Sputum protein profiling identifies a key role for neutrophil extracellular traps in exacerbations of bronchiectasis and treatment response

<b>Introduction:</b> Bronchiectasis (BE) is a heterogeneous disease and antibiotics are a main treatment. Recent trials suggest clinical response to antibiotics is unpredictable. We used proteomic approaches to study patients with BE when clinically stable and following antibiotic treatment. <b>Methods:</b> Sputum samples were collected from 20 BE patients on day one of an exacerbation, and 14 days post-antibiotic treatment. Label Free LC/MS was used to profile sputum samples. Biomarkers, including neutrophil extracellular traps (NETs) were measured using immunoassays. Results were validated in 333 stable patients with BE. <b>Results:</b> 20 patients were included in the proteomic study. 55% of patients had Pseudomonas aeruginosa (PA) infection. In the proteomic analysis, there was a differential response to antibiotics in patients with baseline PA. The expression of NET proteins showed a greater decrease after antibiotic treatment in the non-PA group. Three endotypes of BE treatment response were identified with distinct proteomic patterns: type 1 events associated with NET clearance and improvements in symptoms/FEV1, type 2 events with minimal proteomic changes and minimal clinical response, type 3 events where response was mixed. Candidate biomarkers were validated which showed heterogeneous responses post antibiotics. In a validation study in 333 stable patients, sputum NET complexes correlated with FEV1% predicted(p&lt;0.0001), risk of severe exacerbation(p&lt;0.0001) and the BE severity index(p&lt;0.0001). <b>Conclusion:</b> We identified novel endotypes of BE exacerbations and treatment responses which may be used in future for personalised therapy.