Cytokine mRNA expressions after racing at a high altitude and at sea level in horses with exercise-induced pulmonary hemorrhage

Objective - To determine concentrations of cytokine mRNA in horses with exercise-induced pulmonary hemorrhage (EIPH) after racing. Animals - 97 Thoroughbreds. Procedures - Following tracheobronchoscopy, the severity of EIPH was graded (scale of 0 to 4), and venous blood samples were collected from 10 horses in each grade. After RNA isolation and cDNA synthesis, real-time PCR assay was conducted to detect cytokine-specific mRNA for interleukin (IL)-1, IL-6, and IL-10; interferon (INF)-γ; and tumor necrosis factor (TNF)-α. Results - Neither location nor grade of EIPH affected the expression of IL-1 and INF-γ. There was significantly greater overall expression of IL-6 mRNA at sea level, with significantly more IL-6 expressed in horses with grade 4 EIPH than in horses with grade 0, 1, or 2 EIPH. At a high altitude, no difference was detected for IL-6 expression among the various EIPH grades. There was significantly greater overall expression of TNF-α mRNA at a high altitude; however, there was no difference within the various grades of EIPH. Expression of IL-10 was significantly affected by grade of EIPH because horses with grade 3 EIPH expressed significantly more IL-10 mRNA than did horses with grade 0 or 2 EIPH; this expression was not affected by location. Conclusions and Clinical Relevance - At sea level, increased IL-6 expression was associated with more severe EIPH, and altitude may affect gene expressions of the proinflammatory cytokine TNF-α and anti-inflammatory cytokine IL-6. Studies on protein concentrations of cytokine expression are needed. The pathophysiologic importance of these findings remains to be explained.