Open Access Open Badges Research article

Contact activation products are new potential biomarkers to evaluate the risk of thrombotic events in systemic lupus erythematosus

Jennie Bäck1, Christian Lood2, Anders A Bengtsson2, Kristina Nilsson Ekdahl13 and Bo Nilsson1*

Author Affiliations

1 Department of Immunology, Genetics and Pathology, Rudbeck Laboratory C5:3, Uppsala University, Dag Hammarskjölds väg 20, SE-751 85 Uppsala, Sweden

2 Department of Clinical Sciences Lund, Section of Rheumatology, Skåne University Hospital and Lund University, SE-221 85 Lund, Sweden

3 Linnæus Center for Biomaterials Chemistry, Linnæus University, SE-391 82 Kalmar, Sweden

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Arthritis Research & Therapy 2013, 15:R206  doi:10.1186/ar4399

Published: 4 December 2013



Patients with systemic lupus erythematosus (SLE) have persistent platelet activation and an increased risk of thrombotic events, which cannot be accounted for by traditional cardiovascular risk factors. Factor (F)XII has a potentially important role in thrombus formation and is triggered by activated platelets. We therefore asked whether the contact system is involved in inflammation and vascular disease (VD) in SLE.


Fibrin clots were incubated with purified FXII or whole blood, and the activation and regulation of FXII were studied. Plasma from SLE patients with (n = 31) or without (n = 38) previous VD and from matched healthy controls (n = 68) were analyzed for the presence of complexes formed between contact system enzymes and antithrombin (AT) or C1 inhibitor (C1INH) and evaluated with regard to clinical data and laboratory parameters.


Fibrin clots elicited FXII activation and acted as co-factors for AT. In clotting plasma, the levels of FXIIa-AT increased, and FXIIa-C1INH decreased. A similar reciprocal relationship existed in SLE patients. FXIIa-AT was elevated in the SLE patients with a history of VD, while the corresponding levels of factor FXIIa-C1INH were significantly decreased. FXIIa-AT correlated strongly with platelet parameters. The odds ratio for VD among the SLE patients was 8.9 if they had low levels of FXIIa-C1INH, 6.1 for those with high levels of FXIIa-AT, and increased to 23.4 for those with both decreased levels of FXIIa-C1INH and increased levels of FXIIa-AT.


Activation of FXII is elicited by fibrin during thrombotic reactions in vitro and in vivo, and fibrin acts as a heparin-like co-factor and regulates AT. Patients with SLE had altered levels of FXIIa-serpin complexes, supporting that the contact system is involved in this disease. FXIIa-serpin complexes are strongly associated with previous VD in SLE patients, suggesting that these complexes are potential biomarkers for monitoring and assessing the risk of thrombotic events in SLE.