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Cleavage of C3 by neutral proteases from granulocytes in pleural empyema
Abstract:
The possibility of direct inactivation of C3 by granular enzymes from polymorphonuclear leukocytes (PMNLs) in pleural empyema was examined. As a group, pleural empyema from 10 patients with purulent effusions and a positive bacteriologic culture cleaved significantly more 125I-labeled C3 bound to Sepharose (18.4% +/- 7.3%) than did 19 sterile pleural effusions (2.4% +/- 0.9%; P less than 0.001) and sonicates from bacterial strains commonly found in empyema (1.4% +/- 0.2%). Granular enzymes from 7 X 10(6) PMNLs cleaved 78.5% of 125I-labeled C3 bound to Sepharose. When proteolysis of 125I-labeled C3 after incubation with pleural empyema or PMNL granular enzymes was examined with polyacrylamide gel electrophoresis, breakdown products were similar. Granulocyte elastase-like activity was detected in four samples of pleural empyema. Granulocyte elastase inhibitors, as well as 10% human serum, effectively suppressed cleavage of C3 and elastase-like activity. In pleural empyemas, granula enzymes from PMNLs, especially elastase, apparently contribute to low complement-mediated opsonic activity by direct inactivation of C3.
Insights
Polymorphonuclear leukocyte (PMNL) granular enzymes in pleural empyema directly inactivate complement C3. This inactivation, particularly by elastase, reduces complement-mediated opsonic activity in empyema fluid.
Area of Science:
- Immunology
- Biochemistry
Background:
- Pleural empyema is associated with impaired opsonic activity.
- The role of polymorphonuclear leukocytes (PMNLs) in complement C3 inactivation within empyema fluid is not fully understood.
Purpose of the Study:
- To investigate the direct inactivation of complement C3 by granular enzymes from PMNLs in pleural empyema.
- To determine the contribution of PMNL-derived enzymes to reduced opsonic activity in empyema.
Main Methods:
- Assessing C3 cleavage by pleural empyema fluid and PMNL granular enzymes using 125I-labeled C3.
- Analyzing C3 proteolysis products via polyacrylamide gel electrophoresis.
- Detecting granulocyte elastase-like activity and evaluating inhibition by elastase inhibitors and human serum.
Main Results:
- Pleural empyema fluid significantly cleaved C3 compared to sterile effusions and bacterial sonicates.
- PMNL granular enzymes demonstrated potent C3 cleavage activity.
- Granulocyte elastase-like activity was present in empyema samples, and its inhibition suppressed C3 cleavage.
Conclusions:
- PMNL granular enzymes, especially elastase, directly inactivate C3 in pleural empyema.
- This C3 inactivation by PMNL enzymes contributes to diminished complement-mediated opsonic activity in empyema.
- Targeting PMNL-derived enzymes may offer therapeutic potential for empyema.
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