Inflammatory and mucociliary dysfunction based endotypes across the spectrum of chronic airway diseases.

Background: There is substantial overlap between features of COPD, asthma, bronchiectasis(BE) and cystic fibrosis(CF). Each is characterised by inflammation and mucociliary dysfunction.

Research Question: Is there a relationship between inflammation and mucociliary clearance in chronic respiratory conditions and can biology rather than disease labels stratify patients into therapeutically relevant subtypes?

Study Design And Methods: Patients were categorized by primary disease and clinical characteristics, spontaneous sputum was collected, inflammatory markers (neutrophil elastase(NE) and 19 cytokines), sputum properties (DNA content, mucins, rheology, dry weight) and microbiome (long read 16S sequencing) were measured. K-means clustering was performed and parameters compared between and within disease groups. Controls were former smokers without respiratory disease.

Results: The study included patients with asthma(76), COPD(91), BE(54), CF(24) and controls(26). Nine c ytokines (IFN-γ, IL-4, IL-5, Eotaxin, Eotaxin-3, TARC, G-CSF, Fractalkine, IL-22), NE, dry weight, mucins and sputum rheology parameters were significantly different between disease groups and controls (p<0.05). K-means clustering identified 2 clusters defined by neutrophilic or Th2 inflammation. The Th2 cluster was associated with lower sputum dry weight, DNA content and higher MUC5B. Rheological parameters G', G'' and G* were significantly higher in the eosinophilic group while Tan(delta) was higher in the neutrophilic group, indicating a higher viscous to elastic ratio. (p<0.05 all comparisons). The neutrophilic cluster was associated with decreased alpha diversity (p=0.04) and increased presence of proteobacteria in their sputum microbiome compared to the Th2 cluster (p=0.01). More neutrophilic inflammation was present in CF and BE (42% of COPD and 46% of asthma patients were neutrophilic vs 78% of BE and 87% of CF,p<0.0001). Both clusters were present in all disease groups.

Interpretation: Airways diseases have heterogenous mucus properties. Patients cluster according to inflammatory endotype rather than disease label. Assessment based on disease labels may be aided by endotyping using inflammatory and mucociliary clearance biomarkers. 299/300 words.