Histologic and ultrastructural features of the clara cell adenoma of the mouse lung
Kauffman, S.L.; Alexander, L.; Sass, L.
Laboratory Investigation; A Journal of Technical Methods and Pathology 40(6): 708-716
1979
ISSN/ISBN: 0023-6837 PMID: 449277 Document Number: 150795
Lung adenomas were induced by transplacental exposure of Swiss Bagg-Webster mice to ethylnitrosourea on the 16th day of gestation. The lungs of postnatal animals 1-3 mo. of age were examined grossly and step sections were made of the right lower lobe for light microscopy. Additional tumors were fixed in Palade's solution and prepared for light microscopy and EM. Tumors were classified on the basis of predominant histologic pattern as alveolar or bronchiolar, and the cell type comprising the tumors was identified by EM. The tumors were represented in nearly equal numbers in the right lower lobes. EM examination showed that the bronchiolar papillary tumors consisted of Clara cells, the nonciliated epithelial cell of the terminal bronchioles, whereas alveolar tumors consisted of type II alveolar cells. The Clara cell was not previously recognized as a progenitor cell of murine lung adenomas. These cells form tumors with distinct histopathologic features that allow for their separation from the type II cell adenomas. A review of previous studies pertaining to biologic differences between alveolar and papillary tumors suggests that the Clara cell tumor may have a malignant potential not shared by the type II cell adenoma. Mouse lung adenomas should be identified according to their cell of origin to evaluate possible biologic differences between the 2 types.