1Department of Pathobiology, School of Veterinary Medicine, Shiraz University, Shiraz, Iran
2Graduated from School of Veterinary Medicine, Shiraz University, Shiraz, Iran
Ovine pulmonary adenocarcinoma (OPA) was studied in the lungs of 15 naturally-affected sheep (9 with classical and 6 atypical lesions) by transmission electron microscopy. Two lung samples from normal sheep were used to develop the ultrastructural criteria. Pathologic lesions consisted of focal-multifocal to coalescent nodules or masses in the cranioventral or diaphragmatic lobes. Ultrastructural characteristics of tumor cells in the alveoli and bronchioles allowed categorization of these cells into three groups; neoplastic alveolar type (AT) Пcells in the alveoli contained numerous cytoplasmic lamellar bodies, well developed rough endoplasmic reticulum and glycogen particles; neoplasticclara cells in the bronchioles contained apical electron-dense granules and well-developed smooth endoplasmic reticulum; undifferentiated tumor cells in the alveoli and bronchioles lacked characteristic lamellar bodies or electron-dense granules. Neither complete virions nor viral inclusions were seen in the neoplastic cells. In the present study, there were no ultrastructural differences in the neoplastic cells betweenclassical and atypical forms. It seems that type II pneumocytes and clara cells are the origin of the neoplasia in the alveoli and bronchioles, respectively.