Ultrastructural localization of bronchial antileukoprotease in central and peripheral human airways by a gold-labeling technique using monoclonal antibodies.

The present report describes the ultrastructural localization of bronchial antileukoprotease (ALP) in human central and peripheral airways by using polyclonal as well as monoclonal ALP-specific antibodies in a two-step gold-labeling procedure. In the serous cells of bronchial glands, ALP could be demonstrated in secretory granules. These granules, among which 4 phenotypes could be distinguished morphologically in ultrathin sections, showed the following labeling patterns: phenotype I, which had an electron lucent, fine granular content, and phenotype II, which was homogeneously electron dense, both showed gold label over their entire area. The granules expressing zonal differences in electron density (phenotype III) showed only label in their electron-dense cores and the electron-lucent granules (phenotype IV) showed a minimal labeling. Sometimes gold particles could be observed in the rough endoplasmic reticulum and nuclear envelope, suggesting that ALP is present in these cell organelles. In the bronchiolar epithelium, ALP could be localized only in the secretory granules of Clara cells and goblet cells. These findings indicate that ALP is also synthesized in bronchioli. To our knowledge this is the first time that a well-defined protein has been described that is produced and secreted by human Clara cells.