The nasal basal cell population shifts toward a diseased phenotype with impaired barrier formation capacity in allergic rhinitis.

BACKGROUND: The integrity of the airway epithelium is guarded by the airway basal cells that serve as progenitor cells and restore wounds in case of injury. Basal cells are a heterogenous population, and specific changes in their behavior are associated with chronic barrier disruption-mechanisms that have not been studied in detail in allergic rhinitis (AR). OBJECTIVE: We aimed to study basal cell subtypes in AR and healthy controls. METHODS: Single-cell RNA sequencing (scRNA-Seq) of the nasal epithelium was performed on nonallergic and house dust mite-allergic AR patients to reveal basal cell diversity and to identify allergy-related alterations. Flow cytometry, immunofluorescence staining, and in vitro experiments using primary basal cells were performed to confirm phenotypic findings at the protein level and functionally. RESULTS: The scRNA-Seq, flow cytometry, and immunofluorescence staining revealed that basal cells are abundantly and heterogeneously present in the nasal epithelium, suggesting specialized subtypes. The total basal cell fraction within the epithelium in AR is increased compared to controls. scRNA-Seq demonstrated that potentially beneficial basal cells are missing in AR epithelium, while an activated population of allergy-associated basal cells is more dominantly present. Furthermore, our in vitro proliferation, wound healing assay and air-liquid interface cultures show that AR-associated basal cells have altered progenitor capacity compared to nonallergic basal cells. CONCLUSIONS: The nasal basal cell population is abundant and diverse, and it shifts toward a diseased state in AR. The absence of potentially protective subtypes and the rise of a proinflammatory population suggest that basal cells are important players in maintaining epithelial barrier defects in AR.

Monoclonal antibody or aspirin desensitization in NSAID-exacerbated respiratory disease (N-ERD)?

Nonsteroidal anti-inflammatory drug (NSAID)-exacerbated respiratory disease (N-ERD) is a clinical syndrome characterized by nasal polyposis, asthma, and intolerance to aspirin/NSAID. It affects approximately 15% cases of severe asthma, 10% of nasal polyps and 9% of rhinosinusitis. N-ERD results in associated asthma exacerbations, oral corticosteroids bursts, corticosteroid-dependent disease, and multiple endoscopic sinus surgeries. Unknown influences cause polyp epithelium to release alarmins, such as IL-33 and TSLP. These cytokines activate lymphoid cells, both Th2 and ILC2, to release cytokines such as IL5, IL4 and IL13, resulting in complex type 2 inflammation involving mast cells, eosinophils and platelets. Arachidonic acid released from such cells is metabolized into mediators. N-ERD is characterized by an imbalance in eicosanoid levels, especially CysLTs, PDG and PGE2. Patients with N-ERD present nasal symptoms (congestion, hyposmia/anosmia, nasal discharge) and lower airways symptoms (cough, sneezing, shortness of breath, chest tightness), anosmia, severe hyposmia as well as severe asthma which impacts the quality of life in this disease and leads to safety concerns in patients daily lives. Despite the variety of treatment strategies, the likelihood of recurrence of symptoms is high in patients with N-ERD. The most important strategies for treating N-ERD are listed as following: drug therapies, aspirin desensitization, monoclonal antibodies and other therapies associated. N-ERD treatment remains a major challenge in the current situation. Selecting the appropriate patient for aspirin desensitization, monoclonal antibodies or both is essential. This review provides an overview on aspirin desensitization and biologics in N-ERD and might help in decision making from both the perspective of the physician and patient. Patient characteristics, safety, efficacy, health care costs, but also patient preferences are all factors to take into account when it comes to a choice between biologics or aspirin desensitization.

Corrigendum: Innate lymphoid cells are required to induce airway hyperreactivity in a murine neutrophilic asthma model.

[This corrects the article DOI: 10.3389/fimmu.2022.849155.].

Peribronchial Inflammation Resulting from Regulatory T Cell Deficiency Damages the Respiratory Epithelium and Disturbs Barrier Function.

Regulatory T cells (Tregs) that express the transcription factor Foxp3 have a critical role in limiting inflammatory processes and tissue damage. Whether Tregs are functional in maintaining epithelial barriers and in control of tight junction expression has not yet been explored. In this study, we investigated the effect of Treg deficiency on the airway epithelial barrier in an experimental murine model in which diphtheria toxin was repeatedly injected in Foxp3-diphtheria toxin receptor (DTR) mice to deplete Tregs. This resulted in spontaneous peribronchial inflammation and led to a systemic and local increase of IL-4, IL-5, CCL3, IFN-γ, and IL-10 and a local (lung) increase of IL-6 and IL-33 and decreased amphiregulin levels. Moreover, Treg depletion increased airway permeability and decreased epithelial tight junction (protein and mRNA) expression. CTLA4-Ig treatment of Treg-depleted mice almost completely prevented barrier dysfunction together with suppression of lung inflammation and cytokine secretion. Treatment with anti-IL-4 partly reversed the effects of Treg depletion on tight junction expression, whereas neutralization of IL-6 of IFN-γ had either no effect or only a limited effect. We conclude that Tregs are essential to protect the epithelial barrier at the level of tight junctions by restricting spontaneous T cell activation and uncontrolled secretion of cytokines, in particular IL-4, in the bronchi.

Innate Lymphoid Cells Are Required to Induce Airway Hyperreactivity in a Murine Neutrophilic Asthma Model.

Rationale: Non-allergic asthma is driven by multiple endotypes of which neutrophilic and pauci-granulocytic asthma have been best established. However, it is still puzzling what drives inflammation and airway hyperreactivity (AHR) in these patients and how it can be treated effectively. Recently, a potential role of the innate immune system and especially the innate lymphoid cells (ILC) has been proposed. Objective: In this study, we investigated the effects of LPS inhalation on airway inflammation and AHR as a potential model for elucidating the pathogenesis of non-allergic asthma. Methods: Wild-type (BALB/c), SCID, IL-17A-/-, and Rag2-/- γC-/- mice were endonasally exposed to lipopolysaccharide (LPS, 2 µg) on four consecutive days. Twenty-four hours after the last exposure, AHR to methacholine was assessed. Cytokine levels and ILC subpopulations were determined in lung tissue. Cellular differential analysis was performed in BAL fluid. Main Results: In this study, we developed a murine model for non-allergic neutrophilic asthma. We found that repeated endonasal applications of low-dose LPS in BALB/c mice led to AHR, BAL neutrophilia, and a significant increase in lung ILC3 as well as a significant increase in lung chemokines KC and MIP-2 and cytokines IL-1ß, IL-17A, IL-22, and TNF. The adoptive transfer of ILC in Rag2-/- γC-/- mice showed that ILC played a causal role in the induction of AHR in this model. Antagonising IL-1ß, but not IL-17A or neutrophils, resulted in a partial reduction in LPS-induced AHR. Conclusion: In conclusion, we report here a murine model for neutrophilic asthma where ILC are required to induce airway hyperreactivity.

Erratum: Lacticaseibacillus casei AMBR2 Restores Airway Epithelial Integrity in Chronic Rhinosinusitis With Nasal Polyps.

This corrects the article on p. 560 in vol. 13, PMID: 34212544.

Taste Receptors: The Gatekeepers of the Airway Epithelium.

Taste receptors are well known for their role in the sensation of taste. Surprisingly, the expression and involvement of taste receptors in chemosensory processes outside the tongue have been recently identified in many organs including the airways. Currently, a clear understanding of the airway-specific function of these receptors and the endogenous activating/inhibitory ligands is lagging. The focus of this review is on recent physiological and clinical data describing the taste receptors in the airways and their activation by secreted bacterial compounds. Taste receptors in the airways are potentially involved in three different immune pathways (i.e., the production of nitric oxide and antimicrobial peptides secretion, modulation of ciliary beat frequency, and bronchial smooth muscle cell relaxation). Moreover, genetic polymorphisms in these receptors may alter the patients' susceptibility to certain types of respiratory infections as well as to differential outcomes in patients with chronic inflammatory airway diseases such as chronic rhinosinusitis and asthma. A better understanding of the function of taste receptors in the airways may lead to the development of a novel class of therapeutic molecules that can stimulate airway mucosal immune responses and could treat patients with chronic airway diseases.

Mometasone furoate and fluticasone furoate are equally effective in restoring nasal epithelial barrier dysfunction in allergic rhinitis.

Tight junction defects (TJ) have been associated with a defective epithelial barrier function in allergic rhinitis (AR). Intranasal corticosteroids are potent drugs frequently used to treat AR and are shown to restore epithelial integrity by acting on TJs and by reducing type 2 cytokine production. However, the effect of different classes of intranasal corticosteroids on the epithelial barrier has not been studied. Therefore, we compared the effect of 2 intranasal corticosteroids, ie, fluticasone furoate (FF) and mometasone furoate (MF) on epithelial barrier function. Both FF and MF similarly increased trans-epithelial electrical resistance of primary nasal epithelial cell cultures from AR patients. In a house dust mite-induced allergic asthma mouse model, FF and MF had similar beneficial effects on fluorescein isothiocyanate-dextran 4 kDa mucosal permeability, eosinophilic infiltration and IL-13 levels. Both molecules increased mRNA expression of the TJ proteins occludin and zonula occludens-1, thereby restoring epithelial barrier function. Lastly, we showed that long-term FF treatment also increased expression of occludin in AR patients compared to controls. In conclusion, both FF and MF effectively restore epithelial barrier function by increasing expression of TJ proteins in AR patients.

The nasal mutualist Dolosigranulum pigrum AMBR11 supports homeostasis via multiple mechanisms.

Comparing the nasal microbiome of healthy individuals and chronic rhinosinusitis (CRS) patients revealed Dolosigranulum pigrum as a species clearly associated with nasal health, although isolates obtained from healthy individuals are scarce. In this study, we explored the properties of this understudied lactic acid bacterium by integrating comparative genomics, habitat mining, cultivation, and functional characterization of interaction capacities. Mining 10.000 samples from the Earth Microbiome Project of 17 habitat types revealed that Dolosigranulum is mainly associated with the human nasal cavity. D. pigrum AMBR11 isolated from the nose of a healthy individual exerted antimicrobial activity against Staphylococcus aureus, decreased proinflammatory cytokine production in airway epithelial cells, and Galleria mellonella larvae mortality induced by this important nasal pathobiont. Furthermore, the strain protected the nasal barrier function in a mouse model using interleukin-4 as disruptive cytokine. Hence, D. pigrum AMBR11 is a mutualist with high potential as topical live biotherapeutic product.

A multicenter real-life study on the multiple reasons for uncontrolled allergic rhinitis.

BACKGROUND: Recent data show uncontrolled disease in 35% of allergic rhinitis (AR) patients on medical treatment. The reasons for uncontrolled disease can arbitrarily be divided into disease-related, diagnosis-related, treatment-related, and patient-related factors. However, the relative importance of these factors in uncontrolled disease remains speculative. This explorative study aimed at determining the factors causing uncontrolled AR on four different continents worldwide, identifying the most common reasons for uncontrolled disease in AR. METHODS: Patients with uncontrolled AR (n = 430) were asked to fill out a questionnaire and underwent a clinical examination at the outpatient clinic in five university outpatient clinics (Leuven [Belgium], Beijing [China], Kinshasa [Congo], Bangalore [India], and Philadelphia [US]). Two independent physicians evaluated the reason or multiple reasons for uncontrolled disease. The study was coordinated from the University Hospital of Leuven. RESULTS: In uncontrolled AR patients, 76% of patients showed two or more reasons for uncontrolled disease according to the physicians' evaluation. Disease-related factors (64%) were considered most often the reason for uncontrolled disease, followed by treatment- (56%), patient- (54%), and diagnosis-related (47%) factors. There is limited variability in observations across different centers worldwide. CONCLUSION: We here define the multiple reasons for uncontrolled AR across different continents, with disease-related factors being most frequently associated with uncontrolled disease. A better understanding of uncontrolled disease will guide us in defining strategies to improve AR care.

Lacticaseibacillus casei AMBR2 Restores Airway Epithelial Integrity in Chronic Rhinosinusitis With Nasal Polyps.

PURPOSE: A defective epithelial barrier has been demonstrated in chronic rhinosinusitis with nasal polyps (CRSwNP). Lactobacilli are shown to restore epithelial barrier defects in gastrointestinal disorders, but their effect on the airway epithelial barrier is unknown. In this study, hence, we evaluated whether the nasopharyngeal isolates Lacticaseibacillus casei AMBR2 and Latilactobacillus sakei AMBR8 could restore nasal epithelial barrier integrity in CRSwNP. METHODS: Ex vivo trans-epithelial tissue resistance and fluorescein isothiocyanate-dextran 4 kDa (FD4) permeability of nasal mucosal explants were measured. The relative abundance of lactobacilli in the maxillary sinus of CRSwNP patients was analyzed by amplicon sequencing of the V4 region of the 16S rRNA gene. The effect of spray-dried L. casei AMBR2 and L. sakei AMBR8 on epithelial integrity was investigated in vitro in primary nasal epithelial cells (pNECs) from healthy controls and patients with CRSwNP as well as in vivo in a murine model of interleukin (IL)-4 induced barrier dysfunction. The activation of Toll-like receptor 2 (TLR2) was explored in vitro by using polyclonal antibodies. RESULTS: Patients with CRSwNP had a defective epithelial barrier which positively correlated with the relative abundance of lactobacilli-specific amplicons in the maxillary sinus. L. casei AMBR2, but not L. sakei AMBR8, increased the trans-epithelial electrical resistance (TEER) of pNECs from CRSwNP patients in a time-dependent manner. Treatment of epithelial cells with L. casei AMBR2 promoted the tight junction proteins occludin and zonula occludens-1 reorganization. Furthermore, L. casei AMBR2 prevented IL-4-induced nasal permeability in vivo and in vitro. Finally, the beneficial effect of L. casei AMBR2 on nasal epithelial cells in vitro was TLR2-dependent as blocking TLR2 receptors prevented the increase in TEER. CONCLUSIONS: A defective epithelial barrier in CRSwNP may be associated with a decrease in relative abundance of lactobacilli-specific amplicons. L. casei AMBR2 would restore nasal epithelial integrity and can be a novel therapeutic strategy for CRSwNP.

A TRiP Through the Roles of Transient Receptor Potential Cation Channels in Type 2 Upper Airway Inflammation.

PURPOSE OF REVIEW: Despite their high prevalence, the pathophysiology of allergic rhinitis (AR) and chronic rhinosinusitis (CRS) remains unclear. Recently, transient receptor potential (TRP) cation channels emerged as important players in type 2 upper airway inflammatory disorders. In this review, we aim to discuss known and yet to be explored roles of TRP channels in the pathophysiology of AR and CRS with nasal polyps. RECENT FINDINGS: TRP channels participate in a plethora of cellular functions and are expressed on T cells, mast cells, respiratory epithelial cells, and sensory neurons of the upper airways. In chronic upper airway inflammation, TRP vanilloid 1 is mostly studied in relation to nasal hyperreactivity. Several other TRP channels such as TRP vanilloid 4, TRP ankyrin 1, TRP melastatin channels, and TRP canonical channels also have important functions, rendering them potential targets for therapy. The role of TRP channels in type 2 inflammatory upper airway diseases is steadily being uncovered and increasingly recognized. Modulation of TRP channels may offer therapeutic perspectives.

Tackling nasal symptoms in athletes: Moving towards personalized medicine.

Adequate nasal breathing is indispensable for athletes, and nasal symptoms have been shown to interfere with their subjective feeling of comfortable breathing and quality of life. Nasal symptoms are caused by either structural abnormalities or mucosal pathology. Structural pathologies are managed differently from mucosal disease, and therefore, adequate diagnosis is of utmost importance in athletes in order to choose the correct treatment option for the individual. Literature suggests that nasal symptoms are more prevalent in athletes compared to the general population and certain sports environments might even trigger the development of symptoms. Given the high demands of respiratory function in athletes, insight into triggering factors is of high importance for disease prevention. Also, it has been suggested that athletes are more neglectful to their symptoms and hence remain undertreated, meaning that special attention should be paid to education of athletes and their caregivers. This review aims at giving an overview of nasal physiology in exercise as well as the possible types of nasal pathology. Additionally, diagnostic and treatment options are discussed and we focus on unmet needs for the management and prevention of these symptoms in athletes within the concept of precision medicine.

Airway Basal Cells, Protectors of Epithelial Walls in Health and Respiratory Diseases.

The airway epithelium provides a critical barrier to the outside environment. When its integrity is impaired, epithelial cells and residing immune cells collaborate to exclude pathogens and to heal tissue damage. Healing is achieved through tissue-specific stem cells: the airway basal cells. Positioned near the basal membrane, airway basal cells sense and respond to changes in tissue health by initiating a pro-inflammatory response and tissue repair via complex crosstalks with nearby fibroblasts and specialized immune cells. In addition, basal cells have the capacity to learn from previous encounters with the environment. Inflammation can indeed imprint a certain memory on basal cells by epigenetic changes so that sensitized tissues may respond differently to future assaults and the epithelium becomes better equipped to respond faster and more robustly to barrier defects. This memory can, however, be lost in diseased states. In this review, we discuss airway basal cells in respiratory diseases, the communication network between airway basal cells and tissue-resident and/or recruited immune cells, and how basal cell adaptation to environmental triggers occurs.

Staphylococcus aureus enterotoxin B disrupts nasal epithelial barrier integrity.

BACKGROUND: Staphylococcus aureus colonization and release of enterotoxin B (SEB) has been associated with severe chronic rhinosinusitis with nasal polyps (CRSwNP). The pathogenic mechanism of SEB on epithelial barriers, however, is largely unexplored. OBJECTIVE: We investigated the effect of SEB on nasal epithelial barrier function. METHODS: SEB was apically administered to air-liquid interface (ALI) cultures of primary polyp and nasal epithelial cells of CRSwNP patients and healthy controls, respectively. Epithelial cell integrity and tight junction expression were evaluated. The involvement of Toll-like receptor 2 (TLR2) activation was studied in vitro with TLR2 monoclonal antibodies and in vivo in tlr2-/- knockout mice. RESULTS: SEB applied to ALI cultures of polyp epithelial cells decreased epithelial cell integrity by diminishing occludin and zonula occludens (ZO)-1 protein expression. Antagonizing TLR2 prevented SEB-induced barrier disruption. SEB applied in the nose of control mice increased mucosal permeability and decreased mRNA expression of occludin and ZO-1, whereas mucosal integrity and tight junction expression remained unaltered in tlr2-/- mice. Furthermore, in vitro SEB stimulation resulted in epithelial production of IL-6 and IL-8, which was prevented by TLR2 antagonization. CONCLUSION & CLINICAL RELEVANCE: SEB damages nasal polyp epithelial cell integrity by triggering TLR2 in CRSwNP. Our results suggest that SEB might represent a driving factor of disease exacerbation, rather than a causal factor for epithelial defects in CRSwNP. Interfering with TLR2 triggering might provide a way to avoid the pathophysiological consequences of S. aureus on inflammation in CRSwNP.

Prevalence and triggers of self-reported nasal hyperreactivity in adults with asthma.

BACKGROUND: Nasal hyperreactivity (NHR) is a common feature of various rhinitis subtypes and represents a novel phenotype of rhinitis. It is being reported in two-thirds of adult rhinitis patients irrespective of the atopic status. Data on the prevalence of NHR in patients with asthma are lacking, as well as the nature of evoking triggers. METHODS: Postal questionnaires were distributed to an unselected group of asthmatic patients in Leuven (Belgium, n = 190) and completed by 114 patients. In Mexico City (Mexico) and Brasov (Romania), respectively, 97 out of 110 and 80 out of 100 asthmatic patients attending the outpatient clinic completed the questionnaire. Non-asthmatic volunteers were recruited amongst university and hospital co-workers in Leuven (n = 53). The presence of self-reported NHR, the type of triggers evoking nasal and bronchial symptoms, medication use, self-reported allergy, and environmental factors were evaluated. RESULTS: Overall, 69% of asthma patients reported NHR, with 32% having more than 4 triggers evoking NHR. These triggers included mainly exposure to temperature and humidity changes, cigarette smoke, and strong odours. A higher prevalence of NHR was detected in allergic compared to non-allergic asthma patients (73% vs. 53% p < 0.01). The prevalence of NHR correlated with asthma severity, ranging from 63% (VAS ≤3) to 81% (VAS ≥7). BHR was found more frequently in patients with NHR compared to without NHR (89% vs. 53%, p < 0.0001). CONCLUSION: NHR represents a clinical phenotype of upper airway disease affecting over two-thirds of asthma patients and correlates with asthma severity. Targeting NHR in patients with asthma is often overlooked and should be reinforced in the future to achieve better symptom control.

Epithelial barriers in allergy and asthma.

The respiratory epithelium provides a physical, functional, and immunologic barrier to protect the host from the potential harming effects of inhaled environmental particles and to guarantee maintenance of a healthy state of the host. When compromised, activation of immune/inflammatory responses against exogenous allergens, microbial substances, and pollutants might occur, rendering individuals prone to develop chronic inflammation as seen in allergic rhinitis, chronic rhinosinusitis, and asthma. The airway epithelium in asthma and upper airway diseases is dysfunctional due to disturbed tight junction formation. By putting the epithelial barrier to the forefront of the pathophysiology of airway inflammation, different approaches to diagnose and target epithelial barrier defects are currently being developed. Using single-cell transcriptomics, novel epithelial cell types are being unraveled that might play a role in chronicity of respiratory diseases. We here review and discuss the current understandings of epithelial barrier defects in type 2-driven chronic inflammation of the upper and lower airways, the estimated contribution of these novel identified epithelial cells to disease, and the current clinical challenges in relation to diagnosis and treatment of allergic rhinitis, chronic rhinosinusitis, and asthma.