IL-6 and IL-13 in induced sputum of COPD and asthma patients: correlation with respiratory tests

Background: IL-6 is strongly implicated in the development of chronic obstructive pulmonary disease (COPD). IL-13 is the well-documented central mediator in allergic asthma. IL-6 is attributed to the proinflammatory activities in COPD as well as asthma. In COPD patients exacerbation is increased by serum IL-6. The association of IL-13 as well as IL-6 with the impaired respiratory function of asthma patients remains controversial.

Objectives: The aim of this study was to compare the concentration of IL-6 and IL-13 in the induced sputum of asthma and COPD patients, and to assess the possible association of these cytokines with the impairment of lung function.

Methods: Twenty-six subjects with COPD and 18 subjects with asthma were enrolled in this study. IL-6 and IL-13 levels were measured in induced sputum by ELISA and correlated with the results of respiratory tests.

Results: The induced sputum of COPD patients had a significantly higher IL-6 level than the sputum of asthma subjects while no significant differences were found in the levels of IL-13. There was a statistically significant negative correlation between IL-6 level and FEV(1) or FEV(1)/FVC in asthma patients (r = -0.59 and -0.54, respectively) and a negative correlation that did not reach statistical significance between IL-6 level and FEV(1), FEV(1)% or FVC in COPD subjects (r = -0.30, -0.30 and -0.38, respectively). There was no relationship between concentrations of IL-13 and impaired respiratory function.

Conclusions: Our results confirmed that IL-6, but not of IL-13, is associated with respiratory disorders in both asthma and COPD patients.