Background: Viral infections are common triggers of asthma exacerbations and the epithelial response to a viral mimic differs across asthma severity. We hypothesized that a cluster analysis of the epithelial response to a viral mimic would identify distinct viral exacerbation endotypes.

Methods: 50 patients with asthma were included. All participants underwent bronchoscopy with collection of bronchial brushings. Bronchial epithelial cells were expanded and stimulated with the viral replication mimic poly (I:C) in vitro. A cluster analysis of standardized protein release of INFb, IL13, IL1b, IL33, IL4, IL6, IL8, CCL5, TNFa and TSLP after poly (I:C) stimulation was performed.

Results: Four clusters were identified. Cluster 1 was the largest and consisted of patients with mild-to-moderate asthma, little T2 inflammation and low protein induction. Cluster 3 was the smallest, consisted of steroid-naïve well-controlled patients without T2 inflammation, and was characterized by predominant IL33, IL4 and IL13 induction. Cluster 2 and 4 were both characterized by marked T2 inflammation, with cluster 2 clinically resembling the late-onset severe eosinophilic non-allergic phenotype and characterized by predominant TSLP and CCL5 protein induction. Cluster 4 ? characterized by predominant CCL5 and IFNb induction ? consisted of patients with less severe asthma and preserved lung function.

Conclusion: Clustering of the bronchial epithelial immune response to a viral mimic identified clinically recognizable viral exacerbation endotypes. Induction of alarmins differed markedly with TSLP associated with severe eosinophilic disease and IL-33 with mild steroid-naïve disease.