Increased Sputum IL-17A Level in Non-asthmatic Eosinophilic Bronchitis

Area of Science:

• Immunology
• Respiratory Medicine
• Pathophysiology

Background:

• Non-asthmatic eosinophilic bronchitis (NAEB) is a common cause of chronic cough characterized by airway eosinophilic inflammation without hyper-responsiveness.
• While the Th2 pathway is implicated in NAEB, the role of non-Th2 pathways remains unclear.
• Interleukin-17A (IL-17A), a Th17 pathway cytokine, is known to be involved in asthma pathogenesis, but its role in NAEB is not well understood.

Purpose of the Study:

• To investigate the levels of IL-17A in the airways of individuals with NAEB.
• To explore the relationship between IL-17A levels and airway function parameters in NAEB and asthma patients.

Main Methods:

• Sputum supernatant IL-17A concentrations were measured in 12 NAEB patients, 16 asthma patients (9 eosinophilic, 7 non-eosinophilic), and 9 healthy controls.
• Airway function was assessed, and correlations between IL-17A levels and parameters like FENO, FEV1/FVC%, MMEF%pred, and sputum neutrophil percentage were analyzed.

Main Results:

• IL-17A levels were significantly increased in NAEB, eosinophilic asthma (EA), and non-eosinophilic asthma (NEA) groups compared to healthy controls.
• Sputum IL-17A levels showed positive correlations with fractional exhaled nitric oxide (FENO) and sputum neutrophil percentage.
• Negative correlations were observed between IL-17A levels and FEV1/FVC% and MMEF%pred.

Conclusions:

• The Th17 pathway, indicated by elevated IL-17A concentrations in sputum supernatant, appears to contribute to the pathophysiology of NAEB.
• These findings suggest that IL-17A may play a role not only in asthma but also in NAEB.