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

Cystic fibrosis (CF) and primary ciliary dyskinesia (PCD) are characterized by neutrophilic airway inflammation but differ in clinical features.

We investigated relationships of pulmonary and systemic inflammatory markers with functional and structural lung disease.

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.

42 patients (21 CF, 21 PCD) of similar age (median CF 27 y [12-59], PCD 27 y [11-62]) and lung function (median ppFEV₁CF 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.

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.