Soluble forms of P-selectin and intercellular adhesion molecule-3 in synovial fluids

A number of adhesion molecules have been identified in synovial tissues of patients with rheumatoid arthritis (RA). Some of them are upregulated and may play an important role in the inflammatory processes of the diseased joint. In addition to synovial tissue cell surface expression, synovial fluids contain soluble forms of many adhesion molecules, such as intercellular adhesion molecule-1, E-selectin (sE-selectin), and L-selectin. In this study, we investigated the expression of soluble P-selectin (sP-selectin) and intercellular adhesion molecule-3 (sICAM-3) in synovial fluids from patients with RA, osteoarthritis (OA), and other forms of arthritis. sP-selectin and sICAM-3 levels in RA synovial fluids were significantly increased compared to those in OA. The levels of sP-selectin++ in synovial fluids correlated with sICAM-3 and sE-selectin in synovial fluids. The levels of sICAM-3 in synovial fluids correlated with synovial fluid leukocyte counts and erythrocyte sedimentation rate. In vitro, synovial fluid mononuclear cells produced sICAM-3 spontaneously. Elevated levels of sP-selectin and sICAM-3 in RA synovial fluids compared to OA may indicate inflammatory interactions between endothelial cells, leukocytes, and other synovial cells in the diseased joint.