Function and Structure Relationships With Inflammation Differ in Two Chronic Suppurative Lung Diseases

RATIONALE: Cystic fibrosis (CF) and primary ciliary dyskinesia (PCD) are characterized by neutrophilic airway inflammation but differ in clinical features. OBJECTIVES: We investigated relationships of pulmonary and systemic inflammatory markers with functional and structural lung disease. METHODS: Systemic (CRP, IgG, IL-6, and IL-8) and sputum (calprotectin, IL-6, and IL-8) markers were measured at baseline. Relationships were explored with spirometry, lung clearance index and lung computed tomography (CT) scores at baseline and with spirometry 10 years later. RESULTS: CF 59% 40-99, PCD 67% 30-101) were enrolled in 2009. Systemic inflammation was significantly higher in CF (Neutrophils, p < 0.05, IL-6 and 8, p < 0.01). Conversely, sputum IL-6 and 8 were higher in PCD (p < 0.01). In CF, sputum IL-6 counter-intuitively correlated with better CT scores (r = -0.51/p < 0.05) at baseline and with better spirometry (r = 0.58, p < 0.05) 10 years later. Conversely, high sputum IL-6 at baseline was associated with worse lung function in PCD (r = 0.81/p = 0.001) after 10 years. CONCLUSION: This study emphasizes the differences of functional and structural aspects in both diseases. Markers that predict long-term outcome in PCD and in CF were identified. The most striking and unanticipated finding was that sputum IL-6 correlated with better CT scores and lung function in CF. This paradox merits further research but challenges whether sputum IL-6 in CF is always a bad prognostic indicator.