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Department of Medicine and Cardiovascular Research Institute, University of California, San Francisco, California 94143
Neutrophils, eosinophils, and their
proinflammatory constituents are important mediators of airway disease,
and high levels of neutrophil proteases and eosinophil cationic protein
(ECP) are found in sputum from patients with cystic fibrosis (CF). To investigate whether neutrophil proteases or CF sputum causes eosinophil degranulation, purified eosinophils from atopic asthmatic subjects were
incubated for 2 h with neutrophil elastase, cathepsin G, and CF sputum,
and the release of ECP was measured. We found that the percent release
of ECP was higher after incubation with neutrophil elastase
(10
5 M) than with a buffer
control [6.1 ± 0.8 (SE) vs. 1.7 ± 0.1%; P < 0.003] and represented
>50% of the release caused by positive controls
[Ca2+ ionophore A-23187 (5 × 10
6 M) or
serum-coated Sephadex beads]. The release of ECP after incubation
with cathepsin G (2.3 ± 0.2%) and CF sputum (6.2 ± 2.0%) was
also significantly higher than that with a buffer control (P < 0.05). Neutralization of free
elastase activity with
1-proteinase inhibitor reduced
the mean percent degranulation of eosinophils by neutrophil elastase by
50% (P = 0.0004) and by CF sputum by 75% (P = 0.02). Preincubation of
eosinophils with cytochalasin B (10 mg/ml) and depletion of the
incubation medium of Ca2+ also
significantly attenuated degranulation of eosinophils incubated with
purified free neutrophil elastase or CF sputum
(P < 0.05). We conclude that
neutrophil proteases, especially neutrophil elastase, and elastase-rich
CF sputum cause degranulation of eosinophils in a mechanism partially
dependent on Ca2+ and actin filaments.
eosinophil cationic protein
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