POLYETHYLENE PARTICLES STIMULATE MONOCYTE CHEMOTACTIC AND ACTIVATING FACTOR PRODUCTION IN SYNOVIAL MONONUCLEAR-CELLS IN-VIVO - AN IMMUNOHISTOCHEMICAL STUDY IN RABBITS

We report that polyethylene particles can activate mononuclear cells w ithin the joint to produce the monocyte chemotactic and activating fac tor (MCAF) and to a lesser degree interleukin 8 (IL-8) as judged by im munohistological staining. Polyethylene particles suspended in hyaluro nic acid were injected weekly for 12 weeks into the right knee joint o f New Zealand white rabbits. The average size of the particles was 7 ( 3-12) mu m in diameter. The left knee joint was injected with hyaluron ic acid as the control. The animals were killed after 13 weeks. On the control side, the synovial membrane was histologically normal, withou t signs of inflammation. In the knees that were injected with polyethy lene particles, histological analysis showed a weak inflammatory respo nse, consisting of mononuclear cells, multi-nucleated giant cells and polyethylene particles. In the vicinity of the particles, the presence of mononuclear cells that were highly positive for MCAF was noted, wh ereas IL-8 was present in endothelial cells and in the lining layer, b ut not in cells in the vicinity of polyethylene particles, suggesting that polyethylene particles are able to activate cytokine metabolism i n a differentiated way in the synovial monocytes.