Abstract
Clara cells in terminal bronchioles are important in the production of surfactant, catabolysation and metabolic activation of various chemicals, and in the carcinogenesis of lung cancer. Many round mitochondria with decreased cristae and rich endoplasmic reticuli of the Clara cell suggest that the Clara cell has a function similar to that of the hepatic cell. Furthermore, the style of secretion of the Clara cell probably has a special function related to respiration. The air bladder of the Gar-pike fish shows a lung-like structure and has cells resembling the Clara cell and type II alveolar cells. Lungs of other animals also have Clara cells in their bronchioles with some individual differences. Mice Clara cells were activated by the beta-adrenergic stimulator, nicotine, and cold stimuli and were targets of paraquat and oxygen toxicity. Tumorigenesis by 4-nitroquinoline-1-oxide on mouse lung was increased by pretreatment with a beta-stimulator. The site of the location of the Clara cells was the focus of asbestosis, centrilobular emphysema, and respiratory distress syndrome in infants as well as adult. In cases of diffuse panbronchiolitis and alveolar proteinosis, alteration of the Clara cell was noticed. About 70% of human pulmonary adenocarcinomas resembled the Clara cell type in ultrastructure and showed characteristic clinical behaviour. In conclusion, the Clara cell is an important key to resolve the pathogenesis of peripheral lung disease, especially of peripheal lung cancer.
