A re-examination of former concepts is required to meet today’s medical challenges in allergic rhinitis. Previously, neutrophils have been treated as a relatively homogenous cell population found in the nose both when the patient is suffering at the height of the allergic season as well as when the patient report no symptoms. However, new data indicates that neutrophils can be divided into different subsets with diverse roles in inflammation. We showed increased levels of neutrophils in peripheral blood, nasal biopsies and nasal lavage fluid (NAL) from allergic patients during the pollen season compared to healthy controls. A closer examination revealed that the activated subset of neutrophils, CD16high CD62Ldim, outweighed the normal form CD16high CD62Lhigh in nasal tissue among these patients. This skewed distribution was not seen in controls. The normal subset prevailed in peripheral blood from patients as well as controls, whereas CD16high CD62Ldim and CD16dim CD62Ldim subsets, the latter considered “end state” neutrophils before apoptosis, were elevated in NAL. Functional in vitro experiments revealed that activated neutrophils exhibit a T cell priming capacity and an ability to enhance eosinophil migration. Activated neutrophils may thus contribute to allergic inflammation seen in allergic rhinitis by priming T cells and attracting eosinophils.

Background: Previous research has emphasized the importance of eosinophils in allergic asthma, while paying less attention to neutrophils. The known functionality of neutrophils in the inflammatory process has recently changed and knowledge about subsets of neutrophils, as characterized by their expression of CD16 and CD62L, has surfaced. Their specific roles in asthma are still unknown.Objective: To study the functional differences between subsets of neutrophils by characterizing the impact of individual subsets on airway smooth muscle reactivity. Methods:The direct effect of neutrophils on airway hyperresponsiveness was assessed by co-culturing different subsets of neutrophils (produced by LPS in vitro stimulation) with human isolated small airways or murine tracheae with subsequent evaluation of smooth muscle reactivity to bradykinin in myographs. Supernatants and tissue were saved for ELISA and immunohistochemistry.Results: The CD16 high CD62L dim neutrophils were found to enhance the response to bradykinin in both human isolated small airways and murine tracheae. No such effects were obtained for the other subsets. The response is due to an upregulation of bradykinin receptor 2 through release of TNFα from the neutrophil.Conclusions and Clinical Relevance: The present study introduces a new concept regarding the role of neutrophils and defines a novel direct link between a specific activated neutrophil subset and airway smooth muscle, establishing neutrophils as important players in the development of asthmatic airway hyperactivity.

Despite the introduction of vaccines, COVID-19 still affects millions of people worldwide. A better understanding of pathophysiology and the discovery of novel therapies are needed. One of the cells of interest in COVID-19 is the neutrophil. This cell type is being recruited to a site of inflammation as one of the first immune cells. In this project, we investigated a variety of neutrophils phenotypes during COVID-19 by measuring the expression of markers for migration, maturity, activation, gelatinase granules and secondary granules using flow cytometry. We show that neutrophils during COVID-19 exhibit altered phenotypes compared to healthy individuals. The activation level including NETs production and maturity of neutrophils seem to last longer during COVID-19 than expected for innate immunity. Neutrophils as one of the drivers of severe cases of COVID-19 are considered as potential treatment targets. However, for a successful implementation of treatment, there is a need for a better understanding of neutrophil functions and phenotypes in COVID-19. Our study answers some of those questions.

8. Morita H, Arae K, Unno H, et al. An interleukin-33-mast cell-interleukin-2 axis suppresses papain-induced allergic inflammation by promoting regulatory T cell numbers. Immunity 2015;43:175-186. 9. Sugita K, Steer CA, Martinez-Gonzalez I, et al. Type 2 innate lymphoid cells disrupt bronchial epithelial barrier integrity by targeting tight junctions through IL-13 in asthmatic patients.

MP-AzeFlu is relatively new a pharmaceutical drug used in the treatment of allergic rhinitis. It is comprised of azelastine hydrochloride (AZE), a potent histamine-H1-receptor antagonist and fluticasone propionate (FP), corticosteroid. It's somewhat bitter taste (often considered a disadvantage) can be attributed to AZE. We here hypothesize that MP-AzeFlu may induce some of its beneficial effects through activation of bitter taste receptors (Tas2R), which have recently been described in human airways. In the nose Tas2Rs induce secretion of antimicrobial peptides and increase ciliary activity, while in the lung they cause airway smooth muscle relaxation. The mechanisms behind Tas2R-mediated effects are not yet fully known. In order to evaluate the role of Tas2R in the effects induced by MP-AzeFlu the dilatory response of pre-contracted isolated airways from Balb/c mice was investigated in tissue bath myographs in the presence or absence of various well-characterized pharmacological antagonists or their corresponding vehicles. MP-AzeFlu caused a potent dose-dependent relaxation of pre-contracted airways, an effect probably mediated by its AZE component. The dilatory effect of MP-AzeFlu and AZE both mimicked the response induced by the Tas2R agonist, chloroquine, but was independent of histamine receptor (H1-, H2-and H3-), prostaglandins, cAMP and cGMP involvement, all known to be common pathways for airway dilation. Other bitter-tasting antihistamines (i.e. olopatadine and desloratadine) also relaxed airway segments. These data support the notion that MP-AzeFlu has the ability to activate Tas2R in the same way as chloroquine. The effect appears to be mediated by AZE, but not via the histamine receptor. Activation of Tas2R by MP-AzeFlu may contribute to its superior efficacy over FP observed in controlled clinical trials in patients with moderate/severe allergic rhinitis.

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Additional supporting information may be found online in the Supporting Information section.

Introduction: Allergic asthmatics with both an early (EAR) and a late allergic reaction (LAR) following allergen exposure are termed 'dual responders' (DR), while 'single responders' (SR) only have an EAR. Mechanisms that differentiate DR from SR are largely unknown, particularly regarding the role and phenotypes of neutrophils.Therefore, we aimed to study neutrophils in DR and SR asthmatics.Methods: Thirty-four allergic asthmatics underwent an inhaled allergen challenge, samples were collected before and up to 24 h post-challenge. Cell differentials were counted from bronchial lavage, alveolar lavage and blood; and tissue neutrophils were quantified in immune-stained bronchial biopsies. Lavage neutrophil nuclei lobe segmentation was used to classify active (1-4 lobes) from suppressive neutrophils (≥5 lobes). Levels of transmigration markers: soluble (s)CD62L and interleukin-1Ra, and activity markers: neutrophil elastase (NE), DNA-histone complex and dsDNA were measured in lavage fluid and plasma. Results:Compared with SR at baseline, DR had more neutrophils in their bronchial airways at baseline, both in the lavage (p = .0031) and biopsies (p = .026) and elevated bronchial neutrophils correlated with less antitransmigratory IL-1Ra levels (r = −0.64).DR airways had less suppressive neutrophils and more 3-lobed (active) neutrophils (p = .029) that correlated with more bronchial lavage histone (p = .020) and more plasma NE (p = .0016). Post-challenge, DR released neutrophil extracellular trap factors in the blood earlier and had less pro-transmigratory sCD62L during the late phase (p = .0076) than in SR. Conclusion:DR have a more active airway neutrophil phenotype at baseline and a distinct neutrophil response to allergen challenge that may contribute to the development of an LAR. Therefore, neutrophil activity should be considered during targeted diagnosis and bio-therapeutic development for DR.