Foxp3(+) regulatory T cells in tuberculosis. Adv Exp Med Biol. 2013;783:165-180. [PMID: 23468109 DOI: 10.1007/978-1-4614-6111-1_9]

Uncovering the Bronchoalveolar Single-Cell Landscape of Patients With Pulmonary Tuberculosis With Human Immunodeficiency Virus Type 1 Coinfection

BACKGROUND

Coinfection of human immunodeficiency virus type 1 (HIV-1) is the most significant risk factor for tuberculosis (TB). The immune responses of the lung are essential to restrict the growth of Mycobacterium tuberculosis and avoid the emergence of the disease. Nevertheless, there is still limited knowledge about the local immune response in people with HIV-1-TB coinfection.

METHODS

We employed single-cell RNA sequencing (scRNA-seq) on bronchoalveolar lavage fluid from 9 individuals with HIV-1-TB coinfection and 10 with pulmonary TB.

RESULTS

A total of 19 058 cells were grouped into 4 major cell types: myeloid cells, T/natural killer (NK) cells, B cells, and epithelial cells. The myeloid cells and T/NK cells were further divided into 10 and 11 subsets, respectively. The proportions of dendritic cell subsets, CD4+ T cells, and NK cells were lower in the HIV-1-TB coinfection group compared to the TB group, while the frequency of CD8+ T cells was higher. Additionally, we identified numerous differentially expressed genes between the CD4+ and CD8+ T-cell subsets between the 2 groups.

CONCLUSIONS

HIV-1 infection not only affects the abundance of immune cells in the lungs but also alters their functions in patients with pulmonary TB.

Bacteriophage therapy for the treatment of Mycobacterium tuberculosis infections in humanized mice

The continuing emergence of new strains of antibiotic-resistant bacteria has renewed interest in phage therapy; however, there has been limited progress in applying phage therapy to multi-drug resistant Mycobacterium tuberculosis (Mtb) infections. In this study, we show that bacteriophage strains D29 and DS6A can efficiently lyse Mtb H37Rv in 7H10 agar plates. However, only phage DS6A efficiently kills H37Rv in liquid culture and in Mtb-infected human primary macrophages. We further show in subsequent experiments that, after the humanized mice were infected with aerosolized H37Rv, then treated with DS6A intravenously, the DS6A treated mice showed increased body weight and improved pulmonary function relative to control mice. Furthermore, DS6A reduces Mtb load in mouse organs with greater efficacy in the spleen. These results demonstrate the feasibility of developing phage therapy as an effective therapeutic against Mtb infection.

Ex vivo and in vivo evidence that cigarette smoke-exposed T regulatory cells impair host immunity against Mycobacterium tuberculosis

Introduction

A strong epidemiologic link exists between cigarette smoke (CS) exposure and susceptibility to tuberculosis (TB). Macrophage and murine studies showed that CS and nicotine impair host-protective immune cells against Mycobacterium tuberculosis (MTB) infection. While CS and nicotine may activate T regulatory cells (Tregs), little is known about how CS may affect these immunosuppressive cells with MTB infection.

Methods

We investigated whether CS-exposed Tregs could exacerbate MTB infection in co-culture with human macrophages and in recipient mice that underwent adoptive transfer of Tregs from donor CS-exposed mice.

Results

We found that exposure of primary human Tregs to CS extract impaired the ability of unexposed human macrophages to control an MTB infection by inhibiting phagosome-lysosome fusion and autophagosome formation. Neutralizing CTLA-4 on the CS extract-exposed Tregs abrogated the impaired control of MTB infection in the macrophage and Treg co-cultures. In Foxp3+GFP+DTR+ (Thy1.2) mice depleted of endogenous Tregs, adoptive transfer of Tregs from donor CS-exposed B6.PL(Thy1.1) mice with subsequent MTB infection of the Thy1.2 mice resulted in a greater burden of MTB in the lungs and spleens than those that received Tregs from air-exposed mice. Mice that received Tregs from donor CS-exposed mice and infected with MTB had modest but significantly reduced numbers of interleukin-12-positive dendritic cells and interferon-gamma-positive CD4+ T cells in the lungs, and an increased number of total programmed cell death protein-1 (PD-1) positive CD4+ T cells in both the lungs and spleens.

Discussion

Previous studies demonstrated that CS impairs macrophages and host-protective T effector cells in controlling MTB infection. We now show that CS-exposed Tregs can also impair control of MTB in co-culture with macrophages and in a murine model.

Bacteriophage therapy for the treatment of Mycobacterium tuberculosis infections in humanized mice

The continuing emergence of new strains of antibiotic-resistant bacteria has renewed interest in phage therapy; however, there has been limited progress in applying phage therapy to multi-drug resistant Mycobacterium tuberculosis (Mtb) infections. In this study, we tested three bacteriophage strains for their Mtb-killing activities and found that two of them efficiently lysed Mtb H37Rv in 7H10 agar plates. However, only phage DS6A efficiently killed H37Rv in liquid culture and in Mtb-infected human primary macrophages. In subsequent experiments, we infected humanized mice with aerosolized H37Rv, then treated these mice with DS6A intravenously to test its in vivo efficacy. We found that DS6A treated mice showed increased body weight and improved pulmonary function relative to control mice. Furthermore, DS6A reduced Mtb load in mouse organs with greater efficacy in the spleen. These results demonstrated the feasibility of developing phage therapy as an effective therapeutic against Mtb infection.

Host-directed immunotherapy of viral and bacterial infections: past, present and future

The advent of COVID-19 and the persistent threat of infectious diseases such as tuberculosis, malaria, influenza and HIV/AIDS remind us of the marked impact that infections continue to have on public health. Some of the most effective protective measures are vaccines but these have been difficult to develop for some of these infectious diseases even after decades of research. The development of drugs and immunotherapies acting directly against the pathogen can be equally challenging, and such pathogen-directed therapeutics have the potential disadvantage of selecting for resistance. An alternative approach is provided by host-directed therapies, which interfere with host cellular processes required for pathogen survival or replication, or target the host immune response to infection (immunotherapies) to either augment immunity or ameliorate immunopathology. Here, we provide a historical perspective of host-directed immunotherapeutic interventions for viral and bacterial infections and then focus on SARS-CoV-2 and Mycobacterium tuberculosis, two major human pathogens of the current era, to indicate the key lessons learned and discuss candidate immunotherapeutic approaches, with a focus on drugs currently in clinical trials.

Manipulation and exploitation of host immune system by pathogenic Mycobacterium tuberculosis for its advantage

Mycobacterium tuberculosis (Mtb) can become a long-term infection by evading the host immune response. Coevolution of Mtb with humans has resulted in its ability to hijack the host's immune systems in a variety of ways. So far, every Mtb defense strategy is essentially dependent on a subtle balance that, if shifted, can promote Mtb proliferation in the host, resulting in disease progression. In this review, the authors summarize many important and previously unknown mechanisms by which Mtb evades the host immune response. Besides recently found strategies by which Mtb manipulates the host molecular regulatory machinery of innate and adaptive immunity, including the intranuclear regulatory machinery, costimulatory molecules, the ubiquitin system and cellular intrinsic immune components will be discussed. A holistic understanding of these immune-evasion mechanisms is of foremost importance for the prevention, diagnosis and treatment of tuberculosis and will lead to new insights into tuberculosis pathogenesis and the development of more effective vaccines and treatment regimens.

Immune regulatory effect of osteopontin gene therapy in a murine model of multi-drug resistant pulmonary tuberculosis

Tuberculosis (TB) has been for many years a major public health problem since treatment is long and sometimes ineffective favoring the increase of multi-drug-resistant mycobacteria (MDR). Gene therapy is a novel and effective tool to regulate immune responses. In this study we evaluated the therapeutic effect of an adenoviral vector codifying osteopontin (AdOPN), a molecule known for their roles to favour Th1 and Th17 type-cytokine expression which are crucial in TB containment. A single-dose of AdOPN administration in BALB/c mice suffering late progressive pulmonary MDR-TB, produced significant lower bacterial load and pneumonia, due to higher expression of IFN-γ, IL-12 and IL-17 in coexistence with increase of granulomas in number and size, resulting in higher survival, in contrast with mice treated with the control adenovirus that codify the green fluorescent protein (AdGFP). Combined therapy of AdOPN with a regimen of 2nd line antibiotics produced a better control of bacterial load in lung during the first days of treatment, suggesting that AdOPN can shorten chemotherapy. Taken together, gene therapy with AdOPN leads to higher immune responses against TB infection, resulting in a new potential treatment against pulmonary TB that can co-adjuvant chemotherapy.

A Pulmonary Lactobacillus murinus Strain Induces Th17 and RORγt+ Regulatory T Cells and Reduces Lung Inflammation in Tuberculosis

The lungs harbor multiple resident microbial communities, otherwise known as the microbiota. There is an emerging interest in deciphering whether the pulmonary microbiota modulate local immunity, and whether this knowledge could shed light on mechanisms operating in the response to respiratory pathogens. In this study, we investigate the capacity of a pulmonary Lactobacillus strain to modulate the lung T cell compartment and assess its prophylactic potential upon infection with Mycobacterium tuberculosis, the etiological agent of tuberculosis. In naive mice, we report that a Lactobacillus murinus (Lagilactobacillus murinus) strain (CNCM I-5314) increases the presence of lung Th17 cells and of a regulatory T cell (Treg) subset known as RORγt⁺ Tregs. In particular, intranasal but not intragastric administration of CNCM I-5314 increases the expansion of these lung leukocytes, suggesting a local rather than systemic effect. Resident Th17 and RORγt⁺ Tregs display an immunosuppressive phenotype that is accentuated by CNCM I-5314. Despite the well-known ability of M. tuberculosis to modulate lung immunity, the immunomodulatory effect by CNCM I-5314 is dominant, as Th17 and RORγt⁺ Tregs are still highly increased in the lung at 42-d postinfection. Importantly, CNCM I-5314 administration in M. tuberculosis-infected mice results in reduction of pulmonary inflammation, without increasing M. tuberculosis burden. Collectively, our findings provide evidence for an immunomodulatory capacity of CNCM I-5314 at steady state and in a model of chronic inflammation in which it can display a protective role, suggesting that L. murinus strains found in the lung may shape local T cells in mice and, perhaps, in humans.

CCL1 and IL-2Ra differentiate Tuberculosis disease from latent infection Irrespective of HIV infection in low TB burden countries

OBJECTIVES

To evaluate the performance of selected host immunological biomarkers in differentiating tuberculosis (TB) disease from latent TB infection (LTBI) in HIV uninfected and infected individuals enrolled in TB low-burden countries.

DESIGN

Participants with TB disease (N = 85) and LTBI (N = 150) were recruited from prospective cohorts at hospitals in Norway and Denmark. Plasma concentrations of 54 host markers were assessed by Luminex multiplex immunoassays. Using receiver operator characteristic curves and general discriminant analysis, we determined the abilities of individual and combined biomarkers to discriminate between TB disease and LTBI including when patients were stratified according to HIV infection status.

RESULTS

Regardless of the groups compared, CCL1 and IL-2Ra were the most accurate single biomarkers in differentiating TB disease from LTBI. Regardless of HIV status, a 4-marker signature (CCL1+RANTES+CRP+MIP-1α) derived from a training set (n = 155) differentiated TB disease from LTBI in the test set (n = 67) with a sensitivity of 56.0% (95% CI, 34.9-75.6) and a specificity of 85.7% (95% CI, 71.5-94.6). A 5-marker signature derived from the HIV uninfected group (CCL1+RANTES+MIP-1α+procalcitonin+IP-10) performed in HIV-infected individuals with a sensitivity of 75.0% and a specificity of 96.7% after leave-one-out cross validation. A 2-marker signature (CCL1+TNF-α) identified in HIV-infected persons performed in HIV-uninfected with a sensitivity and specificity of 66.7% and 100% respectively in the test set.

CONCLUSIONS

Plasma CCL1 and IL-2Ra have potential as biomarkers for differentiating TB disease from LTBI in low TB burden settings unaffected by HIV infection. Combinations between these and other biomarkers in bio-signatures for global use warrant further exploration.

The double-edged sword of Tregs in M tuberculosis, M avium, and M absessus infection

Immunity against different Mycobacteria species targeting the lung requires distinctly different pulmonary immune responses for bacterial clearance. Many parameters of acquired and regulatory immune responses differ quantitatively and qualitatively from immunity during infection with Mycobacteria species. Nontuberculosis Mycobacteria species (NTM) Mycobacterium avium- (M avium), Mycobacterium abscessus-(M abscessus), and the Mycobacteria species Mycobacterium tuberculosis-(Mtb). Herein, we discuss the potential implications of acquired and regulatory immune responses in the context of animal and human studies, as well as future directions for efforts to treat Mycobacteria diseases.

Elevation in the counts of IL-35-producing B cells infiltrating into lung tissue in mycobacterial infection is associated with the downregulation of Th1/Th17 and upregulation of Foxp3+Treg

IL-35 is an anti-inflammatory cytokine and is thought to be produced by regulatory T (Treg) cells. A previous study found that IL-35 was upregulated in the serum of patients with active tuberculosis (ATB), and IL-35-producing B cells infiltrated to tuberculous granuloma of patients with ATB. Purified B cells from such patients generated more IL-35 after stimulation by antigens of Mycobacterium tuberculosis and secreted more IL-10. However, the function and the underlying mechanisms of IL-35-producing B cells in TB progression have not been investigated. The present study found that the expression of mRNA of IL-35 subsets Ebi3 and p35 was elevated in mononuclear cells from peripheral blood, spleen, bone marrow, and lung tissue in a mouse model infected with Mycobacterium bovis BCG, as tested by real-time polymerase chain reaction. Accordingly, the flow cytometry analysis showed that the counts of a subset of IL-35⁺ B cells were elevated in the circulating blood and in the spleen, bone marrow, and lung tissue in BCG-infected mice, whereas anti-TB therapy reduced IL-35-producing B cells. Interestingly, BCG infection could drive the infiltration of IL-35-producing B cells into the lung tissue, and the elevated counts of IL-35-producing B cells positively correlated with the bacterial load in the lungs. Importantly, the injection of exogenous IL-35 stimulated the elevation in the counts of IL-35-producing B cells and was associated with the downregulation of Th1/Th17 and upregulation of Foxp3⁺Treg.The study showed that a subset of IL-35-producing B cells might take part in the downregulation of immune response in mycobacterial infection.

DosR antigen Rv1737c induces activation of macrophages dependent on the TLR2 pathway

Latent Mycobacterium tuberculosis (Mtb) infection (LTBI) is the main clinical manifestation after Mtb exposure. During the latent phase, Mtb retards the attempts of eradication by the host immune system. The dormancy survival regulator (DosR) is held as essential for Mtb persistence. Rv1737c is predominantly expressed by the Mtb in latent infection. However, the role of Rv1737c in the immune evasion is still largely unknown. In this study, we have characterized the Rv1737c functions in the recruitment and activation of macrophages, which play a cardinal role in the innate and adaptive immunity. For the first time, we have revealed that Rv1737c induced the tolerogenic phenotype of macrophages by upregulating the expression of indoleamine 2,3-dioxygenase 1 (IDO1). Rv1737c-activated macrophages upregulated interleukin (IL)-4, IL-10, and Foxp3 T cells proliferation in vitro. Furthermore, the interaction of Rv1737c with macrophages was found to depend on the Toll-like receptor 2 (TLR2) pathway. It augmented nuclear factor κB (NF-κB) phosphorylation and co-stimulatory molecule expression. Thus, this study provides a crucial insight into a strategy adopted by Mtb to survive in the host by inducing tolerogenic macrophage expansion.

The Effect of Age on the Immunogenicity of the Live Attenuated Zoster Vaccine Is Predicted by Baseline Regulatory T Cells and Varicella-Zoster Virus-Specific T Cell Immunity

Older age is associated with increased infectious morbidity and decreased immune responses to vaccines, but the mechanisms that mediate this effect are incompletely understood. The efficacy and immunogenicity of the live attenuated zoster vaccine (ZVL) have a very-well-described negative association with the age of the vaccinee. In a study of 600 ZVL recipients 50 to >80 years of age, we investigated immunological factors that might explain the effect of age on the immunogenicity of ZVL. Using FluoroSpot assays and flow cytometry, we determined that varicella-zoster virus (VZV)-specific peak T helper 1 (VZV-Th1) responses to ZVL were independently predicted by prevaccination VZV-Th1 responses, regulatory T cells (Treg), and PD1-expressing immune checkpoint T cells (Tcheck) but not by the age of the vaccinee. Persistence of VZV-Th1 1 year after vaccination was independently predicted by the factors mentioned above, by peak VZV-Th1 responses to ZVL, and by the age of the vaccinee. We further demonstrated by ex vivo blocking experiments the mechanistic role of PD1 and CTLA4 as modulators of decreased VZV-Th1 responses in the study participants. VZV-specific cytotoxic T cell (VZV-CTL) and T follicular helper responses to ZVL did not correlate with age, but similar to other Th1 responses, VZV-CTL peak and baseline responses were independently correlated. These data expand our understanding of the factors affecting the magnitude and kinetics of T cell responses to ZVL in older adults and show the importance of prevaccination Treg and Tcheck in modulating the immunogenicity of ZVL. This presents new potential interventions to increase vaccine responses in older adults.IMPORTANCE Vaccination is the most effective method to protect older adults against viral infections. However, the immunogenicity of viral vaccines in older adults is notoriously poor. The live attenuated zoster vaccine (ZVL) provides the best example of a gradual decrease of vaccine immunogenicity with every 10-year age increase above 50 years. Here we show that the abundance of regulatory T cells before vaccine administration to older adults has a significant inhibitory effect on immune responses to ZVL and, together with baseline immunity to varicella-zoster virus, explains the effect of age on the immunogenicity of ZVL. Moreover, in vitro blockade of regulatory T cell mechanisms of action with biologic modulators restores immune responses to varicella-zoster virus in vaccinees. Collectively, these observations suggest that immune modulators that block regulatory T cell activity may increase responses to viral attenuated vaccines in older adults.

Serum selenium levels in tuberculosis patients: A systematic review and meta-analysis

INTRODUCTION

Tuberculosis (TB) is associated with increased mortality. The high risk of micronutrients deficiency, including selenium, in TB patients is of great concern because it increases the risk of death. However, it is not clear whether selenium supplementation could improve the treatment outcomes in TB patients. We conducted a systematic review and meta-analysis to provide an update on the existing evidence about low selenium levels in TB patients.

METHODS

In this systematic review and meta-analysis, EMBASE, Medline and the International Journal of Tuberculosis and Lung Disease were searched to identify observational studies on selenium and TB published up until April 2018. Studies comparing blood selenium levels in TB patients to controls were included. Data extraction was performed by two investigators. The quality of the studies was assessed using the Newcastle-Ottawa Quality Assessment Scale. Random effects analysis was performed to calculate the pooled effect size and 95% confidence interval (CI).

RESULTS

Of the 605 studies initially identified, only six were eligible. Of them, four were carried out in Asia, and one each in Africa and South America. The random pooled effect size was 1.6 (CI: 0.9, 2.4). This means that the probability is 160% for an individual with TB to have low levels of selenium as compared to an individual without TB. Heterogeneity across the studies was substantial (I² = 95.1%). Potential sources of heterogeneity included study design and selenium measurement methods.

CONCLUSION

Our review provides compelling evidence that serum selenium is lower in TB patients as compared with controls. Therefore, it is advisable to individually assess selenium status in TB patients and decide whether selenium supplement is needed or not.

Frequency of Circulating CD4+Ki67+HLA-DR- T Regulatory Cells Prior to Treatment for Multidrug Resistant Tuberculosis Can Differentiate the Severity of Disease and Predict Time to Culture Conversion

Identifying a blood circulating cellular biomarker that can be used to assess severity of disease and predict the time to culture conversion (TCC) in patients with multidrug resistant tuberculosis (MDR-TB) would facilitate monitoring response to treatment and may be of value in the design of future drug trials. We report on the frequency of blood Ki67⁺HLA-DR^- CD4+ T regulatory (Treg) cells in predicting microbiological outcome before initiating second-line treatment for MDR-TB. Fifty-one patients with MDR-TB were enrolled and followed over 18 months; a subset of patients was sputum culture (SC) negative at baseline (n = 9). SC positive patients were divided into two groups, based on median TCC: rapid responders (≤71 days TCC; n = 21) and slow responders (>71 days TCC; n = 21). Whole blood at baseline, months 2 and 6 was stimulated with M tuberculosis (Mtb) antigens and Treg cells were then identified as CD3⁺CD4⁺CD25^hiFoxP3⁺CD127^-CD69^- and further delineated as Ki67⁺HLA-DR^- Treg. The frequency of these cells was significantly enlarged at baseline in SC positive relative to SC negative and smear positive relative to smear negative patients and in those with lung cavitation. This difference was further supported by unsupervised hierarchical clustering showing a significant grouping at baseline of total and early differentiated memory Treg cells in slow responders. Conversely, there was a clustering of a lower proportion of Treg cells and activated IFNγ-expressing T cells at baseline in the rapid responders. Examining changes over time revealed a more gradual reduction of Treg cells in slow responders relative to rapid responders to treatment. Receiver operating curve analysis showed that baseline Mtb-stimulated Ki67⁺HLA-DR^- Treg cells could predict the TCC of MDR-TB treatment response with 81.2% sensitivity and 85% specificity (AUC of 0.87, p < 0.0001), but this was not the case after 2 months of treatment. In conclusion, our data show that the frequency of a highly defined Mtb-stimulated blood Treg cell population at baseline can discriminate MDR-TB disease severity and predict time to culture clearance.

Regulatory T cells antagonize proinflammatory response of IL-17 during cutaneous tuberculosis

Background

The clinical forms of cutaneous tuberculosis (CTB) consist of a spectrum that reflects the host's immune response to Mycobacterium tuberculosis; it provides an ideal model to study the immunological dysregulation in humans. IL-17 plays an important role in initial immune response and is involved in both immune-mediated protection and pathology during M. tuberculosis infection. TGF-β producing regulatory T-cells (Tregs) are high in leprosy patients and responsible for immune suppression. However, in CTB, the involvement of Tregs and Th17 remains unevaluated.

Objective

To study the role of proinflammatory Th17 and Treg cells in the human CTB.

Methods

Blood and skin biopsies of CTB patients and healthy controls (HC) were included in the study. Flow cytometric analysis of IL-17, FOXP3, and TGF-β in blood was done followed by immunohistochemistry on paraffin-embedded skin sections. Expression of IFN-γ, TGF-β, and IL-17 was evaluated by quantitative real-time PCR.

Results

We found significant (P<0.0002) lower expression of proinflammatory IL-17 and IFN-γ (P<0.01) in CTB skins as compared to HC. However, the frequency of TGF-β producing Treg cells was found to be high in CTB patients (P<0.001) as compared to HC. A similar type of profile was observed by flow cytometric analysis. Treg cells produced suppressive cytokine TGF-β which showed a positive correlation with FOXP3 gene expression.

Conclusion

Our study found an increase in lineage-specific CD4⁺ Tregs in CTB as compared to the HC individuals. Such cells secrete TGF-β, a suppressive cytokine and may play a role in negatively regulating the T-cell immune responses in CTB. In addition, Tregs with TGF-β may downregulate Th17 cell responses leading to the antigen-specific anergy associated with CTB patients.

Translational Potential of Therapeutics Targeting Regulatory Myeloid Cells in Tuberculosis

Despite recent advances in tuberculosis (TB) drug development and availability, successful antibiotic treatment is challenged by the parallel development of antimicrobial resistance. As a result, new approaches toward improving TB treatment have been proposed in an attempt to reduce the high TB morbidity and mortality rates. Host-directed therapies (HDTs), designed to modulate host immune components, provide an alternative approach for improving treatment outcome in both non-communicable and infectious diseases. Many candidate immunotherapeutics, designed to target regulatory myeloid immune components in cancer, have so far proven to be of value as repurposed HDT in TB. Several of these studies do however lack detailed description of the mechanism or host pathway affected by TB HDT treatment. In this review, we present an argument for greater appreciation of the role of regulatory myeloid cells, such as myeloid-derived suppressor cells (MDSC), as potential targets for the development of candidate TB HDT compounds. We discuss the role of MDSC in the context of Mycobacterium tuberculosis infection and disease, focussing primarily on their specific cellular functions and highlight the impact of HDTs on MDSC frequency and function.

Protective immune mechanisms of Yifei Tongluo, a Chinese herb formulation, in the treatment of mycobacterial infection

Yifei Tongluo (YFTL) is a traditional Chinese medicine (TCM) formulation which has been shown clinical efficacy in treatment of patients with multidrug-resistant tuberculosis in China. However, the underlying mechanisms of the effects of YFTL are lacking. This study investigated the effects of YFTL on immune regulation with a mouse lung infection model with Bacille Calmette-Guérin (BCG). We found that compared with untreated mice, the lung mycobacterial load in YFTL-treated mice was significantly reduced, accompanied by alleviated pulmonary inflammation with reduction of pro-inflammatory cytokines and increase of prostaglandin E2 (PGE2). Flow cytometry analyses showed that Th1 cells were significantly higher in the lungs of YFTL-treated mice at early infection time. The results suggest that YFTL-treatment down-regulates pulmonary inflammation, which facilitates a rapid infiltration of Th1 cells into the lungs. Moreover, the Th1 cells in the lungs were resolved faster at later time concomitant with increased the regulatory T cells (Tregs). The reduction of mycobacterial burden associated with improved tissue pathology, faster Th1 cell trafficking, and accelerated resolution of Th1 cells in the lungs of YFTL-treated mice indicates that YFTL improves mycobacterial clearance by maintaining lung homeostasis and dynamically regulating T cells in the lung parenchyma, and suggests that YFTL can be used as host-directed therapies that target immune responses to mycobacterial infection.

The Phagocyte Oxidase Controls Tolerance to Mycobacterium tuberculosis Infection

Protection from infectious disease relies on two distinct strategies: antimicrobial resistance directly inhibits pathogen growth, whereas infection tolerance protects from the negative impact of infection on host health. A single immune mediator can differentially contribute to these strategies in distinct contexts, confounding our understanding of protection to different pathogens. For example, the NADPH-dependent phagocyte oxidase (Phox) complex produces antimicrobial superoxide and protects from tuberculosis (TB) in humans. However, Phox-deficient mice display no sustained resistance defects to Mycobacterium tuberculosis, suggesting a more complicated role for NADPH Phox complex than strictly controlling bacterial growth. We examined the mechanisms by which Phox contributes to protection from TB and found that mice lacking the Cybb subunit of Phox suffered from a specific defect in tolerance, which was caused by unregulated Caspase-1 activation, IL-1β production, and neutrophil influx into the lung. These studies imply that a defect in tolerance alone is sufficient to compromise immunity to M. tuberculosis and highlight a central role for Phox and Caspase-1 in regulating TB disease progression.

Interplay of DDP4 and IP-10 as a Potential Mechanism for Cell Recruitment to Tuberculosis Lesions

INTRODUCTION

Mycobacterium tuberculosis is one of the world's most successful pathogens equipped to establish itself within the human host as a subclinical infection without overt disease. Unable to eradicate the bacteria, the immune system contains the infection in a granuloma structure. Th1 cells that are essential for infection control are recruited to the site of infection directed by chemokines, predominantly CXCL10. It has previously been shown that CXCL10 in the plasma of patients chronically infected with hepatitis C virus is present primarily in an antagonist form. This is due to N-terminal truncation by the enzyme DPP4, which results in the antagonist form that is capable of binding its receptor CXCR3, but does not induce signaling. We aimed to explore whether such CXCL10 antagonism may have an impact on the pathogenesis of tuberculosis (TB).

RESULTS

We measured plasma levels of agonist and antagonist CXCL10 by Simoa digital ELISA, as well as DPP4 enzyme activity in the plasma of 20 patients with active TB infection, 10 patients with pneumonia infection, and a group of 10 healthy controls. We found higher levels of total and antagonist CXCL10 and reduced DPP4 enzyme activity in the plasma of TB patients compared to controls. We traced the source of CXCL10 secretion using immunohistochemical and confocal analysis to multinucleated giant cells in the TB lesions, and variable expression by macrophages. Interestingly, these cells were associated with DPP4-positive T cells. Moreover, the analysis of lymphocytes at the site of TB infection (bronchoalveolar lavage) showed a reduced frequency of CXCR3+ T cells.

INTERPRETATION

Our data suggests that CXCL10 antagonism may be an important regulatory mechanism occurring at the site of TB pathology. CXCL10 can be inactivated shortly after secretion by membrane bound DPP4 (CD26), therefore, reducing its chemotactic potential. Given the importance of Th1 cell functions and IFN-γ-mediated effects in TB, our data suggest a possible unappreciated regulatory role of DPP4 in TB.

PERSPECTIVES

DPP4 is the target for a class of enzyme inhibitors used in the treatment of diabetes, and the results from this study suggest that these drugs could be repurposed as an adjunct immunotherapy of patients with TB and MDR-TB.

The significance role of regulatory T cells in the persistence of infections by intracellular bacteria

Regulatory T cells (Treg cells), are considered as effective immune cells playing a key role in immune response during cancers, autoimmune and infectious diseases. Regulatory T lymphocytes are divided into two main subgroups: natural Treg cells that generated during maturation in the thymus and have the suppressive activity that is critical for the establishment and maintenance of homeostasis in the body and induced Treg cells (iTreg) that are originated from naive T cells following the self-antigen recognition. In recent years, the roles of Treg in immune responses to microbial infections have received increased attention in researches. Several reports suggested the pivotal role of Treg cells in controlling responses to bacterial infections and demonstrated the impact of regulatory cells on one or more stages in the pathogenesis of bacterial infections. In this review, we describe the significance of regulatory T cells in the immunopathology of bacterial infections by focusing on specific bacterial infections including Mycobacteria, Listeria monocytogenes, and Bordetella pertussis. Moreover, suppressive mechanisms of regulatory T cells during bacterial infection including cell-cell contact, local secretion of inhibitory cytokines and local competition for growth factors will be discussed.

G allele at -924 A > G position of FoxP3 gene promoter as a risk factor for tuberculosis

BACKGROUND

Forkhead box protein 3 (FoxP3) is an important factor for development and function of Regulatory T cells (Treg). Studies have found an association between common gene polymorphisms in FoxP3 and some infectious diseases. The aim of this study was to evaluate possible associations between two Single nucleotide polymorphisms (SNPs) in the promoter of the FoxP3 gene to susceptibility to tuberculosis (TB) and the alteration of Foxp3 gene expression.

METHODS

The pattern distribution of genotype at two position, -3279 A > C (rs3761548) and -924 A > G (rs2232365) on the promoter of FoxP3 gene was evaluated using polymerase chain reaction-single specific primer (PCR-SSP) method in 183 tuberculosis patients and 183 healthy control. In addition the quantity of FoxP3 gene expression at mRNA level was identified by the real-time PCR.

RESULTS

The frequency of G allele at -924 A > G was significantly higher was higher in TB patients (59.5%) than control group (39.5%) (P ≤ 0.05). In addition, our data viewed approximately 5- folds more FoxP3 gene expression in female patients with GG genotype in comparison to female healthy cases with the same genotype (P ≤ 0.001). There was no statistically significant differences between the distribution pattern of -3279 A > C polymorphism in patients and healthy individuals along with it effect on the FoxP3 gene expression among both groups (P > 0.05).

CONCLUSIONS

Our outcome suggests that the -924 A > G polymorphism leads to enhance FoxP3 gene expression and susceptibility to tuberculosis in the sex dependent manner. This event may rise the count of Treg cells and modulate the immune response against tuberculosis.

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.

Regulation of Immunity to Tuberculosis

Immunity against Mycobacterium tuberculosis requires a balance between adaptive immune responses to constrain bacterial replication and the prevention of potentially damaging immune activation. Regulatory T (Treg) cells express the transcription factor Foxp3+ and constitute an essential counterbalance of inflammatory Th1 responses and are required to maintain immune homeostasis. The first reports describing the presence of Foxp3-expressing CD4+ Treg cells in tuberculosis (TB) emerged in 2006. Different Treg cell subsets, most likely specialized for different tissues and microenvironments, have been shown to expand in both human TB and animal models of TB. Recently, additional functional roles for Treg cells have been demonstrated during different stages and spectrums of TB disease. Foxp3+ regulatory cells can quickly expand during early infection and impede the onset of cellular immunity and persist during chronic TB infection. Increased frequencies of Treg cells have been associated with a detrimental outcome of active TB, and may be dependent on the M. tuberculosis strain, animal model, local environment, and the stage of infection. Some investigations also suggest that Treg cells are required together with effector T cell responses to obtain reduced pathology and sterilizing immunity. In this review, we will first provide an overview of the regulatory cells and mechanisms that control immune homeostasis. Then, we will review what is known about the phenotype and function of Treg cells from studies in human TB and experimental animal models of TB. We will discuss the potential role of Treg cells in the progression of TB disease and the relevance of this knowledge for future efforts to prevent, modulate, and treat TB.

T Cell Responses and Regulation and the Impact of In Vitro IL-10 and TGF-β Modulation During Treatment of Active Tuberculosis

Mycobacterium tuberculosis (Mtb) is particularly challenging for the immune system being an intracellular pathogen, and a variety of T cell subpopulations are activated by the host defence mechanism. In this study, we investigated T cell responses and regulation in active TB patients with drug-sensitive Mtb (N = 18) during 24 weeks of efficient anti-TB therapy. T cell activation, differentiation, regulatory T cell (Treg) subsets, Mtb-induced T cell proliferation and in vitro IL-10 and TGF-β modulation were analysed by flow cytometry at baseline and after 8 and 24 weeks of therapy, while soluble cytokines in culture supernatants were analysed by a 9-plex Luminex assay. Successful treatment resulted in significantly reduced co-expression of HLA-DR/CD38 and PD-1/CD38 on both CD4⁺ and CD8⁺ T cells, while the fraction of CD4⁺ CD25^high CD127^low Tregs (P = 0.017) and CD4⁺ CD25^high CD127^low CD147⁺ Tregs (P = 0.029) showed significant transient increase at week 8. In vitro blockade of IL-10/TGF-β upon Mtb antigen stimulation significantly lowered the fraction of ESAT-6-specific CD4⁺ CD25^high CD127^low Tregs at baseline (P = 0.047), while T cell proliferation and cytokine production were unaffected. Phenotypical and Mtb-specific T cell signatures may serve as markers of effective therapy, while the IL-10/TGF-β pathway could be a target for early inhibition to facilitate Mtb clearance. However, larger clinical studies are needed for verification before concluding.

Imbalance of Th17 and Treg in peripheral blood mononuclear cells of active tuberculosis patients

Objective

Maintaining a right balance between Th17 and Treg might be critical to the immunopathogenesis of active tuberculosis (TB). This study aimed to assess whether the Th17/Treg balance is altered in active TB patients.

Methods

250 study subjects (90 active TB patients, 80 latent TB subjects, and 80 healthy controls) were recruited for the study. The expression of Th17 and Treg in peripheral blood mononuclear cells (PBMCs) in the 250 subjects was investigated by flow cytometry. Plasma levels of cytokines IL-17 and IL-10, which are related to Th17 and Treg, respectively, were determined by ELISA.

Results

The percentages of Th17 and Treg in PBMCs from active TB patients were significantly higher than those from latent TB or control groups (Th17: 4.31 ± 1.35% vs. 1.58 ± 0.71% or 1.15 ± 0.49%, p < 0.05; Treg: 11.44 ± 2.69% vs. 7.54 ± 1.56% or 4.10 ± 0.99%, p < 0.05). The expression of IL-17 and IL-10 was significantly increased in active TB patients in comparison to that in latent TB or control groups (IL-17: 16.85 ± 9.68 vs. 7.23 ± 5.19 or 8.21 ± 5.51 pg/mL, p < 0.05; IL-10: 28.70 ± 11.27 vs. 20.25 ± 8.57 or 13.94 ± 9.00 pg/mL, p < 0.05).

Conclusions

Our study demonstrated an altered balance of Treg/Th17 in active TB patients, with higher percentages of Th17 and Treg in PBMCs. Further research on this imbalance may offer a new direction for TB treatment.

The COX- inhibitor indomethacin reduces Th1 effector and T regulatory cells in vitro in Mycobacterium tuberculosis infection

BACKGROUND

Tuberculosis (TB) causes a major burden on global health with long and cumbersome TB treatment regimens. Host-directed immune modulating therapies have been suggested as adjunctive treatment to TB antibiotics. Upregulated cyclooxygenase-2 (COX-2)-prostaglandin E2 (PGE2) signaling pathway may cause a dysfunctional immune response that favors survival and replication of Mycobacterium tuberculosis (Mtb).

METHODS

Blood samples were obtained from patients with latent TB (n = 9) and active TB (n = 33) before initiation of anti-TB chemotherapy. COX-2 expression in monocytes and ESAT-6 and Ag85 specific T cell cytokine responses (TNF-α, IFN-γ, IL-2), proliferation (carboxyfluorescein succinimidyl ester staining) and regulation (FOXP3+ T regulatory cells) were analysed by flow cytometry and the in vitro effects of the COX-1/2 inhibitor indomethacin were measured.

RESULTS

We demonstrate that indomethacin significantly down-regulates the fraction of Mtb specific FOXP3+ T regulatory cells (ESAT-6; p = 0.004 and Ag85; p < 0.001) with a concomitant reduction of Mtb specific cytokine responses and T cell proliferation in active TB. Although active TB tend to have higher levels, there are no significant differences in COX-2 expression between unstimulated monocytes from patients with active TB compared to latent infection. Monocytes in both TB groups respond with a significant upregulation of COX-2 after in vitro stimulation.

CONCLUSIONS

Taken together, our in vitro data indicate a modulation of the Th1 effector and T regulatory cells in Mtb infection in response to the COX-1/2 inhibitor indomethacin. The potential role as adjunctive host-directed therapy in TB disease should be further evaluated in both animal studies and in human clinical trials.

EFIS lecture. Immune response to tuberculosis: How to control the most successful pathogen on earth

Tuberculosis (TB) remains a major health threat and general agreement exists that better control measures are needed. These include better diagnostics, drugs and vaccines. In particular, vaccines will be critical for better TB control. Based on knowledge about protective immunity against TB, a vaccine was created, VPM1002, which shows high protective efficacy and safety in experimental animal models. The vaccine has proven safe and immunogenic in human adults and neonates and is currently assessed in clinical trials in the context of HIV exposure. As a next step, a phase III efficacy trial in adults and a phase IIb efficacy trial in neonates are being planned. Biosignatures that differentially diagnose TB disease versus latent infection with high sensitivity and specificity have been designed. Most recently, a prognostic biosignature which predicts progression from latent infection to active TB has been identified. Biosignatures are not only of great value for improved diagnosis and prognosis of TB, they can also provide guidelines for better understanding of molecular mechanisms underlying disease. Accordingly, distinct biomarkers of diagnostic and prognostic value but of unknown biological function are being characterized functionally. In this way, deeper insights have been obtained on the role of type I interferon and of neutrophils in TB in experimental animal models of TB. In conclusion, clinical and basic research further supported by computational biology can complement each other in the pursuit of knowledge-based development of improved intervention measures for TB control.

Effects of B Cell Depletion on Early Mycobacterium tuberculosis Infection in Cynomolgus Macaques

Although recent studies in mice have shown that components of B cell and humoral immunity can modulate the immune responses against Mycobacterium tuberculosis, the roles of these components in human and nonhuman primate infections are unknown. The cynomolgus macaque (Macaca fascicularis) model of M. tuberculosis infection closely mirrors the infection outcomes and pathology in human tuberculosis (TB). The present study used rituximab, an anti-CD20 antibody, to deplete B cells in M. tuberculosis-infected macaques to examine the contribution of B cells and humoral immunity to the control of TB in nonhuman primates during the acute phase of infection. While there was no difference in the overall pathology, disease profession, and clinical outcome between the rituximab-treated and untreated macaques in acute infection, analyzing individual granulomas revealed that B cell depletion resulted in altered local T cell and cytokine responses, increased bacterial burden, and lower levels of inflammation. There were elevated frequencies of T cells producing interleukin-2 (IL-2), IL-10, and IL-17 and decreased IL-6 and IL-10 levels within granulomas from B cell-depleted animals. The effects of B cell depletion varied among granulomas in an individual animal, as well as among animals, underscoring the previously reported heterogeneity of local immunologic characteristics of tuberculous granulomas in nonhuman primates. Taken together, our data clearly showed that B cells can modulate the local granulomatous response in M. tuberculosis-infected macaques during acute infection. The impact of these alterations on disease progression and outcome in the chronic phase remains to be determined.

TIM3 Mediates T Cell Exhaustion during Mycobacterium tuberculosis Infection

While T cell immunity initially limits Mycobacterium tuberculosis infection, why T cell immunity fails to sterilize the infection and allows recrudescence is not clear. One hypothesis is that T cell exhaustion impairs immunity and is detrimental to the outcome of M. tuberculosis infection. Here we provide functional evidence for the development T cell exhaustion during chronic TB. Second, we evaluate the role of the inhibitory receptor T cell immunoglobulin and mucin domain–containing-3 (TIM3) during chronic M. tuberculosis infection. We find that TIM3 expressing T cells accumulate during chronic infection, co-express other inhibitory receptors including PD1, produce less IL-2 and TNF but more IL-10, and are functionally exhausted. Finally, we show that TIM3 blockade restores T cell function and improves bacterial control, particularly in chronically infected susceptible mice. These data show that T cell immunity is suboptimal during chronic M. tuberculosis infection due to T cell exhaustion. Moreover, in chronically infected mice, treatment with anti-TIM3 mAb is an effective therapeutic strategy against tuberculosis.

Tuberculosis is a leading cause of morbidity and mortality across the globe. Fortunately, most people infected with M. tuberculosis mount a protective immune response and only a small fraction develops active disease. Impairment of immunity late during the course of disease can lead to bacterial recrudescence; however, why immunity fails is poorly understood. We investigated whether T cell exhaustion develops and contributes to immunological impairment during disease. Our studies provide definitive evidence that CD4⁺ T cells become functionally exhausted early after infection, and subsequently, CD8⁺ T cells also show signs of dysfunction. T cell exhaustion in both subsets was associated with the expression of multiple inhibitory receptors. Exhausted T cells expressed TIM3 plus other inhibitory receptors (e.g., PD1, TIM3, Lag-3, and 2B4), TIM3⁺PD1⁺ T cells were more likely to be poor producers of IL-2, IFNγ, and TNF and instead produce IL-10. Evaluation of gene expression by Nanostring confirmed that TIM3⁺PD1⁺ T cells in the lungs of infected mice had a transcriptional profile characteristic of exhausted T cells. Thus, this phenotype identified T cells that were truly exhausted and correlates well with previously established paradigm that co-expression of TIM3 with other inhibitory receptors such as PD1 contributes to impairment of T cell function during chronic inflammatory conditions. Most importantly, treatment of chronically infected mice with blocking antibodies specific for TIM3 led to a significant gain in bacterial control. Treatment was associated with an increase in IL-2, IFNγ, and TNF production by T cells. Based on this key result, we infer that TIM3-mediated T cell exhaustion impairs host resistance to M. tuberculosis. Thus, these data suggest that blockade of inhibitory T cell signals has the potential to be a therapeutic strategy against tuberculosis. The data in our report significantly advances our current knowledge of the biology of TIM3, the role of inhibitory T cell receptors during chronic infection, and the pathogenesis of tuberculosis.

Evasion of Innate and Adaptive Immunity by Mycobacterium tuberculosis

Through thousands of years of reciprocal coevolution, Mycobacterium tuberculosis has become one of humanity's most successful pathogens, acquiring the ability to establish latent or progressive infection and persist even in the presence of a fully functioning immune system. The ability of M. tuberculosis to avoid immune-mediated clearance is likely to reflect a highly evolved and coordinated program of immune evasion strategies that interfere with both innate and adaptive immunity. These include the manipulation of their phagosomal environment within host macrophages, the selective avoidance or engagement of pattern recognition receptors, modulation of host cytokine production, and the manipulation of antigen presentation to prevent or alter the quality of T-cell responses. In this article we review an extensive array of published studies that have begun to unravel the sophisticated program of specific mechanisms that enable M. tuberculosis and other pathogenic mycobacteria to persist and replicate in the face of considerable immunological pressure from their hosts. Unraveling the mechanisms by which M. tuberculosis evades or modulates host immune function is likely to be of major importance for the development of more effective new vaccines and targeted immunotherapy against tuberculosis.

Tuberculous pleurisy drives marked effector responses of γδ, CD4+, and CD8+ T cell subpopulations in humans

Although tuberculous pleurisy (TP) presumably involves a hypersensitivity reaction, there is limited evidence indicating overreactive effector responses of γδ T cells and αβ T cells and their interrelation with Foxp3(+) Tregs in pleural and other compartments. We found that TP induced reciprocal representations of Foxp3(+) Tregs and Mtb phosphoantigen-specific Vγ2Vδ2 T cells in different anatomic compartments. Patients with TP exhibited appreciable numbers of "proliferating" Ki-67(+) Vγ2Vδ2 T cells in the airway where Foxp3(+) Tregs were not dominant, whereas striking increases in Foxp3(+) Tregs in the blood and pleural compartments coincided with low frequencies of Vγ2Vδ2 T cells. Interestingly, anti-tuberculosis chemotherapy control of Mtb infection in patients with TP reversed reciprocal representations of Foxp3(+) Tregs and proliferating Vγ2Vδ2 T cells. Surprisingly, despite high-level Foxp3(+) Tregs, TP appeared to drive overreactive responses of IFN-γ-producing Vγ2Vδ2, CD4(+)CD25(+), and CD8(+)CD25(+) T effector subpopulations, whereas IL-22-producing Vγ2Vδ2 T cells increased subtly. Th1 effector responses were sustained despite remarkable declines in Foxp3(+) Tregs at 1 mo after the treatment. Overreactive T effector responses of Mtb-reactive γδ T cells, αβ CD25(+)CD4(+), and CD25(+)CD8(+) T cell subpopulations appear to be immune features for TP. Increased Foxp3(+) Tregs might be responsive to overreactive TP but unable to influence T effector responses despite having an inverse relation with proliferating Vγ2Vδ2 T cells.

Whole genome response in guinea pigs infected with the high virulence strain Mycobacterium tuberculosis TT372

In this study we conducted a microarray-based whole genomic analysis of gene expression in the lungs after exposure of guinea pigs to a low dose aerosol of the Atypical Beijing Western Cape TT372 strain of Mycobacterium tuberculosis, after harvesting lung tissues three weeks after infection at a time that effector immunity is starting to peak. The infection resulted in a very large up-regulation of multiple genes at this time, particularly in the context of a "chemokine storm" in the lungs. Overall gene expression was considerably reduced in animals that had been vaccinated with BCG two months earlier, but in both cases strong signatures featuring gamma interferon [IFNγ] and tumor necrosis factor [TNFα] were observed indicating the potent TH1 response in these animals. Even though their effects are not seen until later in the infection, even at this early time point gene expression patterns associated with the potential emergence of regulatory T cells were observed. Genes involving lung repair, response to oxidative stress, and cell trafficking were strongly expressed, but interesting these gene patterns differed substantially between the infected and vaccinated/infected groups of animals. Given the importance of this species as a relevant and cost-effective small animal model of tuberculosis, this approach has the potential to provide new information regarding the effects of vaccination on control of the disease process.

Immunodeficiency in a Child with Rapadilino Syndrome: A Case Report and Review of the Literature

Rapadilino syndrome is a genetic disease characterized by a characteristic clinical tableau. It is caused by mutations in RECQL4 gene. Immunodeficiency is not described as a classical feature of the disease. We present a 2-year-old girl with Rapadilino syndrome with important lymphadenopathies and pneumonia due to disseminated Mycobacterium lentiflavum infection. An immunological work-up showed several unexpected abnormalities. Repeated blood samples showed severe lymphopenia. Immunophenotyping showed low T, B, and NK cells. No Treg cells were seen. T cell responses to stimulations were insufficient. The IL12/IL23 interferon gamma pathway was normal. Gamma globulin levels and vaccination responses were low. With this report, we aim to stress the importance of screening immunodeficiency in patients with RECQL4 mutations for immunodeficiency and the need to further research into its physiopathology.

STIM1 controls T cell-mediated immune regulation and inflammation in chronic infection

Chronic infections induce a complex immune response that controls pathogen replication, but also causes pathology due to sustained inflammation. Ca2+ influx mediates T cell function and immunity to infection, and patients with inherited mutations in the gene encoding the Ca2+ channel ORAI1 or its activator stromal interaction molecule 1 (STIM1) are immunodeficient and prone to chronic infection by various pathogens, including Mycobacterium tuberculosis (Mtb). Here, we demonstrate that STIM1 is required for T cell-mediated immune regulation during chronic Mtb infection. Compared with WT animals, mice with T cell-specific Stim1 deletion died prematurely during the chronic phase of infection and had increased bacterial burdens and severe pulmonary inflammation, with increased myeloid and lymphoid cell infiltration. Although STIM1-deficient T cells exhibited markedly reduced IFN-γ production during the early phase of Mtb infection, bacterial growth was not immediately exacerbated. During the chronic phase, however, STIM1-deficient T cells displayed enhanced IFN-γ production in response to elevated levels of IL-12 and IL-18. The lack of STIM1 in T cells was associated with impaired activation-induced cell death upon repeated TCR engagement and pulmonary lymphocytosis and hyperinflammation in Mtb-infected mice. Chronically Mtb-infected, STIM1-deficient mice had reduced levels of inducible regulatory T cells (iTregs) due to a T cell-intrinsic requirement for STIM1 in iTreg differentiation and excessive production of IFN-γ and IL-12, which suppress iTreg differentiation and maintenance. Thus, STIM1 controls multiple aspects of T cell-mediated immune regulation to limit injurious inflammation during chronic infection.

Early dynamics of T helper cell cytokines and T regulatory cells in response to treatment of active Mycobacterium tuberculosis infection

Biomarkers that can identify tuberculosis (TB) disease and serve as markers for efficient therapy are requested. We have studied T cell cytokine production [interferon (IFN)-γ, interleukin (IL)-2, tumour necrosis factor (TNF)-α] and degranulation (CD107a) as well as subsets of CD4(+) T regulatory cells (Tregs ) after in-vitro Mycobacterium tuberculosis (Mtb) antigen stimulation [early secretory antigenic target (ESAT)-6, culture filtrate protein (CFP)-10, antigen 85 (Ag85)] in 32 patients with active tuberculosis (TB) disease throughout 24 weeks of effective TB treatment. A significant decline in the fraction of Mtb-specific total IFN-γ and single IFN-γ-producing T cells was already observed after 2 weeks of treatment, whereas the pool of single IL-2(+) cells increased over time for both CD4(+) and CD8(+) T cells. The Treg subsets CD25(high) CD127(low) , CD25(high) CD147(++) and CD25(high) CD127(low) CD161(+) expanded significantly after Mtb antigen stimulation in vitro at all time-points, whereas the CD25(high) CD127(low) CD39(+) Tregs remained unchanged. The fraction of CD25(high) CD127(low) Tregs increased after 8 weeks of treatment. Thus, we revealed an opposing shift of Tregs and intracellular cytokine production during treatment. This may indicate that functional signatures of the CD4(+) and CD8(+) T cells can serve as immunological correlates of early curative host responses. Whether such signatures can be used as biomarkers in monitoring and follow-up of TB treatment needs to be explored further.

Evaluation of CD4+ CD25+ FoxP3+ Regulatory T cells and FoxP3 and CTLA-4 gene Expression in Patients wwith Newly Diagnosed Tuberculosis in Northeast of Iran

Background:

Tuberculosis (TB) is the world's second most common infectious disease after Human Immunodeficiency Virus Infection/Acquired Immunodeficiency Syndrome (HIV/AID) and the most frequent cause of mortality especially in developing countries. T regulatory (Treg) cells, which have suppressive activity and express forkhead winged-helix family transcriptional repressor p3 (FoxP3), suppress the immune responses against pathogens such as Mycobacterium tuberculosis. There are controversial results regarding the role of FoxP3 expressing cells in the blood of patients with TB.

Objectives:

The aim of this study was to evaluate the frequency CD4+ CD25+ Treg cells, and FoxP3 and Cytotoxic T Lymphocyte Antigen 4 (CTLA-4) gene expressions in peripheral blood of patients with tuberculosis and patients with positive tuberculin skin test before and after Peripheral Blood Mononuclear Cells (PBMCs) activation with Purified Protein Derivative (PPD).

Patients and Methods:

In this cross-sectional study, Peripheral Mononuclear Cells (PBMCs) were isolated from peripheral blood of 29 patients with newly diagnosed pulmonary TB and 19 patients with positive tuberculin skin test. The PBMCs were activated with PPD for 72 hours. Activated cells were harvested, RNA was extracted and cDNA was synthesized. A real-time Taqman method was designed and optimized for evaluation of Foxp3 gene expression and SYBR Green method was used and optimized for evaluation of CTLA-4 gene expression. A flow cytometry analysis was used to evaluate the frequency of CD4+ CD25+ Foxp3+ regulatory T cells in both groups.

Results:

There was no significant difference in the frequency of CD4+ CD25+ FoxP3+ regulatory T cells between the two groups. Expression of FoxP3 and CTLA-4 in peripheral blood of patients with newly diagnosed TB was significantly lower than the control group after and before activation with PPD.

Conclusions:

The expression of FoxP3 and CTLA-4 in PBMCs of patients with newly diagnosed TB was low, which might suggest that Treg cells may be sequestered in the lungs.

Latent tuberculosis infection: myths, models, and molecular mechanisms

The aim of this review is to present the current state of knowledge on human latent tuberculosis infection (LTBI) based on clinical studies and observations, as well as experimental in vitro and animal models. Several key terms are defined, including "latency," "persistence," "dormancy," and "antibiotic tolerance." Dogmas prevalent in the field are critically examined based on available clinical and experimental data, including the long-held beliefs that infection is either latent or active, that LTBI represents a small population of nonreplicating, "dormant" bacilli, and that caseous granulomas are the haven for LTBI. The role of host factors, such as CD4(+) and CD8(+) T cells, T regulatory cells, tumor necrosis factor alpha (TNF-α), and gamma interferon (IFN-γ), in controlling TB infection is discussed. We also highlight microbial regulatory and metabolic pathways implicated in bacillary growth restriction and antibiotic tolerance under various physiologically relevant conditions. Finally, we pose several clinically important questions, which remain unanswered and will serve to stimulate future research on LTBI.

Identification of novel Mycobacterium tuberculosis CD4 T-cell antigens via high throughput proteome screening

Elicitation of CD4 IFN-gamma T cell responses to Mycobacterium tuberculosis (MTB) is a rational vaccine strategy to prevent clinical tuberculosis. Diagnosis of MTB infection is based on T-cell immune memory to MTB antigens. The MTB proteome contains over four thousand open reading frames (ORFs). We conducted a pilot antigen identification study using 164 MTB proteins and MTB-specific T-cells expanded in vitro from 12 persons with latent MTB infection. Enrichment of MTB-reactive T-cells from PBMC used cell sorting or an alternate system compatible with limited resources. MTB proteins were used as single antigens or combinatorial matrices in proliferation and cytokine secretion readouts. Overall, our study found that 44 MTB proteins were antigenic, including 27 not previously characterized as CD4 T-cell antigens. Antigen truncation, peptide, NTM homology, and HLA class II tetramer studies confirmed malate synthase G (encoded by gene Rv1837) as a CD4 T-cell antigen. This simple, scalable system has potential utility for the identification of candidate MTB vaccine and biomarker antigens.

Role of cytokines and other factors involved in the Mycobacterium tuberculosis infection

Mycobacterium tuberculosis (Mtb) is a pathogen that is widely distributed geographically and continues to be a major threat to world health. Bacterial virulence factors, nutritional state, host genetic condition and immune response play an important role in the evolution of the infection. The genetically diverse Mtb strains from different lineages have been shown to induce variable immune system response. The modern and ancient lineages strains induce different cytokines patterns. The immunity to Mtb depends on Th1-cell activity [interferon-γ (IFN-γ), interleukin-12 (IL-12) and tumor necrosis factor-α (TNF-α)]. IL-1β directly kills Mtb in murine and human macrophages. IL-6 is a requirement in host resistance to Mtb infection. IFN-γ, TNF-α, IL-12 and IL-17 are participants in Mycobacterium-induced granuloma formation. Other regulating proteins as IL-27 and IL-10 can prevent extensive immunopathology. CXCL 8 enhances the capacity of the neutrophil to kill Mtb. CXCL13 and CCL19 have been identified as participants in the formation of granuloma and control the Mtb infection. Treg cells are increased in patients with active tuberculosis (TB) but decrease with anti-TB treatment. The increment of these cells causes down- regulation of adaptive immune response facilitating the persistence of the bacterial infection. Predominance of Th2 phenotype cytokines increases the severity of TB. The evolution of the Mtb infection will depend of the cytokines network and of the influence of other factors aforementioned.

Understanding and overcoming the barriers to T cell-mediated immunity against tuberculosis

Despite the overwhelming success of immunization in reducing, and even eliminating, the global threats posed by a wide spectrum of infectious diseases, attempts to do the same for tuberculosis (TB) have failed to date. While most effective vaccines act by eliciting neutralizing antibodies, T cells are the primary mediators of adaptive immunity against TB. Unfortunately, the onset of the T cell response after aerosol infection with Mycobacterium tuberculosis (Mtb), the bacterium that causes TB, is exceedingly slow, and systemically administered vaccines only modestly accelerate the recruitment of effector T cells to the lungs. This delay seems to be orchestrated by Mtb itself to prolong the period of unrestricted bacterial replication in the lung that characterizes the innate phase of the response. When T cells finally arrive at the site of infection, multiple layers of regulation have been established that limit the ability of T cells to control or eradicate Mtb. From this understanding, emerges a strategy for achieving immunity. Lung resident memory T cells may recognize Mtb-infected cells shortly after infection and confer protection before regulatory networks are allowed to develop. Early studies using vaccines that elicit lung resident T cells by targeting the lung mucosa have been promising, but many questions remain. Due to the fundamental nature of these questions, and the need to understand and manipulate the early events in the lung after aerosol infection, only coordinated approaches that utilize tractable animal models to inform human TB vaccine trials will move the field toward its goal.

T-regulatory cells and programmed death 1+ T cells contribute to effector T-cell dysfunction in patients with chronic obstructive pulmonary disease

RATIONALE

Previous studies from our laboratory have shown that peripheral blood mononuclear cells (PBMCs) from patients with chronic obstructive pulmonary disease (COPD) prone to exacerbations with nontypeable Haemophilus influenzae have impaired responses to lipoprotein P6. We hypothesized that an underlying immunosuppressive network could be responsible for the defective antibacterial immunity observed in these patients. We evaluated T regulatory cells (Tregs), myeloid-derived suppressor cells (MDSC), and exhausted T effector cells (programmed death 1 [PD-1](+)) in patients with COPD, because these cells are known to play a pivotal role in suppressing immune responses.

OBJECTIVES

We performed an in-depth characterization of Tregs, T effector cells, and MDSC in COPD and correlated their levels and function with disease severity.

METHODS

Treg, effector T cell, and MDSC frequency from patients with COPD and healthy subjects' PBMCs were analyzed by flow cytometry. Treg immunosuppressive capacity was measured by in vitro suppression assay. The frequency of interferon-γ producing T cells and T-cell proliferation were measured after blocking CTLA-4 and PD-1. Plasma proinflammatory and immunosuppressive cytokine levels were measured.

MEASUREMENTS AND MAIN RESULTS

Significantly increased levels of Tregs, MDSC, and PD-1(+) exhausted effector T cells were present in patients with COPD compared with healthy subjects. Tregs from patients with COPD suppressed P6-specific T-cell proliferation to a greater extent than Tregs from healthy subjects. Plasma levels of Treg-generated cytokines, IL-10, and transforming growth factor-β were elevated. Blockade of CTLA-4 resulted in significant augmentation of T-cell IFN-γ production in patients with COPD.

CONCLUSIONS

Functionally suppressive Tregs, MDSCs, and exhausted PD-1(+) T cells contribute to effector T-cell dysfunction in COPD.

Tuberculosis vaccines--rethinking the current paradigm

The vaccine discovery paradigm in tuberculosis (TB) has been to mimic the natural immune response to infection. With an emphasis on interferon (IFN)-γ as the main protective cytokine, researchers have selected dominant antigens and administered them in delivery systems to promote strong T helper (Th)1 responses. However, the Bacillus Calmette-Guérin (BCG) vaccine is a strong inducer of Th1 cells, yet has limited protection in adults, and further boosting by the Modified-Vaccinia-Ankara (MVA)85A vaccine failed to enhance efficacy in a clinical trial. We review the current understanding of host-pathogen interactions in TB infection and propose that rather than boosting Th1 responses, we should focus on understanding protective immune responses that are lacking or insufficiently promoted by BCG that can intervene at critical stages of the TB life cycle.

Regulatory T cells modulate granulomatous inflammation in an HLA-DP2 transgenic murine model of beryllium-induced disease

Susceptibility to chronic beryllium disease (CBD) is linked to certain HLA-DP molecules, including HLA-DP2. To elucidate the molecular basis of this association, we exposed mice transgenic (Tg) for HLA-DP2 to beryllium oxide (BeO) via oropharyngeal aspiration. As opposed to WT mice, BeO-exposed HLA-DP2 Tg mice developed mononuclear infiltrates in a peribronchovascular distribution that were composed of CD4(+) T cells and included regulatory T (Treg) cells. Beryllium-responsive, HLA-DP2-restricted CD4(+) T cells expressing IFN-γ and IL-2 were present in BeO-exposed HLA-DP2 Tg mice and not in WT mice. Using Be-loaded HLA-DP2-peptide tetramers, we identified Be-specific CD4(+) T cells in the mouse lung that recognize identical ligands as CD4(+) T cells derived from the human lung. Importantly, a subset of HLA-DP2 tetramer-binding CD4(+) T cells expressed forkhead box P3, consistent with the expansion of antigen-specific Treg cells. Depletion of Treg cells in BeO-exposed HLA-DP2 Tg mice exacerbated lung inflammation and enhanced granuloma formation. These findings document, for the first time to our knowledge, the development of a Be-specific adaptive immune response in mice expressing HLA-DP2 and the ability of Treg cells to modulate the beryllium-induced granulomatous immune response.

Host-directed therapeutics for tuberculosis: can we harness the host?

Treatment of tuberculosis (TB) remains challenging, with lengthy treatment durations and complex drug regimens that are toxic and difficult to administer. Similar to the vast majority of antibiotics, drugs for Mycobacterium tuberculosis are directed against microbial targets. Although more effective drugs that target the bacterium may lead to faster cure of patients, it is possible that a biological limit will be reached that can be overcome only by adopting a fundamentally new treatment approach. TB regimens might be improved by including agents that target host pathways. Recent work on host-pathogen interactions, host immunity, and host-directed interventions suggests that supplementing anti-TB therapy with host modulators may lead to shorter treatment times, a reduction in lung damage caused by the disease, and a lower risk of relapse or reinfection. We undertook this review to identify molecular pathways of the host that may be amenable to modulation by small molecules for the treatment of TB. Although several approaches to augmenting standard TB treatment have been proposed, only a few have been explored in detail or advanced to preclinical and clinical studies. Our review focuses on molecular targets and inhibitory small molecules that function within the macrophage or other myeloid cells, on host inflammatory pathways, or at the level of TB-induced lung pathology.

Analysis of Th1, Th17 and regulatory T cells in tuberculosis case contacts

We have hypothesized that individuals infected with Mycobacteriumtuberculosis that exhibit different patterns of immune reactivity in serial interferon (IFN)-γ release assays (IGRA's) correspond to different status within the immune spectrum of latent tuberculosis (TB). Accordingly, we analyzed the possible association between the consistent results (negative or positive) in an IGRA test and relevant immune parameters, mainly the levels of Th1 and Th17 lymphocytes and T regulatory (Treg) cells in the peripheral blood of TB case contacts. We found that individuals with a persistently positive IGRA showed increased levels of Th1 and Th17 lymphocytes upon in vitro stimulation with MTB antigens. In addition, a significant increase in the proportion of CD4+CTLA-4+ and CD4+Foxp3+ cells was detected in assays with blood samples from these individuals. Our data support that different immune phenotypes can be identified into the spectrum of latent TB, by combining different parameters of immune reactivity against MTB.