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Activated neutrophils disrupt endothelial monolayer integrity by an oxygen radical-independent mechanism
Abstract:
We have measured the effect of activated neutrophils on endothelial monolayer integrity in vitro by assessing the capacity of endothelial monolayers on polycarbonate filters to exclude 125I-albumin. Although formylmethionyl-leucyl-phenylalanine (FMLP)-activated neutrophils failed to induce 51Cr-release or detachment after 4 hours of incubation with endothelial monolayers cultured in polystyrene wells, FMLP-activated neutrophils produced a marked increase in the passage of 125I-albumin across bovine aortic or pulmonary artery endothelial monolayers on polycarbonate filters. This effect was evident as early as 30 minutes following the addition of FMLP-activated neutrophils to the monolayer and reached 180% over control values at 2 hours (p = 0.001). Light and transmission electron microscopic examination of the polycarbonate filters exposed to FMLP-activated neutrophils revealed focal disruption of the endothelial monolayers. Chronic granulomatous disease neutrophils produced similar disruption of the endothelial monolayer at 2 hours. Moreover, catalase and superoxide dismutase failed to reduce significantly the neutrophil-mediated increase in 125I-albumin passage at 2 hours. Cell-free postsecretory supernatants of FMLP-activated neutrophils, leukotriene C4, and platelet activating factor did not induce a significant increase in 125I-albumin passage across the endothelial monolayers. Of note, FMLP-activated neutrophils from a patient with a congenital abnormality of neutrophil adhesion and chemotaxis did not induce disruption of the monolayer or increase 125I-albumin passage. We conclude that activated neutrophils mediate rapid, nonlytic disruption of endothelial monolayer integrity by an oxygen radical-independent mechanism that requires neutrophil-endothelial contact.
Insights
Activated neutrophils rapidly disrupt endothelial monolayer integrity through direct contact, increasing 125I-albumin passage. This effect is oxygen radical-independent and requires functional neutrophil adhesion and chemotaxis.
Area of Science:
- Immunology
- Cell Biology
- Vascular Biology
Background:
- Neutrophils play a critical role in inflammation and immune responses.
- Endothelial monolayer integrity is crucial for vascular homeostasis.
- Understanding neutrophil-endothelial interactions is vital for inflammatory disease research.
Purpose of the Study:
- To investigate the in vitro effect of activated neutrophils on endothelial monolayer integrity.
- To determine the mechanism by which activated neutrophils disrupt endothelial barriers.
- To assess the role of oxygen radicals and neutrophil adhesion in this process.
Main Methods:
- Endothelial monolayers cultured on polycarbonate filters were incubated with activated neutrophils.
- 125I-albumin passage across monolayers was measured to assess barrier function.
- Light and transmission electron microscopy were used to examine endothelial disruption.
- Experiments included neutrophils from patients with specific functional defects and the use of enzyme inhibitors.
Main Results:
- Formylmethionyl-leucyl-phenylalanine (FMLP)-activated neutrophils significantly increased 125I-albumin passage across endothelial monolayers.
- This effect was observed as early as 30 minutes and peaked at 2 hours, showing a 180% increase over controls.
- Microscopic analysis revealed focal disruption of endothelial monolayers.
- The disruption was oxygen radical-independent and required functional neutrophil adhesion and chemotaxis, as neutrophils from patients with adhesion defects did not cause disruption.
Conclusions:
- Activated neutrophils rapidly disrupt endothelial monolayer integrity through a nonlytic, oxygen radical-independent mechanism.
- Neutrophil-endothelial contact is essential for mediating this disruption.
- Functional neutrophil adhesion and chemotaxis are critical for the breakdown of the endothelial barrier.