A novel alveolar type I cell-specific biochemical marker of human acute lung injury

Currently there is no recognized biochemical or molecular marker for human parenchymal lung injury analogous to markers for acute myocardial injury. I njury to the alveolar epithelial barrier is of central importance in the pa thogenesis of and recovery from acute lung injury, In animal models, an alv eolar type I cell-specific protein, RTI40, has been shown to be an accurate marker of alveolar epithelial damage. We now report that HTI56, a novel ap ical plasma membrane protein specific to the human type I cell, is a bioche mical marker for lung injury. Using a sensitive, quantitative, light-based ELISA, we measured HTI56 in pulmonary edema fluid from 15 patients with a c linical diagnosis of acute lung injury and 12 control patients with hydrost atic (cardiogenic) pulmonary edema, HTI56 was also measured in plasma from these two groups and from 11 normal volunteers, The amount: of HTI56 was 4. 3-fold higher (p < 0.0001) in alveolar edema fluid and 1.4-fold higher (p < 0.05) in plasma from the patients with acute lung injury, compared with pa tients with hydrostatic pulmonary edema, To our knowledge, this study is th e first to utilize a specific marker of alveolar epithelial damage in human disease and demonstrates the feasibility of using a blood test to detect l ung parenchymal damage.