Sputum YKL-40 levels and pathophysiology of asthma and chronic obstructive pulmonary disease

Background: Recent evidence suggests that YKL-40, also called chitinase-3-like-1 protein, is involved in the pathogenesis of asthma and chronic obstructive pulmonary disease (COPD). Details of sputum YKL-40 in asthma and COPD, however, remain unknown.

Objectives: To clarify associations of sputum YKL-40 levels with clinical indices in asthma and COPD.

Methods: Thirty-nine patients with asthma, 14 age-matched never-smokers as controls, 45 patients with COPD, and 7 age-matched smokers as controls were recuited for this study. Sputum YKL-40 levels were measured and YKL-40 expression in sputum cells was evaluated by immunocytochemistry.

Results: Sputum YKL-40 levels were higher in patients with COPD (346 ± 325 ng/ml) than in their smoker controls (125 ± 122 ng/ml; p < 0.05), but were not significantly different between patients with asthma (117 ± 170 ng/ml) and their controls (94 ± 44 ng/ml; p = 0.15). In patients with asthma only, sputum YKL-40 levels were positively correlated with disease severity (r = 0.34, p = 0.034) and negatively correlated with pre- and postbronchodilator %FEV(1) (r = -0.47 and -0.42, respectively; p < 0.01) and forced mid-expiratory flow (r = -0.48 and -0.46, respectively, p < 0.01). Sputum YKL-40 levels were positively correlated with sputum neutrophil counts in asthma (r = 0.55, p < 0.001) and with neutrophil and macrophage counts in COPD (r = 0.45 and 0.65, respectively, p < 0.01). YKL-40 was expressed in the cytoplasm of sputum neutrophils and macrophages in all groups.

Conclusions: Elevated sputum YKL-40 reflects airflow obstruction in asthma whereas the roles of YKL-40 in the proximal airways in COPD remain to be elucidated.