[Distribution of epithelial cells in respiratory bronchioles, with special reference to influence of cigarette...

Using lung lobes resected surgically for coin lesions, 5 microns-thick sections were made from normal tissues not accompanying emphysema and the proportion of various types of epithelial cells seen in respiratory bronchioles was estimated under a light microscope. The respiratory bronchioles which were cut perpendicularly to the long axis were categorized into three types; type 1 respiratory bronchioles the circumference of which had alveolar orifices in less than one third of its area; type 2, alveolar orifice were recognized in from one third to two thirds of the total area, and type 3, in more than two thirds. Taking several reports into consideration, type 1 respiratory bronchioles are likely to be located proximally, type 3, more distally and type 2, in intermediate locations. In type 1, a large part of bronchiolar walls was covered with columnar cells, whereas the area distributed by these cells was reduced and the area devoid of epithelium increased in type 2. Almost the entire surface of the bronchiolar wall was devoid of epithelium in type 3. Moreover, in smokers and ex-smokers, the proportion of the area not containing epithelium was larger than in non-smokers, which was distinct in type 1. An ultrastructural study revealed the area where no epithelium was seen by light microscopy to be covered with type 1 alveolar cells. In addition, the total pathological score introduced by semiquantitative assessment of fibrosis, muscle hypertrophy, mural inflammation, pigment and intralumenal macrophages was larger in smokers. Distribution of epithelial cells seems to be noteworthy in the assessment of structural changes of respiratory bronchioles due to smoking.