EFFECT OF SYNOVIAL-MEMBRANE INFECTION IN-VITRO ON EQUINE SYNOVIOCYTESAND CHONDROCYTES

Objective-To determine the functional response of synovium to infectio n, and the influence of infected synovium on articular cartilage metab olism. Sample Population-Synovium and articular cartilage explants fro m the midcarpal and tarsocrural joints of adult horses. Procedure-For experiment 1, synovium explants were incubated as follows. control-inc ubation in standard medium, infected (I)-incubation with Staphylococcu s aureus, and infected-filtered (IF)-incubation with medium collected from the infected group and filtered (0.22-mu m filter). Daily collect ed medium was assayed for interleukin 1 beta (IL-1 beta), IL-6, tumor necrosis factor, and hyaluronan (HA) concentrations. For experiment 2, cartilage explants were incubated as follows. control-incubation in s tandard medium, and IF-incubation in medium collected from infected sy novium cultures and filtered. After 48 hours, explant proteoglycan syn thesis and endogenous proteoglycan and glycosaminoglycan contents were determined, Results-IL-1 beta and IL-6 values were significantly incr eased in synovium explants from the and IF groups. Hyaluronan concentr ation was lower in I and IF groups. Proteoglycan synthesis and content , and total glycosaminoglycan and chondroitin sulfate concentrations, were significantly decreased in cartilage from the IF group. Conclusio ns-Bacterial infection was associated with decreased HA concentration and increased mediator release. These effects were also observed despi te elimination of bacteria. Exposure to sterile but previously infecte d medium decreased articular cartilage matrix synthesis and compositio n. Clinical Relevance-Resident synovial cells may contribute appreciab ly to articular damage during bacterial infection in the absence of mi grant inflammatory cells. This response is prolonged despite eliminati on of the bacteria.