Oxidized phosphatidylcholine in alveolar macrophages in idiopathic interstitial pneumonias

It has been suggested that oxidative stress plays a pathogenic role in idiopathic interstitial pneumonias. Macrophage- or neutrophil-derived oxidants seem to be important sources of oxidative stress in this group of inflammatory disorders. Recent experimental studies have revealed that oxidative injury during inflammation or apoptosis can change phosphatidylcholine of cell membrane into its oxidized form, which serves as a ligand for macrophage scavenger receptor CD36. Recently, we developed a monoclonal antibody against oxidized phosphatidylcholine. Using this novel antibody, we performed an immunohistochemical investigation to clarify the localization of oxidized phosphatidylcholine in lung tissues of idiopathic interstitial pneumonias and a relationship between oxidized phosphatidylcholine localization and CD36 expression. Lung specimens obtained from patients with desquamative (n = 8) or usual interstitial pneumonia (n = 15) were studied. Thirteen normal lung tissues were also examined as controls. Antibodies against oxidized phosphatidylcholine, CD36, epithelial cells, macrophages, and neutrophils were used as primary antibodies. The positive cell number was counted by computer-aided morphometry. While there were no oxidized phosphatidylcholine-positive cells in normal lungs, lungs of desquamative or usual interstitial pneumonia contained large numbers of oxidized phosphatidylcholine-positive cells in the alveolar spaces. Double-staining analysis revealed that most oxidized phosphatidylcholine-positive cells were macrophages. The oxidized phosphatidylcholine-positive cells were increased in association with the increase in the densities of macrophages (Rs = 0.87, p < 0.0001) and neutrophils (Rs = 0.89, p < 0.0001). Accumulated macrophages also showed distinct CD36 expression. These findings suggest that oxidative stress and the related product, oxidized phosphatidylcholine, play an important role in the pathophysiology of idiopathic interstitial pneumonias.