Cell‐derived microparticles in synovial fluid from inflamed arthritic joints support coagulation exclusively via a factor VII–dependent mechanism

Abstract

Objective. To determine the cellular origin of synovial microparticles, their procoagulant properties, and their relationship to local hypercoagulation.Methods. Microparticles in synovial fluid and plasma from patients with rheumatoid arthritis (RA; n ‫؍‬ 10) and patients with other forms of arthritis (non-RA; n ‫؍‬ 10) and in plasma from healthy subjects (n ‫؍‬ 20) were isolated by centrifugation. Microparticles were identified by flow cytometry. The ability of microparticles to support coagulation was determined in normal plasma. Concentrations of prothrombin fragment F 1؉2 (by enzyme-linked immunosorbent assay [ELISA]) and thrombin-antithrombin (TAT) complexes (by ELISA) were determined as estimates of the coagulation activation status in vivo.Results. Plasma from patients and healthy controls contained comparable numbers of microparticles, which originated from platelets and erythrocytes. Synovial microparticles from RA patients and non-RA patients originated mainly from monocytes and granulocytes; few originated from platelets and erythrocytes. Synovial microparticles bound less annexin V (which binds to negatively charged phospholipids) than did plasma microparticles, exposed tissue factor, and supported thrombin generation via factor VII. F 1؉2 (median 66 nM) and TAT complex (median 710 g/liter) concentrations were elevated in synovial fluid compared with plasma from the patients (1.6 nM and 7.0 g/liter, respectively) as well as the controls (1.0 nM and 2.9 g/liter, respectively). Conclusion. Synovial fluid contains high numbers of microparticles derived from leukocytes that are strongly coagulant via the factor VII-dependent pathway. We propose that these microparticles contribute to the local hypercoagulation and fibrin deposition in inflamed joints of patients with RA and other arthritic disorders.

Cyclosporine Induces Endothelial Cell Release of Complement-Activating Microparticles

“…6,20 Injury-associated microparticles provide a surface that may enable initiation of complement activation, and the small size of microparticles may enable them to enter most body fluids. 31,32 Microparticles are present in normal serum and circulate in continuous contact with complement proteins. Thus, the nature of the microparticles and their abundance in plasma may have a profound influence on complement homeostasis throughout the body.…”

Platelet and red blood cell interactions and their role in rheumatoid arthritis

“…These RBCinduced responses were found to be sustained even after the removal of the initial agonist trigger and following inhibition of TX synthesis. It has been established that majority of the cell-derived microparticles occurring within circulation and a few occurring within the synovial space, as described by investigators, originate from RBCs [77,78]. These RMPs effected expansion of the T lymphocyte pool via antigen presentation.…”

“…Interactions of these particles with platelets have also triggered thrombotic signalling [77,81]. Assays of thrombin production were able to confirm that RBCs and their products were capable of independent thrombin generation, once stimulated [82,83].…”

The role of proteases in pathologies of the synovial joint

“…It has been proposed that pannus formation in rheumatoid arthritis is initiated by the formation of fibrin clots within the synovial fluid at the synovial surface, which provide a scaffold into which synovial fibroblast-like cells migrate (Sánchez-Pernaute et al, 2003). This model proposes that, as is observed in other inflammatory conditions (Berckmans et al, 2002), inflammation induces an influx of plasma components into the synovial fluid including components of the coagulation cascade which become activated; but that in rheumatoid arthritis there is an imbalance between coagulation and fibrinolysis leading to the formation and persistence of clots (Andersen & Gormsen, 1970). The coagulation cascade comprises a proteolytic activation series of serine protease ending in thrombin which then cleaves fibrinogen to fibrin (Cirino, Napoli, Bucci, & Cicala, 2000), whereas fibrinolysis is mediated by plasmin, which is generated by the activa- Table 3 Summary of proteases with pathological roles in synovium Saarinen et al (1994) tion of plasminogen by proteases such as urokinase-type plasminogen activator (uPA) and tissue plasminogan activator (Cesarman-Maus & Hajjar, 2005).…”