Increased neutrophils and cytokines, TNF-α and IL-8, in induced sputum of non-asthmatic patients with chronic dry cough

Abstract

Background - The pathogenesis of non-asthmatic chronic dry cough remains unclear. Methods - A study was undertaken to determine whether airway inflammation could be a contributing factor by analysing inflammatory cells and cytokines in induced sputum from 19 patients with chronic dry cough of varying aetiology, excluding asthma and bronchiectasis, and from 10 normal controls. The associated causes for the chronic cough were postnasal drip (n = 5), gastro-oesophageal reflux (n = 4), and idiopathic (n = 10). All patients had an enhanced cough reflex to capsaicin. Results - Sputum neutrophilia (median (interquartile 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-α (TNF-α) were also significantly increased compared with normal controls (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 (34.4) and 12.6 (33.6) pg/ml, p < 0.01 (95% CI 8.8 to 69.8) for TNF-α). Conclusion - Neutrophils and cytokines associated with neutrophil chemotaxis and activation may contribute to the pathogenesis of non-asthmatic chronic dry cough.