Beta-thromboglobulin in inflammatory synovial fluid

Activated platelets release substances which potentially can contribute to joint lesions in inflammatory arthritides. To elucidate a possible participation of platelets in inflammatory joint reactions, the concentrations of the platelet protein beta-thromboglobulin (beta-TG) were measured in 90 inflammatory synovial fluids. Seven percent of the patients with rheumatoid arthritis and none of the patients with other inflammatory joint diseases (e.g., Reiter's disease, reactive or crystal arthritides) had beta-TG concentrations in synovial fluid exceeding the upper normal range of plasma beta-TG. The absent or very modest signs of local platelet activation were contrasted by the pronounced neutrophilic and monocytic activation, as assessed by the measurements of some granule proteins: lactoferrin, myeloperoxidase, lysozyme, and ferritin. No correlation was found between these inflammatory cell markers and beta-TG. A positive correlation (p less than 0.001) was noted between beta-TG and beta 2-microglobulin, which appeared in particularly high amounts in rheumatoid arthritis. This correlation may reflect a disturbed permeability of synovial membrane for LMW proteins or a related activation of platelets and lymphocytes. The present results do not give any evidence of platelet activation playing a major role in proliferative or destructive processes in arthritis.