The inducible nitric oxide synthase locus confers protection against aerogenic challenge of both clinical and laboratory strains of Mycobacterium tuberculosis in mice

Spatially Resolved Molecular Analysis of Host Response to Medical Device Implantation Using the 3D OrbiSIMS Highlights a Critical Role for Lipids

A key goal for implanted medical devices is that they do not elicit a detrimental immune response. Macrophages play critical roles in the modulation of the host immune response and are the cells responsible for persistent inflammatory reactions to implanted biomaterials. Two novel immune-instructive polymers that stimulate pro- or anti-inflammatory responses from macrophages in vitro are investigated. These also modulate in vivo foreign body responses (FBR) when implanted subcutaneously in mice. Immunofluorescent staining of tissue abutting the polymer reveals responses consistent with pro- or anti-inflammatory responses previously described for these polymers. Three Dimensional OrbiTrap Secondary Ion Mass Spectrometry (3D OrbiSIMS) analysis to spatially characterize the metabolites in the tissue surrounding the implant, providing molecular histology insight into the metabolite response in the host is applied. For the pro-inflammatory polymer, monoacylglycerols (MG) and diacylglycerols (DG) are observed at increased intensity, while for the anti-inflammatory coating, the number of phospholipid species detected decreased, and pyridine and pyrimidine levels are elevated. Small molecule signatures from single-cell studies of M2 macrophages in vitro correlate with the in vivo observations, suggesting potential for prediction. Metabolite characterization by the 3D OrbiSIMS is shown to provide insight into the mechanism of bio-instructive materials as medical devices and to inform on the FBR to biomaterials.

The Interplay between Mycobacterium tuberculosis and Human Microbiome

Tuberculosis (TB), a respiratory disease caused by Mycobacterium tuberculosis (Mtb), is a significant cause of mortality worldwide. The lung, a breeding ground for Mtb, was once thought to be a sterile environment, but has now been found to host its own profile of microbes. These microbes are critical in the development of the host immune system and can produce metabolites that aid in host defense against various pathogens. Mtb infection as well as antibiotics can shift the microbial profile, causing dysbiosis and dampening the host immune response. Additionally, increasing cases of drug resistant TB have impacted the success rates of the traditional therapies of isoniazid, rifampin, pyrazinamide, and ethambutol. Recent years have produced tremendous research into the human microbiome and its role in contributing to or attenuating disease processes. Potential treatments aimed at altering the gut-lung bacterial axis may offer promising results against drug resistant TB and help mitigate the effects of TB.

Adenoviral Vector Codifying for TNF as a Co-Adjuvant Therapy against Multi-Drug-Resistant Tuberculosis

Mycobacterium tuberculosis is the main causal agent of pulmonary tuberculosis (TB); the treatment of this disease is long and involves a mix of at least four different antibiotics that frequently lead to abandonment, favoring the surge of drug-resistant mycobacteria (MDR-TB), whose treatment becomes more aggressive, being longer and more toxic. Thus, the search for novel strategies for treatment that improves time or efficiency is of relevance. In this work, we used a murine model of pulmonary TB produced by the MDR-TB strain to test the efficiency of gene therapy with adenoviral vectors codifying TNF (AdTNF), a pro-inflammatory cytokine that has protective functions in TB by inducing apoptosis, granuloma formation and expression of other Th1-like cytokines. When compared to the control group that received an adenoviral vector that codifies for the green fluorescent protein (AdGFP), a single dose of AdTNF at the chronic active stage of the disease produced total survival, decreasing bacterial load and tissue damage (pneumonia), which correlated with an increase in cells expressing IFN-γ, iNOS and TNF in pneumonic areas and larger granulomas that efficiently contain and eliminate mycobacteria. Second-line antibiotic treatment against MDR-TB plus AdTNF gene therapy reduced bacterial load faster within a week of treatment compared to empty vector plus antibiotics or antibiotics alone, suggesting that AdTNF is a new potential type of treatment against MDR-TB that can shorten second-line chemotherapy but which requires further experimentation in other animal models (non-human primates) that develop a more similar disease to human pulmonary TB.

Monitoring the immune response of macrophages in tuberculous granuloma through the expression of CD68, iNOS and HLA-DR in naturally infected beef cattle

Bovine tuberculosis still represents a universal threat that creates a wider range of public and animal health impacts. One of the most important steps in the pathogenesis of this disease and granuloma formation is the phagocytosis of tuberculous bacilli by macrophages. Mycobacteria replicate in macrophages, which are crucial to the pathophysiology of mycobacterial infections; however, scarce information is available about the dynamics of the granuloma-stage immunological response. Therefore, immunohistochemistry was used in this work to evaluate the expression of CD68, iNOS, and HLA-DR in different stages of TB granulomas from naturally infected cattle with tuberculosis. Two thousand, one hundred and fifty slaughtered beef cattle were examined during the period from September 2020 to March 2022. Sixty of them showed gross tuberculous pulmonary lesions and samples were collected from all of them for histopathological examination, Ziehl-Neelsen (ZN) staining, and bacteriological culturing. Selected samples that yielded a positive result for ZN and mycobacterial culturing were subjected to an immunohistochemical study of CD68, iNOS, and HLA-DR expression by macrophages according to granuloma stages. Immunohistochemical analysis revealed that the immunolabeling of CD68+, iNOS+, and HLA-DR+ macrophages significantly reduced as the stage of granuloma increased from stage I to stage IV (P < 0.003, P < 0.002, and P < 0.002, respectively). The distribution of immunolabeled macrophages was similar for the three markers, with immunolabeled macrophages distributed throughout early-stage granulomas (I, II), and surrounding the necrotic core in late-stage granulomas (III, IV). Our results suggest a polarization to the pro-inflammatory environment and increased expression of CD68+, iNOS+, and HLA-DR+ macrophages in the early stages of granulomas (I, II), which may play a protective role in the immune response of naturally infected beef cattle with tuberculosis.

NOS2/miR-493-5p Signaling Regulates in the LPS-Induced Inflammatory Response in the RAW264.7 Cells

Tuberculosis (TB) is a fatal infectious disease; however, the molecular mechanisms underlying the pathogenicity of TB remain elusive. The present study aims to identify potential biomarkers associated with Mycobacterium tuberculosis (M.tb) infection by using integrated bioinformatics and in vitro validation studies. GSE50050, GSE78706, and GSE108844 data from the gene expression omnibus (GEO) database were downloaded to identify differentially expressed genes (DEGs). The functions of DEGs were further subjected to gene ontology (GO) and KEGG pathway analysis. The hub genes from the DEGs were determined based on the protein-protein interaction (PPI) network analysis. Finally, the hub genes were experimentally validated using the in vitro functional studies. A total of 26 common DEGs were identified among GSE50050, GSE78706, and GSE108844. The functional enrichment analysis showed that the common DEGs were associated with cytokines response and TB pathways. The PPI network analysis identified nine hub genes. Further in vitro studies showed that nitric oxide synthase 2 (NOS2) was up-regulated in RAW264.7 cells upon lipopolysaccharides (LPS) stimulation, which was accompanied by increased inflammatory cytokines release. Furthermore, NOS2 was found to be a target of miR-493-5p, which was confirmed by luciferase reporter assay. NOS2 was repressed by miR-493-5p overexpression and was up-regulated after miR-493-5p inhibition in RAW264.7 cells. The rescue experiments showed that LPS-induced increase in the inflammatory cytokines of the RAW264.7 cells was significantly attenuated by NOS2 knockdown and miR-493-5p overexpression. Collectively, our results for the first time demonstrated that NOS2/miR-493-5p signaling pathway may potentially involve in the inflammatory response during bacterial infection such as M. tb infection.

A nod to the bond between NOD2 and mycobacteria

Mycobacteria are responsible for several human and animal diseases. NOD2 is a pattern recognition receptor that has an important role in mycobacterial recognition. However, the mechanisms by which mutations in NOD2 alter the course of mycobacterial infection remain unclear. Herein, we aimed to review the totality of studies directly addressing the relationship between NOD2 and mycobacteria as a foundation for moving the field forward. NOD2 was linked to mycobacterial infection at 3 levels: (1) genetic, through association with mycobacterial diseases of humans; (2) chemical, through the distinct NOD2 ligand in the mycobacterial cell wall; and (3) immunologic, through heightened NOD2 signaling caused by the unique modification of the NOD2 ligand. The immune response to mycobacteria is shaped by NOD2 signaling, responsible for NF-κB and MAPK activation, and the production of various immune effectors like cytokines and nitric oxide, with some evidence linking this to bacteriologic control. Absence of NOD2 during mycobacterial infection of mice can be detrimental, but the mechanism remains unknown. Conversely, the success of immunization with mycobacteria has been linked to NOD2 signaling and NOD2 has been targeted as an avenue of immunotherapy for diseases even beyond mycobacteria. The mycobacteria-NOD2 interaction remains an important area of study, which may shed light on immune mechanisms in disease.

Reinventing the human tuberculosis (TB) granuloma: Learning from the cancer field

Tuberculosis (TB) remains one of the deadliest infectious diseases in the world and every 20 seconds a person dies from TB. An important attribute of human TB is induction of a granulomatous inflammation that creates a dynamic range of local microenvironments in infected organs, where the immune responses may be considerably different compared to the systemic circulation. New and improved technologies for in situ quantification and multimodal imaging of mRNA transcripts and protein expression at the single-cell level have enabled significantly improved insights into the local TB granuloma microenvironment. Here, we review the most recent data on regulation of immunity in the TB granuloma with an enhanced focus on selected in situ studies that enable spatial mapping of immune cell phenotypes and functions. We take advantage of the conceptual framework of the cancer-immunity cycle to speculate how local T cell responses may be enhanced in the granuloma microenvironment at the site of Mycobacterium tuberculosis infection. This includes an exploratory definition of "hot", immune-inflamed, and "cold", immune-excluded TB granulomas that does not refer to the level of bacterial replication or metabolic activity, but to the relative infiltration of T cells into the infected lesions. Finally, we reflect on the current knowledge and controversy related to reactivation of active TB in cancer patients treated with immune checkpoint inhibitors such as PD-1/PD-L1 and CTLA-4. An understanding of the underlying mechanisms involved in the induction and maintenance or disruption of immunoregulation in the TB granuloma microenvironment may provide new avenues for host-directed therapies that can support standard antibiotic treatment of persistent TB disease.

How mycobacterium tuberculosis infection could lead to the increasing risks of chronic fatigue syndrome and the potential immunological effects: a population-based retrospective cohort study

Background

Chronic fatigue syndrome (CFS) has been shown to be associated with infections. Tuberculosis (TB) is a highly prevalent infectious disease. Patients with chronic fatigue syndrome and post-tuberculosis experience similar symptoms. Furthermore, chronic fatigue syndrome and tuberculosis share similar plasma immunosignatures. This study aimed to clarify the risk of chronic fatigue syndrome following the diagnosis of Mycobacterium tuberculosis infection (MTI), by analyzing the National Health Insurance Research Database of Taiwan.

Methods

7666 patients aged 20 years or older with newly diagnosed Mycobacterium tuberculosis infection during 2000–2011 and 30,663 participants without Mycobacterium tuberculosis infection were identified. Both groups were followed up until the diagnoses of chronic fatigue syndrome were made at the end of 2011.

Results

The relationship between Mycobacterium tuberculosis infection and the subsequent risk of chronic fatigue syndrome was estimated through Cox proportional hazards regression analysis, with the incidence density rates being 3.04 and 3.69 per 1000 person‐years among the non‐Mycobacterium tuberculosis infection and Mycobacterium tuberculosis infection populations, respectively (adjusted hazard ratio [HR] = 1.23, with 95% confidence interval [CI] 1.03–1.47). In the stratified analysis, the Mycobacterium tuberculosis infection group were consistently associated with a higher risk of chronic fatigue syndrome in the male sex (HR = 1.27, 95% CI 1.02–1.58) and age group of ≥ 65 years old (HR = 2.50, 95% CI 1.86–3.38).

Conclusions

The data from this population‐based retrospective cohort study revealed that Mycobacterium tuberculosis infection is associated with an elevated risk of subsequent chronic fatigue syndrome.

Emerging Role of Exosomes in Tuberculosis: From Immunity Regulations to Vaccine and Immunotherapy

Exosomes are cell-derived nanovesicles carrying protein, lipid, and nucleic acid for secreting cells, and act as significant signal transport vectors for cell-cell communication and immune modulation. Immune-cell-derived exosomes have been found to contain molecules involved in immunological pathways, such as MHCII, cytokines, and pathogenic antigens. Tuberculosis (TB), caused by Mycobacterium tuberculosis (MTB), remains one of the most fatal infectious diseases. The pathogen for tuberculosis escapes the immune defense and continues to replicate despite rigorous and complicate host cell mechanisms. The infected-cell-derived exosomes under this circumstance are found to trigger different immune responses, such as inflammation, antigen presentation, and activate subsequent pathways, highlighting the critical role of exosomes in anti-MTB immune response. Additionally, as a novel kind of delivery system, exosomes show potential in developing new vaccination and treatment of tuberculosis. We here summarize recent research progress regarding exosomes in the immune environment during MTB infection, and further discuss the potential of exosomes as delivery system for novel anti-MTB vaccines and therapies.

Targeting endogenous gaseous signaling molecules as novel host-directed therapies against tuberculosis infection

Tuberculosis (TB) is a chronic pulmonary disease caused by Mycobacterium tuberculosis which is a major cause of morbidity and mortality worldwide. Due to the complexity of disease and its continuous global spread, there is an urgent need to improvise the strategies for prevention, diagnosis, and treatment. The current anti-TB regimen lasts for months and warrants strict compliance to clear infection and to minimize the risk of development of multi drug-resistant tuberculosis. This underscores the need to have new and improved therapeutics for TB treatment. Several studies have highlighted the unique ability of Mycobacterium tuberculosis to exploit host factors to support its survival inside the intracellular environment. One of the key players to mycobacterial disease susceptibility and infection are endogenous gases such as oxygen, nitric oxide, carbon monoxide and hydrogen sulfide. Nitric oxide and carbon monoxide as the physiological gaseous messengers are considered important to the outcome of Mycobacterium tuberculosis infection. The role of hydrogen sulfide in human tuberculosis is yet not fully elucidated, but this gas has been shown to play a significant role in bacterial respiration, growth and pathogenesis. This review will focus on the host factors majorly endogenous gaseous signaling molecules which contributes to Mycobacterium tuberculosis survival inside the intracellular environment and highlight the potential therapeutic targets.

Metabolic Regulation of Immune Responses to Mycobacterium tuberculosis: A Spotlight on L-Arginine and L-Tryptophan Metabolism

Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis (TB), is a leading cause of death worldwide. Despite decades of research, there is still much to be uncovered regarding the immune response to Mtb infection. Here, we summarize the current knowledge on anti-Mtb immunity, with a spotlight on immune cell amino acid metabolism. Specifically, we discuss L-arginine and L-tryptophan, focusing on their requirements, regulatory roles, and potential use as adjunctive therapy in TB patients. By continuing to uncover the immune cell contribution during Mtb infection and how amino acid utilization regulates their functions, it is anticipated that novel host-directed therapies may be developed and/or refined, helping to eradicate TB.

Human tuberculosis and Mycobacterium tuberculosis complex: A review on genetic diversity, pathogenesis and omics approaches in host biomarkers discovery

Mycobacterium tuberculosis complex (MTBC) refers to a group of mycobacteria encompassing nine members of closely related species that causes tuberculosis in animals and humans. Among the nine members, Mycobacterium tuberculosis (M. tuberculosis) remains the main causative agent for human tuberculosis that results in high mortality and morbidity globally. In general, MTBC species are low in diversity but exhibit distinctive biological differences and phenotypes among different MTBC lineages. MTBC species are likely to have evolved from a common ancestor through insertions/deletions processes resulting in species speciation with different degrees of pathogenicity. The pathogenesis of human tuberculosis is complex and remains poorly understood. It involves multi-interactions or evolutionary co-options between host factors and bacterial determinants for survival of the MTBC. Granuloma formation as a protection or survival mechanism in hosts by MTBC remains controversial. Additionally, MTBC species are capable of modulating host immune response and have adopted several mechanisms to evade from host immune attack in order to survive in humans. On the other hand, current diagnostic tools for human tuberculosis are inadequate and have several shortcomings. Numerous studies have suggested the potential of host biomarkers in early diagnosis of tuberculosis, in disease differentiation and in treatment monitoring. "Multi-omics" approaches provide holistic views to dissect the association of MTBC species with humans and offer great advantages in host biomarkers discovery. Thus, in this review, we seek to understand how the genetic variations in MTBC lead to species speciation with different pathogenicity. Furthermore, we also discuss how the host and bacterial players contribute to the pathogenesis of human tuberculosis. Lastly, we provide an overview of the journey of "omics" approaches in host biomarkers discovery in human tuberculosis and provide some interesting insights on the challenges and directions of "omics" approaches in host biomarkers innovation and clinical implementation.

The Association of Tuberculosis Mono-infection and Tuberculosis-Human Immunodeficiency Virus (TB-HIV) Co-infection in the Pathogenesis of Hypertensive Disorders of Pregnancy

PURPOSE OF REVIEW

This review highlights the impact of TB mono-infection and TB-HIV co-infection on the pathogenesis of adverse maternal outcomes such as hypertensive disorders of pregnancy (HDP) and adverse fetal outcomes such as recurrent spontaneous abortion (RSA), fetal growth restriction (FGR), and low birth weight.

RECENT FINDINGS

Research has shown that HDP, such as severe pre-eclampsia (PE) and eclampsia, as well as adverse fetal outcomes such as recurrent spontaneous abortion, fetal growth restriction, and low birth weight, are higher in women diagnosed with TB mono-infection and even higher in TB-HIV co-infection compared to those without TB. This is speculated to occur due to exaggerated activation of both angiogenic factors such as vascular endothelial growth factor (VEGF), nitric oxide (NO), angiotensin 2, (Ang 2), intracellular adhesion molecules (ICAMs), and inflammatory cytokines such as interleukin 2 (IL-2), (IL-17), and interferon-gamma (INF-γ). There is a lack of information with regard to the pathogenesis of adverse maternal and fetal outcomes upon TB mono-infection and TB-HIV co-infection; therefore, further investigations on the impact of TB mono-infection and TB-HIV co-infection on adverse maternal and fetal outcomes are urgently needed. This will assist in improving diagnostic procedures in pregnant women affected with TB as wells as TB-HIV co-infection.

Use Chou's 5-steps rule to evaluate protective efficacy induced by antigenic proteins of Mycobacterium tuberculosis encapsulated in chitosan nanoparticles

The study focuses on whether antigenic proteins encapsulated in biopolymeric nanoparticles can augment protective efficacy. Chitosan nanoparticles (ChN) were prepared by ionic gelation method and Culture Filtrate Proteins (CFP) - CFP-10 and CFP-21 of Mycobacterium tuberculosis (Mtb) were encapsulated in ChN. The binding efficiency of nanoparticles with CFP-10 and CFP-21 proteins was confirmed by UV-Spectrophotometer. The efficacy of nanoparticles-encapsulated antigenic proteins administered intraperitoneal against Mtb aerosol infection was evaluated in Balb/c mice. Protection study was done by bacterial counts [CFU]. CFP-10 and CFP-21 proteins primed cells demonstrated a Th1 bias T cell response in an ex vivo assay. ChN-CFP10 and ChN-CFP21 nanoparticles have both protective and therapeutic potential against Mtb. In the group of mice immunized with CHN-CFP-10 the number of colonies reduced significantly from day 15 to day 60. ChN-CFP-21 showed maximum protection in ChN-CFP-21 immunized mice. ChN-CFP-10 and ChN-CFP-21 clearly showed enhanced protection against Mtb.

Acute hypercalcemia and hypervitaminosis D associated with pulmonary tuberculosis in an elderly patient : A case report and review of the literature

An 80-year-old man was referred to our hospital for further examination of fever, cough and left pleural effusion. The laboratory findings showed acute inflammation, and the elevation of albumin-corrected serum calcium and 1,25-dihydroxyvitamin D3. A chest CT revealed centrilobular particulate opacity in the bilateral lung fields and left pleural effusion, indicating acute hypercalcemia and hypervitaminosis D associated with pulmonary tuberculosis. By the confirmation of Mycobacterium tuberculosis on polymerase chain reaction and cultures of the sputum and pleural effusion, a diagnosis of pulmonary tuberculosis was made. The patient successfully completed a 9-month course of the anti-tuberculosis treatment, and bilateral infiltrative shadows and left pleural effusion in chest X-ray disappeared. Symptoms progressively improved and serum level of albumin-corrected calcium and 1,25-dihydroxyvitamin D3 eventually normalized. While pulmonary tuberculosis is an infrequent cause of hypercalcemia, it should be considered in patients with hypercalcemia and elevated serum level of 1,25-dihydroxyvitamin D3. J. Med. Invest. 66 : 351-354, August, 2019.

Increased susceptibility to Mycobacterium tuberculosis infection in a diet-induced murine model of type 2 diabetes

Tuberculosis (TB)-type 2 diabetes mellitus (T2D) comorbidity is re-emerging as a global public health problem. T2D is a major risk factor for increased susceptibility to TB infection and reactivation leading to higher morbidity and mortality. The pathophysiological mechanisms of T2D contributing to TB susceptibility are not fully understood, but likely involve dysregulated immune responses. In this study, a diet-induced murine model that reflects the cardinal features of human T2D was used to assess the immune responses following an intravenous Mycobacterium tuberculosis (Mtb) infection. In this study, T2D significantly increased mortality, organ bacillary burden and inflammatory lesions compared to non-diabetic controls. Organ-specific pro-inflammatory cytokine responses were dysregulated as early as one day post-infection in T2D mice. Macrophages derived from T2D mice showed reduced bacterial internalization and killing capacity. An early impairment of antimycobacterial functions of macrophages in diabetes is a key mechanism that leads to increased susceptibility of T2D.

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.

Recombinant BCG With Bacterial Signaling Molecule Cyclic di-AMP as Endogenous Adjuvant Induces Elevated Immune Responses After Mycobacterium tuberculosis Infection

Bacillus Calmette-Guerin (BCG) is a live attenuated vaccine against tuberculosis (TB) and remains the most commonly used vaccine worldwide. However, BCG has varied protective efficiency in adults and has safety concerns in immunocompromised population. Thus, effective vaccines are necessary for preventing the prevalence of TB. Cyclic di-AMP (c-di-AMP) is a bacterial second messenger which regulates various cellular processes and host immune response. Previous work found that c-di-AMP regulates bacterial physiological function, pathogenicity and host type I IFN response. In this study, we constructed a recombinant BCG (rBCG) by overexpressing DisA, the diadenylate cyclase of Mycobacterium tuberculosis (Mtb), and observed the physiological changes of rBCG-DisA. The immunological characteristics of rBCG-DisA were investigated on humoral and cellar immune responses in a mice infection model. Our study demonstrated that overexpression of DisA in BCG does not affect the growth but reduces the length of BCG. rBCG-DisA-immunized mice show similar humoral and cellar immune responses in BCG-immunized mice. After Mtb infection, the splenic lymphocytes from both BCG and rBCG-DisA-immunized mice produced more IFN-γ, IL-2, and IL-10 than the un-immunized (UN) mice, while the cytokine levels of the rBCG-DisA group increased significantly than those of the BCG group. The transcription of IFN-β, IL-1β and autophagy related genes (Atgs) were up-regulated in macrophages after treated with c-di-AMP or bacterial infection. The productions of IL-6 were increased after Mtb challenge, especially in the rBCG-DisA-immunized mice. Strikingly, H3K4me3, the epigenetic marker of innate immune memory, was found in both two immunized groups, and the rBCG-DisA group showed stronger expression of H3K4me3 than that of BCG. In addition, the pathological changes of rBCG-DisA immunized mice were similar to that of BCG-immunized mice. The bacterial burdens in the lungs and spleens of BCG- and rBCG-DisA-immunized mice were significantly decreased, but there was no significant difference between the two immunized groups. Together, these results suggested that compared to BCG, rBCG-DisA vaccination, induces stronger immune responses but did not provided additional protection against Mtb infection in this study, which may be related to the innate immunity memory. Hence, c-di-AMP is a promising immunomodulator for a further developed BCG as a better vaccine.

Iron Supplementation Therapy, A Friend and Foe of Mycobacterial Infections?

Iron is an essential element that is required for oxygen transfer, redox, and metabolic activities in mammals and bacteria. Mycobacteria, some of the most prevalent infectious agents in the world, require iron as growth factor. Mycobacterial-infected hosts set up a series of defense mechanisms, including systemic iron restriction and cellular iron distribution, whereas mycobacteria have developed sophisticated strategies to acquire iron from their hosts and to protect themselves from iron’s harmful effects. Therefore, it is assumed that host iron and iron-binding proteins, and natural or synthetic chelators would be keys targets to inhibit mycobacterial proliferation and may have a therapeutic potential. Beyond this hypothesis, recent evidence indicates a host protective effect of iron against mycobacterial infections likely through promoting remodeled immune response. In this review, we discuss experimental procedures and clinical observations that highlight the role of the immune response against mycobacteria under various iron availability conditions. In addition, we discuss the clinical relevance of our knowledge regarding host susceptibility to mycobacteria in the context of iron availability and suggest future directions for research on the relationship between host iron and the immune response and the use of iron as a therapeutic agent.

Regulation of mycobacterial infection by macrophage Gch1 and tetrahydrobiopterin

Inducible nitric oxide synthase (iNOS) plays a crucial role in controlling growth of Mycobacterium tuberculosis (M.tb), presumably via nitric oxide (NO) mediated killing. Here we show that leukocyte-specific deficiency of NO production, through targeted loss of the iNOS cofactor tetrahydrobiopterin (BH4), results in enhanced control of M.tb infection; by contrast, loss of iNOS renders mice susceptible to M.tb. By comparing two complementary NO-deficient models, Nos2-/- mice and BH4 deficient Gch1fl/flTie2cre mice, we uncover NO-independent mechanisms of anti-mycobacterial immunity. In both murine and human leukocytes, decreased Gch1 expression correlates with enhanced cell-intrinsic control of mycobacterial infection in vitro. Gene expression analysis reveals that Gch1 deficient macrophages have altered inflammatory response, lysosomal function, cell survival and cellular metabolism, thereby enhancing the control of bacterial infection. Our data thus highlight the importance of the NO-independent functions of Nos2 and Gch1 in mycobacterial control.

IRAK4 activity controls immune responses to intracellular bacteria Listeria monocytogenes and Mycobacterium smegmatis

IL-1 receptor-associated kinase (IRAK) 4 is a central enzyme of the TLR pathways. This study tested the hypothesis that IRAK4 kinase activity is prerequisite for regulating innate immunity during infections with intracellular bacteria. To this end, we analyzed responses of macrophages obtained from mice expressing wild-type (WT) IRAK4 or its kinase-inactive K213M mutant (IRAK4^KI ) upon infection with intracellular bacteria Listeria monocytogenes or Mycobacterium smegmatis. In contrast to robust induction of cytokines by macrophages expressing kinase-sufficient IRAK4, IRAK4^KI macrophages expressed decreased TNF-α, IL-6, IL-1β, and C-C motif chemokine ligand 5 upon infection with L. monocytogenes or M. smegmatis. Bacterial infection of IRAK4^KI macrophages led to attenuated activation of IRAK1, MAPKs and NF-κB, impaired induction of inducible NO synthase mRNA and secretion of NO, but resulted in elevated microbial burdens. Compared with WT animals, systemic infection of IRAK4^KI mice with M. smegmatis or L. monocytogenes resulted in decreased levels of serum IL-6 and CXCL-1 but increased bacterial burdens in the spleen and liver. Thus, a loss of IRAK4 kinase activity underlies deficient cytokine and microbicidal responses during infection with intracellular bacteria L. monocytogenes or M. smegmatis via impaired activation of IRAK1, MAPKs, and NF-κB but increases bacterial burdens, correlating with decreased induction of NO.

Th1 cytokines, true functional signatures for protective immunity against TB?

The lack of an effective preventative vaccine against tuberculosis (TB) presents a great challenge to TB control. Since it takes an extremely long time to accurately determine the protective efficacy of TB vaccines, there is a great need to identify the surrogate signatures of protection to facilitate vaccine development. Unfortunately, antigen-specific Th1 cytokines that are currently used to evaluate the protective efficacy of the TB vaccine, do not align with the protection and failure of TB vaccine candidates in clinical trials. In this review, we discuss the limitation of current Th1 cytokines as surrogates of protection and address the potential elements that should be considered to finalize the true functional signatures of protective immunity against TB.

Nitric Oxide in the Pathogenesis and Treatment of Tuberculosis

Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis (TB), is globally known as one of the most important human pathogens. Mtb is estimated to infect nearly one third of the world's population with many subjects having a latent infection. Thus, from an estimated 2 billion people infected with Mtb, less than 10% may develop symptomatic TB. This indicates that the host immune system may constrain pathogen replication in most infected individuals. On entering the lungs of the host, Mtb initially encounters resident alveolar macrophages which can engulf and subsequently eliminate intracellular microbes via a plethora of bactericidal mechanisms including the generation of free radicals such as reactive oxygen and nitrogen species. Nitric oxide (NO), a key anti-mycobacterial molecule, is detected in the exhaled breath of patients infected with Mtb. Recent knowledge regarding the regulatory role of NO in airway function and Mtb proliferation paves the way of exploiting the beneficial effects of this molecule for the treatment of airway diseases. Here, we discuss the importance of NO in the pathogenesis of TB, the diagnostic use of exhaled and urinary NO in Mtb infection and the potential of NO-based treatments.

Nitric oxide prevents a pathogen-permissive granulocytic inflammation during tuberculosis

Nitric oxide (NO) contributes to protection from tuberculosis (TB). It is generally assumed that this protection is due to direct inhibition of Mycobacterium tuberculosis (Mtb) growth, which prevents subsequent pathological inflammation. In contrast, we report NO primarily protects mice by repressing an interleukin-1 and 12/15-lipoxygenase dependent neutrophil recruitment cascade that promotes bacterial replication. Using Mtb mutants as indicators of the pathogen's environment, we inferred that granulocytic inflammation generates a nutrient-replete niche that supports Mtb growth. Parallel clinical studies indicate that a similar inflammatory pathway promotes TB in patients. The human 12/15 lipoxygenase ortholog, ALOX12, is expressed in cavitary TB lesions, the abundance of its products correlate with the number of airway neutrophils and bacterial burden, and a genetic polymorphism that increases ALOX12 expression is associated with TB risk. These data suggest that Mtb exploits neutrophilic inflammation to preferentially replicate at sites of tissue damage that promote contagion.

A single-stranded DNA aptamer against mannose-capped lipoarabinomannan enhances anti-tuberculosis activity of macrophages through downregulation of lipid-sensing nuclear receptor peroxisome proliferator-activated receptor γ expression

Mannose-capped lipoarabinomannan (ManLAM) is an immunomodulatory epitope of Mycobacterium tuberculosis (Mtb). An aptamer (ZXL1) that specifically binds to ManLAM from the virulent Mtb H37Rv strain was previously generated and it was found that ZXL1 functions as an antagonist, inhibiting the ManLAM-induced immunosuppression of DCs. In the present study, it was found that ZXL1 inhibits Mtb entry into murine macrophages and that ZXL1 enhances IL-1β and IL-12 mRNA expression and cytokine production in ManLAM-treated macrophages but decreases IL-10 production. Inducible nitric oxide synthase expression in macrophages was upregulated in the presence of ZXL1 after stimulation with ManLAM. ZXL1 was also found to inhibit expression of lipid-sensing nuclear receptor peroxisome proliferator-activated receptor γ (PPAR-γ). These results suggest that ZXL1 promotes anti-tuberculosis activity through downregulation of PPAR-γ expression, which may contribute to M1 macrophage polarization and Mtb killing by macrophages.

M2 macrophages or IL-33 treatment attenuate ongoing Mycobacterium tuberculosis infection

The protective effects of mycobacterial infections on lung allergy are well documented. However, the inverse relationship between tuberculosis and type 2 immunity is still elusive. Although type 1 immunity is essential to protection against Mycobacterium tuberculosis it might be also detrimental to the host due to the induction of extensive tissue damage. Here, we determined whether lung type 2 immunity induced by allergen sensitization and challenge could affect the outcome of M. tuberculosis infection. We used two different protocols in which sensitization and allergen challenge were performed before or after M. tuberculosis infection. We found an increased resistance to M. tuberculosis only when allergen exposure was given after, but not before infection. Infected mice exposed to allergen exhibited lower bacterial load and cellular infiltrates in the lungs. Enhanced resistance to infection after allergen challenge was associated with increased gene expression of alternatively activated macrophages (M2 macrophages) and IL-33 levels. Accordingly, either adoptive transfer of M2 macrophages or systemic IL-33 treatment was effective in attenuating M. tuberculosis infection. Notably, the enhanced resistance induced by allergen exposure was dependent on IL-33 receptor ST2. Our work indicates that IL-33 might be an alternative therapeutic treatment for severe tuberculosis.

Anti-mycobacterial function of macrophages is impaired in a diet induced model of type 2 diabetes

Type 2 diabetes (T2D) is one of the major risk factors for tuberculosis (TB). In this study, a diet induced murine model of T2D (DIMT2D) was developed and characterized in the context of metabolic, biochemical and histopathological features following diet intervention. Mycobacterial susceptibility was investigated using Mycobacterium fortuitum as a surrogate. Phagocytic capability of alveolar macrophages and resident peritoneal macrophages were determined by in vitro assays using mycolic acid coated beads and M. fortuitum. Results demonstrated that bacillary loads were significantly higher in liver, spleen, and lungs of diabetic mice compared to controls. Higher inflammatory lesions and impaired cytokine kinetics (TNF-α, MCP-1, IL-12, IFN-γ) were also observed in diabetic mice. Macrophages isolated from diabetic mice had lower uptake of mycolic acid coated beads, reduced bacterial internalization and killing and altered cytokine responses (TNF-α, IL-6, MCP-1). This model will be useful to further investigate different facets of host-pathogen interactions in TB-T2D.

Type I IFN Inhibits Alternative Macrophage Activation during Mycobacterium tuberculosis Infection and Leads to Enhanced Protection in the Absence of IFN-γ Signaling

Tuberculosis causes ∼1.5 million deaths every year, thus remaining a leading cause of death from infectious diseases in the world. A growing body of evidence demonstrates that type I IFN plays a detrimental role in tuberculosis pathogenesis, likely by interfering with IFN-γ–dependent immunity. In this article, we reveal a novel mechanism by which type I IFN may confer protection against Mycobacterium tuberculosis infection in the absence of IFN-γ signaling. We show that production of type I IFN by M. tuberculosis–infected macrophages induced NO synthase 2 and inhibited arginase 1 gene expression. In vivo, absence of both type I and type II IFN receptors led to strikingly increased levels of arginase 1 gene expression and protein activity in infected lungs, characteristic of alternatively activated macrophages. This correlated with increased lung bacterial burden and pathology and decreased survival compared with mice deficient in either receptor. Increased expression of other genes associated with alternatively activated macrophages, as well as increased expression of Th2-associated cytokines and decreased TNF expression, were also observed. Thus, in the absence of IFN-γ signaling, type I IFN suppressed the switching of macrophages from a more protective classically activated phenotype to a more permissive alternatively activated phenotype. Together, our data support a model in which suppression of alternative macrophage activation by type I IFN during M. tuberculosis infection, in the absence of IFN-γ signaling, contributes to host protection.

A Single ssDNA Aptamer Binding to Mannose-Capped Lipoarabinomannan of Bacillus Calmette-Guérin Enhances Immunoprotective Effect against Tuberculosis

Because Mycobacterium bovis, termed bacillus Calmette-Guérin (BCG), the only available used tuberculosis (TB) vaccine, retains immunomodulatory properties that limit its protective immunogenicity, there are continuous efforts to identify the immunosuppression mechanism as well as new strategies for improving the immunogenicity of BCG. Here, an ssDNA aptamer "antibody" BM2 specifically bound to the mannose-capped lipoarabinomannan (ManLAM) of BCG was selected. BM2 significantly blocked ManLAM-mannose receptor (MR) binding, triggered ManLAM-CD44 signaling, and enhanced M1 macrophage and Th1 activation via cellular surface CD44 in vitro and in vivo. BM2 enhanced immunoprotective effects of BCG against virulent Mycobacterium tuberculosis H37Rv infection in mice and monkeys models. Thus, we report a new mechanism of the interaction between ManLAM and CD44 on macrophages and CD4(+) T cells and reveal that ManLAM-binding membrane molecule CD44 is a novel target for the enhancement of BCG immunogenicity, and BM2 has strong potential as an immune enhancer for BCG.

Synthesis and biological activity of furoxan derivatives against Mycobacterium tuberculosis

Tuberculosis (TB) remains a serious health problem responsible to cause millions of deaths annually. The scenario becomes alarming when it is evaluated that the number of new drugs does not increase proportionally to the emergence of resistance to the current therapy. Furoxan derivatives, known as nitric oxide (NO) donors, have been described to exhibit antitubercular activity. Herein, a novel series of hybrid furoxan derivatives (1,2,5-oxadiazole 2-N-oxide) (compounds 4a-c, 8a-c and 14a-c) were designed, synthesized and evaluated in vitro against Mycobacterium tuberculosis (MTB) H37Rv (ATCC 27294) and a clinical isolate MDR-TB strain. The furoxan derivatives have exhibited MIC90 values ranging from 1.03 to 62 μM (H37Rv) and 7.0-50.0 μM (MDR-TB). For the most active compounds (8c, 14a, 14b and 14c) the selectivity index ranged from 3.78 to 52.74 (MRC-5 cells) and 1.25-34.78 (J774A.1 cells). In addition, it was characterized for those compounds logPo/w values between 2.1 and 2.9. All compounds were able to release NO at levels ranging from 0.16 to 44.23%. Among the series, the phenylsulfonyl furoxan derivatives (compounds 14a-c) were the best NO-donor with the lowest MIC90 values. The most active compound (14c) was also stable at different pHs (5.0 and 7.4). In conclusion, furoxan derivatives were identified as new promising compounds useful to treat tuberculosis.

Mycobacterial Metabolic Syndrome: LprG and Rv1410 Regulate Triacylglyceride Levels, Growth Rate and Virulence in Mycobacterium tuberculosis

Mycobacterium tuberculosis (Mtb) mutants lacking rv1411c, which encodes the lipoprotein LprG, and rv1410c, which encodes a putative efflux pump, are dramatically attenuated for growth in mice. Here we show that loss of LprG-Rv1410 in Mtb leads to intracellular triacylglyceride (TAG) accumulation, and overexpression of the locus increases the levels of TAG in the culture medium, demonstrating a role of this locus in TAG transport. LprG binds TAG within a large hydrophobic cleft and is sufficient to transfer TAG from donor to acceptor membranes. Further, LprG-Rv1410 is critical for broadly regulating bacterial growth and metabolism in vitro during carbon restriction and in vivo during infection of mice. The growth defect in mice is due to disrupted bacterial metabolism and occurs independently of key immune regulators. The in vivo essentiality of this locus suggests that this export system and other regulators of metabolism should be considered as targets for novel therapeutics.

Of the estimated 2 billion people worldwide currently infected with Mycobacterium tuberculosis (Mtb), surprisingly few go on to develop active tuberculosis (TB) disease. The vast majority, 95 percent, of infected individuals develop latent TB, remaining infected but without disease. Despite its importance in global health, the question of what determines whether an infected individual will develop active or latent TB remains largely unanswered. Changes in how Mtb grows in response to stressors presented by the host environment likely play an important role in this process. In particular, the manifold ways in which Mtb synthesizes, degrades, and transports lipids dictates its growth in an infected host. Here, we show that lipid transport is an important function of two TB genes known to be required for Mtb’s ability to cause disease in the mouse model of infection. Using a variety of genetic and biochemical techniques, we found that the products of these genes prevent the cytosolic accumulation of a lipid associated with non-growing Mtb under the metabolic conditions it encounters during infection. Our results indicate an important role for the metabolism of Mtb in its ability to orchestrate a productive infection and cause disease.

Th1 and Th17 Cells in Tuberculosis: Protection, Pathology, and Biomarkers

The outcome of Mycobacterium tuberculosis (Mtb) infection ranges from a complete pathogen clearance through asymptomatic latent infection (LTBI) to active tuberculosis (TB) disease. It is now understood that LTBI and active TB represent a continuous spectrum of states with different degrees of pathogen “activity,” host pathology, and immune reactivity. Therefore, it is important to differentiate LTBI and active TB and identify active TB stages. CD4⁺ T cells play critical role during Mtb infection by mediating protection, contributing to inflammation, and regulating immune response. Th1 and Th17 cells are the main effector CD4⁺ T cells during TB. Th1 cells have been shown to contribute to TB protection by secreting IFN-γ and activating antimycobacterial action in macrophages. Th17 induce neutrophilic inflammation, mediate tissue damage, and thus have been implicated in TB pathology. In recent years new findings have accumulated that alter our view on the role of Th1 and Th17 cells during Mtb infection. This review discusses these new results and how they can be implemented for TB diagnosis and monitoring.

Hypercalcaemic crisis in an elderly patient with pulmonary tuberculosis

Tuberculosis is an uncommon but recognized cause of hypercalcaemia, though calcium levels are seldom severely elevated and rarely result in symptoms. In the elderly patient however, several competing aetiologies may contribute to hypercalcaemia and the diagnostic evaluation may be confounded by polypharmacy as well as multiple co-existing medical conditions. We present here a case of an elderly man who presented with pulmonary tuberculosis and concomitant delirium secondary to hypercalcaemic crisis. Treatment with anti-tuberculous drugs, together with supportive care, eventually led to resolution of hypercalcaemia and restoration of mental function.

Mycobacterium tuberculosis Is a Natural Ornithine Aminotransferase (rocD) Mutant and Depends on Rv2323c for Growth on Arginine

Mycobacterium tuberculosis (Mtb) possesses a genetic repertoire for metabolic pathways, which are specific and fit to its intracellular life style. Under in vitro conditions, Mtb is known to use arginine as a nitrogen source, but the metabolic pathways for arginine utilization have not been identified. Here we show that, in the presence of arginine, Mtb upregulates a gene cluster which includes an ornithine aminotransferase (rocD) and Rv2323c, a gene of unknown function. Isotopologue analysis by using ¹³C- or ¹⁵N-arginine revealed that in Mtb arginine is not only used as nitrogen source but also as carbon source for the formation of amino acids, in particular of proline. Surprisingly, rocD, which is widespread in other bacteria and is part of the classical arginase pathway turned out to be naturally deleted in Mtb, but not in non-tuberculous mycobacteria. Mtb lacking Rv2323c showed a growth defect on arginine, did not produce proline from arginine, and incorporated less nitrogen derived from arginine in its core nitrogen metabolism. We conclude that the highly induced pathway for arginine utilization in Mtb differs from that of other bacteria including non-tuberculous mycobacteria, probably reflecting a specific metabolic feature of intracellular Mtb.

Protein energy malnutrition during vaccination has limited influence on vaccine efficacy but abolishes immunity if administered during Mycobacterium tuberculosis infection

Protein energy malnutrition (PEM) increases susceptibility to infectious diseases, including tuberculosis (TB), but it is not clear how PEM influences vaccine-promoted immunity to TB. We demonstrate that PEM during low-level steady-state TB infection in a mouse model results in rapid relapse of Mycobacterium tuberculosis, as well as increased pathology, in both Mycobacterium bovis BCG-vaccinated and unvaccinated animals. PEM did not change the overall numbers of CD4 T cells in BCG-vaccinated animals but resulted in an almost complete loss of antigen-specific cytokine production. Furthermore, there was a change in cytokine expression characterized by a gradual loss of multifunctional antigen-specific CD4 T cells and an increased proportion of effector cells expressing gamma interferon and tumor necrosis factor alpha (IFN-γ(+) TNF-α(+) and IFN-γ(+) cells). PEM during M. tuberculosis infection completely blocked the protection afforded by the H56-CAF01 subunit vaccine, and this was associated with a very substantial loss of the interleukin-2-positive memory CD4 T cells promoted by this vaccine. Similarly, PEM during the vaccination phase markedly reduced the H56-CAF01 vaccine response, influencing all cytokine-producing CD4 T cell subsets, with the exception of CD4 T cells positive for TNF-α only. Importantly, this impairment was reversible and resupplementation of protein during infection rescued both the vaccine-promoted T cell response and the protective effect of the vaccine against M. tuberculosis infection.

Interferon γ and Tumor Necrosis Factor Are Not Essential Parameters of CD4+ T-Cell Responses for Vaccine Control of Tuberculosis

BACKGROUND

Mycobacterium tuberculosis infects one third of the world's population and causes >8 million cases of tuberculosis annually. New vaccines are necessary to control the spread of tuberculosis. T cells, interferon γ (IFN-γ), and tumor necrosis factor (TNF) are necessary to control M. tuberculosis infection in both humans and unvaccinated experimental animal models. However, the immune responses necessary for vaccine efficacy against M. tuberculosis have not been defined. The multifunctional activity of T-helper type 1 (TH1) cells that simultaneously produce IFN-γ and TNF has been proposed as a candidate mechanism of vaccine efficacy.

METHODS

We used a mouse model of T-cell transfer and aerosolized M. tuberculosis infection to assess the contributions of TNF, IFN-γ, and inducible nitric oxide synthase (iNOS) to vaccine efficacy.

RESULTS

CD4(+) T cells were necessary and sufficient to transfer protection against aerosolized M. tuberculosis, but neither CD4(+) T cell-produced TNF nor host cell responsiveness to IFN-γ were necessary. Transfer of Tnf(-/-) CD4(+) T cells from vaccinated donors to Ifngr(-/-) recipients was also sufficient to confer protection. Activation of iNOS to produce reactive nitrogen species was not necessary for vaccine efficacy.

CONCLUSIONS

Induction of TH1 cells that coexpress IFN-γ and TNF is not a requirement for vaccine efficacy against M. tuberculosis, despite these cytokines being essential for control of M. tuberculosis in nonvaccinated animals.

Exploitation of Mycobacterium tuberculosis reporter strains to probe the impact of vaccination at sites of infection

Mycobacterium tuberculosis (Mtb) remains a major public health problem, with an effective vaccine continuing to prove elusive. Progress in vaccination strategies has been hampered by a lack of appreciation of the bacterium's response to dynamic changes in the host immune environment. Here, we utilize reporter Mtb strains that respond to specific host immune stresses such as hypoxia and nitric oxide (hspX'::GFP), and phagosomal maturation (rv2390c'::GFP), to investigate vaccine-induced alterations in the environmental niche during experimental murine infections. While vaccination undoubtedly decreased bacterial burden, we found that it also appeared to accelerate Mtb's adoption of a phenotype better equipped to survive in its host. We subsequently utilized a novel replication reporter strain of Mtb to demonstrate that, in addition to these alterations in host stress response, there is a decreased percentage of actively replicating Mtb in vaccinated hosts. This observation was supported by the differential sensitivity of recovered bacteria to the front-line drug isoniazid. Our study documents the natural history of the impact that vaccination has on Mtb's physiology and replication and highlights the value of reporter Mtb strains for probing heterogeneous Mtb populations in the context of a complex, whole animal model.

Differential control of Mincle-dependent cord factor recognition and macrophage responses by the transcription factors C/EBPβ and HIF1α

Trehalose-6,6-dimycolate (TDM), the mycobacterial cord factor, and its synthetic analog Trehalose-6,6-dibehenate (TDB) bind to the C-type lectin receptors macrophage-inducible C-type lectin (Mincle) and Mcl to activate macrophages. Genetically, the transcriptional response to TDB/TDM has been defined to require FcRγ-Syk-Card9 signaling. However, TDB/TDM-triggered kinase activation has not been studied well, and it is largely unknown which transcriptional regulators bring about inflammatory gene expression. In this article, we report that TDB/TDM caused only weak Syk-phosphorylation in resting macrophages, consistent with low basal Mincle expression. However, LPS-priming caused MYD88-dependent upregulation of Mincle, resulting in enhanced TDB/TDM-induced kinase activation and more rapid inflammatory gene expression. TLR-induced Mincle expression partially circumvented the requirement for Mcl in the response to TDB/TDM. To dissect transcriptional responses to TDB/TDM, we mined microarray data and identified early growth response (Egr) family transcription factors as direct Mincle target genes, whereas upregulation of Cebpb and Hif1a required new protein synthesis. Macrophages and dendritic cells lacking C/EBPβ showed nearly complete abrogation of TDB/TDM responsiveness, but also failed to upregulate Mincle. Retroviral rescue of Mincle expression in Cebpb-deficient cells restored induction of Egr1, but not of G-CSF. This pattern of C/EBPβ dependence was also observed after stimulation with the Dectin-1 ligand Curdlan. Inducible expression of hypoxia-inducible factor 1α (HIF1α) also required C/EBPβ. In turn, HIF1α was not required for Mincle expression, kinase activation, and Egr1 or Csf3 expression, but critically contributed to NO production. Taken together, we identify C/EBPβ as central hub in Mincle expression and inflammatory gene induction, whereas HIF1α controls Nos2 expression. C/EBPβ also connects TLR signals to cord factor responsiveness through MYD88-dependent upregulation of Mincle.

Cell-autonomous effector mechanisms against mycobacterium tuberculosis

Few pathogens run the gauntlet of sterilizing immunity like Mycobacterium tuberculosis (Mtb). This organism infects mononuclear phagocytes and is also ingested by neutrophils, both of which possess an arsenal of cell-intrinsic effector mechanisms capable of eliminating it. Here Mtb encounters acid, oxidants, nitrosylating agents, and redox congeners, often exuberantly delivered under low oxygen tension. Further pressure is applied by withholding divalent Fe²⁺, Mn²⁺, Cu²⁺, and Zn²⁺, as well as by metabolic privation in the form of carbon needed for anaplerosis and aromatic amino acids for growth. Finally, host E3 ligases ubiquinate, cationic peptides disrupt, and lysosomal enzymes digest Mtb as part of the autophagic response to this particular pathogen. It is a testament to the evolutionary fitness of Mtb that sterilization is rarely complete, although sufficient to ensure most people infected with this airborne bacterium remain disease-free.

Expression levels of 10 candidate genes in lung tissue of vaccinated and TB-infected cynomolgus macaques

The expression of ten tuberculosis candidate genes in lung and lymph nodes of cynomolgus macaques vaccinated and experimentally infected with Mycobacterium tuberculosis (Mtb) was quantified. The expression of TNFα, IL10, IL1β, TLR4, IL17, IL6, IL12, and iNOS in the lungs of vaccinated animals was higher than that of non-vaccinated animals.

The intracellular environment of human macrophages that produce nitric oxide promotes growth of mycobacteria

Nitric oxide (NO) is a diffusible radical gas produced from the activity of nitric oxide synthase (NOS). NOS activity in murine macrophages has a protective role against mycobacteria through generation of reactive nitrogen intermediates (RNIs). However, the production of NO by human macrophages has remained unclear due to the lack of sensitive reagents to detect NO directly. The purpose of this study was to investigate NO production and the consequence to mycobacteria in primary human macrophages. We found that Mycobacterium bovis BCG or Mycobacterium tuberculosis infection of human macrophages induced expression of NOS2 and NOS3 that resulted in detectable production of NO. Treatment with gamma interferon (IFN-γ), l-arginine, and tetrahydrobiopterin enhanced expression of NOS2 and NOS3 isoforms, as well as NO production. Both of these enzymes were shown to contribute to NO production. The maximal level of NO produced by human macrophages was not bactericidal or bacteriostatic to M. tuberculosis or BCG. The number of viable mycobacteria was increased in macrophages that produced NO, and this requires expression of nitrate reductase. An narG mutant of M. tuberculosis persisted but was unable to grow in human macrophages. Taken together, these data (i) enhance our understanding of primary human macrophage potential to produce NO, (ii) demonstrate that the level of RNIs produced in response to IFN-γ in vitro is not sufficient to limit intracellular mycobacterial growth, and (iii) suggest that mycobacteria may use RNIs to enhance their survival in human macrophages.

The immune response in tuberculosis

There are 9 million cases of active tuberculosis reported annually; however, an estimated one-third of the world's population is infected with Mycobacterium tuberculosis and remains asymptomatic. Of these latent individuals, only 5-10% will develop active tuberculosis disease in their lifetime. CD4(+) T cells, as well as the cytokines IL-12, IFN-γ, and TNF, are critical in the control of Mycobacterium tuberculosis infection, but the host factors that determine why some individuals are protected from infection while others go on to develop disease are unclear. Genetic factors of the host and of the pathogen itself may be associated with an increased risk of patients developing active tuberculosis. This review aims to summarize what we know about the immune response in tuberculosis, in human disease, and in a range of experimental models, all of which are essential to advancing our mechanistic knowledge base of the host-pathogen interactions that influence disease outcome.

Microenvironments in tuberculous granulomas are delineated by distinct populations of macrophage subsets and expression of nitric oxide synthase and arginase isoforms

Macrophages in granulomas are both antimycobacterial effector and host cell for Mycobacterium tuberculosis, yet basic aspects of macrophage diversity and function within the complex structures of granulomas remain poorly understood. To address this, we examined myeloid cell phenotypes and expression of enzymes correlated with host defense in macaque and human granulomas. Macaque granulomas had upregulated inducible and endothelial NO synthase (iNOS and eNOS) and arginase (Arg1 and Arg2) expression and enzyme activity compared with nongranulomatous tissue. Immunohistochemical analysis indicated macrophages adjacent to uninvolved normal tissue were more likely to express CD163, whereas epithelioid macrophages in regions where bacteria reside strongly expressed CD11c, CD68, and HAM56. Calprotectin-positive neutrophils were abundant in regions adjacent to caseum. iNOS, eNOS, Arg1, and Arg2 proteins were identified in macrophages and localized similarly in granulomas across species, with greater eNOS expression and ratio of iNOS/Arg1 expression in epithelioid macrophages as compared with cells in the lymphocyte cuff. iNOS, Arg1, and Arg2 expression in neutrophils was also identified. The combination of phenotypic and functional markers support that macrophages with anti-inflammatory phenotypes localized to outer regions of granulomas, whereas the inner regions were more likely to contain macrophages with proinflammatory, presumably bactericidal, phenotypes. Together, these data support the concept that granulomas have organized microenvironments that balance antimicrobial anti-inflammatory responses to limit pathology in the lungs.

Division of labor between lung dendritic cells and macrophages in the defense against pulmonary infections

The lung is highly exposed to the external environment. For this reason, the lung needs to handle a number of potential threats present in inhaled air such as viruses or bacteria. Dendritic cells (DCs) and macrophages (MFs) play an important role in orchestrating the immune responses to these challenges. The severe lung inflammation caused by some pathogens poses a unique challenge to the immune system: the potential insult must be eliminated rapidly whereas tissue inflammation must be controlled in order to avoid collateral damages that can lead to acute respiratory failure. Immune responses to infectious agents are initiated and controlled by various populations of antigen-presenting cells with specialized functions, which include conventional DCs (cDCs), monocyte-derived DCs (moDCs), plasmacytoid DCs (pDCs), and alveolar MFs (AMFs). This review will discuss the role of these different cells in responses to pulmonary infections, with a focus on influenza virus and Mycobacterium tuberculosis.