Clinical relevance of sputum bronchial epithelial cells: A retrospective cross-sectional study

RATIONALE: Bronchial epithelium provides a physical barrier, facilitates mucociliary transport and is involved in regulating various immune responses. Bronchial epithelial cells (BECs) are quantified as part of sputum differential cell counts; however, significance of elevated BEC numbers is not known. We hypothesized that they may be higher in patients whose respiratory symptom is predominantly a cough. OBJECTIVES: Our aim of the study was to characterize patients with increased sputum BECs based on clinical and inflammatory variables. METHODS AND MEASUREMENTS: We conducted a retrospective cross-sectional study utilizing a database containing clinical and inflammatory characteristics of patients who underwent sputum differential cell counts at a tertiary care center in Hamilton, Ontario, Canada. Total and differential cell counts were performed on non-saliva contaminated, DTT-dispersed, sputum cytospins. The BEC high group includes patients with sputum BEC% ≥ 4.4% (90th percentile of normal), whereas the control group includes patients with sputum BEC% < 4.4%. MAIN RESULTS: A total of 7% (239/3420) of patient samples had increased epithelial cells in sputum. Compared to an equal number of control subjects, the patients with elevated BECs were younger, predominately had cough and wheezing, required higher dose of corticosteroids, had higher FEV1 and FVC, and had either eosinophilic or paucigranulocytic inflammatory endotype. There was no significant difference in terms of airway hyperresponsiveness. CONCLUSIONS: Elevated BECs are associated with younger age, higher corticosteroid dose, symptoms of cough and wheezing, and predominately an eosinophilic or paucigranulocytic inflammatory endotype. Mechanisms linking these need to be studied.