Novel serum biomarkers provide evidence for an involvement of the CCL3:CCL5 axis in fatal musculoskeletal injuries in Thoroughbred racehorses.

Overview

• This study identifies new blood-based markers in Thoroughbred racehorses that are linked to fatal musculoskeletal injuries.
• The findings suggest that the interaction between certain immune system proteins, specifically the CCL3 and CCL5 chemokines, plays a role in these serious injuries.

Background and Importance

• Fatal musculoskeletal (MSK) injuries in Thoroughbred racehorses cause significant welfare concerns, harm the sport’s public image, and result in major economic losses.
• Currently, there are no blood tests or biomarkers that can help predict which horses are at risk of fatal MSK injuries.
• The researchers hypothesized that components of the immune system and inflammation might serve as indicators or predictors of such injuries.

Study Design and Methods

• Serum samples were collected from three groups of Thoroughbred horses:
  • 44 horses with fatal musculoskeletal injuries
  • 63 horses with nonfatal injuries
  • 554 control horses (aged 2-5 years) undergoing routine testing for equine infectious anemia
• A total of 12 immune-related and immune-regulatory markers in the serum were measured using fluorescent bead-based multiplex assays, a technique allowing simultaneous detection of multiple proteins.
• The analysis focused on identifying markers that differentiate fatal injury cases from controls.

Key Findings

• Four biomarkers showed significant differences in horses with fatal MSK injuries compared to controls:
  • C-C motif chemokine ligand 3 (CCL3)
  • C-C motif chemokine ligand 5 (CCL5)
  • C-C motif chemokine ligand 11 (CCL11)
  • Soluble CD14 (a protein involved in immune response)
• A majority (70.4%) of horses with fatal injuries had two to four of these biomarkers elevated, while nearly all controls (99.1%) had zero or one elevated biomarker.
• Levels of CCL3, CCL5, and CCL11 correlated with the severity of fractures.
• The ratio of CCL3 to CCL5 identified over 81% of horses with fatal MSK injuries, suggesting its potential as a strong indicator.

Interpretation and Implications

• The involvement of CCL3 and CCL5, chemokines that guide immune cells to sites of inflammation or injury, suggests immune and inflammatory processes play a mechanistic role in the development or progression of fatal musculoskeletal injuries.
• The balance between CCL3 and CCL5 (their ratio) may be particularly important, indicating a specific ‘axis’ involved in injury pathogenesis.
• The novel biomarkers identified could reflect disruptions in normal bone remodeling processes in the affected horses.

Potential Applications and Future Directions

• These serum biomarkers could be developed into blood tests for early detection of horses at risk for serious MSK injury.
• Routine monitoring of these markers may allow timely veterinary assessments and diagnostic imaging, possibly preventing fatal injuries by early intervention.
• Further prospective studies are needed to validate these biomarkers, confirm their predictive value, and clarify their role in bone biology and injury mechanisms.