Neutrophil phenotypes in bronchial airways differentiate single from dual responding allergic asthmatics

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. Allergic asthmatics underwent an inhaled allergen challenge with samples taken from the airway and blood at baseline and after the challenge. Dual responding allergic asthmatics (DR) had more 2‐ to 3‐lobed (known as ‘active’) and less ≥5‐lobed (‘suppressive’) airway neutrophils correlating with less circulating IL‐1Ra than single responders (SR) at baseline. Following an inhaled allergen challenge, DR had more circulating NETosis factors than SR during the early allergic reaction phase (EAR).