Reverse translation in tuberculosis: neutrophils provide clues for understanding development of active disease

miR-223: a key regulator of pulmonary inflammation

Small noncoding RNAs, known as microRNAs (miRNAs), are vital for the regulation of diverse biological processes. miR-223, an evolutionarily conserved anti-inflammatory miRNA expressed in cells of the myeloid lineage, has been implicated in the regulation of monocyte-macrophage differentiation, proinflammatory responses, and the recruitment of neutrophils. The biological functions of this gene are regulated by its expression levels in cells or tissues. In this review, we first outline the regulatory role of miR-223 in granulocytes, macrophages, endothelial cells, epithelial cells and dendritic cells (DCs). Then, we summarize the possible role of miR-223 in chronic obstructive pulmonary disease (COPD), acute lung injury (ALI), coronavirus disease 2019 (COVID-19) and other pulmonary inflammatory diseases to better understand the molecular regulatory networks in pulmonary inflammatory diseases.

Expression of specific HLA class II alleles is associated with an increased risk for active tuberculosis and a distinct gene expression profile

Several HLA allelic variants have been associated with protection from or susceptibility to infectious and autoimmune diseases. Here, we examined whether specific HLA alleles would be associated with different Mycobacterium tuberculosis (Mtb) infection outcomes. The HLA alleles present at the -A, -B, -C, -DPA1, -DPB1, -DQA1, -DQB1, -DRB1, and -DRB3/4/5 loci were determined in a cohort of 636 individuals with known Mtb infection outcomes from South Africa and the United States. Among these individuals, 203 were QuantiFERON (QFT) negative, and 433 were QFT positive, indicating Mtb exposure. Of these, 99 QFT positive participants either had active tuberculosis (TB) upon enrollment or were diagnosed in the past. We found that DQA1*03:01, DPB1*04:02, and DRB4*01:01 were significantly more frequent in individuals with active TB (susceptibility alleles), as judged by Odds Ratios and associated p-values, while DPB1*105:01 was associated with protection from active TB. Peripheral blood mononuclear cells (PMBCs) from a subset of individuals were stimulated with Mtb antigens, revealing individuals who express any of the three susceptibility alleles were associated with lower magnitude of responses. Furthermore, we defined a gene signature associated with individuals expressing the susceptibility alleles that was characterized by lower expression of APC-related genes. In summary, we have identified specific HLA alleles associated with susceptibility to active TB and found that the expression of these alleles was associated with a decreased Mtb-specific T cell response and a specific gene expression signature. These results will help understand individual risk factors in progressing to active TB.

Differential Role of Type 2 Diabetes as a Risk Factor for Tuberculosis in the Elderly versus Younger Adults

The elderly are understudied despite their high risk of tuberculosis (TB). We sought to identify factors underlying the lack of an association between TB and type 2 diabetes (T2D) in the elderly, but not adults. We conducted a case-control study in elderly (≥65 years old; ELD) vs. younger adults (young/middle-aged adults (18-44/45-64 years old; YA|MAA) stratified by TB and T2D, using a research study population (n = 1160) and TB surveillance data (n = 8783). In the research study population the adjusted odds ratio (AOR) of TB in T2D was highest in young adults (AOR 6.48) but waned with age becoming non-significant in the elderly. Findings were validated using TB surveillance data. T2D in the elderly (vs. T2D in younger individuals) was characterized by better glucose control (e.g., lower hyperglycemia or HbA1c), lower insulin resistance, more sulphonylureas use, and features of less inflammation (e.g., lower obesity, neutrophils, platelets, anti-inflammatory use). We posit that differences underlying glucose dysregulation and inflammation in elderly vs. younger adults with T2D, contribute to their differential association with TB. Studies in the elderly provide valuable insights into TB-T2D pathogenesis, e.g., here we identified insulin resistance as a novel candidate mechanism by which T2D may increase active TB risk.

MicroRNAs as immune regulators and biomarkers in tuberculosis

Tuberculosis (TB), which is caused by Mycobacterium tuberculosis (Mtb), is one of the most lethal infectious disease worldwide, and it greatly affects human health. Some diagnostic and therapeutic methods are available to effectively prevent and treat TB; however, only a few systematic studies have described the roles of microRNAs (miRNAs) in TB. Combining multiple clinical datasets and previous studies on Mtb and miRNAs, we state that pathogens can exploit interactions between miRNAs and other biomolecules to avoid host mechanisms of immune-mediated clearance and survive in host cells for a long time. During the interaction between Mtb and host cells, miRNA expression levels are altered, resulting in the changes in the miRNA-mediated regulation of host cell metabolism, inflammatory responses, apoptosis, and autophagy. In addition, differential miRNA expression can be used to distinguish healthy individuals, patients with TB, and patients with latent TB. This review summarizes the roles of miRNAs in immune regulation and their application as biomarkers in TB. These findings could provide new opportunities for the diagnosis and treatment of TB.

How mycobacteria take advantage of the weakness in human immune system in the modern world

Tuberculosis (TB) infection remains a global health threat in recent decades partly due to a marked increase in the number of susceptible patients, including those with diabetes mellitus (DM) and who receive biologics. Immunity in TB infection is complex as Mycobacterium tuberculosis (MTB) is a highly adaptive pathogen and may evade the immune defense through various ways. Recent advances in TB immunity have revealed that granulomatous inflammation in TB infection is highly dynamic and the early influx of neutrophils may lead to excessive inflammation and pulmonary cavitation, which provide niches for MTB not only to survive but also to spread to other sites. Furthermore, reactive oxygen species have been found to play a crucial role among pathogenesis of TB infection in diabetics (DM-TB) through regulating inflammasome activation and the production of IL-1β, which in turn modulates the inflammatory network in TB infection, leading to dysfunctional inflammatory responses and tissue remodeling. To understand the exact immunological mechanisms underlying TB infection hence is essential for developing novel adjunctive host-directed therapy (HDT) aiming to alleviate excessive inflammation and tissue destruction and, at the same time, enhance the efficacy of currently available choices of anti-mycobacterial agents. Here we reviewed current epidemiological challenges of global TB control, novel immunological mechanisms underlying dysregulated inflammation in TB infection, especially in DM-TB, and some potential applications of adjunctive HDT in TB treatment.

Th1, Th17, and Th1Th17 Lymphocytes during Tuberculosis: Th1 Lymphocytes Predominate and Appear as Low-Differentiated CXCR3+CCR6+ Cells in the Blood and Highly Differentiated CXCR3+/-CCR6- Cells in the Lungs

Th1 lymphocytes are considered the main mediators of protection against tuberculosis (TB); however, their phenotypic characteristics and relationship with Th17 and Th1Th17 populations during TB are poorly understood. We have analyzed Th1, Th17, and Th1Th17 lymphocytes in the blood and pulmonary lesions of TB patients. The populations were identified based on the production of IFN-γ and/or IL-17 and the coexpression of CXCR3 (X3) and CCR6 (R6). In the blood, IL-17⁺ and IFN-γ⁺IL-17⁺ lymphocytes were barely detectable (median, <0.01% of CD4⁺ lymphocytes), whereas IFN-γ⁺ lymphocytes predominated (median, 0.45%). Most IFN-γ⁺ lymphocytes (52%) were X3⁺R6⁺, suggesting their "nonclassical" (ex-Th17) nature. In the lungs, IL-17⁺ and IFN-γ⁺IL-17⁺ lymphocytes were more frequent (0.3%, p < 0.005), yet IFN-γ⁺ cells predominated (11%). Phenotypically, lung CD4⁺ cells were X3^+/loR6^- The degree of differentiation of blood effector CD4⁺ lymphocytes (evaluated based on CD62L/CD27/CD28 coexpression) increased as follows: X3⁺R6⁺ < X3⁺R6^- < X3^-R6^-, with X3^-R6^- cells being largely terminally differentiated CD62L^-CD27^-CD28^- cells. Lung CD4⁺ lymphocytes were highly differentiated, recalling blood X3^+/-R6^- populations. Following in vitro stimulation with anti-CD3/anti-CD28 Abs, X3⁺R6⁺CD4⁺ lymphocytes converted into X3⁺R6^- and X3^-R6^- cells. The results demonstrate that, during active TB, Th1 lymphocytes predominate in blood and lungs, document differences in X3/R6 expression by blood and lung CD4⁺ cells, and link the pattern of X3/R6 expression with the degree of cell differentiation. These findings add to the understanding of immune mechanisms operating during TB and are relevant for the development of better strategies to control it.

Immunological roulette: Luck or something more? Considering the connections between host and environment in TB

Accurate prediction of which patient will progress from a sub-clinical Mycobacterium tuberculosis infection to active tuberculosis represents an elusive, yet critical, clinical research objective. From the individual perspective, progression can be considered to be the product of a series of unfortunate events or even a run of bad luck. Here, we identify the subtle physiological relationships that can influence the odds of progression to active TB and how this progression may reflect directed dysbiosis in a number of interrelated systems. Most infected individuals who progress to disease have apparently good immune responses, but these responses are, at times, compromised by either local or systemic environmental factors. Obvious disease promoting processes, such as tissue-damaging granulomata, usually manifest in the lung, but illness is systemic. This apparent dichotomy between local and systemic reflects a clear need to define the factors that promote progression to active disease within the context of the body as a physiological whole. We discuss aspects of the host environment that can impact expression of immunity, including the microbiome, glucocorticoid-mediated regulation, catecholamines and interaction between the gut, liver and lung. We suggest the importance of integrating precision medicine into our analyses of experimental outcomes such that apparently conflicting results are not contentious, but rather reflect the impact of these subtle relationships with our environment and microbiota.

Mycobacterial infection induces higher interleukin-1β and dysregulated lung inflammation in mice with defective leukocyte NADPH oxidase

Granulomatous inflammation causes severe tissue damage in mycobacterial infection while redox status was reported to be crucial in the granulomatous inflammation. Here, we used a NADPH oxidase 2 (NOX2)-deficient mice (Ncf1^-/-) to investigate the role of leukocyte-produced reactive oxygen species (ROS) in mycobacterium-induced granulomatous inflammation. We found poorly controlled mycobacterial proliferation, significant body weight loss, and a high mortality rate after M. marinum infection in Ncf1^-/- mice. Moreover, we noticed loose and neutrophilic granulomas and higher levels of interleukin (IL)-1β and neutrophil chemokines in Ncf1^-/- mice when compared with those in wild type mice. The lack of ROS led to reduced production of IL-1β in macrophages, whereas neutrophil elastase (NE), an abundant product of neutrophils, may potentially exert increased inflammasome-independent protease activity and lead to higher IL-1β production. Moreover, we showed that the abundant NE and IL-1β were present in the caseous granulomatous inflammation of human TB infection. Importantly, blocking of IL-1β with either a specific antibody or a recombinant IL-1 receptor ameliorated the pulmonary inflammation. These findings revealed a novel role of ROS in the early pathogenesis of neutrophilic granulomatous inflammation and suggested a potential role of IL-1 blocking in the treatment of mycobacterial infection in the lung.

Host-directed therapies for bacterial and viral infections

Host-directed therapy (HDT) is a novel approach in the field of anti-infectives for overcoming antimicrobial resistance.

HDT aims to interfere with host cell factors that are required by a pathogen for replication or persistence, to enhance protective immune responses against a pathogen, to reduce exacerbated inflammation and to balance immune reactivity at sites of pathology.

HDTs encompassing the 'shock and kill' strategy or the delivery of recombinant interferons are possible approaches to treat HIV infections. HDTs that suppress the cytokine storm that is induced by some acute viral infections represent a promising concept.

In tuberculosis, HDT aims to enhance the antimicrobial activities of phagocytes through phagosomal maturation, autophagy and antimicrobial peptides. HDTs also curtail inflammation through interference with soluble (such as eicosanoids or cytokines) or cellular (co-stimulatory molecules) factors and modulate granulomas to allow the access of antimicrobials or to restrict tissue damage.

Numerous parallels between the immunological abnormalities that occur in sepsis and cancer indicate that the HDTs that are effective in oncology may also hold promise in sepsis.

Advances in immune phenotyping, genetic screening and biosignatures will help to guide drug therapy to optimize the host response. Combinations of canonical pathogen-directed drugs and novel HDTs will become indispensable in treating emerging infections and diseases caused by drug-resistant pathogens.

Host-directed therapy (HDT) aims to interfere with host cell factors that are required by a pathogen for replication or persistence. In this Review, Kaufmannet al. describe recent progress in the development of HDTs for the treatment of viral and bacterial infections and the challenges in bringing these approaches to the clinic.

Despite the recent increase in the development of antivirals and antibiotics, antimicrobial resistance and the lack of broad-spectrum virus-targeting drugs are still important issues and additional alternative approaches to treat infectious diseases are urgently needed. Host-directed therapy (HDT) is an emerging approach in the field of anti-infectives. The strategy behind HDT is to interfere with host cell factors that are required by a pathogen for replication or persistence, to enhance protective immune responses against a pathogen, to reduce exacerbated inflammation and to balance immune reactivity at sites of pathology. Although HDTs encompassing interferons are well established for the treatment of chronic viral hepatitis, novel strategies aimed at the functional cure of persistent viral infections and the development of broad-spectrum antivirals against emerging viruses seem to be crucial. In chronic bacterial infections, such as tuberculosis, HDT strategies aim to enhance the antimicrobial activities of phagocytes and to curtail inflammation through interference with soluble factors (such as eicosanoids and cytokines) or cellular factors (such as co-stimulatory molecules). This Review describes current progress in the development of HDTs for viral and bacterial infections, including sepsis, and the challenges in bringing these new approaches to the clinic.

Granulomas and Inflammation: Host-Directed Therapies for Tuberculosis

Tuberculosis (TB) remains a leading global health problem that is aggravated by emergence of drug-resistant strains, which account for increasing number of treatment-refractory cases. Thus, eradication of this disease will strongly require better therapeutic strategies. Identification of host factors promoting disease progression may accelerate discovery of adjunct host-directed therapies (HDTs) that will boost current treatment protocols. HDTs focus on potentiating key components of host anti-mycobacterial effector mechanisms, and limiting inflammation and pathological damage in the lung. Granulomas represent a pathological hallmark of TB. They are comprised of impressive arrangement of immune cells that serve to contain the invading pathogen. However, granulomas can also undergo changes, developing caseums and cavities that facilitate bacterial spread and disease progression. Here, we review current concepts on the role of granulomas in pathogenesis and protective immunity against TB, drawing from recent clinical studies in humans and animal models. We also discuss therapeutic potential of inflammatory pathways that drive granuloma progression, with a focus on new and existing drugs that will likely improve TB treatment outcomes.

Neutrophil Extracellular Traps in Pulmonary Diseases: Too Much of a Good Thing?

Neutrophil extracellular traps (NETs) arise from the release of granular and nuclear contents of neutrophils in the extracellular space in response to different classes of microorganisms, soluble factors, and host molecules. NETs are composed by decondensed chromatin fibers coated with antimicrobial granular and cytoplasmic proteins, such as myeloperoxidase, neutrophil elastase (NE), and α-defensins. Besides being expressed on NET fibers, NE and MPO also regulate NET formation. Furthermore, histone deimination by peptidylarginine deiminase 4 (PAD4) is a central step to NET formation. NET formation has been widely demonstrated to be an effective mechanism to fight against invading microorganisms, as deficiency in NET release or dismantling NET backbone by bacterial DNases renders the host susceptible to infections. Therefore, the primary role of NETs is to prevent microbial dissemination, avoiding overwhelming infections. However, an excess of NET formation has a dark side. The pathogenic role of NETs has been described for many human diseases, infectious and non-infectious. The detrimental effect of excessive NET release is particularly important to lung diseases, because NETs can expand more easily in the pulmonary alveoli, causing lung injury. Moreover, NETs and its associated molecules are able to directly induce epithelial and endothelial cell death. In this regard, massive NET formation has been reported in several pulmonary diseases, including asthma, chronic obstructive pulmonary disease, cystic fibrosis, respiratory syncytial virus bronchiolitis, influenza, bacterial pneumonia, and tuberculosis, among others. Thus, NET formation must be tightly regulated in order to avoid NET-mediated tissue damage. Recent development of therapies targeting NETs in pulmonary diseases includes DNA disintegration with recombinant human DNase, neutralization of NET proteins, with anti-histone antibodies and protease inhibitors. In this review, we summarize the recent knowledge on the pathophysiological role of NETs in pulmonary diseases as well as some experimental and clinical approaches to modulate their detrimental effects.

Innate myeloid cell TNFR1 mediates first line defence against primary Mycobacterium tuberculosis infection

TNF is crucial for controlling Mycobacterium tuberculosis infection and understanding how will help immunomodulating the host response. Here we assessed the contribution of TNFR1 pathway from innate myeloid versus T cells. We first established the prominent role of TNFR1 in haematopoietic cells for controlling M. tuberculosis in TNFR1 KO chimera mice. Further, absence of TNFR1 specifically on myeloid cells (M-TNFR1 KO) recapitulated the uncontrolled M. tuberculosis infection seen in fully TNFR1 deficient mice, with increased bacterial burden, exacerbated lung inflammation, and rapid death. Pulmonary IL-12p40 over-expression was attributed to a prominent CD11b⁺ Gr1^high cell population in infected M-TNFR1 KO mice. By contrast, absence of TNFR1 on T-cells did not compromise the control of M. tuberculosis infection over 6-months. Thus, the protective TNF/TNFR1 pathway essential for controlling primary M. tuberculosis infection depends on innate macrophage and neutrophil myeloid cells, while TNFR1 pathway in T cells is dispensable.

The human immune response to tuberculosis and its treatment: a view from the blood

The immune response upon infection with the pathogen Mycobacterium tuberculosis is poorly understood, hampering the discovery of new treatments and the improvements in diagnosis. In the last years, a blood transcriptional signature in tuberculosis has provided knowledge on the immune response occurring during active tuberculosis disease. This signature was absent in the majority of asymptomatic individuals who are latently infected with M. tuberculosis (referred to as latent). Using modular and pathway analyses of the complex data has shown, now in multiple studies, that the signature of active tuberculosis is dominated by overexpression of interferon-inducible genes (consisting of both type I and type II interferon signaling), myeloid genes, and inflammatory genes. There is also downregulation of genes encoding B and T-cell function. The blood signature of tuberculosis correlates with the extent of radiographic disease and is diminished upon effective treatment suggesting the possibility of new improved strategies to support diagnostic assays and methods for drug treatment monitoring. The signature suggested a previously under-appreciated role for type I interferons in development of active tuberculosis disease, and numerous mechanisms have now been uncovered to explain how type I interferon impedes the protective response to M. tuberculosis infection.

Versatile myeloid cell subsets contribute to tuberculosis-associated inflammation

Tuberculosis (TB), a chronic bacterial infectious disease caused by Mycobacterium tuberculosis (Mtb), typically affects the lung and causes profound morbidity and mortality rates worldwide. Recent advances in cellular immunology emphasize the complexity of myeloid cell subsets controlling TB inflammation. The specialization of myeloid cell subsets for particular immune processes has tailored their roles in protection and pathology. Among myeloid cells, dendritic cells (DCs) are essential for the induction of adaptive immunity, macrophages predominantly harbor Mtb within TB granulomas and polymorphonuclear neutrophils (PMNs) orchestrate lung damage. However, within each myeloid cell population, diverse phenotypes with unique functions are currently recognized, differentially influencing TB pneumonia and granuloma functionality. More recently, myeloid-derived suppressor cells (MDSCs) have been identified at the site of Mtb infection. Along with PMNs, MDSCs accumulate within the inflamed lung, interact with granuloma-residing cells and contribute to exuberant inflammation. In this review, we discuss the contribution of different myeloid cell subsets to inflammation in TB by highlighting their interactions with Mtb and their role in lung pathology. Uncovering the manifold nature of myeloid cells in TB pathogenesis will inform the development of future immune therapies aimed at tipping the inflammation balance to the benefit of the host.

Protection and pathology in TB: learning from the zebrafish model

Zebrafish has earned its place among animal models of tuberculosis. Its natural pathogen, Mycobacterium marinum, shares major virulence factors with the human pathogen Mycobacterium tuberculosis. In adult zebrafish, which possess recombination-activated adaptive immunity, it can cause acute infection or a chronic progressive disease with containment of mycobacteria in well-structured, caseating granulomas. In addition, a low-dose model that closely mimics human latent infection has recently been developed. These models are used alongside infection of optically transparent zebrafish embryos and larvae that rely on innate immunity and permit non-invasive visualization of the early stages of developing granulomas that are inaccessible in other animal models. By microinjecting mycobacteria intravenously or into different tissues, systemic and localized infections can be induced, each useful for studying particular aspects of early pathogenesis, such as phagocyte recruitment, granuloma expansion and maintenance, vascularization of granulomas, and the phagocyte-mediated dissemination of mycobacteria. This has contributed to new insights into the mycobacteria-driven mechanisms that promote granuloma formation, the double-edged role of inflammation, the mechanisms of macrophage cell death that favor disease progression, and the host-protective role of autophagy. As a result, zebrafish models are now increasingly used to explore strategies for adjunctive therapy of tuberculosis with host-directed drugs.

Innate and Adaptive Cellular Immune Responses to Mycobacterium tuberculosis Infection

Host resistance to Mycobacterium tuberculosis (Mtb) infection requires the coordinated efforts of innate and adaptive immune cells. Diverse pulmonary myeloid cell populations respond to Mtb with unique contributions to both host-protective and potentially detrimental inflammation. Although multiple cell types of the adaptive immune system respond to Mtb infection, CD4 T cells are the principal antigen-specific cells responsible for containment of Mtb infection, but they can also be major contributors to disease during Mtb infection in several different settings. Here, we will discuss the role of different myeloid populations as well as the dual nature of CD4 T cells in Mtb infection with a primary focus on data generated using in vivo cellular immunological studies in experimental animal models and in humans when available.

Striking the Right Balance Determines TB or Not TB

Mycobacterium tuberculosis continues to be one of the most successful pathogens on earth. Upon inhalation of M. tuberculosis by a healthy individual, the host immune system will attempt to eliminate these pathogens using a combination of immune defense strategies. These include the recruitment of macrophages and other phagocytes to the site of infection, production of cytokines that enhance the microbicidal capacity of the macrophages, as well as the activation of distinct subsets of leukocytes that work in concert to fight the infection. However, being as successful as it is, M. tuberculosis has evolved numerous strategies to subvert host immunity at virtual every level. As a consequence, one third of the world inhabitants carry M. tuberculosis, and tuberculosis continuous to cause disease in more than 8 million people with deadly consequences in well over 1 million patients each year. In this review, we discuss several of the strategies that M. tuberculosis employs to circumvent host immunity, as well as describe some of the mechanisms that the host uses to counter such subversive strategies. As for many other infectious diseases, the ultimate outcome is usually defined by the relative strength of the virulence strategies employed by the tubercle bacillus versus the arsenal of immune defense mechanisms of the infected host.

Identifcation of differentially expressed long non-coding RNAs in CD4+ T cells response to latent tuberculosis infection

Objective

To identify differentially expressed long non-coding RNAs (lncRNAs) in CD4⁺ T cells triggered upon latent tuberculosis (TB) infection.

Methods

Expression profiles of lncRNAs and mRNAs in CD4⁺ T cells from individuals with latent TB infection (LTBI), active TB and healthy controls were analyzed by microarray assay and four lncRNAs were selected for validation using real time-quantitative polymerase chain reaction (RT-qPCR). Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway based approaches were used to investigate biological functions and signaling pathways affected by the differentially expressed mRNAs.

Results

LncRNAs and mRNAs in CD4⁺ T cells were involved in LTBI and active TB disease. Compared with healthy controls, 449 lncRNAs and 461 mRNAs were deregulated in LTBI group, 1,113 lncRNAs and 1,490 mRNAs were deregulated in active TB group, as well as 163 lncRNAs and 187 mRNAs were differentially expressed in both LTBI and active TB group. It was worth noting that 41 lncRNAs and 60 mRNAs were deregulated between three groups. Most deregulated lncRNAs were from intergenic regions (∼50%), natural antisense to protein-coding loci (∼20%), or intronic antisense to protein-coding loci (∼10%). Significantly enriched signaling pathways based on deregulated mRNAs were mainly involved in mitogen-activated protein kinase (MAPK) signaling pathway, cytokine–cytokine receptor interaction, Toll-like receptor signaling pathway, etc.

Conclusions

The study was the first report of differentially expressed lncRNAs in CD4⁺ T cells response to TB infection and indicated that some lncRNAs may be involved in regulating host immune response to TB infection. Future studies are needed to further elucidate potential roles of these deregulated lncRNAs in LTBI and its reactivation.