Clara cell protein in serum and bronchoalveolar lavage

The 10 kDa Clara cell protein was measured in serum and bronchoalveolar lavage (BAL) from 39 healthy subjects (14 smokers, 25 nonsmokers) and from 41 patients with respiratory disease (chronic obstructive pulmonary disease (COPD), sarcoidosis, lung cancer). Clara cell protein appears as one of the most abundant respiratory tract derived proteins, with values averaging 7% of the total protein content of lung lavages from healthy nonsmokers. A significant reduction of Clara cell protein was found in BAL from smokers and patients with COPD or lung cancer. The same pattern of change was found in the concentrations of Clara cell protein in serum. Pulmonary sarcoidosis did not affect absolute values of Clara cell protein in lung lavages but was associated with elevated levels in serum. Changes in lung lavage Clara cell protein differed from that of albumin, beta 2-microglobulin or the secretory component, since the latter were unaffected by smoking or COPD but increased in sarcoidosis and lung cancer. These results indicate that Clara cell protein in BAL or serum might serve as a sensitive indicator of nonciliated bronchial cell dysfunction.