EXPRESSION OF ALVEOLAR TYPE-II CELL MARKERS IN ACINAR ADENOCARCINOMASAND ADENOID CYSTIC CARCINOMAS ARISING FROM SEGMENTAL BRONCHI - A STUDY IN A HETEROTOPIC BRONCHOGENIC-CARCINOMA MODEL IN DOGS

The type II alveolar epithelial cell is one of two pluripotential stem cell phenotypes in normal mammalian lung morphogenesis, cells manifes ting this phenotype have been found to constitute bronchioloalveolar r egions of canine adenocarcinomas. We now studied type II cell expressi on in canine acinar adenocarcinomas and adenoid cystic (bronchial glan d) carcinomas, using the same bronchogenic carcinoma model (subcutaneo us bronchial autografts treated with 3-methylcholanthrene). Distinctiv e features of type II cells are the approximately cuboid cell shape, l arge and roundish nucleus, immunofluorescent staining of the cytoplasm for the surfactant protein SP-A, and presence of multilamellar bodies or their precursory forms. Cells with these type II cell characterist ics were found in the basal epithelial layer of all tumor lesions and in upper layers as far as the lumen, singly or in clusters, they were also found in early invasive carcinomatous lesions but not in bronchia l glands or bronchial epithelium before carcinogen exposure. Immunoblo ts of tumor homogenates showed reactive proteins within size classes o f SP-A (28 to 36 kd) or its dimeric form (56 to 72 kd). These findings and those previously reported are consistent with the concept that ch emical carcinogenesis in the adult bronchial epithelium may lead to ty pe II cell carcinomas of varying glandular (acinar, adenoidcystic or b ronchioloalveolar) growth patterns.