Pulmonary Function is Negatively Correlated with Sputum Inflammatory Markers and Cough Clearability in Subjects with Cystic Fibrosis but Not Those with Chronic Bronchitis

Background: Polymorphonuclear neutrophil (PMN)-dominated inflammation is prominent in the airways of subjects with cystic fibrosis (CF) and chronic bronchitis (CB). Interleukin (IL)-8, myeloperoxidase (MPO), and DNA are markers of neutrophilic inflammation. We hypothesized that sputum MPO, DNA, and IL-8 concentrations would negatively correlate with pulmonary function and sputum transportability.

Methods: We measured pulmonary function and analyzed sputum IL-8, MPO, and DNA concentrations, as well as the transport properties of sputum samples obtained from 16 subjects with CF and 15 subjects with CB. We also evaluated changes in these measurements in paired sputum samples from these subjects obtained 2 to 12 months apart.

Results: IL-8 and MPO concentrations in the sputum of CF subjects was inversely correlated with FEV(1) percent predicted (IL-8: r = -0.40; p = 0.003; MPO: r = -0.38; p = 0.003) and FVC percent predicted (IL-8: r = -0.4; p = 0.02; MPO: r = -0.4; p = 0.02). IL-8 and DNA concentrations were inversely correlated with sputum cough transportability (CTR) [IL-8: r = -0.4; p = 0.02; DNA: r = -0.36; p = 0.048]. Changes in DNA concentration in sputum samples from CF subjects over time were inversely correlated with changes in FEV(1) percent predicted (r = -0.58; p = 0.02), FVC percent predicted (r = -0.74; p = 0.002), and CTR (r = -0.59; p = 0.02). There was no correlation among pulmonary function, sputum properties, and inflammatory markers in the sputum from subjects with CB.

Conclusions: The sputum concentrations of IL-8, MPO, and DNA appear to be closely associated with pulmonary function in subjects with CF but not in subjects with CB.