The complement system plays a pathophysiological role in systemic lupus 
erythematosus (SLE). This study aims to investigate whether an association 
exists between the ficolins that are part of the lectin complement pathway and 
SLE. EDTA plasma samples from 68 Danish SLE patients and 29 healthy donors were 
included in the study. Plasma concentrations of Ficolin-1, -2, and -3 were 
determined in specific sandwich ELISAs. Lectin pathway activity via Ficolin-3 
was measured in ELISA on acetylated bovine serum albumin (acBSA) and measured as 
Ficolin-3 binding and deposition of C4, C3 and the terminal complement complex 
(TCC). SLE patients had increased levels of Ficolin-3, 21.6μg/ml as compared to 
17.0μg/ml in healthy controls (P=0.0098). The Ficolin-1 plasma concentration was 
negatively correlated with SLE Disease Activity Index (SLEDAI) (Rho=-0.29, 
P=0.015) and positively correlated to the [Systemic Lupus International 
Collaborating Clinics (SLICC)/American College of Rheumatology (ACR) Damage 
Index] (SDI) (Rho=0.27, P=0.026). The Ficolin-1 concentration was also 
associated with the occurrence of arterial (P=0.0053) but not venous thrombosis 
(P=0.42). Finally, deposition of C4, C3 and TCC in the Ficolin-3 pathway were 
all correlated to SLEDAI, respectively (P<0.0076). The Ficolin-1 association to 
SLEDAI and SDI as well as arterial thrombosis shown in this study suggests that 
Ficolin-1 may be a potential new biomarker for patients with SLE. Furthermore, 
Ficolin-3 mediated complement activation may be valuable in monitoring disease 
activity in SLE patients due to the high sensitivity for complement consumption 
in the assay independent of the Ficolin-3 concentration.