Tumor necrosis factor activity in the circulation of horses given endotoxin.

The research investigates the effects of endotoxin on horses by studying the cytotoxic activity in their serum and plasma. The findings suggest that tumor necrosis factor is a major contributor to these cytotoxic effects, supporting the hypothesis that it is an early mediator of endotoxin’s effects in the horse.

Objective of the Research

• The researchers aimed to understand the cytotoxic activity in the blood of horses subjected to endotoxin treatment.
• The study also aimed to unravel the role of tumor necrosis factor (TNF) in mediating the effects of endotoxins in horses.

Methodology and Findings

• Researchers tested the serum and plasma from horses injected with endotoxin for cytotoxic activity. Two specific cell lines, L929 and WEHI 164 clone 13, were used for this purpose.
• It was found that while both cell lines were sensitive to the cytotoxic effects of equine serum, the use of isopropanol in the WEHI assay led to a precipitation artifact. This limited the assay’s use to samples with less than 2 mg of protein/ml.
• Whether adult horses were given continuous low-dose infusions of LPS, or foals were treated with a sublethal IV bolus, cytotoxic activity was detected in all serum or plasma samples taken between 30 minutes to 4 hours after the LPS infusion began.
• The research found that in horses given either continuous or bolus LPS infusions, circulating cytotoxic activity peaked at 1 to 2 hours before decreasing dramatically.

Relationship Between Temperature and Cytotoxic Activity

• An interesting observation was that the onset of elevated temperature, or pyrexia, coincided with the appearance of circulating cytotoxic activity.
• However, even after the cytotoxic activity disappeared, the high temperature persisted.
• They also found that treating horses with flunixin meglumine appeared to moderate the temperature effect but had no significant impact on the circulating cytotoxic activity.

Link to Tumor Necrosis Factor (TNF)

• The treatments of serum samples with an antibody raised against a segment of human tumor necrosis factor resulted in the removal of more than 90% of serum cytotoxicity.
• This strongly suggested that the cytotoxic activity seen was largely attributable to TNF, providing strong evidence that TNF is an early acting mediator of the effects of endotoxin in horses.