Culture and characterization of human tracheal gland cells

In order to study the composition and regulation of human tracheal gland (HTG) cell secretion, we cultured HTG cells isolated by enzymatic digestion from tracheal mucosa obtained 30 to 60 min after death. On microscopic observation, isolated cells were mainly composed of secretory glandular cells. Maximal HTG cell growth was observed when cells were cultured on type I collagen in the presence of 2% Ultroser G. Under these conditions, 3 to 6 HTG cell passages, corresponding to 20 to 30 population doublings, could be achieved. Lysozyme and bronchial inhibitor (Brl), two secretory protein markers specific to the serous HTG cells, were released in the culture medium, maximal secretion being observed 7 days after the cells had reached confluency. At that time, Brl could be detected, with an immunoperoxidase technique, in about 90% of the cells in culture, suggesting that most cells in culture were serous cells. Using transmission electron microscopy, after in situ fixation, HTG cells exhibited an epithelioid appearance at confluency. Using the biotin-streptavidin gold technique, we identified Brl in cytoplasmic vesicles and in small, immature electron-dense secretory granules. In high cell density cultures, we observed dome formation, suggesting active ion transport mechanisms in HTG cell culture. At confluency, a dose-dependent increase of Brl secretion was induced by phenylephrine, isoproterenol, and carbochol. These results suggest that HTG cell culture provides a useful tool to study the biochemistry and regulation of human tracheobronchial gland cell secretion.