Production of bronchial papilloma with calcitonin-like immunoreactivity in rats exposed to urban ambient air.

In order to assess the effect of prolonged inhalation of polluted ambient air on the respiratory tract, 30 Sprague-Dawley rats were kept in facilities built close to a street with heavy traffic in the City of Yokohama for 18 months in an atmosphere of either filtered (filtered group) or non-filtered polluted ambient air (exposed group), and the histology of the lung was examined. Scattered areas of chronic inflammation were seen from the nasal to bronchiolar mucosae in both the groups. Rats which inhaled the urban ambient air showed deposition of dust particles in the alveolar space and the peribronchiolar tissue, but no deposition was recognized in the filtered group. In both the filtered and exposed groups, papillary hyperplasia showing a positive immunoreaction to calcitonin was noted in the bronchobronchiolar epithelium. The hyperplasia was thus shown to have endocrine differentiation and this was considered to be pulmonary endocrine cell hyperplasia. In the exposed group, 2 bronchial papillomas were induced, and were shown to contain cells giving a positive immunoreaction to calcitonin. A histogenetical sequence was suggested in these 2 lesions because of their histological and immunohistochemical similarities.