Mycobacterium bovis bacillus Calmette-Guérin killed by extended freeze-drying targets plasmacytoid dendritic cells to regulate lung inflammation

Development of mode of action networks related to the potential role of PPARγ in respiratory diseases

The peroxisome proliferator-activated receptor γ (PPARγ) is a key transcription factor, operating at the intercept of metabolic control and immunomodulation. It is ubiquitously expressed in multiple tissues and organs, including lungs. There is a growing body of information supporting the role of PPARγ signalling in respiratory diseases. The aim of the present study was to develop mode of action (MoA) networks reflecting the relationships between PPARγ signalling and the progression/alleviation of a spectrum of lung pathologies. Data mining was performed using the resources of the NIH PubMed and PubChem information systems. By linking available data on pathological/therapeutic effects of PPARγ modulation, knowledge-based MoA networking at different levels of biological organization (molecular, cellular, tissue, organ, and system) was performed. Multiple MoA networks were developed to relate PPARγ modulation to the progress or the alleviation of pulmonary disorders, triggered by diverse pathogenic, genetic, chemical, or mechanical factors. Pharmacological targeting of PPARγ signalling was discussed with regard to ligand- and cell type-specific effects in the context of distinct disease inductor- and disease stage-dependent patterns. The proposed MoA networking analysis allows for a better understanding of the potential role of PPARγ modulation in lung pathologies. It presents a mechanistically justified basis for further computational, experimental, and clinical monitoring studies on the dynamic control of PPARγ signalling in respiratory diseases.

The function of peroxisome proliferator-activated receptors PPAR-γ and PPAR-δ in Mycobacterium leprae-induced foam cell formation in host macrophages

Leprosy is a chronic infectious disease caused by Mycobacterium leprae (M. leprae). In lepromatous leprosy (LL), skin macrophages, harboring extensive bacterial multiplication, gain a distinctive foamy appearance due to increased intracellular lipid load. To determine the mechanism by which M. leprae modifies the lipid homeostasis in host cells, an in vitro M. leprae infection system, using human macrophage precursor THP-1 cells and M. leprae prepared from the footpads of nude mice, was employed. RNA extracted from skin smear samples of patients was used to investigate host gene expressions before and after multidrug therapy (MDT). We found that a cluster of peroxisome proliferator-activated receptor (PPAR) target genes associated with adipocyte differentiation were strongly induced in M. leprae-infected THP-1 cells, with increased intracellular lipid accumulation. PPAR-δ and PPAR-γ expressions were induced by M. leprae infection in a bacterial load-dependent manner, and their proteins underwent nuclear translocalization after infection, indicating activation of PPAR signaling in host cells. Either PPAR-δ or PPAR-γ antagonist abolished the effect of M. leprae to modify host gene expressions and inhibited intracellular lipid accumulation in host cells. M. leprae-specific gene expressions were detected in the skin smear samples both before and after MDT, whereas PPAR target gene expressions were dramatically diminished after MDT. These results suggest that M. leprae infection activates host PPAR signaling to induce an array of adipocyte differentiation-associated genes, leading to accumulation of intracellular lipids to accommodate M. leprae parasitization. Certain PPAR target genes in skin lesions may serve as biomarkers for monitoring treatment efficacy.

Leprosy is a chronic infectious disease caused by Mycobacterium leprae (M. leprae). Lipid-enriched intracellular environment is important for the parasitization of M. leprae. During anti-leprosy treatment, chemotherapy-killed bacilli can remain in host tissues for a long time, making it difficult to determine the treatment efficacy by Zeihl-Nelson’s staining-based bacterial index (BI) test. In this study, we found that host peroxisome proliferator-activated receptor (PPAR) signaling is responsible for modification of intracellular lipid homeostasis to accommodate M. leprae parasitization in host macrophages. In skin smear samples of patients, M. leprae-derived gene expressions were detected both before and after anti-leprosy treatment, whereas human PPAR target gene expressions were dramatically diminished after the treatment. These results further our understanding of M. leprae intracellular parasitization, and suggest that PPAR signaling may be a novel therapeutic target for treating M. leprae infection and monitoring the expressions of certain PPAR target genes in skin lesions may be helpful to evaluate the treatment efficacy and recurrent infection.

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.

Extended Freeze-Dried BCG Instructed pDCs Induce Suppressive Tregs and Dampen EAE

Several clinical observations have shown that Bacillus Calmette-Guérin (BCG) vaccine has beneficial impact on patients suffering from different chronic inflammatory diseases. Here we evaluated whether BCG inactivated by Extended Freeze-Drying (EFD) which circumvents all the side effects linked to the live bacteria, could influence the development of experimental autoimmune encephalomyelitis (EAE), a mouse model for Multiple Sclerosis. EFD BCG strongly attenuates inflammation, both systemically and at the central nervous system (CNS) level, alleviating EAE. Mechanistically, EFD BCG directly impacts the phenotype of plasmacytoid dendritic cells (pDCs), and promotes their ability to induce suppressive IL-10 secreting regulatory T cells (Tregs) that inhibit encephalitogenic CD4⁺ T cells. When co-cultured with human allogenic naive CD4⁺ T cells, EFD BCG exposed human pDCs similarly induce the differentiation of IL-10 producing Tregs. Our study provides evidence that EFD BCG could be used as an immunomodulator of encephalitogenic T cells in multiple sclerosis patients.

Immunization with Bacillus Calmette-Guérin (BCG) alleviates neuroinflammation and cognitive deficits in APP/PS1 mice via the recruitment of inflammation-resolving monocytes to the brain

The immune system plays a crucial role in the progression of Alzheimer's disease (AD). Recently, immune-dependent cascade induced by systemic immune activation has been verified to play a beneficial role in AD mouse models. Here, we tested whether Bacillus Calmette-Guérin (BCG) immunization alters AD pathology and cognitive dysfunction in APP/PS1 AD mouse model, and with 4Aβ1-15 vaccination as positive control. It was found that BCG treatment reversed the cognitive decline to the extent observed in 4Aβ1-15 group, but did not reduce the β-amyloid (Aβ) burden in the brain. Then, we demonstrated the enhanced recruitment of inflammation-resolving monocytes across the choroid plexus and perivascular spaces to cerebral sites of plaque pathology in APP/PS1 mice immunized with BCG. Furthermore, elevated splenocyte Foxp3⁺ regulatory T cell levels in the control APP/PS1 mice were down-regulated back to the wild-type (WT) levels by BCG treatment but not 4Aβ1-15 vaccination. In addition, BCG treatment induced the production of more circulating interferon (IFN)-γ than the controls and 4Aβ1-15 vaccination. Though the similar reductions in brain levels of pro-inflammatory cytokines were observed in the BCG and 4Aβ1-15 groups compared to the controls, only BCG had the great effect in upregulating cerebral anti-inflammatory cytokine levels as well as elevating the expression of neurotrophic factors in the brain of APP/PS1 mice. Thus, it is suggested that BCG exerts a beneficial immunomodulatory effect in APP/PS1 mice through mitigation of systemic immune suppression, induction of IFN-γ response and alleviation of the neuroinflammatory response.

Age-related Defects in Ocular and Nasal Mucosal Immune System and the Immunopathology of Dry Eye Disease

Dry eye disease (DED) is a prevalent public health concern that affects up to 30% of adults and is particularly chronic and severe in the elderly. Two interconnected mechanisms cause DED: (1) an age-related dysfunction of lacrimal and meibomian glands, which leads to decreased tear production and/or an increase in tear evaporation; and (2) an age-related uncontrolled inflammation of the surface of the eye triggered by yet-to-be-determined internal immunopathological mechanisms, independent of tear deficiency and evaporation. In this review we summarize current knowledge on animal models that mimic both the severity and chronicity of inflammatory DED and that have been reliably used to provide insights into the immunopathological mechanisms of DED, and we provide an overview of the opportunities and limitations of the rabbit model in investigating the role of both ocular and nasal mucosal immune systems in the immunopathology of inflammatory DED and in testing novel immunotherapies aimed at delaying or reversing the uncontrolled age-related inflammatory DED.

Mycobacterium tuberculosis RpfE promotes simultaneous Th1- and Th17-type T-cell immunity via TLR4-dependent maturation of dendritic cells

Reciprocal induction of the Th1 and Th17 immune responses is essential for optimal protection against Mycobacterium tuberculosis (Mtb); however, only a few Mtb antigens are known to fulfill this task. A functional role for resuscitation-promoting factor (Rpf) E, a latency-associated member of the Rpf family, in promoting naïve CD4(+) T-cell differentiation toward both Th1 and Th17 cell fates through interaction with dendritic cells (DCs) was identified in this study. RpfE induces DC maturation by increasing expression of surface molecules and the production of IL-6, IL-1β, IL-23p19, IL-12p70, and TNF-α but not IL-10. This induction is mediated through TLR4 binding and subsequent activation of ERK, p38 MAPKs, and NF-κB signaling. RpfE-treated DCs effectively caused naïve CD4(+) T cells to secrete IFN-γ, IL-2, and IL-17A, which resulted in reciprocal expansions of the Th1 and Th17 cell response along with activation of T-bet and RORγt but not GATA-3. Furthermore, lung and spleen cells from Mtb-infected WT mice but not from TLR4(-/-) mice exhibited Th1 and Th17 polarization upon RpfE stimulation. Taken together, our data suggest that RpfE has the potential to be an effective Mtb vaccine because of its ability to activate DCs that simultaneously induce both Th1- and Th17-polarized T-cell expansion.

The interplay between bacillus Calmette-Guérin and Treg cells and its role to prevent or cure inflammatory diseases

Clinical evidence indicates that Bacillus Calmette-Guérin (BCG) vaccination exerts anti-inflammatory effects in diseases such as asthma, multiple sclerosis or Type 1 diabetes. Although the exact mechanisms for this activity remain debated, the capacity of mycobacteria to induce regulatory T cells (Tregs) in vivo has been widely reported. However, adverse events associated with live BCG prevent its repeated use, especially in immunocompromised individuals. This article reviews the preclinical data showing a potent, systemic and long-term anti-inflammatory effect in animal models of allergic asthma, inflammatory bowel disease and atherosclerosis with a preparation of BCG inactivated by Extended Freeze-Drying (EFD BCG). It also presents the characteristics of EFD BCG-induced Tregs which play a crucial role in the immunomodulation of various inflammatory diseases. Finally, it compares EFD BCG with other approaches based on the therapeutic use of Tregs in humans.

Der p2 recombinant bacille Calmette-Guerin priming of bone marrow-derived dendritic cells suppresses Der p2-induced T helper17 function in a mouse model of asthma

BACKGROUND AND OBJECTIVE

Previous studies have demonstrated that our recombinant bacille Calmette-Guerin (rBCG), which expresses Der p2 in house dust mite (Der p2 rBCG) suppresses asthmatic airway inflammation by regulating the phenotype and function of dendritic cells (DC) and reprogramming T helper (Th) 0 cell differentiation into different T cell (Th1/Th2/Treg) subtypes. However, the exact role of Der p2 rBCG in reprogramming Th17 differentiation and the relevant mechanisms are not known. The aim of this study was to examine whether Der p2 rBCG-mediated inhibition of allergic airway inflammation is mediated by regulating Th17 differentiation in a murine asthma model.

METHODS

Primary mouse bone marrow-derived dendritic cells (BMDC) were infected with Der p2 rBCG and adoptively transferred to Der p2-intranasally sensitized mice. The role of Der p2 rBCG-BMDC on the regulation of airway inflammation and Th17 cell differentiation was assessed.

RESULTS

Adoptive transfer of Der p2 rBCG-BMDC suppressed airway inflammation and mucin secretion. Der p2 rBCG-BMDC inhibited excessive Th17 immune responses but not BCG-BMDC. Furthermore, Der p2 rBCG decreased jagged-2 and increased delta-like-4 expressions on BMDC to a greater extent than BCG.

CONCLUSIONS

These findings suggest that DC plays a key role in Der p2 rBCG-induced immunoregulation. Der p2 rBCG also displayed a potent inhibitory effect on Th17 differentiation, and these findings increase our understanding of the cellular basis of Der p2 BCG-mediated inhibition of asthma.

Microorganism-induced suppression of allergic airway disease: novel therapies on the horizon?

Allergic airway disease is a major global health burden, and novel treatment options are urgently needed. Numerous epidemiological and experimental studies suggest that certain helminths and bacteria protect against respiratory allergies. These microorganisms are strong regulators of the immune system, and various potential regulatory mechanisms by which they protect against allergic airway inflammation have been proposed. Whereas early studies addressed the beneficial effect of natural infections, the focus now shifts toward identifying the dominant protective molecules and exploring their efficacy in models of allergic airway disease. In this article, we will review the evidence for microbe-mediated protection from allergic airway disease, the potential modes of action involved and discuss advances as well as limitations in the translation of this knowledge into novel treatment strategies against allergic airway disease.

Airborne pollutant ROFA enhances the allergic airway inflammation through direct modulation of dendritic cells in an uptake-dependent mechanism

Studies suggest that airborne pollutants are important cofactors in the exacerbation of lung diseases. The role of DC on the exacerbation of lung inflammation induced by particulate matter pollutants is unclear. We evaluated the effects of residual oil fly ash (ROFA) on the phenotype and function of bone marrow-derived dendritic cells (BMDCs) in vitro and lung dendritic cells (DCs) in vivo, and the subsequent T-cell response. In a model of asthma, exposure to ROFA exacerbated pulmonary inflammation, which was attributed to the increase of eosinophils, IL-5- and IFN-γ-producing T cells, and goblet cells as well as decreased number of Treg and pDC. However, the ROFA showed no ability to modulate the production of anaphylactic IgE. In vitro studies showed that ROFA directly induced the maturation of DCs up-regulating the expression of co-stimulatory molecules and cytokines and MMP production in an uptake-dependent and oxidative stress-dependent manner. Furthermore, ROFA-pulsed BMDC transferred to allergic mice exacerbated eosinophilic inflammation as well as promoted increased epithelial and goblet cells changes. Thus, pollutants may constitute an important and risk factor in the exacerbation of asthma with inhibition of the negative regulatory signals in the lung, with enhanced mDC activation that sustains the recruitment of effector T lymphocytes and eosinophil.

Anti-HMGB1 neutralizing antibody ameliorates neutrophilic airway inflammation by suppressing dendritic cell-mediated Th17 polarization

We demonstrate that high mobility group box 1 protein (HMGB1) directs Th17 skewing by regulating dendritic cell (DC) function. First, our in vitro studies reveal that recombinant HMGB1 (rHMGB1) activates myeloid DCs to produce IL-23 in vitro, and rHMGB1-activated DCs prime naïve lymphocytes to produce the Th17 cytokine IL-17A. Second, we demonstrate that anti-HMGB1 neutralizing antibody attenuates HMGB1 expression, neutrophilic inflammation, airway hyperresponsiveness, and Th17-related cytokine secretion in vivo by using a murine model of neutrophilic asthma induced by ovalbumin (OVA) plus lipopolysaccharide (LPS). Furthermore, anti-HMGB1 neutralizing antibody decreases the number of Th17 cells in lung cells and suppresses the production of IL-23 by lung CD11C⁺ APCs. Finally, we show that intranasal adoptive transfer of rHMGB1-activated DCs was sufficient to restore lung neutrophilic inflammation and the Th17 response in a DC-driven model of asthma, whereas the transfer of rHMGB1 plus anti-HMGB1-treated mDCs significantly reduced these inflammation phenotypes. These data suggest, for the first time, that HMGB1 drives the DC-polarized Th17-type response in allergic lung inflammation and that blocking HMGB1 may benefit the attenuation of neutrophilic airway inflammation in asthma.

Inhibition of IFN-γ promotes anti-asthma effect of Mycobacterium bovis Bacillus Calmette-Guerin neonatal vaccination: a murine asthma model

OBJECTIVE

The Mycobacterium bovis Bacillus Calmette-Guerin (BCG) neonatal vaccination inhibits allergy-induced pathologic changes. However, the mechanisms underlying this process are unclear. This study aimed to investigate the role of interferon (IFN)-γ and interleukin (IL)-17 in the protective effects of the BCG neonatal vaccination on allergic pulmonary inflammation and airway hyperresponsiveness (AHR).

METHODS

Wild type (WT)-neonate and IL-17 knock out (KO) neonate mice were vaccinated with BCG. A murine asthma model was developed by sensitization and then challenging with ovalbumin (OVA). Recombinant IL-17 or recombinant IFN-γ was delivered to the airway to overexpress IL-17 or IFN-γ. An anti-IFN-γ neutralizing antibody was used to block the effects of IFN-γ.

RESULTS

We found exogenous IL-17 delivered to the airway reversed the anti-asthma effects of the neonatal BCG vaccination. BCG neonatal vaccination further reduced OVA-induced inflammation and AHR in IL-17 KO mice. Inhibition of IFN-γ in BCG neonatal vaccinated OVA-induced asthma model mice led to a further reduction in airway inflammation and AHR. In addition, airway inflammation and AHR were robust following treatment with exogenous IFN-γ. Neutralizing IL-17 was not sufficient to block OVA-induced airway inflammation and AHR. In IL-17 KO mice, airway inflammation and AHR did not occur following treatment with an anti-IFN-γ neutralizing antibody.

CONCLUSIONS

In an OVA-induced murine asthma model, inhibition of IFN-γ enhanced the anti-asthma effects of BCG neonatal vaccination.

Mycobacterium bovis BCG killed by extended freeze-drying induces an immunoregulatory profile and protects against atherosclerosis

OBJECTIVES

Atherosclerosis is an inflammatory disease of the arterial wall that leads to myocardial infarction and stroke. Regulatory T cells (Tregs) and IL-10 exert significant anti-atherogenic effects in experimental models of atherosclerosis by modulating vascular inflammation. We have previously shown that Mycobacterium bovis BCG killed by extended freeze-drying (EFD BCG) decreases lung and colon inflammation by recruiting IL-10-producing Tregs. Therefore, the aim of this study was to investigate the effect of EFD BCG on the development of atherosclerosis.

DESIGN

We used two strains of atherosclerosis-prone mice: Ldlr(-/-) (four or six EFD BCG injections) and Apoe(-/-) (six injections).

RESULTS

In both models, EFD BCG significantly reduced the size of atherosclerotic lesions, increased IL-10 production and reduced the serum levels of pro-inflammatory cytokines (IL-6, IL-13, KC and tumour necrosis factor-α). Shortly after treatment with EFD BCG, the number of plasmacytoid dendritic cells (pDCs) and Foxp3(+) Tregs in the draining lymph nodes increased. EFD BCG also led to accumulation of Tregs, but not of pDCs in the spleen, and reduced activity of NF-κB and increased activity of PPAR-γ in both the spleen and vascular tissue of treated mice.

CONCLUSION

EFD BCG has atheroprotective effects through IL-10 production and Treg expansion. These findings support a novel approach to the prevention and treatment of atherosclerosis.

Salmonella enterica serovar Typhimurium infection-induced CD11b+ Gr1+ cells ameliorate allergic airway inflammation

Allergies are mainly characterized as an unrestrained Th2-biased immune response. Epidemiological data associate protection from allergic diseases with the exposure to certain infectious agents during early stages of life. Modulation of the immune response by pathogens has been considered to be a major factor influencing this protection. Recent evidence indicates that immunoregulatory mechanisms induced upon infection ameliorate allergic disorders. A longitudinal study has demonstrated reduced frequency and incidence of asthma in children who reported a prior infection with Salmonella. Experimental studies involving Salmonella enterica serovar Typhimurium-infected murine models have confirmed protection from induced allergic airway inflammation; however, the underlying cause leading to this amelioration remains incompletely defined. In this study, we aimed to delineate the regulatory function of Salmonella Typhimurium infection in the amelioration of allergic airway inflammation in mice. We observed a significant increase in CD11b+ Gr1+ myeloid cell populations in mice after infection with S. Typhimurium. Using in vitro and in vivo studies, we confirmed that these myeloid cells reduce airway inflammation by influencing Th2 cells. Further characterization showed that the CD11b+ Gr1+ myeloid cells exhibited their inhibitory effect by altering GATA-3 expression and interleukin-4 (IL-4) production by Th2 cells. These results indicate that the expansion of myeloid cells upon S. Typhimurium infection could potentially play a significant role in curtailing allergic airway inflammation. These findings signify the contribution of myeloid cells in preventing Th2-mediated diseases and suggest their possible application as therapeutics.

Asthma: the importance of dysregulated barrier immunity

Chronic asthma is an inflammatory disease of the airway wall that leads to bronchial smooth muscle hyperreactivity and airway obstruction, caused by inflammation, goblet cell metaplasia, and airway wall remodeling. In response to allergen presentation by airway DCs, T-helper lymphocytes of the adaptive immune system control many aspects of the disease through secretion of IL-4, IL-5, IL-13, IL-17, and IL-22, and these are counterbalanced by cytokines produced by Treg cells. Many cells of the innate immune system such as mast cells, basophils, neutrophils, eosinophils, and innate lymphoid cells also play an important role in disease pathogenesis. Barrier epithelial cells are being ever more implicated in disease pathogenesis than previously thought, as these cells have in recent years been shown to sense exposure to allergens via pattern recognition receptors and to activate conventional and inflammatory-type DCs and other innate immune cells through the secretion of thymic stromal lymphopoietin, granulocyte-macrophage colony stimulating factor, IL-1, IL-33, and IL-25. Understanding this cytokine crosstalk between barrier epithelial cells, DCs, and immune cells provides important insights into the mechanisms of allergic sensitization and asthma progression as discussed in this review.

Bacillus Calmette-Guérin Suppresses Asthmatic Responses via CD4(+)CD25(+) Regulatory T Cells and Dendritic Cells

Purpose

Bacillus Calmette-Guérin (BCG) is known to suppress the asthmatic responses in a murine model of asthma and to induce dendritic cells (DCs) maturation. Mature DCs play a crucial role in the differentiation of regulatory T cells (Tregs), which are known to regulate allergic inflammatory responses. To investigate whether BCG regulates Tregs in a DCs-mediated manner, we analyzed in a murine model of asthma.

Methods

BALB/c mice were injected intraperitoneally with BCG or intravenously with BCG-stimulated DCs and then sensitized and challenged with ovalbumin (OVA). Mice were analysed for bronchial hyperresponsiveness (BHR), the influx of inflammatory cells in the bronchoalveolar lavage (BAL) fluid, and histopathological changes in the lung. To identify the mechanisms, IgE, IgG₁ and IgG_2a in the serum were analysed and the CD25₊ Tregs in the mice were depleted with anti-CD25 monoclonal antibody (mAb).

Results

BCG and the transfer of BCG-stimulated DCs both suppressed all aspects of the asthmatic responses, namely, BHR, the production of total IgE and OVA-specific IgE and IgGs, and pulmonary eosinophilic inflammation. Anti-CD25mAb treatment reversed these effects.

Conclusions

BCG can attenuate the allergic inflammation in a mouse model of asthma by a Tregs-related mechanism that is mediated by DCs.

Impact of Bacillus Calmette-Guérin Moreau vaccine on lung remodeling in experimental asthma

We analyzed the effects of different administration routes and application times of the BCG-Moreau strain on airway and lung inflammation and remodeling in a murine model of allergic asthma. BALB/c mice (n=168) were divided into two groups. The first group received BCG-Moreau strain while the second group received saline using the same protocol. BCG or saline were intradermally or intranasally injected one or two months before the induction of asthma. Mice were further sensitized and challenged with ovalbumin or received saline. Twenty-four hours after the last challenge, BCG prevented the triggering of pro-inflammatory cytokines, probably by increasing Foxp3 and interleukin (IL)-10, modulating eosinophil infiltration and collagen fiber deposition, thus reducing airway hyperresponsiveness. In conclusion, BCG-Moreau prevented lung remodeling in the present model of allergic asthma, regardless of administration route and time of vaccination. These beneficial effects may be related to the increase in regulatory T cells and to IL-10 production in tandem with decreased Th2 cytokines (IL-4, IL-5, and IL-13).

Der p 2 recombinant bacille Calmette-Guérin targets dendritic cells to inhibit allergic airway inflammation in a mouse model of asthma

BACKGROUND

Previous studies showed that a recombinant bacille Calmette-Guérin (rBCG) which expressed the Der p 2 of house dust mites (Der p 2 rBCG) could suppress asthmatic airway inflammation. There are two possible mechanisms: (1) Der p 2 rBCG elicits immune deviation from Th2 to Th1, and (2) Der p 2 rBCG induces antigen-specific regulatory T cells. However, the role of dendritic cell (DC) Der p 2 rBCG in this protective effect and in reprogramming T-cell commitment still needs to be studied.

OBJECTIVES

The aim of this study was to determine whether DCs play a central role in the Der p 2 rBCG-mediated inhibition of allergic airway inflammation.

METHODS

DCs were collected from Der p 2 rBCG-immunized mice (Der p 2 rBCG-DCs) and adoptively transferred to Der p 2-sensitized mice. The effects of DCs on airway inflammation and immune regulation were analyzed.

RESULTS

Adoptive transfer of DCs from Der p 2 rBCG-immunized mice suppressed asthmatic responses, including airway inflammation, mucin secretion and airway responsiveness. Der p 2 rBCG-DCs could effectively inhibit excessive Th2 immune responses and induced a subtype of CD4+CD25+Foxp3+ anti-specific regulatory T cells in this asthma model. Furthermore, Der p 2 rBCG immunization recruited more plasmacytoid DCs in abdominal draining lymph nodes.

CONCLUSIONS

These findings suggest that DCs played a key role in Der p 2 rBCG-induced immunoregulation. Compared with BCG, Der p 2 rBCG displayed a more potent inhibitory effect on asthma responses, which may be related to the increase in plasmacytoid DC recruitment. These results improve our understanding of the cellular basis of Der p 2 BCG-mediated inhibition of asthma.

PPARγ Expression and Function in Mycobacterial Infection: Roles in Lipid Metabolism, Immunity, and Bacterial Killing

Tuberculosis continues to be a global health threat, with drug resistance and HIV coinfection presenting challenges for its control. Mycobacterium tuberculosis, the etiological agent of tuberculosis, is a highly adapted pathogen that has evolved different strategies to subvert the immune and metabolic responses of host cells. Although the significance of peroxisome proliferator-activated receptor gamma (PPARγ) activation by mycobacteria is not fully understood, recent findings are beginning to uncover a critical role for PPARγ during mycobacterial infection. Here, we will review the molecular mechanisms that regulate PPARγ expression and function during mycobacterial infection. Current evidence indicates that mycobacterial infection causes a time-dependent increase in PPARγ expression through mechanisms that involve pattern recognition receptor activation. Mycobacterial triggered increased PPARγ expression and activation lead to increased lipid droplet formation and downmodulation of macrophage response, suggesting that PPARγ expression might aid the mycobacteria in circumventing the host response acting as an escape mechanism. Indeed, inhibition of PPARγ enhances mycobacterial killing capacity of macrophages, suggesting a role of PPARγ in favoring the establishment of chronic infection. Collectively, PPARγ is emerging as a regulator of tuberculosis pathogenesis and an attractive target for the development of adjunctive tuberculosis therapies.

Early secreted antigen ESAT-6 of Mycobacterium tuberculosis promotes protective T helper 17 cell responses in a toll-like receptor-2-dependent manner

Despite its relatively poor efficacy, Bacillus Calmette-Guérin (BCG) has been used as a tuberculosis (TB) vaccine since its development in 1921. BCG induces robust T helper 1 (Th1) immune responses but, for many individuals, this is not sufficient for host resistance against Mycobacterium tuberculosis (M. tb) infection. Here we provide evidence that early secreted antigenic target protein 6 (ESAT-6), expressed by the virulent M. tb strain H37Rv but not by BCG, promotes vaccine-enhancing Th17 cell responses. These activities of ESAT-6 were dependent on TLR-2/MyD88 signalling and involved IL-6 and TGF-β production by dendritic cells. Thus, animals that were previously infected with H37Rv or recombinant BCG containing the RD1 region (BCG::RD1) exhibited improved protection upon re-challenge with virulent H37Rv compared with mice previously infected with BCG or RD1-deficient H37Rv (H37RvΔRD1). However, TLR-2 knockout (TLR-2⁻/⁻) animals neither showed Th17 responses nor exhibited improved protection in response to immunization with H37Rv. Furthermore, H37Rv and BCG::RD1 infection had little effect on the expression of the anti-inflammatory microRNA-146a (miR146a) in dendritic cells (DCs), whereas BCG and H37RvΔRD1 profoundly induced its expression in DCs. Consistent with these findings, ESAT-6 had no effect on miR146a expression in uninfected DCs, but dramatically inhibited its upregulation in BCG-infected or LPS-treated DCs. Collectively, our findings indicate that, in addition to Th1 immunity induced by BCG, RD1/ESAT-6-induced Th17 immune responses are essential for optimal vaccine efficacy.

Neonatal lung immune responses show a shift of cytokines and transcription factors toward Th2 and a deficit in conventional and plasmacytoid dendritic cells

The high incidence of lung-damaging life-threatening respiratory infections in infants may be related to the immaturity of their immune systems. To determine whether lung immune features differ in early life compared with those in adulthood, whole lung as well as lung T lymphocyte and DC responses were investigated in BALB/c neonates versus adults. Higher expression of GATA-3 and rapid and sustained production of type 2 cytokines by lung explants after in vitro exposure to anti-CD3 was the hallmark of the neonatal period, suggestive of a Th2 bias. Neonatal lung GATA-3-producing cells were identified as CD3(+), CD4 and CD8 double-negative T lymphocytes, a subset found at a higher frequency in neonatal than adult lung. The neonatal lungs contained fewer conventional DCs, with a lower ratio of CD103(+) to CD11b(+) DCs, and a much lower number of plasmacytoid DCs in comparison with adult lungs. Yet, when stimulated in vivo by BCG, neonatal lung DCs matured and primed adult naïve CD4(+) T cells toward Th1 as efficiently as adult BCG-primed lung DCs. Conversely, both adult and neonatal BCG-primed lung DCs induced a Th2 cytokine response from neonatal naïve lymph node T cells, suggestive of an intrinsic feature of neonatal T lymphocytes.

Mycobacterium bovis Bacillus Calmette-Guérin killed by extended freeze-drying reduces colitis in mice

BACKGROUND & AIMS

Mycobacterium bovis Bacillus Calmette-Guérin (BCG), killed by extended freeze-drying (EFD), induces secretion of interleukin-10 and reduces lung inflammation in a mouse model of asthma. We investigated the effects of EFD BCG in mouse models of inflammatory bowel disease.

METHODS

EFD BCG was administered subcutaneously to mice with colitis induced by dextran sodium sulfate (DSS), oxazolone, or adoptive transfer of CD4(+)CD45RB(high)Foxp3(-) T cells from C57Bl/6 Foxp3GFP mice to RAG2(-/-) mice.

RESULTS

EFD BCG, administered either before induction of DSS and oxazolone colitis or after development of acute or chronic DSS-induced colitis, reduced symptom scores, loss of body weight, and inflammation. Although transfer of CD4(+)CD45RB(high)Foxp3(-) cells induced colitis in RAG2(-/-) mice, administration of EFD BCG at the time of the transfer converted Foxp3(-) T cells to Foxp3(+) T cells and the mice did not develop colitis. EFD BCG protected mice from colitis via a mechanism that required expansion of T regulatory cells and production of interleukin-10 and transforming growth factor β. EFD BCG activated the retinoid X receptor (RXR)-α-peroxisome proliferator-activated receptor (PPAR)-γ heterodimer, blocked translocation of nuclear factor κB to the nucleus, and reduced colonic inflammation; it did not increase the number of colon tumors that formed in mice with chronic DSS-induced colitis.

CONCLUSIONS

EFD BCG controls severe colitis in mice by expanding T regulatory cell populations and PPAR-γ and might be developed to treat patients with inflammatory bowel disease.

Inhibition of allergen-induced airway remodeling by neonatal bacillus Calmette-Guerin vaccination is associated with interferon-gamma-producing T cells but not regulatory T cells in mice

BACKGROUND

Epidemiological assessments of patients and studies using animal models show that exposure to Mycobacterium bovis bacillus Calmette-Guerin (BCG) vaccine in early life prevents asthma development. However, little is known about the potential of neonatal BCG vaccination in preventing the development of airway remodeling of asthma.

OBJECTIVE

To investigate the effects of multiple BCG vaccinations of neonates on the airway remodeling in mice and the accompanied pulmonary T cell responses.

METHODS

BALB/c neonates were vaccinated with BCG 3 times. At 5 and 7 weeks of age, the mice were sensitized and then challenged with aerosolized ovalbumin (OVA) 3 times per week for 8 successive weeks. The extent of airway remodeling and induced pulmonary T cell responses were characterized.

RESULTS

Multiple BCG vaccinations of neonates reduced OVA-induced remodeling events, including levels of peribronchial α-smooth muscle actin, peribronchial fibrosis, and airway epithelial mucin accumulation. The BCG vaccinations also decreased peribronchial cells expression of transforming growth factor beta 1 (TGF-β1). In contrast, BCG vaccinations increased the frequency of interferon-gamma (IFN-γ)-producing T cells in the lung and IFN-γ level in BALF, with no effects on pulmonary regulatory T cells and IL-17-producing T cells.

CONCLUSIONS

Our data suggest that multiple BCG vaccinations of neonates reduced metrics characteristic of allergen-induced airway remodeling. More importantly, this decrease was not associated with an increased number of pulmonary regulatory T cells but instead correlated with an increase of IFN-γ-producing T cells.

Treatment with the TLR7 agonist R848 induces regulatory T-cell-mediated suppression of established asthma symptoms

The evolution of allergic asthma is tightly controlled by effector and regulatory cells, as well as cytokines such as IL-10 and/or TGF-β, and it is widely acknowledged that environmental exposure to allergens and infectious agents can influence these processes. In this context, the recognition of pathogen-associated motifs, which trigger TLR activation pathways, plays a critical role with important consequences for disease progression and outcome. We addressed the question whether the TLR7 ligand resiquimod (R848), which has been shown to be protective in several experimental allergic asthma protocols, can also suppress typical asthma symptoms once the disease is established. To this end, we used an OVA-induced experimental model of murine allergic asthma in which R848 was injected after a series of challenges with aerosolized OVA. We found that the treatment attenuated allergic symptoms through a mechanism that required Tregs, as assessed by the expansion of this population in the lungs of mice having received R848, and the loss of R848-mediated suppression of allergic responses after in vivo Treg depletion. IL-10 provided only a minor contribution to this suppressive effect that was largely mediated through a TGF-β-dependent pathway, a finding that opens new therapeutic opportunities for the pharmacological targeting of Tregs.

The TLR7 agonist R848 alleviates allergic inflammation by targeting invariant NKT cells to produce IFN-gamma

It has been documented that TLR7 stimulation triggers not only antiviral responses, but also alleviates experimental asthma. Considering the implication of invariant NKT (iNKT) cells in both situations, we postulated that they might contribute to the anti-inflammatory effect of TLR7 ligands. We show in this study that spleen cells activated by the TLR7 agonist resiquimod (R848) attenuate allergic inflammation upon adoptive transfer when they are recovered from wild-type, but not from iNKT cell-deficient Jα18(-/-) mice, which proves the specific involvement of this regulatory population. Furthermore, we provide evidence that IFN-γ is critical for the protective effect, which is lost when transferred iNKT cells are sorted from IFN-γ-deficient mice. In support of a direct activation of iNKT cells through TLR7 signaling in vivo, we observed a prompt increase of serum IFN-γ levels, associated with upregulation of CD69 expression on iNKT cells. Moreover, we demonstrate that iNKT cells effectively express TLR7 and respond to R848 in vitro by producing high levels of IFN-γ in the presence of IL-12, consistent with the conclusion that their contribution to the alleviation of allergic inflammation upon treatment with TLR7 ligands is mediated through IFN-γ.

The role of dendritic and epithelial cells as master regulators of allergic airway inflammation

Lung dendritic cells bridge innate and adaptive immunity, integrating a variety of stimuli from allergens, microbial colonisation, environmental pollution, and innate immune cells into a signal for T lymphocytes of the adaptive immune system. Dendritic cells have a pivotal role in the activation of T helper (Th) 2 cells and allergic inflammation. Lung dendritic cells can also prevent harmful immune responses to innocuous inhaled antigens via induction of regulatory T cells or Th1 cells. In our Review, we discuss how understanding the biology of dendritic cells is crucial for understanding the interaction between allergens, the environment, and genetics, and focus on how dendritic cells conspire with airway epithelial cells and innate pro-Th2 cells to cause allergic sensitisation and asthma.