Alveolar cells, types

Despite the fact that most of the alveolar surface is composited of alveolar epithelium, three primary types of cells are present in the alveoli type I alveolar cells, type II alveolar cells, and alveolar macrophages. Type I alveolar cells are also referred to as squamous pulmonary epithelial cells and are the continuous lining of the alveolar sac. Type II alveolar cells are also referred to as septal cells. Type II alveolar cells secrete the alveolar fluid that is necessary to keep the surface moist and to maintain surface tension of the alveolar fluid surface tension is necessary to keep the alveoli from collapsing. Alveolar fluid is a suitable environment for proteins when compared to the low pH and high protease levels associated with the intestine... 

The amplification of thyroglobulin, thyroid peroxidase and TTF-1 mRNA can be a valuable sensitive method for the detection of micrometastases, minimal residual cancer cells and circulating tumor cells of papillary and follicular thyroid carcinoma. TTF-1 can be also used for the detection ofthyroid medullary carcinoma and different lung neoplasia derived from alveolar cells type II and Clara cells (mainly adenocarcinoma). The presence of circulating tumor cells is associated with poor prognosis and... 

Fehrenbach H. Alveolar epithelial type n cell defender of the alveolus revisited. Respir Res 2001 2(1) 33 46. 

More specifically, the blood-gas interface consists of the alveolar epithelium, capillary endothelium, and interstitium. The alveolar wall is made up of a single layer of flattened type I alveolar cells. The capillaries surrounding the alveoli also consist of a single layer of cells — endothelial cells. In between the alveolar epithelium and capillary endothelium is a very small amount of interstitium. Taken together, only 0.5 pm separates the air in the alveoli from the blood in the capillaries. The extreme thinness of the blood-gas interface further facilitates gas exchange by way of diffusion. 

The human alveolar epithelium consists of two cell types type I (alveolar epithelial type I [ATI], pneumocyte I) and type n (alveolar epithelial type II... 

Figure 11.1 Ultrastructure of the human lung alveolar barrier. The tissue specimen is obtained via lung resection surgery. (A) Section through a septal wall of an alveolus. The wall is lined by a thin cellular layer formed by alveolar epithelial type I cells (ATI). Connective tissues (ct) separate ATI cells from the capillary endothelium (en) within which an erythrocyte (er) and granulocyte (gc) can be seen. The minimal distance between the alveolar airspace (ai) and erythrocyte is about 800-900 nm. The endothelial nucleus is denoted as n. (B) Details of the lung alveolar epithelial and endothelial barriers. Numerous caveolae (arrows) are seen in the apical and basal plasma membranes of an ATI cell as well as endothelial cell (en) membranes. Caveolae may partake transport of some solutes (e.g., albumin). (C) ATII cells (ATII) are often localised in the comers of alveoli where septal walls branch off. (D) ATII cells are characterised by numerous multilamellar bodies (mlb) which contain components of surfactant. A mitochondrion is denoted as mi.

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. 

The rat cell line R3/1 was established from cells obtained from broncho-alveolar tissues of foetal Wistar rats at 20 days of gestation. This cell line displays a phenotype with several characteristic features of ATI cells. R3/1 cells were analysed to show a positive expression for mRNA and protein content of markers related to the ATI cell type (e.g., Tla, ICAM-1, connexin-43 and caveolin-1 and -2) [79], Whether or not this cell line can form functional tight junctions is currently under investigation in our laboratories. 

Newman GR, Campbell L, von Ruhland C, Jasani B, Gumbleton M (1999) Caveolin and its cellular and subcellular immunolocalisation in lung alveolar epithelium implications for alveolar epithelial type I cell function. Cell Tissue Res 295(1) 111-120... 

BorokZ, Liebler JM, Lubman RL, Foster MJ, Zhou B, Li X, Zabski SM, Kim KJ, Crandall ED (2002) Na transport proteins are expressed by rat alveolar epithelial type I cells. Am J Physiol 282(4) L599-L608... 

Demling N, Ehrhardt C, Kasper M, Laue M, Knels L, Rieber EP (2006) Promotion of cell adherence and spreading a novel function of RAGE, the highly selective differentiation marker of human alveolar epithelial type I cells. Cell Tissue Res 323(3) 475-488... 

Shirasawa M, Fujiwara N, Hirabayashi S, Ohno H, Iida J, Makita K, Hata Y (2004) Receptor for advanced glycation end-products is a marker of type I lung alveolar cells. Genes Cells 9(2) 165-174... 

Chen Z, Jin N, Narasaraju T, Chen J, McFarland LR, Scott M, Liu L (2004) Identification of two novel markers for alveolar epithelial type I and II cells. Biochem Biophys Res Commun 319(3) 774—780... 

Johnson MD, Widdicombe JH, Allen L, Barbry P, Dobbs LG (2002) Alveolar epithelial type I cells contain transport proteins and transport sodium, supporting an active role for type I cells in regulation of lung hquid homeostasis. Proc Natl Acad Sci USA 99(4) 1966-1971... 

Chen J, Chen Z, Narasaraju T, Jin N, Liu L (2004) Isolation of highly pure alveolar epithelial type I and type II cells from rat lungs. Lab Invest 84(6) 727-735 Erratum in Lab Invest 85(9) 1181 (2005)... 

An ideal in vitro model for the characterization of aerosol formulations would incorporate cell types from various regions of the lung (tracheal, bronchial, and alveolar) and would facilitate simulation of deposition mechanisms by impaction, sedimentation, and diffusion of a high-metered singlebolus inhalation. In the future, such systems may reduce the need for animal studies and may offer to correlate in a predictive way the results from such in vitro tests to clinical bioavailability data after pulmonary drug delivery in vivo. 

Stephens et al have shown that, in rats, the degenerative changes in Type I alveolar cells occur after exposure to ozone at concentrations as low as 0.2 ppm for 3 h and that cells are replaced by Type II alveolar cells beginning a day after the exposure. With electron microscopy, Bils noted that the swelling of the epithelial alveolar lining cells of mice occurred after exposure to ozone at 0.6-1.3 ppm for 4 h. These changes... 

Degenerative changes in Type 1 alveolar cells later replaced by Type II cells... 

The alveolar epithelium consists of so-called Type I and Type II cells. Type I cells cover over 90% of the alveolar surface, have a large surface, and are thin. Type II cells are larger in numbers but are small. Therefore, they cover only about 7% of the surface of the alveoli. Type II cells produce the phospholipids that make up the surfactant layer. 

N02 is a relatively insoluble deep lung irritant capable of producing pulmonary edema. The type I cells of the alveoli appear to be the cells chiefly affected on acute exposure. At higher exposure, both type I and type II alveolar cells are damaged. Exposure to 25 ppm of N02 is irritating to some individuals 50 ppm is moderately irritating to the eyes and nose. Exposure... 

Clara cells, type II cells and alveolar macrophages) in vitro ... 

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