Serum and BAL Clara cell 10 kDa protein (CC10) levels and CC10-positive bronchiolar cells are decreased in smokers.

Cigarette smoking has diverse effects on the structure and function of the lung. Smoking appears to reduce the levels of Clara cell 10 kDa protein (CC10) in the alveolar lining fluid, but the influence of smoking serum on CC10 levels is still debated, and it has not been clear whether smoking reduces the number of CC10-producing lung cells. The aims of this study were to clarify the influence of smoking on CC10 levels in the alveolar lining fluid and bloodstream, and on the number of CC10-producing lung cells. CC10 concentrations were measured in sera and bronchoalveolar lavage (BAL) fluids, by means of enzyme-linked immunosorbent assay using monoclonal and polyclonal antibody, and the immunohistochemical expression of CC10 was examined in the lungs of nonsmokers and smokers using the monoclonal antibody, TY-5, against CC10/human urinary protein-1. CC10 concentrations in sera and in BAL fluids from healthy smokers were significantly lower than in healthy nonsmokers. Immunohistochemical expression of CC10 was found exclusively in nonciliated bronchiolar epithelial cells. As compared to that of nonsmokers, the mean percentage of CC10-positive bronchiolar epithelial cells was significantly decreased in lung tissue specimens obtained from smokers who had normal results in pulmonary function tests. It was concluded that smoking reduces the proportion of Clara cell 10 kDa protein-producing bronchiolar epithelial cells, resulting in decreased levels of Clara cell 10 kDa protein in the lower respiratory tract and in the bloodstream. The protein is a new blood biochemical and immunohistochemical marker, reflecting structural changes in peripheral airways induced by cigarette smoking.