Substance P-induced airway hyperreactivity is mediated by neuronal M(2) receptor dysfunction

Control of myeloid cell functions by nociceptors

The immune system has evolved to protect the host from infectious agents, parasites, and tumor growth, and to ensure the maintenance of homeostasis. Similarly, the primary function of the somatosensory branch of the peripheral nervous system is to collect and interpret sensory information about the environment, allowing the organism to react to or avoid situations that could otherwise have deleterious effects. Consequently, a teleological argument can be made that it is of advantage for the two systems to cooperate and form an “integrated defense system” that benefits from the unique strengths of both subsystems. Indeed, nociceptors, sensory neurons that detect noxious stimuli and elicit the sensation of pain or itch, exhibit potent immunomodulatory capabilities. Depending on the context and the cellular identity of their communication partners, nociceptors can play both pro- or anti-inflammatory roles, promote tissue repair or aggravate inflammatory damage, improve resistance to pathogens or impair their clearance. In light of such variability, it is not surprising that the full extent of interactions between nociceptors and the immune system remains to be established. Nonetheless, the field of peripheral neuroimmunology is advancing at a rapid pace, and general rules that appear to govern the outcomes of such neuroimmune interactions are beginning to emerge. Thus, in this review, we summarize our current understanding of the interaction between nociceptors and, specifically, the myeloid cells of the innate immune system, while pointing out some of the outstanding questions and unresolved controversies in the field. We focus on such interactions within the densely innervated barrier tissues, which can serve as points of entry for infectious agents and, where known, highlight the molecular mechanisms underlying these interactions.

Unique Allergic Asthma Phenotypes in Offspring of House Dust Mite-exposed Mice

Asthma is a heterogeneous inflammatory airway disease that develops in response to a combination of genetic predisposition and environmental exposures. Patients with asthma are grouped into phenotypes with shared clinical features and biomarker profiles to help tailor specific therapies. However, factors driving development of specific phenotypes are poorly understood. Prenatal exposure to maternal asthma is a unique risk factor for childhood asthma. Here we tested whether maternal asthma skews asthma phenotypes in offspring. We compared airway hyperreactivity and inflammatory and neurotrophin lung signatures before and after allergen challenge in offspring born to mice exposed to house dust mite (HDM) or vehicle during pregnancy. Maternal HDM exposure potentiated offspring responses to HDM allergen, significantly increasing both airway hyperreactivity and airway eosinophilia compared with control mice. Maternal HDM exposure broadly skewed the offspring cytokine response from a classic allergen-induced T-helper cell type 2 (Th2)-predominant signature in HDM-treated offspring of vehicle-exposed mothers, toward a mixed Th17/Th1 phenotype in HDM-treated offspring of HDM-exposed mothers. Morphologic analysis determined that maternal HDM exposure also increased airway epithelial sensory nerve density and induced distinct neurotrophin signatures to support airway hyperinnervation. Our results demonstrate that maternal allergen exposure alters fetal lung development and promotes a unique inflammatory phenotype at baseline and in response to allergen that persists into adulthood.

Eosinophils in the Gastrointestinal Tract: Key Contributors to Neuro-Immune Crosstalk and Potential Implications in Disorders of Brain-Gut Interaction

Eosinophils are innate immune granulocytes actively involved in defensive responses and in local and systemic inflammatory processes. Beyond these effector roles, eosinophils are fundamental to maintaining homeostasis in the tissues they reside. Gastrointestinal eosinophils modulate barrier function and mucosal immunity and promote tissue development through their direct communication with almost every cellular component. This is possible thanks to the variety of receptors they express and the bioactive molecules they store and release, including cytotoxic proteins, cytokines, growth factors, and neuropeptides and neurotrophines. A growing body of evidence points to the eosinophil as a key neuro-immune player in the regulation of gastrointestinal function, with potential implications in pathophysiological processes. Eosinophil–neuron interactions are facilitated by chemotaxis and adhesion molecules, and the mediators released may have excitatory or inhibitory effects on each cell type, with physiological consequences dependent on the type of innervation involved. Of special interest are the disorders of the brain–gut interaction (DBGIs), mainly functional dyspepsia (FD) and irritable bowel syndrome (IBS), in which mucosal eosinophilia and eosinophil activation have been identified. In this review, we summarize the main roles of gastrointestinal eosinophils in supporting gut homeostasis and the evidence available on eosinophil–neuron interactions to bring new insights that support the fundamental role of this neuro-immune crosstalk in maintaining gut health and contributing to the pathophysiology of DBGIs.

IL-5 Exposure In Utero Increases Lung Nerve Density and Airway Reactivity in Adult Offspring

Asthma is characterized by airway hyperreactivity and inflammation. In the lungs, parasympathetic and sensory nerves control airway tone and induce bronchoconstriction. Dysregulation of these nerves results in airway hyperreactivity. Humans with eosinophilic asthma have significantly increased sensory nerve density in airway epithelium, suggesting that type 2 cytokines and inflammatory cells promote nerve growth. Similarly, mice with congenital airway eosinophilia also have airway hyperreactivity and increased airway sensory nerve density. Here, we tested whether this occurs during development. We show that transgenic mice that overexpress IL-5, a cytokine required for eosinophil hematopoiesis, give birth to wild-type offspring that have significantly increased airway epithelial nerve density and airway hyperreactivity that persists into adulthood. These effects are caused by in utero exposure to maternal IL-5 and resulting fetal eosinophilia. Allergen exposure of these adult wild-type offspring results in severe airway hyperreactivity, leading to fatal reflex bronchoconstriction. Our results demonstrate that fetal exposure to IL-5 is a developmental origin of airway hyperreactivity, mediated by hyperinnervation of airway epithelium.

Mechanisms of organophosphorus pesticide toxicity in the context of airway hyperreactivity and asthma

Numerous epidemiologic studies have identified an association between occupational exposures to organophosphorus pesticides (OPs) and asthma or asthmatic symptoms in adults. Emerging epidemiologic data suggest that environmentally relevant levels of OPs may also be linked to respiratory dysfunction in the general population and that in utero and/or early life exposures to environmental OPs may increase risk for childhood asthma. In support of a causal link between OPs and asthma, experimental evidence demonstrates that occupationally and environmentally relevant OP exposures induce bronchospasm and airway hyperreactivity in preclinical models. Mechanistic studies have identified blockade of autoinhibitory M2 muscarinic receptors on parasympathetic nerves that innervate airway smooth muscle as one mechanism by which OPs induce airway hyperreactivity, but significant questions remain regarding the mechanism(s) by which OPs cause neuronal M2 receptor dysfunction and, more generally, how OPs cause persistent asthma, especially after developmental exposures. The goals of this review are to 1) summarize current understanding of OPs in asthma; 2) discuss mechanisms of OP neurotoxicity and immunotoxicity that warrant consideration in the context of OP-induced airway hyperreactivity and asthma, specifically, inflammatory responses, oxidative stress, neural plasticity, and neurogenic inflammation; and 3) identify critical data gaps that need to be addressed in order to better protect adults and children against the harmful respiratory effects of low-level OP exposures.

Eosinophil and airway nerve interactions in asthma

Airway eosinophils are increased in asthma and are especially abundant around airway nerves. Nerves control bronchoconstiction and in asthma, airway hyperreactivity (where airways contract excessively to inhaled stimuli) develops when eosinophils alter both parasympathetic and sensory nerve function. Eosinophils release major basic protein, which is an antagonist of inhibitory M₂ muscarinic receptors on parasympathetic nerves. Loss of M₂ receptor inhibition potentiates parasympathetic nerve-mediated bronchoconstriction. Eosinophils also increase sensory nerve responsiveness by lowering neurons' activation threshold, stimulating nerve growth, and altering neuropeptide expression. Since sensory nerves activate parasympathetic nerves via a central neuronal reflex, eosinophils' effects on both sensory and parasympathetic nerves potentiate bronchoconstriction. This review explores recent insights into mechanisms and effects of eosinophil and airway nerve interactions in asthma.

Colonisation of Irish patients with chronic obstructive pulmonary disease by Streptococcus pneumoniae and analysis of the pneumococcal vaccine coverage: a non-interventional, observational, prospective cohort study

OBJECTIVES

To characterise the pattern of colonisation and serotypes of Streptococcus pneumoniae among patients with chronic obstructive pulmonary disease (COPD) who currently receive the 23-valent pneumococcal polysaccharide vaccine (PPV-23) according to vaccination status, use of antibiotics and steroids. To investigate the prevalence of PPV-23 and 13-valent pneumococcal conjugate vaccine (PCV-13) serotypes within the study cohort.

DESIGN

A non-interventional, observational, prospective cohort study with a 12 -month follow-up period inclusive of quarterly study visits.

SETTING

Beaumont Hospital and The Royal College of Surgeons in Ireland Clinical Research Centre, Dublin, Ireland.

PARTICIPANTS

Patients with an established diagnosis of COPD attending a tertiary medical centre.

PRIMARY OUTCOME MEASURE

Colonisation rate of S. pneumoniae in patients with COPD and characterisation of serotypes of S. pneumoniae with correlation to currently available pneumococcal vaccines. Sputum and oropharyngeal swab samples were collected for the isolation of S. pneumoniae.

SECONDARY OUTCOME MEASURE

Seasonality of colonisation of S. pneumoniae and its relationship with the incidence of exacerbations of COPD.

RESULTS

S. pneumoniae was detected in 16 of 417 samples, a colonisation incident rate of 3.8% and in 11 of 133 (8%) patients at least once during the study. The majority of S. pneumoniae isolates were identified in spring and were non-vaccine serotypes for either the PPV-23 or PCV-13 (63%). The colonisation incident rate of S. pneumoniae fluctuated over the four seasons with a peak of 6.6% in spring and the lowest rate of 2.2% occurring during winter. Antibiotic use was highest during periods of low colonisation.

CONCLUSIONS

There is seasonal variation in S. pneumoniae colonisation among patients with COPD which may reflect antibiotic use in autumn and winter. The predominance of non-vaccine types suggests that PCV-13 may have limited impact among patients with COPD in Ireland who currently receive PPV-23.

TRIAL REGISTRATION NUMBER

NCT02535546; post-results.

In patients with severe uncontrolled asthma, does knowledge of adherence and inhaler technique using electronic monitoring improve clinical decision making? A protocol for a randomised controlled trial

INTRODUCTION

Many patients with asthma remain poorly controlled despite the use of inhaled corticosteroids and long-acting beta agonists. Poor control may arise from inadequate adherence, incorrect inhaler technique or because the condition is refractory. Without having an objective assessment of adherence, clinicians may inadvertently add extra medication instead of addressing adherence. This study aims to assess if incorporating objectively recorded adherence from the Inhaler Compliance Assessment (INCA) device and lung function into clinical decision making provides more cost-effective prescribing and improves outcomes.

METHODS AND ANALYSIS

This prospective, randomised, multicentre study will compare the impact of using information on adherence to influence asthma treatment. Patients with severe uncontrolled asthma will be included. Data on adherence, inhaler technique and electronically recorded peak expiratory flow rate will be used to promote adherence and guide a clinical decision protocol to guide management in the active group. The control group will receive standard inhaler and adherence education. Medications will be adjusted using a protocol based on Global Initiativefor Asthma (GINA) recommendations. The primary outcome is the between-group difference in the proportion of patients who have refractory disease and are prescribed appropriate medications at the end of 32 weeks. A co-primary outcome is the difference between groups in the rate of adherence to salmeterol/fluticasone inhaler over the last 12 weeks. Secondary outcomes include changes in symptoms, lung function, type-2 cytokine biomarkers and clinical outcomes between both groups. Cost-effectiveness and cost-utility analyses of the INCA device intervention will be performed. The economic impact of a national implementation of the INCA-SUN programme will be evaluated.

ETHICS AND DISSEMINATION

The results of the study will be published as a manuscript in peer-reviewed journals. The study has been approved by the ethics committees in the five participating hospitals.

TRIAL REGISTRATION

NCT02307669; Pre-results.

Targeting patients with asthma for omalizumab therapy: choosing the right patient to get the best value for money

The asthma syndrome has many manifestations, termed phenotypes, that arise by specific cellular and molecular mechanisms, termed endotypes. Understanding an individual's asthma phenotype helps clinicians make rational therapeutic decisions while the understanding of endotypes has led to the development of specific precision medications. Allergic asthma is an example of an asthma phenotype and omalizumab, a monoclonal antibody that neutralizes serum immunoglobulin (Ig)E, is a specific targeted treatment which was developed as a result of an understanding of the endotype of allergic asthma. Omalizumab has been widely used in clinical practice in Europe for over a decade as an add-on therapy to treat patients who have severe refractory allergic asthma. Over this period, many centres have reported their experience with omalizumab as an add-on therapy in patients with severe asthma. These 'real world' clinical effectiveness studies have confirmed the benefits, cost-effectiveness and clinical utility of this medication. Combining the outcomes of both sources of research has yielded important insights that may benefit patients with severe asthma, clinicians who treat them, as well as the funding agencies that reimburse the cost of this medication. The purpose of this review is to describe how to identify and evaluate a patient with asthma for whom treatment with omalizumab may be of clinical and cost-effective benefit. The assessment and investigations used to confirm allergic asthma, the objective assessment of adherence to asthma therapy and the expected benefits of add-on omalizumab treatment are described.

Eosinophil peroxidase activates cells by HER2 receptor engagement and β1-integrin clustering with downstream MAPK cell signaling

Eosinophils account for 1–3% of peripheral blood leukocytes and accumulate at sites of allergic inflammation, where they play a pathogenic role. Studies have shown that treatment with mepolizumab (an anti-IL-5 monoclonal antibody) is beneficial to patients with severe eosinophilic asthma, however, the mechanism of precisely how eosinophils mediate these pathogenic effects is uncertain. Eosinophils contain several cationic granule proteins, including Eosinophil Peroxidase (EPO). The main significance of this work is the discovery of EPO as a novel ligand for the HER2 receptor. Following HER2 activation, EPO induces activation of FAK and subsequent activation of β1-integrin, via inside-out signaling. This complex results in downstream activation of ERK1/2 and a sustained up regulation of both MUC4 and the HER2 receptor. These data identify a receptor for one of the eosinophil granule proteins and demonstrate a potential explanation of the proliferative effects of eosinophils.

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Eosinophil peroxidase (EPO) is confirmed as a ligand for the HER2 receptor.

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EPO activation of HER2 leads to activation of FAK, ERK and β1 integrin.

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EPO induces a sustained upregulation of MUC4 and HER2.

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Possible mechanism for the proliferative effects of eosinophils is uncovered.

Activated eosinophils in association with enteric nerves in inflammatory bowel disease

Enteric neural dysfunction leads to increased mucous production and dysmotility in inflammatory bowel disease (IBD). Prior studies have shown that tissue eosinophilia is related to disease activity. We hypothesized that interactions between eosinophils and nerves contribute to neural dysfunction in IBD. Tissue from patients with intractable IBD, endoscopic biopsies from patients with steroid responsive IBD, both when active and quiescent, and control tissue were studied. Immunohistochemical studies showed that eosinophils localize to nerves in the mucosal layer of patients with Crohn’s disease (CD) (p<0.001) and ulcerative colitis (UC), (p<0.01). Eosinophils localized to substance P and choline acetyltransferase (ChAT) immunostained nerves. Real time PCR of laser capture micro-dissected enteric ganglia demonstrated Intercellular Adhesion Molecule 1 (ICAM-1) mRNA was increased 7-fold in UC (n = 4), (p = 0.03), and 10-fold in CD (n = 3), (p = 0.05). Compared with controls, eotaxin-3 (CCL-26) mRNA was increased 9-fold in UC (p = 0.04) and 15-fold in CD (p = 0.06). Eosinophil numbers correlated with disease activity, while deposition of major basic protein (MBP) and eosinophil Transforming Growth Factor β -1 (TGFβ-1) expression were seen in therapeutically responsive disease. These data indicate a significant localization of eosinophils to nerves in IBD, mediated through neurally expressed ICAM-1 and eotaxin-3. This cell/neural interaction may influence the function of nerves and contribute to symptoms in IBD.

Cellular bases for interactions between immunocytes and enteroendocrine cells in the intestinal mucosal barrier of rhesus macaques

The roles of the interactions between nervous, endocrine, and immune systems have been well established in human health and diseases. At present, little is known about the cellular bases for neural-endocrine-immune networks in the gastrointestinal mucosa. In the current study, duodenum, jejunum, ileum, cecum, colon, and rectum autopsies from 15 rhesus macaques and endoscopic duodenal biopsies from 12 rhesus macaques were collected, and the spatial relationships between the endocrine cells and immune cells in the intestinal mucosa were examined by transmission electron microscopy. Eight types of enteroendocrine cells similar to human enterochromaffin cells (EC), D1, G, I, K, L, N, and S cells were found to lie within a one-cell-size distance from immunocytes, in particular the eosinophils in the epithelia or lamina propria. Close apposition of large areas of plasma membranes between many types of enteroendocrine cells and immunocytes, especially between EC, K, S cells and eosinophils, were observed in the epithelia for the first time. These data indicate that complex interactions occur between diverse types of enteroendocrine cells and various immune cells through paracrine mechanisms or via mechanisms dependent on cell-to-cell contact; such interactions might play key roles in maintaining the gut mucosal barrier integrity of rhesus macaques.

Three days after a single exposure to ozone, the mechanism of airway hyperreactivity is dependent on substance P and nerve growth factor

Ozone causes persistent airway hyperreactivity in humans and animals. One day after ozone exposure, airway hyperreactivity is mediated by release of eosinophil major basic protein that inhibits neuronal M(2) muscarinic receptors, resulting in increased acetylcholine release and increased smooth muscle contraction in guinea pigs. Three days after ozone, IL-1β, not eosinophils, mediates ozone-induced airway hyperreactivity, but the mechanism at this time point is largely unknown. IL-1β increases NGF and the tachykinin substance P, both of which are involved in neural plasticity. These experiments were designed to test whether there is a role for NGF and tachykinins in sustained airway hyperreactivity following a single ozone exposure. Guinea pigs were exposed to filtered air or ozone (2 parts per million, 4 h). In anesthetized and vagotomized animals, ozone potentiated vagally mediated airway hyperreactivity 24 h later, an effect that was sustained over 3 days. Pretreatment with antibody to NGF completely prevented ozone-induced airway hyperreactivity 3 days, but not 1 day, after ozone and significantly reduced the number of substance P-positive airway nerve bundles. Three days after ozone, NK(1) and NK(2) receptor antagonists also blocked this sustained hyperreactivity. Although the effect of inhibiting NK(2) receptors was independent of ozone, the NK(1) receptor antagonist selectively blocked vagal hyperreactivity 3 days after ozone. These data confirm mechanisms of ozone-induced airway hyperreactivity change over time and demonstrate 3 days after ozone that there is an NGF-mediated role for substance P, or another NK(1) receptor agonist, that enhances acetylcholine release and was not present 1 day after ozone.

Eosinophils in innate immunity: an evolving story

Eosinophils are innate immune leukocytes found in relatively low numbers within the blood. Terminal effector functions of eosinophils, deriving from their capacity to release their content of tissue-destructive cationic proteins, have historically been considered primary effector mechanisms against specific parasites, and are likewise implicated in tissue damage accompanying allergic responses such as asthma. However, the past decade has seen dramatic advancements in the field of eosinophil immunobiology, revealing eosinophils to also be key participants in many other facets of innate immunity, from bridging innate and adaptive immune responses to orchestrating tissue remodeling events. Here, we review the multifaceted functions of eosinophils in innate immunity that are currently known, and discuss new avenues in this evolving story.

Granulocytes: effector cells or immunomodulators in the immune response to helminth infection?

Granulocytes are effector cells in defence against helminth infections. We review the current evidence for the role of granulocytes in protective immunity against different helminth infections and note that for each parasite species the role of granulocytes as effector cells can vary. Emerging evidence also points to granulocytes as immunomodulatory cells able to produce many cytokines, chemokines and modulatory factors which can bias the immune response in a particular direction. Thus, the role of granulocytes in an immunomodulatory context is discussed including the most recent data that points to an important role for basophils under this guise.

Neural control of airway inflammation

Abnormal neural function contributes to the pathogenesis of airway disease. In addition to affecting airway physiology, the nerves produce and release inflammatory mediators, contributing to the recruitment and activation of leukocytes. Activated inflammatory cells in turn affect the function of airway nerves, changing the production and release of neurotransmitters. Cross-talk between airway nerves and leukocytes helps to maintain chronic inflammation and accentuates neural control of the airways.

Anti-inflammatory and immunosuppressive effects of the enaminone E121

Asthma is a chronic inflammatory disease of the airways. The treatment of asthma is far from optimal and hence the need for novel therapeutic agents exists. The purpose of this study was to assess the anti-asthma effects of an enaminone, E121, and also its effects on human peripheral blood mononuclear cell proliferation and cytokine release. The effects of E121 were assessed in an ovalbumin-induced model of airway inflammation and airway hyperresponsiveness. In addition, the effects of E121 on phytohemagglutinin (PHA), anti-CD3 monoclonal antibody and lipopolysaccharide (LPS)-induced human peripheral blood mononuclear cell proliferation and cytokine release, respectively, were assessed. Treatment of mice with E121 significantly decreased the ovalbumin-induced increase in airway total cell influx and eosinophil infiltration and this was associated with an inhibition of ovalbumin-induced airway hyperresponsiveness. Moreover, E121 reduced PHA and anti-CD3-induced human peripheral blood mononuclear cell proliferation in vitro. E121 also inhibited PHA, anti-CD3 monoclonal antibody and LPS-induced cytokine release from human peripheral blood mononuclear cell cultures. These findings indicate that E121 exhibits anti-inflammatory and immunosuppressive activities.

Attenuated methacholine airway response following repeat testing in a murine model of allergic airways disease

A progressive attenuation of airway reactivity to methacholine is observed in normal individuals with successive bronchial provocation testing. The absence of this attenuation in asthma is thought to be due airway inflammation. The authors investigated this phenomenon in a mouse model of allergic airways disease. Repeated measurements of airway response were carried out in mice sensitized/challenged with ovalbumin or saline, and in untreated mice. Saline-treated and untreated mice showed reduced airway reactivity following repeated testing. This was also observed in ovalbumin-treated mice in the second and third tests compared to the previous test (P < .05). This attenuation was not associated with airway inflammation, which remained high in the ovalbumin group. The results suggest that attenuation of airway reactivity with repeated methacholine challenge is due to factors other than airway inflammation.

Muscarinic receptors in the ocular surface

PURPOSE OF REVIEW

A wide distribution of the eye's muscarinic receptor system has been found and several roles for the muscarinic system in the eye proposed, although functional consequences of muscarinic receptor activation are not always fully characterized. The present paper reviews current knowledge about the presence of muscarinic receptors in the ocular surface and the implication of alterations on their expression and/or functioning in eye diseases.

RECENT FINDINGS

Several authors have described alterations in muscarinic receptor subtype expression in the eye under pathological conditions. In conjunctiva of vernal keratoconjunctivitis patients, the expression of muscarinic receptor subtypes is altered in both the epithelium and stroma. Under proinflammatory conditions, M2-muscarinic receptor expression is upregulated in conjunctival epithelial cells in vitro. M3-muscarinic receptor altered distribution has been found in the lacrimal gland of NOD mice.

SUMMARY

The cholinergic muscarinic system plays diverse roles. Alteration in the expression and/or functioning of muscarinic receptors may be implicated in the etiopathogenesis of some ocular diseases. Their pharmacological regulation may therefore have therapeutic value. Knowledge of the specific receptor subtypes expressed in each tissue may help to avoid some undesired secondary side effects in some cases when muscarinic agonists or antagonists are used.

The role of the conjunctival epithelium in ocular allergy

PURPOSE OF REVIEW

The epithelium of target organs is playing an increasing role in allergy. Several studies have shown that epithelial cells participate actively in inflammatory processes. This review will focus on recent advances in the role of conjunctival epithelium in allergy as a potential target for therapeutic interventions.

RECENT FINDINGS

Several studies have already shown the involvement of ocular surface epithelial cells in allergic inflammatory diseases, because they are able to produce and secrete cytokines and chemokines upon stimulation. They also express adhesion molecules as well as receptors for several substances implicated in inflammation. Some studies have also shown that conjunctival epithelial cells express co-stimulatory molecules when they interact with activated T cells, adding more evidence to the important role that epithelial cells play in the pathogenesis of ocular inflammatory diseases. Recent reports have also demonstrated that during inflammatory conditions, conjunctival epithelial cells show an altered expression of their neuroreceptors, suggesting that a modulation of neural regulation may be of therapeutic value.

SUMMARY

The ocular surface epithelium is not just a simple physical barrier to the entrance of foreign bodies. It participates in the allergic inflammatory process by being influenced by inflammatory molecules, and by secreting inflammatory cytokines and chemokines. Moreover, the epithelium not only actively participates in the inflammation process but can also initiate it. This relevant spectrum of actions makes epithelium an attractive target for therapeutic interventions.

Neurotrophins and neurotrophin receptors in allergic asthma

The neurotrophins nerve growth factor, brain-derived neurotrophic factor, neurotrophin-3 (NT-3) and NT-4 play a pivotal role in the development of the nervous system. Despite their well-known effects on neurons, elevated neurotrophin concentrations have been observed under pathological conditions in sera of patients with inflammatory disorders. Patients with asthma feature both airway inflammation and an abnormal airway reactivity to many unspecific stimuli, referred to as airway hyperresponsiveness, which is, at least partly, neuronally controlled. Interestingly, these patients show increased levels of neurotrophins in the blood as well as locally in the lung. It has been demonstrated that neurotrophin release from immune cells is triggered by allergen contact. The presence of neurotrophins and the neurotrophin receptors p75 (p75NTR), tyrosine kinase A (TrkA), TrkB and TrkC have been described in several immune cells. There is strong evidence for an involvement of neurotrophins in regulation of hematopoiesis and, in addition, in modulation of immune cell function in mature cells circulating in blood or resting in lymphatic organs and peripheral tissues. The aim of this review is to demonstrate possible roles of neurotrophins during an allergic reaction in consideration of the temporospatial compartimentalization.

Stress enhances airway reactivity and airway inflammation in an animal model of allergic bronchial asthma

OBJECTIVE

Despite the long-standing clinical assumption that stress and asthma morbidity are associated, convincing experimental evidence on mechanisms has been unavailable. A wide range of immunological, endocrinological, and neuronal pathways are known to mediate and modulate a systemic stress response. Interestingly, most of these mediators play a crucial role in initiating and perpetuating symptoms associated with bronchial asthma. To explore potential mechanisms linking stress to asthma exacerbation we developed an animal model that combines allergic airway inflammation and exposure to stress.

METHODS

CBA/J mice were sensitized by intraperitoneal injection of ovalbumin (OVA) and challenged with OVA aerosol via the airways. Additionally, some mice were stressed by exposure to an ultrasonic stressor. Airway hyperreactivity (AHR) was measured in vitro by electric field stimulation (EFS) of tracheal smooth muscle elements. Bronchoalveolar lavage fluid (BAL) was obtained and cell numbers determined. Cytokine levels of IL-4, IL-5, and IFN-gamma in BAL were determined by ELISA.

RESULTS

Our findings demonstrate that exogenously applied stress dramatically enhances airway reactivity in OVA-sensitized and challenged mice. Further, stress significantly increases allergen-induced airway inflammation identified by increased leukocyte (ie, eosinophil) numbers in bronchoalveolar lavage fluids.

CONCLUSIONS

We found further evidence that stress can indeed exacerbate airway hyperreactivity and airway inflammation in an animal model of allergic bronchial asthma and now introduce a novel murine model to identify stress-triggered pathways, including mediators as neurohormones, neuropeptides, and markers of inflammation.

Muscarinic acetylcholine receptors and airway diseases

Parasympathetic nerves provide the dominant autonomic innervation of the airways. Release of acetylcholine from parasympathetic nerves activates postjunctional muscarinic receptors present on airway smooth muscle, submucosal glands, and blood vessels to cause bronchoconstriction, mucus secretion, and vasodilatation, respectively. Acetylcholine also feeds back onto prejunctional muscarinic receptors to enhance or inhibit further acetylcholine release. In asthma and chronic obstructive pulmonary disease, bronchoconstriction and mucus secretion is increased and the airways are hyperresponsive to contractile agents. These changes are due to increased parasympathetic nerve activity. The number and function of postjunctional muscarinic receptors in the airways are unchanged in animal models of asthma. Rather, it is the supply of acetylcholine to the postjunctional cells (smooth muscle and submucosal gland) that is increased. The increase in acetylcholine release occurs because prejunctional, inhibitory M(2) muscarinic receptors on the parasympathetic nerves are dysfunctional. M(2) muscarinic receptor dysfunction and subsequent airway hyperreactivity have been demonstrated to occur in animals in response to a variety of triggers, including antigen challenge, virus infection, ozone exposure, and vitamin A deficiency. In humans, there is evidence that loss of M(2) muscarinic receptor function is related to asthma. The mechanisms by which neuronal M(2) muscarinic receptor function is lost and its relevance to human airway disease are discussed in this review.

An in vivo guinea pig preparation for studying the autonomic regulation of airway smooth muscle tone

The autonomic nervous system plays a primary role in regulating airway smooth muscle tone. Here, we describe the development of an in vivo guinea pig model that permits systematic studies of the autonomic control of airway smooth muscle. The model is based on preparations previously described and utilizes measurements of isometric tension in a perfused segment of extrathoracic guinea pig trachea in situ. It has the advantage that the autonomic innervation to the tracheal segment under study can be physiologically or pharmacologically isolated and studied independently from other mechanisms regulating airway smooth muscle tone. Initial experiments were conducted to optimize model conditions. Subsequent experiments were designed to highlight the usefulness of this preparation for studying parasympathetic regulation of airway caliber. The results of the study demonstrate the utility of this model for future studies into the neural regulation of bronchomotor tone and the mechanisms of airway obstruction and hyperreactivity associated with disease.

Tachykinins and neuro-immune interactions in asthma

Excitatory non-adrenergic-non-cholinergic neuropeptides, such as the tachykinins substance P and neurokinin A, and its receptors are present in human and animal airways. Tachykinins are biologically active at extremely low concentrations. These peptides can cause potent inflammatory effects and can affect airway function in a way that resembles features of asthma. Local release of tachykinins affects blood vessels (vasodilatation and increased vascular permeability) and bronchial smooth muscle (bronchoconstrition and hyperresponsiveness). Neuropeptide research has revealed that tachykinins also play an important modulatory role in immune reactions. Tachykinins stimulate immune cells, such as mast cells, lymphocytes, and macrophages and are chemotactic for neutrophils and eosinophils. Vice versa, a range of immune cell mediators can also induce the release of tachykinins from excitatory NANC nerve endings in the airways. In the last 20 years, significant advances have been made in investigations of the interaction between immune cells and nervous systems in chronic inflammatory diseases such as asthma.

Effects of dexamethasone on antigen-induced airway eosinophilia and M(2) receptor dysfunction

In antigen-challenged guinea pigs, airway hyperreactivity is due to recruitment of eosinophils to the airway nerves and dysfunction of M(2) muscarinic receptors. M(2) receptor dysfunction is caused by eosinophil major basic protein, which is an allosteric antagonist at the receptor. Because glucocorticoids inhibit airway hyperreactivity in humans and in animal models of asthma, we tested whether dexamethasone treatment (6 microg. kg(-)(1). d(-)(1) for 3 d, intraperitoneal) before antigen challenge prevents M(2) receptor dysfunction and airway hyperreactivity. Guinea pigs were sensitized to ovalbumin via intraperitoneal injections, and were challenged with ovalbumin via inhalation. Twenty-four hours later, hyperreactivity and M(2) receptor function were tested. Antigen-challenged animals were hyperreactive to vagal stimulation, and demonstrated loss of M(2) receptor function. Dexamethasone pretreatment prevented hyperreactivity and M(2) receptor dysfunction in antigen-challenged guinea pigs. Antigen challenge resulted in recruitment of eosinophils to the airways and to the airway nerves. Dexamethasone prevented recruitment of eosinophils to the airway nerves but did not affect total eosinophil influx into the airways. These results demonstrate that dexamethasone prevents antigen-induced hyperreactivity by protecting neuronal M(2) muscarinic receptors from antagonism by eosinophil major basic protein, and this protective mechanism appears to be by specifically inhibiting eosinophil recruitment to the airway nerves.

Tachykinin-induced bronchoconstriction in sheep is NK-1 receptor mediated and exhibits tachyphylaxis

OBJECTIVE

Tachykinins are mediators of airway hyper-reactivity and inflammation. There is in vitro evidence that ovine responses to tachykinins correlate closely to human responses. This study was designed to characterize the effect of intravenously administered tachykinins on sheep lung resistance in vivo to determine the effect of dose timing on reproducibility of responses and the induction of tachyphylaxis. We then used this information to help further characterize the response with several pharmacological agents.

METHODOLOGY

Substance P (SP) was administered by infusion to conscious merino ewes and lung resistance (RL) was measured. Infusions were given at 30, 60, 120 min and 24 h intervals. The effect of various agents on the response to SP was then assessed.

RESULTS

Substance P led to a transient increase in RL, mean (+/- SEM) 754.8 (+/- 139)% of baseline, with marked tachyphylaxis at 30, 60 and 120 min. Phosphoramidon increased the peak response to 1151.5 +/- 196%. Atropine and CP 96 345 abolished the response to SP, while indomethacin, sodium cromoglycate and pyrilamine had no significant effect. Substance P had a greater effect on RL than did neurokinin A.

CONCLUSIONS

Substance P increases RL in sheep via a cholinergic mechanism which is mediated by NK-1 receptors, and is subject to tachyphylaxis. These findings have implications for the design of studies using the ovine model in the evaluation of tachykinin antagonists as potential therapeutic agents.

Mechanisms of allergic rhinitis

The pathogenesis of allergic rhinitis can be better appreciated by understanding the numerous protective mechanisms available for mucosal defense. The system of TH2 lymphocytes, IgE production, mast cell degranulation, eosinophil infiltration, and resident cell responses are central to our understanding and treatment of allergic rhinitis. Histamine remains preeminent in causing the cardinal symptoms of the immediate allergic reaction: itching, watery discharge, and nasal swelling. Recruitment and activation mechanisms responsible for the late-phase allergic response are also reviewed.

Eosinophil recruitment to the airway nerves

Increased vagal reflexes contribute to bronchoconstriction in asthma. Antigen challenge of sensitized animals induces vagal hyperresponsiveness. This review will discuss the evidence that eosinophils increase release of acetylcholine from the parasympathetic nerves. After antigen challenge, eosinophils are actively recruited to the airway nerves, possibly through expression of chemotactic substances and adhesion molecules by the nerves. Tachykinins acting on neurokinin 1 receptors activate the eosinophils. Activated eosinophils release eosinophil major basic protein (MBP), which is an endogenous antagonist for M2 muscarinic receptors. The M2 muscarinic receptors on the parasympathetic nerves in the lungs normally inhibit release of acetylcholine. When M2 receptors are blocked by MBP, acetylcholine release is increased, resulting in hyperresponsiveness. Neutralization of MBP with polyanionic substances restores M2 receptor function and eliminates hyperresponsiveness. Antibodies to MBP prevent M2 receptor dysfunction and hyperresponsiveness, as do antibodies to the adhesion molecule very late antigen 4, which prevent eosinophil migration. A low dose of dexamethasone, which does not affect total eosinophil influx into the lungs and airways, prevents eosinophils from clustering around the nerves and prevents antigen-induced M2 dysfunction and hyperresponsiveness. Furthermore, animal studies show that viral infections, which are important precipitants of asthma attacks, and exposure to air pollutants such as ozone can also activate airway eosinophils, leading to a chain of events similar to that seen after antigen challenge. Finally, a similar clustering of eosinophils around airway nerves, as well as release of MBP onto the nerves, is seen in fatal asthma, suggesting that similar mechanisms may be involved in human airway hyperresponsiveness.