Relationship of neutrophil cytoplasmic protein (L1) to acute and chronic lung disease.

L1 protein is a neutrophil cytoplasmic protein and its measurement in body fluids probably reflects neutrophil turnover. The serum range in normal subjects is wide (60-5700 microgram/l) with a median value of 547 microgram/l but lower (2P less than 0.01) than in patients with chronic obstructive bronchitis (median, 750; range, 99-500 microgram/l). Patients with "emphysema" do not have increased serum L1 protein concentrations. On the other hand patients with a variety of active lung diseases have raised concentrations compared to normal subjects suggesting that L1 protein is a marker of inflammation within the lung. The secretion concentration of L1 protein reflects its purulent nature and rapid falls in both serum and secretion L1 concentration occur with treatment. The results suggest that sequential L1 measurements may provide a measure of the inflammatory state of the lung and a rapid indication of the response to treatment.