Interleukin-17 in sputum correlates with airway hyperresponsiveness to methacholine

Interleukin-17 (IL-17) is a novel cytokine secreted by activated human memory CD4+ T cells. In vivo IL-17 recruits neutrophils into the airways via the release of CXC chemokines (interleukin-8) from bronchial epithelial cells. Since neutrophils are implicated in pathogenesis of chronic obstructive pulmonary disease (COPD) chronic bronchitis (CB) and asthma, we hypothesized that there would be increased concentration of IL-17 in the airways of these patients. To test this hypothesis, we measured levels of IL-17 in induced sputum of COPD patients, chronic bronchitis and asthmatics and compared them with healthy controls.

Levels of IL-17 in induced sputum were measured via ELISA method in 19 COPD, 16 CB, 10 asthma and 11 control subjects. Airway responsiveness to methacholine was performed in people with FEV1 higher than 70% of predicted.

There were no significant differences in IL-17 levels between control group and the other groups. However, levels of IL-17 in sputum of COPD patients were significantly lower than in asthma (P=0.004) and in CB (P=0.01) groups. Medians and (ranges) were as follows: asthma--37.6 pg/ml (18.8-55.7 pg/ml), CB 293 pg/ml (18.8-49.7 pg/ml) and COPD 24.6 pg/ml (0-34.1 pg/ml). Comparison of healthy control subjects (PC20 > 8 mg/ml) to a group with bronchial hyperreactivity, which consisted of asthmatics and CB patients, whose PC20 was less than 8 mg/ml, revealed that levels of IL-17 were significantly increased in the second group (P=0.02). Also, levels of IL-17 were significantly increased (P=0.02) in the asthmatic patients with bronchial hyperreactivity compared to healthy subjects. Moreover levels of IL-17 in sputum of all studied subjects correlated negatively with PC20 (r=-0.51, P=0.002).

According to our results IL-17 is probably not involved in pathogenesis of stable COPD, but it may play a role in people with airway hyperresponsiveness.