6).

Result

BALB/c mice vaccinated with the C6 construct along with a BCG vaccine exhibited an expansion of both CD4 and CD8 T cell memory populations and augmented IFN-γ and TNF-α cytokine release. Furthermore, enhancement of dendritic cell and macrophage activation was noted. Consequently, illustrating the elicitation of immunity that helps in the protection against Mtb infection; which was evident by a significant reduction in the Mtb burden in the lungs and spleen of C6 + BCG administered animals.

Conclusion

Overall, the results suggest that a C6 + BCG vaccination approach may serve as an effective vaccination strategy in future attempts to control TB.

MiRNAs in tuberculosis: Their decisive role in the fate of TB

Tuberculosis (TB) is one of the most lethal global infectious diseases. Despite the availability of much higher levels of technology in health and medicine, tuberculosis still remains a serious global health problem. Mycobacterium tuberculosis has the capacity for prolonged survival inside macrophages by exploiting host metabolic and energy pathways and perturbing autophagy and apoptosis of infected cells. The mechanism(s) underlying this process are not completely understood but evidence suggests that mycobacteria subvert the host miRNA network to enable mycobacterial survival. We present here a comprehensive review on the role of miRNAs in TB immune escape mechanisms and the potential for miRNA-based TB therapeutics. Further validation studies are required to (i) elucidate the precise effect of TB on host miRNAs, (ii) determine the inhibition of mycobacterial burden using miRNA-based therapies and (iii) identify novel miRNA biomarkers that may prove useful in TB diagnosis and treatment monitoring.

Small but mighty: a functional look at bacterial sHSPs

Small heat shock proteins (sHSPs) are widespread in every kingdom of life, being indispensable for protein quality control networks. Alongside canonical chaperone functions, sHSPs seem to have been a very plastic scaffold for acquiring multiple related functions across evolution. This review aims to summarize what is known about sHSPs functioning in the Bacteria Kingdom.

Understanding the early host immune response against Mycobacterium tuberculosis

Generation of immune response is a crucial activity of host defense against any microbial attack. When facultative organism Mycobacterium tuberculosis (MTB) invades its host, various pathways are activated in the host to mount immune responses against invading pathogen for nullifying its actions. During this host-pathogen interaction, interplay of complex network of cytokines and chemokines, initiation of phagocytosis, and formation of granuloma play an important role in containing MTB infections at host side. Simultaneously, MTB also evolves a plethora of specialized mechanisms to evade the host’s killing cascades on other side, and during this bilateral cross-talk, many mycobacterial products play crucial role in survival of MTB inside the host. Hence, a better understanding of these phenomena is necessary not only for getting clear picture of pathogenesis of MTB, but also for developing effective, preventive, and therapeutic modalities against the pathogen. With some suggestions on future work, an insight into diversity of immune response of host against MTB was provided in the present review.

Latent Tuberculosis Infection (LTBI) and Its Potential Targets: An Investigation into Dormant Phase Pathogens

One-third of the world's population harbours the latent tuberculosis infection (LTBI) with a lifetime risk of reactivation. Although, the treatment of LTBI relies significantly on the first-line therapy, identification of novel drug targets and therapies are the emerging focus for researchers across the globe. The current review provides an insight into the infection, diagnostic methods and epigrammatic explanations of potential molecular targets of dormant phase bacilli. This study also includes current preclinical and clinical aspects of tubercular infections and new approaches in antitubercular drug discovery.

Emerging Themes for the Role of Antibodies in Tuberculosis

The best way to debunk a scientific dogma is to throw irrefutable evidence at it. This is especially true if the dogma in question has been nurtured over many decades, as is the case with the apparent redundancy of antibodies (Abs) against intracellular pathogens. Although not fully compelling yet, that ‘hard core’ evidence is nevertheless now slowly beginning to emerge. This is true for several clinically relevant infections but none more so than Mycobacterium tuberculosis, the archetype intracellular pathogen that poses a great health challenge to the mankind. Here, prompted by a spate of recent high-profile reports on the effects of Abs in various experimental models of tuberculosis, we step back and take a critical look at the progress that has been made in the last 5 years and highlight some of the strengths and shortcomings of the presented evidence. We conclude that the tide of the opinion has begun to turn in favour of Abs but we also caution against overinterpreting the currently available limited evidence. For, until definitive evidence that can withstand even the most rigorous of experimental tests is produced, the dogma may yet survive. Or indeed, we may find that the truth is hidden somewhere in between the dogma and the unfulfilled scientific prophecy.

Tissue Transparency In Vivo

In vivo tissue transparency in the visible light spectrum is beneficial for many research applications that use optical methods, whether it involves in vivo optical imaging of cells or their activity, or optical intervention to affect cells or their activity deep inside tissues, such as brain tissue. The classical view is that a tissue is transparent if it neither absorbs nor scatters light, and thus absorption and scattering are the key elements to be controlled to reach the necessary transparency. This review focuses on the latest genetic and chemical approaches for the decoloration of tissue pigments to reduce visible light absorption and the methods to reduce scattering in live tissues. We also discuss the possible molecules involved in transparency.

A Case for Antibodies as Mechanistic Correlates of Immunity in Tuberculosis

Tuberculosis infects one quarter of the world's population and is the leading cause of death by a single infectious agent, responsible for a reported 1.3 million deaths in 2017. While Mycobacterium tuberculosis is treatable with antibiotic therapy, the increased prevalence of drug resistance, coupled with the variable efficacy of the only widely approved vaccine, has highlighted the need for creative approaches to therapeutic and vaccine development. Historically, a productive immune response to M. tuberculosis has been thought to be nearly entirely cell-mediated, with humoral immunity being largely dismissed. However, in this review, we will discuss the historical skepticism surrounding the role of the humoral immune response to M. tuberculosis, and examine more recent evidence suggesting that antibodies may play a valuable role in host defense against the pathogen. Despite the amount of data portraying antibodies in a negative light, emerging data have begun to highlight the unexpected role of antibodies in M. tuberculosis control. Specifically, it has become clear that antibody features of both the variable and constant domain (Fc) ultimately determine the extent to which antibodies modulate disease. Thus, a more precise definition of the antigen-binding and innate immune recruiting functions of antibodies that contribute to M. tuberculosis restriction, are sure to help guide the development of next-generation therapeutics and vaccines to curb this global epidemic.

Dodecameric structure of a small heat shock protein from Mycobacterium marinum M

Small heat shock proteins (sHSPs) are ATP-independent molecular chaperones present ubiquitously in all kingdoms of life. Their low molecular weight subunits associate to form higher order structures. Under conditions of stress, sHSPs prevent aggregation of substrate proteins by undergoing rapid changes in their conformation or stoichiometry. Polydispersity and dynamic nature of these proteins have made structural investigations through crystallography a daunting task. In pathogens like Mycobacteria, sHSPs are immuno-dominant antigens, enabling survival of the pathogen within the host and contributing to disease persistence. We characterized sHSPs from Mycobacterium marinum M and determined the crystal structure of one of these. The protein crystallized in three different conditions as dodecamers, with dimers arranged in a tetrahedral fashion to form a closed cage-like architecture. Interestingly, we found a pentapeptide bound to the dodecamers revealing one of the modes of sHSP-substrate interaction. Further, we have observed that ATP inhibits the chaperoning activity of the protein.

Modelling a Silent Epidemic: A Review of the In Vitro Models of Latent Tuberculosis

Tuberculosis (TB) is the primary cause of death by a single infectious agent; responsible for around two million deaths in 2016. A major virulence factor of TB is the ability to enter a latent or Non-Replicating Persistent (NRP) state which is presumed untreatable. Approximately 1.7 billion people are latently infected with TB and on reactivation many of these infections are drug resistant. As the current treatment is ineffective and diagnosis remains poor, millions of people have the potential to reactivate into active TB disease. The immune system seeks to control the TB infection by containing the bacteria in a granuloma, where it is exposed to stressful anaerobic and nutrient deprived conditions. It is thought to be these environmental conditions that trigger the NRP state. A number of in vitro models have been developed that mimic conditions within the granuloma to a lesser or greater extent. These different models have all been utilised for the research of different characteristics of NRP Mycobacterium tuberculosis, however their disparity in approach and physiological relevance often results in inconsistencies and a lack of consensus between studies. This review provides a summation of the different NRP models and a critical analysis of their respective advantages and disadvantages relating to their physiological relevance.

A Systematic Review on Novel Mycobacterium tuberculosis Antigens and Their Discriminatory Potential for the Diagnosis of Latent and Active Tuberculosis

Background: Current immunodiagnostic tests for tuberculosis (TB) are based on the detection of an immune response toward mycobacterial antigens injected into the skin or following an in-vitro simulation in interferon gamma-release assays. Both tests have limited sensitivity and are unable to differentiate between tuberculosis infection (LTBI) and active tuberculosis disease (aTB). To overcome this, the use of novel Mycobacterium tuberculosis (M. tuberculosis) stage-specific antigens for the diagnosis of LTBI and aTB has gained interest in recent years. This review summarizes current evidence on novel antigens used for the immunodiagnosis of tuberculosis and discrimination of LTBI and aTB. In addition, results on measured biomarkers after stimulation with novel M. tuberculosis antigens were also reviewed.

Methods: A systematic literature review was performed in Pubmed, EMBASE and web of science searching articles from 2000 up until December 2017. Only articles reporting studies in humans using novel antigens were included.

Results: Of 1,533 articles screened 34 were included in the final analysis. A wide range of novel antigens expressed during different stages and types of LTBI and aTB have been assessed. M. tuberculosis antigens Rv0081, Rv1733c, Rv1737c, Rv2029c, Rv2031 and Rv2628, all encoded by the dormancy of survival regulon, were among the most widely studied antigens and showed the most promising results. These antigens have been shown to have best potential for differentiating LTBI from aTB. In addition, several studies have shown that the inclusion of cytokines other than IFN-γ can improve sensitivity.

Conclusion: There is limited evidence that the inclusion of novel antigens as well as the measurement of other biomarkers than IFN-γ may improve sensitivity and may lead to a discrimination of LTBI from aTB.

Mycobacterium tuberculosis host cell interaction: Role of latency associated protein Acr-1 in differential modulation of macrophages

Mycobacterium tuberculosis (M.tb) contrives intracellular abode as a strategy to combat antibody onslaught. Additionally, to thrive against hostile ambiance inside host macrophages, the pathogen inhibits phago-lysosomal fusion. Finally, to further defy host cell offensives, M.tb opts for dormant phase, where it turns off or slows down most of its metabolic process as an added stratagem. While M.tb restrains most of its metabolic activities during dormancy, surprisingly latency-associated alpha-crystallin protein (Acr-1) is expressed most prominently during this phase. Interestingly, several previous studies described the potential of Acr-1 to induce the robust immuno-prophylactic response in the immunized host. It is intriguing to comprehend the apparent discrepancy that the microbe M.tb overexpresses a protein that has the potential to prime host immune system against the pathogen itself. Keeping this apparent ambiguity into consideration, it is imperative to unravel intricacies involved in the exploitation of Acr-1 by M.tb during its interaction with host immune cells. The present study suggests that Acr-1 exhibits diverse role in the maturation of macrophages (MΦs) and related immunological responses. The early encounter of bone marrow derived immune cells (pre-exposure during differentiation to MΦs) with Acr-1 (AcrMΦpre), results in hampering of their function. The pre-exposure of naïve MΦs with Acr-1 induces the expression of TIM-3 and IL-10. In contrast, exposure of fully differentiated MΦs to Acr-1 results in their down-modulation and induces the phosphorylation of STAT-1 and STAT-4 in host MΦs. Furthermore, Acr-1 mediated activation of MΦs results in the induction of Th1 and Th17 phenotype by activated T lymphocyte.

Ursolic acid and carvacrol may be potential inhibitors of dormancy protein small heat shock protein16.3 of Mycobacterium tuberculosis

Small heat shock protein16.3 (sHSP16.3) is a crucial protein for survival of Mycobacterium tuberculosis (MTB) in its host. Besides, this protein acts as a molecular chaperone during stress and is indispensable for MTB's growth, virulence and cell-wall thickening. sHSP16.3 is also a promising candidate for vaccine, serodiagnosis and drug design as well. In the present study, we have targeted sHSP16.3 with two phytochemicals, namely ursolic acid and carvacrol using in silico approach. Molecular docking analysis showed that both phytochemicals (ursolic acid and carvacrol) have docked with sHSP16.3 and shown tendency to inhibit the function of this vital protein of MTB. In addition, both compounds have exhibited strong compatibility with sHSP16.3 during whole 60 ns duration of molecular dynamics simulation. Further, the molecular mechanic/generalized Born/Poisson-Boltzmann surface area (MM/G/P/BSA) free energies were calculated which showed that both phytocompounds have stable and favourable binding energies causing strong binding with binding site of sHSP16.3. Taking together, the data of present study suggest that both phytocompounds may be potential inhibitor of sHSP16.3 of MTB and a best alternative to standard anti-tuberculosis drugs.

Advances in the development of molecular genetic tools for Mycobacterium tuberculosis

Mycobacterium tuberculosis, a clinically relevant Gram-positive bacterium of great clinical relevance, is a lethal pathogen owing to its complex physiological characteristics and development of drug resistance. Several molecular genetic tools have been developed in the past few decades to study this microorganism. These tools have been instrumental in understanding how M. tuberculosis became a successful pathogen. Advanced molecular genetic tools have played a significant role in exploring the complex pathways involved in M. tuberculosis pathogenesis. Here, we review various molecular genetic tools used in the study of M. tuberculosis. Further, we discuss the applications of clustered regularly interspaced short palindromic repeat interference (CRISPRi), a novel technology recently applied in M. tuberculosis research to study target gene functions. Finally, prospective outcomes of the applications of molecular techniques in the field of M. tuberculosis genetic research are also discussed.

Fluorescent Mycobacterium tuberculosis reporters: illuminating host-pathogen interactions

The pathogenesis of Mycobacterium tuberculosis (Mtb) is intrinsically linked to its intimate and enduring interaction with its host, and understanding Mtb-host interactions at a molecular level is critical to attempts to decrease the significant burden of tuberculosis disease. The marked heterogeneity that exists in lesion progression and outcome during Mtb infection necessitates the development of methods that enable in situ analyses of Mtb biology and host response within the spatial context of tissue structure. Fluorescent reporter Mtb strains have thus come to the forefront as an approach with broad utility for the study of the Mtb-host interface, enabling visualization of the bacteria during infection, and contributing to the discovery of several facets such as non-uniformity in microenvironments and Mtb physiology in vivo, and their relation to the host immune response or therapeutic intervention. We review here the different types of fluorescent reporters and ways in which they have been utilized in Mtb studies, and expand on how they may further be exploited in combination with novel imaging and other methodologies to illuminate key aspects of Mtb-host interactions.

Expression of Rv2031c-Rv2626c fusion protein in Mycobacterium smegmatis enhances bacillary survival and modulates innate immunity in macrophages

Dormancy-associated antigens encoded by the dormancy survival regulon (DosR) genes are required for survival of Mycobacterium tuberculosis (Mtb) in macrophages. However, mechanisms underlying survival of Mtb in macrophages remains to be elucidated. A recombinant Mycobacterium smegmatis strain (rMs) expressing a fusion protein of two dormancy‑associated antigens Rv2031c and Rv2626c from Mtb was constructed in the present study. In an in vitro culture, growth rate of rMs was lower compared with Ms. A total of 24 h following infection of murine macrophages with rMs or Ms, percentage of viable cells decreased and the number of bacteria in viable cells increased compared with Ms, demonstrating that virulence and intracellular survival of rMs were enhanced. Compared with macrophages infected with Ms, necrosis of macrophages infected with rMs was increased, while apoptosis was inhibited. Macrophages infected with rMs secreted more interferon‑γ and interleukin‑6, but fewer nitric oxide and tumor necrosis factor‑α, compared with macrophages infected with Ms. The present study demonstrated that the fusion protein composed of dormancy‑associated antigens Rv2031c and Rv2626c in Ms serves a physiological function of a dormancy‑associated antigen and modulates innate immunity of host macrophages, therefore favoring intracellular bacillary survival.