Am. J. Respir. Crit. Care Med., Vol 154, No. 6, 12 1996, 1829-1833.
Activated neutrophils secrete stored alpha 1-antitrypsin
P Paakko, M Kirby, RM du Bois, A Gillissen, VJ Ferrans and RG Crystal
Department of Pathology, University of Oulu, Finland.
Neutrophil elastase (NE), a potent serine protease, is stored in primary
granules of neutrophils and released following neutrophil activation.
Alpha-1-antitrypsin (alpha 1-AT), the major inhibitor of NE, is synthesized
by mature neutrophils. In the context of the maintenance of tissue
homeostasis, we hypothesized that neutrophils may be able to store alpha
1-AT, thus having it available for release concordantly with NE.
Immunofluorescence and quantitative flow- cytometric studies of neutrophils
and monocytes labeled with fluorescein-conjugated alpha 1-AT-antibody
demonstrated larger amounts of cytoplasmic alpha 1-AT in neutrophils than
in monocytes. [35S]methionine-labeling and anti-alpha 1-AT
immunoprecipitation analysis showed that although both neutrophils and
monocytes synthesize alpha 1-AT, the proportion of newly synthesized
intracellular alpha 1- AT was much higher in neutrophils than in monocytes.
Flow-cytometric analysis showed that in the presence of surface stimulation
with cytochalasin B followed by formyl-methionyleucylphenylalanine (fMLP),
mean intracellular alpha 1-AT was decreased in stimulated neutrophils
compared with that in resting cells, suggesting that the stored alpha 1- AT
was rapidly released following surface triggering. Evaluation of
surface-stimulated neutrophils by [35S]methionine labeling and anti- alpha
1-AT immunoprecipitation demonstrated increased secretion of alpha 1-AT
compared with that of resting neutrophils, with some of the secreted alpha
1-AT capable of forming complexes with NE. Thus, neutrophils respond to
surface stimulation not only by secreting NE but also by secreting its
inhibitor, alpha 1-AT, suggesting that these cells have an inherent
mechanism for damping the local effects of NE, their most powerful
proteolytic enzyme.
