Synthesis and Secretion of Interleukin-15 by Freshly Isolated Human Bronchial Epithelial Cells

Background: Interleukin-15 (IL-15), which shares many functional activities of IL-2, is proposed as a potential modulator of T and natural killer (NK) cell-mediated inflammatory diseases. Since IL-15 gene is expressed in various cell types including epithelial cells, we examined how proinflammatory modulators affect IL-15 gene expression in both freshly isolated human bronchial epithelial cells (HBECs) and the human bronchial epithelial cell line BEAS-2B.

Methods: HBECs were obtained from 25 patients with primary lung cancer by bronchial brushing under bronchofiberscopy. The expressions of IL-15 and its receptor were examined using reverse transcription-polymerase chain reaction (RT-PCR), Northern blot analysis and enzyme-linked immunosorbent assay.

Results: IL-15 mRNA was constitutively expressed in the cells and was upregulated by several proinflammatory cytokines such as IL-1beta, tumor necrosis factor-alpha, interferon-gamma (IFN-gamma) and lipopolysaccharide. In addition, IFN-gamma but not other cytokines induced the synthesis and secretion of IL-15 protein. Investigation of IL-15 receptor expression using RT-PCR showed that IL-15Ralpha and IL-2Rbeta chains but not IL-2Ralpha or gamma chain were constitutively expressed in these cells.

Conclusions: Bronchial epithelial cells may contribute to T and NK cell-mediated airway inflammation through IL-15 production.