Elevated levels of cytokeratin 19 in the bronchoalveolar lavage fluid of patients with chronic airway inflammatory diseases--a specific marker for bronchial epithelial injury.

Cytokeratin 19 (CK19) is a specific cytoskeletal structure of simple epithelia, including bronchial epithelial cells (BEC). Since CK19 is released from injured bronchial epithelium, we investigated the levels of CK19 fragments in the bronchoalveolar lavage fluid (BALF) of eight patients with chronic airway inflammatory diseases (CAID) using an enzyme-linked immunosorbent assay (ELISA). Included in our test group were four cases of chronic bronchitis, three cases of bronchiectasis, and one case of diffuse panbronchiolitis. There were also 15 control subjects (five asymptomatic smokers and 10 nonsmokers). BALF from the nonsmokers as well as from the asymptomatic smokers contained few CK19 fragments (0.2 +/- 0.2 and 1.9 +/- 0.8 pg/ml, respectively). In contrast, significantly high levels of CK19 were present in the BALF of patients with CAID (21.7 +/- 5.7 pg/ml; p < 0.01 versus nonsmoking controls). In addition, CK19 fragment concentrations in BALF correlated significantly with the number of neutrophils (r = 0.722, p < 0.01) but not with the numbers of macrophages or lymphocytes in BALF. BALF from patients with CAID contained high levels of neutrophil elastase (NE) activity, suggesting that NE might be an important stimulus for the release of CK19 from BEC. To prove this, we incubated BET-1A cells, a human immortalized bronchial epithelial cell line, both in the absence and the presence of inflammatory mediators (including NE, tumor necrosis factor-alpha [TNF-alpha], and hydrogen peroxide). We then measured the concentration of CK19 fragments in the culture supernatants with ELISA. BET-1A cells released CK19 fragments into their culture supernatants after treatment with NE but not after treatment with TNF or hydrogen peroxide. Further, we demonstrated that CK19 cleaved by NE could not be detected by ELISA. Our results suggest that CK19 measurement in BALF is useful for assessing the presence of bronchial epithelial injuries.