Airway expression of calcitonin gene-related peptide in T-cell peptide-induced late asthmatic reactions in atopics

Neuroimmune interplay during type 2 inflammation: Symptoms, mechanisms, and therapeutic targets in atopic diseases

Type 2 inflammation is characterized by overexpression and heightened activity of type 2 cytokines, mediators, and cells that drive neuroimmune activation and sensitization to previously subthreshold stimuli. The consequences of altered neuroimmune activity differ by tissue type and disease; they include skin inflammation, sensitization to pruritogens, and itch amplification in atopic dermatitis and prurigo nodularis; airway inflammation and/or hyperresponsiveness, loss of expiratory volume, airflow obstruction and increased mucus production in asthma; loss of sense of smell in chronic rhinosinusitis with nasal polyps; and dysphagia in eosinophilic esophagitis. We describe the neuroimmune interactions that underlie the various sensory and autonomic pathologies in type 2 inflammatory diseases and present recent advances in targeted treatment approaches to reduce type 2 inflammation and its associated symptoms in these diseases. Further research is needed to better understand the neuroimmune mechanisms that underlie chronic, sustained inflammation and its related sensory pathologies in diseases associated with type 2 inflammation.

Navigating the blurred path of mixed neuroimmune signaling

Evolution has created complex mechanisms to sense environmental danger and protect tissues, with the nervous and immune systems playing pivotal roles. These systems work together, coordinating local and systemic reflexes to restore homeostasis in response to tissue injury and infection. By sharing receptors and ligands, they influence the pathogenesis of various diseases. Recently, a less-explored aspect of neuroimmune communication has emerged: the release of neuropeptides from immune cells and cytokines/chemokines from sensory neurons. This article reviews evidence of this unique neuroimmune interplay and its impact on the development of allergy, inflammation, itch, and pain. We highlight the effects of this neuroimmune signaling on vital processes such as host defense, tissue repair, and inflammation resolution, providing avenues for exploration of the underlying mechanisms and therapeutic potential of this signaling.

Further Understanding of Neuro-Immune Interactions in Allergy: Implications in Pathophysiology and Role in Disease Progression

The complicated interaction between the central and the autonomic (sympathetic, parasympathetic, and enteric) nervous systems on the one hand and the immune system and its components, on the other hand, seems to substantially contribute to allergy pathophysiology, uncovering an under-recognized association that could have diagnostic and therapeutic potentials. Neurons connect directly with and regulate the function of many immune cells, including mast cells, the cells that have a leading role in allergic disorders. Proinflammatory mediators such as cytokines, neurotrophins, chemokines, and neuropeptides are released by immune cells, which stimulate sensory neurons. The release of neurotransmitters and neuropeptides caused by the activation of these neurons directly impacts the functional activity of immune cells and vice versa, playing a decisive role in this communication. Successful application of Pavlovian conditioning in allergic disorders supports the existence of a psychoneuroimmunological interplay in classical allergic hypersensitivity reactions. Activation of neuronal homeostatic reflexes, like sneezing in allergic rhinitis, coughing in allergic asthma, and vomiting in food allergy, offers additional evidence of a neuroimmunological interaction that aims to maintain homeostasis. Dysregulation of this interaction may cause overstimulation of the immune system that will produce profound symptoms and exaggerated hemodynamic responses that will lead to severe allergic pathophysiological events, including anaphylaxis. In this article, we have systematically reviewed and discussed the evidence regarding the role of the neuro-immune interactions in common allergic clinical modalities like allergic rhinitis, chronic rhinosinusitis, allergic asthma, food allergy, atopic dermatitis, and urticaria. It is essential to understand unknown – to most of the immunology and allergy experts – neurological networks that not only physiologically cooperate with the immune system to regulate homeostasis but also pathogenetically interact with more or less known immunological pathways, contribute to what is known as neuroimmunological inflammation, and shift homeostasis to instability and disease clinical expression. This understanding will provide recognition of new allergic phenotypes/endotypes and directions to focus on specialized treatments, as the era of personalized patient-centered medicine, is hastening apace.

Transient receptor potential cation channel subfamily V (TRPV) and its importance in asthma

Transient receptor potential (TRP) ion channels play critical roles in physiological and pathological conditions. Increasing evidence has unveiled the contribution of TRP vanilloid (TRPV) family in the development of asthma. The TRPV family is a group (TRPV1-TRPV6) of polymodal channels capable of sensing thermal, acidic, mechanical stress, and osmotic stimuli. TRPVs can be activated by endogenous ligands including, arachidonic acid derivatives or endocannabinoids. While TRPV1-TRPV4 are non-selective cation channels showing a predominance for Ca2+ over Na + influx, TRPV5 and TRPV6 are only Ca2+ permeable selective channels. Asthma is a chronic inflammatory bronchopulmonary disorder involving airway hyperresponsiveness (AHR) and airway remodeling. Patients suffering from allergic asthma display an inflammatory pattern driven by cytokines produced in type-2 helper T cells (Th2) and type 2 innate lymphoid cells (ILC2s). Ion channels are essential regulators in airway smooth muscle (ASM) and immune cells physiology. In this review, we summarize the contribution of TRPV1, TRPV2, and TRPV4 to the pathogenesis of asthma. TRPV1 is associated with hypersensitivity to environmental pollutants and chronic cough, inflammation, AHR, and remodeling. TRPV2 is increased in peripheral lymphocytes of asthmatic patients. TRPV4 contributes to ASM cells proliferation, and its blockade leads to a reduced eosinophilia, neutrophilia, as well as an abolished AHR. In conclusion, TRPV2 may represent a novel biomarker for asthma in children; meanwhile, TRPV1 and TRPV4 seem to be essential contributors to the development and exacerbations of asthma. Moreover, these channels may serve as novel therapeutic targets for this ailment.

Regulatory Peptides in Asthma

Numerous regulatory peptides play a critical role in the pathogenesis of airway inflammation, airflow obstruction and hyperresponsiveness, which are hallmarks of asthma. Some of them exacerbate asthma symptoms, such as neuropeptide Y and tachykinins, while others have ameliorating properties, such as nociception, neurotensin or β-defensin 2. Interacting with peptide receptors located in the lungs or on immune cells opens up new therapeutic possibilities for the treatment of asthma, especially when it is resistant to available therapies. This article provides a concise review of the most important and current findings regarding the involvement of regulatory peptides in asthma pathology.

The Importance of Metabolism for Immune Homeostasis in Allergic Diseases

There is increasing evidence that the metabolic status of T cells and macrophages is associated with severe phenotypes of chronic inflammation, including allergic inflammation. Metabolic changes in immune cells have a crucial role in their inflammatory or regulatory responses. This notion is reinforced by metabolic diseases influencing global energy metabolism, such as diabetes or obesity, which are known risk factors of severity in inflammatory conditions, due to the metabolic-associated inflammation present in these patients. Since several metabolic pathways are closely tied to T cell and macrophage differentiation, a better understanding of metabolic alterations in immune disorders could help to restore and modulate immune cell functions. This link between energy metabolism and inflammation can be studied employing animal, human or cellular models. Analytical approaches rank from classic immunological studies to integrated analysis of metabolomics, transcriptomics, and proteomics. This review summarizes the main metabolic pathways of the cells involved in the allergic reaction with a focus on T cells and macrophages and describes different models and platforms of analysis used to study the immune system and its relationship with metabolism.

Neuroimmune Pathophysiology in Asthma

Asthma is a chronic inflammation of lower airway disease, characterized by bronchial hyperresponsiveness. Type I hypersensitivity underlies all atopic diseases including allergic asthma. However, the role of neurotransmitters (NT) and neuropeptides (NP) in this disease has been less explored in comparison with inflammatory mechanisms. Indeed, the airway epithelium contains pulmonary neuroendocrine cells filled with neurotransmitters (serotonin and GABA) and neuropeptides (substance P[SP], neurokinin A [NKA], vasoactive intestinal peptide [VIP], Calcitonin-gene related peptide [CGRP], and orphanins-[N/OFQ]), which are released after allergen exposure. Likewise, the autonomic airway fibers produce acetylcholine (ACh) and the neuropeptide Y(NPY). These NT/NP differ in their effects; SP, NKA, and serotonin exert pro-inflammatory effects, whereas VIP, N/OFQ, and GABA show anti-inflammatory activity. However, CGPR and ACh have dual effects. For example, the ACh-M3 axis induces goblet cell metaplasia, extracellular matrix deposition, and bronchoconstriction; the CGRP-RAMP1 axis enhances Th2 and Th9 responses; and the SP-NK1R axis promotes the synthesis of chemokines in eosinophils, mast cells, and neutrophils. In contrast, the ACh-α7nAChR axis in ILC2 diminishes the synthesis of TNF-α, IL-1, and IL-6, attenuating lung inflammation whereas, VIP-VPAC1, N/OFQ-NOP axes cause bronchodilation and anti-inflammatory effects. Some NT/NP as 5-HT and NKA could be used as biomarkers to monitor asthma patients. In fact, the asthma treatment based on inhaled corticosteroids and anticholinergics blocks M3 and TRPV1 receptors. Moreover, the administration of experimental agents such as NK1R/NK2R antagonists and exogenous VIP decrease inflammatory mediators, suggesting that regulating the effects of NT/NP represents a potential novel approach for the treatment of asthma.

A TRPA1 inhibitor suppresses neurogenic inflammation and airway contraction for asthma treatment

Despite the development of effective therapies, a substantial proportion of asthmatics continue to have uncontrolled symptoms, airflow limitation, and exacerbations. Transient receptor potential cation channel member A1 (TRPA1) agonists are elevated in human asthmatic airways, and in rodents, TRPA1 is involved in the induction of airway inflammation and hyperreactivity. Here, the discovery and early clinical development of GDC-0334, a highly potent, selective, and orally bioavailable TRPA1 antagonist, is described. GDC-0334 inhibited TRPA1 function on airway smooth muscle and sensory neurons, decreasing edema, dermal blood flow (DBF), cough, and allergic airway inflammation in several preclinical species. In a healthy volunteer Phase 1 study, treatment with GDC-0334 reduced TRPA1 agonist-induced DBF, pain, and itch, demonstrating GDC-0334 target engagement in humans. These data provide therapeutic rationale for evaluating TRPA1 inhibition as a clinical therapy for asthma.

A degradatory fate for CCR4 suggests a primary role in Th2 inflammation

CCR4 is the sole receptor for the chemokines CCL22 and CCL17. Clinical studies of asthmatic airways have shown levels of both ligands and CCR4⁺ Th2 cells to be elevated, suggestive of a role in disease. Consequently, CCR4 has aroused much interest as a potential therapeutic target and an understanding of how its cell surface expression is regulated is highly desirable. To this end, receptor expression, receptor endocytosis, and chemotaxis were assessed using transfectants expressing CCR4, CCR4⁺ human T cell lines, and human Th2 cells polarized in vitro. CCL17 and CCL22 drove rapid endocytosis of CCR4 in a dose-dependent manner. Replenishment at the cell surface was slow and sensitive to cycloheximide, suggestive of de novo synthesis of CCR4. Constitutive CCR4 endocytosis was also observed, with the internalized CCR4 found to be significantly degraded over a 6-h incubation. Truncation of the CCR4 C-terminus by 40 amino acids had no effect on cell surface expression, but resulted in significant impairment of ligand-induced endocytosis. Consequently, migration to both CCL17 and CCL22 was significantly enhanced. In contrast, truncation of CCR4 did not impair constitutive endocytosis or degradation, suggesting the use of alternative receptor motifs in these processes. We conclude that CCR4 cell surface levels are tightly regulated, with a degradative fate for endocytosed receptor. We postulate that this strict control is desirable, given that Th2 cells recruited by CCR4 can induce the further expression of CCR4 ligands in a positive feedback loop, thereby enhancing allergic inflammation.

Allergen-induced asthma, chronic rhinosinusitis and transforming growth factor-β superfamily signaling: mechanisms and functional consequences

Introduction: Often co-associated, asthma and chronic rhinosinusitis (CRS) are complex heterogeneous disease syndromes. Severity in both is related to tissue inflammation and abnormal repair (termed remodeling). Understanding signaling factors that can modulate, integrate the activation, and regulation of such key processes together is increasingly important. The transforming growth factor (TGF)-β superfamily of ligands comprise a versatile system of immunomodulatory molecules that are gaining recognition as having an essential function in the immunopathogenesis of asthma. Early data suggest an important role in CRS as well. Abnormal or dysregulated signaling may contribute to disease pathogenesis and severity.Areas covered: The essential biology of this complex family of growth factors in relation to the excess inflammation and remodeling that occurs in allergic asthma and CRS is reviewed. The need to understand the integration of signaling pathways together is highlighted. Studies in human airway tissue are evaluated and only selected key animal models relevant to human disease discussed given the highly context-dependent signaling and function of these ligands.Expert opinion: Abnormal or dysregulated TGF-β superfamily signaling may be central to the excess inflammation and tissue remodeling in asthma, and possibly CRS. Therefore, the TGF-β superfamily signaling pathways represent an emerging and attractive therapeutic target.

Neuro-immune crosstalk and allergic inflammation

The neuronal and immune systems exhibit bidirectional interactions that play a critical role in tissue homeostasis, infection, and inflammation. Neuron-derived neuropeptides and neurotransmitters regulate immune cell functions, whereas inflammatory mediators produced by immune cells enhance neuronal activation. In recent years, accumulating evidence suggests that peripheral neurons and immune cells are colocalized and affect each other in local tissues. A variety of cytokines, inflammatory mediators, neuropeptides, and neurotransmitters appear to facilitate this crosstalk and positive-feedback loops between multiple types of immune cells and the central, peripheral, sympathetic, parasympathetic, and enteric nervous systems. In this Review, we discuss these recent findings regarding neuro-immune crosstalk that are uncovering molecular mechanisms that regulate inflammation. Finally, neuro-immune crosstalk has a key role in the pathophysiology of allergic diseases, and we present evidence indicating that neuro-immune interactions regulate asthma pathophysiology through both direct and indirect mechanisms.

Neuropeptides in asthma, chronic obstructive pulmonary disease and cystic fibrosis

The nervous system mediates key airway protective behaviors, including cough, mucus secretion, and airway smooth muscle contraction. Thus, its involvement and potential involvement in several airway diseases has become increasingly recognized. In the current review, we focus on the contribution of select neuropeptides in three distinct airway diseases: asthma, chronic obstructive pulmonary disease (COPD), and cystic fibrosis. We present data on some well-studied neuropeptides, as well as call attention to a few that have not received much consideration. Because mucus hypersecretion and mucus obstruction are common features of many airway diseases, we place special emphasis on the contribution of neuropeptides to mucus secretion. Finally, we highlight evidence implicating involvement of neuropeptides in mucus phenotypes in asthma, COPD and cystic fibrosis, as well as bring to light knowledge that is still lacking in the field.

Neuro-immune interactions in allergic diseases: novel targets for therapeutics

Recent studies have highlighted an emerging role for neuro-immune interactions in mediating allergic diseases. Allergies are caused by an overactive immune response to a foreign antigen. The peripheral sensory and autonomic nervous system densely innervates mucosal barrier tissues including the skin, respiratory tract and gastrointestinal (GI) tract that are exposed to allergens. It is increasingly clear that neurons actively communicate with and regulate the function of mast cells, dendritic cells, eosinophils, Th2 cells and type 2 innate lymphoid cells in allergic inflammation. Several mechanisms of cross-talk between the two systems have been uncovered, with potential anatomical specificity. Immune cells release inflammatory mediators including histamine, cytokines or neurotrophins that directly activate sensory neurons to mediate itch in the skin, cough/sneezing and bronchoconstriction in the respiratory tract and motility in the GI tract. Upon activation, these peripheral neurons release neurotransmitters and neuropeptides that directly act on immune cells to modulate their function. Somatosensory and visceral afferent neurons release neuropeptides including calcitonin gene-related peptide, substance P and vasoactive intestinal peptide, which can act on type 2 immune cells to drive allergic inflammation. Autonomic neurons release neurotransmitters including acetylcholine and noradrenaline that signal to both innate and adaptive immune cells. Neuro-immune signaling may play a central role in the physiopathology of allergic diseases including atopic dermatitis, asthma and food allergies. Therefore, getting a better understanding of these cellular and molecular neuro-immune interactions could lead to novel therapeutic approaches to treat allergic diseases.

Interactions of the immune and sensory nervous systems in atopy

A striking feature underlying all atopic disorders, such as asthma, atopic dermatitis, and food allergy, is the presence of pathologic sensory responses, reflexes, and behaviors. These symptoms, exemplified by chronic airway irritation and cough, chronic itch and scratching, as well as gastrointestinal discomfort and dysfunction, are often cited as the most debilitating aspects of atopic disorders. Emerging studies have highlighted how the immune system shapes the scope and intensity of sensory responses by directly modulating the sensory nervous system. Additionally, factors produced by neurons have demonstrated novel functions in propagating atopic inflammation at barrier surfaces. In this review, we highlight new studies that have changed our understanding of atopy through advances in characterizing the reciprocal interactions between the immune and sensory nervous systems.

Biased agonism at chemokine receptors: obstacles or opportunities for drug discovery?

Chemokine receptors are typically promiscuous, binding more than one ligand, with the ligands themselves often expressed in different spatial localizations by multiple cell types. This is normally a tightly regulated process; however, in a variety of inflammatory disorders, dysregulation results in the excessive or inappropriate expression of chemokines that drives disease progression. Biased agonism, the phenomenon whereby different ligands of the same receptor are able to preferentially activate one signaling pathway over another, adds another level of complexity to an already complex system. In this minireview, we discuss the concept of biased agonism within the chemokine family and report that targeting single signaling axes downstream of chemokine receptors is not only achievable, but may well present novel opportunities to target chemokine receptors, allowing the fine tuning of receptor responses in the context of allergic inflammation and beyond.

Asthma is a risk factor for new onset chronic migraine: Results from the American migraine prevalence and prevention study

OBJECTIVES

To test the hypothesis that in persons with episodic migraine (EM), asthma is a risk factor for the onset of chronic migraine (CM).

BACKGROUND

Migraine and asthma are comorbid chronic disorders with episodic attacks thought to involve inflammatory and neurological mechanisms. Herein, we assess the influence of asthma on the clinical course of EM.

METHODS

To be eligible for this observational cohort study, AMPP Study participants had to meet criteria for EM in 2008, complete the validated six-item asthma questionnaire from the European Community Respiratory Health Survey (ECRHS) in 2008, and provide follow-up data in 2009. Using the ECRHS, we defined asthma as a binary variable (present or absent) based on an empirical cut score and developed a Respiratory Symptom Severity Score (RSSS) based on the number of positive responses (no severity = 0 positive responses, low severity = 1-2 positive responses, moderate severity = 3-4 positive responses, high severity = 5-6 positive responses). Chronic migraine was the primary outcome measure and was defined as those with ≥15 headache days per month on the 2009 AMPP Study survey. We used logistic regression in separate models to assess the influence of asthma as a binary variable (Model 1) and RSSS score categories (Model 2 using no respiratory symptoms as the reference) on CM onset after adjusting for sociodemographic factors, headache day frequency, migraine preventive medication use, and medication overuse.

RESULTS

The eligible sample for this study included 4446 individuals with EM in 2008 of whom 17% had asthma. This group had a mean age of 50.4 and was 80.8% female. In 2009, new onset CM developed in 2.9% (131/4446) of the 2008 EM cohort, including 5.4% (40/746) of the asthma subgroup and 2.5% (91/3700) of the non-asthma subgroup. In comparison to those without asthma, the adjusted odds for individuals with asthma and EM in 2008 to develop CM in 2009 were greater than two (adjusted odds ratio [aOR] 2.1; 95% CI: 1.4-3.1). Using the RSSS, the aOR for CM onset increased with the number of asthma symptoms, but only those in the high RSSS category showed a statistically significant increase in the odds of chronic migraine onset in comparison with the no RSSS reference group (aOR 3.3; 95% CI 1.7-6.2).

CONCLUSIONS

Asthma is associated with an increased risk of new onset CM 1 year later among individuals with EM, with the highest risk being among those with the greatest number of respiratory symptoms. The exact mechanisms underlying this association are unknown, but could suggest mast cell degranulation, autonomic dysfunction, or shared genetic or environmental factors.

Targeting chemokine receptors in disease--a case study of CCR4

Since their early 1990s, the chemokine receptor family of G protein-coupled receptors (GPCRs) has been the source of much pharmacological endeavour. Best known for their key roles in recruiting leukocytes to sites of infection and inflammation, the receptors present themselves as plausible drug targets for therapeutic intervention. In this article, we will focus our attention upon CC Chemokine Receptor Four (CCR4) which has been implicated in diseases as diverse as allergic asthma and lymphoma. We will review the discovery of the receptors and their ligands, their perceived roles in disease and the successful targeting of CCR4 by both small molecule antagonists and monoclonal antibodies. We will also discuss future directions and strategies for drug discovery in this field.

Elevations in T-helper-2-initiating cytokines (interleukin-33, interleukin-25 and thymic stromal lymphopoietin) in lesional skin from chronic spontaneous ('idiopathic') urticaria

BACKGROUND

The mechanism of wealing in chronic spontaneous urticaria (CSU) is largely unknown. We previously demonstrated increased expression of T-helper 2 [interleukin (IL)-4 and IL-5] cytokines in skin biopsies from CSU. This suggested that Th2-initiating cytokines [IL-33, IL-25 and thymic stromal lymphopoietin (TSLP)], released through innate immune mechanisms, may play a role in pathogenesis.

OBJECTIVES

To identify Th2-initiating cytokines in lesional and nonlesional skin from patients with CSU and to compare the results with a control group.

METHODS

Paired biopsies (one from a 4-8 h spontaneous weal and one from uninvolved skin) were taken from eight patients with CSU and nine control subjects, and studied by immunohistochemistry and confocal microscopy.

RESULTS

There were increases in IL-4(+) and IL-5(+) cells in lesional skin vs. controls (P = 0·03 and P < 0·001, respectively) and marked elevations in the numbers of IL-33(+), IL-25(+) and TSLP(+) cells in the dermis of lesional skin vs. both nonlesional skin (P = 0·002, P = 0·01 and P = 0·04, respectively) and controls (P = 0·001, P < 0·001 and P = 0·005, respectively). There was also a correlation between the numbers of IL-33(+) and IL-25(+) cells (r = 0·808, P = 0·015). IL-33 localized to CD31(+) endothelial cells, CD90(+) fibroblasts, CD68(+) macrophages and tryptase(+) mast cells, whereas IL-25 was expressed by epithelial cells, mast cells and major basic protein-positive eosinophils. IL-33 and IL-25 were constitutively expressed in the epidermis of both controls and patients with CSU.

CONCLUSIONS

Increased expression of Th2-initiating cytokines in lesional skin in CSU suggests that innate pathways might play a role in the mechanism of wealing. As Th2-initiating cytokines play a role in mast cell activation, inflammation and vascular leakage in CSU, these findings may also have therapeutic implications.

Calcitonin gene-related peptide and vascular endothelial growth factor are expressed in lesional but not uninvolved skin in chronic spontaneous urticaria

BACKGROUND

The mechanisms for producing weals in chronic spontaneous (idiopathic) urticaria (CSU) are incompletely understood. Leucocyte infiltration with vascular leakage and expression of the potent vasoactive agents' calcitonin gene-related peptide (CGRP) and vascular endothelial growth factor (VEGF) are features of late-phase allergic skin reactions, previously proposed as a model of CSU.

OBJECTIVE

To measure CGRP and VEGF expression in lesional and non-lesional skin from CSU patients and to compare results with a control group.

METHODS

Eight paired biopsies (one from 4-8 h spontaneous weals and one from uninvolved skin) were taken from eight patients with CSU and nine control subjects and studied by immunohistochemistry and confocal microscopy.

RESULTS

Lesional skin in CSU contained significantly more CGRP+ and VEGF+ cells than non-lesional skin. No significant differences were observed in CGRP and VEGF expression between non-lesional skin and controls. In lesional skin, VEGF and CGRP co-localised to UEA-1+ blood vessels. CGRP was also expressed by neutrophils and eosinophils and to a lesser extent by CD90(+) fibroblasts, mast cells, CD3(+) and CD68(+) cells. CGRP and VEGF expression was not related to the duration of disease.

CONCLUSION AND CLINICAL RELEVANCE

Increased expression of CGRP and VEGF in lesional, but not uninvolved, skin indicates that these potent vasoactive agents may play a role in wealing and tissue oedema in CSU so representing novel targets in therapy.

Deficiency of RAMP1 attenuates antigen-induced airway hyperresponsiveness in mice

Asthma is a chronic inflammatory disease affecting the lung, characterized by breathing difficulty during an attack following exposure to an environmental trigger. Calcitonin gene-related peptide (CGRP) is a neuropeptide that may have a pathological role in asthma. The CGRP receptor is comprised of two components, which include the G-protein coupled receptor, calcitonin receptor-like receptor (CLR), and receptor activity-modifying protein 1 (RAMP1). RAMPs, including RAMP1, mediate ligand specificity in addition to aiding in the localization of receptors to the cell surface. Since there has been some controversy regarding the effect of CGRP on asthma, we sought to determine the effect of CGRP signaling ablation in an animal model of asthma. Using gene-targeting techniques, we generated mice deficient for RAMP1 by excising exon 3. After determining that these mice are viable and overtly normal, we sensitized the animals to ovalbumin prior to assessing airway resistance and inflammation after methacholine challenge. We found that mice lacking RAMP1 had reduced airway resistance and inflammation compared to wildtype animals. Additionally, we found that a 50% reduction of CLR, the G-protein receptor component of the CGRP receptor, also ameliorated airway resistance and inflammation in this model of allergic asthma. Interestingly, the loss of CLR from the smooth muscle cells did not alter the airway resistance, indicating that CGRP does not act directly on the smooth muscle cells to drive airway hyperresponsiveness. Together, these data indicate that signaling through RAMP1 and CLR plays a role in mediating asthma pathology. Since RAMP1 and CLR interact to form a receptor for CGRP, our data indicate that aberrant CGRP signaling, perhaps on lung endothelial and inflammatory cells, contributes to asthma pathophysiology. Finally, since RAMP-receptor interfaces are pharmacologically tractable, it may be possible to develop compounds targeting the RAMP1/CLR interface to assist in the treatment of asthma.

Recent progress in the development of antagonists to the chemokine receptors CCR3 and CCR4

INTRODUCTION

The chemokine receptors CCR3 and CCR4 have been shown to be important therapeutic targets for the treatment of a variety of diseases. Although only two chemokine receptor inhibitors have been approved so far, there are numerous compounds that are in various stages of development.

AREAS COVERED

In this review article, the authors provide an update on the progress made in the identification of antagonists against the chemokine receptors CCR3 and CCR4 from 2009 to the present. The rationale of writing this review article is to cover the most important approaches to identifying antagonists to these two receptors, which could prove to be useful therapeutics in treating proinflammatory diseases.

EXPERT OPINION

Pharmaceutical companies have expended a considerable amount of money and effort to identify potent inhibitors of CCR3 and CCR4 for the treatment of asthma and atopic diseases. Although a variety of compounds have been described and several have progressed into the clinic, none have so far made it as approved drugs. There are, however, novel approaches such as mogamulizumab, a monoclonal antibody to CCR4 currently is in clinical trials for cancer and ASM8, an antisense nucleotide to CCR3, which is in Phase II clinical trials for asthma that might still prove to be successful new therapeutics.

CCL17/thymus and activation-regulated chemokine induces calcitonin gene-related peptide in human airway epithelial cells through CCR4

BACKGROUND

Calcitonin gene-related peptide (CGRP) is a potent arterial and venous vasodilator. Increased airway epithelial cell expression of CGRP, together with increased CCL17 expression, was previously observed in a model of provoked asthma in atopic human subjects.

OBJECTIVE

We sought to determine whether CCL17 induces CCR4-dependent CGRP synthesis and secretion by human airway epithelial cells.

METHODS

Human airway epithelial cell lines (BEAS-2B and A549) and human primary airway cells were cultured with CCL17 or various other cytokines, and CGRP expression was measured by using RT-PCR, quantitative immunofluorescence, and enzyme immunoassay. CCR4 expression was determined in cultured cells by using flow cytometry and in bronchial biopsy specimens by using immunohistochemistry.

RESULTS

CCL17 induced a several thousand-fold increase in CGRP mRNA expression and released peptide product from BEAS-2B and A549 cells in a time- and concentration-dependent fashion. Concentration-dependent CCL17-induced release of CGRP by primary human airway epithelial cells was also observed. Under comparable conditions, CCL17 induced greater CGRP release from BEAS-2B cells than either IL-13, a cytokine mixture (TNF-α, GM-CSF, and IL-1), or CCL22. CCR4 was expressed by BEAS-2B and A549 cells and internalized after ligation with CCL17. CCL17-induced CGRP release was inhibited by a specific anti-CCR4 blocking antibody. Bronchial biopsy specimens obtained from healthy volunteers and asthmatic patients before and after provoked asthma all exhibited CCR4 staining of equivalent intensity, indicating that the receptor is constitutively expressed.

CONCLUSIONS

CCL17-induced, CCR4-dependent release of CGRP by human airway epithelial cells represents a novel inflammatory pathway and a possible target in patients with asthma and allergic disease.

Perspectives on some recent studies on RAMPs

This book on RAMPs covers a number of aspects on the biology of RAMPs. However, due to the uniqueness of some recent studies, they were not covered under a general title. Therefore, in this chapter, we describe three recent studies wherein RAMPs were found to be important players in cancer, hypertension and asthma.

The neuropeptide calcitonin gene-related peptide affects allergic airway inflammation by modulating dendritic cell function

BACKGROUND

The neuropeptide calcitonin gene-related peptide (CGRP) is released in the lung by sensory nerves during allergic airway responses. Pulmonary dendritic cells (DC) orchestrating the allergic inflammation could be affected by CGRP.

OBJECTIVE

To determine the immunomodulatory effects of CGRP on DC function and its impact on the induction of allergic airway inflammation.

METHODS

CGRP receptor expression on lung DC was determined by RT-PCR and immunofluorescence staining. The functional consequences of CGRP receptor triggering were evaluated in vitro using bone marrow-derived DC. DC maturation and the induction of ovalbumin (OVA)-specific T cell responses were analysed by flow cytometry. The in vivo relevance of the observed DC modulation was assessed in a DC-transfer model of experimental asthma. Mice were sensitized by an intrapharyngeal transfer of OVA-pulsed DC and challenged with OVA aerosol. The impact of CGRP pretreatment of DC on airway inflammation was characterized by analysing differential cell counts and cytokines in bronchoalveolar lavage fluid (BALF), lung histology and cytokine responses in mediastinal lymph nodes.

RESULTS

RT-PCR, immunofluorescence and cAMP assay demonstrated the expression of functionally active CGRP receptors in lung DC. RT-PCR revealed a transcriptional CGRP receptor down-regulation during airway inflammation. CGRP specifically inhibited the maturation of in vitro generated DC. Maturation was restored by blocking with the specific antagonist CGRP(8-37) . Consequently, CGRP-pretreated DC reduced the activation and proliferation of antigen-specific T cells and induced increased the numbers of T regulatory cells. The transfer of CGRP-pretreated DC diminished allergic airway inflammation in vivo, shown by reduced eosinophil numbers and increased levels of IL-10 in BALF.

CONCLUSIONS AND CLINICAL RELEVANCE

CGRP inhibits DC maturation and allergen-specific T cell responses, which affects the outcome of the allergic airway inflammation in vivo. This suggests an additional mechanism by which nerve-derived mediators interfere with local immune responses. Thus, CGRP as an anti-inflammatory mediator could represent a new therapeutic tool in asthma therapy.

Calcitonin gene-related peptide- and vascular endothelial growth factor-positive inflammatory cells in late-phase allergic skin reactions in atopic subjects

BACKGROUND

Allergen-induced late-phase skin reactions are characterized by erythema and edema, but the vasoactive mediators involved remain unclear. Limited evidence from human studies suggests that calcitonin gene-related peptide (CGRP) and vascular endothelial growth factor (VEGF), potent vasodilator and permeability factors, respectively, are expressed by infiltrating inflammatory cells in certain allergic tissue reactions.

OBJECTIVE

We sought to determine whether tissue swelling in allergen-challenged skin sites in atopic subjects is associated with the infiltration of CGRP(+) and VEGF(+) inflammatory cells.

METHODS

Skin biopsy specimens were obtained from atopic subjects at various times after cutaneous allergen challenge and studied by means of single and double immunohistochemistry and in situ hybridization.

RESULTS

CGRP-immunoreactive and CGRP mRNA-positive cell numbers were increased in biopsy specimens from sites of late-phase skin reactions compared with those at the control site (P = .03 and P = .03, respectively). Their numbers paralleled the development and resolution of the edematous late-phase skin reaction, both peaking at 6 hours after allergen challenge. The majority of CGRP-immunoreactive cells were neutrophils and CD3(+) cells, whereas eosinophils were CGRP negative. VEGF-immunopositive cell numbers were also increased in 6-hour biopsy specimens from late-phase skin reactions compared with those seen at control sites (P = .001) with a lesser but significant response (P = .008) at 24 hours. VEGF(+) cells were largely eosinophils, neutrophils, and CD68(+) macrophages.

CONCLUSIONS

Late-phase skin reactions in atopic subjects were associated with the infiltration of inflammatory cells expressing CGRP and VEGF, suggesting that these vasoactive factors might play a role in the erythema and edema characteristic of allergic inflammation. They could also be considered targets in attempts to control allergic inflammation.

Expression of functional receptor activity modifying protein 1 by airway epithelial cells with dysregulation in asthma

BACKGROUND

Epithelial cell expression of calcitonin gene-related peptide (CGRP) is a feature of provoked asthma. Receptor activity modifying protein 1 (RAMP1) and the calcitonin receptor-like receptor combine to form the CGRP1 receptor.

OBJECTIVE

To determine whether functional RAMP1 is expressed by airway epithelial cells and whether there are alterations in asthma.

METHODS

BEAS-2B and A549 cells lines were studied by RT-PCR, confocal microscopy, a quantitative immunofluorescence assay, and ELISA. Bronchial biopsies from normal subjects and subjects with asthma were examined by immunohistochemistry and in situ hybridization.

RESULTS

Inflammatory cytokines induced CGRP release and CGRP mRNA in BEAS-2B and A549 epithelial cell lines. RAMP1 was highly expressed by resting, unstimulated BEAS-2B and A549 cells. CGRP induced internalization of RAMP1 and IL-6 production, both of which were inhibited by the CGRP antagonist, CGRP(8-37). Activation of BEAS-2B and A549 cells by inflammatory cytokines induced CGRP secretion, binding of CGRP to RAMP1, and RAMP1 internalization, which was blocked by CGRP (8-37). RAMP1 immunoreactivity and RAMP1 mRNA expression in bronchial biopsies from subjects with asthma were significantly lower than in normal subjects (P = .002 and P = .007, respectively). Inhalational challenge of atopic subjects with asthma with allergen-derived peptides produced a significant decrease in the numbers of RAMP1-positive epithelial cells in responders (P = .027) but not nonresponders.

CONCLUSION

Receptor activity modifying protein 1 was expressed both by airway epithelial cells in culture and in bronchial biopsies from normal subjects and internalized after epithelial cell activation through autocrine feedback of CGRP. There is an apparent dysregulation of RAMP1 in asthmatic epithelium, suggesting continuous stimulation of pathways involving CGRP.

The allergen specificity of the late asthmatic reaction

BACKGROUND

Allergen inhalation challenge in asthma may induce both early (EAR) and late (LAR) asthmatic reactions. The EAR is IgE and mast cell dependent. The mechanism of the LAR is less well defined and we have hypothesized may be allergen dependent. The aim of this study was to investigate the allergen specificity of the LAR to allergen inhalation in asthma.

METHODS

In a randomized, double-blind, crossover design six asthmatic volunteers with dual sensitization to house dust mite (HDM) allergen and grass pollen (GP) allergen underwent inhalation allergen challenge with these separate allergens on two occasions separated by 14 days. Lung function changes were followed for 8-h postchallenge. Bronchial reactivity (histamine PC(20)) and airway inflammation, assessed by induced sputum differential cell count, were measured 24-h pre and postallergen challenge. The allergen inhalation challenges were matched to achieve the same magnitude of EAR.

RESULTS

Despite comparable group mean EAR percent falls in FEV(1) (25.8% following GP and 28.0% following HDM (P = 0.917), the LAR was statistically greater on the HDM challenge day (13.0%vs 22.8% [P = 0.046]) and was associated with a significant airway eosinophil recruitment (mean (SD) of 5.4 (4.8)% to 22.1 (18.2)% (P = 0.028) that was not evident on the GP allergen challenge day.

CONCLUSIONS

These findings identify the allergen specificity of the LAR and indicate that factors independent of IgE contribute to the LAR. Such findings have relevance both to the understanding of the allergen-induced airway responses in asthma and the need for homogeneity in inhaled-allergen challenge studies in asthma.

Effects of omalizumab on markers of inflammation in patients with allergic asthma

Asthma is a chronic inflammatory disease of the airways in which immunoglobulin E (IgE) plays a key role by activating a variety of inflammatory cells through interactions with FcepsilonRI and FcepsilonRII receptors. The role of IgE in allergic inflammation provided the rationale for developing omalizumab, a humanized monoclonal anti-IgE antibody, for patients with moderate-to-severe or severe allergic asthma. The reductions in circulating levels of IgE resulting from omalizumab treatment leads to reductions in FcepsilonRI expression on mast cells, basophils and dendritic cells. This combined effect results in attenuation of several markers of inflammation, including peripheral and bronchial tissue eosinophilia and levels of granulocyte macrophage colony stimulating factor, interleukin (IL)-2, IL-4, IL-5 and IL-13. By blocking IgE binding to its receptors and diminishing dendritic cell FcepsilonRI receptor expression, omalizumab may also reduce allergen presentation to T cells and the production of Th2 cytokines. The anti-inflammatory effects of omalizumab may, therefore, explain the reductions in asthma exacerbations and symptoms seen in clinical trials in patients with moderate-to-severe or severe, persistent, inadequately controlled allergic asthma.

The role of neuro-immune cross-talk in the regulation of inflammation and remodelling in asthma

Despite recent advances in the development of anti-asthmatic medication, asthma continues to be a major health problem worldwide. The symptoms of asthmatic patients include wheezing, chest tightness, cough and shortness of breath, which, together with airway hyperresponiveness, previously have been attributed to a dysfunction of airway nerves. However, research in the last two decades identified Th2-sensitization and the subsequent allergic reaction to innocuous environmental antigens as a basic immunological mechanism leading to chronic airway inflammation. Recent evidence suggests that the development of allergic asthma is influenced by events and circumstances in early childhood and even in utero. Allergen, ozone or stress exposure, as well as RSV infection in early life could be able to induce irreversible changes in the developing epithelial-mesenchymal trophic unit of the airways. The co-existence of chronic inflammation and neural dysfunction have recently drawn attention to the involvement of interaction pathways between the nervous and the immune system in the airways. Intensive basic research has accumulated morphological as well as functional evidence for the interaction between nerves and immune cells. Neuropeptides and neurotrophins have come into focus of attention as the key mediators of neuro-immune interactions, which lead to the development of several pharmacological compounds specifically targeting these molecules. This review will integrate our current knowledge on the involvement of neuro-immune pathways in asthma on the cellular and molecular level. It will summarize the results of pharmacological studies addressing the potential of neuropeptides and neurotrophins as novel therapeutic targets in asthma.

The development of allergic inflammation

Allergic disorders, such as anaphylaxis, hay fever, eczema and asthma, now afflict roughly 25% of people in the developed world. In allergic subjects, persistent or repetitive exposure to allergens, which typically are intrinsically innocuous substances common in the environment, results in chronic allergic inflammation. This in turn produces long-term changes in the structure of the affected organs and substantial abnormalities in their function. It is therefore important to understand the characteristics and consequences of acute and chronic allergic inflammation, and in particular to explore how mast cells can contribute to several features of this maladaptive pattern of immunological reactivity.

Latex allergy: a model for therapy

Allergy to natural rubber latex products emerged as an important clinical condition following an increase in the use of latex gloves for barrier protection in the early 1980s. In addition to latex glove users, other high-risk groups with different latex exposure include spina bifida patients and others with multiple surgical procedures. Subjects with fruit and vegetable allergy are also at risk due to cross-reactive allergens. Following the significant advances in the identification and characterization of common aeroallergens, latex allergy was well placed to become an excellent model of therapy. Awareness of latex allergy and modes of sensitization enabled epidemiological studies to inform allergen avoidance initiatives, substantially reducing inadvertent exposure in major hospitals in Western countries. Spina bifida is often identified in utero or soon after birth, allowing vigorous latex allergen avoidance with enhanced efficacy of primary prevention. However, changing demographics of latex allergy and technological revolution in countries such as China and India are predicted to unleash a second wave of latex allergy reemphasizing the incentive for improved manufacturing procedures for latex products. The desirable high tensile strength and elasticity of natural rubber latex have made the commercial identification of good alternatives very difficult but this would also be attractive for primary prevention. In addition, an effective specific immunotherapy regimen would be valuable for selected high-risk atopic individuals. Current subcutaneous and sublingual immunotherapy schedules have been tested for treatment of latex allergy with evidence of efficacy but the risks of adverse events are high. For such potent allergens as latex, hypoallergenic but T cell-reactive preparations are required for clinical use. Identification of allergenic components of latex products, with generation of monoclonal antibodies and recombinant allergens, allowed sequence determination and mapping of T cell and B cell epitopes. Together, these reagents and data facilitated improved diagnostics and investigation of novel-specific therapeutics. Potential hypoallergenic latex preparations identified include modified non-IgE-reactive allergen molecules and short T cell epitope peptides. The co-administration of adjunct therapies such as anti-IgE or corticosteroids and of appropriate adjuvants for induction of regulatory T cell response offers promise for clinically effective, safe latex-specific vaccines.

Airway hyperresponsiveness and bronchial mucosal inflammation in T cell peptide-induced asthmatic reactions in atopic subjects

BACKGROUND

Subjects with allergic asthma develop isolated late asthmatic reactions after inhalation of allergen-derived T cell peptides. Animal experiments have shown that airway hyperresponsiveness (AHR) is CD4+ cell-dependent. It is hypothesised that peptide inhalation produces increases in non-specific AHR and a T cell-dominant bronchial mucosal inflammatory response.

METHODS

Bronchoscopy, with bronchial biopsies and bronchoalveolar lavage (BAL), was performed in 24 subjects with cat allergy 6 h after aerosol inhalation of short overlapping peptides derived from Fel d 1, the major cat allergen. Biopsy specimens and BAL fluid were studied using immunohistochemistry and ELISA.

RESULTS

Twelve of the 24 subjects developed an isolated late asthmatic reaction without a preceding early (mast cell/histamine-dependent) reaction characteristic of whole allergen inhalation. These responders had significant between-group differences (responders vs non-responders) in the changes (peptide vs diluent) in AHR (p = 0.007) and bronchial mucosal CD3+ (p = 0.005), CD4+ (p = 0.006) and thymus- and activation-regulated chemokine (TARC)+ (p = 0.003) but not CD8+ or CD25+ cells or eosinophils, basophils, mast cells and macrophages. The between-group difference for neutrophils was p = 0.05 but with a non-significant within-group value (peptide vs diluent, responders, p = 0.11). In BAL fluid there was a significant between-group difference in TARC (p = 0.02) but not in histamine, tryptase, basogranulin, C3a or C5a, leukotrienes C(4)/D(4)/E(4), prostaglandins D(2) or F(2alpha).

CONCLUSIONS

Direct activation of allergen-specific airway T cells by peptide inhalation in patients with atopic asthma leads to increased AHR with local increases in CD3+ and CD4+ cells and TARC but no significant changes in eosinophils or basophil/mast cell products. These findings support previous animal experiments which showed a CD4+ dependence for AHR.