Background: It has been shown that interleukin (IL)-18 levels in induced sputum are reduced in asthmatic and healthy smokers. However, in chronic obstructive pulmonary disease (COPD) patients, recent data show an overproduction in the lungs and increased serum levels of IL-18, suggesting that IL-18 may be involved in the pathogenesis of COPD. Method: In order to assess the relation of IL-18 with pulmonary function and airway inflammation in COPD, IL-18, tumour necrosis factor-a, and IL-8 levels were measured by ELISA in sputum supernatants obtained from patients with bronchitis type COPD (n Z 28), and healthy subjects (18 smokers and 17 non-smokers). Cellular localization of IL-18 was assessed by immunocytochemistry.Results: The levels of IL-18 were significantly higher in sputum supernatants of COPD patients compared to healthy smokers and non-smokers (p < 0.05). IL-18 production was localized to sputum macrophages. IL-18 levels were inversely correlated with FEV 1 (% predicted) (r Z À0.572, p Z 0.002) and FEV 1 /FVC ratio in COPD smokers (r Z À0.608, p Z 0.001). No correlations were found between IL-18 levels and inflammatory markers studied in induced sputum obtained from COPD patients, healthy smokers and non-smokers. Conclusion:In patients with COPD, increased levels of IL-18 in induced sputum were associated with airflow limitation, suggesting that IL-18 may be implicated in the pathogenesis of COPD.

These results indicate a "dose-response" effect of chronic exposure to a polluted environment on bronchial and systemic inflammation in professional firefighters.

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