Increased neutrophils and cytokines, TNF-alpha and IL-8, in induced sputumof non-asthmatic patients with chronic dry cough

Background-The pathogenesis of non-asthmatic chronic dry cough remains uncl ear. Methods-A study was undertaken to determine whether airway inflammation cou ld be a contributing factor by analysing inflammatory cells and cytokines i n induced sputum from 19 patients with chronic dry cough of varying aetiolo gy, excluding asthma and bronchiectasis, and from 10 normal controls. The a ssociated causes for the chronic cough were postnasal drip (n = 5), gastro- oesophageal reflux (n = 4), and idiopathic (n = 10). All patients had an en hanced cough reflex to capsaicin. Results-Sputum neutrophilia (median (inte rquartile range)) was found in the patients with chronic cough (59.4 (27.1) %) compared with the normal controls (28.4 (22.0)%; p<0.01, 95% CI 11.3 to 42.2). Sputum levels of interleukin-8 (IL-8) and tumour necrosis factor-alp ha (TNF-alpha) were also significantly increased compared with normal contr ols (0.57 (1.08) and 0.25 (0.72) ng/ml; p<0.05 (95% CI 0.05 to 1.75) for IL -8; 48.3 (34.3) and 12.6 (33.6) pg/ml, p<0.01 (95% CI 8.8 to 69.8) for TNF- alpha). Conclusion-Neutrophils and cytokines associated with neutrophil chemotaxis and activation may contribute to the pathogenesis of non-asthmatic chronic dry cough.