An ultrastructural and cytochemical study of the pulmonary lesions and multinucleate giant cells in porcine dermatosis vegetans

The pulmonary lesions and multinucleate giant cell formations in porcine dermatosis vegetans were studied ultrastructurally and cytochemically in seven affected pigs that ranged from one to 120 days of age. At birth, no pulmonary lesions were observed. By seven days of age, there was a moderate infiltration of monocytes/macrophages in the alveoli and interstitium. These changes progressed, and by two weeks of age there was pronounced infiltration of macrophages and lymphocytes in the alveoli. Close apposition of macrophages and lymphocytes was observed, and cellular contact was demonstrated. By three to four weeks of age, small aggregates with epithelioid cells, macrophages, and lymphocytes resembling granulomas were present. In an older pig, aged four months, the inflammatory changes waned. Large macrophages, and large and small multinucleate cells shared common morphological characteristics of cytoplasm endowed with organelles, primary and secondary lysosomes, Golgi profiles, and granular endoplasmic reticulum. Cytochemically, macrophages and MGCs were positive for acid phosphatase. The present study showed that the initial pulmonary changes share morphological characteristics with a granulomatous inflammatory response, and evolve into small granulomas with macrophages, epithelioid cells and lymphocytes. Morphologically, these changes share characteristics with epithelioid cell granulomas. Macrophages and MGCs share common ultrastructural traits, and are positive for acid phosphatase. MGCs seem to evolve in the course of the granulomatous inflammatory response and are probably of monocyte/macrophage origin.