Mast cell-derived neurotrophin 4 mediates allergen-induced airway hyperinnervation in early life

Fecal microbiota transplants (FMT) of three distinct human communities to germ-free mice exacerbated inflammation and decreased lung function in their offspring

Despite explosive rise in allergies, little is known about early life gut microbiota effects on postnatal respiratory function. We hypothesized that Enterobacteriaceae-dominant gut microbiota from eczemic infants increases Type 2 inflammation and decreases lung function in transplanted mice, while Bacteroidaceae-dominant gut microbiota from non-eczemic infants is protective. Fecal microbiota transplants (FMT) from eczemic infants "Infant A" and non-eczemic infants "Infant B" were successfully transplanted into germ-free C57BL/6 mice, passing to offspring unchanged. Infant A and B, Adult C-human-derived (positive control), and Mouse (negative control) microbiotas all in C57BL/6 mice were tested for effects on airway function in nonallergic (phosphate-buffered saline [PBS]) and allergic (house dust mite [HDM]) conditions. Baseline lung mechanics in mice with human microbiotas (HUmicrobiota) were significantly impaired compared to Mouse microbiota controls (MOmicrobiota) with or without HDM; respiratory system resistance (Rrs) was increased (P < 0.05-P < 0.01), and respiratory system compliance (Crs) was decreased (P < 0.05-P < 0.01). HUMicrobiota mice showed a statistically significant impairment compared to MOmicrobiota mice in lung parameters Rrs, Ers, Rn, and G at baseline, and at multiple methacholine (MCh) doses with baseline removed. Impairment manifested as increased small airway resistance and tissue resistance. HDM significantly elevated IL-4, eosinophils, lung inflammation, and mucus cell metaplasia, and decreased macrophages and lung function (P < 0.05) in mice of all microbiotas, yet each HUmicrobiota produced distinct features. Infant B and Adult C mice had elevated basal levels of total IgE compared to MOmicrobiota and Infant A mice (P < 0.05). In HUmicrobiota mice given HDM, only Adult C had elevated IL-5 and IL-13 (P < 0.05), only Adult C and Infant B mice had elevated neutrophils (P < 0.05), and only Infant A had elevated lymphocytes (P < 0.01).

IMPORTANCE

Fecal microbiota transplants (FMT) of three distinct human communities to germ-free mice exacerbated inflammation and decreased lung function in their offspring. Taxa formerly described to induce an allergic response (agonists) and pro-inflammatory taxa were abundant in HUmicrobiotas compared to MOmicrobiota controls, while taxa formerly described to reduce allergic responses (antagonists) and anti-inflammatory taxa were numerous in MOmicrobiotas and low in HUmicrobiotas. Thus, we largely rejected our hypotheses because data supported multiple pro-inflammatory allergy agonists functioning in a community-wide fashion to impair lung function in the absence of antagonistic anti-inflammatory taxa. Structure of HUmicrobiotas played a key role in determining varied allergic responses and resulting lung impairment, yet, strikingly, all mice with HUmicrobiotas had impaired lung function even in the absence of allergens. Using a comparative approach, we showed that composition of gut microbiota can alter innate/immune regulation in the gut-lung axis to increase baseline lung function responses and the risk of allergic sensitization.

Mast cells in oral lichen planus and oral lichenoid lesions related to dental amalgam contact

The aim of this study was to analyze the expression of mast cell markers toluidine blue, c-kit, and tryptase and presence of mononuclear inflammatory cells in oral lichen planus (OLP) and oral lichenoid lesions related to dental amalgam. Nineteen specimens of OLP, OLLC, and healthy oral mucosa were selected. Mononuclear inflammatory cells were analyzed. Histochemical and immunohistochemical analyses were performed using toluidine blue, anti-c-kit and anti-tryptase reagents, and the results were quantified in areas A and B of connective tissue. Mast cells of all OLP and OLLC samples were positive for toluidine blue, c-kit, and tryptase. The density of toluidine blue+, c-kit+ and tryptase+ mast cells was higher in tissue with OLP and OLLC compared with healthy controls (p < 0.05). No difference was noted in mast cells density between OLP and OLLC (p > 0.05). The density of tryptase+ mast cells was higher in the subepithelial region (area A) than the region below it (Area B) in OLLC (p = 0.047). The mononuclear inflammatory cell density was higher in OLLC compared to OLP, but without statistical significance (p > 0.05). A positive statistical correlation was found between mononuclear immune cells and density of c-kit+ and tryptase+ mast cells in OLP (r = 0.943 and r = 0.886, respectively). Our data demonstrate that the etiopathogenesis process of OLP and OLLC modulates the expansion and degranulation of mast cells; mast cells density, however, was similar between OLP and OLLC. The distribution of mast cells appears to vary along the lamina propria.

Therapeutic application of PPE2 protein of Mycobacterium tuberculosis in inhibiting tissue inflammation

There is an increasing need to develop biological anti-inflammatory agents that are more targeted, effective, and with lesser side effects as compared to conventional chemical drugs. In the present study, we found that Mycobacterium tuberculosis protein PPE2 and a synthetic derivative peptide can suppress the mast cell population and inhibit several vasoactive and fibrogenic mediators and pro-inflammatory cytokines induced by mast cells in formalin-induced tissue injury. PPE2 was found to inhibit transcription from the promoter of stem cell factor, important for mast cell maintenance and migration. Thus, PPE2/peptide can be used as a potent nonsteroidal therapeutic agent for the treatment of inflammation and tissue injury.

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.

Neuro-Immune Regulation in Inflammation and Airway Remodeling of Allergic Asthma

Allergic asthma is a common chronic inflammation of the airways and causes airway remodeling eventually. For a long time, investigators have been focusing on the immunological mechanism of asthma. However, in recent years, the role of neuro-regulation in the occurrence of asthma has gradually attracted investigators’ attention. In this review, we firstly describe neuro-immune regulation in inflammation of allergic asthma from two aspects: innate immunity and adaptive immunity. Secondly, we introduce neuro-immune regulation in airway remodeling of asthma. Finally, we prospect the role of pulmonary neuroendocrine cells in the development of asthma. In general, the amount of researches is limited. Further researches on the neural regulation during the occurrence of asthma will help us clarify the mechanism of asthma more comprehensively and find more effective ways to prevent and control asthma.

Airway Sensory Nerve Plasticity in Asthma and Chronic Cough

Airway sensory nerves detect a wide variety of chemical and mechanical stimuli, and relay signals to circuits within the brainstem that regulate breathing, cough, and bronchoconstriction. Recent advances in histological methods, single cell PCR analysis and transgenic mouse models have illuminated a remarkable degree of sensory nerve heterogeneity and have enabled an unprecedented ability to test the functional role of specific neuronal populations in healthy and diseased lungs. This review focuses on how neuronal plasticity contributes to development of two of the most common airway diseases, asthma and chronic cough, and discusses the therapeutic implications of emerging treatments that target airway sensory nerves.

Management Strategies to Reduce Exacerbations in non-T2 Asthma

There have been considerable advances in our understanding of asthmatic airway inflammation, resulting in a paradigm shift of classifying individuals on the basis of either the presence or the absence of type 2 (T2) inflammatory markers. Several novel monoclonal antibody therapies targeting T2 cytokines have demonstrated significant clinical effects including reductions in acute exacerbations and improvements in asthma-related quality of life and lung function for individuals with T2-high asthma. However, there have been fewer advancements in developing therapies for those without evidence of T2 airway inflammation (so-called non-T2 asthma). Here, we review the heterogeneity of molecular mechanisms responsible for initiation and regulation of non-T2 inflammation and discuss both current and potential future therapeutic options for individuals with non-T2 asthma.

Neuroimmune regulatory networks of the airway mucosa in allergic inflammatory disease

Communication between the nervous and immune systems serves a key role in host‐protective immunity at mucosal barrier sites including the respiratory tract. In these tissues, neuroimmune interactions operate in bidirectional circuits that can sense and respond to mechanical, chemical, and biologic stimuli. Allergen‐ or helminth‐induced products can produce airway inflammation by direct action on nociceptive afferents and adjacent tissues. The activity of nociceptive afferents can regulate innate and adaptive immune responses via neuropeptides and neurotransmitter signaling. This review will summarize recent work investigating the role of neuropeptides CGRP, VIP, neuromedins, substance P, and neurotransmitters dopamine and the B2‐adrenoceptor agonists epinepherine/norepinepherine, each of which influence type 2 immunity by instructing mast cell, innate lymphoid cell type 2, dendritic cell, and T cell responses, both in the airway and the draining lymph node. Afferents in the airway also contain receptors for alarmins and cytokines, allowing their activity to be modulated by immune cell secreted products, particularly those secreted by mast cells. Taken together, we propose that further investigation of how immunoregulatory neuropeptides shape respiratory inflammation in experimental systems may reveal novel therapeutic targets for addressing the increasing prevalence of chronic airway disease in humans.

Airway Sensory Nerve Density Is Increased in Chronic Cough

Rationale: Chronic cough is characterized by frequent urges to cough and a heightened sensitivity to inhaled irritants. Airway sensory nerves trigger cough. We hypothesized that sensory nerve density is increased in chronic cough, which may contribute to excessive and persistent coughing.Objectives: To measure airway nerve density (axonal length) and complexity (nerve branching, neuropeptide expression) in humans with and without chronic cough.Methods: Bronchoscopic human airway biopsies were immunolabeled for nerves and the sensory neuropeptide substance P. Eosinophil peroxidase was also quantified given previous reports showing associations between eosinophils and nerve density. Three-dimensional image z-stacks of epithelium and subepithelium were generated using confocal microscopy, and from these z-stacks, total nerve length, the number of nerve branch points, substance P expression, and eosinophil peroxidase were quantified within each airway compartment.Measurements and Main Results: Nerve length and the number of branch points were significantly increased in epithelium, but not subepithelium, in chronic cough compared with healthy airways. Substance P expression was scarce and was similar in chronic cough and healthy airways. Nerve length and branching were not associated with eosinophil peroxidase nor with demographics such as age and sex in either group.Conclusions: Airway epithelial sensory nerve density is increased in chronic cough, suggesting sensory neuroplasticity contributes to cough hypersensitivity.

Exploring the origin and regulatory role of mast cells in asthma

PURPOSE OF REVIEW

Mast cells have previously been thought to function solely as effector cells in asthma but more recent studies have indicated that mast cells may play a more central role in propagating and regulating lower airway inflammation in asthma.

RECENT FINDINGS

Initial studies have found increased numbers of mast cell progenitors (MCPs) in the peripheral blood of patients with asthma and these cells could contribute to the increased number of progenitors identified in the airways of patients with asthma. There are unique subpopulations of mast cells within the asthmatic airway, which are characterized by their physical location and distinguished by their expression profile of mast cell proteases. Intraepithelial mast cells are tightly associated with type-2 (T2) inflammation but additional studies have suggested a role for anti-mast cell therapies as a treatment for T2-low asthma. Mast cells have recently been shown to closely communicate with the airway epithelium and airway smooth muscle to regulate lower airway inflammation and airway hyperresponsiveness.

SUMMARY

Recent studies have better illuminated the central role of mast cells in regulating lower airway inflammation and airway hyperresponsiveness.

Tespa1 plays a role in the modulation of airway hyperreactivity through the IL-4/STAT6 pathway

BACKGROUND

Thymocyte-expressed, positive selection-associated 1 (Tespa1) is a critical signaling molecule in thymocyte development. This study aimed to investigate the regulatory effect of Tespa1 on mast cells in the pathogenesis of asthma and its relationship with the interleukin (IL)-4/signal transducers and activators of transcription 6 (STAT6) signaling pathway.

METHODS

Tespa1 mRNA expression analysis and IgE levels were carried out using the induced sputum of 33 adults with stable asthma and 36 healthy controls. Tespa1-knockout mice (Tespa1-/-, KO) and C57BL/6 background (wild-type, WT) mice were sensitized and treated with ovalbumin (OVA) to establish an asthma model. Pathological changes, number and activity of mast cells, and changes in activation of the IL-4/STAT6 pathway in lung tissue were detected. The changes of tryptase expression and STAT6 activation after mast cell gene knockout were analyzed in vitro. The changes of enzyme expression and STAT6 activation after mast cell gene knockout were analyzed in vitro. The association between the Tespa1 and p-STAT6 was analyzed by co-immunoprecipitation method.

RESULTS

Compared with the healthy controls, Tespa1 expression was decreased, and IgE levels were elevated in the sputum of asthmatic patients. Animal experiments showed that Tespa1-/- mice exhibited more severe inflammation, higher quantity of goblet cells and mast cells in the bronchium, and greater expression of mast cell tryptase, which is induced by ovalbumin, than WT mice. And IL-4, IL-13, phospho-Janus kinase 1, and p-STAT6 expressions presented a higher increase in the Tespa1-/- mouse model than in the WT mouse model. Further in vitro studies confirmed that IL-4 could more significantly promote tryptase and p-STAT6 activities in Tespa1-/- mast cells than their WT counterparts. Correlation analysis results showed a negative correlation between Tespa1 and p-STAT6. Co-immunoprecipitation results demonstrated an association between Tespa1 and p-STAT6.

CONCLUSIONS

Altogether, our results indicate that Tespa1 can negatively regulate mast cell activity, and this event is related to the mast cell IL-4/STAT6 signaling pathway and could be therapeutically exploited to treat asthma attacks.

Cytokines and beyond: Regulation of innate immune responses during helminth infection

Parasitic helminth infection elicits a type 2 cytokine-mediated inflammatory response. During type 2 inflammation, damaged or stimulated epithelial cells exposed to helminths and their products produce alarmins and cytokines including IL-25, IL-33, and thymic stromal lymphopoietin. These factors promote innate immune cell activation that supports the polarization of CD4+ T helper type 2 (Th2) cells. Activated innate and Th2 cells produce the cytokines IL-4, -5, -9, and -13 that perpetuate immune activation and act back on the epithelium to cause goblet cell hyperplasia and increased epithelial cell turnover. Together, these events facilitate worm expulsion and wound healing processes. While the role of Th2 cells in this context has been heavily studied, recent work has revealed that epithelial cell-derived cytokines are drivers of key innate immune responses that are critical for type 2 anti-helminth responses. Cutting-edge studies have begun to fully assess how other factors and pathways, including lipid mediators, chemokines, Fc receptor signaling, danger-associated molecular pattern molecules, and direct cell-cell interactions, also participate in shaping innate cell-mediated type 2 inflammation. In this review, we discuss how these pathways intersect and synergize with pathways controlled by epithelial cell-derived cytokines to coordinate innate immune responses that drive helminth-induced type 2 inflammation.

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.

Age-Related Dopaminergic Innervation Augments T Helper 2-Type Allergic Inflammation in the Postnatal Lung

Young children are more susceptible to developing allergic asthma than adults. As neural innervation of the peripheral tissue continues to develop after birth, neurons may modulate tissue inflammation in an age-related manner. Here we showed that sympathetic nerves underwent a dopaminergic-to-adrenergic transition during post-natal development of the lung in mice and humans. Dopamine signaled through a specific dopamine receptor (DRD4) to promote T helper 2 (Th2) cell differentiation. The dopamine-DRD4 pathway acted synergistically with the cytokine IL-4 by upregulating IL-2-STAT5 signaling and reducing inhibitory histone trimethylation at Th2 gene loci. In murine models of allergen exposure, the dopamine-DRD4 pathway augmented Th2 inflammation in the lungs of young mice. However, this pathway operated marginally after sympathetic nerves became adrenergic in the adult lung. Taken together, the communication between dopaminergic nerves and CD4⁺ T cells provides an age-related mechanism underlying the susceptibility to allergic inflammation in the early lung.

Mast Cell-Mediated Orchestration of the Immune Responses in Human Allergic Asthma: Current Insights

Improving the lung function after experimental allergen challenge by blocking of mast cell (MC) mediators and the capability of MC mediators (including histamine, prostaglandin (PG) D2, and leukotriene (LT) C4) in induction of mucosal edema, bronchoconstriction, and mucus secretion provide evidence that MCs play a key role in pathophysiology of asthma. In asthma, the number of MCs increases in the airways and infiltration of MCs in a variety of anatomical sites including the epithelium, the submucosal glands, and the smooth muscle bundles occurs. MC localization within the ASM is accompanied with the hypertrophy and hyperplasia of the layer, and smooth muscle dysfunction that is mainly observed in forms of bronchial hyperresponsiveness, and variable airflow obstruction. Owing to the expression of a wide range of surface receptors and releasing various cytoplasmic mediators, MCs orchestrate the pathologic events of the disease. MC-released preformed mediators including chymase, tryptase, and histamine and de novo synthesized mediators such as PGD2, LTC4, and LTE4 in addition of cytokines mainly TGFβ1, TSLP, IL-33, IL-4, and IL-13 participate in pathogenesis of asthma. The release of MC mediators and MC/airway cell interactions during remodeling phase of asthma results in persistent cellular and structural changes in the airway wall mainly epithelial cell shedding, goblet cell hyperplasia, hypertrophy of ASM bundles, fibrosis in subepithelial region, abnormal deposition of extracellular matrix (ECM), increased tissue vascularity, and basement membrane thickening. We will review the current knowledge regarding the participation of MCs in each stage of asthma pathophysiology including the releasing mediators and their mechanism of action, expression of receptors by which they respond to stimuli, and finally the pharmaceutical products designed based on the strategy of blocking MC activation and mediator release.

Airway Innervation and Plasticity in Asthma

Airway nerves represent a mechanistically and therapeutically important aspect that requires better highlighting in the context of diseases such as asthma. Altered structure and function (plasticity) of afferent and efferent airway innervation can contribute to airway diseases. We describe established anatomy, current understanding of how plasticity occurs, and contributions of plasticity to asthma, focusing on target-derived growth factors (neurotrophins). Perspectives toward novel treatment strategies and future research are provided.

Sex-specific airway hyperreactivity and sex-specific transcriptome remodeling in neonatal piglets challenged with intra-airway acid

Acute airway acidification is a potent stimulus of sensory nerves and occurs commonly with gastroesophageal reflux disease, cystic fibrosis, and asthma. In infants and adults, airway acidification can acutely precipitate asthma-like symptoms, and treatment-resistant asthma can be associated with gastroesophageal reflux disease. Airway protective behaviors, such as mucus secretion and airway smooth muscle contraction, are often exaggerated in asthma. These behaviors are manifested through activation of neural circuits. In some populations, the neural response to acid might be particularly important. For example, the immune response in infants is relatively immature compared with adults. Infants also have a high frequency of gastroesophageal reflux. Thus, in the current study, we compared the transcriptomes of an airway-nervous system circuit (e.g., tracheal epithelia, nodose ganglia, and brain stem) in neonatal piglets challenged with intra-airway acid. We hypothesized that the identification of parallel changes in the transcriptomes of two neutrally connected tissues might reveal the circuit response, and, hence, molecules important for the manifestation of asthma-like features. Intra-airway acid induced airway hyperreactivity and airway obstruction in male piglets. In contrast, female piglets displayed airway obstruction without airway hyperreactivity. Pairwise comparisons revealed parallel changes in genes directly implicated in airway hyperreactivity ( scn10a) in male acid-challenged piglets, whereas acid-challenged females exhibited parallel changes in genes associated with mild asthma ( stat 1 and isg15). These findings reveal sex-specific responses to acute airway acidification and highlight distinct molecules within a neural circuit that might be critical for the manifestation of asthma-like symptoms in pediatric populations.

Neurotrophins in Asthma

PURPOSE OF REVIEW

Asthma is a chronic airway disease that affects more than 300 million people worldwide. Current treatment focuses on symptomatic relief by temporally dampening inflammation and relaxing the airway. Novel combative strategies against asthma and hopefully a cure are yet to be developed. The goal of this review is to summarize recent literature on neurotrophins (NTs) in experimental models and clinical settings of asthma research.

RECENT FINDINGS

We highlight studies of early phases of asthma that collectively reveal a profound impact of elevated NT levels following initial detrimental insults on long-term airway dysfunction. We hope this review will foster insights into the complex interaction between NTs, nerves, immune cells, and airway structural cells during a critical time window of development and disease susceptibility. Future studies are required to better understand the role of NTs in asthma pathophysiology and to evaluate whether NTs and their receptors may serve as new drug targets.

Targeting acetylcholine receptor M3 prevents the progression of airway hyperreactivity in a mouse model of childhood asthma

Asthma often progresses into adulthood from early-life episodes of adverse environmental exposures. However, how the injury to developing lungs contributes to the pathophysiology of persistent asthma remains poorly understood. In this study, we identified an age-related mechanism along the cholinergic nerve-airway smooth muscle (ASM) axis that underlies prolonged airway hyperreactivity (AHR) in mice. We showed that ASM continued to mature until ∼3 wk after birth. Coinciding with postnatal ASM maturation, there was a critical time window for the development of ASM hypercontractility after cholinergic stimulation. We found that allergen exposure in neonatal mice, but not in adult mice, elevated the level and activity of cholinergic nerves (termed neuroplasticity). We demonstrated that cholinergic neuroplasticity is necessary for the induction of persistent AHR after neonatal exposure during rescue assays in mice deficient in neuroplasticity. In addition, early intervention with cholinergic receptor muscarinic (ChRM)-3 blocker reversed the progression of AHR in the neonatal exposure model, whereas β2-adrenoceptor agonists had no such effect. Together, our findings demonstrate a functional relationship between cholinergic neuroplasticity and ASM contractile phenotypes that operates uniquely in early life to induce persistent AHR after allergen exposure. Targeting ChRM3 may have disease-modifying benefits in childhood asthma.-Patel, K. R., Bai, Y., Trieu, K. G., Barrios, J., Ai, X. Targeting acetylcholine receptor M3 prevents the progression of airway hyperreactivity in a mouse model of childhood asthma.

Early life allergen-induced mucus overproduction requires augmented neural stimulation of pulmonary neuroendocrine cell secretion

Pulmonary neuroendocrine cells (PNECs) are the only innervated airway epithelial cells. To what extent neural innervation regulates PNEC secretion and function is unknown. Here, we discover that neurotrophin 4 (NT4) plays an essential role in mucus overproduction after early life allergen exposure by orchestrating PNEC innervation and secretion of GABA. We found that PNECs were the only cellular source of GABA in airways. In addition, PNECs expressed NT4 as a target-derived mechanism underlying PNEC innervation during development. Early life allergen exposure elevated the level of NT4 and caused PNEC hyperinnervation and nodose neuron hyperactivity. Associated with aberrant PNEC innervation, the authors discovered that GABA hypersecretion was required for the induction of mucin Muc5ac expression. In contrast, NT4^-/- mice were protected from allergen-induced mucus overproduction and changes along the nerve-PNEC axis without any defects in inflammation. Last, GABA installation restored mucus overproduction in NT4^-/- mice after early life allergen exposure. Together, our findings provide the first evidence for NT4-dependent neural regulation of PNEC secretion of GABA in a neonatal disease model. Targeting the nerve-PNEC axis may be a valid treatment strategy for mucus overproduction in airway diseases, such as childhood asthma.-Barrios, J., Patel, K. R., Aven, L., Achey, R., Minns, M. S., Lee, Y., Trinkaus-Randall, V. E., Ai, X. Early life allergen-induced mucus overproduction requires augmented neural stimulation of pulmonary neuroendocrine cell secretion.

Asthma-like airway inflammation and responses in a rat model of atopic dermatitis induced by neonatal capsaicin treatment

Recent studies have shown that approximately 70% of patients with severe atopic dermatitis (AD) develop asthma. Development of AD in infancy and subsequent other atopic diseases such as asthma in childhood is referred to as atopic march. However, a causal link between the diseases of atopic march has remained largely unaddressed, possibly due to lack of a proper animal model. Recently, we developed an AD rat model showing chronically relapsing dermatitis and scratching behaviors induced by neonatal capsaicin treatment. Here, we investigated whether our model also showed asthmatic changes, with the aim of expanding our AD model into an atopic march model. First, we confirmed that capsaicin treatment (50 mg/kg within 24 h after birth) induced dermatitis and scratching behaviors until 6 weeks of age. After that, the mRNA expression of Th1 and Th2 cytokines, such as IFN-γ and TNF-α, and IL-4, IL-5, and IL-13, respectively, was quantified with quantitative real-time polymerase chain reaction in the skin and the lungs. The number of total cells and eosinophils was counted in bronchoalveolar lavage (BAL) fluid. The levels of IgE in the serum and BAL fluid were determined with enzyme-linked immunosorbent assay. Paraffin-embedded sections (4 μm) were stained with hematoxylin/eosin to analyze the morphology of the lung and the airway. Airway responsiveness was measured in terms of airway resistance and compliance using the flexiVent system. In the capsaicin-treated rats, persistent dermatitis developed, and scratching behaviors increased over several weeks. The levels of IgE in the serum and BAL fluid as well as the mRNA expression of Th2 cytokines, including IL-4, IL-5, and IL-13, in both the skin and the lungs were elevated, and the number of eosinophils in the BAL fluid was also increased in the capsaicin-treated rats compared to control rats. Morphological analysis of the airway revealed smooth muscle hypertrophy and extensive mucus plug in the capsaicin-treated rats. Functional studies demonstrated an increment of the airway resistance and a decrement of lung compliance in the capsaicin-treated rats compared to control rats. Taken together, our findings suggested that neonatal capsaicin treatment induced asthma-like airway inflammation and responses in juvenile rats.

The Role of Neurotrophins in Inflammation and Allergy

Allergic inflammation is the result of a specific pattern of cellular and humoral responses leading to the activation of the innate and adaptive immune system, which, in turn, results in physiological and structural changes affecting target tissues such as the airways and the skin. Eosinophil activation and the production of soluble mediators such as IgE antibodies are pivotal features in the pathophysiology of allergic diseases. In the past few years, however, convincing evidence has shown that neurons and other neurosensory structures are not only a target of the inflammatory process but also participate in the regulation of immune responses by actively releasing soluble mediators. The main products of these activated sensory neurons are a family of protein growth factors called neurotrophins. They were first isolated in the central nervous system and identified as important factors for the survival and differentiation of neurons during fetal and postnatal development as well as neuronal maintenance later in life. Four members of this family have been identified and well defined: nerve growth factor, brain-derived neurotrophic factor, neurotrophin 3, and neurotrophin 4/5. Neurotrophins play a critical role in the bidirectional signaling mechanisms between immune cells and the neurosensory network structures in the airways and the skin. Pruritus and airway hyperresponsiveness, two major features of atopic dermatitis and asthma, respectively, are associated with the disruption of the neurosensory network activities. In this chapter, we provide a comprehensive description of the neuroimmune interactions underlying the pathophysiological mechanisms of allergic and inflammatory diseases.