Antileukoprotease Is Associated with Elastin Fibers in the Extracellular Matrix of the Human Lung: An Immunoelectron Microscopic Study

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Abstract
Human lung antileukoprotease (ALP) is a potent inhibitor of neutrophil elastase that is locally produced by submucosal bronchial glands and by secretory cells in the bronchiolar epithelium. In a recent light microscopic investigation, ALP was detected in the connective tissue matrix of the lung. The present immunoelectron microscopic study was performed in order to extend our knowledge about the exact localization of ALP in the extracellular matrix of the lung. Both elastin and ALP were detected in central and peripheral human lung specimens using specific antibodies in a two-step, gold-labeling procedure. ALP could be demonstrated in the parenchymal matrix of the alveolar walls exclusively in association with the amorphous elastin fibers. In addition, the subepithelial connective tissue of the bronchial wall also showed a clear labeling for ALP, which was present exclusively over the elastin fibers. The results of this study strongly suggest that ALP plays a modulating role in destructive pulmonary diseases such as emphysema in which degradation of elastin fibers by elastase is thought to occur.