Extracellular ATP triggers and maintains asthmatic airway inflammation by activating dendritic cells

The modulation of haemolymph arginine kinase on the extracellular ATP induced bactericidal immune responses in the Pacific oyster Crassostrea gigas

Arginine kinase is an important phosphagen kinase (PK) which plays an essential role in ATP buffering systems in invertebrates. In the present study, an arginine kinase (designated CgAK) was isolated by the lipopolysaccharide (LPS) affinity chromatography from the haemolymph of Crassostrea gigas. CgAK could directly bind to LPS in a concentration-dependent manner with the dissociation constant (Kd) of 2.46 × 10(-6) M. The interaction with LPS significantly decreased the ATP hydrolytic activity of CgAK, which in turn lead to the accumulation of ATP in vitro. The extracellular ATP stimulation could induce Ca(2+) influx, reactive oxygen species (ROS) production, and the release of lysosomal enzyme in the cellular immune response. In addition, ATP stimulation provoked the bactericidal activity towards Escherichia coli, and the scavenging ROS with N-acetyl-l-cysteine (NAC) abrogated the bactericidal activity, indicating that ATP stimulation could induce ROS-dependent antimicrobial activity in haemocytes. Collectively, the results demonstrated that the haemolymph CgAK could serve as an important purinergic regulator to modulate extracellular ATP, which might further have an important effect on the purinergic signaling-activated innate immune response of oyster.

Extracellular ATP Induces Vascular Inflammation and Atherosclerosis via Purinergic Receptor Y2 in Mice

OBJECTIVE

A solid body of evidence supports a role of extracellular ATP and its P2 receptors in innate and adaptive immunity. It promotes inflammation as a danger signal in various chronic inflammatory diseases. Thus, we hypothesize contribution of extracellular ATP and its receptor P2Y2 in vascular inflammation and atherosclerosis.

APPROACH AND RESULTS

Extracellular ATP induced leukocyte rolling, adhesion, and migration in vivo as assessed by intravital microscopy and in sterile peritonitis. To test the role of extracellular ATP in atherosclerosis, ATP or saline as control was injected intraperitoneally 3× a week in low-density lipoprotein receptor(-/-) mice consuming high cholesterol diet. Atherosclerosis significantly increased after 16 weeks in ATP-treated mice (n=13; control group, 0.26 mm2; ATP group, 0.33 mm2; P=0.01). To gain into the role of ATP-receptor P2Y2 in ATP-induced leukocyte recruitment, ATP was administered systemically in P2Y2-deficient or P2Y2-competent mice. In P2Y2-deficient mice, the ATP-induced leukocyte adhesion was significantly reduced as assessed by intravital microscopy. P2Y2 expression in atherosclerosis was measured by real-time polymerase chain reaction and immunohistochemistry and demonstrates an increased expression mainly caused by influx of P2Y2-expressing macrophages. To investigate the functional role of P2Y2 in atherogenesis, P2Y2-deficient low-density lipoprotein receptor(-/-) mice consumed high cholesterol diet. After 16 weeks, P2Y2-deficient mice showed significantly reduced atherosclerotic lesions with decreased macrophages compared with P2Y2-competent mice (n=11; aortic arch: control group, 0.25 mm(2); P2Y2-deficient, 0.14 mm2; P=0.04). Mechanistically, atherosclerotic lesions from P2Y2-deficient mice expressed less vascular cell adhesion molecule-1 and intercellular adhesion molecule-1 RNA.

CONCLUSIONS

We show that extracellular ATP induces vascular inflammation and atherosclerosis via activation of P2Y2.

Ecto-ATPase CD39 Inactivates Isoprenoid-Derived Vγ9Vδ2 T Cell Phosphoantigens

In humans, Vγ9Vδ2 T cells respond to self and pathogen-associated, diphosphate-containing isoprenoids, also known as phosphoantigens (pAgs). However, activation and homeostasis of Vγ9Vδ2 T cells remain incompletely understood. Here, we show that pAgs induced expression of the ecto-ATPase CD39, which, however, not only hydrolyzed ATP but also abrogated the γδ T cell receptor (TCR) agonistic activity of self and microbial pAgs (C5 to C15). Only mevalonate-derived geranylgeranyl diphosphate (GGPP, C20) resisted CD39-mediated hydrolysis and acted as a regulator of CD39 expression and activity. GGPP enhanced macrophage differentiation in response to the tissue stress cytokine interleukin-15. In addition, GGPP-imprinted macrophage-like cells displayed increased capacity to produce IL-1β as well as the chemokine CCL2 and preferentially activated CD161-expressing CD4(+) T cells in an innate-like manner. Our studies reveal a previously unrecognized immunoregulatory function of CD39 and highlight a particular role of GGPP among pAgs.

Regulation and Function of the Nucleotide Binding Domain Leucine-Rich Repeat-Containing Receptor, Pyrin Domain-Containing-3 Inflammasome in Lung Disease

Inflammasomes are specialized inflammatory signaling platforms that govern the maturation and secretion of proinflammatory cytokines, such as IL-1β and IL-18, through the regulation of caspase-1-dependent proteolytic processing. Several nucleotide binding domain leucine-rich repeat-containing receptor (NLR) family members (i.e., NLR family, pyrin domain containing [NLRP] 1, NLRP3, and NLR family, caspase recruitment domain containing-4 [NLRC4]) as well as the pyrin and hemopoietic expression, interferon-inducibility, nuclear localization domain-containing family member, absent in melanoma 2, can form inflammasome complexes in human cells. In particular, the NLRP3 inflammasome is activated in response to cellular stresses through a two-component pathway, involving Toll-like receptor 4-ligand interaction (priming) followed by a second signal, such as ATP-dependent P2X purinoreceptor 7 receptor activation. Emerging studies suggest that the NLRP3 inflammasome can exert pleiotropic effects in human diseases with potentially both pro- and antipathogenic sequelae. Whereas NLRP3 inflammasome activation can serve as a vital component of host defense against invading bacteria and pathogens, excessive activation of the inflammasome can lead to inflammation-associated tissue injury in the setting of chronic disease. In addition, pyroptosis, an inflammasome-associated mode of cell death, contributes to host defense. Recent research has described the regulation and function of the NLRP3 inflammasome in various pulmonary diseases, including acute lung injury and acute respiratory distress syndrome, sepsis, respiratory infections, chronic obstructive pulmonary disease, asthma, pulmonary hypertension, cystic fibrosis, and idiopathic pulmonary fibrosis. The NLRP3 and related inflammasomes, and their regulated cytokines or receptors, may represent novel diagnostic or therapeutic targets in pulmonary diseases and other diseases in which inflammation contributes to pathogenesis.

Dendritic cells in lung immunopathology

Dendritic cells (DCs) lie at the heart of the innate immune system, specialised at recognising danger signals in many forms including foreign material, infection or tissue damage and initiating powerful adaptive immune and inflammatory responses. In barrier sites such as the lung, the instrumental role that DCs play at the interface between the environment and the host places them in a pivotal position in determining the severity of inflammatory disease. The past few years has seen a significant increase in our fundamental understanding of the subsets of DCs involved in pulmonary immunity, as well as the mechanisms by which they are activated and which they may use to coordinate downstream inflammation and pathology. In this review, we will summarise current understanding of the multi-faceted role that DCs play in the induction, maintenance and regulation of lung immunopathology, with an emphasis on allergic pulmonary disease.

P2X7 receptors induce degranulation in human mast cells

Mast cells play important roles in host defence against pathogens, as well as being a key effector cell in diseases with an allergic basis such as asthma and an increasing list of other chronic inflammatory conditions. Mast cells initiate immune responses through the release of newly synthesised eicosanoids and the secretion of pre-formed mediators such as histamine which they store in specialised granules. Calcium plays a key role in regulating both the synthesis and secretion of mast-cell-derived mediators, with influx across the membrane, in particular, being necessary for degranulation. This raises the possibility that calcium influx through P2X receptors may lead to antigen-independent secretion of histamine and other granule-derived mediators from human mast cells. Here we show that activation of P2X7 receptors with both ATP and BzATP induces robust calcium rises in human mast cells and triggers their degranulation; both effects are blocked by the P2X7 antagonist AZ11645373, or the removal of calcium from the extracellular medium. Activation of P2X1 receptors with αβmeATP also induces calcium influx in human mast cells, which is significantly reduced by both PPADS and NF 449. P2X1 receptor activation, however, does not trigger degranulation. The results indicate that P2X7 receptors may play a significant role in contributing to the unwanted activation of mast cells in chronic inflammatory conditions where extracellular ATP levels are elevated.

Blockade of Extracellular ATP Effect by Oxidized ATP Effectively Mitigated Induced Mouse Experimental Autoimmune Uveitis (EAU)

Various pathological conditions are accompanied by ATP release from the intracellular to the extracellular compartment. Extracellular ATP (eATP) functions as a signaling molecule by activating purinergic P2 purine receptors. The key P2 receptor involved in inflammation was identified as P2X7R. Recent studies have shown that P2X7R signaling is required to trigger the Th1/Th17 immune response, and oxidized ATP (oxATP) effectively blocks P2X7R activation. In this study we investigated the effect of oxATP on mouse experimental autoimmune uveitis (EAU). Our results demonstrated that induced EAU in B6 mice was almost completely abolished by the administration of small doses of oxATP, and the Th17 response, but not the Th1 response, was significantly weakened in the treated mice. Mechanistic studies showed that the therapeutic effects involve the functional change of a number of immune cells, including dendritic cells (DCs), T cells, and regulatory T cells. OxATP not only directly inhibits the T cell response; it also suppresses T cell activation by altering the function of DCs and Foxp3⁺ T cell. Our results demonstrated that inhibition of P2X7R activation effectively exempts excessive autoimmune inflammation, which may indicate a possible therapeutic use in the treatment of autoimmune diseases.

Impaired P2X1 Receptor-Mediated Adhesion in Eosinophils from Asthmatic Patients

Eosinophils play an important role in the pathogenesis of asthma and can be activated by extracellular nucleotides released following cell damage or inflammation. For example, increased ATP concentrations were reported in bronchoalveolar lavage fluids of asthmatic patients. Although eosinophils are known to express several subtypes of P2 receptors for extracellular nucleotides, their function and contribution to asthma remain unclear. In this article, we show that transcripts for P2X1, P2X4, and P2X5 receptors were expressed in healthy and asthmatic eosinophils. The P2X receptor agonist α,β-methylene ATP (α,β-meATP; 10 μM) evoked rapidly activating and desensitizing inward currents (peak 18 ± 3 pA/pF at -60 mV) in healthy eosinophils, typical of P2X1 homomeric receptors, which were abolished by the selective P2X1 antagonist NF449 (1 μM) (3 ± 2 pA/pF). α,β-meATP-evoked currents were smaller in eosinophils from asthmatic patients (8 ± 2 versus 27 ± 5 pA/pF for healthy) but were enhanced following treatment with a high concentration of the nucleotidase apyrase (17 ± 5 pA/pF for 10 IU/ml and 11 ± 3 pA/pF for 0.32 IU/ml), indicating that the channels are partially desensitized by extracellular nucleotides. α,β-meATP (10 μM) increased the expression of CD11b activated form in eosinophils from healthy, but not asthmatic, donors (143 ± 21% and 108 ± 11% of control response, respectively). Furthermore, α,β-meATP increased healthy (18 ± 2% compared with control 10 ± 1%) but not asthmatic (13 ± 1% versus 10 ± 0% for control) eosinophil adhesion. Healthy human eosinophils express functional P2X1 receptors whose activation leads to eosinophil αMβ2 integrin-dependent adhesion. P2X1 responses are constitutively reduced in asthmatic compared with healthy eosinophils, probably as the result of an increase in extracellular nucleotide concentration.

Regulation of allergic inflammation by the ectoenzyme E-NPP3 (CD203c) on basophils and mast cells

Adenosine 5'-triphosphate (ATP) is released from dying or damaged cells, as well as from activated cells. Once secreted, extracellular ATP induces several immune responses via P2X and P2Y receptors. Basophils and mast cells release ATP upon FcεRI-crosslinking, and ATP activates basophils and mast cells in an autocrine manner. Nucleotide-converting ectoenzymes, such as E-NTPD1, E-NTPD7, and E-NPP3, inhibit ATP-dependent immune responses by hydrolyzing ATP, thereby contributing to immune response regulation. E-NPP3 is a well-known activation marker for human basophils. E-NPP3's physiologic function has recently been disclosed in mice. E-NPP3 is rapidly induced on basophils and mast cells after FcεRI-crosslinking and hydrolyzes extracellular ATP on cell surfaces to prevent ATP-dependent excess activation of basophils and mast cells. In the absence of E-NPP3, basophils and mast cells are overactivated and mice suffer from severe chronic allergic inflammation. Thus, the ATP-hydrolyzing ectoenzymes E-NPP3 has a nonnegligible role in the regulation of basophil- and mast cell-mediated allergic responses.

Airway responses towards allergens - from the airway epithelium to T cells

The prevalence of allergic diseases such as allergic rhinitis is increasing, affecting up to 30% of the human population worldwide. Allergic sensitization arises from complex interactions between environmental exposures and genetic susceptibility, resulting in inflammatory T helper 2 (Th2) cell-derived immune responses towards environmental allergens. Emerging evidence now suggests that an epithelial dysfunction, coupled with inherent properties of environmental allergens, can be responsible for the inflammatory responses towards allergens. Several epithelial-derived cytokines, such as thymic stromal lymphopoietin (TSLP), IL-25 and IL-33, influence tissue-resident dendritic cells (DCs) as well as Th2 effector cells. Exposure to environmental allergens does not elicit Th2 inflammatory responses or any clinical symptoms in nonatopic individuals, and recent findings suggest that a nondamaged, healthy epithelium lowers the DCs' ability to induce inflammatory T-cell responses towards allergens. The purpose of this review was to summarize the current knowledge on which signals from the airway epithelium, from first contact with inhaled allergens all the way to the ensuing Th2-cell responses, influence the pathology of allergic diseases.

IL-12 and IL-4 activate a CD39-dependent intrinsic peripheral tolerance mechanism in CD8(+) T cells

Immune responses to protein antigens involve CD4(+) and CD8(+) T cells, which follow distinct programs of differentiation. Naïve CD8 T cells rapidly develop cytotoxic T-cell (CTL) activity after T-cell receptor stimulation, and we have previously shown that this is accompanied by suppressive activity in the presence of specific cytokines, i.e. IL-12 and IL-4. Cytokine-induced CD8(+) regulatory T (Treg) cells are one of several Treg-cell phenotypes and are Foxp3(-) IL-10(+) with contact-dependent suppressive capacity. Here, we show they also express high level CD39, an ecto-nucleotidase that degrades extracellular ATP, and this contributes to their suppressive activity. CD39 expression was found to be upregulated on CD8(+) T cells during peripheral tolerance induction in vivo, accompanied by release of IL-12 and IL-10. CD39 was also upregulated during respiratory tolerance induction to inhaled allergen and on tumor-infiltrating CD8(+) T cells. Production of IL-10 and expression of CD39 by CD8(+) T cells was independently regulated, being respectively blocked by extracellular ATP and enhanced by an A2A adenosine receptor agonist. Our results suggest that any CTL can develop suppressive activity when exposed to specific cytokines in the absence of alarmins. Thus negative feedback controls CTL expansion under regulation from both nucleotide and cytokine environment within tissues.

Mitochondria in lung disease

Mitochondria are a distinguishing feature of eukaryotic cells. Best known for their critical function in energy production via oxidative phosphorylation (OXPHOS), mitochondria are essential for nutrient and oxygen sensing and for the regulation of critical cellular processes, including cell death and inflammation. Such diverse functional roles for organelles that were once thought to be simple may be attributed to their distinct heteroplasmic genome, exclusive maternal lineage of inheritance, and ability to generate signals to communicate with other cellular organelles. Mitochondria are now thought of as one of the cell's most sophisticated and dynamic responsive sensing systems. Specific signatures of mitochondrial dysfunction that are associated with disease pathogenesis and/or progression are becoming increasingly important. In particular, the centrality of mitochondria in the pathological processes and clinical phenotypes associated with a range of lung diseases is emerging. Understanding the molecular mechanisms regulating the mitochondrial processes of lung cells will help to better define phenotypes and clinical manifestations associated with respiratory disease and to identify potential diagnostic and therapeutic targets.

The role of danger signals and ectonucleotidases in acute graft-versus-host disease

Allogeneic hematopoietic cell transplantation (allo-HCT) represents the only curative treatment approach for many patients with benign or malignant diseases of the hematopoietic system. However, post-transplant morbidity and mortality are significantly increased by the development of acute graft-versus-host disease (GvHD). While alloreactive T cells act as the main cellular mediator of the GvH reaction, recent evidence suggests a critical role of the innate immune system in the early stages of GvHD initiation. Danger-associated molecular patterns released from the intracellular space as well as from the extracellular matrix activate antigen-presenting cells and set pro-inflammatory pathways in motion. This review gives an overview about danger signals representing therapeutic targets with a clinical perspective with a particular focus on extracellular nucleotides and ectonucleotidases.

Increased expression of upstream TH2-cytokines in a mouse model of viral-induced asthma exacerbation

Background

Exacerbations of asthma caused by respiratory viral infections are serious conditions in need of novel treatment. To this end animal models of asthma exacerbations are warranted. We have shown that dsRNA challenges or rhinoviral infection produce exacerbation effects in mice with ovalbumin (OVA)-induced allergic asthma. However, house dust mite (HDM) is a more human asthma-relevant allergen than OVA. We thus hypothesised that dsRNA challenges in mice with HDM-induced experimental asthma would produce important translational features of asthma exacerbations.

Method

Mouse airways were challenged locally with HDM or saline three times a week for three weeks to establish experimental asthma. Then daily local dsRNA challenges were given for three consecutive days to induce exacerbation. Bronchoalveolar lavage fluid (BALF) was analysed for inflammatory cells, total protein, the necrosis marker LDH and the alarmin ATP. Lung homogenates were analysed for mRNA expression (RT-qPCR) of TNF-α, CCL2, CCL5, IL-1β, IL-33, thymic stromal lymphopoietin (TSLP), and IL-25 as well as pattern recognition receptors (PRRs) RIG-I, MDA5 and TLR3. Lung tissue IL-33 was analysed with ELISA and PRRs were quantified by western blot. Immunohistochemistry indicated lung distribution of IL-33.

Results

HDM challenge alone caused sustained increase in BALF total protein, eosinophils, lymphocytes and neutrophils, and transient increase in lung tissue expression of TSLP, IL-33 and TNF-α. dsRNA-induced exacerbation markedly and dose-dependently exaggerated these effects. Further, BALF levels of LDH and ATP, and lung tissue expression of CCL2, CCL5, IL-1β, IL-25 and PRRs were increased exclusively at the exacerbations. Lung protein levels of IL-33 were transiently increased by HDM and further increased at exacerbation.

Conclusion

We demonstrate several novel aspects of HDM-induced experimental asthma and added exacerbation effects of dsRNA. General inflammatory parameters in BALF such as exuded proteins, mixed granulocytes, LDH and ATP were increased at the present exacerbations as they are in human asthma exacerbations. We suggest that this model of asthma exacerbation involving dsRNA challenges given to mice with established HDM-induced asthma has translational value and suggest that it may be particularly suited for in vivo studies involving pharmacological effects on exacerbation-induced expression of major upstream TH₂-cytokines; IL-33, TSLP and IL-25, as well as PRRs.

Electronic supplementary material

The online version of this article (doi:10.1186/s12967-016-0808-x) contains supplementary material, which is available to authorized users.

CD39+ regulatory T cells attenuate allergic airway inflammation

BACKGROUND

The suppressive mechanism of regulatory T cells (Tregs) has remained incompletely clarified. Recent studies found that CD39 expressed by Tregs may participate in the immunoregulatory role of Tregs. CD39-induced ATP hydrolysis and/or adenosine generation contribute to the suppressive mechanism of Tregs. Previous studies suggested that ATP is involved in allergic airway inflammation by acting on type 2 purinergic (P2) receptors, but the role of CD39 and CD39(+) Tregs in allergic airway inflammation has not been elaborated.

OBJECTIVE

To investigate the role and underlying mechanism of CD39 expression by Tregs in allergic airway inflammation.

METHODS

A model of allergic asthma was developed with ovalbumin-alum in female Cd39 wild type (Cd39(+/+) ) and deficient (Cd39(-/-) ) C57BL/6 mice. Foxp3-GFP knock-in Cd39(+/+) and Cd39(-/-) mice were used to sort CD4(+) GFP(+) cells (Tregs) for exploring the role of CD39 expression by Tregs in allergic asthma. The effects of modulating CD39 activity with ARL67156 (inhibitor) or apyrase were also observed.

RESULTS

ARL67156 greatly worsened airway inflammation including increased lung inflammatory cells infiltration, goblet cell hyperplasia, and higher levels of Th2 and Th17 cytokines in bronchoalveolar lavage fluid (BALF), accompanied by an increment in transcription factor (GATA-3 and RORγt) and P2R (P2Y2, P2Y4 and P2Y6) mRNA expression in lungs. This potentiating effect was rescued by intratracheal injection of apyrase. Airway inflammation was markedly increased in Cd39(-/-) mice compared to Cd39(+/+) mice. In contrast to CD39(-) Tregs, CD39(+) Tregs showed stronger suppressive effects on airway inflammation. In vitro suppression assay suggested that CD39(+) Tregs have more potent suppressive effect on cytokines secretion from CD4(+) CD25(-) responder T cells and the inhibitory effects were reduced by addition of adenosine A2A receptor antagonist.

CONCLUSION

CD39 expressed on Tregs participates in the regulation of limiting allergic airway inflammation by regulating extracellular ATP and/or adenosine. CD39 may represent a new therapeutic target for asthma.

Role of P2 Receptors as Modulators of Rat Eosinophil Recruitment in Allergic Inflammation

ATP and other nucleotides are released from cells through regulated pathways or following the loss of plasma membrane integrity. Once outside the cell, these compounds can activate P2 receptors: P2X ionotropic receptors and G protein-coupled P2Y receptors. Eosinophils represent major effector cells in the allergic inflammatory response and they are, in fact, associated with several physiological and pathological processes. Here we investigate the expression of P2 receptors and roles of those receptors in murine eosinophils. In this context, our first step was to investigate the expression and functionality of the P2X receptors by patch clamping, our results showed a potency ranking order of ATP>ATPγS> 2meSATP> ADP> αβmeATP> βγmeATP>BzATP> UTP> UDP>cAMP. This data suggest the presence of P2X1, P2X2 and P2X7. Next we evaluate by microfluorimetry the expression of P2Y receptors, our results based in the ranking order of potency (UTP>ATPγS> ATP > UDP> ADP >2meSATP > αβmeATP) suggests the presence of P2Y2, P2Y4, P2Y6 and P2Y11. Moreover, we confirmed our findings by immunofluorescence assays. We also did chemotaxis assays to verify whether nucleotides could induce migration. After 1 or 2 hours of incubation, ATP increased migration of eosinophils, as well as ATPγS, a less hydrolysable analogue of ATP, while suramin a P2 blocker abolished migration. In keeping with this idea, we tested whether these receptors are implicated in the migration of eosinophils to an inflammation site in vivo, using a model of rat allergic pleurisy. In fact, migration of eosinophils has increased when ATP or ATPγS were applied in the pleural cavity, and once more suramin blocked this effect. We have demonstrated that rat eosinophils express P2X and P2Y receptors. In addition, the activation of P2 receptors can increase migration of eosinophils in vitro and in vivo, an effect blocked by suramin.

Transient receptor potential cation channel, subfamily V, member 4 and airway sensory afferent activation: Role of adenosine triphosphate

BACKGROUND

Sensory nerves innervating the airways play an important role in regulating various cardiopulmonary functions, maintaining homeostasis under healthy conditions and contributing to pathophysiology in disease states. Hypo-osmotic solutions elicit sensory reflexes, including cough, and are a potent stimulus for airway narrowing in asthmatic patients, but the mechanisms involved are not known. Transient receptor potential cation channel, subfamily V, member 4 (TRPV4) is widely expressed in the respiratory tract, but its role as a peripheral nociceptor has not been explored.

OBJECTIVE

We hypothesized that TRPV4 is expressed on airway afferents and is a key osmosensor initiating reflex events in the lung.

METHODS

We used guinea pig primary cells, tissue bioassay, in vivo electrophysiology, and a guinea pig conscious cough model to investigate a role for TRPV4 in mediating sensory nerve activation in vagal afferents and the possible downstream signaling mechanisms. Human vagus nerve was used to confirm key observations in animal tissues.

RESULTS

Here we show TRPV4-induced activation of guinea pig airway-specific primary nodose ganglion cells. TRPV4 ligands and hypo-osmotic solutions caused depolarization of murine, guinea pig, and human vagus and firing of Aδ-fibers (not C-fibers), which was inhibited by TRPV4 and P2X3 receptor antagonists. Both antagonists blocked TRPV4-induced cough.

CONCLUSION

This study identifies the TRPV4-ATP-P2X3 interaction as a key osmosensing pathway involved in airway sensory nerve reflexes. The absence of TRPV4-ATP-mediated effects on C-fibers indicates a distinct neurobiology for this ion channel and implicates TRPV4 as a novel therapeutic target for neuronal hyperresponsiveness in the airways and symptoms, such as cough.

Decreased expression of ectonucleotidase E-NPP1 in leukocytes from subjects with severe asthma exacerbation

Several studies suggest that ATP and related nucleotides play a role in the pathophysiology of asthma. However, the functionality of ectonucleotidases in this disease has been scantly investigated. We studied total ectonucleotidase activity in leukocytes from patients suffering from asthma exacerbation and explored the expression of E-NTPDase 1, 2, 3, and 8, and E-NPP1, 2, and 3, in their polymorphonuclear cells by immunofluorescence and qPCR. Leukocytes from patients with mild or moderate asthma exacerbation had similar ectonucleotidase activity than leukocytes from healthy subjects, while in patients with severe asthma exacerbation, this activity was lower. Of the ectonucleotidases studied, only E-NPP1 displayed diminished immunofluorescence and a significant decrease in its mRNA expression, both in patients with severe asthma exacerbation. This reduced E-NPP1 expression could be responsible for increased amounts of ATP or other nucleotides, capable of worsening asthma exacerbation, and warranting further investigation.

NTPDase1/CD39 and aberrant purinergic signalling in the pathogenesis of COPD

Purinergic receptor activation via extracellular ATP is involved in the pathogenesis of chronic obstructive pulmonary disease (COPD). Nucleoside triphosphate diphosphohydrolase-1/CD39 hydrolyses extracellular ATP and modulates P2 receptor signalling.We aimed to investigate the expression and function of CD39 in the pathogenesis of cigarette smoke-induced lung inflammation in patients and preclinical mouse models. CD39 expression and soluble ATPase activity were quantified in sputum and bronchoalveolar lavage fluid (BALF) cells in nonsmokers, smokers and COPD patients or mice with cigarette smoke-induced lung inflammation. In mice, pulmonary ATP and cytokine concentrations, inflammation and emphysema were analysed in the presence or absence of CD39.Following acute cigarette smoke exposure CD39 was upregulated in BALF cells in smokers with further increases in COPD patients. Acute cigarette smoke exposure induced CD39 upregulation in murine lungs and BALF cells, and ATP degradation was accelerated in airway fluids. CD39 inhibition and deficiency led to augmented lung inflammation; treatment with ATPase during cigarette smoke exposure prevented emphysema.Pulmonary CD39 expression and activity are increased in COPD. CD39 deficiency leads to enhanced emphysema in mice, while external administration of a functional CD39 analogue partially rescues the phenotype. The compensatory upregulation of pulmonary CD39 might serve as a protective mechanism in cigarette smoke-induced lung damage.

Lack of association between increased mitochondrial DNA4977 deletion and ATP levels of sputum cells from chronic obstructive pulmonary disease patients versus healthy smokers

In this study we looked at smokers with and without chronic obstructive pulmonary disease (COPD) patients in order to evaluate the incidence of 4977 base pair (bp) mtDNA (mtDNA⁴⁹⁷⁷) deletion and mtDNA copy number in sputum cells and in peripheral blood leukocytes (PBLs) in relation to mitochondrial function and oxidative stress status. Twenty-five COPD patients who were current smokers, 22 smokers and 23 healthy nonsmokers (for only PBLs studies) participated in this study. The 4977-bp deletion was detected in all examined samples within 40 cyles of PCR amplification, using a quantitative real time PCR. The frequency of the mtDNA⁴⁹⁷⁷ was significantly higher in the sputum cells of patients with COPD compared to smokers without COPD (p < 0.0001). This difference was not observed in PBLs. Levels of cellular oxidative stress were significantly higher in the sputum cells of subjects with COPD than in the smoker group. However, mtDNA copy number, mitochondrial membrane potential (ΔΨm) and cellular ATP levels in PBLs and sputum cells were not significantly different between the studied groups. The Pearson analysis revealed no correlations between the accumulation of mtDNA⁴⁹⁷⁷, and intracellular ATP content and ΔΨm values of the sputum cells, although there was a positive correlation between the increase in the percentage of deleted mtDNA⁴⁹⁷⁷ and the levels of cellular oxidative stress in COPD patients (r = 0.80, p < 0.0001). Our studies may suggest that the accumulation of mtDNA⁴⁹⁷⁷ in the sputum cells of smokers with COPD does not seem to have an important impact on mitochondrial dysfunction in relation to ATP production and ΔΨm when compared to those of healthy smokers.

The Roles of Mitochondrial Damage-Associated Molecular Patterns in Diseases

SIGNIFICANCE

Mitochondria, vital cellular power plants to generate energy, are involved in immune responses. Mitochondrial damage-associated molecular patterns (DAMPs) are molecules that are released from mitochondria to extracellular space during cell death and include not only proteins but also DNA or lipids. Mitochondrial DAMPs induce inflammatory responses and are critically involved in the pathogenesis of various diseases.

RECENT ADVANCES

Recent studies elucidate the molecular mechanisms by which mitochondrial DAMPs are released and initiate immune responses by use of genetically modulated cells or animals. Importantly, the levels of mitochondrial DAMPs in patients are often associated with severity and prognosis of human diseases, such as infection, asthma, ischemic heart disease, and cancer.

CRITICAL ISSUES

Although mitochondrial DAMPs can represent proinflammatory molecules in various experimental models, their roles in human diseases may be multifunctional and complex. It remains unclear where and how mitochondrial DAMPs are liberated into extracellular spaces and exert their biological functions particularly in vivo. In addition, while mitochondria can secrete several types of DAMPs during cell death, the interaction of each mitochondrial DAMP (e.g., synergistic effects) remains unclear.

FUTURE DIRECTIONS

Regulation of mitochondrial DAMP-mediated immune responses may be important to alter the progression of human diseases. In addition, measuring mitochondrial DAMPs in patients may be clinically useful as biomarkers to predict prognosis or response to therapies. Further studies of the mechanisms by which mitochondrial DAMPs impact the initiation and progression of diseases may lead to the development of therapeutics specifically targeting this pathway. Antioxid.

ATP releases ATP or other nucleotides from human peripheral blood leukocytes through purinergic P2 receptors

AIMS

Almost every eukaryotic cell releases ATP under certain conditions. The idea that ATP induces the release of ATP has been scantly investigated.

METHODS

We explored this possibility by assessing the rate of exogenous ATP breakdown (measured by phosphates production) by human peripheral blood leukocytes. The role of P2Y and P2X receptors was evaluated pharmacologically, by patch clamp, or by flow cytometry.

KEY FINDINGS

In mononuclear and/or polymorphonuclear cells, ATP increased phosphates formation in a time- and concentration-dependent manner. Uncoupling of P2Y receptors with N-ethylmaleimide and antagonism of P2Y and P2X receptors through suramin reduced phosphate formation after 500μM ATP, suggesting that part of the phosphate production was due to activation of P2 receptors, with subsequent release of ATP or other nucleotides. Similar results were obtained with UTP and ATPγS. Gadolinium (connexins inhibitor) also significantly reduced the ATP-induced phosphate production. Blockade of P2X receptors with SKF 96365 or NF023 did not modify the phosphate production. In monocytes, 500μM ATP induced inward currents suggestive of P2X1 activation, but higher concentrations (1-5mM) induced inward currents suggestive of P2X7 activation. We discarded a role of adenosine in the ATP-evoked nucleotides release. Flow cytometry identified that almost all mononuclear and polymorphonuclear cells expressed P2Y1,2,4,6,11 receptors.

SIGNIFICANCE

500μM ATP induced the release of ATP or other nucleotides through activation of P2Y2,4,6,11 receptors in human leukocytes, and probably via P2X receptors at higher concentrations. This ATP-induced nucleotides release constitutes a potential mechanism leading to amplification of ATP signaling.

Effect of P2X4R on airway inflammation and airway remodeling in allergic airway challenge in mice

P2X4 receptor (P2X4R) is the most widely expressed subtype of the P2XRs in the purinergic receptor family. Adenosine triphosphate (ATP), a ligand for this receptor, has been implicated in the pathogenesis of asthma. ATP-P2X4R signaling is involved in pulmonary vascular remodeling, and in the proliferation and differentiation of airway and alveolar epithelial cell lines. However, the role of P2X4R in asthma remains to be elucidated. This aim of the present study was to investigate the effects of P2X4R in a murine experimental asthma model. The asthmatic model was established by the inhalation of ovalbumin (OVA) in BALB/c mice. The mice were treated with P2X4R-specific agonists and antagonists to investigate the role of this receptor in vivo. Pathological changes in the bronchi and lung tissues were examined using hematoxylin and eosin staining, Masson's trichrome staining and Alcian blue staining. The inflammatory cells in the bronchoalveolar lavage fluid were counted, and the expression levels of P2X4R, α-smooth muscle actin (α-SMA) and proliferating cell nuclear antigen (PCNA) were detected using western blotting. In the OVA-challenged mice, inflammation, infiltration, collagen deposition, mucus production, and the expression levels of P2X4R and PCNA were all increased; however, the expression of α-SMA was decreased, compared with the mice in the control group. Whereas treatment with the P2X4R agonist, ATP, enhanced the allergic reaction, treatment with the P2X4R antagonist, 5-BDBD, attenuated the allergic reaction. The results suggested that ATP-P2X4R signaling may not only contribute to airway inflammation, but it may also contribute to airway remodeling in allergic asthma in mice.

Sexual maturation protects against development of lung inflammation through estrogen

Increasing levels of estrogen and progesterone are suggested to play a role in the gender switch in asthma prevalence during puberty. We investigated whether the process of sexual maturation in mice affects the development of lung inflammation in adulthood and the contributing roles of estrogen and progesterone during this process. By inducing ovalbumin-induced lung inflammation in sexually mature and immature (ovariectomized before sexual maturation) adult mice, we showed that sexually immature adult mice developed more eosinophilic lung inflammation. This protective effect of "puberty" appears to be dependent on estrogen, as estrogen supplementation at the time of ovariectomy protected against development of lung inflammation in adulthood whereas progesterone supplementation did not. Investigating the underlying mechanism of estrogen-mediated protection, we found that estrogen-treated mice had higher expression of the anti-inflammatory mediator secretory leukoprotease inhibitor (SLPI) and lower expression of the proasthmatic cytokine IL-33 in parenchymal lung tissue and that their expressions colocalized with type II alveolar epithelial cells (AECII). Treating AECII directly with SLPI significantly inhibited IL-33 production upon stimulation with ATP. Our data suggest that estrogen during puberty has a protective effect on asthma development, which is accompanied by induction of anti-inflammatory SLPI production and inhibition of proinflammatory IL-33 production by AECII.

Metabolic adaptation of tissues to stress releases metabolites influencing innate immunity

Recent developments have demonstrated that metabolic rewiring imposed by adaptation of tissues to stress leads to the release of various metabolites which directly or indirectly impact innate immune responses and inflammation. Some metabolites can behave as second messengers and leave local cues in tissues. Immune cells which infiltrate stressed tissues reorient their metabolism to cope with these microenvironmental cues while preserving their effector functions in tissues.

A Novel Function for P2Y2 in Myeloid Recipient-Derived Cells during Graft-versus-Host Disease

Acute graft-versus-host disease (GvHD) is a life-threatening complication of allogeneic hematopoietic cell transplantation. During the initiation phase of acute GvHD, endogenous danger signals such as ATP are released and inform the innate immune system via activation of the purinergic receptor P2X7 that a noninfectious damage has occurred. A second ATP-activated purinergic receptor involved in inflammatory diseases is P2Y2. In this study, we used P2y2(-/-) mice to test the role of this receptor in GvHD. P2y2(-/-) recipients experienced reduced GvHD-related mortality, IL-6 levels, enterocyte apoptosis, and histopathology scores. Chimeric mice with P2y2 deficiency restricted to hematopoietic tissues survived longer after GvHD induction than did wild-type mice. P2y2 deficiency of the recipient was connected to lower levels of myeloperoxidase in the intestinal tract of mice developing GvHD and a reduced myeloid cell signature. Selective deficiency of P2Y2 in inflammatory monocytes decreased GvHD severity. Mechanistically, P2y2(-/-) inflammatory monocytes displayed defective ERK activation and reactive oxygen species production. Compatible with a role of P2Y2 in human GvHD, the frequency of P2Y2(+) cells in inflamed GvHD lesions correlated with histopathological GvHD severity. Our findings indicate a novel function for P2Y2 in ATP-activated recipient myeloid cells during GvHD, which could be exploited when targeting danger signals to prevent GvHD.

Immune Dysfunction in Patients with Chronic Obstructive Pulmonary Disease

Chronic obstructive pulmonary disease (COPD) is a complex chronic disease. Chronic inflammation is the hallmark of COPD, involving the interplay of a wide variety of cells in the lung microenvironment. Cigarette smoke (CS) induces chronic lung inflammation and is considered a key etiological factor in the development and pathogenesis of COPD. Structural and inflammatory cells in the lung respond to CS exposure by releasing proinflammatory mediators that recruit additional inflammatory immune cells, which collectively contribute to the establishment of a chronic inflammatory microenvironment. Chronic inflammation contributes to lung damage, compromises innate and adaptive immune responses, and facilitates the recurrent episodes of respiratory infection that punctuate and further contribute to the pathological manifestations of the stable disease. A number of studies support the conclusion that immune dysfunction leads to exacerbations and disease severity in COPD. Our group has clearly demonstrated that CS exacerbates lung inflammation and compromises immunity to respiratory pathogens in a mouse model of COPD. We have also investigated the phenotype of immune cells in patients with COPD compared with healthy control subjects and found extensive immune dysfunction due to the presence and functional activity of T regulatory cells, CD4(+)PD-1(+) exhausted effector T cells and myeloid-derived suppressor cells. Manipulation of these immunosuppressive networks in COPD could provide a rational strategy to restore functional immune responses, reduce exacerbations, and improve lung function. In this review, we discuss the role of immune dysfunction in COPD that may contribute to recurrent respiratory infections and disease severity.

Effects of Aerosolized Adenosine 5'-Triphosphate in Smokers and Patients With COPD

BACKGROUND

Extracellular adenosine 5'-triphosphate (ATP) stimulates vagal C and Aδ fibers in the lung, resulting in pronounced bronchoconstriction and cough mediated by P2X2/3 receptors located on vagal sensory nerve terminals. We investigated the effects of nebulized ATP on cough and symptoms in control subjects, healthy smokers, and patients with COPD and compared these responses to the effects of inhaled adenosine, the metabolite of ATP.

METHODS

We studied the effects of inhaled ATP and adenosine monophosphate (AMP) on airway caliber, perception of dyspnea assessed by the Borg score, cough sensitivity, and ATP in exhaled breath condensate in healthy nonsmokers (n = 10), healthy smokers (n = 14), and patients with COPD (n = 7).

RESULTS

In comparison with healthy subjects, ATP induced more dyspnea, cough, and throat irritation in smokers and patients with COPD, and the effects of ATP were more pronounced than those of AMP. The concentration of ATP in the exhaled breath condensate of patients with COPD was elevated compared with that of healthy subjects.

CONCLUSIONS

Smokers and patients with COPD manifest hypersensitivity to extracellular ATP, which may play a mechanistic role in COPD.

ATP drives eosinophil effector responses through P2 purinergic receptors

BACKGROUND

Eosinophils recognize various stimuli, such as cytokines, chemokines, immunoglobulins, complement, and external pathogens, resulting in their accumulation in mucosal tissues and the progression of inflammation. Eosinophils are also involved in innate Th2-type immune responses mediated through endogenous danger signals, including IL-33, uric acid (UA), or ATP, in non-sensitized mice exposed to environmental allergens. However, the mechanism involved in eosinophil responses to these danger signals remains insufficiently understood.

METHODS

We examined migration, adhesion, superoxide production and degranulation of human eosinophils. Isolated eosinophils were incubated with monosodium urate (MSU) crystals and ATPγS, a non-hydrolysable ATP analogue. To determine the involvement of P2 or P2Y2 receptors in eosinophil responses to UA and ATP, eosinophils were preincubated with a pan-P2 receptor inhibitor, oxidized ATP (oATP), or anti-P2Y2 antibody before incubation with MSU crystals or ATPγS.

RESULTS

MSU crystals induced adhesion of eosinophils to recombinant human (rh)-ICAM-1 and induced production of superoxide. oATP abolished eosinophil responses to MSU crystals, suggesting involvement of endogenous ATP and its receptors. Furthermore, exogenous ATP, as ATPγS, induced migration of eosinophils through a model basement membrane, adhesion to rh-ICAM-1, superoxide generation, and degranulation of eosinophil-derived neurotoxin (EDN). oATP and anti-P2Y2 significantly reduced these eosinophil responses.

CONCLUSIONS

ATP serves as an essential mediator of functional responses in human eosinophils. Eosinophil responses to ATP may be implicated in airway inflammation in patients with asthma.

MicroRNA-155 modulates P2R signaling and Th2 priming of dendritic cells during allergic airway inflammation in mice

BACKGROUND

Dendritic cells (DCs) are the professional antigen-presenting cells (APCs) in the lung. They are known to be key players in the induction and maintenance of allergic asthma by cross-linking innate and adaptive immune responses. MicroRNAs (miRNAs) are known to influence cell fate and function by translational suppression or induction of messenger RNA (mRNA) degradation. miR-155 has been shown to be a crucial regulator of the immune system. However, its function in the pathogenesis of allergic airway inflammation (AAI) is not completely elucidated yet.

METHODS

Wild type (WT) and miR-155-deficient (miR-155(-/-) ) mice were used in ovalbumin (OVA) and house dust mite (HDM) models of AAI. Adoptive transfer of sensitized DCs to the lungs, migration, and T-cell priming assays were used to investigate the functional relevance of miR-155 in DCs.

RESULTS

miR-155(-/-) mice showed reduced eosinophilic airway inflammation compared to WT mice in both models of AAI. Furthermore, miR-155(-/-) DCs showed limited Th2 priming capacity and failed to induce airway inflammation in allergen-exposed WT mice. miR-155 deficiency on DCs was also associated with impaired purinergic receptor signaling, as miR-155(-/-) DCs showed reduced chemotaxis and IL-1beta secretion upon stimulation with ATP, probably due to direct targeting of ectonucleoside triphosphate diphosphohydrolases (ENTPD) by miR-155.

CONCLUSIONS

miR-155 deficiency alleviates AAI by diminishing Th2 priming capacity and ATP-/P2R-induced activation of DCs in mice, suggesting this miRNA as a potential therapeutic target of AAI.

Rhinoviral stimuli, epithelial factors and ATP signalling contribute to bronchial smooth muscle production of IL-33

BACKGROUND

Bronchial smooth muscle cells (BSMCs) from severe asthmatics have been shown to overexpress the Th2-driving and asthma-associated cytokine IL-33. However, little is known regarding factors involved in BSMC production of IL-33. Rhinovirus (RV) infections cause asthma exacerbations, which exhibit features of Th2-type inflammation. Here, we investigated the effects of epithelial-derived media and viral stimuli on IL-33 expression in human BSMCs.

METHODS

Primary human BSMCs from healthy (n = 3) and asthmatic (n = 3) subjects were stimulated with conditioned media from primary human bronchial epithelial cells (BECs), double-stranded (ds)RNA, dsRNA/LyoVec, or infected with RV. BSMCs were also pretreated with the purinergic receptor antagonist suramin. IL-33 expression was analysed by RT-qPCR and western blot and ATP levels were determined in cell supernatants.

RESULTS

RV infection and activation of TLR3 by dsRNA increased IL-33 mRNA and protein in healthy and asthmatic BSMCs. These effects were inhibited by dexamethasone. BSMC expression of IL-33 was also increased by stimulation of RIG-I-like receptors using dsRNA/LyoVec. Conditioned media from BECs induced BSMC expression of IL-33, which was further enhanced by dsRNA. BEC-derived medium and viral-stimulated BSMC supernatants exhibited elevated ATP levels. Blocking of purinergic signalling with suramin inhibited BSMC expression of IL-33 induced by dsRNA and BEC-derived medium.

CONCLUSIONS

RV infection of BSMCs and activation of TLR3 and RIG-I-like receptors cause expression and production of IL-33. Epithelial-released factor(s) increase BSMC expression of IL-33 and exhibit positive interaction with dsRNA. Increased BSMC IL-33 associates with ATP release and is antagonised by suramin. We suggest that epithelial-derived factors contribute to baseline BSMC IL-33 production, which is further augmented by RV infection of BSMCs and stimulation of their pathogen-recognising receptors.

DAMPs from Cell Death to New Life

Our body handles tissue damage by activating the immune system in response to intracellular molecules released by injured tissues [damage-associated molecular patterns (DAMPs)], in a similar way as it detects molecular motifs conserved in pathogens (pathogen-associated molecular patterns). DAMPs are molecules that have a physiological role inside the cell, but acquire additional functions when they are exposed to the extracellular environment: they alert the body about danger, stimulate an inflammatory response, and finally promote the regeneration process. Beside their passive release by dead cells, some DAMPs can be secreted or exposed by living cells undergoing a life-threatening stress. DAMPs have been linked to inflammation and related disorders: hence, inhibition of DAMP-mediated inflammatory responses is a promising strategy to improve the clinical management of infection- and injury-elicited inflammatory diseases. However, it is important to consider that DAMPs are not only danger signals but also central players in tissue repair. Indeed, some DAMPs have been studied for their role in tissue healing after sterile or infection-associated inflammation. This review is focused on two exemplary DAMPs, HMGB1 and adenosine triphosphate, and their contribution to both inflammation and tissue repair.

Role of platelets in allergic airway inflammation

Increasing evidence suggests an important role for platelets and their products (e.g., platelet factor 4, β-thromboglobulin, RANTES, thromboxane, or serotonin) in the pathogenesis of allergic diseases. A variety of changes in platelet function have been observed in patients with asthma, such as alterations in platelet secretion, expression of surface molecules, aggregation, and adhesion. Moreover, platelets have been found to actively contribute to most of the characteristic features of asthma, including bronchial hyperresponsiveness, bronchoconstriction, airway inflammation, and airway remodeling. This review brings together the current available data from both experimental and clinical studies that have investigated the role of platelets in allergic airway inflammation and asthma. It is anticipated that a better understanding of the role of platelets in the pathogenesis of asthma might lead to novel promising therapeutic approaches in the treatment of allergic airway diseases.

Epithelial function and dysfunction in asthma

Asthma was previously defined as an allergic Th2-mediated inflammatory immune disorder. Recently, this paradigm has been challenged because not all pathological changes observed in the asthmatic airways are adequately explained simply as a result of Th2-mediated processes. Contemporary thought holds that asthma is a complex immune disorder involving innate as well as adaptive immune responses, with the clinical heterogeneity of asthma perhaps a result of the different relative contribution of these two systems to the disease. Epidemiological studies show that exposure to certain environmental substances is strongly associated with the risk of developing asthma. The airway epithelium is first barrier to interact with, and respond to, environmental agents (pollution, viral infection, allergens), suggesting that it is a key player in the pathology of asthma. Epithelial cells play a key role in the regulation of tissue homeostasis by the modulation of numerous molecules, from antioxidants and lipid mediators to growth factors, cytokines, and chemokines. Additionally, the epithelium is also able to suppress mechanisms involved in, for example, inflammation in order to maintain homeostasis. An intrinsic alteration or defect in these regulation mechanisms compromises the epithelial barrier, and therefore, the barrier may be more prone to environmental substances and thus more likely to exhibit an asthmatic phenotype. In support of this, polymorphisms in a number of genes that are expressed in the bronchial epithelium have been linked to asthma susceptibility, while environmental factors may affect epigenetic mechanisms that can alter epithelial function and response to environmental insults. A detailed understanding of the regulatory role of the airway epithelium is required to develop new therapeutic strategies for asthma that not only address the symptoms but also the underlining pathogenic mechanism(s) and prevent airway remodelling.

CARMA3 Is Critical for the Initiation of Allergic Airway Inflammation

Innate immune responses to allergens by airway epithelial cells (AECs) help initiate and propagate the adaptive immune response associated with allergic airway inflammation in asthma. Activation of the transcription factor NF-κB in AECs by allergens or secondary mediators via G protein-coupled receptors (GPCRs) is an important component of this multifaceted inflammatory cascade. Members of the caspase recruitment domain family of proteins display tissue-specific expression and help mediate NF-κB activity in response to numerous stimuli. We have previously shown that caspase recruitment domain-containing membrane-associated guanylate kinase protein (CARMA)3 is specifically expressed in AECs and mediates NF-κB activation in these cells in response to stimulation with the GPCR agonist lysophosphatidic acid. In this study, we demonstrate that reduced levels of CARMA3 in normal human bronchial epithelial cells decreases the production of proasthmatic mediators in response to a panel of asthma-relevant GPCR ligands such as lysophosphatidic acid, adenosine triphosphate, and allergens that activate GPCRs such as Alternaria alternata and house dust mite. We then show that genetically modified mice with CARMA3-deficient AECs have reduced airway eosinophilia and proinflammatory cytokine production in a murine model of allergic airway inflammation. Additionally, we demonstrate that these mice have impaired dendritic cell maturation in the lung and that dendritic cells from mice with CARMA3-deficient AECs have impaired Ag processing. In conclusion, we show that AEC CARMA3 helps mediate allergic airway inflammation, and that CARMA3 is a critical signaling molecule bridging the innate and adaptive immune responses in the lung.

The role of the NLRP3 inflammasome in pulmonary diseases

Respiratory diseases and lung injuries are one of the leading causes of death in the world. One critical component of these diseases is exaggerated inflammatory response. The recently discovered inflammasome is believed to play a key role in inflammation. The inflammasome is an oligomer of intracellular proteins that, once activated by an insult or damage signal, produces mature cytokines from the interleukin-1 family that mediate an inflammatory response. Previous research has provided evidence that suggests the role of the inflammasome in the pathogenesis of many chronic respiratory diseases and acute lung injuries, such as transfusion-related acute lung injury, ventilator-induced lung injury, asthma, chronic obstructive pulmonary disease and pulmonary fibrosis. This article summarizes recent research on the inflammasome and reviews proposed molecular models of the role of the inflammasome in several prominent lung diseases and injuries.

The ectoenzyme E-NPP3 negatively regulates ATP-dependent chronic allergic responses by basophils and mast cells

Crosslinking of the immunoglobulin receptor FcεRI activates basophils and mast cells to induce immediate and chronic allergic inflammation. However, it remains unclear how the chronic allergic inflammation is regulated. Here, we showed that ecto-nucleotide pyrophosphatase-phosphodiesterase 3 (E-NPP3), also known as CD203c, rapidly induced by FcεRI crosslinking, negatively regulated chronic allergic inflammation. Basophil and mast cell numbers increased in Enpp3(-/-) mice with augmented serum ATP concentrations. Enpp3(-/-) mice were highly sensitive to chronic allergic pathologies, which was reduced by ATP blockade. FcεRI crosslinking induced ATP secretion from basophils and mast cells, and ATP activated both cells. ATP clearance was impaired in Enpp3(-/-) cells. Enpp3(-/-)P2rx7(-/-) mice showed decreased responses to FcεRI crosslinking. Thus, ATP released by FcεRI crosslinking stimulates basophils and mast cells for further activation causing allergic inflammation. E-NPP3 decreases ATP concentration and suppresses basophil and mast cell activity.

Comprehensive metabolomics identifies the alarmin uric acid as a critical signal for the induction of peanut allergy

BACKGROUND

Food allergy, in particular peanut allergy, is a growing concern in Western countries. The prevalence of allergy to peanut, which currently stands at 1.4%, nearly tripled between 1997 and 2008. Allergic sensitization is a particularly difficult process to study as it is clinically silent. We sought to identify key pathways and mediators critically involved in the induction of allergic sensitization to peanut.

METHODS

Comprehensive metabolomics analysis with liquid chromatography-mass spectrometry was used to detect metabolite changes in mice (C57BL/6) undergoing sensitization. Loss-of-function and gain-of-function studies were performed in mice subjected to two models of peanut sensitization and anaphylaxis that involved either oral or epicutaneous sensitization. Flow cytometric analyses on dendritic cells (DCs) in vitro and in vivo were used to investigate the mechanisms of immune activation.

RESULTS

Elevated levels of uric acid (UA) were detected in mice undergoing sensitization as well as in peanut-allergic children who were not challenged with peanut. In mice, the depletion of UA during sensitization prevented the development of peanut-specific immunoglobulins IgE and IgG1 as well as anaphylaxis while exogenous delivery of UA crystals (monosodium urate, MSU) restored the allergic phenotype. Monosodium urate enhanced CD86 and OX40L expression on DCs, independent of Toll-like receptors 2 and 4, the NLRP3 inflammasome, and IL-1β, via a PI3K signaling pathway.

CONCLUSION

Overproduction of the UA alarmin in the local microenvironment plays a critical role in the induction of peanut-allergic sensitization, likely due to its ability to activate DCs. These finding suggest that cellular damage or tissue injury may be an essential requisite for the development of allergic sensitization to foods.

Allergens and the airway epithelium response: gateway to allergic sensitization

Allergic sensitization to inhaled antigens is common but poorly understood. Although lung epithelial cells were initially merely regarded as a passive barrier impeding allergen penetrance, we now realize that they recognize allergens through expression of pattern recognition receptors and mount an innate immune response driven by activation of nuclear factor κB. On allergen recognition, epithelial cells release cytokines, such as IL-1, IL-25, IL-33, thymic stromal lymphopoietin, and GM-CSF, and endogenous danger signals, such as high-mobility group box 1, uric acid, and ATP, that activate the dendritic cell network and other innate immune cells, such as basophils and type 2 innate lymphoid cells. Different allergens stimulate different aspects of this general scheme, and common environmental risk factors for sensitization, such as cigarette smoke and diesel particle exposure, do so as well. All of this is influenced by genetic polymorphisms affecting epithelial pattern recognition, barrier function, and cytokine production. Therefore, epithelial cells are crucial in determining the outcome of allergen inhalation.

Mechanisms of epithelial wound detection

Efficient wound healing requires the coordinated responses of various cell types within an injured tissue. To react to the presence of a wound, cells have to first detect it. Judging from their initial biochemical and morphological responses, many cells including leukocytes, epithelial cells, and endothelial cells detect wounds from over hundreds of micrometers within seconds-to-minutes. Wound detection involves the conversion of an injury-induced homeostatic perturbation, such as cell lysis, an unconstrained epithelial edge, or permeability barrier breakdown, into a chemical or physical signal. The signal is spatially propagated through the tissue to synchronize protective responses of cells near the wound site and at a distance. This review summarizes the triggers and mechanisms of wound detection in animals.

The immunology of asthma

Asthma is a common disease that affects 300 million people worldwide. Given the large number of eosinophils in the airways of people with mild asthma, and verified by data from murine models, asthma was long considered the hallmark T helper type 2 (TH2) disease of the airways. It is now known that some asthmatic inflammation is neutrophilic, controlled by the TH17 subset of helper T cells, and that some eosinophilic inflammation is controlled by type 2 innate lymphoid cells (ILC2 cells) acting together with basophils. Here we discuss results from in-depth molecular studies of mouse models in light of the results from the first clinical trials targeting key cytokines in humans and describe the extraordinary heterogeneity of asthma.

Purinergic signaling modulates human visceral adipose inflammatory responses: implications in metabolically unhealthy obesity

Obesity is accompanied by chronic inflammation of VAT, which promotes metabolic changes, and purinergic signaling has a key role in a wide range of inflammatory diseases. Therefore, we addressed whether fat inflammation could be differentially modulated by this signaling pathway in the MUO and in individuals who remain MHO. Our results show that the necrotized VAT of both groups released greater levels of ATP compared with lean donors. Interestingly, MUO tissue SVCs showed up-regulation and engagement of the purinergic P2X7R. The extracellular ATP concentration is regulated by an enzymatic process, in which CD39 converts ATP and ADP into AMP, and CD73 converts AMP into adenosine. In VAT, the CD73 ectoenzyme was widely distributed in immune and nonimmune cells, whereas CD39 expression was restricted to immune CD45PAN⁺ SVCs. Although the MUO group expressed the highest levels of both ectoenzymes, no difference in ATP hydrolysis capacity was found between the groups. As expected, MUO exhibited the highest NLRP3 inflammasome expression and IL-1β production. MUO SVCs also displayed up-regulation of the A2AR, allowing extracellular adenosine to increase IL-1β local secretion. Additionally, we demonstrate that metabolic parameters and BMI are positively correlated with purinergic components in VAT. These findings indicate that purinergic signaling is a novel mechanism involved in the chronic inflammation of VAT underlying the metabolic changes in obesity. Finally, our study reveals a proinflammatory role for adenosine in sustaining IL-1β production in this tissue.

P2Y2R deficiency attenuates experimental autoimmune uveitis development

We aimed to study the role of the nucleotide receptor P2Y2R in the development of experimental autoimmune uveitis (EAU). EAU was induced in P2Y2+/+ and P2Y2-/- mice by immunization with IRBP peptide or by adoptive transfer of in vitro restimulated semi-purified IRBP-specific enriched T lymphocytes from spleens and lymph nodes isolated from native C57Bl/6 or P2Y2+/+ and P2Y2-/- immunized mice. Clinical and histological scores were used to grade disease severity. Splenocytes and lymph node cell phenotypes were analyzed using flow cytometry. Semi-purified lymphocytes and MACS-purified CD4+ T lymphocytes from P2Y2+/+ and P2Y2-/- immunized mice were tested for proliferation and cytokine secretion. Our data show that clinical and histological scores were significantly decreased in IRBP-immunized P2Y2-/- mice as in P2Y2-/- mice adoptively transfered with enriched T lymphocytes from C57Bl/6 IRBP-immunized mice. In parallel, naïve C57Bl/6 mice adoptively transferred with T lymphocytes from P2Y2-/- IRBP-immunized mice also showed significantly less disease. No differences in term of spleen and lymph node cell recruitment or phenotype appeared between P2Y2-/- and P2Y2+/+ immunized mice. However, once restimulated in vitro with IRBP, P2Y2-/- T cells proliferate less and secrete less cytokines than the P2Y2+/+ one. We further found that antigen-presenting cells of P2Y2-/- immunized mice were responsible for this proliferation defect. Together our data show that P2Y2-/- mice are less susceptible to mount an autoimmune response against IRBP. Those results are in accordance with the danger model, which makes a link between autoreactive lymphocyte activation, cell migration and the release of danger signals such as extracellular nucleotides.

Identification and characterization of vancomycin-resistant Enterococcus species frequently isolated from laboratory mice

To determine the prevalence of drug resistant bacteria colonizing laboratory mice, we isolated and characterized vancomycin-resistant Enterococcus species (VRE) from commercially available mice. A total of 24 VRE isolates were obtained from 19 of 21 mouse strains supplied by 4 commercial breeding companies. Of these, 19 isolates of E. gallinarum and 5 isolates of E. casseliflavus possessing the vanC1 and vanC2/3 genes intrinsically, exhibited intermediate resistance to vancomycin respectively. In addition, these isolates also exhibited diverse resistant patterns to erythromycin, tetracycline, and ciprofloxacin, whereas the use of antibiotics had not been undertaken in mouse strains tested in this study. Although 6 virulence-associated genes (ace, asa, cylA, efaA, esp, and gelE) and secretion of gelatinase and hemolysin were not detected in all isolates, 23 of 24 isolates including the isolates of E. casselifalvus secreted ATP into culture supernatants. Since secretion of ATP by bacteria resident in the intestinal tract modulates the local immune responses, the prevalence of ATP-secreting VRE in mice therefore needs to be considered in animal experiments that alter the gut microflora by use of antibiotics.

Real-time imaging of ATP release induced by mechanical stretch in human airway smooth muscle cells

Airway smooth muscle (ASM) cells within the airway walls are continually exposed to mechanical stimuli, and exhibit various functions in response to these mechanical stresses. ATP acts as an extracellular mediator in the airway. Moreover, extracellular ATP is considered to play an important role in the pathophysiology of asthma and chronic obstructive pulmonary disease. However, it is not known whether ASM cells are cellular sources of ATP secretion in the airway. We therefore investigated whether mechanical stretch induces ATP release from ASM cells. Mechanical stretch was applied to primary human ASM cells cultured on a silicone chamber coated with type I collagen using a stretching apparatus. Concentrations of ATP in cell culture supernatants measured by luciferin-luciferase bioluminescence were significantly elevated by cyclic stretch (12 and 20% strain). We further visualized the stretch-induced ATP release from the cells in real time using a luminescence imaging system, while acquiring differential interference contrast cell images with infrared optics. Immediately after a single uniaxial stretch for 1 second, strong ATP signals were produced by a certain population of cells and spread to surrounding spaces. The cyclic stretch-induced ATP release was significantly reduced by inhibitors of Ca(2+)-dependent vesicular exocytosis, 1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid tetraacetoxymethyl ester, monensin, N-ethylmaleimide, and bafilomycin. In contrast, the stretch-induced ATP release was not inhibited by a hemichannel blocker, carbenoxolone, or blockade of transient receptor potential vanilloid 4 by short interfering RNA transfection or ruthenium red. These findings reveal a novel property of ASM cells: mechanically induced ATP release may be a cellular source of ATP in the airway.