Manganese superoxide dismutase and catalase are coordinately expressed in the alveolar region in chronic interstitial pneumonias and granulomatous diseases of the lung

Free radicals have been suggested to play an important role in the pathogen esis of interstitial lung diseases, the most important of which are chronic interstitial pneumonias such as usual interstitial pneumonia (UIP) and des quamative interstitial pneumonia (DIP) and granulomatous lung diseases such as sarcoidosis. Because manganese superoxide dismutase (MnSOD) and catalas e are two important intracellular antioxidant enzymes that probably play a central role in lung defense, the localization and intensity of these two e nzymes were assessed by immunohistochemistry in biopsies of UIP (n = 9), DI P (n = 11), pulmonary sarcoidosis (n = 14), and extrinsic allergic alveolit is (n = 6). The mRNA of these enzymes in selected samples of bronchoalveola r lavage was assessed by Northern blotting. Catalase, but not MnSOD, was co nstitutively expressed, especially in type II pneumocytes of the healthy lu ng of nonsmoking individuals. In contrast, manganese SOD immunoreactivity w as markedly upregulated in all of the interstitial lung diseases investigat ed, whereas no increased expression of catalase could be detected in any ca se. Both enzymes were expressed, especially in type II pneumocytes and alve olar macrophages of DIP and UIP, in the well-preserved areas of the lung, i n the acute fibromyxoid lesions of UIP, and in the granulomas of sarcoidosi s and extrinsic allergic alveolitis. The simultaneous expression of MnSOD a nd catalase in the alveolar region suggests their protective role against t he progression of lung disease.