Neutrophil elastase (NE), is an important host defence against lung pathogens. Maintaining a homeostatic balance between proteases such as NE and anti-proteases such as secretory leukocyte protease inhibitor (SLPI), is important to prevent tissue damage. In the cystic fibrosis (CF) lung, elevated protease levels and impaired anti-protease defences contribute to tissue destruction.
We assessed lung function and sputum SLPI and NE levels from Pseudomonas aeruginosa infected and non-infected CF patients (median age 20 years at recruitment) during different phases of clinical disease. Healthy, never smokers served as healthy controls (HC). Sputum total cell counts (TCC) and colony forming units of P. aeruginosa were also determined in each sputum sample.
Compared to HC, sputum SLPI was significantly reduced and NE increased in all CF subjects whether infected with P. aeruginosa or not, but the presence of P. aeruginosa worsened these parameters. Females with chronic P. aeruginosa infection had significantly lower sputum SLPI levels than males (p < 0.001). Higher sputum SLPI levels were associated with a significantly reduced rate of longitudinal decline in FEV % predicted (p < 0.05). Antibiotic treatment in P. aeruginosa-infected patients significantly decreased sputum TCC and increased SLPI levels, which positively correlated with improved lung function.
Airway SLPI is deficient in CF, which appears more marked in P. aeruginosa-infected female patients. Importantly, a reduced anti-protease to protease ratio is associated with accelerated lung function decline. Treatment of an exacerbation is accompanied by partial recovery of anti-protease defences and significant improvement in lung function, an important clinical outcome.

© 2023 Asian Pacific Society of Respirology.