Figure 4.

Free extracellular neutrophil elastase (NE) activity in children with cystic fibrosis is limited by BAL fluid antiprotease activity and by compartmentalization on airway leukocytes. (A) Activity of recombinant NE was measured in vitro by Förster resonance energy transfer in the absence or presence of BAL fluid from children with cystic fibrosis with either low or high intrinsic NE activity. Results were compared with the unopposed activity of recombinant NE in the absence of BAL fluid (100%). (B) Surface NE antigen was measured by flow cytometry in cystic fibrosis blood and airway neutrophils and macrophages (n = 6). *P < 0.05. MFI = median fluorescence intensity.