Cytotoxicity of stimulated equine neutrophils on equine endothelial cells in culture.

The research article discusses how the secretion from activated immune cells called neutrophils can damage endothelial cells, which line the interior surface of blood vessels, even in the absence of direct contact. This discovery is particularly relevant for diseases characterized by intense immune response, indicating that harm may extend beyond the immediate area of inflammation.

Objective and Methodology

• The researchers aimed to examine the effect of activated neutrophils on endothelial cells during acute inflammation situations. Equine neutrophils and endothelial cells derived from horse carotid arteries were used in the experiments.
• The interaction was observed in two scenarios: one with direct contact where endothelial cells were covered with activated neutrophils, and one where only the supernatant (the fluid part containing the secretions but no neutrophils) was used.

Understanding Cytotoxicity

• The damage or cytotoxicity caused to the endothelial cells was measured by the release of a radioactive chromium isotope (51Cr) and by performing light microscopy observations.
• To understand the specific role of reactive oxygen species, which are known to be involved in tissue damage during inflammation, the researchers treated the endothelial cells with two systems. These systems were designed to generate superoxide anion and hydrogen peroxide or hypochlorite, chemicals released during inflammation.

Results and Conclusion

• Major damage was observed when endothelial cells were in direct contact with stimulated neutrophils, as evidenced by a 50% loss of endothelial cells and noticeable changes in surviving cells.
• The supernatant of activated neutrophils also demonstrated significant toxicity to the endothelial cells. This toxicity correlated with the amount of neutrophils originally used and the concentration of myeloperoxidase, an enzyme found in neutrophils, in the supernatant.
• While the toxicity of the reactive oxygen species generating system on endothelial cells was relatively low, it was significantly increased by the addition of myeloperoxidase. Hypochlorite on its own was found to be highly toxic.
• From these results, the researchers concluded that neutrophils activated during inflammation release substances (like the enzyme myeloperoxidase) that can harm endothelial cells even without direct contact. Such findings suggest that in diseases with heightened neutrophil activation, cellular damage could extend beyond the immediate inflammation site.