Sputum proteomics shows association between asthma duration and NETosis

<bold>Background:</bold> The MEX study was a multi-centre UK study that phenotyped residual exacerbations in anti-IL5 treated severe asthma patients with induced sputum samples at pre & stable on mepolizumab & exacerbation. <bold>Aim:</bold> to further understand mechanisms contributing to airway inflammation in severe asthma through sputum proteomic & cytokine analyses. <bold>Methods:</bold> Proteomic analysis (Olink®, 1463 protein panel) & high sensitivity cytokine analysis using ELISAs were performed on sputum pre-mepolizumab(n=28), stable on mepolizumab(n=43) & at first exacerbation(n=26). <bold>Results:</bold> Clustering of proteins while stable on mepolizumab identified two clusters. The pattern of differential protein expression across clusters was also observed pre-mepolizumab & at exacerbation, Fig 1. Cluster 1 (15/43, 35%) were younger at diagnosis, had a longer duration of asthma, lower FEV1% & higher ACQ5. Cluster 1 had increased expression of IL1β, IL 33, IL6/6R, MPO, YKL40, GMCSF, TSLP & Neutrophil extracellular trap (NETosis) proteins which significantly correlated with duration of asthma. There was no difference in sputum eosinophil or neutrophils across the 2 groups. <bold>Conclusion:</bold> this work reveals a subgroup of patients with long duration of disease, worse clinical parameters, increased markers of neutrophil activation & NETosis independent of sputum endotype. This suggests the presence of biology not treated by targeted T2 biologics & may contribute to poorer outcomes on biologics. <fig><object-id>erj;64/suppl_68/OA1074/F1</object-id><object-id>F1</object-id><object-id>F1</object-id><graphic></graphic></fig>