The effect of lower airway inflammation on inflammatory cytokine gene expression in bronchoalveolar lavage fluid and whole blood in racing Thoroughbreds.

This study investigates the relationship between lower airway inflammation and inflammatory cytokine gene expression in the blood and bronchoalveolar lavage fluid (BALF) of racing Thoroughbreds. The findings suggest that exercise increases levels of IL-8 inflammatory cytokine in the blood, however, lower airway inflammation doesn’t cause increased cytokine in resting blood or BALF.

Objective and Hypothesis

• The researchers aimed to better understand the role of immune response in mild to moderate equine asthma (MEA) in racehorses – a health issue that’s not entirely understood.
• The hypothesis was that racing Thoroughbreds with lower airway inflammation would present higher levels of inflammatory cytokine gene expression in both BALF and resting blood compared to healthy ones, and the level in blood collected post-race would be even higher.

Methods

• The study was observational and involved 38 racing Thoroughbreds from which a variety of samples were drawn, including 30 resting blood samples, 22 post-race BALF samples, and 41 post-race blood samples.
• They measured the inflammatory cytokine gene expression from the collected samples to identify any variations between racehorses with lower airway inflammation and the control group.

Results

• A significant number (79%) of racehorses were diagnosed with lower airway inflammation.
• The research revealed that there was no significant difference in gene expression in BALF or resting blood between both groups of horses.
• The gene expression of IL-8 inflammatory cytokine was found to be higher in post-race blood compared to resting blood, irrespective of the health status, indicating the effect of exercise on IL-8 gene expression.
• The study also found correlations between increased proportions of BALF neutrophils with increased IL-1β gene expression, and BALF mast cells with increased TNF-α gene expression in post-race blood.

Conclusions

• Lower airway inflammation is common in racehorses, even without respiratory signs or exercise intolerance.
• Exercise was identified as a factor capable of increasing IL-8 gene expression level in peripheral blood.
• Inflammatory cytokine gene expression was not found increased in BALF or resting blood in horses with lower airway inflammation, thus challenging its diagnostic value in clinical practice.