Intra-articular interleukin-1β induces early synovitis in an ex vivo autologously perfused equine forelimb model

Objective: To evaluate an ex vivo model of synovitis induced by IA lipopolysaccharide (LPS) and IL-1β in isolated, perfused equine forelimbs. Methods: Forelimbs and blood were collected from 12 clinically unremarkable horses following slaughter at a licensed abattoir. In 8 limbs, 2 of 3 phalangeal joints were injected with LPS (0.5 to 5 ng, 4 limbs) or IL-1β (100 ng, 4 limbs) diluted in 1 mL of distilled water. All limbs were perfused with autologous perfusate for 8 hours. Synovial fluid cytology and synovium sample histology scores for synovitis (0 = no changes and 3 = marked changes) were assessed. Results: Comparing start and end, LPS dose significantly correlated with decreased percentages of synovial neutrophils (median, -0.759) and lymphocytes (median, -0.718), reduced neutrophil presence (median, -0.726), and increased percentage of monocytes (median, 0.880), without correlation to histology. Joints with IL-1β showed significantly higher leukocyte scores in synovium vessels compared to joints in control limbs (IL-1β: median, 32.67 [range, 0.67 to 42.33]; control: median, 1 [range, 0.67 to 41.5]), whereas integrity scores of synovial membrane (IL-1β: median, 28.33 [range, 1 to 60.33]; control: median, 33.3 [range, 6.33 to 67.33]) and leukocyte migration scores to synovial tissue (IL-1β: median, 25 [range, 1 to 61]; control: median, 35.33 [range, 5 to 66]) were significantly higher in controls. Conclusions: This synovitis model in autologous perfused limbs suggests IL-1β may be suitable for short-term studies of early joint inflammation. Clinical Relevance: This model may reduce in vivo experiments when testing IA therapies in early joint inflammation.