Abstract
Neutrophilic asthma features increased airway classical monocytes: Sputum eosinophil and neutrophil count vary in asthma, however conventional sputum analysis does not distinguish macrophages from monocutes or identify monocyte functional subsets. We aimed to use flow cytometry to quantify sputum macrophages, monocytes and their subsets and test their relationship to inflammatory and clinical features of asthma.
Flow cytometry was performed on induced sputum from 53 participants (45 asthma, 8 non-asthma). Conventional monocyte subsets (classical [CM], intermediate [IM], non-classical [NCM]) were identified by surface CD14/CD16. CD206, a marker of monocyte tissue differentiation, was measured. Relationship of macrophage and monocyte measures to airway inflammatory phenotype (paucigranulocytic [PGA] <3% eosinophils, <61% neutrophils; eosinophilic [EA] ≥3% eosinophils, <61% neutrophils; neutrophilic [NA] <3% eosinophils, ≥61% neutrophils) and asthma severity (defined by ERS/ATS guidelines) was tested.
Macrophage number (p=0.02) and proportion (p=0.02) were reduced in asthma compared to non-asthma. CM proportion (p=0.02) but not number was increased in asthma. CM number was increased in NA vs PGA (p=0.02). CD206- monocyte number was increased in NA vs EA (p=0.006). NCM proportion was elevated in severe (n=12) vs non-severe (n=33) asthma (p=0.03).
This is the first demonstration that sputum monocyte numbers and activation status are altered in asthma. NA features increased numbers of CM and CD206- monocytes, suggestive of increased recruitment of inflammatory monocytes in concert with neutrophils. Further investigation how airway monocyte dysregulation impacts on disease activity in neutrophilic and severe asthma is merited.
Footnotes
Cite this article as: European Respiratory Journal 2020; 56: Suppl. 64, 1109.
This abstract was presented at the 2020 ERS International Congress, in session “Respiratory viruses in the "pre COVID-19" era”.
This is an ERS International Congress abstract. No full-text version is available. Further material to accompany this abstract may be available at www.ers-education.org (ERS member access only).
- Copyright ©the authors 2020