Effects of Intra-Articular Lipopolysaccharide Injection on Systemic Cytokine Gene Expression and Leukocyte Population in Young Horses
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Nineteen yearling Quarter Horses were utilized in a randomized, complete block design to evaluate systemic cytokine gene expression and circulating leukocyte population in young horses following an intra-articular lipopolysaccharide (LPS) challenge. Horses were administered an injection of 0.25 ng (n = 7) or 0.50 ng (n = 6) of LPS or lactated Ringer?s solution (n = 6; control). Blood was collected via jugular catheter at pre-injection h 0 and at 2, 6, 12, and 24 h following aseptic injection of the left radiocarpal joint. Aseptic arthrocentesis was performed at the same times to sample synovial fluid for a companion study. Total RNA was isolated from leukocytes using a commercially available kit and real-time PCR was used to determine relative gene expression of the cytokines; interleukin (IL)-1beta (beta), IL-6, IL-8, IL-10, and tumor necrosis factor-alpha (TNF-alpha). Determination of total leukocyte subpopulations and differentials was performed by Texas Veterinary Medical Diagnostic Laboratory. Data were analyzed using the PROC MIX procedure of SAS. Gene expression of all cytokines analyzed was unaffected by treatment. However, changes over time were observed in some cytokines. Interleukin-1? was increased above baseline at 6, 12, and 24 h (P = 0.04), IL-6 was decreased slightly at 6 and 12 h and then increased at 24 h (P = 0.002), and TNF-alpha was increased at 6 and 12 h (P = 0.01). Only IL-8 exceeded a 2-fold change in expression (P = 0.01), peaking at 12 h and indicating greater responsiveness to arthrocentesis than was observed in the other cytokines. No treatment effects on the leukocyte population were observed; however, total circulating leukocytes increased over time (P = 0.04), peaking at 6 h post-injection. Similarly, an increase over time was observed in monocytes (P = 0.002) and in platelets (P = 0.01) at 24 h post-injection. The results indicate that regardless of treatment, a mild immune response was elicited, likely due to repeated arthrocentesis. Future experiments should consider the effects of arthrocentesis and potential systemic inflammatory response, even in control animals, when administering intra-articular LPS to young horses.
Mueller, Carrie (2011). Effects of Intra-Articular Lipopolysaccharide Injection on Systemic Cytokine Gene Expression and Leukocyte Population in Young Horses. Master's thesis, Texas A&M University. Available electronically from