Background: Most patients with cystic fibrosis (CF) die of respiratory failure due to chronic infection and destructive neutrophilic inflammation.

Objective: To identify potential therapeutic targets by characterising the neutrophil stimulating mediators in the CF airway.

Methods: Spontaneously expectorated CF sputum was extracted in phosphate buffered saline for assays of neutrophil chemotaxis, intracellular calcium mobilisation and cell shape change. Mediators were purified by ion exchange, C₁₈ reversed phase and size exclusion chromatography.

Results: A pool of CF sputum contained considerable neutrophil stimulating activity but neutralisation of interleukin (IL)8/CXCL8 had little inhibitory effect on neutrophil chemotactic (10149 (2023) migrating cells vs 8661 (2597) at 62 mg sputum/ml; NS) or shape change (% forward scatter increase 46 (8) vs 38 (5) at 19 mg sputum/ml; p<0.05) responses. Furthermore, the CF sputum pool induced an elevation in intracellular calcium ions even after desensitisation of the neutrophils to IL8. Chromatography identified contributions to the neutrophil shape change inducing activity from IL8, other CXC chemokines, leukotriene (LT) B₄ and two formyl peptides. There was also suggestive evidence for contributions from platelet activating factor (PAF) and C5a. Using non-chromatographed individual sputum samples, anti-IL8 alone did have an inhibitory effect on neutrophil chemotaxis (median inhibition 41%; p = 0.0002). However, even in this experiment, there were clearly significantly important, non-IL8 mediated, effects of CF sputum on neutrophils, and an inhibitor cocktail of anti-IL8 plus CXCR2, LTB₄, formyl peptide, PAF and C5a receptor antagonists inhibited chemotaxis by a median of 97% (p = 0.0002).

Conclusion: Many chemoattractants contribute to the neutrophil stimulating activity in CF sputum although the relative contribution of these mediators differs in different patients. Selective blockade of single mediators may not be sufficient to control neutrophil recruitment and activation in the CF airway.