Expression of FURIN
FURIN levels in sputum were significantly higher in SA than in MMA or HV (Fig 1C ). In univariate linear regression analyses, FURIN levels were significantly associated with sputum eosinophils (%), sputum neutrophils (%), blood neutrophils (%), post-BD FEV1 (% predicted), and severe asthma (Table 1 ). On multivariate analysis, sputum neutrophils (%) and severe asthma remained significantly associated with sputum FURIN levels (0.555; 95% CI: 0.336 to 0.775; p <0.001; and 0.381; 0.005 to 0.757; p =0.047, respectively) (Fig 2A ). The relationship between sputum FURIN levels and neutrophils (%) was not affected by further adjustments including OCS use (0.545; 95% CI: 0.324 to 0.767;p <0.001). Spearman’s correlation coefficient (r ) between sputum FURIN levels and neutrophils (%) was 0.60 (p <0.001) (Fig 3A ).
In bronchial brushing, FURIN levels were positively associated with male gender and blood neutrophils (%) (0.320; 95% CI: 0.095 to 0.545;p =0.006; and 0.279; 95% CI: 0.025 to 0.534; p =0.032, respectively) (Fig 2B ). In bronchial biopsy, there was no association with any baseline parameters (Fig 2C ).