Thrombomodulin levels in the plasma and joint fluid from patients with rheumatoid arthritis

The hemostatic mechanism is thought to contribute to the inflammatory process of rheumatoid arthritis (RA). Thrombomodulin (TM), an inhibitor of blood coagulation, is synthesized by various cells which are recognized in the inflammatory lesions of RA. To elucidate a possible relation of TM with the process of RA, therefore, we measured soluble forms of TM in the plasma and joint fluid (JF) from RA patients by a recently developed sandwich enzyme immunoassay using monoclonal antibodies. TM levels in the plasma and JF were not significantly elevated in RA patients, although TM levels in plasma were positively correlated with those in JF. The plasma TM levels were related to renal functions (serum creatinine levels), but the levels showed no connection with systemic inflammatory indices of RA such as erythrocyte sedimentation rates, serum C-reactive protein levels and Lansbury's activity index. In the JF, TM levels were not correlated with the numbers of neutrophils or monocytes/macrophages associated with articular inflammations. Our results indicate that TM levels in the plasma and JF do not reflect systemic and articular inflammations of RA, and suggest that TM molecules in JF are mainly recruited from circulating TM.