Tracheo-bronchial epithelium

Chapter 10 In Vitro Models of the Tracheo-Bronchial Epithelium... 

Figure 10.1 Typical tracheo-bronchial and bronchiolar epithelia showing the major cell types. The tracheo-bronchial epithelium showing the pseudostratified nature of the columnar epithelium, principally composed of ciliated cells (C), interspersed with goblet cells (G), brush cells (Br), serous cells (S), Kulchitsky s cells (K) and basal cells (B). The bronchiolar epithelium showing the cuboidal nature of the epithelium, principally composed of ciliated cells (C), Clara cells (Cl) and infrequent basal cells. Muc = mucus Ci = cilia N = nucleus Sec = secretory granules.

The tracheo-bronchial epithelium forms the interface between the conducting airways and inspired air. As described above, the epithelium is layered upon a connective tissue substratum consisting of a basement membrane, lamina propria, and submucosa [6], The submucosa contains elastic fibres, a muscularis mucosa, connective tissues and seromucous glands. Lymphatics are also located in the bronchial walls [2],... 

While all the aforementioned cell types form the epithelial surface of the airways, basal cells reside deep in the tracheo-bronchial epithelium and are not directly in contact with the airway lumen. Basal cells are considered as the stem cell or progenitor cell of the bronchial epithelium and are pyramidal in shape with a low cytoplasmic/nuclear volume ratio [8, 15-17],... 

A variety of cell culture systems for the modelling of the tracheo-bronchial epithelium are available. These include primary cultures and cell lines of human and animal origins, plus airway cells with characteristics of lung disease such as CF. The advantages and limitations of using a simple culture system compared to one that recreates to a greater extent the epithelial structure and function in vitro should be considered according to the pre-clinical application required. However, this choice is complicated by the lack of comparative data, both between the different cell systems and for in vitro-in vivo correlation, upon which to base such decisions. 

While a number of immortalised cell lines emanating from different cell types of the airway (i.e., tracheo-bronchial) epithelium of lungs from various mammalian species are available (see Chap. 10), reliable and continuously growing cell lines that possess AEC morphology and phenotype are not reported to date. Most studies use cell lines of alveolar epithelial origin for drug absorption studies, while the observations are hard or meaningless to extend to in vivo human situation. 

Trimethylolmelamine by condensation with formaldehyde forms a synthetic, which is dried by spraying and put on the market in a micronized form. After inhalation of the merchandise (73.6 mg/1) for various periods (see Table 9) rats showed a marked dilatation of the rough endoplasmic reticulum of the serous cells in the tracheo-bronchial epithelium (Schiller 1978 Fig. 88). 

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