Mechanisms of neutrophil accumulation in the lungs against bacteria

Induced Pluripotent Stem Cells Regulate Triggering Receptor Expressed on Myeloid Cell-1 Expression and the p38 Mitogen-Activated Protein Kinase Pathway in Endotoxin-Induced Acute Lung Injury

Induced pluripotent stem cells (iPSCs) can attenuate the pathological severity and neutrophil migration of lipopolysaccharide (LPS)-induced acute lung injury (ALI). However, interactions that may occur between iPSCs and the triggering receptor expressed on myeloid cells (TREM) family of proteins remain unclear. In this study, murine iPSCs (miPSCs) were delivered via tail vein injection to wild type, TREM-1 knockout (KO), and TREM-2 KO C57BL/6 mice 4 hours after an intratracheal delivery of LPS. Twenty-four hours later, the bronchoalveolar lavage fluid and lung tissue were collected to perform histology, immunohistochemistry, neutrophil counts, Western blot assays, and enzyme-linked immunosorbent assays. Neutrophils were also isolated from the bone marrow to perform in vitro migration assays. In the lung tissues collected, LPS increased the expression of TREM-1 and TREM-2, with the TREM-2 KO mice expressing more TREM-1 than the wild-type mice. The TREM-2 KO mice also exhibited greater severity of LPS-induced ALI, enhanced neutrophil infiltration in the lung tissues, and a higher ratio of phosphorylated p38 to total p38 (p-p38/p38) in neutrophils. The p-p38/p38 ratio and the expression of vascular cell adhesion molecule-1 and certain proinflammatory cytokines (macrophage inflammatory protein-2, tumor necrosis factor-α, interleukin-6, and interleukin-1β) were increased in whole lung extracts following LPS-induced ALI, and these levels were even more in LPS-treated TREM-2 KO mice. These effects were reduced when miPSCs were administered. Thus, the results of this study suggest that miPSCs attenuate the role of neutrophils in lung inflammation and injury induced by LPS by reducing their expression of TREM-1 and p38 mitogen-activated protein kinase signaling. Stem Cells 2019;37:631-639.

TesG is a type I secretion effector of Pseudomonas aeruginosa that suppresses the host immune response during chronic infection

Pseudomonas aeruginosa is a versatile Gram-negative pathogen with intricate intracellular regulatory networks that enable it to adapt to and flourish in a variety of biotic and abiotic habitats. However, the mechanism permitting the persistent survival of P. aeruginosa within host tissues and causing chronic symptoms still remains largely elusive. By using in situ RNA sequencing, here we show that P. aeruginosa adopts different metabolic pathways and virulence repertoires to dominate the progression of acute and chronic lung infections. Notably, a virulence factor named TesG, which is controlled by the vital quorum-sensing system and secreted by the downstream type I secretion system, can suppress the host inflammatory response and facilitate the development of chronic lung infection. Mechanically, TesG can enter the intracellular compartment of macrophages through clathrin-mediated endocytosis, competitively inhibit the activity of eukaryotic small GTPase and thus suppress subsequent neutrophil influx, cell cytoskeletal rearrangement of macrophages and the secretion of cytokines and chemokines. Therefore, the identification of TesG in this study reveals a type I secretion apparatus of P. aeruginosa that functions during the host-pathogen interaction, and may open an avenue for the further mechanistic study of chronic respiratory diseases and the development of antibacterial therapy.

Antibacterial activity of a polysaccharide produced from Chaetomium globosum CGMCC 6882

In present work, a polysaccharide (GCP) was produced by Chaetomium globosum CGMCC 6882 and characterized. GCP was composed of arabinose, galactose, glucose, xylose, mannose and glucuronic acid in a molar ratio of 0.64: 2.58: 23.53: 0.90: 2.47: 0.27 with molecular weight of 8.093 × 10⁴ Da and polydispersity (Mw/Mn) of 1.014. Antibacterial characteristics and mechanism of GCP against Escherichia coli and Staphlococcus aureus were investigated by analysis of inhibition zones, minimum inhibitory concentration (MIC), alkaline phosphatase and β-galactosidase activities, electrical conductivity and bacterial morphology. Results showed that the MIC of GCP against E. coli and S. aureus were 1.75 mg/mL and 0.67 mg/mL, respectively. Moreover, GCP exerted antibacterial activities by disrupting the inner membrane and increasing the cell permeability, but had no influences on cell wall. This work indicated that GCP could be explored as a promising antibacterial agent in food and pharmaceutical industries.

Protectin DX Exhibits Protective Effects in Mouse Model of Lipopolysaccharide-Induced Acute Lung Injury

Background:

Acute lung injury (ALI) is a severe disease with high mortality and poor prognosis. Protectin DX (PDX), a pro-resolving lipid mediator, exhibits protective effects in ALI. Our experiment aimed to explore the effects and related mechanisms of PDX in mice with ALI induced by lipopolysaccharide (LPS).

Methods:

BALB/c mice were randomly divided into five groups: sham, LPS, LPS plus 1 ng of PDX (LPS + PDX-1 ng), LPS plus 10 ng of PDX (LPS + PDX-10 ng), and LPS plus 100 ng of PDX (LPS + PDX-100 ng). Bronchoalveolar lavage fluids (BALFs) were collected after 24 h, and total cells, polymorphonuclear leukocytes, monocyte-macrophages, and lymphocytes in BALF were enumerated. The concentration of interleukin (IL)-1β, IL-6, IL-10, tumor necrosis factor-alpha (TNF-α), macrophage inflammatory protein (MIP)-1α, and MIP-2 in BALF was determined, and histopathological changes of the lung were observed. The concentration of protein in BALF and lung wet/dry weight ratios were detected to evaluate pulmonary edema. After determining the optimal dose of PDX, neutrophil–platelet interactions in whole blood were evaluated by flow cytometry.

Results:

The highest dose of PDX (100 ng/mouse) failed to provide pulmonary protective effects, whereas lower doses of PDX (1 ng/mouse and 10 ng/mouse), especially 1 ng PDX, alleviated pulmonary histopathological changes, mitigated LPS-induced ALI and pulmonary edema, inhibited neutrophil infiltration, and reduced pro-inflammatory mediator (IL-1β, IL-6, TNF-α, and MIP-1α) levels. Meanwhile, 1 ng PDX exhibited pro-resolving functions in ALI including upregulation of monocyte-macrophage numbers and anti-inflammatory mediator IL-10 levels. The flow cytometry results showed that PDX could inhibit neutrophil–platelet interactions in ALI.

Conclusion:

PDX exerts protective effects in LPS-induced ALI by mitigating pulmonary inflammation and abrogating neutrophil–platelet interactions.

Alcohol enhances type 1 interferon-α production and mortality in young mice infected with Mycobacterium tuberculosis

In the current study, we used a mouse model and human blood samples to determine the effects of chronic alcohol consumption on immune responses during Mycobacterium tuberculosis (Mtb) infection. Alcohol increased the mortality of young mice but not old mice with Mtb infection. CD11b+Ly6G+ cells are the major source of IFN-α in the lungs of Mtb-infected alcohol-fed young mice, and IFN-α enhances macrophage necroptosis in the lungs. Treatment with an anti-IFNAR-1 antibody enhanced the survival of Mtb-infected alcohol-fed young mice. In response to Mtb, peripheral blood mononuclear cells (PBMCs) from alcoholic young healthy individuals with latent tuberculosis infection (LTBI) produced significantly higher amounts of IFN-α than those from non-alcoholic young healthy LTBI+ individuals and alcoholic and non-alcoholic old healthy LTBI+ individuals. Our study demonstrates that alcohol enhances IFN-α production by CD11b+Ly6G+ cells in the lungs of young Mtb-infected mice, which leads to macrophage necroptosis and increased mortality. Our findings also suggest that young alcoholic LTBI+ individuals have a higher risk of developing active TB infection.

Chronic alcohol consumption modulates the host immune defense mechanism(s) and makes the host susceptible to various fungal, viral and bacterial infections, including Mycobacterium tuberculosis (Mtb). However, limited information is available about the mechanisms involved in alcohol-mediated host susceptibility to Mtb and other intracellular bacterial infections. In the current study, we fed control and alcohol diets to young and old mice and determined the mortality rates and the immune mechanisms involved in host susceptibility to Mtb infection. We found that alcohol increases the mortality of young mice but not old mice infected with Mtb. The increased mortality in alcohol-fed Mtb-infected young mice was due to IFN-α production by CD11b+Ly6G+ cells. We also found that PBMCs from young alcoholic individuals with latent tuberculosis infection (LTBI) produced significantly higher amounts of IFN-α than those from young non-alcoholic, old alcoholic and old non-alcoholic LTBI+ individuals. Our findings suggest that young alcoholic LTBI+ individuals have a higher risk of developing active TB infection. Our studies provide the first evidence that chronic alcohol consumption induces IFN-α production in young Mtb-infected mice and increases their mortality rates. Further characterization of CD11b+Ly6G+ cells and delineation of the mechanisms through which alcohol enhances IFN-α production in Ly6G+ cells during Mtb infection will facilitate the development of therapies for alcoholic individuals with latent and active Mtb.

Synthesis & molecular modeling studies of bronchodilatory active indole–pyridine conjugates

Aim: Synthesis of novel bronchodilatory active indole–pyridine conjugates. Results/methodology: Indole–pyridine conjugates (6a–n, 8a–i and 10a–c) were synthesized in a facile pathway through reaction of 2-[(1-alkyl-1H-indol-3-yl)methylene]malononitriles 4a,b with the corresponding ketone-containing compounds (5a–f, 7a–c and 9a,b) in the presence of sodium alkoxide. Single (6l, 8 g) and powder (6k, 8d) x-ray studies supported the structures. Results: Histamine precontracted isolated tracheal rings of guinea pig exhibited the potent bronchodilation properties of 6c (about double-fold potency relative to the standard reference, theophylline). Some of the synthesized conjugates (8d, 6c, 6f and 6e) revealed promising reduction of IL-8 production during lipopolysaccharide-induced airway inflammatory bioassay. Computational studies (3D pharmacophore, 2D-QSAR ‘quantitative structure–activity relationship’) showed high approximations to the bronchodilation properties and explained the parameters controlling biological observations.

Neutrophil-Based Drug Delivery Systems

White blood cells (WBCs) are a major component of immunity in response to pathogen invasion. Neutrophils are the most abundant WBCs in humans, playing a central role in acute inflammation induced by pathogens. Adhesion to vasculature and tissue infiltration of neutrophils are key processes in acute inflammation. Many inflammatory/autoimmune disorders and cancer therapies have been found to be involved in activation and tissue infiltration of neutrophils. A promising strategy to develop novel targeted drug delivery systems is the targeting and exploitation of activated neutrophils. Herein, a new drug delivery platform based on neutrophils is reviewed. There are two types of drug delivery systems: neutrophils as carriers and neutrophil-membrane-derived nanovesicles. It is discussed how nanoparticles hijack neutrophils in vivo to deliver therapeutics across blood vessel barriers and how neutrophil-membrane-derived nanovesicles target inflamed vasculature. Finally, the potential applications of neutrophil-based drug delivery systems in treating inflammation and cancers are presented.

MEDI3902 Correlates of Protection against Severe Pseudomonas aeruginosa Pneumonia in a Rabbit Acute Pneumonia Model

Pseudomonas aeruginosa is among the most formidable antibiotic-resistant pathogens and is a leading cause of hospital-associated infections. With dwindling options for antibiotic-resistant infections, a new paradigm for treatment and disease resolution is required. MEDI3902, a bispecific antibody targeting the P. aeruginosa type III secretion (T3S) protein PcrV and Psl exopolysaccharide, was previously shown to mediate potent protective activity in murine infection models. With the current challenges associated with the clinical development of narrow-spectrum agents, robust preclinical efficacy data in multiple animal species are desirable. Here, we sought to develop a rabbit P. aeruginosa acute pneumonia model to further evaluate the activity of MEDI3902 intervention. In the rabbit model of acute pneumonia, prophylaxis with MEDI3902 exhibited potent dose-dependent protection, whereas those receiving control IgG developed fatal hemorrhagic necrotizing pneumonia between 12 and 54 h after infection. Blood biomarkers (e.g., partial pressure of oxygen [pO₂], partial pressure of carbon dioxide [pCO₂], base excess, lactate, and creatinine) were grossly deranged for the vast majority of control IgG-treated animals but remained within normal limits for MEDI3902-treated animals. In addition, MEDI3902-treated animals exhibited a profound reduction in P. aeruginosa organ burden and a marked reduction in the expression of proinflammatory mediators from lung tissue, which correlated with reduced lung histopathology. These results confirm that targeting PcrV and Psl via MEDI3902 is a promising candidate for immunotherapy against P. aeruginosa pneumonia.

Silver Nanoparticles Impair Retinoic Acid-Inducible Gene I-Mediated Mitochondrial Antiviral Immunity by Blocking the Autophagic Flux in Lung Epithelial Cells

Silver nanoparticles (AgNPs) are microbicidal agents which could be potentially used as an alternative to antivirals to treat human infectious diseases, especially influenza virus infections where antivirals have generally proven unsuccessful. However, concerns about the use of AgNPs on humans arise from their potential toxicity, although mechanisms are not well-understood. We show here, in the context of an influenza virus infection of lung epithelial cells, that AgNPs down-regulated influenza induced CCL-5 and -IFN-β release (two cytokines important in antiviral immunity) through RIG-I inhibition, while enhancing IL-8 production, a cytokine important for mobilizing host antibacterial responses. AgNPs activity was independent of coating and was not observed with gold nanoparticles. Down-stream analysis indicated that AgNPs disorganized the mitochondrial network and prevented the antiviral IRF-7 transcription factor influx into the nucleus. Importantly, we showed that the modulation of RIG-I-IRF-7 pathway was concomitant with inhibition of either classical or alternative autophagy (ATG-5- and Rab-9 dependent, respectively), depending on the epithelial cell type used. Altogether, this demonstration of a AgNPs-mediated functional dichotomy (down-regulation of IFN-dependent antiviral responses and up-regulation of IL-8-dependent antibacterial responses) may have practical implications for their use in the clinic.

Qi-Dong-Huo-Xue-Yin Inhibits Inflammation in Acute Lung Injury in Mice via Toll-Like Receptor 4/Caveolin-1 Signaling

Acute lung injury (ALI) is a critical illness with no current effective treatment. Caveolin-1 indirectly activates inflammation-associated signaling pathways by inhibiting endothelial nitric oxide synthase (eNOS). This induces an imbalance between pro- and anti-inflammatory cytokine levels, which are involved in the pathogenesis of ALI. The compound Chinese prescription Qi-Dong-Huo-Xue-Yin (QDHXY) is efficacious for ALI treatment via an anti-inflammatory effect; however, the exact underlying mechanism is unknown. Therefore, we explored the protective effect of QDHXY against lipopolysaccharide- (LPS-) induced ALI in mice. Histopathological changes in mouse lung tissues were studied. Furthermore, alterations in the serum levels of pro- and anti-inflammatory cytokines were investigated. The levels of tumor necrosis factor- (TNF-)α, interleukin- (IL-) 6, IL-1β, and interferon-γ-induced protein 10 in bronchoalveolar lavage fluid were measured. Additionally, the expression levels of myeloid differentiation factor 88 (MyD88), caveolin-1, and eNOS were assessed. QDHXY significantly reduced lung infiltration with inflammatory cells and the production of serum pro- and anti-inflammatory cytokines and inhibited the expression of TNF-α, IL-1β, caveolin-1, and MyD88 but not eNOS. These indicate that QDHXY significantly improved the balance between pro- and anti-inflammatory cytokine levels, possibly by inhibiting the caveolin-1 signaling pathway. Therefore, QDHXY may be a potential treatment for ALI.

Towards the use of breath for detecting mycobacterial infection: a case study in a murine model

In the present research, the potential of breath analysis by comprehensive two-dimensional gas chromatography coupled to mass spectrometry (GC×GC-MS) was investigated for the discrimination between healthy and infected mice. A pilot study employing a total of 16 animals was used to develop a method for breath analysis in a murine model for studying Mycobacterium tuberculosis complex (MTBC) using the M. bovis bacillus Calmette-Guérin. Breath was collected in Tedlar bags and concentrated onto thermal desorption tubes for subsequent analysis by GC×GC-MS. Immunological test and bacterial cell count in bronchoalveolar lavage fluid and mice lung homogenate confirmed the presence of bacteria in the infected group. From the GC×GC-MS analysis, 23 molecules were found to mainly drive the separation between control and infected mice and their tentative identification is provided.This study shows that the overall used methodology is able to differentiate breath between healthy and infected animals, and the information herein can be used to further develop the mouse breath model to study MTBC pathogenesis, evaluate pre-clinical drug regimen efficacy, and to further develop the concept of breath-based diagnostics.

Leptospirosis in human: Biomarkers in host immune responses

Leptospirosis remains one of the most widespread zoonotic diseases caused by spirochetes of the genus Leptospira, which accounts for high morbidity and mortality globally. Leptospiral infections are often found in tropical and subtropical regions, with people exposed to contaminated environments or animal reservoirs are at high risk of getting the infection. Leptospirosis has a wide range of clinical manifestations with non-specific signs and symptoms and often misdiagnosed with other acute febrile illnesses at early stage of infection. Despite being one of the leading causes of zoonotic morbidity worldwide, there is still a gap between pathogenesis and human immune responses during leptospiral infection. It still remains obscure whether the severity of the infection is caused by the pathogenic properties of the Leptospira itself, or it is a consequence of imbalance host immune factors. Hence, in this review, we seek to summarize the past and present milestone findings on the biomarkers of host immune response aspects during human leptospiral infection, including cytokine and other immune mediators. A profound understanding of the interlink between virulence factors and host immune responses during human leptospirosis is imperative to identify potential biomarkers for diagnostic and prognostic applications as well as designing novel immunotherapeutic strategies in future.

NLRP3 inflammasome induced liver graft injury through activation of telomere-independent RAP1/KC axis

Acute-phase inflammation plays a critical role in liver graft injury. Inflammasomes, multi-molecular complexes in the cytoplasm, are responsible for initiating inflammation. Here, we aimed to explore the role of inflammasomes in liver graft injury and further to investigate the regulatory mechanism. In a clinical liver transplant cohort, we found that intragraft expression of nucleotide-binding oligomerization domain-like receptor family pyrin domain containing 3 (NLRP3) inflammasomes was significantly up-regulated post-transplantation. Importantly, overexpression of NLRP3 was strongly associated with poor liver function characterized by high levels of ALT, AST, and urea, as well as neutrophil infiltration after transplantation. The significant correlation between NLRP3 and IL-1β mRNA levels led us to focus on one of the associated upstream regulators, telomere-independent repressor activator protein 1 (RAP1), which was further proved to be co-localized with NLRP3 in neutrophils. In the liver of a mouse model (hepatic ischaemia/reperfusion and hepatectomy model) and isolated neutrophils from RAP1^-/- mice, the expression levels of NLRP3 and keratinocyte chemoattractant (KC) were significantly down-regulated in contrast to those in wild types. The levels of ALT and AST, as well as the neutrophil infiltration, were also decreased by RAP1 deficiency. In our clinical validation, intragraft KC expression was associated with NLRP3 and co-localized with RAP1 in neutrophils. Furthermore, NLRP3 inflammasomes were up-regulated by recombinant KC in the isolated neutrophils and liver of the mouse model. Our data demonstrated that NLRP3 inflammasomes, activated by the RAP1/KC axis, played a critical role in initiating inflammation during the early stage of liver graft injury. Targeting RAP1/KC/NLRP3 inflammasomes may offer a new therapeutic strategy against liver graft injury. Copyright © 2017 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Differences in inflammatory marker patterns for adult community-acquired pneumonia patients induced by different pathogens

INTRODUCTION

The inflammatory marker patterns of community-acquired Pneumonia (CAP) induced by different microorganisms in adult patients remained unclear.

OBJECTIVES

We aim to explore the inflammatory marker patterns of adult CAP patients induced by different pathogens.

METHODS

Adult CAP patients with definite etiologies were enrolled from September 2010 to June 2012. They were divided into three groups according to the causative pathogens: typical bacteria, Mycoplasma pneumoniae (MP), and viruses. Twenty-seven cytokines and bactericidal/permeability-increasing protein (BPI) levels of serum collected within 7 days onset in these groups were compared.

RESULTS

One hundred twenty-four cases were enrolled for serum detection and analysis, including 10 typical bacterial pneumonia patients, 56 cases with MP pneumonia and 58 with viral pneumonia. Three kinds (PDGF-BB, IP-10, RANTES) of 27 cytokines and BPI levels were significantly elevated in patients with acute pneumonia than healthy controls. Distinct inflammatory marker patterns were released by different pathogens: typical bacterial pneumonia patients had highest levels of BPI, IL-6, IL-8, IL-1rα; while patients caused by MP presented higher levels of PDGF-BB, IL-17A, G-CSF than those caused by viruses. Rhinovirus owned a higher inflammatory response level than the other viruses. The area under the curve (AUC) of PDGF-BB to differentiate MP and virus infection was biggest, which was 0.708.

CONCLUSION

Distinct inflammatory marker patterns were released by different pathogens during acute pneumonia. Significantly increased level of PDGF-BB was observed in acute pneumonia for the first time. It showed a better ability to differentiate MP and virus infection.

Composition and pathogenic potential of a microbial bioremediation product used for crude oil degradation

A microbial bioremediation product (MBP) used for large-scale oil degradation was investigated for microbial constituents and possible pathogenicity. Aerobic growth on various media yielded >108 colonies mL-1. Full-length 16S rDNA sequencing and fatty acid profiling from morphologically distinct colonies revealed ≥13 distinct genera. Full-length 16S rDNA library sequencing, by either Sanger or long-read PacBio technology, suggested that up to 21% of the MBP was composed of Arcobacter. Other high abundance microbial constituents (>6%) included the genera Proteus, Enterococcus, Dysgonomonas and several genera in the order Bacteroidales. The MBP was most susceptible to ciprofloxacin, doxycycline, gentamicin, and meropenam. MBP exposure of human HT29 and A549 cells caused significant cytotoxicity, and bacterial growth and adherence. An acellular MBP filtrate was also cytotoxic to HT29, but not A549. Both MBP and filtrate exposures elevated the neutrophil chemoattractant IL-8. In endotracheal murine exposures, bacterial pulmonary clearance was complete after one-week. Elevation of pro-inflammatory cytokines IL-1β, IL-6, and TNF-α, and chemokines KC and MCP-1 occurred between 2h and 48h post-exposure, followed by restoration to baseline levels at 96h. Cytokine/chemokine signalling was accompanied by elevated blood neutrophils and monocytes at 4h and 48h, respectively. Peripheral acute phase response markers were maximal at 24h. All indicators examined returned to baseline values by 168h. In contrast to HT29, but similar to A549 observations, MBP filtrate did not induce significant murine effects with the indicators examined. The results demonstrated the potentially complex nature of MBPs and transient immunological effects during exposure. Products containing microbes should be scrutinized for pathogenic components and subjected to characterisation and quality validation prior to commercial release.

The mito-DAMP cardiolipin blocks IL-10 production causing persistent inflammation during bacterial pneumonia

Bacterial pneumonia is a significant healthcare burden worldwide. Failure to resolve inflammation after infection precipitates lung injury and an increase in morbidity and mortality. Gram-negative bacteria are common in pneumonia and increased levels of the mito-damage-associated molecular pattern (DAMP) cardiolipin can be detected in the lungs. Here we show that mice infected with Klebsiella pneumoniae develop lung injury with accumulation of cardiolipin. Cardiolipin inhibits resolution of inflammation by suppressing production of anti-inflammatory IL-10 by lung CD11b⁺Ly6G^intLy6C^loF4/80⁺ cells. Cardiolipin induces PPARγ SUMOylation, which causes recruitment of a repressive NCOR/HDAC3 complex to the IL-10 promoter, but not the TNF promoter, thereby tipping the balance towards inflammation rather than resolution. Inhibition of HDAC activity by sodium butyrate enhances recruitment of acetylated histone 3 to the IL-10 promoter and increases the concentration of IL-10 in the lungs. These findings identify a mechanism of persistent inflammation during pneumonia and indicate the potential of HDAC inhibition as a therapy.

Non-resolving bacterial pneumonia results in lung tissue damage owing to overactive inflammation. Here the authors show that the mitochondrial DAMP cardiolipin contributes to persistent inflammation by SUMOylating PPARγ, which promotes binding of the corepressor NCOR/HDAC3 complex to the IL-10 promoter.

Corticotropin-releasing hormone improves survival in pneumococcal pneumonia by reducing pulmonary inflammation

The use of glucocorticoids to reduce inflammatory responses is largely based on the knowledge of the physiological action of the endogenous glucocorticoid, cortisol. Corticotropin‐releasing hormone (CRH) is a neuropeptide released from the hypothalamic–pituitary–adrenal axis of the central nervous system. This hormone serves as an important mediator of adaptive physiological responses to stress. In addition to its role in inducing downstream cortisol release that in turn regulates immune suppression, CRH has also been found to mediate inflammatory responses in peripheral tissues. Streptococcus pneumoniae is a microorganism commonly present among the commensal microflora along the upper respiratory tract. Transmission of disease stems from the resident asymptomatic pneumococcus along the nasal passages. Glucocorticoids are central mediators of immune suppression and are the primary adjuvant pharmacological treatment used to reduce inflammatory responses in patients with severe bacterial pneumonia. However, controversy exists in the effectiveness of glucocorticoid treatment in reducing mortality rates during S. pneumoniae infection. In this study, we compared the effect of the currently utilized pharmacologic glucocorticoid dexamethasone with CRH. Our results demonstrated that intranasal administration of CRH increases survival associated with a decrease in inflammatory cellular immune responses compared to dexamethasone independent of neutrophils. Thus, providing evidence of its use in the management of immune and inflammatory responses brought on by severe pneumococcal infection that could reduce mortality risks.

Modulatory potential of resveratrol during lung inflammatory disease

Neutrophils are the first cells to achieve the sites of infection or inflammation in the lungs. The massive accumulation of these cells is associated with acute and chronic lung injury. Therefore, they have been implicated in the pathogenesis of many lung diseases through the release of reactive oxygen intermediates, proteolytic enzymes and Neutrophil Extracellular Traps (NETs). The excessive and continuous release of NETs, fibers composed by decondensed chromatin coated with neutrophil proteins, are associated to the impairment of lung function in different pathological settings. Flavonoids inhibit the respiratory burst of neutrophils in mammals. However, one of these flavonoids, resveratrol has a particular chemical property. It reduce Cu(II) to Cu(I) form with concomitant formation of reactive oxygen species, which can produce DNA breakage as reported in several in vitro models. We hypothesize that direct resveratrol administration in lungs can cleave DNA in NETs, improving lung function during acute airway infections or chronic inflammatory lung diseases. If the hypothesis is correct, the control of NET formation can be used to reduce the inflammatory environment in lung after neutrophil stimuli. Additionally, the production of proinflammatory cytokines by neutrophils could be also diminished by resveratrol administration. In this sense, this flavonoid provides a multifaceted opportunity for treatment of lung diseases with strong or chronic neutrophil activation.

A Non-invasive and Technically Non-intensive Method for Induction and Phenotyping of Experimental Bacterial Pneumonia in Mice

Although community-acquired pneumonia remains a major public health problem, murine models of bacterial pneumonia have recently facilitated significant preclinical advances in our understanding of the underlying cellular and molecular pathogenesis. In vivo mouse models capture the integrated physiology and resilience of the host defense response in a manner not revealed by alternative, simplified ex vivo approaches. Several methods have been described in the literature for intrapulmonary inoculation of bacteria in mice, including aerosolization, intranasal delivery, peroral endotracheal cannulation under 'blind' and visualized conditions, and transcutaneous endotracheal cannulation. All methods have relative merits and limitations. Herein, we describe in detail a non-invasive, technically non-intensive, inexpensive, and rapid method for intratracheal delivery of bacteria that involves aspiration (i.e., inhalation) by the mouse of an infectious inoculum pipetted into the oropharynx while under general anesthesia. This method can be used for pulmonary delivery of a wide variety of non-caustic biological and chemical agents, and is relatively easy to learn, even for laboratories with minimal prior experience with pulmonary procedures. In addition to describing the aspiration pneumonia method, we also provide step-by-step procedures for assaying the subsequent in vivo pulmonary innate immune response of the mouse, in particular, methods for quantifying bacterial clearance and the cellular immune response of the infected airway. This integrated and simple approach to pneumonia assessment allows for rapid and robust evaluation of the effect of genetic and environmental manipulations upon pulmonary innate immunity.

Multifaceted effects of Francisella tularensis on human neutrophil function and lifespan

Francisella tularensis in an intracellular bacterial pathogen that causes a potentially lethal disease called tularemia. Studies performed nearly 100 years ago revealed that neutrophil accumulation in infected tissues correlates directly with the extent of necrotic damage during F. tularensis infection. However, the dynamics and details of bacteria-neutrophil interactions have only recently been studied in detail. Herein, we review current understanding regarding the mechanisms that recruit neutrophils to F. tularensis-infected lungs, opsonization and phagocytosis, evasion and inhibition of neutrophil defense mechanisms, as well as the ability of F. tularensis to prolong neutrophil lifespan. In addition, we discuss distinctive features of the bacterium, including its ability to act at a distance to alter overall neutrophil responsiveness to exogenous stimuli, and the evidence which suggests that macrophages and neutrophils play distinct roles in tularemia pathogenesis, such that macrophages are major vehicles for intracellular growth and dissemination, whereas neutrophils drive tissue destruction by dysregulation of the inflammatory response.

Klf10 deficiency in mice exacerbates pulmonary inflammation by increasing expression of the proinflammatory molecule NPRA

KLF10 is a transforming growth factor (TGF)-β/Smad downstream regulated gene. KLF10 binds to the promoter of target genes and mimics the effects of TGF-β as a transcriptional factor. In our laboratory, we noted that Klf10 deficiency in mice is associated with significant inflammation of the lungs. However, the precise mechanism of this association remains unknown. We previously identified NPRA as a target gene potentially regulated by KLF10 through direct binding; NPRA knockout have known that prevented lung inflammation in a mouse model of allergic asthma. Here, we further explored the regulatory association between KLF10 and NPRA on the basis of the aforementioned findings. Our results demonstrated that KLF10 acts as a transcriptional repressor of NPRA and that KLF10 binding reduces NPRA expression in vitro. Compared with wild-type mice, Klf10-deficient mice were more sensitive to lipopolysaccharide or ovalbumin challenge and showed more severe inflammatory histological changes in the lungs. Moreover, Klf10-deficient mice showed pulmonary neutrophil accumulation. These findings collectively reveal the precise site where KLF10 signaling affects pulmonary inflammation by attenuating NPRA expression. They also verify the importance of KLF10 and atrial natriuretic peptide/NPRA in exerting influences on chronic pulmonary disease pathogenesis.

A Critical Role for P2X7 Receptor-Induced VCAM-1 Shedding and Neutrophil Infiltration during Acute Lung Injury

Pulmonary neutrophils are the initial inflammatory cells that are recruited during lung injury and are crucial for innate immunity. However, pathological recruitment of neutrophils results in lung injury. The objective of this study is to determine whether the novel neutrophil chemoattractant, soluble VCAM-1 (sVCAM-1), recruits pathological levels of neutrophils to injury sites and amplifies lung inflammation during acute lung injury. The mice with P2X7 receptor deficiency, or treated with a P2X7 receptor inhibitor or anti-VCAM-1 Abs, were subjected to a clinically relevant two-hit LPS and mechanical ventilation-induced acute lung injury. Neutrophil infiltration and lung inflammation were measured. Neutrophil chemotactic activities were determined by a chemotaxis assay. VCAM-1 shedding and signaling pathways were assessed in isolated lung epithelial cells. Ab neutralization of sVCAM-1 or deficiency or antagonism of P2X7R reduced neutrophil infiltration and proinflammatory cytokine levels. The ligands for sVCAM-1 were increased during acute lung injury. sVCAM-1 had neutrophil chemotactic activities and activated alveolar macrophages. VCAM-1 is released into the alveolar airspace from alveolar epithelial type I cells through P2X7 receptor-mediated activation of the metalloproteinase ADAM-17. In conclusion, sVCAM-1 is a novel chemoattractant for neutrophils and an activator for alveolar macrophages. Targeting sVCAM-1 provides a therapeutic intervention that could block pathological neutrophil recruitment, without interfering with the physiological recruitment of neutrophils, thus avoiding the impairment of host defenses.

The effects of direct hemoperfusion using a polymyxin B-immobilized column in a pig model of severe Pseudomonas aeruginosa pneumonia

Background

Hemoperfusion through a column containing polymyxin B-immobilized fiber (PMX-HP) is beneficial in abdominal sepsis. We assessed the effects of PMX-HP in a model of severe Pseudomonas aeruginosa pneumonia.

Methods

Eighteen pigs with severe P. aeruginosa pneumonia were mechanically ventilated for 76 h. Pigs were randomized to receive standard treatment with fluids and vasoactive drugs, or standard treatment with two 3-h PMX-HP sessions. Antibiotics against P. aeruginosa were never administered. We assessed endotoxemia through the endotoxin activity assay (EA). We measured the static lung elastance, ratio of arterial partial pressure per inspiratory fraction of oxygen (PaO₂/FIO₂), mean arterial pressure, cardiac output, systemic vascular resistance and inotropic score. Finally, every 24 h, we assessed complete blood count.

Results

In comparison with the control group, PMX-HP decreased percentage of circulating neutrophils from 47.4 ± 13.8 to 40.8 ± 11.5 % (p = 0.009). In a subgroup of animals with the worst hemodynamic impairment, EA in the control and PMX-HP groups was 0.50 ± 0.29 and 0.29 ± 0.14, respectively (p = 0.018). Additionally, in the control and PMX-HP groups, static lung elastance was 26.9 ± 8.7 and 25.3 ± 7.5 cm H₂O/L (p = 0.558), PaO₂/FIO₂ was 347.3 ± 61.9 and 356.4 ± 84.0 mmHg (p = 0.118), mean arterial pressure was 81.2 ± 10.3 and 81.6 ± 13.1 mmHg (p = 0.960), cardiac output was 3.30 ± 1.11 and 3.28 ± 1.19 L/min (p = 0.535), systemic vascular resistance was 1982.6 ± 608.4 and 2011.8 ± 750.0 dyne/s/cm^–5 (p = 0.939), and inotropic score was 0.25 ± 0.10 and 0.26 ± 0.18 (p = 0.864).

Conclusions

In mechanically ventilated pigs with severe P. aeruginosa pneumonia, PMX-HP does not have any valuable clinical benefit, and studies are warranted to fully evaluate a potential role of PMX-HP in septic shock associated with severe pulmonary infections.

Electronic supplementary material

The online version of this article (doi:10.1186/s13613-016-0155-3) contains supplementary material, which is available to authorized users.

CXCL1/MGSA Is a Novel Glycosaminoglycan (GAG)-binding Chemokine: STRUCTURAL EVIDENCE FOR TWO DISTINCT NON-OVERLAPPING BINDING DOMAINS

In humans, the chemokine CXCL1/MGSA (hCXCL1) plays fundamental and diverse roles in pathophysiology, from microbial killing to cancer progression, by orchestrating the directed migration of immune and non-immune cells. Cellular trafficking is highly regulated and requires concentration gradients that are achieved by interactions with sulfated glycosaminoglycans (GAGs). However, very little is known regarding the structural basis underlying hCXCL1-GAG interactions. We addressed this by characterizing the binding of GAG heparin oligosaccharides to hCXCL1 using NMR spectroscopy. Binding experiments under conditions at which hCXCL1 exists as monomers and dimers indicate that the dimer is the high-affinity GAG ligand. NMR experiments and modeling studies indicate that lysine and arginine residues mediate binding and that they are located in two non-overlapping domains. One domain, consisting of N-loop and C-helical residues (defined as α-domain) has also been identified previously as the GAG-binding domain for the related chemokine CXCL8/IL-8. The second domain, consisting of residues from the N terminus, 40s turn, and third β-strand (defined as β-domain) is novel. Eliminating β-domain binding by mutagenesis does not perturb α-domain binding, indicating two independent GAG-binding sites. It is known that N-loop and N-terminal residues mediate receptor activation, and we show that these residues are also involved in extensive GAG interactions. We also show that the GAG-bound hCXCL1 completely occlude receptor binding. We conclude that hCXCL1-GAG interactions provide stringent control over regulating chemokine levels and receptor accessibility and activation, and that chemotactic gradients mediate cellular trafficking to the target site.

Spatially distinct neutrophil responses within the inflammatory lesions of pneumonic plague

During pneumonic plague, the bacterium Yersinia pestis elicits the development of inflammatory lung lesions that continue to expand throughout infection. This lesion development and persistence are poorly understood. Here, we examine spatially distinct regions of lung lesions using laser capture microdissection and transcriptome sequencing (RNA-seq) analysis to identify transcriptional differences between lesion microenvironments. We show that cellular pathways involved in leukocyte migration and apoptosis are downregulated in the center of lung lesions compared to the periphery. Probing for the bacterial factor(s) important for the alteration in neutrophil survival, we show both in vitro and in vivo that Y. pestis increases neutrophil survival in a manner that is dependent on the type III secretion system effector YopM. This research explores the complexity of spatially distinct host-microbe interactions and emphasizes the importance of cell relevance in assays in order to fully understand Y. pestis virulence.

Yersinia pestis is a high-priority pathogen and continues to cause outbreaks worldwide. The ability of Y. pestis to be transmitted via respiratory droplets and its history of weaponization has led to its classification as a select agent most likely to be used as a biological weapon. Unrestricted bacterial growth during the initial preinflammatory phase primes patients to be infectious once disease symptoms begin in the proinflammatory phase, and the rapid disease progression can lead to death before Y. pestis infection can be diagnosed and treated. Using in vivo analyses and focusing on relevant cell types during pneumonic plague infection, we can identify host pathways that may be manipulated to extend the treatment window for pneumonic plague patients.

Potential Role of the Gut/Liver/Lung Axis in Alcohol-Induced Tissue Pathology

Both Alcoholic Liver Disease (ALD) and alcohol-related susceptibility to acute lung injury are estimated to account for the highest morbidity and mortality related to chronic alcohol abuse and, thus, represent a focus of intense investigation. In general, alcohol-induced derangements to both organs are considered to be independent and are often evaluated separately. However, the liver and lung share many general responses to damage, and specific responses to alcohol exposure. For example, both organs possess resident macrophages that play key roles in mediating the immune/inflammatory response. Additionally, alcohol-induced damage to both organs appears to involve oxidative stress that favors tissue injury. Another mechanism that appears to be shared between the organs is that inflammatory injury to both organs is enhanced by alcohol exposure. Lastly, altered extracellular matrix (ECM) deposition appears to be a key step in disease progression in both organs. Indeed, recent studies suggest that early subtle changes in the ECM may predispose the target organ to an inflammatory insult. The purpose of this chapter is to review the parallel mechanisms of liver and lung injury in response to alcohol consumption. This chapter will also explore the potential that these mechanisms are interdependent, as part of a gut-liver-lung axis.

Chemokine CXCL1-Mediated Neutrophil Trafficking in the Lung: Role of CXCR2 Activation

The chemokine CXCL1 and its receptor CXCR2 play a crucial role in host immune response by recruiting and activating neutrophils for microbial killing at the tissue site. Dysregulation in this process has been implicated in collateral tissue damage causing disease. CXCL1 reversibly exists as monomers and dimers, and it has been proposed that distinct monomer and dimer activities and the monomer-dimer equilibrium regulate the neutrophil function. However, the molecular mechanisms linking the CXCL1/CXCR2 axis and the neutrophil 'beneficial' and 'destructive' phenotypes are not known. In this study, we characterized neutrophil trafficking and its consequence in the mouse lung by the CXCL1 wild type (WT), which exists as monomers and dimers, and by a nondissociating dimer. Whereas the WT, compared to the dimer, was more active at low doses, both the WT and the dimer elicited a large neutrophil efflux at high doses. Importantly, robust neutrophil recruitment elicited by the WT or dimer was not detrimental to lung tissue integrity and, further, could not be correlated to surface CXCR2 levels. We conclude that the CXCL1 monomer-dimer distribution and receptor interactions are highly coupled and regulate neutrophil trafficking and that injury in the context of disease is a consequence of inappropriate CXCR2 activation at the target tissue and not due to mechanical forces exerted by neutrophils during recruitment.

Streptococcus pneumoniae secretes hydrogen peroxide leading to DNA damage and apoptosis in lung cells

Streptococcus pneumoniae is a leading cause of pneumonia and one of the most common causes of death globally. The impact of S. pneumoniae on host molecular processes that lead to detrimental pulmonary consequences is not fully understood. Here, we show that S. pneumoniae induces toxic DNA double-strand breaks (DSBs) in human alveolar epithelial cells, as indicated by ataxia telangiectasia mutated kinase (ATM)-dependent phosphorylation of histone H2AX and colocalization with p53-binding protein (53BP1). Furthermore, results show that DNA damage occurs in a bacterial contact-independent fashion and that Streptococcus pyruvate oxidase (SpxB), which enables synthesis of H2O2, plays a critical role in inducing DSBs. The extent of DNA damage correlates with the extent of apoptosis, and DNA damage precedes apoptosis, which is consistent with the time required for execution of apoptosis. Furthermore, addition of catalase, which neutralizes H2O2, greatly suppresses S. pneumoniae-induced DNA damage and apoptosis. Importantly, S. pneumoniae induces DSBs in the lungs of animals with acute pneumonia, and H2O2 production by S. pneumoniae in vivo contributes to its genotoxicity and virulence. One of the major DSBs repair pathways is nonhomologous end joining for which Ku70/80 is essential for repair. We find that deficiency of Ku80 causes an increase in the levels of DSBs and apoptosis, underscoring the importance of DNA repair in preventing S. pneumoniae-induced genotoxicity. Taken together, this study shows that S. pneumoniae-induced damage to the host cell genome exacerbates its toxicity and pathogenesis, making DNA repair a potentially important susceptibility factor in people who suffer from pneumonia.

Neutrophils play an important role in protective immunity against Coxiella burnetii infection

Coxiella burnetii is an obligate intracellular Gram-negative bacterium that causes the zoonotic disease Q fever. Although Q fever is mainly transmitted by aerosol infection, study of the immune responses in the lung following pulmonary C. burnetii infection is lacking. Neutrophils are considered the first immune cell to migrate into the lung and play an important role in host defense against aerosol infection with microbial pathogens. However, the role of neutrophils in the host defense against C. burnetii infection remains unclear. To determine the role of neutrophils in protective immunity against C. burnetii infection, the RB6-8C5 antibody was used to deplete neutrophils in mice before intranasal infection with C. burnetii. The results indicated that neutrophil-depleted mice developed more severe disease than their wild-type counterparts, suggesting that neutrophils play an important role in host defense against C. burnetii pulmonary infection. We also found that neither CXC chemokine receptor 2 (CXCR2) nor interleukin-17 (IL-17) receptor (IL-17R) deficiency changed the severity of disease following intranasal C. burnetii challenge, suggesting that keratinocyte-derived chemokine and IL-17 may not play essential roles in the response to C. burnetii infection. However, significantly higher C. burnetii genome copy numbers were detected in the lungs of IL-1R(-/-) mice at 14 days postinfection. This indicates that IL-1 may be important for the clearance of C. burnetii from the lungs following intranasal infection. Our results also suggest that neutrophils are involved in protecting vaccinated mice from C. burnetii challenge-induced disease. This is the first study to demonstrate an important role for neutrophils in protective immunity against C. burnetii infection.

Poly(inosinic-cytidylic) acid-triggered exacerbation of experimental asthma depends on IL-17A produced by NK cells

Viral infection of the respiratory tract represents the major cause of acute asthma exacerbations. dsRNA is produced as an intermediate during replication of respiratory viruses and triggers immune responses via TLR3. This study aimed at clarifying the mechanisms underlying TLR3 triggered exacerbation of experimental allergic asthma. The TLR3 ligand poly(inosinic-cytidylic) acid was applied intranasally to mice with already established experimental allergic asthma. Airway inflammation, cytokine expression, mucus production, and airway reactivity was assessed in wild-type, IL-17A, or IL-23p19-deficient, and in NK cell-depleted mice. Local application of poly(inosinic-cytidylic) acid exacerbated experimental allergic asthma in mice as characterized by enhanced release of proinflammatory cytokines, aggravated airway inflammation, and increased mucus production together with pronounced airway hyperresponsiveness. This was further associated with augmented production of IL-17 by Th17 cells and NK cells. Whereas experimental exacerbation could be induced in IL-23p19-deficient mice lacking mature, proinflammatory Th17 cells, this was not possible in mice lacking IL-17A or in NK cell-depleted animals. These experiments indicate a central role for IL-17 derived from NK cells but not from Th17 cells in the pathogenesis of virus-triggered exacerbation of experimental asthma.

Mechanisms of interferon-γ production by neutrophils and its function during Streptococcus pneumoniae pneumonia

Bacterial pneumonia is a common public health problem associated with significant mortality, morbidity, and cost. Neutrophils are usually the earliest leukocytes to respond to bacteria in the lungs. Neutrophils rapidly sequester in the pulmonary microvasculature and migrate into the lung parenchyma and alveolar spaces, where they perform numerous effector functions for host defense. Previous studies showed that migrated neutrophils produce IFN-γ early during pneumonia induced by Streptococcus pneumoniae and that early production of IFN-γ regulates bacterial clearance. IFN-γ production by neutrophils requires Rac2, Hck/Lyn/Fgr Src family tyrosine kinases, and NADPH oxidase. Our current studies examined the mechanisms that regulate IFN-γ production by lung neutrophils during acute S. pneumoniae pneumonia in mice and its function. We demonstrate that IFN-γ production by neutrophils is a tightly regulated process that does not require IL-12. The adaptor molecule MyD88 is critical for IFN-γ production by neutrophils. The guanine nucleotide exchange factor CalDAG-GEFI modulates IFN-γ production. The CD11/CD18 complex, CD44, Toll-like receptors 2 and 4, TRIF, and Nrf2 are not required for IFN-γ production by neutrophils. The recently described neutrophil-dendritic cell hybrid cell, identified by its expression of Ly6G and CD11c, is present at low numbers in pneumonic lungs and is not a source of IFN-γ. IFN-γ produced by neutrophils early during acute S. pneumoniae pneumonia induces transcription of target genes in the lungs, which are critical for host defense. These studies underline the complexity of the neutrophil responses during pneumonia in the acute inflammatory response and in subsequent resolution or initiation of immune responses.

Toll-like receptor ligands LPS and poly (I:C) exacerbate airway hyperresponsiveness in a model of airway allergy in mice, independently of inflammation

It is well-established that bacterial and viral infections have an exacerbating effect on allergic asthma, particularly aggravating respiratory symptoms, such as airway hyperresponsiveness (AHR). The mechanism by which these infections alter AHR is unclear, but some studies suggest that Toll-like receptors (TLRs) play a role. In this study, we investigated the impact of TLR3 and TLR4 ligands on AHR and airway inflammation in a model of pre-established allergic inflammation. Female BALB/c mice were sensitised and challenged intranasally (i.n.) with either PBS or ovalbumin (OVA) and subsequently i.n. challenged with poly (I:C) (TLR3) or LPS (TLR4) for four consecutive days. The response to methacholine was measured in vivo; cellular and inflammatory mediators were measured in blood, lung tissue and broncheoalveolar lavage fluid (BALF). OVA challenge resulted in an increase in AHR to methacholine, as well as increased airway eosinophilia and TH2 cytokine production. Subsequent challenge with TLR agonists resulted in a significant increase in AHR, but decreased TLR-specific cellular inflammation and production of immune mediators. Particularly evident was a decline in LPS-induced neutrophilia and neutrophil-associated cytokines following LPS and poly (I:C) treatment. The present data indicates that TLRs may play a pivotal role in AHR in response to microbial infection in allergic lung inflammation. These data also demonstrate that aggravated AHR occurs in the absence of an exacerbation in airway inflammation and that allergic inflammation impedes a subsequent inflammatory response to TLRs. These results may parallel clinical signs of microbial asthma exacerbation, including an extended duration of illness and increased respiratory symptoms.

Type I IFN signaling triggers immunopathology in tuberculosis-susceptible mice by modulating lung phagocyte dynamics

General interest in the biological functions of IFN type I in Mycobacterium tuberculosis (Mtb) infection increased after the recent identification of a distinct IFN gene expression signature in tuberculosis (TB) patients. Here, we demonstrate that TB-susceptible mice lacking the receptor for IFN I (IFNAR1) were protected from death upon aerogenic infection with Mtb. Using this experimental model to mimic primary progressive pulmonary TB, we dissected the immune processes affected by IFN I. IFNAR1 signaling did not affect T-cell responses, but markedly altered migration of inflammatory monocytes and neutrophils to the lung. This process was orchestrated by IFNAR1 expressed on both immune and tissue-resident radioresistant cells. IFNAR1-driven TB susceptibility was initiated by augmented Mtb replication and in situ death events, along with CXCL5/CXCL1-driven accumulation of neutrophils in alveoli, followed by the discrete compartmentalization of Mtb in lung phagocytes. Early depletion of neutrophils rescued TB-susceptible mice to levels observed in mice lacking IFNAR1. We conclude that IFN I alters early innate events at the site of Mtb invasion leading to fatal immunopathology. These data furnish a mechanistic explanation for the detrimental role of IFN I in pulmonary TB and form a basis for understanding the complex roles of IFN I in chronic inflammation.

The triggering receptor expressed on myeloid cells 2 inhibits complement component 1q effector mechanisms and exerts detrimental effects during pneumococcal pneumonia

Phagocytosis and inflammation within the lungs is crucial for host defense during bacterial pneumonia. Triggering receptor expressed on myeloid cells (TREM)-2 was proposed to negatively regulate TLR-mediated responses and enhance phagocytosis by macrophages, but the role of TREM-2 in respiratory tract infections is unknown. Here, we established the presence of TREM-2 on alveolar macrophages (AM) and explored the function of TREM-2 in the innate immune response to pneumococcal infection in vivo. Unexpectedly, we found Trem-2(-/-) AM to display augmented bacterial phagocytosis in vitro and in vivo compared to WT AM. Mechanistically, we detected that in the absence of TREM-2, pulmonary macrophages selectively produced elevated complement component 1q (C1q) levels. We found that these increased C1q levels depended on peroxisome proliferator-activated receptor-δ (PPAR-δ) activity and were responsible for the enhanced phagocytosis of bacteria. Upon infection with S. pneumoniae, Trem-2(-/-) mice exhibited an augmented bacterial clearance from lungs, decreased bacteremia and improved survival compared to their WT counterparts. This work is the first to disclose a role for TREM-2 in clinically relevant respiratory tract infections and demonstrates a previously unknown link between TREM-2 and opsonin production within the lungs.

Pseudomonas aeruginosa type-3 secretion system dampens host defense by exploiting the NLRC4-coupled inflammasome

RATIONALE

Pseudomonas aeruginosa, a major problem pathogen responsible for severe infections in critically ill patients, triggers, through a functional type-3 secretion system (T3SS), the activation of an intracellular cytosolic sensor of innate immunity, NLRC4. Although the NLRC4-inflammasome-dependent response contributes to increased clearance of intracellular pathogens, it seems that NLRC4 inflammasome activation decreases the clearance of P. aeruginosa, a mainly extracellular pathogen.

OBJECTIVES

We sought to determine the underlying mechanisms of this effect of the activation of NLRC4 by P. aeruginosa.

METHODS

We established acute lung injury in wild-type and Nlrc4(-/-) mice using sublethal intranasal inocula of P. aeruginosa strain CHA expressing or not a functional T3SS. We studied 96-hour survival, lung injury, bacterial clearance from the lungs, cytokine secretion in bronchoalveolar lavage, lung antimicrobial peptide expression by quantitative polymerase chain reaction, and flow cytometry analysis of lung cells.

MEASUREMENTS AND MAIN RESULTS

Nlrc4(-/-) mice showed enhanced bacterial clearance and decreased lung injury contributing to increased survival against extracellular P. aeruginosa strain expressing a functional T3SS. The mechanism involved decreased NLRC4-inflammasome-driven IL-18 secretion attenuating lung injury caused by excessive neutrophil recruitment. Additionally, in the lungs of Nlrc4(-/-) mice secretion of IL-17 by innate immune cells was increased and responsible for increased expression of lung epithelial antimicrobial peptides. Furthermore, IL-18 secretion was found to repress IL-17 and IL-17-driven lung antimicrobial peptide expression.

CONCLUSIONS

We report a new role of the T3SS apparatus itself, independently of exotoxin translocation. Through NLRC4 inflammasome activation, the T3SS promotes IL-18 secretion, which dampens a beneficial IL-17-mediated antimicrobial host response.

Neutrophils: potential therapeutic targets in tularemia?

The central role of neutrophils in innate immunity and host defense has long been recognized, and the ability of these cells to efficiently engulf and kill invading bacteria has been extensively studied, as has the role of neutrophil apoptosis in resolution of the inflammatory response. In the past few years additional immunoregulatory properties of neutrophils were discovered, and it is now clear that these cells play a much greater role in control of the immune response than was previously appreciated. In this regard, it is noteworthy that Francisella tularensis is one of relatively few pathogens that can successfully parasitize neutrophils as well as macrophages, DC and epithelial cells. Herein we will review the mechanisms used by F. tularensis to evade elimination by neutrophils. We will also reprise effects of this pathogen on neutrophil migration and lifespan as compared with other infectious and inflammatory disease states. In addition, we will discuss the evidence which suggests that neutrophils contribute to disease progression rather than effective defense during tularemia, and consider whether manipulation of neutrophil migration or turnover may be suitable adjunctive therapeutic strategies.

Inhibition of chlorine-induced pulmonary inflammation and edema by mometasone and budesonide

Chlorine gas is a widely used industrial compound that is highly toxic by inhalation and is considered a chemical threat agent. Inhalation of high levels of chlorine results in acute lung injury characterized by pneumonitis, pulmonary edema, and decrements in lung function. Because inflammatory processes can promote damage in the injured lung, anti-inflammatory therapy may be of potential benefit for treating chemical-induced acute lung injury. We previously developed a chlorine inhalation model in which mice develop epithelial injury, neutrophilic inflammation, pulmonary edema, and impaired pulmonary function. This model was used to evaluate nine corticosteroids for the ability to inhibit chlorine-induced neutrophilic inflammation. Two of the most potent corticosteroids in this assay, mometasone and budesonide, were investigated further. Mometasone or budesonide administered intraperitoneally 1h after chlorine inhalation caused a dose-dependent inhibition of neutrophil influx in lung tissue sections and in the number of neutrophils in lung lavage fluid. Budesonide, but not mometasone, reduced the levels of the neutrophil attractant CXCL1 in lavage fluid 6h after exposure. Mometasone or budesonide also significantly inhibited pulmonary edema assessed 1 day after chlorine exposure. Chlorine inhalation resulted in airway hyperreactivity to inhaled methacholine, but neither mometasone nor budesonide significantly affected this parameter. The results suggest that mometasone and budesonide may represent potential treatments for chemical-induced lung injury.

Lactobacillus rhamnosus CRL1505 beneficially modulates the immuno-coagulative response after pneumococcal infection in immunocompromised malnourished mice

This work evaluated the effect of orally or nasally administered Lactobacillus rhamnosus CRL1505 on the resistance of immunocompromised protein-malnourished mice to pneumococcal infection. In particular, we aimed to gain knowledge of the mechanism involved in the immunomodulatory effect of L. rhamnosus CRL1505 in malnourished hosts by evaluating its impact on the immuno-coagulative response. Malnutrition significantly increased lung tissue damage caused by Streptococcus pneumoniae infection. Lung damage was associated with a deregulated activation of coagulation and an altered inflammatory response. Pneumococcal colonization of lung and bacteremia were significantly reduced (p < 0.05) in malnourished mice receiving the CRL1505 strain. Moreover, mice repleted with supplemental L. rhamnosus CRL1505 showed the least alteration of the alveolar–capillary barrier and cell damage in lungs after the infectious challenge, especially when the CRL1505 strain was administered by nasal route. Besides, mice treated with L. rhamnosus CRL1505 showed an improved respiratory innate immune response and a lower activation of coagulation. The results of this work indicate that L. rhamnosus CRL1505 is able to beneficially modulate the inflammation–coagulation interaction after respiratory infections in malnourished hosts.

Coxiella burnetii interaction with neutrophils and macrophages in vitro and in SCID mice following aerosol infection

Coxiella burnetii is an obligate intracellular bacterium that causes acute and chronic Q fever in humans. Human Q fever is mainly transmitted by aerosol infection. However, there is a fundamental gap in the knowledge regarding the mechanisms of pulmonary immunity against C. burnetii infection. This study focused on understanding the interaction between C. burnetii and innate immune cells in vitro and in vivo. Both virulent C. burnetii Nine Mile phase I (NMI) and avirulent Nine Mile phase II (NMII) were able to infect neutrophils, while the infection rates were lower than 29%, suggesting that C. burnetii can infect neutrophils, but infection is limited. Interestingly, C. burnetii inside neutrophils can infect and replicate within macrophages, suggesting that neutrophils cannot kill C. burnetii and C. burnetii may be using infection of neutrophils as an evasive strategy to infect macrophages. To elucidate the mechanisms of the innate immune response to C. burnetii natural infection, SCID mice were exposed to aerosolized C. burnetii. Surprisingly, neutrophil influx into the lungs was delayed until day 7 postinfection in both NMI- and NMII-infected mice. This result suggests that neutrophils may play a unique role in the early immune response against aerosolized C. burnetii. Studying the interaction between C. burnetii and the innate immune system can provide a model system for understanding how the bacteria evade early immune responses to cause infection.

Immunosuppressive MDSCs induced by TLR signaling during infection and role in resolution of inflammation

Ligand-mediated activation of toll-like receptors (TLRs) not only induces inflammation but also immune suppression, which is an emerging area of investigation. Multiple negative feedback intracellular mechanisms have been described that are brought into play to prevent uncontrolled TLR activation. However, the identification of TLR-induced regulatory myeloid cells is a relatively recent development that has ramifications in pathogen-induced disease state as well as in cancer. Our efforts to understand how a high dose of lipopolysaccharide (LPS), a ligand of TLR4, suppresses allergic airway inflammation led to the identification of myeloid cells that are CD11b⁺Gri^int(Ly6G^int)F4/80⁺ and are phenotypically and morphologically similar to myeloid-derived suppressor cells (MDSCs) which are best studied in the context of cancer. MDSCs have been also detected during infection by various bacteria, parasites and viruses, which can engage different TLRs. These TLR-induced myeloid cells produce different types of mediators to influence immune response and inflammation that can be either beneficial or detrimental to the host. One beneficial function of TLR4/MyD88-triggered MDSCs in the lung is to efferocytose apoptotic neutrophils to help resolve inflammation elicited during bacterial pneumonia. A better understanding of the generation and function of these regulatory cells would be helpful to harness their potential or suppress their function for disease-specific immune regulation.

Robust detection of P. aeruginosa and S. aureus acute lung infections by secondary electrospray ionization-mass spectrometry (SESI-MS) breathprinting: from initial infection to clearance

Before breath-based diagnostics for lung infections can be implemented in the clinic, it is necessary to understand how the breath volatiles change during the course of infection, and ideally, to identify a core set of breath markers that can be used to diagnose the pathogen at any point during the infection. In the study presented here, we use secondary electrospray ionization-mass spectrometry (SESI-MS) to characterize the breathprint of Pseudomonas aeruginosa and Staphylococcus aureus lung infections in a murine model over a period of 120 h, with a total of 86 mice in the study. Using partial least squares-discriminant analysis (PLS-DA) to evaluate the time-course data, we were able to show that SESI-MS breathprinting can be used to robustly classify acute P. aeruginosa and S. aureus mouse lung infections at any time during the 120 h infection/clearance process. The variable importance plot from PLS indicates that multiple peaks from the SESI-MS breathprints are required for discriminating the bacterial infections. Therefore, by utilizing the entire breathprint rather than single biomarkers, infectious agents can be diagnosed by SESI-MS independent of when during the infection breath is tested.

STAT1-regulated lung MDSC-like cells produce IL-10 and efferocytose apoptotic neutrophils with relevance in resolution of bacterial pneumonia

Bacterial pneumonia remains a significant burden worldwide. Although an inflammatory response in the lung is required to fight the causative agent, persistent tissue-resident neutrophils in non-resolving pneumonia can induce collateral tissue damage and precipitate acute lung injury. However, little is known about mechanisms orchestrated in the lung tissue that remove apoptotic neutrophils to restore tissue homeostasis. In mice infected with Klebsiella pneumoniae, a bacterium commonly associated with hospital-acquired pneumonia, we show that interleukin (IL)-10 is essential for resolution of lung inflammation and recovery of mice after infection. Although IL-10(-/-) mice cleared bacteria, they displayed increased morbidity with progressive weight loss and persistent lung inflammation in the later phase after infection. A source of tissue IL-10 was found to be resident CD11b(+)Gr1(int)F4/80(+) cells resembling myeloid-derived suppressor cells (MDSCs) that appeared with a delayed kinetics after infection. These cells efficiently efferocytosed apoptotic neutrophils, which was aided by IL-10. The lung neutrophil burden was attenuated in infected signal transducer and activator of transcription 1 (STAT1)(-/-) mice with concomitant increase in the frequency of the MDSC-like cells and lung IL-10 levels. Thus, inhibiting STAT1 in combination with antibiotics may be a novel therapeutic strategy to address inefficient resolution of bacterial pneumonia.

Moutan cortex radicis improves lipopolysaccharide-induced acute lung injury in rats through anti-inflammation

Moutan cortex radicis (MCR) is a Chinese herbal medicine that was widely used over a long period as an analgesic, antipyretic, and anti-inflammatory agent in China. Lipopolysaccharide (LPS)-induced acute lung injury (ALI) in rat models is considered similar to adult respiratory distress syndrome (ARDS) in humans. Therefore, the present study investigates the effect of MCR on ALI. The ALI model was developed through the intra-tracheal (IT) administration of LPS (16mg/kg) to Sprague-Dawley (SD) rats, which formed the LPS group. MCR was orally administered before and after LPS was introduced into rats (MCR-LPS group and LPS-MCR group, respectively). In the MCR-LPS group, rats received MCR 2g/kg/times 3 times before LPS challenge; the LPS-MCR group received MCR 2g/kg/times 3 times after LPS challenge. The results of this experiment indicate that the number of total cells and neutrophils and the concentration of protein exudation in bronchoalveolar lavage fluid (BALF) significantly decreased in the MCR-LPS group. Cytokine levels, including levels of interleukin (IL)-1β, macrophage-inflammatory peptide (MIP)-2, IL-6, and IL-10, in BALF were also significantly inhibited at 16h after LPS administration in the MCR-LPS group. Myeloperoxidase (MPO) activity in lung tissue was reduced in the MCR-LPS and LPS-MCR groups at 16h after LPS administration. Furthermore, leukocyte infiltration and protein exudation in the alveolar space were less severe in the MCR-LPS group than in the LPS group. Therefore, the findings of this study suggest that the administration of MCR prior to LPS improves ALI, possibly mediating ALI through anti-inflammation.

Progress Toward a Human Vaccine Against Coccidioidomycosis

Coccidioidomycosis (San Joaquin Valley fever) is a human respiratory disease caused by a soil-borne mold, and is recognized as an intransigent microbial infection by physicians who treat patients with the potentially life-threatening, disseminated form of this mycosis. Epidemiological studies based on surveys of skin-test reactivity of people who reside in the endemic regions of the Southwestern US have shown that at least 150,000 new infections occur annually. The clinical spectrum of coccidioidomycosis ranges from an asymptomatic insult to a severe pulmonary disease in which the pathogen may spread from the lungs to the skin, bones, brain and other body organs. Escalation of symptomatic infections and increased cost of long-term antifungal treatment warrant a concerted effort to develop a vaccine against coccidioidomycosis. This review examines recently reported strategies used to generate such a vaccine and summarizes current understanding of the nature of protective immunity to this formidable disease.

Neutrophilic inflammatory response and oxidative stress in premenopausal women chronically exposed to indoor air pollution from biomass burning

The possibility of inflammation and neutrophil activation in response to indoor air pollution (IAP) from biomass fuel use has been investigated. For this, 142 premenopausal, never-smoking women (median age, 34 years) who cook exclusively with biomass (wood, dung, crop wastes) and 126 age-matched control women who cook with cleaner fuel liquefied petroleum gas (LPG) were enrolled. The neutrophil count in blood and sputum was significantly higher (p < 0.05) in biomass users than the control group. Flow cytometric analysis revealed marked increase in the surface expression of CD35 (complement receptor-1), CD16 (F(C)γ receptor III), and β(2) Mac-1 integrin (CD11b/CD18) on circulating neutrophils of biomass users. Besides, enzyme-linked immunosorbent assay showed that they had 72%, 67%, and 54% higher plasma levels of the proinflammatory cytokines tumor necrosis factor-alpha, interleukin-6, and interleukin-12, respectively, and doubled neutrophil chemoattractant interleukin-8. Immunocytochemical study revealed significantly higher percentage of airway neutrophils expressing inducible nitric oxide synthase, while the serum level of nitric oxide was doubled in women who cooked with biomass. Spectrophotometric analysis documented higher myeloperoxidase activity in circulating neutrophils of biomass users, suggesting neutrophil activation. Flow cytometry showed excess generation of reactive oxygen species (ROS) by leukocytes of biomass-using women, whereas their erythrocytes contained a depleted level of antioxidant enzyme superoxide dismutase (SOD). Indoor air of biomass-using households had two to four times more particulate matter with diameters of <10 μm (PM(10)) and <2.5 μm (PM(2.5)) as measured by real-time laser photometer. After controlling potential confounders, rise in proinflammatory mediators among biomass users were positively associated with PM(10) and PM(2.5) in indoor air, suggesting a close relationship between IAP and neutrophil activation. Besides, the levels of neutrophil activation and inflammation markers were positively associated with generation of ROS and negatively with SOD, indicating a role of oxidative stress in mediating neutrophilic inflammatory response following chronic inhalation of biomass smoke.

Effect on extrapulmonary sepsis-induced acute lung injury by hemoperfusion with neutral microporous resin column

The aim of this study was to investigate the effect of neutral microporous resin hemoperfusion on oxygenation improvement, removal of inflammatory cytokines in plasma and bronchoalveolar lavage, and mortality in acute lung injury induced by extrapulmonary sepsis. Forty-six patients with acute lung injury induced by extrapulmonary sepsis were randomized to HA type hemoperfusion treatment (N=25) or standard therapy (N=21). Those undergoing hemoperfusion treatment received HA330 hemoperfusion. We measured the plasma and bronchoalveolar lavage concentrations of TNF-α and IL-1, and the following parameters were compared between the control group and the hemoperfusion group on days 0, 3 and 7: lung injury measurements (arterial oxygen tension/fractional inspired oxygen ratio, lung injury score, chest X-ray score); interstitial edema of lung (extravascular lung water). Duration of mechanical ventilation, hospital, 28-day, and intensive care unit mortality were also observed. Patients treated with HA hemoperfusion showed a significant removal of plasma and bronchoalveolar lavage TNF-α and IL-1 over time while in the study. Patients in the HA group also demonstrated not only significant improvement of PaO2 /FiO2 , but also decreased Lung Injury Score and chest X-ray score at days 3 and 7. Furthermore, the measurements of the arterial oxygen tension/fractional inspired oxygen ratio, lung injury score and extravascular lung water (EVLWI) significantly correlated with and the concentration of cytokines in the plasma (all P<0.05). The HA hemoperfusion treatment group had a significant reduction in duration of mechanical ventilation, length of intensive care unit stay, and intensive care unit mortality. Significant removal of inflammatory cytokines from circulation and lung by hemoperfusion treatment using the HA type cartridge may contribute to the improvement of lung injury and intensive care unit outcome in extrapulmonary septic patients.

Delayed resolution of lung inflammation in Il-1rn-/- mice reflects elevated IL-17A/granulocyte colony-stimulating factor expression

IL-1 has been associated with acute lung injury (ALI) in both humans and animal models, but further investigation of the precise mechanisms involved is needed, and may identify novel therapeutic targets. To discover the IL-1 mediators essential to the initiation and resolution phases of acute lung inflammation, knockout mice (with targeted deletions for either the IL-1 receptor-1, i.e., Il-1r1(-/-), or the IL-1 receptor antagonist, i.e., Il-1rn(-/-)) were exposed to aerosolized LPS, and indices of lung and systemic inflammation were examined over the subsequent 48 hours. The resultant cell counts, histology, protein, and RNA expression of key cytokines were measured. Il-1r1(-/-) mice exhibited decreased neutrophil influx, particularly at 4 and 48 hours after exposure to LPS, as well as reduced bronchoalveolar lavage (BAL) expression of chemokines and granulocyte colony-stimulating factor (G-CSF). On the contrary, Il-1rn(-/-) mice demonstrated increased BAL neutrophil counts, increased BAL total protein, and greater evidence of histologic injury, all most notably 2 days after LPS exposure. Il-1rn(-/-) mice also exhibited higher peripheral neutrophil counts and greater numbers of granulocyte receptor-1 cells in their bone marrow, potentially reflecting their elevated plasma G-CSF concentrations. Furthermore, IL-17A expression was increased in the BAL and lungs of Il-1rn(-/-) mice after exposure to LPS, likely because of increased numbers of γδ T cells in the Il-1rn(-/-) lungs. Blockade with IL-17A monoclonal antibody before LPS exposure decreased the resultant BAL neutrophil counts and lung G-CSF expression in Il-1rn(-/-) mice, 48 hours after exposure to LPS. In conclusion, Il-1rn(-/-) mice exhibit delayed resolution in acute lung inflammation after exposure to LPS, a process that appears to be mediated via the G-CSF/IL-17A axis.