Complement in antiphospholipid syndrome, time to target?

Antiphospholipid syndrome (APS) is an acquired autoimmune thrombophilia. Complement system, which shares common actors with the coagulation cascade, is nowadays well established to be implicated in APS pathophysiology by different mechanisms. In APS, complement activation assessment is not included in the routine care despite numerous studies showing the presence of activation fragments (C4d, C3d, and C5b9) at a systemic level in sera and blood cells' surface but also in affected arterial walls, kidneys, placentas, or heart valves. APS patients are treated to prevent thrombosis recurrence by long-term anticoagulation with vitamin K antagonist. Several case reports described the use of an anti-C5 antibody to treat particular forms of APS (recurrent thrombosis, catastrophic APS) but are not sufficient to conclude on its efficacy. There is still a need to identify relevant biomarkers to help establish the role of the various recently developed complement-targeting molecules in the therapeutic approach to APS.