Effect of endotoxin on leukocyte activation and migration into laminar tissue of isolated perfused equine limbs.

This research paper examines the impact of endotoxin on the activation of leukocytes and their movement into the laminar tissue of horses’ limbs. Results indicate that endotoxins significantly stimulate these cells causing an inflammatory reaction similar to that observed in the early stages of laminitis.

Research Objective

The main purpose of this paper is to explore how endotoxin affects the activation of leukocytes, white blood cells integral to the immune response, as well as their infiltration into the laminar tissue of isolated horse limbs. Laminar tissue is a part of the horse’s hoof that is most commonly impacted during laminitis, an inflammatory condition.

Methods

• The study uses right forelimbs from 10 healthy adult horses and 3 left forelimbs gathered post-mortem from a licensed slaughterhouse.
• The right forelimbs were divided into two groups – one group was perfused with 80 ng of endotoxin per liter for 10 hours and the other was perfused under same conditions but without endotoxin. The perfusion method was used to clearly separate the effects of the endotoxin from the natural state of the limbs.
• Post-perfusion, samples were collected from the dorsal laminar tissue of the hooves for immunohistochemical identification of leukocytes and for transmission electron microscopy.
• For comparison, control samples were also collected from the nonperfused left forelimbs.

Results

• The test revealed significantly increased scores for calprotectin and myeloperoxidase stains, markers used to track inflammation and identify the occurrence of leukocytes, in laminar tissue samples from limbs perfused with the endotoxin.
• Ultrastructural examination demonstrated that the endotoxin had caused cellular damage, with the epidermal basal cells losing their contacts, leading to a disintegration of the basement membrane.
• Akin to the behavior seen in laminitis, leukocytes were adhering to and causing breakdown at certain points in the basement membrane.

Conclusions

The significant accumulation of leukocytes in the laminar tissue, kickstarted by the introduction of endotoxin, sparked an inflammatory response in the isolated horse limbs. This reaction mirrored the characteristics of the developmental phase of laminitis. The authors therefore suggest that endotoxin should be considered as a potential cause for certain types of laminitis.