Epithelial lining fluid analysis

A noninvasive bronchoscopic microsampling (BMS) probe was developed to sample biochemical constituents of the epithelial lining fluid in small airways. In this method, intratracheal saline instillation is not required. Therefore, hypoxemia after BAL and dissemination of airway infection can be avoided. We performed the following two studies in acute respiratory distress syndrome (ARDS) patients.

(1) BMS was applied in a control group of seven patients who had hemoptysis or small solitary peripheral nodules but no hypoxemia or other signs of acute inflammation and in four patients with ARDS, to test whether BMS can ascertain the presence of acute pulmonary inflammation without complications. Complications, including a significant decrease in arterial oxygen saturation, were observed neither during nor after BMS. In the ARDS, albumin, lactate dehydrogenase (LDH), IL-6, basic fibroblast growth factor, and neutrophil elastase concentrations in epithelial lining fluid were significantly higher (P < 0.0001, P = 0.012, P < 0.0001, P < 0.0001, and P < 0.0001, respectively) than in the control group.

(2) KL-6 is a pulmonary epithelial mucin more prominently expressed on the surface membrane of alveolar type II cells when these cells are proliferating, stimulated, and/or injured. We hypothesized that high levels of KL-6 in epithelial lining fluid and plasma would reflect the severity of lung injury in patients with acute lung injury (ALI). Epithelial lining fluid was obtained at onset (day 0) and day 1 of ARDS/ALI by BMS in 35 patients. On day 0, KL-6 and albumin concentrations in epithelial lining fluid were significantly higher than in normal controls (P < 0.001), and the concentrations of KL-6 in epithelial lining fluid (P < 0.002) and in plasma (P < 0.0001) were higher in nonsurvivors than in survivors of ALI/ARDS. These observations were corroborated by the immunohistochemical localization of KL-6 protein expression in the lungs of nonsurvivors with ALI and KL-6 secretion from cultured human alveolar type II cells stimulated by proinflammatory cytokines. Because injury to distal lung epithelial cells, including alveolar type II cells, is important in the pathogenesis of ALI, the elevation of KL-6 concentrations in plasma and epithelial lining fluid could be valuable indicators for poor prognosis in clinical ALI.

We are now performing proteomic analysis of ELF obtained from ARDS to find key proteins for its pathogenesis.