Systemic interleukin-26 relates to the risk of exacerbations in smokers with COPD and chronic bronchitis

Background: We lack useful systemic biomarkers that predict the risk of COPD exacerbations. However, we have shown that the local level of the cytokine interleukin (IL)-26 in the lungs is linked to lung function, smoking, COPD exacerbations, chronic bronchitis, and pathogen colonization but there is no corresponding information on systemic IL-26. Aims and objectives: To determine whether systemic IL-26 relates to exacerbations in smokers with COPD and chronic bronchitis (COPD-CB). Methods: IL-26 was quantified (ELISA) in serum from a bi-gender population (26-76 years) of healthy non-smokers (NS), asymptomatic smokers (AS) (>10 pack-years) and smokers with COPD-CB (GOLD stage 1-4). For the COPD-CB group, serum and sputum was harvested at inclusion, every 3 months and when exacerbations occurred, during 15 months. Results: There was no consistent relation between the systemic (median) level of IL-26 during stable disease and the number of exacerbations, nor any consistent change from stable conditions to exacerbation or association with bacteria in sputum. However, in smokers (AS and COPD-CB) systemic IL-26 was higher (25 pg/ml, n=66, p=0.0065) than in NS (7.6 pg/ml, n=8). During the 1st exacerbation, systemic IL-26 was higher (p=0.013) in patients with subsequent exacerbations (29 pg/ml, n=15) than in those with one exacerbation only (16 pg/ml, n=21). Conclusions: Smokers have a higher level of systemic IL-26 than non-smokers. When tested during exacerbations in smokers with COPD-CB, systemic IL-26 bears potential to indicate the risk for forthcoming exacerbations. Prospective, longitudinal studies on large patient populations will be needed to further evaluate this potential.