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

IL-1β effectively induces early synovitis in ex vivo perfused equine limbs, supporting its use in joint inflammation research.

This study evaluated an ex vivo model of synovitis using isolated, autologously perfused equine forelimbs to assess the inflammatory responses induced by intra-articular (IA) lipopolysaccharide (LPS) and interleukin-1β (IL-1β). Forelimbs and blood were harvested from 12 clinically healthy horses post-slaughter. Eight limbs had two of three phalangeal joints injected with either LPS (0.5–5 ng) or IL-1β (100 ng), while the remaining joints served as controls. All limbs were perfused with autologous blood for 8 hours, followed by synovial fluid cytology and synovium histology scoring. LPS dose correlated significantly with shifts in synovial fluid differential cell counts, including decreased neutrophil and lymphocyte percentages and increased monocyte percentages, but did not correlate with histological changes. IL-1β injection produced significantly higher leukocyte scores within synovial vessels compared to controls, indicating vascular margination and early inflammatory recruitment. However, synovial membrane integrity and leukocyte migration into synovial tissue were paradoxically higher in control joints, possibly reflecting baseline variability or model limitations. Despite these nuances, IL-1β demonstrated potential as a reliable inducer of early synovitis in this model. The authors conclude that this ex vivo perfused limb model offers a translatable and ethically advantageous alternative to in vivo experiments for studying early joint inflammation and testing IA therapies, potentially reducing the number of live animal studies required in equine orthopedic research.

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