Tracheal epithelial cells are connected to each other by E-cadherin molecules [23] . Among the isolated ATE cells, 88.3 ± 13.2% expressed E-cadherin and a gap-junction molecule, ZO-1 [23] . E-cadherin-negative cells, including SMA-positive muscle cells and vimentin-positive fibroblast cells, accounted for 5.0 ± 1.4% and 3.5 ± 1.2% of the cultured cells, respectively, indicating the high purity of this primary culture system. In tracheal epithelial cells, b-tubulin IV/b-tubulin, mucin 5AC and cytokeratin 14 (K14) are specific markers of ciliated cells, goblet cells and basal cells, respectively [12, 13, 23] . Basal cells also show high affinity for GSI-B4, a plant lectin that specifically binds the glycoconjugates of basal cells of tracheal epithelia [12, 13] . Figure 2 shows that these three major cell types -ciliated cells, goblet cells and basal cells -were all present in the ATE population, and accounted for 22.8 ± 9.1%, 44.8 ± 9.7% and 41.6 ± 8.4% of the ATE cells, respectively.