Background The increased susceptibility of asthmatics to rhinovirus infection has recently been related to deficient IFN‐λ1 (IL‐29) and IFN‐λ2/3 (IL‐28) production by bronchial epithelial cells and macrophages.

Objectives Here, we studied IFN‐λ mRNA expression in the airways of stable asthmatics in comparison with healthy subjects and in relation to asthma symptoms, non‐invasive parameters of airway inflammation and lung function parameters.

Methods Airway cells were obtained by sputum induction, in 14 healthy and 35 asthmatic adults and 12 asthmatic school‐aged children. IFN‐λ was studied at the mRNA level by quantitative RT‐PCR.

Results Asthmatic adults have increased sputum IL‐28 mRNA but similar IL‐29 mRNA expression in comparison with healthy subjects. In asthmatics, both sputum IL‐28 and IL‐29 mRNA expression correlate with the sputum CD3γ mRNA expression (reflecting infiltrated T cells). IL‐28 (but not IL‐29) mRNA levels correlate with the relative and absolute number of eosinophils present in the sputum sample. Sputum IL‐29 mRNA (but not IL‐28) correlates negatively with asthma symptoms in steroid‐naïve patients and is significantly higher in steroid‐treated than in steroid‐naïve patients. Finally, both IL‐28 and IL‐29 mRNA levels are higher in asthmatic children than in asthmatic adults.

Conclusion Our results show that asthmatic subjects have substantial type III IFN‐λ mRNA levels in the airways. Our data furthermore suggest that IL‐29 could have an immunoprotective role in the lower airways.