Data analysis
Data were downloaded from the tranSMART platform (16). We analysed the gene expression of ACE2, TMPRSS2, and FURIN in the lower airway samples obtained from asthmatics and healthy subjects. Gene expression levels and inflammatory cell counts in sputum were log-transformed to normalize their distribution. One-way ANOVA and Tukey’s multiple comparison tests were utilized to examine differences of the gene expression levels of ACE2, TMPRSS2 and FURIN across the 3 groups (SA, MMA and HV) or the 3 TACs (15). Linear regression analyses were used to examine baseline demographic and clinical parameters in relation to each gene expression level. Multivariate linear regressions were conducted to identify baseline parameters significantly correlated with each gene expression level, with adjustment for age, gender and any parameters showingp values < 0.05 in univariate analyses; when both sputum and blood eosinophils (%) or neutrophils (%) showed pvalues < 0.05, sputum values were chosen for the multivariate model. The Benjamini–Hochberg procedure controlled for false discovery rate. Spearman’s rank correlation was used for correlation analysis.