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 within the joint to produce the monocyte chemotactic and activating factor (MCAF) and to a lesser degree interleukin 8 (IL-8) as judged by immunohistological staining. Polyethylene particles suspended in hyaluronic acid were injected weekly for 12 weeks into the right knee joint of 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 hyaluronic acid as the control. The animals were killed after 13 weeks. On the control side, the synovial membrane was histologically normal, without signs of inflammation. In the knees that were injected with polyethylene particles, histological analysis showed a weak inflammatory response, 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, whereas IL-8 was present in endothelial cells and in the lining layer, but not in cells in the vicinity of polyethylene particles, suggesting that polyethylene particles are able to activate cytokine metabolism in a differentiated way in the synovial monocytes.