Sputum Phagocytes from Healthy Individuals Are Functional and Activated: A Flow Cytometric Comparison with Cells in Bronchoalveolar Lavage and Peripheral Blood

Cells in the bronchial airways of healthy individuals are continuously exposed to inhaled particulates in the size range 2–5 μm, which preferentially deposit in the bronchial rather than the alveolar lung. Induced sputum obtains cells primarily from the surfaces of bronchial airways. Using flow cytometry, we investigated whether sputum phagocytes demonstrate phenotypes indicative of increased functional activation and inflammation compared to phagocytes from the alveolar airways and peripheral blood (PB) in healthy subjects (N = 17). Sputum macrophages demonstrated increased levels of CD11b, increased oxidative burst, and greater phagocytosis than autologous alveolar macrophages. Expression of CD11b, CD64, and HLA-DR in sputum monocytes was upregulated compared to that in PB monocytes. Sputum neutrophils showed increased expression of CD11b, CD64, CD14, and HLA-DR and were more phagocytic than PB neutrophils. In conclusion sputum/bronchial phagocytes from healthy individuals express an inflammatory phenotype and are functionally more active than phagocytes from the alveolar airways and peripheral blood.