lmmunohistochemical analysis of an equine model of synovitis - induced arthritis 1

Objectives-To use lipopolysaccharide (LPS) to create synovitis in the midcarpal joint of ponies, and to assess the morphologic, histochemical, and immunohistochemical effects of synovitis on articular cartilage of the third carpal bone. Animals-2to 3-year-old ponies, 6 control (group 1) and 6 treated (group 2). Procedure-Synovitis was induced in 1 midcarpal joint of group-2 ponies by intra-articular injections of LPS (0.02 pglkg of body weight), morphine (0.1 mglkg), and saline solution (group 2a) and morphine and saline solution alone in the contralateral midcarpal joint (group 2b). Articular cartilage sections and attached synovial membrane from the third carpal bones were examined by immunohistochemical distribution of interleukin 1 p, tumor necrosis factor (TNFI-~L, TNF receptors (P55, P75) and 3-B-3(-) epitopes, and by localization of proteoglycans (metachromatic staining). Proteoglycan extracts were assessed by metachromatic staining or western blotting and immunohistochemical staining, using anti-3-B-3 antibodies. Results-Enhanced immunoreactivity for the cytokines and receptors was found in inflamed synovial membrane and noncalcified cartilage (group 2a more than 2b). Metachromasia of the noncalcified cartilage was greater in group-1 than in group-2a and group-2b specimens. In group 2a, chondrocyte hypertrophy and enhanced immunoreactivity for 3-B-3(-) epitope in areas of increased cytokine immunoreactivity suggested possible phenotypic change of the chondrocytes in response to synovitis. lmmunohistochemical analysis by western blotting of proteoglycan extracts indicated strong 3-B-3(-1 epitope immunolocalization in group-2a, weaker staining in group2b, and barely detectable stain in group-1 specimens, which correlated with in situ immunolocalization. Conclusions-lntra-articular administration of LPS may be used to induce a synovial environment conducive to increased immunoreactivity of interleukin 1 p, TNF-a, and its receptors in equine synovial membrane and articular cartilage. These cytokines may be involved in the early phenotypic change of chondrocytes that is believed to occur in osteoarthritis and is characterized in this study by enhanced 3-B-3(-) epitope immunoreactivity and