Identification of phospholipids in secretory granules of human submucosal gland respiratory cells

Abstract

Although it has been shown that tracheal epithelial cells in culture synthesize and secrete phospholipids, no direct evidence for in situ phospholipid storage in human respiratory secretory epithelial cells has been demonstrated. We used a high-resolution cytochemical enzyme-gold technique to identify and precisely localize phospholipids in human submucosal gland secretory cells. In addition, lysozyme, a specific serous cell marker, was identified using the biotin-streptavidin gold technique with lysozyme antiserum. This double labeling of phospholipids and lysozyme was performed using gold particles of diameters 15 nm and 5 nm, respectively. Quantitation of phospholipid labeling was performed on an image analyzer. Phospholipids were identified in serous granules (8.87 ± 2.21 gold particles/μm2) in a significantly (p<0.05) higher density than in mucous granules (5.57 ± 3.07 gold particles/μm2). These results support the hypothesis that submucosal human airway serous and mucous secretory cells produce phospholipids which may be secreted in the airway lumen.