CAT and pulmonary fibrosis: We thus hypothesized that (A) catalase is diminished in human pulmonary fibrosis and in mouse bleomycin-induced lung injury, (B) a decrease in catalase particularly occurs in bronchiolar epithelial cells and/or in various types of abnormal re-epithelialization in fibrotic lungs, and finally (C) the deficiency in catalase activity in the lungs results in predisposing the lung to worsening lung inflammation and subsequent fibrosis.