Sputum immunoglobulin E levels correlate with eosinophilic airway regardless of atopy

Immunoglobulin E (IgE) is a key molecule that induces mast cell activation in allergic inflammation and contributes to type 2/eosinophilic inflammation in asthmatic airways. This cross-sectional study investigated the role of local IgE in asthmatic airways according to atopy, asthma control, and eosinophilic inflammation. A total of 31 adult patients with moderate-to-severe asthma were enrolled. The study subjects were classified into (1) atopic/non-atopic, (2) controlled/partly controlled/uncontrolled asthma and (3) eosinophilic/non-eosinophilic asthma. Serum/sputum IgE and serum/urine eosinophil-derived neurotoxin (EDN) were measured. Serum IgE levels were higher in atopic asthmatics than in non-atopic asthmatics, whereas no differences were noted in sputum IgE levels. Sputum IgE levels were significantly higher in uncontrolled asthmatics than in partly controlled or controlled asthmatics, and in eosinophilic asthmatics than in non-eosinophilic asthmatics, whereas no differences were noted in serum IgE levels. Significant correlations were observed between serum EDN and serum/sputum IgE levels. The production of local IgE in asthmatic airways could contribute to type 2/eosinophilic inflammation, irrespective of atopy, resulting in poor asthma control. Strategies targeting IgE may be effective in the management of non-atopic and atopic asthma.