Investigation of blood platelets in synovial fluid from patients with rheumatoid arthritis.

Synovial fluid (SF) aspirated from inflamed knee joints from each of 13 patients with adult rheumatoid arthritis (RA) was mixed with ACD in the ratio SF/ACD=9:1 with subsequent addition of an equivalent amount of an edta-tris buffer. The mixture was centrifuged to obtain a platelet-rich supernatant. The platelets were washed three times and counted. The same procedure was performed with SF from non-inflamed knee-joints from 3 patients with osteoarthrosis (OA). Direct immunofluorescence (IF) studies were performed with aliquots of platelet suspensions from each SF. In most RA specimens observed under the microscope before separation of platelets, a few small platelet aggregates were observed and platelets were seen in contact with lymphocytes. In all instances, the platelet count appeared to be positively correlated to the total number of white blood cells. In the OA specimens, relatively few platelets were detected, a few lymphocytes were seen in contact with platelets, but no platelet aggregates or correlation between platelets and white blood cell counts were found. Results of the IF studies of RA specimens provide evidence that IgG, IgM and C3 are located on the platelet surface. On the surface of OA platelets, however, only IgG and C3 were detected. Identical staining results were found with washed peripheral platelets from 3 of the RA and 1 of the OA patients. Neither medical treatment nor Waaler serology influenced the staining results. In inflamed SF from RA patients, both IgG aggregates, immune complexes, collagen, and prostaglandins can induce a platelet release reaction with liberation of vasoactive compounds, chemotactic substances and enzymes which can destroy connective tissue, cartilage and bone structures. Interpretations and the significance of the different results are discussed.