Increased circulating platelet-leucocyte complexes and platelet activationin patients with antiphospholipid syndrome, systemic lupus erythematosus and rheumatoid arthritis

It is possible that platelet activation may play a pathogenic role in the i ncreased risk of thrombosis associated with antiphospholipid antibodies (AP A). In this study, levels of in vivo platelet activation were measured in 2 0 patients with primary antiphospholipid syndrome (PAPS) and 30 systemic lu pus erythematosus (SLE) patients (14 of whom had secondary APS) using sensi tive flow cytometry. Soluble P-selectin levels were also assayed. Platelet CD63 expression was significantly higher in PAPS than normal controls (P = 0.007), as well as SLE patients with and without secondary APS (P = 0.03 an d P = 0.002 respectively). PAC-1 binding was significantly higher in PAPS t han the control group (P = 0.007) and SLE patients without APS (P = 0.015). Platelet-leucocyte complexes were significantly higher in SLE patients tha n both PAPS and the control group, and platelet-monocyte complexes were sig nificantly increased in RAPS compared with the control group, (Platelet-leu cocyte complexes were also significantly higher than controls in 10 rheumat oid arthritis (RA) patients without APA). Soluble P-selectin levels were si gnificantly higher in PAPS and SLE patients than the control group. Platele t CD62p expression. annexin V binding and platelet microparticle numbers we re not increased in PAPS or SLE patients. We conclude that there is evidenc e of increased platelet activation in PAPS and SLE, and this is important t o note as it may have potential therapeutic implications with respect to us e of antiplatelet agents in these patients.