Airway eosinophilic inflammation in bronchiectasis: data from the EMBARC-BRIDGE study.

<bold>Background:</bold> An eosinophilic endotype of bronchiectasis has recently been described based on elevated blood eosinophils. Whether airway eosinophilic inflammation relates to clinical markers of bronchiectasis severity is unknown. <bold>Methods:</bold> Sputum from patients enrolled in a prospective observational study (EMBARC-BRIDGE) was assayed using a novel liquid chromatography-mass spectrometry (LC-MS)-based assay for eosinophil cationic peptide (ECP), eosinophil peroxidase (EPX), major basic protein (MBP), eosinophil derived neurotoxin (EDN) and galectin-10 (Gal-10). Resulting proteomic data were analysed for relationships with clinical parameters. <bold>Results:</bold> 180 patients were included (mean age 67 years, SD 12.4), 55% female, mean severity 7.0 (SD 3.9). All eosinophil biomarkers were detectable in sputum by LC-MS (<bold>Fig 1A</bold>). Eosinophil biomarkers were highly correlated in sputum (Spearman r = 0.5-0.9) and higher levels were suggestive of a blood eosinophil count >300cells/µl. Gal-10, ECP and EDN were significantly elevated in those culturing <italic>Pseudomonas</italic> (p<0.01, <bold>Fig 1B</bold>) and correlated with FEV1% predicted (p<0.01) and radiological severity (Reiff score, p<0.001). Eosinophil proteins correlated with sputum colour (p=0.0002). No relationships with exacerbation were observed. <bold>Conclusion:</bold> Eosinophilic inflammation in sputum is detectable by LC-MS and associates with <italic>Pseudomonas</italic> infection and lung impairment in those with bronchiectasis. <fig><object-id>erj;64/suppl_68/OA2784/F1</object-id><object-id>F1</object-id><object-id>F1</object-id><graphic></graphic></fig>