Tuberculosis pathogenesis and immunity

BCG Against SARS-CoV-2: Second Youth of an Old Age Vaccine?

The sudden outbreak of the COVID-19 pandemic, caused by SARS-CoV-2, has put the whole world into a difficult situation, asking for the immediate development of therapeutics and vaccines against the disease. Bacillus Calmette–Guérin (BCG), an attenuated strain of Mycobacterium bovis, has been administered for decades in many countries against tuberculosis. Today, when a solution against SARS-CoV-2 is urgently needed, the BCG vaccine has again come into the limelight owing to its earlier prevention of non-specific diseases. Data suggest a higher mortality rate of COVID-19 in non-BCG vaccinated countries, whereas the nations opting for BCG immunization have a comparatively lower mortality rate. The BCG vaccine is known to induce ‘trained immunity’ and generate ‘non-specific’ heterologous immune responses. It can confer anti-viral immunity by eliciting the production of pro-inflammatory cytokines, IL-6, TNF-α, IFN-γ, and IL-1β. Though the initial results look promising, a long trail still needs to be followed to avoid false promises. The accuracy of nationwide data, the role of an already activated immune system against ‘cytokine storms’, optimization and timing of vaccine dosage, and balancing demand-supply are some of the relevant issues that must be resolved before reaching a final conclusion.

Innate type 1 immune response, but not IL-17 cells control tuberculosis infection

The role of the innate immune response and host resistance to Mycobacterium tuberculosis infection (TB) is reviewed. Based on our data and the abundant literature, an early type 1 immune response is critical for infection control, while ILC3 and Th17 cells seem to be dispensable. Indeed, in M. tuberculosis infected mice, transcriptomic levels of Il17, Il17ra, Il22 and Il23a were not significantly modified as compared to controls, suggesting a limited role of IL-17 and IL-22 pathways in TB infection control. Neutralization of IL-17A or IL-17F did not affect infection control either. Ongoing clinical studies with IL-17 neutralizing antibodies show high efficacy in patients with psoriasis without increased incidence of TB infection or reactivation. Therefore, both experimental studies in mice and clinical trials in human patients suggest no risk of TB infection or reactivation by therapeutic IL-17 antibodies, unlike by TNF.

Genetics and evolution of tuberculosis pathogenesis: New perspectives and approaches

Tuberculosis is the most lethal infectious disease globally, but the vast majority of people who are exposed to the primary causative pathogen, Mycobacterium tuberculosis (MTB), do not develop active disease. Most people do, however, show signs of infection that remain throughout their lifetimes. In this review, we develop a framework that describes several possible transitions from pathogen exposure to TB disease and reflect on the genetics studies to address many of these. The evidence strongly supports a human genetic component for both infection and active disease, but many of the existing studies, including some of our own, do not clearly delineate what transition(s) is being explicitly examined. This can make interpretation difficult in terms of why only some people develop active disease. Nonetheless, both linkage peaks and associations with either active disease or latent infection have been identified. For transition to active disease, pathways defined as active TB altered T and B cell signaling in rheumatoid arthritis and T helper cell differentiation are significantly associated. Pathways that affect transition from exposure to infection are less clear-cut, as studies of this phenotype are less common, and a primary response, if it exists, is not yet well defined. Lastly, we discuss the role that interaction between the MTB lineage and human genetics can play in TB disease, especially severity. Severity of TB is at present the only way to study putative co-evolution between MTB and humans as it is impossible in the absence of disease to know the MTB lineage(s) to which an individual has been exposed. In addition, even though severity has been defined in multiple heterogeneous ways, it appears that MTB-human co-evolution may shape pathogenicity. Further analysis of co-evolution, requiring careful analysis of paired samples, may be the best way to completely assess the genetic basis of TB.

The Echo of Pulmonary Tuberculosis: Mechanisms of Clinical Symptoms and Other Disease-Induced Systemic Complications

Clinical symptoms of active tuberculosis (TB) can range from a simple cough to more severe reactions, such as irreversible lung damage and, eventually, death, depending on disease progression. In addition to its clinical presentation, TB has been associated with several other disease-induced systemic complications, such as hyponatremia and glucose intolerance. Here, we provide an overview of the known, although ill-described, underlying biochemical mechanisms responsible for the clinical and systemic presentations associated with this disease and discuss novel hypotheses recently generated by various omics technologies. This summative update can assist clinicians to improve the tentative diagnosis of TB based on a patient's clinical presentation and aid in the development of improved treatment protocols specifically aimed at restoring the disease-induced imbalance for overall homeostasis while simultaneously eradicating the pathogen. Furthermore, future applications of this knowledge could be applied to personalized diagnostic and therapeutic options, bettering the treatment outcome and quality of life of TB patients.

Fighting Persistence: How Chronic Infections with Mycobacterium tuberculosis Evade T Cell-Mediated Clearance and New Strategies To Defeat Them

Chronic bacterial infections are caused by pathogens that persist within their hosts and avoid clearance by the immune system. Treatment and/or detection of such pathogens is difficult, and the resulting pathologies are often deleterious or fatal. There is an urgent need to develop protective vaccines and host-directed therapies that synergize with antibiotics to prevent pathogen persistence and infection-associated pathologies. However, many persistent pathogens, such as Mycobacterium tuberculosis, actively target the very host pathways activated by vaccination. These immune evasion tactics blunt the effectiveness of immunization strategies and are impeding progress to control these infections throughout the world. Therefore, it is essential that M. tuberculosis immune evasion-related pathogen virulence strategies are considered to maximize the effectiveness of potential new treatments. In this review, we focus on how Mycobacterium tuberculosis infects antigen-presenting cells and evades effective immune clearance by the adaptive response through (i) manipulating antigen presentation, (ii) repressing T cell-activating costimulatory molecules, and (iii) inducing ligands that drive T cell exhaustion. In this context, we will examine the challenges that bacterial virulence strategies pose to developing new vaccines. We will then discuss new approaches that will help dissect M. tuberculosis immune evasion mechanisms and devise strategies to bypass them to promote long-term protection and prevent disease progression.

Host cytosolic RNA sensing pathway promotes T Lymphocyte-mediated mycobacterial killing in macrophages

Mycobacterial infection leads to activation of the RIG-I/MAVS/TBK1 RNA sensing pathway in macrophages but the consequences of this activation remains poorly defined. In this study, we determined that activation of this RNA sensing pathway stimulates ICAM-1 expression in M.avium-infected macrophage through the inhibition of the E3 ubiquitin ligase CRL4COP1/DET1. CRL4 when active targets the transcription factor ETV5 for degradation by the ubiquitin-proteasome system. In the absence of the ETV5 transcription factor, ICAM-1 expression is significantly decreased. The M.avium-induced ICAM-1 production is required for the formation of immune synapse between infected macrophages and antigen-specific CD4+ T lymphocytes, and is essential for CD4+ T lymphocyte-mediated mycobacterial killing in vitro and in mice. This study demonstrates a previously undefined mechanism by which a host cytosolic RNA sensing pathway contributes to the interplay between mycobacteria infected macrophages and antigen-specific T lymphocytes.

Early cell-autonomous accumulation of neutral lipids during infection promotes mycobacterial growth

Lipids represent an important source of nutrition for infecting mycobacteria, accumulating within the necrotic core of granulomas and present in foamy macrophages associated with mycobacterial infection. In order to better understand the timing, process and importance of lipid accumulation, we developed methods for direct in vivo visualization and quantification of this process using the zebrafish-M. marinum larval model of infection. We find that neutral lipids accumulate cell-autonomously in mycobacterium-infected macrophages in vivo during early infection, with detectable levels of accumulation by two days post-infection. Treatment with ezetimibe, an FDA-approved drug, resulted in decreased levels of free cholesterol and neutral lipids, and a reduction of bacterial growth in vivo. The effect of ezetimibe in reducing bacterial growth was dependent on the mce4 operon, a key bacterial determinant of lipid utilization. Thus, in vivo, lipid accumulation can occur cell-autonomously at early timepoints of mycobacterial infection, and limitation of this process results in decreased bacterial burden.

Research Advances in How the cGAS-STING Pathway Controls the Cellular Inflammatory Response

Double-stranded DNA (dsDNA) sensor cyclic-GMP-AMP synthase (cGAS) along with the downstream stimulator of interferon genes (STING) acting as essential immune-surveillance mediators have become hot topics of research. The intrinsic function of the cGAS-STING pathway facilitates type-I interferon (IFN) inflammatory signaling responses and other cellular processes such as autophagy, cell survival, senescence. cGAS-STING pathway interplays with other innate immune pathways, by which it participates in regulating infection, inflammatory disease, and cancer. The therapeutic approaches targeting this pathway show promise for future translation into clinical applications. Here, we present a review of the important previous works and recent advances regarding the cGAS-STING pathway, and provide a comprehensive understanding of the modulatory pattern of the cGAS-STING pathway under multifarious pathologic states.

Silver Nanoparticles for the Therapy of Tuberculosis

Rapid emergence of aggressive, multidrug-resistant Mycobacteria strain represents the main cause of the current antimycobacterial-drug crisis and status of tuberculosis (TB) as a major global health problem. The relatively low-output of newly approved antibiotics contributes to the current orientation of research towards alternative antibacterial molecules such as advanced materials. Nanotechnology and nanoparticle research offers several exciting new-concepts and strategies which may prove to be valuable tools in improving the TB therapy. A new paradigm in antituberculous therapy using silver nanoparticles has the potential to overcome the medical limitations imposed in TB treatment by the drug resistance which is commonly reported for most of the current organic antibiotics. There is no doubt that AgNPs are promising future therapeutics for the medication of mycobacterial-induced diseases but the viability of this complementary strategy depends on overcoming several critical therapeutic issues as, poor delivery, variable intramacrophagic antimycobacterial efficiency, and residual toxicity. In this paper, we provide an overview of the pathology of mycobacterial-induced diseases, andhighlight the advantages and limitations of silver nanoparticles (AgNPs) in TB treatment.

The Lipid Virulence Factors of Mycobacterium tuberculosis Exert Multilayered Control over Autophagy-Related Pathways in Infected Human Macrophages

Autophagy is an important innate immune defense mechanism that controls Mycobacterium tuberculosis (Mtb) growth inside macrophages. Autophagy machinery targets Mtb-containing phagosomes via xenophagy after damage to the phagosomal membrane due to the Type VII secretion system Esx-1 or via LC3-associated phagocytosis without phagosomal damage. Conversely, Mtb restricts autophagy-related pathways via the production of various bacterial protein factors. Although bacterial lipids are known to play strategic functions in Mtb pathogenesis, their role in autophagy manipulation remains largely unexplored. Here, we report that the lipid virulence factors sulfoglycolipids (SLs) and phthiocerol dimycocerosates (DIMs) control autophagy-related pathways through distinct mechanisms in human macrophages. Using knock-out and knock-in mutants of Mtb and Mycobacterium bovis BCG (Bacille Calmette Guerin) and purified lipids, we found that (i) Mtb mutants with DIM and SL deficiencies promoted functional autophagy via an MyD88-dependent and phagosomal damage-independent pathway in human macrophages; (ii) SLs limited this pathway by acting as TLR2 antagonists; (iii) DIMs prevented phagosomal damage-independent autophagy while promoting Esx-1-dependent xenophagy; (iv) and DIMs, but not SLs, limited the acidification of LC3-positive Mtb compartments. In total, our study reveals an unexpected and intricate role for Mtb lipid virulence factors in controlling autophagy-related pathways in human macrophages, thus providing further insight into the autophagy manipulation tactics deployed by intracellular bacterial pathogens.

Immunology of Mycobacterium tuberculosis Infections

Tuberculosis (TB) is a serious global public health challenge that results in significant morbidity and mortality worldwide. TB is caused by infection with the bacilli Mycobacterium tuberculosis (M. tuberculosis), which has evolved a wide variety of strategies in order to thrive within its host. Understanding the complex interactions between M. tuberculosis and host immunity can inform the rational design of better TB vaccines and therapeutics. This chapter covers innate and adaptive immunity against M. tuberculosis infection, including insights on bacterial immune evasion and subversion garnered from animal models of infection and human studies. In addition, this chapter discusses the immunology of the TB granuloma, TB diagnostics, and TB comorbidities. Finally, this chapter provides a broad overview of the current TB vaccine pipeline.

Lack of association between polymorphism of IL-2 -330T/G and pulmonary tuberculosis among Caucasians

This meta-analysis was conducted to assess the consistency and strength of the relationship between polymorphism of IL-2 -330T/G and susceptibility to pulmonary tuberculosis (TB). PubMed, Web of Knowledge and CNKI were searched to find eligible studies about the relationship between IL-2 -330T/G polymorphism and susceptibility to pulmonary TB. A total of eight studies comprising 971 cases and 1519 controls were grouped together for the purpose of elucidating the relationship between polymorphism of IL-2 -330T/G and pulmonary TB susceptibility. The allele model (G vs. T: odds ratio (OR) = 1.34; 95% confidence interval (CI) 1.05–1.71, P_het = 0.001) and the recessive model (GG+GT vs. TT: OR = 1.60; 95% CI 1.08–2.38, P_het = 0.0001) showed an increased risk of development of pulmonary TB. However, the homozygous model (GG vs. TT: OR = 1.74; 95% CI 0.98–3.09, P_het = 0.0005) and the dominant model (GG vs. TT + TG: OR = 1.30; 95% CI = 0.80-2.14, P_het =  0.001) failed to show an increased incidence of pulmonary TB. When analysis was stratified by ethnicity, no obvious associations were identified in the Caucasian subgroup under all four genetic models. Additionally, heterogeneity disappeared in the analysis of Caucasian subgroup. Our combined data suggested that there was no association between IL-2 -330T/G polymorphism and pulmonary TB among Caucasians.

7-oxo-DHEA enhances impaired M. tuberculosis-specific T cell responses during HIV-TB coinfection

BACKGROUND

Mycobacterium tuberculosis (Mtb) is the causative agent of tuberculosis (TB), affecting approximately one third of the world's population. Development of an adequate immune response will determine disease progression or progress to chronic infection. Risk of developing TB among human immunodeficiency virus (HIV)-coinfected patients (HIV-TB) is 20-30 times higher than those without HIV infection, and a synergistic interplay between these two pathogens accelerates the decline in immunological functions. TB treatment in HIV-TB coinfected persons is challenging and it has a prolonged duration, mainly due to the immune system failure to provide an adequate support for the therapy. Therefore, we aimed to study the role of the hormone 7-oxo-dehydroepiandrosterone (7-OD) as a modulator of anti-tuberculosis immune responses in the context of HIV-TB coinfection.

METHODS

A cross-sectional study was conducted among HIV-TB patients and healthy donors (HD). We characterized the ex vivo phenotype of CD4 + T cells and also evaluated in vitro antigen-specific responses by Mtb stimulation of peripheral blood mononuclear cells (PBMCs) in the presence or absence of 7-OD. We assessed lymphoproliferative activity, cytokine production and master transcription factor profiles.

RESULTS

Our results show that HIV-TB patients were not able to generate successful anti-tubercular responses in vitro compared to HD, as reduced IFN-γ/IL-10 and IFN-γ/IL-17A ratios were observed. Interestingly, treatment with 7-OD enhanced Th1 responses by increasing Mtb-induced proliferation and the production of IFN-γ and TNF-α over IL-10 levels. Additionally, in vitro Mtb stimulation augmented the frequency of cells with a regulatory phenotype, while 7-OD reduced the proportion of these subsets and induced an increase in CD4 + T-bet+ (Th1) subpopulation, which is associated with clinical data linked to an improved disease outcome.

CONCLUSIONS

We conclude that 7-OD modifies the cytokine balance and the phenotype of CD4 + T cells towards a more favorable profile for mycobacteria control. These results provide new data to delineate novel treatment approaches as co-adjuvant for the treatment of TB.

C-type Lectins in Immunity to Lung Pathogens

The respiratory tract is tasked with responding to a constant and vast influx of foreign agents. It acts as an important first line of defense in the innate immune system and as such plays a crucial role in preventing the entry of invading pathogens. While physical barriers like the mucociliary escalator exert their effects through the clearance of these pathogens, diverse and dynamic cellular mechanisms exist for the activation of the innate immune response through the recognition of pathogen-associated molecular patterns (PAMPs). These PAMPs are recognized by pattern recognition receptors (PRRs) that are expressed on a number of myeloid cells such as dendritic cells, macrophages, and neutrophils found in the respiratory tract. C-type lectin receptors (CLRs) are PRRs that play a pivotal role in the innate immune response and its regulation to a variety of respiratory pathogens such as viruses, bacteria, and fungi. This chapter will describe the function of both activating and inhibiting myeloid CLRs in the recognition of a number of important respiratory pathogens as well as the signaling events initiated by these receptors.

Type 2 Diabetes Mellitus and Altered Immune System Leading to Susceptibility to Pathogens, Especially Mycobacterium tuberculosis

There has been an alarming increase in the incidence of Type 2 Diabetes Mellitus (T2DM) worldwide. Uncontrolled T2DM can lead to alterations in the immune system, increasing the risk of susceptibility to infections such as Mycobacterium tuberculosis (M. tb). Altered immune responses could be attributed to factors such as the elevated glucose concentration, leading to the production of Advanced Glycation End products (AGE) and the constant inflammation, associated with T2DM. This production of AGE leads to the generation of reactive oxygen species (ROS), the use of the reduced form of nicotinamide adenine dinucleotide phosphate (NADPH) via the Polyol pathway, and overall diminished levels of glutathione (GSH) and GSH-producing enzymes in T2DM patients, which alters the cytokine profile and changes the immune responses within these patients. Thus, an understanding of the intricate pathways responsible for the pathogenesis and complications in T2DM, and the development of strategies to enhance the immune system, are both urgently needed to prevent co-infections and co-morbidities in individuals with T2DM.

Viral, bacterial, and fungal infections of the oral mucosa: Types, incidence, predisposing factors, diagnostic algorithms, and management

For millions of years, microbiota residing within us, including those in the oral cavity, coexisted in a harmonious symbiotic fashion that provided a quintessential foundation for human health. It is now clear that disruption of such a healthy relationship leading to microbial dysbiosis causes a wide array of infections, ranging from localized, mild, superficial infections to deep, disseminated life-threatening diseases. With recent advances in research, diagnostics, and improved surveillance we are witnessing an array of emerging and re-emerging oral infections and orofacial manifestations of systemic infections. Orofacial infections may cause significant discomfort to the patients and unnecessary economic burden. Thus, the early recognition of such infections is paramount for holistic patient management, and oral clinicians have a critical role in recognizing, diagnosing, managing, and preventing either new or old orofacial infections. This paper aims to provide an update on current understanding of well-established and emerging viral, bacterial, and fungal infections manifesting in the human oral cavity.

Notch4 Negatively Regulates the Inflammatory Response to Mycobacterium tuberculosis Infection by Inhibiting TAK1 Activation

Tuberculosis, caused by Mycobacterium tuberculosis infection, remains a global threat to human health, but knowledge of the molecular mechanisms underlying the pathogenesis of tuberculosis is still limited. Although Notch4, a member of the Notch receptor family, is involved in the initiation of mammary tumors, its function in M. tuberculosis infection remains unclear. In this study, we found that Notch4-deficient mice were more resistant to M. tuberculosis infection, with a much lower bacterial burden and fewer pathological changes in the lungs. Notch4 inhibited M. tuberculosis-induced production of proinflammatory cytokines by interaction with TAK1 and inhibition of its activation. Furthermore, we found that Notch intracellular domain 4 prevented TRAF6 autoubiquitination and suppressed TRAF6-mediated TAK1 polyubiquitination. Finally, Notch inhibitors made mice more resistant to M. tuberculosis infection. These results suggest that Notch4 is a negative regulator of M. tuberculosis-induced inflammatory response, and treatment with a Notch inhibitor could serve as a new therapeutic strategy for tuberculosis.

Metabolic principles of persistence and pathogenicity in Mycobacterium tuberculosis

Metabolism was once relegated to the supply of energy and biosynthetic precursors, but it has now become clear that it is a specific mediator of nearly all physiological processes. In the context of microbial pathogenesis, metabolism has expanded outside its canonical role in bacterial replication. Among human pathogens, this expansion has emerged perhaps nowhere more visibly than for Mycobacterium tuberculosis, the causative agent of tuberculosis. Unlike most pathogens, M. tuberculosis has evolved within humans, which are both host and reservoir. This makes unrestrained replication and perpetual quiescence equally incompatible strategies for survival as a species. In this Review, we summarize recent work that illustrates the diversity of metabolic functions that not only enable M. tuberculosis to establish and maintain a state of chronic infection within the host but also facilitate its survival in the face of drug pressure and, ultimately, completion of its life cycle.

Immunogenicity of late stage specific peptide antigens of Mycobacterium tuberculosis

Global burden of latent TB infection comprises one-third of the world population. Identifying potential Mycobacterium tuberculosis (Mtb) latency associated antigens that can generate protective immunity against the pathogen is crucial for designing an effective TB vaccine. Usually the immune system responds to a small number of amino acids as MHC Class I or Class II peptides. The precision to trigger epitope specific protective T-cell immune response could therefore be achieved with synthetic peptide-based subunit vaccine. In the present study we have considered an immunoinformatic approach using available softwares (ProPred, IEDB, NETMHC, BIMAS, Vaxijen2.0) and docking and visualizing softwares (CABSDOCK, HEX, Pymol, Discovery Studio) to select 10 peptides as latency antigens from 4 proteins (Rv2626, Rv2627, Rv2628, and Rv2032) of DosR regulon of Mtb. As Intracellular IFN-γ secreted by T cells is the most essential cytokine in Th1 mediated protective immunity, these peptides were verified as potential immunogenic epitopes in Peripheral Blood Mononuclear Cells (PBMCs) of 10 healthy contacts of TB patients (HTB) and 10 Category I Pulmonary TB patients (PTB).The antigen-specific CD4 and CD8 T cells expressing intracellular IFN-γ were analyzed using monoclonal antibodies in all subjects by multi-parameter flow cytometry. Both, PTB and HTB individuals responded to DosR peptides by showing increased frequency of IFN-γ⁺CD4 and IFN-γ⁺CD8 T cells. The T-cell responses were significantly higher in PTB patients in comparision to the HTB individuals. Additionally, our synthetic peptides and pools showed higher frequencies of IFN-γ⁺CD4 and IFN-γ⁺CD8 T cells than the peptides of Ag85B. This pilot study can be taken up further in larger sample size which may support the untapped opportunity of designing Mtb DosR inclusive peptide based post-exposure subunit vaccine.

Value of the Ratio of Monocytes to Lymphocytes for Monitoring Tuberculosis Therapy

Objective

The objective of this study was to evaluate the change of the ratio of monocytes to lymphocytes in patients with active tuberculosis, such as to provide reference for clinical diagnosis and treatment.

Methods

All data were collected from the clinical database of The Fifth People's Hospital of Taiyuan, China. A total of 151 patients who had newly diagnosed active tuberculosis with tuberculosis therapy in hospital and 129 healthy controls were selected.

Results

Median ratio of monocytes to lymphocytes was 0.45 (IQR: 0.28–0.67) in patients before treatment and 0.32 (IQR: 0.25–0.46) on discharge (P < 0.001).

Conclusions

Ratio of monocytes to lymphocytes may be applied in diagnosis and the chemotherapeutic efficacy of active tuberculosis.

Advances in Cardiovascular Disease Lipid Research Can Provide Novel Insights Into Mycobacterial Pathogenesis

Cardiovascular disease (CVD) is the leading cause of death in industrialized nations and an emerging health problem in the developing world. Systemic inflammatory processes associated with alterations in lipid metabolism are a major contributing factor that mediates the development of CVDs, especially atherosclerosis. Therefore, the pathways promoting alterations in lipid metabolism and the interplay between varying cellular types, signaling agents, and effector molecules have been well-studied. Mycobacterial species are the causative agents of various infectious diseases in both humans and animals. Modulation of host lipid metabolism by mycobacteria plays a prominent role in its survival strategy within the host as well as in disease pathogenesis. However, there are still several knowledge gaps in the mechanistic understanding of how mycobacteria can alter host lipid metabolism. Considering the in-depth research available in the area of cardiovascular research, this review presents an overview of the parallel areas of research in host lipid-mediated immunological changes that might be extrapolated and explored to understand the underlying basis of mycobacterial pathogenesis.

Tuberculosis's cargoman: bacteria load RNA into host extracellular vesicles

Tuberculosis remains one of the deadliest infectious diseases worldwide. Mycobacterium tuberculosis (M.tb) has developed various mechanisms to manipulate the human host, in particular by disrupting the host phagosome and the immune response. It is becoming evident that secreted extracellular vesicles (EVs) are involved in the dynamic crosstalk between M.tb and the host cells. These vesicles shuttle different cargo components, such as RNA , lipids, and proteins, between cells. In this issue of EMBO Reports , Cheng and Schorey 1 describe a previously unknown EV‐mediated process, regulating M.tb RNA loading into EVs and their internalization by naïve macrophages. They identify the mycobacterial Sec2 secretion system as involved in RNA loading into EVs and show that secreted vesicles contain bacterial RNA that not only promotes IFN ‐β production upon entry into target cells, but also leads to M.tb clearance via the activation of the host's RIG ‐I/MAVS signaling pathway. Importantly, combined treatment with secreted EVs and antibiotics decreases bacterial load in a mouse model, improving lung pathology compared to treatment with antibiotics alone.

Extracellular vesicles deliver Mycobacterium RNA to promote host immunity and bacterial killing

Extracellular vesicles (EVs) have been shown to carry microbial components and function in the host defense against infections. In this study, we demonstrate that Mycobacterium tuberculosis (M.tb) RNA is delivered into macrophage-derived EVs through an M.tb SecA2-dependent pathway and that EVs released from M.tb-infected macrophages stimulate a host RIG-I/MAVS/TBK1/IRF3 RNA sensing pathway, leading to type I interferon production in recipient cells. These EVs also promote, in a RIG-I/MAVS-dependent manner, the maturation of M.tb-containing phagosomes through a noncanonical LC3 pathway, leading to increased bacterial killing. Moreover, treatment of M.tb-infected macrophages or mice with a combination of moxifloxacin and EVs, isolated from M.tb-infected macrophages, significantly lowered bacterial burden relative to either treatment alone. We hypothesize that EVs, which are preferentially removed by macrophages in vivo, can be combined with effective antibiotics as a novel approach to treat drug-resistant TB.

Potentiation of P2RX7 as a host-directed strategy for control of mycobacterial infection

Mycobacterium tuberculosis is the leading worldwide cause of death due to a single infectious agent. Existing anti-tuberculous therapies require long treatments and are complicated by multi-drug-resistant strains. Host-directed therapies have been proposed as an orthogonal approach, but few have moved into clinical trials. Here, we use the zebrafish-Mycobacterium marinum infection model as a whole-animal screening platform to identify FDA-approved, host-directed compounds. We identify multiple compounds that modulate host immunity to limit mycobacterial disease, including the inexpensive, safe, and widely used drug clemastine. We find that clemastine alters macrophage calcium transients through potentiation of the purinergic receptor P2RX7. Host-directed drug activity in zebrafish larvae depends on both P2RX7 and inflammasome signaling. Thus, targeted activation of a P2RX7 axis provides a novel strategy for enhanced control of mycobacterial infections. Using a novel explant model, we find that clemastine is also effective within the complex granulomas that are the hallmark of mycobacterial infection.

Polysaccharide rich extract (PRE) from Tinospora cordifolia inhibits the intracellular survival of drug resistant strains of Mycobacterium tuberculosis in macrophages by nitric oxide induction

Plethora of clinical and scientific information obtained in recent past has strengthened the idea that targeting critical constituents of host immune system may have beneficial outcomes for the treatment of tuberculosis. Macrophages being the primary host for Mycobacterium tuberculosis, offer an attractive target for modulation. Owing to their negligible toxicity, plant derived polysaccharides with the ability to activate macrophages; are suitable candidates for immunomodulation. In the present study, effects of polysaccharide rich extract (PRE) isolated from Tinospora cordifolia, on the survival of intracellular MTB strains and activation of macrophages were investigated. PRE treatment up regulated the expression of pro-inflammatory cytokines such as IL-β, TNF-α, IL-6, IL-12, and IFN-γ in RAW 264.7 cell line. Up regulation in the expression of NOS2 was observed along with concomitant enhanced nitric oxide production post PRE treatment. Surface expression of MHC-II and CD-86 was up regulated after PRE treatment. Above results suggested the classical activation of macrophages by PRE treatment. Furthermore, PRE treatment led to the activation of all the three classes of MAPK i.e p38, ERK and JNK MAPKs. Further, PRE up regulated the expression of cytokines, NOS-2, MHC-II and CD-86 in MTB infected macrophages. PRE treatment inhibited the intracellular survival of drug resistant MTB in macrophages which was partially attributed to PRE mediated NO induction. Thus our data demonstrate classical activation of macrophages by PRE treatment and killing of intracellular MTB by NO induction.

An explant technique for high-resolution imaging and manipulation of mycobacterial granulomas

A central and critical structure in tuberculosis, the mycobacterial granuloma consists of highly organized immune cells, including macrophages that drive granuloma formation through a characteristic epithelioid transformation. Difficulties in imaging within intact animals as well as the inherent caveats of in vitro assembly models have severely limited the study and experimental manipulation of mature granulomas. Here we describe a new ex vivo granuloma culture technique, wherein mature, fully organized granulomas are microdissected and maintained in three-dimensional culture. This approach, in which granulomas retain key bacterial and host characteristics, enables high-resolution microscopy of granuloma macrophage dynamics, including epithelioid macrophage motility and granuloma consolidation. Through mass spectrometry, we find active production of key phosphotidylinositol species identified previously in human granulomas. We describe a method to transfect isolated granulomas, enabling genetic manipulation. In addition, we provide proof-of-concept for host-directed small molecule screens, identifying PKC signaling as an important regulator of granuloma macrophage organization.

Epitope and affinity determination of recombinant Mycobacterium tuberculosis Ag85B antigen towards anti-Ag85 antibodies using proteolytic affinity-mass spectrometry and biosensor analysis

Tuberculosis (TB) is the first cause of death from infectious diseases worldwide. Only a single anti-TB vaccine is currently available for clinical use, but its efficacy is not achieved with certainty. The aim of this work is to provide a basis for the rational design of a neo-glycoconjugate vaccine against TB. Structural characterization of recombinant antigenic proteins from Mycobacterium tuberculosis (MTB) Ag85B (rAg85B, variants, and semi-synthetic glycoconjugates) was initially carried out. Identification of antibody epitope analyses by proteolytic affinity-mass spectrometry and surface plasmon resonance (SPR) biosensor analyses were performed in order to qualitatively identify and quantitatively characterize interaction structures of the antigens with antibodies from different sources. A commercial monoclonal antibody and polyclonal antibodies from different sources (patients with active TB, vaccinated individuals, and a healthy control) were employed to analyze antigen-antibody interactions. These combined approaches provided the identification of different assembled epitope regions on the recombinant MTB antigens, their affinity binding constants in the interactions with specific antibodies, and revealed the importance of protection from excessive glycosylation. The identified epitope peptides should constitute a suitable basis for the design of new specific target vaccines. Graphical abstract ᅟ.

Does the Development of Vaccines Advance Solutions for Tuberculosis?

BACKGROUND

Mycobacterium tuberculosis (Mtb) is considered as one of the most efficacious human pathogens. The global mortality rate of TB stands at approximately 2 million, while about 8 to 10 million active new cases are documented yearly. It is, therefore, a priority to develop vaccines that will prevent active TB. The vaccines currently used for the management of TB can only proffer a certain level of protection against meningitis, TB, and other forms of disseminated TB in children; however, their effectiveness against pulmonary TB varies and cannot provide life-long protective immunity. Based on these reasons, more efforts are channeled towards the development of new TB vaccines. During the development of TB vaccines, a major challenge has always been the lack of diversity in both the antigens contained in TB vaccines and the immune responses of the TB sufferers. Current efforts are channeled on widening both the range of antigens selection and the range of immune response elicited by the vaccines. The past two decades witnessed a significant progress in the development of TB vaccines; some of the discovered TB vaccines have recently even completed the third phase (phase III) of a clinical trial.

OBJECTIVE

The objectives of this article are to discuss the recent progress in the development of new vaccines against TB; to provide an insight on the mechanism of vaccine-mediated specific immune response stimulation, and to debate on the interaction between vaccines and global interventions to end TB.

Tuberculosis and the art of macrophage manipulation

Macrophages are first-line responders against microbes. The success of Mycobacterium tuberculosis (Mtb) rests upon its ability to convert these antimicrobial cells into a permissive cellular niche. This is a remarkable accomplishment, as the antimicrobial arsenal of macrophages is extensive. Normally bacteria are delivered to an acidic, degradative lysosome through one of several trafficking pathways, including LC3-associated phagocytosis (LAP) and autophagy. Once phagocytozed, the bacilli are subjected to reactive oxygen and nitrogen species, and they induce the expression of proinflammatory cytokines, which serve to augment host responses. However, Mtb hijacks these host defense mechanisms, manipulating host cellular trafficking, innate immune responses, and cell death pathways to its benefit. The complex series of measures and countermeasures between host and pathogen ultimately determines the outcome of infection. In this review, we focus on the diverse effectors that Mtb uses in its multipronged effort to subvert the innate immune responses of macrophages. We highlight recent advances in understanding the molecular interface of the Mtb-macrophage interaction.

High dose dry powder inhalers to overcome the challenges of tuberculosis treatment

Tuberculosis (TB) is a major global health burden. The emergence of the human immunodeficiency virus (HIV) epidemic and drug resistance has complicated global TB control. Pulmonary delivery of drugs using dry powder inhalers (DPI) is an emerging approach to treat TB. In comparison with the conventional pulmonary delivery for asthma and chronic obstructive pulmonary disease (COPD), TB requires high dose delivery to the lung. However, high dose delivery depends on the successful design of the inhaler device and the formulation of highly aerosolizable powders. Particle engineering techniques play an important role in the development of high dose dry powder formulations. This review focuses on the development of high dose dry powder formulations for TB treatment with background information on the challenges of the current treatment of TB and the potential for pulmonary delivery. Particle engineering techniques with a particular focus on the spray drying and a summary of the developed dry powder formulations using different techniques are also discussed.

Mycobacterium indicus pranii protein MIP_05962 induces Th1 cell mediated immune response in mice

Utility of Mycobacterium indicus pranii (MIP) as a multistage vaccine against mycobacterial infections demands identification of its protective antigens. We explored antigenicity and immunogenicity of a candidate protein MIP_05962 that depicts homology to HSP18 of M. leprae and antigen1 of Mycobacterium tuberculosis. This protein elicited substantial antibody response in immunized mice along with modulation of cellular immune response towards protective Th1 type. Both CD4⁺ and CD8⁺ subsets from immunized mice produced hallmark protective cytokines, IFN-γ, TNF-α and IL-2. This protein also enhanced the CD4⁺ effector memory that could act as first line of defence during infections. These results point to MIP_05962 as a protective antigen that contributes, in conjunction with others, to the protective immunity of this live vaccine candidate.

Alveolar Macrophages Provide an Early Mycobacterium tuberculosis Niche and Initiate Dissemination

Mycobacterium tuberculosis (Mtb) infection is initiated in the distal airways, but the bacteria ultimately disseminate to the lung interstitium. Although various cell types, including alveolar macrophages (AM), neutrophils, and permissive monocytes, are known to be infected with Mtb, the initially infected cells as well as those that mediate dissemination from the alveoli to the lung interstitium are unknown. In this study, using a murine infection model, we reveal that early, productive Mtb infection occurs almost exclusively within airway-resident AM. Thereafter Mtb-infected, but not uninfected, AM localize to the lung interstitium through mechanisms requiring an intact Mtb ESX-1 secretion system. Relocalization of infected AM precedes Mtb uptake by recruited monocyte-derived macrophages and neutrophils. This dissemination process is driven by non-hematopoietic host MyD88/interleukin-1 receptor inflammasome signaling. Thus, interleukin-1-mediated crosstalk between Mtb-infected AM and non-hematopoietic cells promotes pulmonary Mtb infection by enabling infected cells to disseminate from the alveoli to the lung interstitium.

Metabolomics applied to the discovery of tuberculosis and diabetes mellitus biomarkers

Tuberculosis (TB) and diabetes mellitus Type 2 (DM2) are two diseases as ancient as they are harmful to human health. The outcome for both diseases in part depends on immune and metabolic individual responses. DM2 is increasing yearly, mainly due to environmental, genetic and lifestyle habits. There are multiple evidence that DM2 is one of the most important risk factor of becoming infected with TB or reactivating latent TB. Mass spectrometry-based metabolomics is an important tool for elucidating the metabolites and metabolic pathways that influence the immune responses to M. tuberculosis infection during diabetes. We provide an up-to-date review highlighting the importance and benefit of metabolomics for identifying biomarkers as candidate molecules for diagnosis, disease activity or prognosis.

TRIM22 regulates macrophage autophagy and enhances Mycobacterium tuberculosis clearance by targeting the nuclear factor-multiplicity κB/beclin 1 pathway

Autophagy is a crucial host-defense mechanism against Mycobacterium tuberculosis (Mtb) infection by spanning innate and adaptive immune functions. TRIM22 is a member of tripartite motif family protein which involved in innate immunity and autophagy process. However, its role in the modulation of bacterial infection has not been investigated. Here, we demonstrated that TRIM22 is upregulated in a dose-dependent and time-dependent manner during Mtb infection of THP-1 cells. Downregulation of TRIM22 significantly decreased light chain 3 (LC3)-II protein level and the formation of LC3 puncta, while it markedly increased SQSTM1, a marker of autophagic degradation, in Mtb-infected THP-1 cells. What is more, enhanced bacterial survival was observed in TRIM22 knockdown THP-1 cells, while rapamycin abrogated this effect. In the presence of vector containing TRIM22 in THP-1 cells prior to infection, the survival of Mtb was decreased, while BafA restored this effect. Further study demonstrated that TRIM22 expression was regulated by MicroRNA-20b, and that TRIM22 regulates Mtb-infected THP-1 autophagy via the nuclear factor-κB/beclin 1 pathway. Using a nuclear factor-κB inhibitor BAY 11-7082, we found that TRIM22-induced high expression of LC3-II and the formation of LC3 was substantially attenuated, while the TRIM22-induced low expression of SQSTM1 was markedly increased in BAY 11-7082-treatment cells. In addition, the bacterial survival reduced by TRIM22 was significantly reversed by BAY 11-7082. Overall, these results suggest that TRIM22-augmented autophagy prevents intracellular Mtb to evade autophagic clearance, thereby inhibiting the persistence of Mtb infections.

Mycobacterium tuberculosis Controls Phagosomal Acidification by Targeting CISH-Mediated Signaling

Pathogens have evolved a range of mechanisms to counteract host defenses, notably to survive harsh acidic conditions in phagosomes. In the case of Mycobacterium tuberculosis, it has been shown that regulation of phagosome acidification could be achieved by interfering with the retention of the V-ATPase complexes at the vacuole. Here, we present evidence that M. tuberculosis resorts to yet another strategy to control phagosomal acidification, interfering with host suppressor of cytokine signaling (SOCS) protein functions. More precisely, we show that infection of macrophages with M. tuberculosis leads to granulocyte-macrophage colony-stimulating factor (GM-CSF) secretion, inducing STAT5-mediated expression of cytokine-inducible SH2-containing protein (CISH), which selectively targets the V-ATPase catalytic subunit A for ubiquitination and degradation by the proteasome. Consistently, we show that inhibition of CISH expression leads to reduced replication of M. tuberculosis in macrophages. Our findings further broaden the molecular understanding of mechanisms deployed by bacteria to survive.

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M. tuberculosis interferes with host pathways to control vacuolar acidification

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Infection induces the expression of host CISH and recruitment to the phagosome

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CISH triggers the degradation of H⁺-V-ATPase via SOCS box-mediated ubiquitination

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This defense mechanism complements previous schemes relying on virulence factors

Integrated Multi-Omic Analysis of Mycobacterium tuberculosis H37Ra Redefines Virulence Attributes

H37Ra is a virulence attenuated strain of Mycobacterium tuberculosis widely employed as a model to investigate virulence mechanisms. Comparative high-throughput studies have earlier correlated its avirulence to the presence of specific mutations or absence of certain proteins. However, a recent sequencing study of H37Ra, has disproved several genomic differences earlier reported to be associated with virulence. This warrants further investigations on the H37Ra proteome as well. In this study, we carried out an integrated analysis of the genome, transcriptome, and proteome of H37Ra. In addition to confirming single nucleotide variations (SNVs) and insertion-deletions that were reported earlier, our study provides novel insights into the mutation spectrum in the promoter regions of 7 genes. We also provide transcriptional and proteomic evidence for 3,900 genes representing ~80% of the total predicted gene count including 408 proteins that have not been identified previously. We identified 9 genes whose coding potential was hitherto reported to be absent in H37Ra. These include 2 putative virulence factors belonging to ESAT-6 like family of proteins. Furthermore, proteogenomic analysis enabled us to identify 63 novel proteins coding genes and correct 25 existing gene models in H37Ra genome. A majority of these were found to be conserved in the virulent strain H37Rv as well as in other mycobacterial species suggesting that the differences in the virulent and avirulent strains of M. tuberculosis are not entirely dependent on the expression of certain proteins or their absence but may possibly be ascertained to functional changes.

Tuberculosis in the elderly: Why inflammation matters

Growing old is associated with an increase in the basal inflammatory state of an individual and susceptibility to many diseases, including infectious diseases. Evidence is growing to support the concept that inflammation and disease susceptibility in the elderly is linked. Our studies focus on the infectious disease tuberculosis (TB), which is caused by Mycobacterium tuberculosis (M.tb), a pathogen that infects approximately one fourth of the world's population. Aging is a major risk factor for developing TB, and inflammation has been strongly implicated. In this review we will discuss the relationship between inflammation in the lung and susceptibility to develop and succumb to TB in old age. Further understanding of the relationship between inflammation, age, and M.tb will lead to informed decisions about TB prevention and treatment strategies that are uniquely designed for the elderly.

LysMD3 is a type II membrane protein without an role in the response to a range of pathogens

Germline-encoded receptors recognizing common pathogen-associated molecular patterns are a central element of the innate immune system and play an important role in shaping the host response to infection. Many of the innate immune molecules central to these signaling pathways are evolutionarily conserved. LysMD3 is a novel molecule containing a putative peptidoglycan-binding domain that has orthologs in humans, mice, zebrafish, flies, and worms. We found that the lysin motif (LysM) of LysMD3 is likely related to a previously described peptidoglycan-binding LysM found in bacteria. Mouse LysMD3 is a type II integral membrane protein that co-localizes with GM130+ structures, consistent with localization to the Golgi apparatus. We describe here two lines of mLysMD3-deficient mice for in vivo characterization of mLysMD3 function. We found that mLysMD3-deficient mice were born at Mendelian ratios and had no obvious pathological abnormalities. They also exhibited no obvious immune response deficiencies in a number of models of infection and inflammation. mLysMD3-deficient mice exhibited no signs of intestinal dysbiosis by 16S analysis or alterations in intestinal gene expression by RNA sequencing. We conclude that mLysMD3 contains a LysM with cytoplasmic orientation, but we were unable to define a physiological role for the molecule in vivo.

Acute Modulation of Mycobacterial Cell Envelope Biogenesis by Front-Line Tuberculosis Drugs

Front-line tuberculosis (TB) drugs have been characterized extensively in vitro and in vivo with respect to gene expression and cell viability. However, little work has been devoted to understanding their effects on the physiology of the cell envelope, one of the main targets of this clinical regimen. Herein, we use metabolic labeling methods to visualize the effects of TB drugs on cell envelope dynamics in mycobacterial species. We developed a new fluorophore-trehalose conjugate to visualize trehalose monomycolates of the mycomembrane using super-resolution microscopy. We also probed the relationship between mycomembrane and peptidoglycan dynamics using a dual metabolic labeling strategy. Finally, we found that metabolic labeling of both cell envelope structures reports on drug effects on cell physiology in two hours, far faster than a genetic sensor of cell envelope stress. Our work provides insight into acute drug effects on cell envelope biogenesis in live mycobacteria.

Evaluation of isoprinosine to be repurposed as an adjunct anti-tuberculosis chemotherapy

Isoprinosine (Inos) or immunovir is a synthetic purine derivative with immune-modulatory and antiviral properties. The drug shows apparent in vivo enhancement of host immune responses by inducing pro-inflammatory cytokines and rapid proliferation of T-cell subsets. Strikingly, the cytokines induced by Inos also play crucial roles in providing immune resistance against Mycobacterium tuberculosis (Mtb). Inos has been licensed for several antiviral diseases; however, its efficacy against Mtb has not been tested yet. Since Mtb subverts the host immune system to survive within the host. Therefore, we hypothesized that the immune-stimulatory properties of Inos can be explored as an adjunct therapy for the management of tuberculosis. We have also outlined a systematic direction of study to evaluate if Inos could be repurposed for tuberculosis. The in vivo studies for therapeutic evaluation of Inos alone or in combination with the first line anti-TB drugs in a suitable TB disease model would provide a clearer picture of its utility as a host-directed anti-TB drug and may endow us with a new application of an existing drug to combat tuberculosis.

The Formation and Function of Granulomas

Granulomas are organized aggregates of macrophages, often with characteristic morphological changes, and other immune cells. These evolutionarily ancient structures form in response to persistent particulate stimuli-infectious or noninfectious-that individual macrophages cannot eradicate. Granulomas evolved as protective responses to destroy or sequester particles but are frequently pathological in the context of foreign bodies, infections, and inflammatory diseases. We summarize recent findings that suggest that the granulomatous response unfolds in a stepwise program characterized by a series of macrophage activations and transformations that in turn recruit additional cells and produce structural changes. We explore why different granulomas vary and the reasons that granulomas are protective and pathogenic. Understanding the mechanisms and role of granuloma formation may uncover new therapies for the multitude of granulomatous diseases that constitute serious medical problems while enhancing the protective function of granulomas in infections.

Mycobacterium tuberculosis Molecular Determinants of Infection, Survival Strategies, and Vulnerable Targets

Mycobacterium tuberculosis is the causative agent of tuberculosis, an ancient disease which, still today, represents a major threat for the world population. Despite the advances in medicine and the development of effective antitubercular drugs, the cure of tuberculosis involves prolonged therapies which complicate the compliance and monitoring of drug administration and treatment. Moreover, the only available antitubercular vaccine fails to provide an effective shield against adult lung tuberculosis, which is the most prevalent form. Hence, there is a pressing need for effective antitubercular drugs and vaccines. This review highlights recent advances in the study of selected M. tuberculosis key molecular determinants of infection and vulnerable targets whose structures could be exploited for the development of new antitubercular agents.

Proteomics of Mycobacterium Infection: Moving towards a Better Understanding of Pathogen-Driven Immunomodulation

Intracellular bacteria are responsible for many infectious diseases in humans and have developed diverse mechanisms to interfere with host defense pathways. In particular, intracellular vacuoles are an essential niche used by pathogens to alter cellular and organelle functions, which facilitate replication and survival. Mycobacterium tuberculosis (Mtb), the pathogen causing tuberculosis in humans, is not only able to modulate its intraphagosomal fate by blocking phagosome maturation but has also evolved strategies to successfully prevent clearance by immune cells and to establish long-term survival in the host. Mass spectrometry (MS)-based proteomics allows the identification and quantitative analysis of complex protein mixtures and is increasingly employed to investigate host–pathogen interactions. Major challenges are limited availability and purity of pathogen-containing compartments as well as the asymmetric ratio in protein abundance when comparing bacterial and host proteins during the infection. Recent advances in purification techniques and MS technology helped to overcome previous difficulties and enable the detailed proteomic characterization of infected host cells and their pathogen-containing vacuoles. Here, we summarize current findings of the proteomic analysis of Mycobacterium-infected host cells and highlight progress that has been made to study the protein composition of mycobacterial vacuoles. Current investigations focus on the pathogenicity during Mtb infection, which will allow to better understand pathogen-induced changes and immunomodulation of infected host cells. Consequently, future research in this field will have important implications on host response, pathogen survival, and persistence, induced adaptive immunity and metabolic changes of immune cells promoting the development of novel host-directed therapies in tuberculosis.

Mycobacterium tuberculosis GroEL2 Modulates Dendritic Cell Responses

Mycobacterium tuberculosis successfully subverts the host immune response to promote disease progression. In addition to its known intracellular niche in macrophages, M. tuberculosis interferes with the functions of dendritic cells (DCs), which are the primary antigen-presenting cells of the immune system. We previously showed that M. tuberculosis dampens proinflammatory responses and impairs DC functions through the cell envelope-associated serine protease Hip1. Here we present data showing that M. tuberculosis GroEL2, a substrate of Hip1, modulates DC functions. The full-length GroEL2 protein elicited robust proinflammatory responses from DCs and promoted DC maturation and antigen presentation to T cells. In contrast, the cleaved form of GroEL2, which predominates in M. tuberculosis, was poorly immunostimulatory and was unable to promote DC maturation and antigen presentation. Moreover, DCs exposed to full-length, but not cleaved, GroEL2 induced strong antigen-specific gamma interferon (IFN-γ), interleukin-2 (IL-2), and IL-17A cytokine responses from CD4⁺ T cells. Moreover, the expression of cleaved GroEL2 in the hip1 mutant restored the robust T cell responses to wild-type levels, suggesting that proteolytic cleavage of GroEL2 allows M. tuberculosis to prevent optimal DC-T cell cross talk during M. tuberculosis infection.

The IFNG rs1861494 Single Nucleotide Polymorphism Is Associated with Protection against Tuberculosis Disease in Argentina

Interferon gamma (IFNG) plays a key role during Mycobacterium tuberculosis (Mtb) infection, and several polymorphisms located in its gene are associated with risk of tuberculosis in diverse populations. Nevertheless, the genetic resistance/susceptibility to tuberculosis in Argentina is unknown. The IFNG rs1861494 polymorphism (G→A) was reported to alter the binding of transcription factors to this region, influencing IFNG production. Using a case-control study, we found an association between the AA and AG genotypes and tuberculosis resistance (AA vs. GG: odds ratio (OR) = 0.235, p-value = 0.012; AG vs. GG: OR = 0.303, p-value = 0.044; AA vs. AG: OR = 0.776, p-value = 0.427; AA + AG vs. GG: OR = 0.270, p-value = 0.022). Moreover, Mtb-antigen stimulated peripheral blood mononuclear cells (PBMCs) from healthy donors and AA carriers secreted the highest amounts of IFNG in culture supernatants (p-value = 0.034) and presented the greatest percentage of CD4⁺IFNG⁺ lymphocytes (p-value = 0.035), in comparison with GG carriers. No association between the polymorphism and clinical parameters of tuberculosis severity was detected. However, our findings indicate that the rs1861494 single nucleotide polymorphism (SNP) could be considered as a biomarker of tuberculosis resistance in the Argentinean population.