Effects of repeated arthrocentesis on systemic cytokine expression and leukocyte population in young horses challenged with intra-articular lipopolysaccharide.
Abstract: Osteoarthritis (OA) is a prevalent and economically costly source of lameness in the athletic horse. Previous studies investigating OA pathology have focused on localized trauma to the articular cartilage of a joint, largely ignoring the systemic immune status of the animal. In this study, yearling Quarter Horses were used to evaluate systemic cytokine gene expression and circulating leukocytes following a localized intra-articular inflammatory insult of the endotoxin, lipopolysaccharide (LPS). Treatments for the 35-d experiment included an intra-articular injection of 0.25 ng (n = 7) or 0.50 ng (n = 6) of LPS obtained from Escherichia coli O55:B5 or sterile lactated Ringer's solution (n = 6; control) into the radial carpal joint. Blood and synovial fluid samples were collected at preinjection hour 0 and 2, 6, 12, and 24 h postinjection. Synovial fluid was obtained for a companion study. Total RNA was isolated from plasma leukocytes and real-time PCR was used to determine relative gene expression of the cytokines interleukin (IL)-1beta (β), IL-6, IL-8, IL-10, and tumor necrosis factor-alpha (TNF-α). Total leukocyte subpopulations and differentials were performed using a cell counter. Data were analyzed using the PROC MIXED procedure of SAS. Gene expression of all cytokines were unaffected by intra-articular treatment. However, IL-1β increased above baseline beginning at hour 6 and remained elevated to 24 h (P = 0.04). In contrast, IL-6 decreased from hours 6 to 12 and then increased to 24 h (P = 0.02). Levels of TNF-α increased at 6 and 12 h (P = 0.01) postinjection. Only IL-8 exceeded a 2-fold change in expression (P = 0.01), peaking at 12 h and indicating greater responsiveness to arthrocentesis when compared with 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 postinjection. Similarly, an increase over time was observed in monocytes (P = 0.02) and in platelets (P = 0.01) at 24 h postinjection. The results indicate that regardless of treatment, a mild immune response was elicited, which may be 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.
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This research investigates the systemic immune response, including cytokine gene expression and circulating leukocytes, in young horses following an intra-articular inflammatory trigger. A better understanding of this reaction could provide insights into the pathogenesis of osteoarthritis, a common and expensive cause of lameness in sporting horses.
Research Method
In the 35-day experiment, yearling Quarter Horses were injected into the radial carpal joint with lipopolysaccharide (LPS) derived from Escherichia coli (either 0.25 ng or 0.50 ng) or a lactated Ringer’s solution as a control. The LPS injection serves to trigger an arthritic-like immune response within the joint.
Blood and synovial fluid samples were collected before the injection and at multiple time points (2, 6, 12, and 24 hours) afterwards. The synovial fluid samples were used in a separate study.
The cytokine gene expression patterns for IL-1β, IL-6, IL-8, IL-10, and TNF-α in plasma leukocytes were measured using real-time PCR. These cytokines are critical mediators in the immune response, particularly in inflammation.
Additionally, total leukocyte subpopulations and differentials were counted to evaluate circulating white blood cell populations.
Results
The intra-articular treatment had no effect on gene expression of all cytokines. However, there were changes in levels over time for multiple cytokines. IL-1β levels increased from 6 hours post-injection and remained elevated until the last observed point at 24 hours. IL-6 levels first went down from 6 to 12 hours before increasing at 24 hours. TNF-α levels increased at 6 and 12 hours.
Among all the cytokines, only IL-8 showed more than a two-fold change in expression, suggesting a stronger response to the arthrocentesis process compared to the other cytokines.
The study found no effect of treatment on the population of leukocytes. However, the total counts of circulating leukocytes, monocytes, and platelets all increased over time, indicating a general immune response.
Implications
Despite the variation in treatment, all horses showed a mild immune response, potentially attributable to the repeated arthrocentesis itself. This implies that even the control animals without an intra-articular inflammation trigger may still experience an immune response due to the procedure.
The researchers suggest that future studies examining the responses to intra-articular LPS in young horses should consider the potential impact of arthrocentesis and a possible systemic inflammatory response.
Cite This Article
APA
Hunt CL, Leatherwood JL, Coverdale JA, Sigler DL, Vogelsang MM, Arnold CE.
(2018).
Effects of repeated arthrocentesis on systemic cytokine expression and leukocyte population in young horses challenged with intra-articular lipopolysaccharide.
J Anim Sci, 97(1), 184-191.
https://doi.org/10.1093/jas/sky423
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