Sputum basophils are increased in eosinophilic asthma compared with non-eosinophilic asthma phenotypes

Abstract

Sputum basophil numbers are increased in allergic asthmatics, but it is unclear what role airway basophils play in "TH2-low" asthma phenotypes. Using flow cytometry we found that basophils were significantly increased in all asthmatics (n=26) compared with healthy controls (n=8) (p=0.007) with highest levels observed in eosinophilic asthma (EA; median 0.22%, IQR 0.11-0.47%; n=14) compared with non-EA (0.06%, 0.00-0.20%; n=12; p<0.05). In asthmatics, basophils were positively correlated with sputum eosinophils (r=0.54; p<0.005), and inversely with sputum neutrophils (r=-0.46: p<0.05), but not with FEV₁ (% predicted), FEV₁/FVC, or bronchodilator reversibility. In a subgroup initially identified as inadequately controlled asthma (n=7), there was a trend (p=0.08) towards a reduction in sputum basophils following increased ICS treatment. Our findings suggest that basophils may be particularly important in eosinophilic asthma, and that sputum basophil assessment could be a useful additional indicator of 'TH2-high' asthma.

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