Generation and characterization of human airway normal epithelial cells. (a) The morphology of the primary HNTEC and HNBEC. HNTEC and HNBEC were cocultured and grew rapidly. The colonies of epithelial cells were observed at 2 days after the initial cell isolation. The arrows indicate the colonies of epithelial cells. Magnification 10x. (b) Growth curves of two strains of airway epithelial cells, HNTEC and HNBEC. (c) Cell response to DNA damage. The cells were treated with 0.5 nM actinomycin D for 24 hours. Expression of p53 and p21 was measured with western blotting and quantitative RT-PCR. (d) The colony formation of HNTEC and HNBEC. HNTEC, HNBEC, and A549 cells were used in soft agar assays. Only the lung cancer line A549 formed colonies in soft agar.