Clara cell protein as a marker of Clara cell damage and bronchoalveolar blood barrier permeability

The 16 kDa Clara cell protein (CC16), an abundant component of airway secretions, has recently been proposed in humans as a pulmonary marker measurable not only in bronchoalveolar lavage fluid (BALF) but also in serum. The aim of the present study was to investigate the changes and determinants of CC16 concentrations in these fluids in normal rats and rats with lung injury. Female Sprague–Dawley rats were given a single i.p. injection of arachis oil (n=20) or chemicals in arachis oil (n=10) that mainly damage Clara cells (4‐ipomeanol (IPO) 8 mg·kg‐1 and methylcyclopentadienyl manganese tricarbonyl (MMT) 5 mg·kg‐1) or endothelial cells (α‐naphthylthiourea (ANTU) 5 mg·kg‐1). CC16 concentration (mean±sd in µg·L‐1), measured by a sensitive latex immunoassay, was significantly reduced in BALF of all treated groups (IPO 380±100; MMT 730±200; ANTU 1,070±200; controls 1,700±470). The same pattern of decrease was observed in the labelling of Clara cells with an anti‐CC16 antiserum as well as in the CC16 messenger ribonucleic acid levels assessed by Northern enzyme‐linked immunosorbent assay. In serum, by contrast, CC16 was significantly increased in all treated groups (IPO 31±7; MMT 22±12; ANTU 52±24; controls 15±6). This rise of CC16 in serum was associated with an elevation of albumin in BALF which is an index of increased bronchoalveolar/blood barrier permeability. In conclusion, lung injury induces a decrease of the 16 kDa Clara cell protein in bronchoalveolar lavage fluid owing to a reduced production by damaged Clara cells, and an increase in serum protein levels resulting from its enhanced leakage across the bronchoalveolar/blood barrier. This study provides new insights into the understanding of the changes of lung secretory proteins in bronchoalveolar lavage fluid and serum.