Association between cytokines in induced sputum and severity of chronic obstructive pulmonary disease

Cytokines are known to be increased in induced sputum in chronic obstructive pulmonary disease (COPD). In this study, the relationship between the levels of interleukin-6 (IL-6), interleukin-8 (IL-8), and tumour necrosis factor-alpha (TNF-alpha) in induced sputum of patients with exacerbation of COPD, and the severity of the disease, pulmonary function tests (PFT), arterial blood gases (ABG) were studied. Twenty-four patients with exacerbation of COPD were included in the study. The patients were grouped according to their PFT into two as: Group 1 (FEV1 below 50% of the predicted value, severe-very severe COPD, n=12) and, Group 2 (FEV1 above 50% of the predicted value, mild-moderate COPD, n=12). The levels of IL-6, IL-8 and TNF-alpha in induced sputum of the subjects were measured. The mean levels of IL-6, IL-8 and TNF-alpha in induced sputum were found to be higher in Group 1 (severe-very severe COPD) than in Group 2 (mild-moderate COPD). The differences in IL-6 and IL-8 levels between groups were statistically significant (P<0.05). A significant correlation was observed between the IL-6 value and FEV(1) (r=-0.435, P=0.034), FEV1/FVC (r=-0.446, P=0.029), PaO2 (r=-0.711, P=0.000), SaO2 (r=-0.444, P=0.030) and disease duration (r=0.427, P=0.037), respectively. Also, the level of IL-8 in induced sputum was inversely correlated with FEV1 (r=-0.562, P=0.004), PaO2 (r=-0.540, P=0.006) and SaO2 (r=-0.435, P=0.034). However, all three cytokines were positively correlated with the smoking load (r=0.653, P=0.001; r=0.439, P=0.032; r=0.649, P=0.001). We conclude, therefore, that in exacerbated COPD cases with greater degrees of obstruction of the airways have higher levels of cytokines in induced sputum. This can be interpreted to mean that these cytokines are related to the clinical parameters like the ABG and PFT and seem to be the determinant of the severity of the disease.