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.