Raised interferon-β, type 3 interferon and interferon-stimulated genes - evidence of innate immune activation in neutrophilic asthma.

Background: Interferons play an important role in innate immunity. Previous studies report deficiency in virus induction of interferon (IFN)-α, IFN-β and IFN-λ in bronchial epithelial and bronchial lavage cells in atopic asthmatics. It is now recognized that asthma is a heterogeneous disease comprising different inflammatory phenotypes, some of which may involve innate immune activation in the absence of overt infection.

Objective: The aim of this study was to investigate whether the severity of asthma or a specific cellular sputum pattern may be linked to evidence of innate immune activation.

Methods: Here we investigate the expression of IFN-β, IFN-λ1 (IL-29), IFN-λ2/3 (IL-28A/B) and the interferon-stimulated genes (ISGs) such as myxovirus resistance 1 (Mx1), oligoadenylate synthetase (OAS) and viperin in unstimulated sputum cells in 57 asthmatics (including 16 mild, 19 moderate and 22 severe asthma patients) and compared them with 19 healthy subjects.

Results: We observed increased expression of IFN-β, IFN-λ1/IL-29, OAS and viperin in asthmatics compared with healthy subjects, while IL-28 was not expressed in any group. The overexpression was restricted to neutrophilic asthmatics (sputum neutrophils ≥ 76%), while eosinophilic asthmatics (sputum eosinophils ≥ 3%) did not differ from healthy subjects or even showed a lower expression of Mx1. No difference in interferon or ISG expression was observed according to clinical asthma severity.

Conclusion And Clinical Relevance: Neutrophilic, but not eosinophilic, asthmatics display overexpression of IFN-β, IFN-λ1/IL-29 and ISGs in their sputum cells that may reflect ongoing innate immune activation.