Quantitative analysis of airway epithelial nerve subtypes in refractory/unexplained chronic cough

<bold>Background:</bold> Refractory/unexplained chronic cough (RUCC) is associated with structural changes in airway epithelial nerves compared with healthy controls. Whether remodeling of specific sensory nerve subtypes underlies these changes is unknown. <bold>Method:</bold> Healthy volunteers (HV) and RUCC subjects completed 24h cough monitoring, patient reported outcomes and bronchoscopy. Endobronchial biopsies (1-6 per subject) were taken from the right main bronchus, and immunostained with pan-neuronal protein PGP9.5, substance P, and neurofilament heavy chain. Image Z stacks were obtained using confocal microscopy. Nerve length and branch points were quantified from nerve models (Imaris software) by a blinded reviewer. <bold>Results:</bold> RUCC (n=24) vs. HV (n=15) were recruited, median age 60y vs. 34y (p=<0.01) & FEV1 97% vs. 101% (p=0.70). RUCC day cough severity VAS median 62mm and 24h cough freq. mean 28c/h. An interim analysis in n=3 RUCC and n=5 HV found nerve length and branch points increased in RUCC vs. HV (PGP9.5 length 2255±216µm vs. 745±103µm, p<0.05; branch points 52±11 vs. 9±2, p<0.05) but the subset of neurofilament-positive fibers (putative A fibres) were similar between groups (length 1454±424 µm vs. 1277±492µm p>0.05), as was neuronal substance P expression (266±255µm3 vs. 75±29µm3 p>0.05). <fig><object-id>erj;64/suppl_68/PA886/F1</object-id><object-id>F1</object-id><object-id>F1</object-id><graphic></graphic></fig> <bold>Conclusion:</bold> Airway nerve density was increased in RUCC compared with HV, particularly in PGP9.5 positive epithelial fibres, thought to be C fibres