A novel 2-stage approach that detects complement activation in patients with antiphospholipid antibody syndrome.
INTRODUCTION
The antiphospholipid syndrome (APS) is marked by autoantibodies that recognize anionic phospholipids in a cofactor-dependent manner. A role for complement has been implicated in the pathophysiology, however, elevations of complement activation markers have not been consistently demonstrated in clinical studies. We therefore designed a proof-of-principle study to determine whether complement activation might be detectable in APS by first exposing plasmas to phospholipid vesicles.


METHODS
We examined complement activation markers in patients with APS, non-APS thrombosis, systemic lupus erythematosus, cancer, patients with antiphospholipid antibodies without thrombosis (APL) and healthy controls. Direct measurements of plasma C5a and sC5b-9 levels were compared to levels that were generated in normal serum by phospholipid vesicles that had been pre-incubated with the same plasmas. We then determined the effects of the C5 inhibitor, eculizumab, examined the complement pathways involved, and determined whether the effects could be reproduced with purified IgGs and β2-glycoprotein I (β2GPI).


RESULTS
Plasma levels of C5a and sC5b-9 were higher, but not significantly increased in APS patients compared to healthy controls. In contrast, phospholipid vesicles pre-incubated with APS plasmas generated significantly higher levels than healthy controls and the other groups, except for APL patients. Complement activation was abrogated by addition of eculizumab. The results with substrate sera indicated that the alternative and classical/lectin pathways were involved. The results were reproducible with purified IgGs and β2GPI.


CONCLUSION
This proof-of-principle study confirms a role for complement in APS and opens the possibility of monitoring complement activation by including phospholipid vesicles in assay systems.
['Rand|Jacob H|JH|', 'Wu|Xiao-Xuan|XX|', 'Wolgast|Lucia R|LR|', 'Lei|Victor|V|', 'Conway|Edward M|EM|']
D000328:Adult D017152:Antibodies, Antiphospholipid D016736:Antiphospholipid Syndrome D003167:Complement Activation D005260:Female D006801:Humans D008297:Male D008875:Middle Aged D055815:Young Adult
Complement activation Autoantibodies Phospholipids Thrombosis Vascular endothelial cells