Structural characterization of the bronchial epithelium of subjects with chronic bronchitis and in asymptomatic smokers

A morphometric study was carried out on biopsy specimens taken from 40 smokers (27 with chronic bronchitis and 13 asymptomatic) submitted to bronchoscopy to identify and quantify the possible structural differences between the two groups. The chronic bronchitic group had a mean age of 65.67 years and 57.04 pack-years of smoking, the asymptomatic group had a mean age of 44.69 years and 22.62 pack-years of smoking. 70 biopsy specimens (45 from chronic bronchitics and 25 from asymptomatic smokers), in which large areas of best-preserved and perpendicularly cut epithelium were present, were considered suitable for the study and examined by light and transmission electron microscopy. The mean thickness of surface epithelium (p < 0.001), the number of layers of basal cells (p < 0.001), the intercellular space of the superficial zone of the epithelium (p < 0.05) and the percentage of abnormal bronchial cilia (p < 0.05) were significantly greater in patients with chronic bronchitis than in asymptomatic smokers. No significant difference between the two groups was observed in the thickness of the lamina reticularis of the basement membrane. Goblet cell hyperplasia was more marked in chronic bronchitics than in the asymptomatic smokers (p < 0.001), whereas the frequency of epidermoid metaplasia did not show a significant difference. The morphological study of the bronchial epithelium has allowed the identification of transitional cells, which gives rise to the concept that epidermoid metaplasia may result from conversion of mucous cells. This finding suggests that the different histologic types appearing in lung tumours may originate from one undifferentiated pluripotential stem cell, which is able to differentiate into different histogenetic types.