Background Bronchiectasis is a progressive neutrophilic inflammatory lung disease associated with abnormal local cytokine release with possible systemic overspill. Early data suggests that interleukin-17 (IL-17) could be involved in the enhanced infiltration of neutrophils in the lungs, via the induction of IL-8 release, and has emerged as a possible biomarker for other chronic neutrophilic lung diseases.

Aims

1. to investigate the potential use of IL-17 and IL-8 as biomarkers of disease severity in bronchiectasis by utilising a multidimensional clinical severity scoring system, the Bronchiectasis Severity Index (BSI).

2. correlate sputum neutrophils and pathogen status with serum or sputum IL-17 and IL-8 levels.

Methods Spontaneous sputa and sera were collected from stable adult bronchiectasis patients attending a specialist clinic. We quantified both IL-17 and IL -8 concentrations in the pulmonary compartment (sputum) and the systemic compartment (serum) of 119 stable bronchiectasis patients and 26 healthy volunteers. Sputum neutrophils were conducted using standard methods.

Results The mean patient age was 65 years, with 24% in mild BSI, 39% moderate BSI and 46% (43% idiopathic, 24% post infectious). IL-17 in the sputum of bronchiectasis patients was found to be two-fold greater than in serum suggesting “local” release (10 pg/ml vs 5 pg/ml). Statistical analysis revealed a significant correlation between these two variables, suggesting a “spillover” of cytokines from the lungs (p < 0.001).

However, there was no significant difference in serum IL-17 levels between bronchiectasis and healthy subjects (0 ± 2 pg/ml). In addition, no significant correlation was found between IL-8 and IL-17 levels in the sputum of patients. Sputum IL-17 levels were found to have a significant negative correlation with BSI severity scoring, but this was not reproduced when individual BSI parameters were analysed. IL-8 similarly performed poorly in correlating with BSI. In contrast more severe BSI scores were significantly associated with higher% neutrophils in sputa (p = 0.045).

Conclusions The clinical utility of IL-17 and IL-8 as biomarkers for the prediction of disease severity in bronchiectasis patients appears poor. These data may also suggest targeting these chemokines are of limited value. Focus in bronchiectasis may need shifted from neutrophil chemokines to factors that inhibit apoptosis and/or promote neutrophil persistence in the airway.