Relation of sputum inflammatory markers to symptoms and lung function changes in COPD exacerbations

Abstract

Background - Although it is presumed that exacerbations of chronic obstructive pulmonary disease (COPD) are associated with increased airway inflammation, there is little information available on inflammatory markers during an exacerbation and the relationship with severity or time course of recovery. A study was undertaken to investigate the sputum cell and cytokine characteristics of COPD when stable and during an exacerbation. Methods - Induced sputum samples from 57 patients with moderate to severe COPD were analysed (44 samples were taken during a stable period and 37 during an exacerbation). The patients recorded daily symptoms on diary cards. Cell counts and sputum levels of interleukin (IL)-6 and IL-8 were measured. Results - Patients with ≥ 3 exacerbations/year had higher median stable sputum levels of IL-6 (110 (95% CI 11 to 215) pg/ml) and IL-8 (6694 (95% CI 3120 to 11,995) pg/ml) than those with ≤ 2 exacerbations/year (22 (95% CI 12 to 93) and 1628 (95% CI 607 to 4812) pg/ml, respectively). Median IL-6 levels were increased during exacerbations compared with stable conditions. The levels of IL-6 during exacerbations were related to the presence of a cold and to the total cell count and eosinophil and lymphocyte numbers, while IL-8 was positively correlated with all sputum cell counts. Sputum cell counts and cytokine levels during an exacerbation did not predict the size and duration of lung function changes in the exacerbation. Conclusions - Patients with more frequent exacerbations have higher baseline sputum cytokine levels, which may predict the frequency of future exacerbations.