Airway inflammatory phenotypes of asthmatic patients

Abstract

To analyze the airway inflammatory phenotypes and clinical features of severe asthma compared to mild-moderate ("common") asthma. A total of 946 cases of asthma were retrospectively analyzed in our hospital from January 2013 to December 2014. Sixty-one patients were classified to the severe asthma group, and 885 patients to the common asthma group. Severe asthma was diagnosed based on the protocol from ATS/ERS guidelines. All patients received induced sputum cell counts and pulmonary function tests, and 543 of them received fractional exhaled nitric oxide (FeNO) tests. The airway inflammatory phenotypes were defined and the clinical features of patients of severe asthma were studied. The distribution of airway inflammatory phenotypes of asthma was as follows: eosinophilic subtype (46.6%, 441/946), mixed granulocytic subtype (27.5%, 260/946), neutrophilic subtype (21.5%, 203/946), and paucigranulocytic subtype (4.4%, 42/946). There were no differences between the severe asthma group and the common asthma group in the distributions. Compared with common asthma patients, severe asthma patients had higher sputum eosinophil percentages (29.1 % ± 28.5% vs 22.2% ± 25.2%, t = 1.98, P < 0.05), higher FeNO values [(66.4 ± 64.1) ppb vs (48.0 ± 43.7) ppb, P < 0.01], lower percentages of FEV1% pred [(63.7 ± 24.1) % vs (84.7 ± 23.7)%, P < 0.01], and lower ratios of FEV1/FVC [(56.4 ± 15.1) % vs (69.1 ± 14.5)% P < 0.01]. In severe asthma patients, FeNO values were higher in the eosinophilic subtype and mixed granulocytic subtype (P < 0.05). Neutrophilic subtype patients had the lowest sputum eosinophil percentage [(1.8 ± 0.8)%, P < 0.01], the lowest percentage of FEV1% pred [(46.6 ± 16.1)%, P < 0.01], and the lowest ratios of FEV1/FVC [(45.2 ± 16.1)%, P < 0.01]. The common airway inflammatory phenotypes included eosinophilic subtype, mixed granulocytic subtype and neutrophilic subtype, in both severe and common asthma patients. Severe asthma patients had more severe eosinophilic airway inflammation and poorer lung function. Neutrophilic subtype might be the most intractable subtype with severely damaged pulmonary function in severe asthma.