Free secretory component and other proteins in human lung lavage

Subsegmental bronchoalveolar lavage of the lingula and right middle lobe was performed in a group of normal subjects (32 cigarette smokers and 24 nonsmokers) to analyze the recoverable fluid for its content of respiratory cells, several proteins including IgG and IgA, and free secretory component, a glycoprotein elaborated by serous bronchial epithelial cells. The lavage fluid obtained from the smokers consistently demonstrated an increased cell yield, reflecting primarily an increase in alveolar macrophages. In addition, the number of polymorphonuclear granulocytes was 10-fold greater in smokers, and the total number of lymphocytes recovered was approximately twice that of nonsmokers. As in previous studies, the analysis of proteins contained in bronchoalveolar lavage (BAL) revealed an increase in the ratio of IgA to albumin in both smokers and nonsmokers, as compared with serum; but an increase in the IgG/albumin ratio in BAL was found only in smokers. The total amount of secretory component recovered in lung lavage was significantly decreased in 20% of the cigarette smokers. Surprisingly, this decrease did not correlate directly with pack-yr smoked. It is possible that this glycoprotein may be an indicator of biochemical dysfunction of epithelial cells after inhalant exposure to cigarette smoke, which occurs relatively early after exposure, and perhaps is independent of smoking history.