Sustained production of secretory component by human tracheal epithelial cells in primary culture

Secretory immunoglobulin A (sIgA) is an important initial defense against environmental agents in the airway. The purposes of our study were to determine whether human tracheal epithelial (HTE) cells produce secretory component (SC), the receptor for dimeric IgA (dIgA), to determine whether HTE cells in primary culture continue to produce SC, and if so, to develop a model for studying SC metabolism in the airway. Immunoperoxidase staining of the human trachea using antibody raised against human SC reveals that many surface epithelial cells and the cells of the submucosal glands express SC but basal cells do not. HTE cells, obtained from tracheal specimens at necropsy, contain 10-51 ng of SC/10(5) cells, at the time of isolation. However, when these cells are placed in culture on plastic, SC release diminishes with time (from 19.6 ng/10(5) cells on day 2 to 6.4 on day 8) despite continued cell proliferation. In contrast, HTE cells cultured on floating collagen gels increase SC release over the same period (26.2 ng/10(5) cells on day 2 and 193.9 on day 8). HTE cells cultured on collagen-coated and uncoated nitrocellulose filters also produced SC at least through day 8 (collagen coated, 21.5 ng/10(5); uncoated, 6.3). Furthermore, SC was released preferentially to the apical surface (4:1 ratio) under both conditions. This system will allow us to study the production, processing, and release of SC by HTE cells and further understand the transport and function of secretory IgA in the airway.