Neutrophil responses to Mycobacterium tuberculosis infection in genetically susceptible and resistant mice

Deficiency in the glycosyltransferase Gcnt1 increases susceptibility to tuberculosis through a mechanism involving neutrophils

Modulation of immunity and disease by glycans is increasingly recognized. However, how host glycosylation shapes and is shaped by tuberculosis remains poorly understood. We show that deficiency in the glucosaminyl (N-acetyl) transferase 1 (Gcnt1), a key enzyme for core-2 O-glycans biosynthesis, drives susceptibility to Mycobacterium tuberculosis infection. The increased susceptibility of Gcnt1 deficient mice was characterized by extensive lung immune pathology, mechanistically related to neutrophils. Uninfected Gcnt1 deficient mice presented bone marrow, blood and lung neutrophilia, which further increased with infection. Blood neutrophilia required Gcnt1 deficiency in the hematopoietic compartment, relating with enhanced granulopoiesis, but normal cellular egress from the bone marrow. Interestingly, for the blood neutrophilia to translate into susceptibility to M. tuberculosis infection, Gnct1 deficiency in the stroma was also necessary. Complete Gcnt1 deficiency associated with increased lung expression of the neutrophil chemoattractant CXCL2. Lastly, we demonstrate that the transcript levels of various glycosyltransferase-encoding genes were altered in whole blood of active tuberculosis patients and that sialyl Lewis x, a glycan widely present in human neutrophils, was detected in the lung of tuberculosis patients. Our findings reveal a previously unappreciated link between Gcnt1, neutrophilia and susceptibility to M. tuberculosis infection, uncovering new players balancing the immune response in tuberculosis.

Mycobacterium tuberculosis Lipoarabinomannan Activates Human Neutrophils via a TLR2/1 Mechanism Distinct from Pam3CSK4

Neutrophils, polymorphonuclear (PMN) leukocytes, play an important role in the early innate immune response to Mycobacterium tuberculosis infection in the lung. Interactions between PMN and mycobacterial lipids impact the activation state of these migrated cells with consequences for the surrounding tissue in terms of resolution versus ongoing inflammation. We hypothesized that lipoarabinomannan from M. tuberculosis (Mtb LAM) would prime human PMN in a TLR2-dependent manner and investigated this with specific comparison with the purified synthetic TLR2 agonists, Pam₃CSK₄ and FSL-1. In contrast to Pam₃CSK₄ and FSL-1, we found Mtb LAM did not induce any of the classical PMN priming phenotypes, including enhancement of NADPH oxidase activity, shedding of l-selectin, or mobilization of CD11b. However, exposure of PMN to Mtb LAM did elicit pro- and anti-inflammatory cytokine production and release in a TLR2/1-dependent manner, using the TLR1 single-nucleotide polymorphism rs5743618 (1805G/T) as a marker for TLR2/1 specificity. Moreover, Mtb LAM did not elicit p38 MAPK phosphorylation or endocytosis, although these processes occurred with Pam₃CSK₄ stimulation, and were necessary for the early priming events to occur. Interestingly, Mtb LAM did not abrogate priming responses elicited by Pam₃CSK₄ Notably, subfractionation of light membranes from Pam₃CSK₄ versus Mtb LAM-stimulated cells demonstrated differential patterns of exocytosis. In summary, Mtb LAM activates PMN via TLR2/1, resulting in the production of cytokines but does not elicit early PMN priming responses, as seen with Pam₃CSK₄ We speculate that the inability of Mtb LAM to prime PMN may be due to differential localization of TLR2/1 signaling.

Neutrophil-to-Monocyte-Plus-Lymphocyte Ratio as a Potential Marker for Discriminating Pulmonary Tuberculosis from Nontuberculosis Infectious Lung Diseases

OBJECTIVE

To determine whether NMLR has more statistical strength than NLR in discriminating TB from non-TB infectious lung diseases.

METHODS

Among patients who underwent 3 or more TB culture tests with molecular study between January 2016 and December 2017, 110 patients with TB, and 159 patients diagnosed with non-TB infectious lung diseases were enrolled. The original complete blood count (CBC) parameters and modified CBC indices, including NLR and NMLR, were analyzed.

RESULTS

The NLR and NMLR were significantly lower in TB patients than in patients with other infectious lung diseases. However, the area under the curve (AUC) for NMLR (0.90; 95% confidence interval [CI], 0.86-0.93) was significantly greater than that for NLR (0.88 [0.84-0.92]).

CONCLUSIONS

The neutrophil-to-monocyte-plus-lymphocyte ratio (NMLR) can be used as a new index that is more powerful than neutrophil-to-lymphocyte ratio (NLR) in discriminating tuberculosis (TB) from non-TB infectious lung diseases.NMLR had more statistical strength than NLR in discriminating TB from non-TB infectious lung diseases.

Inhibition of type I interferon signaling abrogates early Mycobacterium bovis infection

Background

Mycobacterium bovis (M. bovis) is the principal causative agent of bovine tuberculosis; however, it may also cause serious infection in human being. Type I IFN is a key factor in reducing viral multiplication and modulating host immune response against viral infection. However, the regulatory pathways of Type I IFN signaling during M. bovis infection are not yet fully explored. Here, we investigate the role of Type I IFN signaling in the pathogenesis of M. bovis infection in mice.

Methods

C57BL/6 mice were treated with IFNAR1-blocking antibody or Isotype control 24 h before M. bovis infection. After 21 and 84 days of infection, mice were sacrificed and the role of Type I IFN signaling in the pathogenesis of M. bovis was investigated. ELISA and qRT-PCR were performed to detect the expression of Type I IFNs and related genes. Lung lesions induced by M. bovis were assessed by histopathological examination. Viable bacterial count was determined by CFU assay.

Results

We observed an abundant expression of Type I IFNs in the serum and lung tissues of M. bovis infected mice. In vivo blockade of Type I IFN signaling reduced the recruitment of neutrophils to the lung tissue, mediated the activation of macrophages leading to an increased pro-inflammatory profile and regulated the inflammatory cytokine production. However, no impact was observed on T cell activation and recruitment in the early acute phase of infection. Additionally, blocking of type I IFN signaling reduced bacterial burden in the infected mice as compared to untreated infected mice.

Conclusions

Altogether, our results reveal that Type I IFN mediates a balance between M. bovis-mediated inflammatory reaction and host defense mechanism. Thus, modulating Type I IFN signaling could be exploited as a therapeutic strategy against a large repertoire of inflammatory disorders including tuberculosis.

Mycobacterium tuberculosis Drives Expansion of Low-Density Neutrophils Equipped With Regulatory Activities

In human tuberculosis (TB) neutrophils represent the most commonly infected phagocyte but their role in protection and pathology is highly contradictory. Moreover, a subset of low-density neutrophils (LDNs) has been identified in TB, but their functions remain unclear. Here, we have analyzed total neutrophils and their low-density and normal-density (NDNs) subsets in patients with active TB disease, in terms of frequency, phenotype, functional features, and gene expression signature. Full-blood counts from Healthy Donors (H.D.), Latent TB infected, active TB, and cured TB patients were performed. Frequency, phenotype, burst activity, and suppressor T cell activity of the two different subsets were assessed by flow cytometry while NETosis and phagocytosis were evaluated by confocal microscopy. Expression analysis was performed by using the semi-quantitative RT-PCR array technology. Elevated numbers of total neutrophils and a high neutrophil/lymphocyte ratio distinguished patients with active TB from all the other groups. PBMCs of patients with active TB disease contained elevated percentages of LDNs compared with those of H.D., with an increased expression of CD66b, CD33, CD15, and CD16 compared to NDNs. Transcriptomic analysis of LDNs and NDNs purified from the peripheral blood of TB patients identified 12 genes differentially expressed: CCL5, CCR5, CD4, IL10, LYZ, and STAT4 were upregulated, while CXCL8, IFNAR1, NFKB1A, STAT1, TICAM1, and TNF were downregulated in LDNs, as compared to NDNs. Differently than NDNs, LDNs failed to phagocyte live Mycobacterium tuberculosis (M. tuberculosis) bacilli, to make oxidative burst and NETosis, but caused significant suppression of antigen-specific and polyclonal T cell proliferation which was partially mediated by IL-10. These insights add a little dowel of knowledge in understanding the pathogenesis of human TB.

[Immunological aspects of tuberculosis pathogenesis]

The morphological aspects of TB pathogenesis are well described in the publications. Much is also known about the main stages of development and formation of specific adaptive immunity. However, from our point of view, not enough attention is being paid to the involvement of the immune system in the pathogenesis of clinically relevant TB abnormalities, as well as various forms of the disease. Nevertheless, there is no doubt that the variety of clinical manifestations of any disease associated with the penetration of a foreign agent into the body, and Mycobacterium tuberculosis (MTB) in particular, is due to the collective interaction of the infectious agent and the individual response of the macroorganism to this infectious agent. The mosaic of such interactions usually imposes its own adjustments on the development of different forms of the process, its speed and direction, as well as the outcomes. Certainly, the response of a macroorganism to MTB is an integral part of pathogenesis and consists of many general components including the responses associated with the mechanisms of natural and acquired immunity. Intensity of these reactions depends on the characteristics of an agent (MTB) and a macroorganism. For the development of TB disease, massiveness of TB infection, dose and duration of MTB exposure to the human body, as well as virulence of MTB and the level of body's protection during the exposure play a very important role. TB pathogenesis is somewhat different in primary MTB infection and re - infection. With primary infection, 88-90% of individuals do not have clinical manifestations, and only the tuberculin skin test conversion signals the onset of infection. In some cases, without any use of anti-TB drugs limited abnormalities may result in spontaneous cure with the minimal residual changes in the lungs, intrathoracic lymph nodes and tissues of other organs, often in the form of calcifications and limited areas of fibrosis in more advanced cases. Only 10-12% of newly infected individuals develop TB with severe clinical manifestations requiring TB therapy. The absence of clinical manifestations of primary TB infection can be explained by a high level of natural resistance of the human body to tuberculosis, and sometimes can be an effect of acquired protection due to BCG vaccination. This review attempts to discuss the role of immune mechanisms in the pathogenesis both at the beginning of disease development, and in the process of its various manifestations. Issues of genetically determined resistance or susceptibility to TB are not being covered in detail in this manuscript.

High content analysis of granuloma histology and neutrophilic inflammation in adult zebrafish infected with Mycobacterium marinum

Infection of zebrafish with natural pathogen Mycobacterium marinum is a useful surrogate for studying the human granulomatous inflammatory response to infection by Mycobacterium tuberculosis. The adaptive immune system of the adult stage zebrafish offers an advance on the commonly used embryo infection model as adult zebrafish form granulomas with striking similarities to human-M. tuberculosis granulomas. Here, we present workflows to perform high content analyses of granulomas in adult zebrafish infected with M. marinum by cryosectioning to take advantage of strong endogenous transgenic fluorescence adapted from common zebrafish embryo infection tools. Specific guides to classifying granuloma necrosis and organisation, quantifying bacterial burden and leukocyte infiltration of granulomas, visualizing foam cell formation, analysing extracellular matrix remodelling and granuloma fibrosis are also provided. We use these methods to characterize neutrophil recruitment to M. marinum granulomas across time and find an inverse relation to granuloma necrosis suggesting granuloma necrosis is not a marker of immunopathology in the natural infection system of the adult zebrafish-M. marinum pairing. The methods can be easily translated to studying the zebrafish adaptive immune response to other chronic and granuloma-forming pathogens.

Anatomic and Cellular Niches for Mycobacterium tuberculosis in Latent Tuberculosis Infection

Latent tuberculosis has been recognized for over a century, but discovery of new niches, where Mycobacterium tuberculosis resides, continues. We evaluated literature on M.tuberculosis locations during latency, highlighting that mesenchymal and hematopoietic stem cells harbor organisms in sensitized asymptomatic individuals.

Isoniazid and host immune system interactions: A proposal for a novel comprehensive mode of action

The known mode of action of isoniazid (INH) is to inhibit bacterial cell wall synthesis following activation by the bacterial catalase-peroxidase enzyme KatG in Mycobacterium tuberculosis (Mtb). This simplistic model fails to explain (a) how isoniazid penetrates waxy granulomas with its very low lipophilicity, (b) how isoniazid kills latent Mtb lacking a typical cell wall, and (c) why isoniazid treatment time is remarkably long in contrast to most other antibiotics. To address these questions, a novel comprehensive mode of action of isoniazid has been proposed here. Briefly, isoniazid eradicates latent tuberculosis (TB) by prompting slow differentiation of pro-inflammatory monocytes and providing protection against reactive species-induced "self-necrosis" of phagocytes. In the case of active TB, different immune cells form INH-NAD⁺ adducts to inhibit Mtb's cell wall biosynthesis. This additionally suggests that the antibacterial properties of INH do not rely on KatG of Mtb. As such, isoniazid-resistant TB needs to be re-evaluated.

Immunometabolism of Phagocytes During Mycobacterium tuberculosis Infection

Tuberculosis (TB), caused by Mycobacterium tuberculosis (Mtb) remains as a leading killer among infectious diseases worldwide. The nature of the host immune response dictates whether the initial Mtb infection is cleared or progresses toward active disease, and is ultimately determined by intricate host-pathogen interactions that are yet to be fully understood. The early immune response to infection is mediated by innate immune cells, including macrophages and neutrophils that can phagocytose Mtb and mount an antimicrobial response. However, Mtb can exploit these innate immune cells for its survival and dissemination. Recently, it has become clear that the immune response and metabolic remodeling are interconnected, which is highlighted by the rapid evolution of the interdisciplinary field of immunometabolism. It has been proposed that the net outcome to Mtb infection—clearance or chronic disease—is likely a result of combined immunologic and metabolic activities of the immune cells. Indeed, host cells activated by Mtb infection have strikingly different metabolic requirements than naïve/non-infected cells. Macrophages activated by Mtb-derived molecules or upon phagocytosis acquire a phenotype similar to M1 with elevated production of pro-inflammatory molecules and rely on glycolysis and pentose phosphate pathway to meet their bioenergetic and metabolic requirements. In these macrophages, oxidative phosphorylation and fatty acid oxidation are dampened. However, the non-infected/naive, M2-type macrophages are anti-inflammatory and derive their energy from oxidative phosphorylation and fatty acid oxidation. Similar metabolic adaptations also occur in other phagocytes, including dendritic cells, neutrophils upon Mtb infection. This metabolic reprogramming of innate immune cells during Mtb infection can differentially regulate their effector functions, such as the production of cytokines and chemokines, and antimicrobial response, all of which can ultimately determine the outcome of Mtb-host interactions within the granulomas. In this review, we describe key immune cells bolstering host innate response and discuss the metabolic reprogramming in these phagocytes during Mtb infection. We focused on the major phagocytes, including macrophages, dendritic cells and neutrophils and the key regulators involved in metabolic reprogramming, such as hypoxia-inducible factor-1, mammalian target of rapamycin, the cellular myelocytomatosis, peroxisome proliferator-activator receptors, sirtuins, arginases, inducible nitric acid synthase and sphingolipids.

Live Vaccination Generates Both Disease Tolerance and Host Resistance During Chronic Pulmonary Infection With Highly Virulent Francisella tularensis SchuS4

Disease tolerance can preserve host homeostasis and limit the negative impact of infections. We report that vaccinated mice survived pulmonary challenge with the extremely virulent SchuS4 strain of Francisella tularensis for at least 100 days, despite the persistence of large numbers (~104) of organisms. Transfer of 100 of these resident bacteria to naive animals caused 100% lethality, demonstrating that virulence was maintained. Tissue damage in the lung was limited over the course of infection and was associated with increased levels of amphiregulin. Mice depleted of CD4+ cells had reduced amphiregulin and succumbed to infection. In addition, neutralization of interferon-γ or depletion of CD8+ cells resulted in increased pathogen loads, bacteremia, and death of the host. Conversely, depletion of Ly6G+ neutrophils had no effect on survival and actually resulted in reduced bacterial levels. Understanding the interplay between host resistance and disease tolerance will provide new insights into the understanding of chronic infectious diseases.

Efferocytosis of Apoptotic Neutrophils Enhances Control of Mycobacterium tuberculosis in HIV-Coinfected Macrophages in a Myeloperoxidase-Dependent Manner

Tuberculosis remains a big threat, with 1.6 million deaths in 2017, including 0.3 million deaths among patients with HIV. The risk of developing active disease increases considerably during an HIV coinfection. Alveolar macrophages are the first immune cells to encounter the causative agent Mycobacterium tuberculosis, but during the granuloma formation other cells are recruited in order to combat the bacteria. Here, we have investigated the effect of efferocytosis of apoptotic neutrophils by M. tuberculosis and HIV-coinfected macrophages in a human in vitro system. We found that the apo-ptotic neutrophils enhanced the control of M. tuberculosis in single and HIV-coinfected macrophages, and that this was dependent on myeloperoxidase (MPO) and reactive oxygen species in an autophagy-independent manner. We show that MPO remains active in the apoptotic neutrophils and can be harnessed by infected macrophages. In addition, MPO inhibition removed the suppression in M. tuberculosis growth caused by the apoptotic neutrophils. Antimycobacterial components from apoptotic neutrophils could thus increase the microbicidal activity of macrophages during an M. tuberculosis/HIV coinfection. This cooperation between innate immune cells could thereby be a way to compensate for the impaired adaptive immunity against M. tuberculosis seen during a concurrent HIV infection.

MDSCs in infectious diseases: regulation, roles, and readjustment

Many pathogens, ranging from viruses to multicellular parasites, promote expansion of MDSCs, which are myeloid cells that exhibit immunosuppressive features. The roles of MDSCs in infection depend on the class and virulence mechanisms of the pathogen, the stage of the disease, and the pathology associated with the infection. This work compiles evidence supported by functional assays on the roles of different subsets of MDSCs in acute and chronic infections, including pathogen-associated malignancies, and discusses strategies to modulate MDSC dynamics to benefit the host.

Immunity to the Dual Threat of Silica Exposure and Mycobacterium tuberculosis

Exposure to silica and the consequent development of silicosis are well-known health problems in countries with mining and other dust producing industries. Apart from its direct fibrotic effect on lung tissue, chronic and immunomodulatory character of silica causes susceptibility to tuberculosis (TB) leading to a significantly higher TB incidence in silica-exposed populations. The presence of silica particles in the lung and silicosis may facilitate initiation of tuberculous infection and progression to active TB, and exacerbate the course and outcome of TB, including prognosis and survival. However, the exact mechanisms of the involvement of silica in the pathological processes during mycobacterial infection are not yet fully understood. In this review, we focus on the host's immunological response to both silica and Mycobacterium tuberculosis, on agents of innate and adaptive immunity, and particularly on silica-induced immunological modifications in co-exposure that influence disease pathogenesis. We review what is known about the impact of silica and Mycobacterium tuberculosis or their co-exposure on the host's immune system, especially an impact that goes beyond an exclusive focus on macrophages as the first line of the defense. In both silicosis and TB, acquired immunity plays a major role in the restriction and/or elimination of pathogenic agents. Further research is needed to determine the effects of silica in adaptive immunity and in the pathogenesis of TB.

Beyond Killing Mycobacterium tuberculosis: Disease Tolerance

Host defense strategies against infectious diseases are comprised of both host resistance and disease tolerance. Resistance is the ability of the host to prevent invasion or to eliminate the pathogen, while disease tolerance is defined by limiting the collateral tissue damage caused by the pathogen and/or the immune response without exerting direct effects on pathogen growth. Our incomplete understanding of host immunity against tuberculosis (TB) is predominately rooted in our bias toward investigating host resistance. Thus, we must refocus our efforts to understand the entire spectrum of immunity against M. tuberculosis to control TB.

Neutrophils: Innate Effectors of TB Resistance?

Certain individuals are able to resist Mycobacterium tuberculosis infection despite persistent and intense exposure. These persons do not exhibit adaptive immune priming as measured by tuberculin skin test (TST) and interferon-γ (IFN-γ) release assay (IGRA) responses, nor do they develop active tuberculosis (TB). Genetic investigation of individuals who are able to resist M. tuberculosis infection shows there are likely a combination of genetic variants that contribute to the phenotype. The contribution of the innate immune system and the exact cells involved in this phenotype remain incompletely elucidated. Neutrophils are prominent candidates for possible involvement as primers for microbial clearance. Significant variability is observed in neutrophil gene expression and DNA methylation. Furthermore, inter-individual variability is seen between the mycobactericidal capacities of donor neutrophils. Clearance of M. tuberculosis infection is favored by the mycobactericidal activity of neutrophils, apoptosis, effective clearance of cells by macrophages, and resolution of inflammation. In this review we will discuss the different mechanisms neutrophils utilize to clear M. tuberculosis infection. We discuss the duality between neutrophils' ability to clear infection and how increasing numbers of neutrophils contribute to active TB severity and mortality. Further investigation into the potential role of neutrophils in innate immune-mediated M. tuberculosis infection resistance is warranted since it may reveal clinically important activities for prevention as well as vaccine and treatment development.

A novel role for C-C motif chemokine receptor 2 during infection with hypervirulent Mycobacterium tuberculosis

C-C motif chemokine receptor 2 (CCR2) is a major chemokine axis that recruits myeloid cells including monocytes and macrophages. Thus far, CCR2-/- mice have not been found to be susceptible to infection with Mycobacterium tuberculosis (Mtb). Here, using a prototype W-Beijing family lineage 2 Mtb strain, HN878, we show that CCR2-/- mice exhibit increased susceptibility to tuberculosis (TB). Following exposure to Mtb HN878, alveolar macrophages (AMs) are amongst the earliest cells infected. We show that AMs accumulate early in the airways following infection and express CCR2. During disease progression, CCR2-expressing AMs exit the airways and localize within the TB granulomas. RNA-sequencing of sorted airway and non-airway AMs from infected mice show distinct gene expression profiles, suggesting that upon exit from airways and localization within granulomas, AMs become classically activated. The absence of CCR2+ cells specifically at the time of AM egress from the airways resulted in enhanced susceptibility to Mtb infection. Furthermore, infection with an Mtb HN878 mutant lacking phenolic glycolipid (PGL) expression still resulted in increased susceptibility in CCR2-/- mice. Together, these data show a novel role for CCR2 in protective immunity against clinically relevant Mtb infections.

Sex differences in tuberculosis

Tuberculosis is the most prevalent bacterial infectious disease in humans and the leading cause of death from a single infectious agent, ranking above HIV/AIDS. The causative agent, Mycobacterium tuberculosis, is carried by an estimated two billion people globally and claims more than 1.5 million lives each year. Tuberculosis rates are significantly higher in men than in women, reflected by a male-to-female ratio for worldwide case notifications of 1.7. This phenomenon is not new and has been reported in various countries and settings over the last century. However, the reasons for the observed gender bias are not clear, potentially highly complex and discussed controversially in the literature. Both gender- (referring to sociocultural roles and behavior) and sex-related factors (referring to biological aspects) likely contribute to higher tuberculosis rates in men and will be discussed.

Sera from patients with active pulmonary tuberculosis and their household contacts induce nuclear changes in neutrophils

Background

Resident alveolar macrophages, dendritic cells, and immigrating neutrophils (NEU) are the first cells to contact Mycobacterium tuberculosis in the lung. These cells, and additional lymphoid cells in the developing granuloma, release a series of components that may concentrate in the serum and affect disease progression.

Purpose

The aim of this study was to investigate the effect of the serum from tuberculosis (TB) patients and their household contacts (HHC) on the nuclear morphology of NEU.

Materials and methods

NEU from healthy (HLT) people were incubated with sera from patients with active pulmonary TB, their HHC, and unrelated people. Changes in the nuclear morphology of NEU were analyzed by light and electron microscopy.

Results

Sera from patients with TB induced changes in the nuclear morphology of NEU that included pyknosis, swelling, apoptosis, and netosis in some cases. Sera from some HHC induced similar changes, while sera from HLT people had no significant effects. Bacteria did not appear to participate in this phenomenon because bacteremia is not a recognized feature of nonmiliary TB, and because sera from patients that induced nuclear changes maintained their effect after filtration through 0.22 µm membranes. Neither anti-mycobacterial antibodies, TNFα, IL-6, IFNγ, or IL-8 participated in the phenomenon. In contrast, soluble mycobacterial antigens were likely candidates, as small quantities of soluble M. tuberculosis antigens added to the sera of HLT people led to the induction of nuclear changes in NEU in a dose-dependent manner.

Conclusion

These results might help to detect subclinical TB within HHC, thus leading to a recommendation of prophylactic treatment.

Neutrophil Depletion Exacerbates Pregnancy Complications, Including Placental Damage, Induced by Silica Nanoparticles in Mice

Recent advances in nanotechnology have led to the development of nanoparticles with innovative functions in various fields. However, the biological effects of nanoparticles—particularly those on the fetus—need to be investigated in detail, because several previous studies have shown that various nanoparticles induce pregnancy complications in mice. In this regard, our previous findings in mice suggested that the increase in peripheral neutrophil count induced by treatment with silica nanoparticles with a diameter of 70 nm (nSP70) may play a role in the associated pregnancy complications. Therefore, here, we sought to define the role of neutrophils in nSP70-induced pregnancy complications. The peripheral neutrophil count in pregnant BALB/c mice at 24 h after treatment with nSP70 was significantly higher than in saline-treated mice. In addition, maternal body weight, uterine weight, and the number of fetuses in nSP70-treated mice pretreated with anti-antibodies, which deplete neutrophils, were significantly lower than those in nSP70-treated mice pretreated with phosphate-buffered saline or isotype-matched control antibodies. Histology revealed that neutrophil depletion increased nSP70-induced placental damage from the decidua through the spongiotrophoblast layer and narrowed spiral arteries in the placentae. In addition, depletion of neutrophils augmented nSP70-induced cytotoxicity to fetal vessels, which were covered with endothelium. The rate of apoptotic cell death was significantly higher in the placentae of anti-nSP70-treated mice than in those from mice pretreated with isotype-matched control antibodies. Therefore, impairment of placental vessels and apoptotic cell death due to nSP70 exposure is exacerbated in the placentae of nSP70-treated mice pretreated with anti-antibodies. Depletion of neutrophils worsens nSP70-induced pregnancy complications in mice; this exacerbation was due to enhanced impairment of placental vessels and increased apoptotic cell death in maternal placentae. Our results provide basic information regarding the mechanism underlying silica-nanoparticle-induced pregnancy complications.

Susceptibility to Tuberculosis Is Associated With PI3K-Dependent Increased Mobilization of Neutrophils

Neutrophilia is a condition commonly observed in patients with late-stage tuberculosis, but evidence suggests that increased neutrophil influx begins early after infection in susceptible hosts and functions to promote a nutrient-replete niche that promotes Mycobacterium tuberculosis survival and persistence. As the disease progresses, an increase in the number of neutrophil-like cells is observed, all of which exhibit characteristics associated with (i) phenotypic and biochemical features of immaturity, (ii) the inability to activate T-cells, (iii) hyper-inflammation, and (iv) prolonged survival. Transcriptomics reveal a common set of molecules associated with the PI3–Kinase pathway that are dysregulated in patients with active tuberculosis. Closer inspection of their individual biological roles reveal their ability to modulate the IL-17/G–CSF axis, induce leukocyte receptor activation, and regulate apoptosis and motility. This review draws attention to neutrophil hyper-reactivity as a driving force for both the establishment and progression of tuberculosis disease in susceptible individuals.

The increased protection and pathology in Mycobacterium tuberculosis-infected IL-27R-alpha-deficient mice is supported by IL-17A and is associated with the IL-17A-induced expansion of multifunctional T cells

During Mycobacterium tuberculosis (Mtb) infection, mice lacking the IL-27R exhibit lower bacterial burdens but develop an immunopathological sequelae in comparison to wild-type mice. We here show that this phenotype correlates with an enhanced recruitment of antigen-specific CCR6⁺ CD4⁺ T cells and an increased frequency of IL-17A-producing CD4⁺ T cells. By comparing the outcome of Mtb infection in C57BL/6, IL-27R-deficient and IL-27R/IL-17A-double deficient mice, we observed that both the increased protection and elevated immunopathology are supported by IL-17A. Whereas IL-17A neither impacts the development of Tr1 cells nor the expression of PD1 and KLRG1 on T cells in IL-27R-deficient mice during infection, it regulates the presence of multifunctional T-cells in the lungs, co-expressing IFN-γ, IL-2 and TNF. Eventually, IL-17A supports Cxcl9, Cxcl10 and Cxcl13 expression and the granulomatous response in the lungs of infected IL-27R-deficient mice. Taken together, IL-17A contributes to protection in Mtb-infected IL-27R-deficient mice probably through a chemokine-mediated recruitment and strategic positioning of multifunctional T cells in granulomas. As IL-27 limits optimal antimycobacterial protection by inhibiting IL-17A production, blocking of IL-27R-mediated signaling may represent a strategy for improving vaccination and host-directed therapy in tuberculosis. However, because IL-27 also prevents IL-17A-mediated immunopathology, such intervention has to be tightly controlled.

Epidemiologic Evidence of and Potential Mechanisms by Which Second-Hand Smoke Causes Predisposition to Latent and Active Tuberculosis

Many studies have linked cigarette smoke (CS) exposure and tuberculosis (TB) infection and disease although much fewer have studied second-hand smoke (SHS) exposure. Our goal is to review the epidemiologic link between SHS and TB as well as to summarize the effects SHS and direct CS on various immune cells relevant for TB. PubMed searches were performed using the key words "tuberculosis" with "cigarette," "tobacco," or "second-hand smoke." The bibliography of relevant papers were examined for additional relevant publications. Relatively few studies associate SHS exposure with TB infection and active disease. Both SHS and direct CS can alter various components of host immunity resulting in increased vulnerability to TB. While the epidemiologic link of these 2 health maladies is robust, more definitive, mechanistic studies are required to prove that SHS and direct CS actually cause increased susceptibility to TB.

Differential Effect of Viable Versus Necrotic Neutrophils on Mycobacterium tuberculosis Growth and Cytokine Induction in Whole Blood

Neutrophils exert both positive and negative influences on the host response to tuberculosis, but the mechanisms by which these differential effects are mediated are unknown. We studied the impact of live and dead neutrophils on the control of Mycobacterium tuberculosis using a whole blood bioluminescence-based assay, and assayed supernatant cytokine concentrations using Luminex™ technology and ELISA. CD15+ granulocyte depletion from blood prior to infection with M. tuberculosis-lux impaired control of mycobacteria by 96 h, with a greater effect than depletion of CD4+, CD8+, or CD14+ cells (p < 0.001). Augmentation of blood with viable granulocytes significantly improved control of mycobacteria by 96 h (p = 0.001), but augmentation with necrotic granulocytes had the opposite effect (p = 0.01). Both augmentations decreased supernatant concentrations of tumor necrosis factor and interleukin (IL)-12 p40/p70, but necrotic granulocyte augmentation also increased concentrations of IL-10, G-CSF, GM-CSF, and CCL2. Necrotic neutrophil augmentation reduced phagocytosis of FITC-labeled M. bovis BCG by all phagocytes, whereas viable neutrophil augmentation specifically reduced early uptake by CD14+ cells. The immunosuppressive effect of dead neutrophils required necrotic debris rather than supernatant. We conclude that viable neutrophils enhance control of M. tuberculosis in blood, but necrotic neutrophils have the opposite effect-the latter associated with induction of IL-10, growth factors, and chemoattractants. Our findings suggest a mechanism by which necrotic neutrophils may exert detrimental effects on the host response in active tuberculosis.

Tuberculosis and lung damage: from epidemiology to pathophysiology

A past history of pulmonary tuberculosis (TB) is a risk factor for long-term respiratory impairment. Post-TB lung dysfunction often goes unrecognised, despite its relatively high prevalence and its association with reduced quality of life. Importantly, specific host and pathogen factors causing lung impairment remain unclear. Host immune responses probably play a dominant role in lung damage, as excessive inflammation and elevated expression of lung matrix-degrading proteases are common during TB. Variability in host genes that modulate these immune responses may determine the severity of lung impairment, but this hypothesis remains largely untested. In this review, we provide an overview of the epidemiological literature on post-TB lung impairment and link it to data on the pathogenesis of lung injury from the perspective of dysregulated immune responses and immunogenetics.

Host factors driving lung injury in TB likely contribute to variable patterns of pulmonary impairment after TBhttp://ow.ly/a3of30hBsxB

Extracellular Vesicles Released from Mycobacterium tuberculosis-Infected Neutrophils Promote Macrophage Autophagy and Decrease Intracellular Mycobacterial Survival

Tuberculosis is an infectious disease caused by Mycobacterium tuberculosis (Mtb). In the lungs, macrophages and neutrophils are the first immune cells that have contact with the infecting mycobacteria. Neutrophils are phagocytic cells that kill microorganisms through several mechanisms, which include the lytic enzymes and antimicrobial peptides that are found in their lysosomes, and the production of reactive oxygen species. Neutrophils also release extracellular vesicles (EVs) (100-1,000 nm in diameter) to the extracellular milieu; these EVs consist of a lipid bilayer surrounding a hydrophilic core and participate in intercellular communication. We previously demonstrated that human neutrophils infected in vitro with Mtb H37Rv release EVs (EV-TB), but the effect of these EVs on other cells relevant for the control of Mtb infection, such as macrophages, has not been completely analyzed. In this study, we characterized the EVs produced by non-stimulated human neutrophils (EV-NS), and the EVs produced by neutrophils stimulated with an activator (PMA), a peptide derived from bacterial proteins (fMLF) or Mtb, and observed that the four EVs differed in their size. Ligands for toll-like receptor (TLR) 2/6 were detected in EV-TB, and these EVs favored a modest increase in the expression of the co-stimulatory molecules CD80, a higher expression of CD86, and the production of higher amounts of TNF-α and IL-6, and of lower amounts of TGF-β, in autologous human macrophages, compared with the other EVs. EV-TB reduced the amount of intracellular Mtb in macrophages, and increased superoxide anion production in these cells. TLR2/6 ligation and superoxide anion production are known inducers of autophagy; accordingly, we found that EV-TB induced higher expression of the autophagy-related marker LC3-II in macrophages, and the co-localization of LC3-II with Mtb inside infected macrophages. The intracellular mycobacterial load increased when autophagy was inhibited with wortmannin in these cells. In conclusion, our results demonstrate that neutrophils produce different EVs in response to diverse activators, and that EV-TB activate macrophages and promote the clearance of intracellular Mtb through early superoxide anion production and autophagy induction, which is a novel role for neutrophil-derived EVs in the immune response to Mtb.

In-vivo evaluation of apocynin for prevention of Helicobacter pylori-induced gastric carcinogenesis

The emergence of antibiotic-resistant Helicobacter pylori strains impacts the efficacy of eradication therapy and promotes the development of alternative treatment strategies. Apocynin inhibits neutrophil NADPH oxidase and hence may decrease reactive oxygen species-mediated tissue damage in H. pylori-infected stomach tissue. Apocynin was tested in vitro for its cytotoxic and direct antibacterial effects. The therapeutic efficacy of orally administered apocynin (100 mg/kg/day through drinking water or 200 mg/kg/day through combined administration of drinking water and slow-release formulation) was assessed at 9 weeks after infection in the Mongolian gerbil model. Bacterial burdens were quantified by viable plate count and quantitative PCR. Histopathological evaluation of antrum and pylorus provided insight into mucosal inflammation and injury. Apocynin showed no cytotoxic or direct antibacterial effects in vitro or in vivo. Nine weeks of apocynin treatment at 200 mg/kg/day reduced active H. pylori gastritis as neutrophil infiltration in the mucous neck region and pit abscess formation decreased significantly. In our gerbil model, prolonged high-dose apocynin treatment significantly improved H. pylori-induced pit abscess formation without indications of drug toxicity and thus further investigation of the dosage regimen and formulation and the long-term impact on neoplastic development should be carried out.

STAT3 expression by myeloid cells is detrimental for the T- cell-mediated control of infection with Mycobacterium tuberculosis

STAT3 is a master regulator of the immune responses. Here we show that M. tuberculosis-infected stat3^fl/fllysm cre mice, defective for STAT3 in myeloid cells, contained lower bacterial load in lungs and spleens, reduced granuloma extension but higher levels of pulmonary neutrophils. STAT3-deficient macrophages showed no improved control of intracellular mycobacterial growth. Instead, protection associated to elevated ability of stat3^fl/fllysm cre antigen-presenting cells (APCs) to release IL-6 and IL-23 and to stimulate IL-17 secretion by mycobacteria-specific T cells. The increased IL-17 secretion accounted for the improved control of infection since neutralization of IL-17 receptor A in stat3^fl/fllysm cre mice hampered bacterial control. APCs lacking SOCS3, which inhibits STAT3 activation via several cytokine receptors, were poor inducers of priming and of the IL-17 production by mycobacteria-specific T cells. In agreement, socs3^fl/flcd11c cre mice deficient of SOCS3 in DCs showed increased susceptibility to M. tuberculosis infection. While STAT3 in APCs hampered IL-17 responses, STAT3 in mycobacteria-specific T cells was critical for IL-17 secretion, while SOCS3 in T cells impeded IL-17 secretion. Altogether, STAT3 signalling in myeloid cells is deleterious in the control of infection with M. tuberculosis.

We studied the role of STAT3, a major regulator of immunity, in the control of the infection with M. tuberculosis. Stat3^fl/fllysm cre mice, deficient in STAT3 in myeloid cells, showed lower bacterial levels in organs and reduced extension of lung granulomas after infection with M. tuberculosis. STAT3-deficient APCs stimulated with innate receptor agonists released high levels of IL-6 and IL-23, and promoted IL-17 production by mycobacteria-specific CD4+ T cells. Increased IL-17 levels accounted for the increased resistance to M. tuberculosis of the STAT3-deficient mice. Instead, stat3^fl/fllysm cre macrophages showed no improved control of mycobacterial growth. SOCS3 is a negative regulator of STAT3 activation. The ability of socs3^fl/fllysm cre APCs to secrete IL-6 and IL-23 and to stimulate IL-17 production by antigen-specific T cells was reduced. In agreement, mice lacking SOCS3 in DCs showed increased susceptibility to M. tuberculosis infection. Different to a role in myeloid cells, STAT3 expression by mycobacteria-specific T cells was required for IL-17 secretion while SOCS3 in T cells hampered IL-17 production. Therefore, despite STAT3 expression in T cells is required for Th17 differentiation, STAT3 in APCs hampers secretion of Th17 promoting cytokines and the secretion of IL-17 by mycobacteria-specific T cells and reduces the resistance of mice to infection with M. tuberculosis.

Effects of dexamethasone treatment and respiratory vaccination on rectal temperature, complete blood count, and functional capacities of neutrophils in beef steers

The objective of this research was to examine the effects of dexamethasone (DEX) treatment on various aspects of immunity following administration of a multivalent respiratory vaccine, using a model intended to mimic acute versus chronic stress. Angus × Hereford steers ( = 32; 209 ± 8 kg) were stratified by BW and randomly assigned to 1 of 3 treatments: 1) acute stress (ACU), in which 0.5 mg/kg BW DEX was intravenously administered at 1000 h only on d 0; 2) chronic stress (CHR), in which 0.5 mg/kg BW DEX was intravenously administered at 1000 h on d -3 to 0; or 3) control (CON), in which no DEX was administered. Steers were fitted with indwelling jugular catheters and rectal temperature (RT) recording devices on d -4 relative to vaccination and placed in individual stanchions in an environmentally controlled facility. Blood samples were collected and serum was isolated at -74, -50, and -26 h; at 0.5-h intervals from -4 to 6 h; and at 12, 24, 36, 48, and 72 h relative to multivalent respiratory vaccination at 1200 h on d 0. Additional blood samples were used to analyze complete blood cell count (CBC) and functional capacities of neutrophils. There was a treatment × time interaction ( < 0.01) for RT such that DEX treatment in CHR and ACU steers decreased RT on d -3 and 0, respectively. A treatment × time interaction ( < 0.01) was observed for total white blood cells (WBC), neutrophils, lymphocytes, and monocytes. Specifically, DEX increased WBC and neutrophils in CHR and ACU steers ( < 0.001) yet decreased lymphocytes in CHR steers ( = 0.02) compared with CON steers. Neutrophil concentration increased rapidly, within 2 h of the DEX infusion, in ACU steers. Monocytes transiently increased ( < 0.001) in response to DEX treatment in CHR and ACU steers. In contrast, eosinophils were greater ( < 0.01) in CON steers than in ACU and CHR steers. A treatment × time interaction ( = 0.004) was observed for interferon-γ, with CON cattle exhibiting greater concentrations than the ACU and CHR cattle at 5 h after vaccination, through d 3. Treatment also influenced ( ≤ 0.001) the expression of L-selectin on the surface of neutrophils. The percentage of neutrophils engaging in phagocytosis and the oxidative burst were suppressed ( ≤ 0.001) among only the CHR steers, whereas the intensity of the oxidative burst was suppressed ( ≤ 0.001) for both ACU and CHR steers. These data suggest that our model induced acute and chronic immunosuppression and defined the acute response to a multivalent vaccine in CON steers.

Role of aryl hydrocarbon receptor in mesenchymal stromal cell activation: A minireview

Mesenchymal stromal cells (MSCs) possess great therapeutic advantages due to their ability to produce a diverse array of trophic/growth factors related to cytoprotection and immunoregulation. MSC activation via specific receptors is a crucial event for these cells to exert their immunosuppressive response. The aryl-hydrocarbon receptor (AhR) is a sensitive molecule for external signals and it is expressed in MSCs and, upon positive activation, may potentially regulate the MSC-associated immunomodulatory function. Consequently, signalling pathways linked to AhR activation can elucidate some of the molecular cascades involved in MSC-mediated immunosuppression. In this minireview, we have noted some important findings concerning MSC regulation via AhR, highlighting that its activation is associated with improvement in migration and immunoregulation, as well as an increase in pro-regenerative potential. Thus, AhR-mediated MSC activation can contribute to new perspectives on MSC-based therapies, particularly those directed at immune-associated disorders.

In vivo induction of neutrophil extracellular traps by Mycobacterium tuberculosis in a guinea pig model

In 2004, a novel mechanism of cellular death, called 'NETosis', was described in neutrophils. This mechanism, different from necrosis and apoptosis, is characterized by the release of chromatin webs admixed with microbicidal granular proteins and peptides (NETs). NETs trap and kill a variety of microorganisms. Diverse microorganisms, including Mycobacterium tuberculosis, are NET inducers in vitro. The aim of this study was to examine whether M. tuberculosis can also induce NETs in vivo and if the NETs are bactericidal to the microorganism. Guinea pigs were intradermally inoculated with M. tuberculosis H37Rv, and the production of NETs was investigated at several time points thereafter. NETs were detected as early as 30 min post-inoculation and were clearly evident by 4 h post-inoculation. NETs produced in vivo contained DNA, myeloperoxidase, elastase, histones, ROS and acid-fast bacilli. Viable and heat-killed M. tuberculosis, as well as Mycobacterium bovis BCG were efficient NET inducers, as were unilamellar liposomes prepared with lipids from M. tuberculosis. In vitro, guinea pig neutrophils also produced NETs in response to M. tuberculosis. However, neither the in vivo nor the in vitro-produced NETs were able to kill M. tuberculosis. Nevertheless, in vivo, neutrophils might propitiate recruitment and activation of more efficient microbicidal cells.

Severe Tuberculosis in Humans Correlates Best with Neutrophil Abundance and Lymphocyte Deficiency and Does Not Correlate with Antigen-Specific CD4 T-Cell Response

It is generally thought that Mycobacterium tuberculosis (Mtb)-specific CD4⁺ Th1 cells producing IFN-γ are essential for protection against tuberculosis (TB). In some studies, protection has recently been associated with polyfunctional subpopulation of Mtb-specific Th1 cells, i.e., with cells able to simultaneously secrete several type 1 cytokines. However, the role for Mtb-specific Th1 cells and their polyfunctional subpopulations during established TB disease is not fully defined. Pulmonary TB is characterized by a great variability of disease manifestations. To address the role for Mtb-specific Th1 responses during TB, we investigated how Th1 and other immune cells correlated with particular TB manifestations, such as the degree of pulmonary destruction, TB extent, the level of bacteria excretion, clinical disease severity, clinical TB forms, and “Timika X-ray score,” an integrative parameter of pulmonary TB pathology. In comparison with healthy Mtb-exposed controls, TB patients (TBP) did not exhibit deficiency in Mtb-specific cytokine-producing CD4⁺ cells circulating in the blood and differed by a polyfunctional profile of these cells, which was biased toward the accumulation of bifunctional TNF-α⁺IFN-γ⁺IL-2⁻ lymphocytes. Importantly, however, severity of different TB manifestations was not associated with Mtb-specific cytokine-producing cells or their polyfunctional profile. In contrast, several TB manifestations were strongly correlated with leukocyte numbers, the percent or the absolute number of lymphocytes, segmented or band neutrophils. In multiple alternative statistical analyses, band neutrophils appeared as the strongest positive correlate of pulmonary destruction, bacteria excretion, and “Timika X-ray score.” In contrast, clinical TB severity was primarily and inversely correlated with the number of lymphocytes in the blood. The results suggest that: (i) different TB manifestations may be driven by distinct mechanisms; (ii) quantitative parameters and polyfunctional profile of circulating Mtb-specific CD4⁺ cells play a minor role in determining TB severity; and (iii) general shifts in production/removal of granulocytic and lymphocytic lineages represent an important factor of TB pathogenesis. Mechanisms leading to these shifts and their specific role during TB are yet to be determined but are likely to involve changes in human hematopoietic system.

Striking the right immunological balance prevents progression of tuberculosis

INTRODUCTION

Tuberculosis (TB) caused by infection with Mycobacterium tuberculosis (Mtb) is a major burden for human health worldwide. Current standard treatments for TB require prolonged administration of antimycobacterial drugs leading to exaggerated inflammation and tissue damage. This can result in the reactivation of latent TB culminating in TB progression. Thus, there is an unmet need to develop therapies that would shorten the duration of anti-TB treatment and to induce optimal protective immune responses to control the spread of mycobacterial infection with minimal lung pathology.

FINDINGS

Granulomata is the hallmark structure formed by the organized accumulation of immune cells including macrophages, natural killer cells, dendritic cells, neutrophils, T cells, and B cells to the site of Mtb infection. It safeguards the host by containing Mtb in latent form. However, granulomata can undergo caseation and contribute to the reactivation of latent TB, if the immune responses developed to fight mycobacterial infection are not properly controlled. Thus, an optimal balance between innate and adaptive immune cells might play a vital role in containing mycobacteria in latent form for prolonged periods and prevent the spread of Mtb infection from one individual to another.

CONCLUSION

Optimal and well-regulated immune responses against Mycobacterium tuberculosis may help to prevent the reactivation of latent TB. Moreover, therapies targeting balanced immune responses could help to improve treatment outcomes among latently infected TB patients and thereby limit the dissemination of mycobacterial infection.

Innate Immune Responses to Tuberculosis

Tuberculosis remains one of the greatest threats to human health. The causative bacterium, Mycobacterium tuberculosis, is acquired by the respiratory route. It is exquisitely adapted to humans and is a prototypic intracellular pathogen of macrophages, with alveolar macrophages being the primary conduit of infection and disease. However, M. tuberculosis bacilli interact with and are affected by several soluble and cellular components of the innate immune system which dictate the outcome of primary infection, most commonly a latently infected healthy human host, in whom the bacteria are held in check by the host immune response within the confines of tissue granuloma, the host histopathologic hallmark. Such individuals can develop active TB later in life with impairment in the immune system. In contrast, in a minority of infected individuals, the early host immune response fails to control bacterial growth, and progressive granulomatous disease develops, facilitating spread of the bacilli via infectious aerosols. The molecular details of the M. tuberculosis-host innate immune system interaction continue to be elucidated, particularly those occurring within the lung. However, it is clear that a number of complex processes are involved at the different stages of infection that may benefit either the bacterium or the host. In this article, we describe a contemporary view of the molecular events underlying the interaction between M. tuberculosis and a variety of cellular and soluble components and processes of the innate immune system.

Influence of diabetes mellitus on immunity to human tuberculosis

Type 2 diabetes mellitus(DM) is a major risk factor for the development of active pulmonary tuberculosis (TB), with development of DM pandemic in countries where TB is also endemic. Understanding the impact of DM on TB and the determinants of co-morbidity is essential in responding to this growing public health problem with improved therapeutic approaches. Despite the clinical and public health significance posed by the dual burden of TB and DM, little is known about the immunological and biochemical mechanisms of susceptibility. One possible mechanism is that an impaired immune response in patients with DM facilitates either primary infection with Mycobacterium tuberculosis or reactivation of latent TB. Diabetes is associated with immune dysfunction and alterations in the components of the immune system, including altered levels of specific cytokines and chemokines. Some effects of DM on adaptive immunity that are potentially relevant to TB defence have been identified in humans. In this review, we summarize current findings regarding the alterations in the innate and adaptive immune responses and immunological mechanisms of susceptibility of patients with DM to M. tuberculosis infection and disease.

The introduction of mesenchymal stromal cells induces different immunological responses in the lungs of healthy and M. tuberculosis infected mice

Mesenchymal stromal cells (MSC) have strong immunomodulatory properties and therefore can be used to control inflammation and tissue damage. It was suggested recently that MSC injections can be used to treat multi-drug resistant tuberculosis (TB). However, MSC trafficking and immunomodulatory effects of MSC injections during Mycobacterium tuberculosis (Mtb) infection have not been studied. To address this issue we have analyzed MSC distribution in tissues and local immunological effects of MSC injections in Mtb infected and uninfected mice. After intravenous injection, MSC accumulated preferentially in the lungs where they were located as cell aggregates in the alveolar walls. Immunological analysis of MSC effects included detection of activated, IFN-γ and IL-4 producing CD4⁺ lymphocytes, the frequency analysis of dendritic cells (CD11c⁺F4/80) and macrophages (CD11c^-F4/80⁺) located in the lungs, the expression of IA/IE and CD11b molecules by these cells, and evaluation of 23 cytokines/chemokines in lung lysates. In the lungs of uninfected mice, MSC transfer markedly increased the percentage of IFN-γ⁺ CD4⁺ lymphocytes and dendritic cells, elevated levels of IA/IE expression by dendritic cells and macrophages, augmented local production of type 2 cytokines (IL-4, IL-5, IL-10) and chemokines (CCL2, CCL3, CCL4, CCL5, CXCL1), and downregulated type 1 and hematopoietic cytokines (IL-12p70, IFN-γ, IL-3, IL-6, GM-CSF). Compared to uninfected mice, Mtb infected mice had statistically higher “background” frequency of activated CD69⁺ and IFN-γ⁺ CD4⁺ lymphocytes and dendritic cells, and higher levels of cytokines in the lungs. The injections of MSC to Mtb infected mice did not show statistically significant effects on CD4⁺ lymphocytes, dendritic cells and macrophages, only slightly shifted cytokine profile, and did not change pathogen load or slow down TB progression. Lung section analysis showed that in Mtb infected mice, MSC could not be found in the proximity of the inflammatory foci. Thus, in healthy recipients, MSC administration dramatically changed T-cell function and cytokine/chemokine milieu in the lungs, most likely, due to capillary blockade. But, during Mtb infection, i.e., in the highly-inflammatory conditions, MSC did not affect T-cell function and the level of inflammation. The findings emphasize the importance of the evaluation of MSC effects locally at the site of their predominant post-injection localization and question MSC usefulness as anti-TB treatment.

MCL Plays an Anti-Inflammatory Role in Mycobacterium tuberculosis-Induced Immune Response by Inhibiting NF-κB and NLRP3 Inflammasome Activation

Mycobacterium tuberculosis (Mtb) remains a significant menace to global health as it induces granulomatous lung lesions and systemic inflammatory responses during active tuberculosis (TB). Micheliolide (MCL), a sesquiterpene lactone, was recently reported to have a function of relieving LPS-induced inflammatory response, but the regulative role of MCL on the immunopathology of TB still remains unknown. In this experiment, we examined the inhibitory effect of MCL on Mtb-induced inflammatory response in mouse macrophage-like cell line Raw264.7 by downregulating the activation of nuclear factor kappa B (NF-κB) and NLRP3 inflammasome. Evidences showed that MCL decreased the secretion of Mtb-induced inflammatory cytokines (IL-1β and TNF-α) in a dose-dependent manner. Meanwhile, MCL dramatically suppressed Mtb-induced activation of iNOS and COX2 as well as subsequent production of NO. Furthermore, MCL inhibited Mtb-induced phosphorylation of Akt (Ser 473) in Raw264.7. According to our results, MCL plays an important role in modulating Mtb-induced inflammatory response through PI3K/Akt/NF-κB pathway and subsequently downregulating the activation of NLRP3 inflammasome. Therefore, MCL may represent as a potential drug candidate in the adjuvant treatment of TB by regulating host immune response.

The Goldilocks model of immune symbiosis with Mycobacteria and Candida colonizers

Mycobacteria and Candida species include significant human pathogens that can cause localized or disseminated infections. Although these organisms may appear to have little in common, several shared pathways of immune recognition and response are important for both control and infection-related pathology. In this article, we compare and contrast the innate and adaptive components of the immune system that pertain to these infections in humans and animal models. We also explore a relatively new concept in the mycobacterial field: biological commensalism. Similar to the well-established model of Candida infection, Mycobacteria species colonize their human hosts in equilibrium with the immune response. Perturbations in the immune response permit the progression to pathologic disease at the expense of the host. Understanding the immune factors required to maintain commensalism may aid with the development of diagnostic and treatment strategies for both categories of pathogens.

Neutrophils in Tuberculosis: Heterogeneity Shapes the Way?

Infection with M. tuberculosis remains one of the most common infections in the world. The outcome of the infection depends on host ability to mount effective protection and balance inflammatory responses. Neutrophils are innate immune cells implicated in both processes. Accordingly, during M. tuberculosis infection, they play a dual role. Particularly, they contribute to the generation of effector T cells, participate in the formation of granuloma, and are directly involved in tissue necrosis, destruction, and infection dissemination. Neutrophils have a high bactericidal potential. However, data on their ability to eliminate M. tuberculosis are controversial, and the results of neutrophil depletion experiments are not uniform. Thus, the overall roles of neutrophils during M. tuberculosis infection and factors that determine these roles are not fully understood. This review analyzes data on neutrophil defensive and pathological functions during tuberculosis and considers hypotheses explaining the dualism of neutrophils during M. tuberculosis infection and tuberculosis disease.

A Role for Neutrophils in Viral Respiratory Disease

Neutrophils are immune cells that are well known to be present during many types of lung diseases associated with acute respiratory distress syndrome (ARDS) and may contribute to acute lung injury. Neutrophils are poorly studied with respect to viral infection, and specifically to respiratory viral disease. Influenza A virus (IAV) infection is the cause of a respiratory disease that poses a significant global public health concern. Influenza disease presents as a relatively mild and self-limiting although highly pathogenic forms exist. Neutrophils increase in the respiratory tract during infection with mild seasonal IAV, moderate and severe epidemic IAV infection, and emerging highly pathogenic avian influenza (HPAI). During severe influenza pneumonia and HPAI infection, the number of neutrophils in the lower respiratory tract is correlated with disease severity. Thus, comparative analyses of the relationship between IAV infection and neutrophils provide insights into the relative contribution of host and viral factors that contribute to disease severity. Herein, we review the contribution of neutrophils to IAV disease pathogenesis and to other respiratory virus infections.

P2X7 Receptor in Bone Marrow-Derived Cells Aggravates Tuberculosis Caused by Hypervirulent Mycobacterium bovis

Tuberculosis (TB) remains a serious public health problem despite the great scientific advances in the recent decades. We have previously shown that aggressive forms of TB caused by hypervirulent strains of Mycobacterium tuberculosis and Mycobacterium bovis are attenuated in mice lacking the P2X7 receptor, an ion channel activated by extracellular ATP. Therefore, P2X7 receptor is a potential target for therapeutic intervention. In vitro, hypervirulent mycobacteria cause macrophage death by a P2X7-dependent mechanism that facilitates bacillus dissemination. However, as P2X7 receptor is expressed in both bone marrow (BM)-derived cells and lung structural cells, several cellular mechanisms can operate in vivo. To investigate whether the presence of P2X7 receptor in BM-derived cells contributes to TB severity, we generated chimeric mice by adoptive transfer of hematopoietic cells from C57BL/6 or P2X7^-/- mice into CD45.1 irradiated mice. After infection with hypervirulent mycobacteria (MP287/03 strain of M. bovis), P2X7^-/->CD45.1 mice recapitulated the TB resistance observed in P2X7^-/- mice. These chimeric mice showed lower lung bacterial load and attenuated pneumonia compared to C57BL/6>CD45.1 mice. Lung necrosis and bacterial dissemination to the spleen and liver were also reduced in P2X7^-/->CD45.1 mice compared to C57BL/6>CD45.1 mice. Furthermore, an immature-like myeloid cell population showing a Ly6G^int phenotype was observed in the lungs of infected C57BL/6 and C57BL/6>CD45.1 mice, whereas P2X7^-/- and P2X7^-/->CD45.1 mice showed a typical neutrophil (Ly6G^hi) population. This study clearly demonstrates that P2X7 receptor in BM-derived cells plays a critical role in the progression of severe TB.

Interactions between Type 1 Interferons and the Th17 Response in Tuberculosis: Lessons Learned from Autoimmune Diseases

The classical paradigm of tuberculosis (TB) immunity, with a central protective role for Th1 responses and IFN-γ-stimulated cellular responses, has been challenged by unsatisfactory results of vaccine strategies aimed at enhancing Th1 immunity. Moreover, preclinical TB models have shown that increasing IFN-γ responses in the lungs is more damaging to the host than to the pathogen. Type 1 interferon signaling and altered Th17 responses have also been associated with active TB, but their functional roles in TB pathogenesis remain to be established. These two host responses have been studied in more detail in autoimmune diseases (AID) and show functional interactions that are of potential interest in TB immunity. In this review, we first identify the role of type 1 interferons and Th17 immunity in TB, followed by an overview of interactions between these responses observed in systemic AID. We discuss (i) the effects of GM-CSF-secreting Th17.1 cells and type 1 interferons on CCR2⁺ monocytes; (ii) convergence of IL-17 and type 1 interferon signaling on stimulating B-cell activating factor production and the central role of neutrophils in this process; and (iii) synergy between IL-17 and type 1 interferons in the generation and function of tertiary lymphoid structures and the associated follicular helper T-cell responses. Evaluation of these autoimmune-related pathways in TB pathogenesis provides a new perspective on recent developments in TB research.

Effector Mechanisms of Neutrophils within the Innate Immune System in Response to Mycobacterium tuberculosis Infection

Neutrophils have a significant yet controversial role in the innate immune response to Mycobacterium tuberculosis (M. tb) infection, which is not yet fully understood. In addition to neutrophils’ well-known effector mechanisms, they may also help control infection of M. tb through the formation of neutrophil extracellular traps (NETs), which are thought to further promote the killing of M. tb by resident alveolar macrophages. Cytokines such as IFN-γ have now been shown to serve an immunomodulatory role in neutrophil functioning in conjunction to its pro-inflammatory function. Additionally, the unique transcriptional changes of neutrophils may be used to differentiate between infection with M. tb and other bacterial and chronic rheumatological diseases such as Systemic Lupus Erythematosus. Adversely, during the innate immune response to M. tb, inappropriate phagocytosis of spent neutrophils can result in nonspecific damage to host cells due to necrotic lysis. Furthermore, some individuals have been shown to be more genetically susceptible to tuberculosis (TB) due to a “Trojan Horse” phenomenon whereby neutrophils block the ability of resident macrophages to kill M. tb. Despite these aforementioned negative consequences, through the scope of this review we will provide evidence to support the idea that neutrophils, while sometimes damaging, can also be an important component in warding off M. tb infection. This is exemplified in immunocompromised individuals, such as those with human immunodeficiency virus (HIV) infection or Type 2 diabetes mellitus. These individuals are at an increased risk of developing tuberculosis (TB) due to a diminished innate immune response associated with decreased levels of glutathione. Consequently, there has been a worldwide effort to limit and contain M. tb infection through the use of antibiotics and vaccinations. However, due to several significant limitations, the current bacille Calmette-Guerin vaccine (BCG, vaccine against TB) does not meet the criteria for universal utilization for all ages and populations across the globe. New research involving neutrophils has yielded a new vaccine called M. smegmatis-Ag85C-MPT51-HspX (mc²-CMX) that has been shown to elicit a humoral and cellular response against M. tb in mice that is superior to the BCG vaccine.

"Suppressor Factor" of Neutrophils: A Short Story of a Long-Term Misconception

A large body of evidence obtained during the last decade has demonstrated that neutrophils suppress T cell proliferation in different models of inflammation and cell interaction. The commonly used method for assessing cell proliferation and proliferation inhibition is measuring [3H]thymidine incorporation into cells. Earlier, we observed inhibition of [3H]thymidine uptake in experiments on neutrophil-mediated regulation of T cell response in tuberculosis immunity. Here, we used different types of proliferating cells to analyze the nature of the soluble "neutrophil factor" by a variety of methods (dialysis, HPLC, mass spectrometry, and NMR) and unambiguously demonstrated that neutrophils do not synthesize a specific factor inhibiting cell proliferation, but secrete high concentrations of extracellular thymidine that competitively inhibit [3H]thymidine incorporation. Although the physiological significance of thymidine secretion by neutrophils remains unknown, this phenomenon should be carefully considered when designing test systems for studying cell-cell interactions.

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.