The respiratory epithelium comprises a mixed population of ciliated, nonciliated, and mucous-secreting cells from proximal to distal airways. The individual characteristics of these cells create not only an effective physical barrier against various noxious substances, but also a highly sophisticated host defense system by producing and releasing a large number of chemical mediators and cytokines. The bronchial epithelium consists of both, the surface epithelial cells and mucus glands. The surface epithelial cells comprise three principle cell types; basal, goblet, and ciliated cells, of which the latter two form a suprabasal columnar structure. They are necessary for mucociliary clearance.

Studies using human bronchial epithelial cells (BEpiC) have demonstrated that IL-4 and IL-13 stimulation can modify cellular proliferation, but also ciliary beating, and mucous production. Bronchial epithelial cell proliferation depends in part by EGF receptor signaling. They are also useful tools to understand the highly integrated balance between bronchial epithelial proliferation, differentiation, and cell death. Immortalized Human Bronchial Epithelial Cell Line also allow to stablish in vitro models for HIgh Throughput and High Content Screening.