Localisation of a low-molecular-weight bronchial protease inhibitor in the peripheral human lung.

The localisation of a low-molecular-weight bronchial protease inhibitor (LMI) in human peripheral lung tissue was studied by an immunohistochemical method. This inhibitor was found exclusively in a part of the non-ciliated cell population of the bronchiolar epithelium. An inverse relationship was observed between the number of LMI-positive non-ciliated cells per millimetre of basement membrane and the bronchiolar diameter. These findings may have a bearing on the protease-antiprotease theory of the development of pulmonary emphysema, LMI possibly playing a part in the protection of peripheral lung tissue against proteolytic destruction by enzymes liberated from granulocytes or migrating alveolar macrophages.