LAUSR

Rationale: Quantification of type 2 inflammation provided a molecular basis for heterogeneity in asthma. Non‐type 2 pathways that contribute to asthma pathogenesis are not well understood. Objectives: To identify dysregulated pathways beyond type 2 inflammation. Methods: We applied RNA sequencing to airway epithelial brushings obtained from subjects with stable mild asthma not on corticosteroids (n = 19) and healthy control subjects (n = 16). Sequencing reads were mapped to human and viral genomes. In the same cohort, and in a separate group with severe asthma (n = 301), we profiled blood gene expression with microarrays. Measurements and Main Results: In airway brushings from mild asthma on inhaled corticosteroids, RNA sequencing yielded 1,379 differentially expressed genes (false discovery rate < 0.01). Pathway analysis revealed increased expression of type 2 markers, IFN‐stimulated genes (ISGs), and endoplasmic reticulum (ER) stress‐related genes. Airway epithelial ISG expression was not associated with type 2 inflammation in asthma or with viral transcripts but was associated with reduced lung function by FEV1 (&rgr; = ‐0.72; P = 0.0004). ER stress was confirmed by an increase in XBP1 (X‐box binding protein 1) splicing in mild asthma and was associated with both type 2 inflammation and ISG expression. ISGs were also the most activated genes in blood cells in asthma and were correlated with airway ISG expression (&rgr; = 0.55; P = 0.030). High blood ISG expression in severe asthma was similarly unrelated to type 2 inflammation. Conclusions: ISG activation is prominent in asthma, independent of viral transcripts, orthogonal to type 2 inflammation, and associated with distinct clinical features. ER stress is associated with both type 2 inflammation and ISG expression.